Building a Simple Network - Study Notes

Building a Simple Network (ICT)
Study Notes
+W - Technology Skills For Women Series1
(Master Copy)
http://SlideShare.net/OxfordCambridge
1
Men are allowed to read too, if they wish, as the language style and the document format are universal.

Study Notes http://SlideShare.net/OxfordCambridge
2 | P a g e B u i l d i n g a S i m p l e N e t w o r k ( I C T )
Contents
About “+W - Technology Skills For Women” series ................................................................................ 5
Sources: ................................................................................................................................................... 6
A. Application sharing through networks.................................................................................................... 8
1. Major components of a computer system.......................................................................................... 8
Question ................................................................................................................................................ 12
Quiz........................................................................................................................................................ 13
2. Network interface card...................................................................................................................... 13
Quiz........................................................................................................................................................ 15
Quiz........................................................................................................................................................ 16
Summary................................................................................................................................................ 16
B. Understanding binary basics ................................................................................................................. 17
1. Bits, bytes and measurement terms ................................................................................................. 17
Quiz........................................................................................................................................................ 20
2. Conversion between decimal and binary.......................................................................................... 21
Quiz........................................................................................................................................................ 24
Quiz........................................................................................................................................................ 26
3. Conversion between binary and hexadecimal .................................................................................. 26
Quiz........................................................................................................................................................ 29
Quiz........................................................................................................................................................ 31
Summary................................................................................................................................................ 32
C. Using a PC on a network........................................................................................................................ 33
1. Basic Networking Terminology.......................................................................................................... 33
2. Network Applications ........................................................................................................................ 34
3. Computer Networks .......................................................................................................................... 36
Summary................................................................................................................................................ 38
D. Working with PC technology ................................................................................................................. 39
1. Exercise overview .............................................................................................................................. 39
2. Task 1: Identifying PC components ................................................................................................... 39
Step 1 of 1.................................................................................................................................................. 40
Result......................................................................................................................................................... 40
3. Task 2: Interpreting numerical systems ............................................................................................ 40
Step 1 of 5.............................................................................................................................................. 41
Result..................................................................................................................................................... 41
Step 2 of 5.............................................................................................................................................. 42
Result..................................................................................................................................................... 42

Step 3 of 5.............................................................................................................................................. 42
Result..................................................................................................................................................... 42
Step 4 of 5.............................................................................................................................................. 43
Result..................................................................................................................................................... 43
Step 5 of 5.............................................................................................................................................. 43
Result..................................................................................................................................................... 43
E. OSI model layers and functions............................................................................................................. 44
1. Origins of the OSI reference model................................................................................................... 44
Quiz............................................................................................................................................................ 46
Answer....................................................................................................................................................... 46
2. OSI layers and functions.................................................................................................................... 47
Quiz............................................................................................................................................................ 53
Answer....................................................................................................................................................... 53
3. Data communications........................................................................................................................ 53
Quiz............................................................................................................................................................ 55
Answer....................................................................................................................................................... 56
Quiz............................................................................................................................................................ 60
Answer....................................................................................................................................................... 60
4. The TCP/IP protocol stack.................................................................................................................. 60
Quiz............................................................................................................................................................ 62
Answer....................................................................................................................................................... 62
Summary................................................................................................................................................ 62
F. Working with the OSI model ................................................................................................................. 64
Exercise overview.................................................................................................................................. 64
Task1: Networking terms and functions................................................................................................ 64
Result..................................................................................................................................................... 64
Step 2 of 3.............................................................................................................................................. 65
Result..................................................................................................................................................... 65
Step 3 of 3.............................................................................................................................................. 66
Result..................................................................................................................................................... 66
Task 2: Functions of the OSI model....................................................................................................... 66
1 of 1...................................................................................................................................................... 67
Result......................................................................................................................................................... 67
Task 3: The data encapsulation process................................................................................................ 67
Step 1 of 1.............................................................................................................................................. 68
Result..................................................................................................................................................... 68

G. Glossary ................................................................................................................................................. 69
H. Quizzes’ Answers................................................................................................................................... 98

About “+W - Technology Skills For Women” series
Study Notes in the field of technology will be put together under this category for the following reasons:
 to encourage ladies, who wish to do so, to stand up and look over the fence into technology related
topics;
 with apprehension or fear;
 and perhaps consider embracing a career move into this technological path;
 or simply as to broaden their general knowledge; after all ICT is in most aspects of everyday life;
 no matter the decision, their skills, professional strengths, and contribution can only be something
positive for technical and technological fields.

Sources:
 How To Set Up A Home Network, Samara Lynn February 2, 2012, PCMag.com,
http://www.pcmag.com/article2/0,2817,2375207,00.asp
 Chapter 1: Building a Simple Network, Stephen McQuerry, Network World May 29, 2008, Cisco Press
http://www.networkworld.com/subnets/cisco/053008-ch1-ccna-prep-library.html
 Designing and Building the Best Small Office Network From the Ground Up, 2014, Marshall
Breeding,, Network Computing, http://www.networkcomputing.com/netdesign/soho1.html
 CCNA Certification Library (CCNA Self-Study, exam #640-801) 2003, Wendell Odom, Ciscopress,
1587200953
 CCNA INTRO Exam Certification Guide 2003, Wendell Odom, Cisco Press, 1-58720-094-5

Building a Simple Network
Sections:
A. Application sharing through networks
B. Understanding binary basics
C. Using a PC on a network
D. Working with PC technology
E. OSI model layers and functions
F. Working with the OSI model
Learning Objectives:
Topic Name When you have completed this topic, you should be able to
Application sharing
through networks
identify the major components of a computer system and their
functionality, and list the resources required to install a NIC.
Understanding binary
basics
distinguish between the processes used to convert between decimal,
binary, and hexadecimal numbering systems.
Using a PC on a network identify the main purposes and functions of networking.
Working with PC
technology
identify the purpose of major computer components, and calculate
conversions between binary, decimal, and hexadecimal numerical systems.
OSI model layers and
functions
distinguish between the OSI reference model and the TCP/IP stack.
Working with the OSI
model
distinguish between basic computer and networking terms, and between
the principles of the OSI reference model and the TCP/IP protocol stack.

A. Application sharing through networks
After completing this topic, you should be able to identify the major components of a computer system and
their functionality, and list the resources required to install a NIC.
1. Major components of a computer system
2. Network interface card
Summary
1. Major components of a computer system
There are several fundamental elements involved in the networking of computers, including computers
themselves and their components that are designed for network connectivity, as well as other network
devices, such as bridges, hubs, and routers.
Some of the major hardware elements of computers that allow network connectivity include the central
processing unit (CPU), the bus, drives, memory components, ports, and cards.
Many networking devices are special-purpose computers and have many of the same parts as normal PCs.
For you to be able to use the computer as a reliable means of obtaining information, it must be in good
working order.
If the need arises to troubleshoot a simple hardware or software problem, you should be able to recognize,
name, and state the purpose of PC components.
 Drives

 CPU
 Expansion slots
 Bus
 Backplane components
 Motherboard
Drives
There are different drive types – for example the CD-ROM drive, the floppy disk drive, and the hard
disk drive.
The CD-ROM drive is a compact disc read-only memory drive that can read information from a CD-
ROM (combined CD-ROM/DVD-ROM are used nowadays).
The floppy disk drive is a disk drive that can read and write to floppy disks (rarely used nowadays).
The hard disk drive is the device that reads and writes data on a hard disk.
CPU
The CPU is the "brain" of the computer, where most of the calculations take place.
The microprocessor is a silicon chip contained within a CPU.
Expansion slots

The expansion slots are openings in a computer into which you can insert a circuit board to add new
capabilities to the computer.
The expansion card is a printed circuit board that provides added capabilities to the computer.
Bus
A bus is a collection of wires through which data is transmitted from one part of a computer to
another.
The bus connects all the internal computer components to the CPU. The Industry-Standard
Architecture (ISA) and the Peripheral Component Interconnect (PCI) are two types of buses.
Backplane components
The backplane is an area of the computer into which you plug external devices.
The following items are backplane components of a PC:
- interface
- mouse port
- network card
- parallel port

- power cord
- serial port
- sound card
- video card
The interface is a piece of hardware, such as a modem connector, that allows two devices to be
connected together.
The mouse port is a port that is designed for connecting a mouse to a PC.
The network card is an expansion board inserted into a computer to enable connection to a
network.
The parallel port is an interface capable of transferring more than one bit simultaneously, and is
used for connecting external devices, such as printers.
The power cord is a cord connecting an electrical device to an electrical outlet to provide power to
the device.
The serial port is an interface that can be used for serial communication in which only one bit is
transmitted at a time.
The sound card is an expansion board that handles sound functions.
The video card is a board that plugs into a PC to give it display capabilities.
Motherboard
The motherboard is the main circuit board of a computer.
The motherboard utilizes the following primary components:
- power supply
- printed circuit board (PCB)
- random access memory (RAM)
- read-only memory (ROM)
- system unit
The power supply is the component that supplies power to a computer.
The printed circuit board (PCB) is a thin plate on which chips (integrated circuits) and other
electronic components are placed.

Random access memory (RAM) is memory that has new data written into it as well as stored data
read from it. It is also known as read-write memory.
A drawback of RAM is that it requires electrical power to maintain data storage. If the computer is
turned off or loses power, all data stored in RAM is lost unless the data was previously saved to disk.
The read-only memory (ROM) is the computer memory on which data has been prerecorded.
The system unit is the main part of a PC. It is a term that encompasses the chassis, the
microprocessor, the main memory, the bus, and the ports. The system unit does not include the
keyboard, the monitor, or any other external devices connected to the computer.
Because computers are important building blocks in a network, you should be able to identify their major
components.
Question
i
Match the PC components to their descriptions.
Options:
1. Backplane
2. Bus
3. CPU
4. Expansion slots
5. Floppy drive (rarely used nowadays).
Targets:
a. A disk drive that can read and write to floppy disks
b. A part of the computer that allows external devices to be connected
c. Where most of the calculations take place
d. Connects all the internal computer components to the CPU
e. Openings in a computer into which you can insert a circuit board
Laptop computers and notebook computers have become very popular. There are few differences between
the two.
The main difference between PCs and laptops is that laptop components are smaller than those found in a

PC, they are designed to fit together into a smaller physical space, and they use less power when operated.
These smaller components can be difficult to remove.
In a laptop, the expansion slots become Personal Computer Memory Card International Association
(PCMCIA) card slots, or PC slots, through which NICs, modems, hard drives, and other useful devices (usually
the size of a thick credit card) are connected.
PCs are more powerful than laptops, but laptops have the advantage of being portable, which makes it more
convenient to work from home and while traveling between offices.
Quiz
ii
What are the main differences between the components of a desktop PC and a laptop?
Options:
1. It is easier to remove the components from a laptop than the components from a PC
2. Laptops use less power than PCs
3. Laptop components are smaller than those in a PC
4. The slots you connect devices to are called expansion slots in a PC and PCMCIA slots in a laptop
2. Network interface card
A network interface card (NIC) is a printed circuit board that provides network communication capabilities to
and from a personal computer.
Also called a LAN adapter, the NIC plugs into a motherboard and provides a port for connecting to the
network. The NIC constitutes the computer interface with the local area network (LAN).

The NIC communicates with the network through a serial connection, and with the computer
through a parallel connection.
When a NIC is installed in a computer, it requires an interrupt request line (IRQ), an input/output (I/O)
address, a memory space for the operating system (such Windows), and drivers in order to perform its
function.
An IRQ is a signal that informs a CPU that an event needing its attention has occurred. An IRQ is sent over a
bus line to the microprocessor.
An example of an interrupt request being issued is when a key is pressed on a keyboard, and the CPU must
move the character from the keyboard to RAM.
An I/O address is a location in memory used by an auxiliary device to enter or retrieve data from a computer.
When selecting a NIC for a network, you should consider the following:
 type of network
 type of media
 type of expansion slot
type of network
You must choose a NIC to suit the type of network you have. Ethernet NICs are designed for Ethernet
LANs.
type of media
The type of port or connector used by the NIC for network connection is specific to the type of
media, such as twisted-pair.

type of expansion slot
With regard to the type of expansion slot to use, you should consider that because PCI slots are
faster than ISA slots, the latter are being phased out.
Quiz
iii
Which of the following should you take into account when selecting a NIC for a network?
Options:
1. The type of CPU
2. The type of media
3. The type of network
4. The type of expansion slot
The ability to install a NIC correctly is an important aspect of preparing a computer for network connectivity.
To install a NIC, you must know about the following:
 Network card configuration
 Network card diagnostics
 Hardware resource conflicts
Network card configuration
You must know how the network card is configured, including jumpers, "plug-and-play" software,
and erasable programmable read-only memory (EPROM).

Network card diagnostics
You must know the network card diagnostics, including the vendor-supplied diagnostics and
loopback tests (see the documentation that comes with the card).
Hardware resource conflicts
You must know how to resolve hardware resource conflicts, including IRQ, I/O base address, and
direct memory access (DMA), which is used to transfer data from RAM to a device without going
through the CPU.
Quiz
iv
Which options correctly describe the information needed to install a NIC?
Options:
1. Knowledge of how to resolve hardware resource conflicts
2. Knowledge of all types of network cards
3. Knowledge of how the network card is configured
4. Knowledge of how to use the network card diagnostics
Summary
There are several PC components, which include the motherboard, the backplane, the central processing
unit (CPU), the bus, drives, expansion slots, memory components, ports, and cards. A laptop is a portable PC
that uses smaller components, is more power efficient than a PC, and has Personal Computer Memory Card
International Association (PCMCIA) card slots instead of expansion slots.
A network interface card (NIC) is a circuit board that allows a personal computer to communicate with a
network. You need to consider the type of network, media, and expansion slot when selecting a NIC. To
install a NIC, you should know how to configure it, how to use its diagnostics, and be able to resolve
hardware resource conflicts.

B. Understanding binary basics
After completing this topic, you should be able to distinguish between the processes used to convert
between decimal, binary, and hexadecimal numbering systems.
1. Bits, bytes and measurement terms
2. Conversion between decimal and binary
3. Conversion between binary and hexadecimal
Summary
1. Bits, bytes and measurement terms
At the most basic level, computers perform their computations by using 1s and 0s instead of the decimal
system.
Computers are made up of electronic switches. At the lowest levels of computation, computers depend on
these electronic switches to make decisions. Computers react only to electrical impulses, understood by the
computer as either "on" or "off" states (1s or 0s).
Computers can understand and process only data that is in a binary format, represented by 0s and 1s. These
0s and 1s represent the two possible states of an electrical impulse and are referred to as binary digits (bits).
Most computer coding schemes use eight bits to represent a number, letter, or symbol. A series of eight bits
is referred to as a byte. One byte represents a single addressable storage location.

The following are commonly used computer measurement terms:
 Bit (b)
 Byte (B)
 Kilobit (Kb)
 Kilobyte (KB)
 Megabit (Mb)
 Megabyte (MB)
 Gigabit (Gb)
 Gigabyte (GB)
Bit (b)
A bit is the smallest unit of data in a computer. A bit equals 1 or 0 in the binary format in which data
is processed by computers.
Bits per second (bps) is a standard unit of measurement for data transmission.
Byte (B)
A byte is a unit of measure used to describe the size of a data file, the amount of space on a disk or
other storage medium, or the amount of data being sent over a network. One byte equals eight bits
of data.
Bytes per second (Bps) is a standard unit of measurement of the data transmission rate over a
network connection.
Kilobit (Kb)
A kilobit is approximately 1000 bits (1024 bits exactly).
Kilobits per second (Kbps) is a standard unit of measurement of the data transmission rate over a
network connection.

Kilobyte (KB)
A kilobyte is approximately 1000 bytes (1024 bytes exactly).
Kilobytes per second (KBps) is another standard unit of measurement for data transmission.
Megabit (Mb)
A megabit is approximately 1 million bits.
Megabits per second (Mbps) is a standard unit of measurement of the data transmission rate over a
network connection.
Megabyte (MB)
A megabyte is approximately 1 million bytes (1,048,576 bytes exactly). A megabyte is sometimes
referred to as a "meg."
Megabytes per second (MBps) is a standard unit of measurement for data transmission.
Gigabit (Gb)
A gigabit is equal to approximately one billion bits.
Gigabits per second (Gbps) is a standard unit of measurement of the data transmission rate over a
network connection.
Gigabyte (GB)
A gigabyte is equal to approximately one billion bytes.
Gigabytes per second (GBps) is a standard unit of measurement for data transmission.
It is a common error to confuse KB with Kb and MB with Mb. You should remember to do the proper
calculations when comparing transmission speeds that are measured in KBps and those measured in Kbps.
For example, modem software usually shows the connection speed in kilobits per second (for example, 45
Kbps). However, popular browsers display file-download speeds in kilobytes per second, meaning that with a
45-Kbps connection, the download speed would be a maximum of 5.76 KBps. In practice, this download speed
cannot be reached because of other factors consuming bandwidth at the same time.

The following are speed measurement terms commonly used for microprocessors:
 Hz
 MHz
 GHz
Hz
A hertz (hz) is a unit of frequency. It is the rate of change in the state or cycle in a sound wave,
alternating current, or other cyclical waveform. It represents one cycle per second and is used to
describe the speed of a computer microprocessor.
MHz
A megahertz (MHz) represents one million cycles per second. This is a common unit of measurement
of the speed of a processing chip, such as a computer microprocessor.
GHz
A gigahertz (GHz) represents one billion (1,000,000,000) cycles per second. This is a common unit of
measurement of the speed of a processing chip, such as a computer microprocessor.
PC processors are getting faster all the time. The microprocessors used on PCs in the 1980s typically ran
under 10 MHz (the original IBM PC was 4.77 MHz). Today they are measured in GHz.
Quiz
v
Match the measurement terms with their definitions.
Options:
1. Bit
2. Byte
3. GB
4. KB
5. Mb
6. MB

Targets:
a. It equals 1 or 0 in binary format
b. It is equal to 8 bits
c. It is equal to approximately 1000 bytes
d. It is equal to approximately one billion bytes
e. It is equal to approximately one million bits
f. It is equal to approximately one million bytes
2. Conversion between decimal and binary
Converting a decimal number to a binary number is one of the most common procedures performed in
computer operations.
Computers recognize and process data using the binary, or base 2, numbering system. The binary numbering
system uses only two symbols (0 and 1) instead of the ten symbols used in the decimal numbering system.
The position, or place, of each digit represents the number 2 (the base number) raised to a power
(exponent), based on its position (2^0, 2^1, 2^2, 2^3, 2^4, and so on).

Suppose you want to convert the decimal number 253 to a binary number. You can do this by dividing the
number by two each time and taking note of the remaining number.
First you divide 253 by 2, which is equal to 126 with 1 remaining.
Then you divide 126 by 2, which is equal to 63 with 0 remaining.
Finally you divide 1 by 2, which is equal to 0 with 1 remaining.
You should write the binary number in the order of the last bit first. In this case, the binary equivalent of 253
is 11111101.
Suppose you want to convert the decimal number 153 to binary.
Suppose you want to convert the number 35 to a binary number. You can do this using the following steps:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5

Step 1
Step 1: Looking at the figure, you must identify what is the greatest power of 2 that is less than or
equal to 35. Starting with the largest number, 2^5 (32) is smaller than 35. You place a "1" in that
column, a "0" in each preceding place, and calculate how much is left over by subtracting 32 from
35. The result is 3.
Step 2
Step 2: Next you check to see if 16 (the next lower power of 2) fits into 3. Because it does not, a "0"
is placed in that column. The value of the next number is 8, which is larger than 3, so a "0" is placed
in that column too.
Step 3
Step 3: The next value is 4, which is still larger than 3, so it too receives a "0."
Step 4
Step 4: The next value is 2, which is smaller than 3. Because 2 fits into 3, place a "1" in that column.
Now subtract 2 from 3, and the result is 1.
Step 5
Step 5: The value of the last number is 1, which fits in the remaining number. Therefore, you place a
"1" in the last column. The binary equivalent of the decimal number 35 is 100011.
In this case, the place values of 128 and 64 are too high to be considered for the calculation.

Quiz
vi
Which number is the binary equivalent of 197?
Options:
1. 10000101
2. 10100101
3. 11000101
4. 11100101
You can also convert binary numbers to decimal format.
As with decimal-to-binary conversion, there is usually more than one way to convert binary numbers to
decimal numbers.
The figure illustrates one conversion method. Each binary digit has a corresponding decimal position value.
To work out the decimal position values, you start with 1 and then multiply each number by 2.
For example, 1 multiplied by 2 is equal to 2, 2 multiplied by 2 is 4, 4 multiplied by 2 is 8, and so on.
Consider the 8 digits that make up the binary number. If a digit is 1, then you count the corresponding
position value whereas if the digit is 0, then you ignore it.

Next, suppose you want to convert the binary number 10111001 to a decimal number. You can do this using
the following steps:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5
Step 1
Step 1: The binary number has a 1 in the 2^7 (128) bit position, so 128 is added to the decimal total.
Step 2
Step 2: Next the binary number has a 0 in the 2^6 (64) bit position so 64 is not added to the decimal
total (128+0=128). Next there is a 1 in the 2^5 (32) bit position, so the decimal total becomes
128+32=160.
Step 3
Step 3: Next there is a 1 in the 2^4 (16) bit position. Adding the value to the decimal total gives
160+16=176. Then the 2^3 (8) bit position has the binary digit 1, so the value 8 needs to be added to
the decimal total: 176+8=184.
Step 4
Step 4: Next there are 0s in the 2^2 and 2^1 bit positions, so you add 0s to the decimal total:
184+0+0=184.
Step 5

Step 5: Finally, there is a 1 in the 2^0 (1) bit position, so you add 1 to 184 to give the result 185. The
decimal equivalent of the binary number 10111001 is 185.
Quiz
vii
Convert the binary number 11011000 to decimal.
3. Conversion between binary and hexadecimal
The base 16, or hexadecimal (hex), numbering system is used frequently when working with computers
because it can be used to represent binary numbers in a more readable form.
The computer performs computations in binary, but there are instances when the binary output of a
computer is expressed in hexadecimal format to make it easier to read.
Converting a hexadecimal number to binary, and vice versa, is a common task when dealing with the 16-bit
configuration register in Cisco routers. That 16-bit binary number can be represented as a four-digit
hexadecimal number. For example, 0010000100000010 in binary is equal to 2102 in hex.
The most common way for computers and software to express hexadecimal output is using "0x" in front of
the hexadecimal number. Thus, whenever you see "0x," you know that the number that follows is a
hexadecimal number. For example, 0x1234 means 1234 in base 16.
It is referred to as base 16 because it uses 16 symbols. Combinations of these symbols can represent all
possible numbers. Because there are only 10 symbols that represent digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and base
16 requires six more symbols, the extra symbols are the letters A, B, C, D, E, and F.

The "A" represents the decimal number 10, "B" represents 11, "C" represents 12, "D" represents 13, "E"
represents 14, and "F" represents 15.
The position of each symbol (digit) in a hex number represents the base number 16 raised to a power
(exponent) based on its position. Moving from right to left, the first position represents 16^0 (or 1), the
second position represents 16^1 (or 16), the third position represents 16^2 (or 256), and so on.
Network layer 2 MAC addresses are typically written in hex. For Ethernet and Token Ring topologies, these
addresses are 48 bits, or six octets (one octet is eight bits). Because these addresses consist of six distinct
octets, you can write them as 12 hex numbers.
Instead of writing
10101010.11110000.11000001.11100010.011101 11.01010001
you can write the much shorter hex equivalent: AA.F0.C1.E2.77.51. To make handling hex versions of MAC
addresses even easier, the dots are placed only after each four hex digits, as in AAF0.C1E2.7751.

Converting binary to hex is easy because base 16 (hexadecimal) is a power of base 2 (binary). Every four
binary digits (bits) are equal to one hexadecimal digit.
The table compares the binary and hexadecimal numbering systems.
If there is a binary number that looks like 01011011, you can break it into two groups of four bits: 0101 and
1011. When converting these two groups to hex, they become 5 and B, so the hexadecimal equivalent of the
binary 01011011 is 5B.
No matter how large the binary number, you always apply the same conversion.
First you start from the right of the binary number and break the number into groups of four.
If the far left group does not contain four digits, add zeros to the left end until there are four digits (bits) in
every group.
Then you convert each group of four to its hex equivalent.

Suppose you want to convert the binary number 01001110000100110101011110001101 to hexadecimal.
Quiz
viii
Which options are hexadecimal equivalents of 1010110100010011111000111101100?
Options:
1. 1451880940
2. 5689F1EC
3. AD13E3D4
4. 0x5689F1EC
You can also convert hexadecimal numbers to binary format. To convert from hexadecimal to binary, you
convert every hex digit into four binary digits (bits).
For example, to convert hex AC (0xAC) to binary, you first convert hex A, which is 1010 binary, and then
convert hex C, which is 1100 binary. So the conversion of hex AC is 10101100 binary.

Suppose you want to convert the hexadecimal number 1245F7DC9 to binary.

Make sure you include four binary digits for each hexadecimal character, adding zeros to the left of the
number when necessary.
Quiz
ix
Match the binary numbers to their hexadecimal equivalent.
Options:
1. 1100011101011000010
2. 10101101110110101000101
3. 10100101010110001000101000100100011
4. 1011000100111111110
Targets:
a. 52AC45123
b. 56ED45
c. 589FE
d. 63AC2

Summary
The binary numbering system is made up of 0s and 1s. The most common measurement terms are bit, byte,
kilobit (Kb), kilobyte (KB), megabit (Mb), megabyte (MB), gigabit (Gb), and gigabyte (GB). The microprocessor
speeds are hertz (Hz), megahertz (MHz), and gigahertz (GHz).
The decimal numbering system uses ten symbols – 0 - 9. Decimal numbers can be converted to binary. One
way of doing this is to divide the decimal number by two each time, taking note of the remaining number. All
the remaining numbers form the binary equivalent. You can also convert binary numbers to decimal.
The hexadecimal numbering system uses 16 symbols – 0 - 9, and A - F. Hexadecimal numbers often have 0x
in front of them. You can easily convert binary numbers to hexadecimal as each group of four binary digits is
equal to one hexadecimal digit. You can also convert hexadecimal numbers to binary by converting every
hex digit into four binary digits (bits).

C. Using a PC on a network
To review basic networking technologies and common network applications, and identify the main purposes
and functions of networking.
1. Basic Networking Terminology
2. Network Applications
3. Computer Networks
Summary
1. Basic Networking Terminology
Computer networking, like most industries, has its own jargon, which includes technical terms,
abbreviations, and acronyms. Without a good grasp of the terminology, it will be difficult to understand the
concepts and processes involved in networking. The following list of terms and their definitions is intended
to be a quick reference that defines some of the most important words, phrases, and acronyms related to
computer networking:
 A network interface card (NIC), pronounced "nick," is also called the LAN adapter, or just the
network interface. This card typically goes into an ISA, PCI, or PCMCIA (PC card) slot in a computer
and connects to the network medium. It then connects to other computers through the network
media.
 Media refers to the various physical environments through which transmission signals pass.
Common network media include twisted-pair, coaxial, and fiber-optic cable, and even the earth's
atmosphere through which wireless transmission occurs.
 A protocol is a set of rules. In the case of a network protocol, it is a set of rules by which computers
communicate. The term "protocol suite" describes a set of several protocols that perform different
functions related to different aspects of the communication process.
 Cisco IOS software which runs on Cisco equipment and devices, is the industry-leading and most
widely deployed network system software. It delivers intelligent network services for enabling the
rapid deployment of Internet applications.
Cisco IOS software provides a wide range of functionality, from basic connectivity, security, and
network management to technically advanced services. The functionality of Cisco IOS software is the
result of a technological evolution. First-generation networking devices could only store and forward
data packets.
Today, Cisco IOS software can recognize, classify, and prioritize network traffic, optimize routing,
support voice and video applications, and much more. Cisco IOS software runs on most Cisco routers
and Cisco switches. These network devices carry most of the Internet traffic today.
 Network operating system (NOS) usually refers to server software such as Windows NT, Windows
2000 Server, Windows Server 2003, Novell NetWare, UNIX, and Linux. The term sometimes refers to
the networking components of a client operating system such as Windows 95 or the Macintosh OS.
 Connectivity devices refer to several different device types, all of which are used to connect cable
segments, connect two or more smaller networks (or subnets) into a larger network, or divide a
large network into smaller ones. The term encompasses repeaters, hubs, switches, bridges, and
routers.

The following are three categories of networks:
 A local-area network (LAN) is a network that is confined to a limited geographic area. This area can
be a room, a floor, a building, or even an entire campus.
 A metropolitan-area network (MAN) is a network that is larger in size than a LAN and smaller in size
than a WAN. This is a network that covers approximately the area of a large city or metropolitan
area.
 A wide-area network (WAN) is made up of interconnected LANs. It spans wide geographic areas by
using WAN links such as telephone lines or satellite technology to connect computers in different
cities, countries, or even different continents.
Network structure is described in the following two ways:
 The logical topology is the path that the signals take from one computer to another. The logical
topology may or may not correspond to the physical topology. For instance, a network can be a
physical "star," in which each computer connects to a central hub, but inside the hub the data can
travel in a circle, making it a logical "ring."
 The physical topology refers to the layout or physical shape of the network, and includes the
topologies in this table.
Topologies
Bus Computers arranged so that cabling goes from one to another in a linear fashion
Ring When there are no clear beginning points or endpoints within a topology, forming a circle
Star If the systems "meet in the middle" by connecting to a central hub
Mesh When multiple redundant connections make pathways to some or all of the endpoints
2. Network Applications
Network applications are software programs that run between different computers connected together on a
network.
Some of the more common uses of network applications include using a web browser program to find
content from the World Wide Web, or using an e-mail program to send e-mails over the Internet.

Network applications are selected based on the type of work that needs to be done. A complete set of
application-layer programs is available to interface with the Internet. Each application program type is
associated with its own application protocol. Some examples include:
 HTTP is the World-Wide-Web communications protocol used to connect to web servers. Its primary
function is to establish a connection with a web server and transmit HTML pages to the client
browser.
 Post Office Protocol 3 (POP3) is an application-layer protocol supported by e-mail programs for the
retrieval of electronic mail. POP3 is a standard e-mail server commonly used on the Internet. It
provides a message storage container that holds incoming e-mail until users log on and download
their messages.
 File Transfer Protocol (FTP) is a simple file utility program for transferring files between remote
computers, which also provides for basic user authentication.
 Telnet is a remote access application and protocol for connecting to remote computer consoles,
which also provides for basic user authentication. Telnet is not a graphical user interface but is
command-line driven or character mode only.
 Simple Network Management Protocol (SNMP) is used by network management programs for
monitoring the network device status and activities.
It is important to emphasize that the application layer is just another protocol layer in the OSI model or
TCP/IP protocol stack. The programs interface with application layer protocols.
E-mail client applications, such as Microsoft Outlook, Lotus Notes, Pegasus Mail, Mozilla's Thunderbird,
Eudora, KMail, all work with the POP (Post Office Protocol) and IMAP4 (Message Access Protocol) protocols.
Electronic mail enables you to send messages between connected computers. The procedure for sending an
e-mail document involves two separate processes – sending the e-mail to the user's post office, which is a
computer running the POP3 server software, and delivering the e-mail from that post office to the user's e-
mail client computer, which is the recipient.
While popular protocols for retrieving mail include POP3 and IMAP4, sending mail is usually done using the
SMTP protocol.
A user's mailbox can be accessed in two dedicated ways. POP allows the user to download messages one at a
time and only deletes them from the server after they have been successfully saved on local storage. It is
possible to leave messages on the server to permit another client to access them.
Alternatively, IMAP allows users to keep messages on the server, flagging them as appropriate. IMAP
provides folders and sub-folders, which can be shared among different users with possibly different access
rights.
Another important standard supported by most email clients is MIME, which is used to send binary file email
attachments. Attachments are files that are not part of the email proper, but are sent with the email.

The same principle is true with web browsers. The two most popular web browsers are Google Chrome,
Mozilla Firefox, Internet Explorer, Opera, and Safari. The appearance of these web browser programs might
be different, but they both work with the application layer HTTP protocol.
3. Computer Networks
One of the primary purposes of a network is to increase productivity by linking computers and computer
networks, so that people have easy access to information regardless of differences in time, place, or type of
computer system.
Because companies have adopted networks as part of their business strategy, they typically subdivide and
map corporate networks to the corporate business structure. In the figure, the network is defined based on
the grouping of employees (users) into a main office and various remote access locations.
A main office is a site where everyone is connected via a LAN and where the bulk of corporate information is
located. A main office can have hundreds or even thousands of people who depend on network access to do
their jobs. It may have several LANs, or it may be a campus that contains several buildings. Because everyone
needs access to central resources and information, it is common to see a high-speed backbone in a LAN as
well as a data center with high-performance computers or servers and networked applications.
A variety of remote access locations connect to the main office or each other using WAN services as follows:
 In branch offices, smaller groups of people work and connect to each other via a LAN. To connect to
the main office, these users must use WAN services such as Asymmetric digital subscriber line
(ADSL). Although some corporate information may be stored at a branch office, it is more likely that
branch offices have local network resources, such as printers, but have to access information directly
from the main office.
 A home office is where individuals are set up to work from their own home. Home office workers
most likely require on-demand connections to the main office or a branch office to access
information or use network resources such as file servers.
 Individuals who are mobile users connect to the main office LAN when they are at the main office, at
the branch office, or on the road. Their network access needs are based on where they are located.
In order to understand what types of equipment and services to deploy in a network and when to deploy
them, it is important to understand the business and user needs. The figure shows how to map an
organization's business or user requirements to a network.

In this example, the business needs may require LAN connectivity within the campus to interconnect the
servers and end-user PCs, and WAN connectivity to connect the campus to the remote branch office and
telecommuters. The WAN connection to the remote branch office requires a permanent connection, such as
a leased line, and the home office connection requires a dial-up connection, such as ADSL.
Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data
communications technology that enables faster data transmission over copper telephone lines than a
conventional voice band modem can provide. It does this by utilizing frequencies that are not used by a voice
telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service
and voice calls at the same time. ADSL can generally only be distributed over short distances from the
telephone exchange (the last mile), typically less than 4 kilometres (2 mi).
At the telephone exchange the line generally terminates at a digital subscriber line access multiplexer
(DSLAM) where another frequency splitter separates the voice band signal for the conventional phone
network. Data carried by the ADSL are typically routed over the telephone company's data network and
eventually reach a conventional Internet Protocol network.
A digital subscriber line access multiplexer (DSLAM) is a network device, often located in telephone
exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital
communications channel using multiplexing techniques.

Summary
When working with computer applications, it is important that you are familiar with networking
terminology. There are three categories of networks – a LAN, a MAN, and a WAN. The physical topology of a
network is the physical structure of a network. The logical topology of a network is the path that signals
follow through the network.
Network applications are software programs that run between different computers connected on a network.
Each application type has associated protocols depending on the function of the application. HTTP is used by
applications that access the Internet, POP3 is used by applications that access email services, FTP is used by
applications that transfer files, Telnet is used by applications that remotely access other machines, and
SNMP is used by applications that monitor the operation of the network.
Applications interface with protocols in the application layer of the OSI model or TCP/IP stack.
By creating a computer network, you enable access between computers regardless of time, place, or type of
computer system. Because networks are incorporated into the business strategy of a company, a company's
network will usually replicate its business structure. Typically, a network will be subdivided to facilitate the
branch, home, and main office of the company as well as its mobile users.

D. Working with PC technology
After completing this topic, you should be able to identify the purpose of major computer components, and
calculate conversions between binary, decimal, and hexadecimal numerical systems.
1. Exercise overview
2. Task 1: Identifying PC components
3. Task 2: Interpreting numerical systems
1. Exercise overview
In this exercise, you're required to identify the internal components of a PC and calculate conversions
between the three numerical systems – binary, decimal, and hexadecimal.
This involves the following tasks:
 identifying PC components
 converting between numerical systems
2. Task 1: Identifying PC components
Let's look at the internal components of a PC.

Step 1 of 1
Match the PC components to their descriptions.
Options:
1. CD Rom drive
2. Hard disk drive
3. RAM
4. NIC
5. CPU
Targets:
a. A compact disk read-only memory drive
b. A device that reads and writes data on a hard disk
c. An expansion board inserted into a computer to enable connection to a network
d. A silicon-based microprocessor where most of the computer's calculations take place
e. Memory that has new data written into it and has stored data read from it
Resultx
A CD Rom drive is a compact disk read-only memory drive, a hard disk drive is a device that reads and writes
data on a hard disk, RAM is memory that has new data written into it and stored data read from it, a NIC is
an expansion board inserted into a computer to enable connection to a network, and a CPU is a silicon-based
microprocessor where most of the computer's calculations take place.
A CD-ROM drive can read information from a CD-ROM disk.
A hard disk drive reads data from a hard disk. Unlike a CD-ROM drive it can also write data to a disk.
RAM is also known as read-write memory.
The NIC plugs into a motherboard and provides a port for connecting to the network. It is also known as a
LAN adapter.
A CPU acts as the "brain" of the computer.
3. Task 2: Interpreting numerical systems
Let's look at the binary, decimal, and hexadecimal numerical systems.

Step 1 of 5
Match the numerical systems to their descriptions.
Options:
1. Binary
2. Decimal
3. Hexadecimal
Targets:
a. This system uses 16 symbols
b. This system uses 10 symbols
c. This system uses 2 symbols
Result
xi
Binary uses 2 symbols, decimal uses 10 symbols, and hexadecimal uses 16 symbols.
The binary system uses 2 symbols – 0 and 1 – and is also known as base 2.
The decimal system uses 10 symbols – 0 to 9 – and is also known as base 10.
The hexadecimal system uses 16 symbols – 0-9, A-F – and is also known as base 16.
Let's look at some binary conversions.

Step 2 of 5
See if you can convert the binary number 10101000 to decimal.
Result
xii
The decimal equivalent of the binary number 10101000 is 168.
Step 3 of 5
What is the hexadecimal equivalent of 100011000101111?
Options:
1. 462C
2. 462D
3. 462E
4. 462F
Result
The hexadecimal equivalent of 100011000101111 is 462F.
Option 1 is incorrect. 462C is actually the hexadecimal equivalent of 100011000101100.
Option 2 is incorrect. 462D is actually the hexadecimal equivalent of 100011000101101.
Option 3 is incorrect. 462E is actually the hexadecimal equivalent of 100011000101110.
Option 4 is correct. 462F is the hexadecimal equivalent of 100011000101111 – 100 is 4, 0110 is 6, 0010 is 2,
and 1111 is F.
Let's look at a conversion from decimal to binary.

Step 4 of 5
See if you can convert the decimal number 68 to binary.
Result
The decimal number 68 is 1000100 in binary.
Let's look at a conversion from hexadecimal to binary.
Step 5 of 5
What is the binary equivalent of 812C?
Options:
1. 1000000100101011
2. 1000000100101100
3. 1000000100101101
4. 1000000100101110
Result
The binary equivalent of 812C is 1000000100101100.
Option 1 is incorrect. 1000000100101011 is actually the binary equivalent of 812B.
Option 2 is correct. 1000000100101100 is actually the binary equivalent of 812C – 8 is 1000, 1 is 0001, 2 is
0010, and 1100 is C.
Option 3 is incorrect. 1000000100101101 is actually the binary equivalent of 812D.
Option 4 is incorrect. 1000000100101110 is actually the binary equivalent of 812E.

E. OSI model layers and functions
After completing this topic, you should be able to distinguish between the OSI reference model and the
TCP/IP stack.
1. Origins of the OSI reference model
2. OSI layers and functions
3. Data communications
4. The TCP/IP protocol stack
Summary
1. Origins of the OSI reference model
The early development of LANs, MANs, and WANs was chaotic in many ways. The early 1980s saw
tremendous increases in the number and sizes of networks.
As companies realized that they could save money and gain productivity by using networking technology,
they added networks and expanded existing networks as rapidly as new network technologies and products
were introduced.
By the middle of the 1980s, companies began to experience difficulties from all the expansions they had
made. It became more difficult for networks using different specifications and implementations to
communicate with each other.
The companies realized that they needed to move away from proprietary networking systems, those
systems which are privately developed, owned, and controlled.
A standard or technology may be
 proprietary
 open
proprietary
Proprietary means that one company or a small group of companies control(s) all usage of the
technology. In the computer industry, proprietary is the opposite of open.

open
Open means that free usage of the technology is available to the public.
To address the problem of networks being incompatible and unable to communicate with each other, the
International Organization for Standardization (ISO) researched different network schemes.
As a result of this research, the ISO created a model that would help vendors create networks that would be
compatible with, and operate with, other networks.
The Open Systems Interconnection (OSI) reference model, released in 1984, was the descriptive scheme that
the ISO had created. It provided vendors with a set of standards that ensured greater compatibility and
interoperability between the various types of network technologies produced by companies around the
world.
Although other models exist, most network vendors today relate their products to the OSI reference model,
especially when they want to educate customers on the use of their products. It is considered the best tool
available for teaching people about sending and receiving data on a network.
The OSI reference model has seven numbered layers, each illustrating a particular network function. This
separation of networking functions is called layering.

The OSI reference model defines the network functions that occur at each layer.
More importantly, the OSI reference model facilitates an understanding of how information travels
throughout a network.
In addition, the OSI reference model describes how data travels from application programs (for example,
spreadsheets), through a network medium, to an application program located in another computer, even if
the sender and receiver are connected using different network media.
Quiz
Which of the following statements about the OSI model are correct.
Options:
1. It defines the network functions that occur at each layer
2. It is a conceptual framework that specifies how information travels through networks
3. It is a model that describes how data makes its way from one application program to another
throughout a network
4. It was developed in order to help companies communicate with each other using proprietary
network systems.
Answerxiii
(See Endnotes).

2. OSI layers and functions
The practice of moving information between computers is divided into seven techniques in the OSI reference
model.
Each of the seven techniques is represented by its own layer in the model.
The seven layers of the OSI reference model are as follows:
 Layer 7: Application layer
 Layer 6: Presentation layer
 Layer 5: Session layer
 Layer 4: Transport layer
 Layer 3: Network layer
 Layer 2: Data-link layer
 Layer 1: Physical layer
Dividing the network into seven layers provides the following advantages:
 accelerates evolution
 ensures interoperable technology
 facilitates modular engineering
 reduces complexity
 standardizes interfaces
 simplifies teaching and learning
accelerates evolution
Layering accelerates evolution by providing for effective updates and improvements to individual
components without affecting other components or having to rewrite the entire protocol.
ensures interoperable technology
Layering prevents changes in one layer from affecting the other layers, allowing for quicker
development, and ensuring interoperable technology.
facilitates modular engineering
Layering allows different types of network hardware and software to communicate with each other,
thereby facilitating modular engineering.
reduces complexity
Layering breaks network communication into smaller, simpler parts and reduces complexity.
standardizes interfaces

Layering standardizes network component interfaces to allow multiple-vendor development and
support.
simplifies teaching and learning
Layering breaks network communication into smaller components to make learning easier, thereby
simplifying teaching.
Each OSI layer contains a set of functions performed by programs to enable data packets to travel from a
source to a destination on a network.
Now we will look at each layer in the OSI reference model.
The application layer is the OSI layer that is closest to the user. This layer provides network services to the
user's applications. It differs from the other layers in that it does not provide services to any other OSI layer,
but rather, only to applications outside the OSI model.
The application layer establishes the availability of intended communication partners and synchronizes and
establishes agreement on procedures for error recovery and control of data integrity.
The presentation layer ensures that the information that the application layer of one system sends out is
readable by the application layer of another system.
For example, a PC program communicates with another computer, one using extended binary coded decimal
interchange code (EBCDIC) and the other using ASCII to represent the same characters.
If necessary, the presentation layer translates between multiple data formats by using a common format.

The session layer establishes, manages, and terminates sessions between two communicating hosts. It
provides its services to the presentation layer. The session layer also synchronizes dialogue between the
presentation layers of the two hosts and manages their data exchange.
For example, web servers have many users, so there are many communication processes open at a given
time. It is important to keep track of which user communicates on which path.
In addition to session regulation, the session layer offers provisions for efficient data transfer, class of
service, and exception reporting of session layer, presentation layer, and application layer problems.
The transport layer segments data from the sending host's system and reassembles the data into a data
stream on the receiving host's system.
For example, business users in large corporations often transfer large files from field locations to a corporate
site.

Reliable delivery of the files is important, so the transport layer will break down large files into smaller
segments that are less likely to incur transmission problems.
The boundary between the transport layer and the session layer can be thought of as the boundary
between application protocols and data-flow protocols. Whereas the application, presentation, and session
layers are concerned with application issues, the lower four layers are concerned with data transport issues.
The transport layer attempts to provide a data-transport service that shields the upper layers from transport
implementation details. Specifically, issues such as reliability of transport between two hosts are the concern
of the transport layer.
In providing communication service, the transport layer establishes, maintains, and properly terminates
virtual circuits.
Transport error detection and recovery and information flow control are used to provide reliable service.
The network layer provides connectivity and path selection between two host systems that may be located
on geographically separated networks. The growth of the Internet has increased the number of users
accessing information from sites around the world, and it is the network layer that manages this
connectivity.

The data-link layer defines how data is formatted for transmission and how access to the network is
controlled.
The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating,
maintaining, and deactivating the physical link between end systems.
Characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission
distances, physical connectors, and other similar attributes are defined by physical layer specifications.
In summary, the functions of the layers in the OSI model are as follows:
 application network services
 data representation
 interhost communication
 end-to-end connections
 data delivery

 media access
 binary transmission
application network services
The application layer provides network services to any applications requiring access to the network.
data representation
The presentation layer handles data representation. It ensures data is readable, and formats and
structures data. It also negotiates data transfer syntax for the application layer.
interhost communication
The session layer provides interhost communication. In doing this it establishes, manages, and
terminates sessions between applications.
end-to-end connections
The transport layer facilitates end-to-end communications. It handles transportation issues between
hosts and ensures data transport reliability. It also establishes, maintains, and terminates virtual
circuits, and provides reliability through fault detection and recovery information flow control.
data delivery
The network layer ensures data delivery. It provides connectivity and path selection between two
host systems, routes data packets and selects the best path to deliver data.
media access
The data-link layer provides access to the network media. It defines how data is formatted and how
access to the network is controlled.
binary transmission
The physical layer handles binary transmission. It defines the electrical, mechanical, procedural, and
functional specifications for activating, maintaining, and deactivating the physical link. It is
responsible for transmitting the data onto the physical media.

Quiz
What is the function of the session layer?
Options:
1. It routes data packets
2. It ensures reliable transport of data
3. It ensures received data is readable
4. It regulates communication processes
Answerxiv
(See Endnotes).
3. Data communications
All communications on a network originate at a source and are sent to a destination.
The information sent on a network is referred to as data or data packets. If one computer (Host A) wants to
send data to another computer (Host B), the data must first be packaged by a process called encapsulation.
The encapsulation process can be thought of as putting a letter inside an envelope, and then properly
writing the recipient's mail address on the envelope so it can be properly delivered by the postal system.
Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the
data moves down through the layers of the OSI model, each OSI layer adds a header (and a trailer if
applicable) to the data before passing it down to a lower layer.

The headers and trailers contain control information for the network devices and receiver to ensure proper
delivery of the data and to ensure that the receiver can correctly interpret the data.
The figure illustrates how encapsulation occurs. It shows the manner in which data travels through the
layers.
The following eight steps occur in order to encapsulate data:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5
 Step 6
 Step 7
 Step 8

Step 1
Step 1: The user data is sent from an application to the application layer.
Step 2
Step 2: The application layer adds the application layer header (Layer 7 header) to the user data. The
Layer 7 header and the original user data become the data that is passed down to the presentation
layer.
Step 3
Step 3: The presentation layer adds the presentation layer header (Layer 6 header) to the data. This
then becomes the data that is passed down to the session layer.
Step 4
Step 4: The session layer adds the session layer header (Layer 5 header) to the data. This then
becomes the data that is passed down to the transport layer.
Step 5
Step 5: The transport layer adds the transport layer header (Layer 4 header) to the data. This then
becomes the data that is passed down to the network layer.
Step 6
Step 6:The network layer adds the network layer header (Layer 3 header) to the data. This then
becomes the data that is passed down to the data-link layer.
Step 7
Step 7: The data-link layer adds the data-link-layer header and trailer (Layer 2 header and trailer) to
the data. A Layer 2 trailer is usually the frame check sequence (FCS), which is used by the receiver to
detect whether or not the data is in error. This then becomes the data that is passed down to the
physical layer.
Step 8
Step 8:The physical layer then transmits the bits onto the network media.
Quiz
When a user sends information across a network it first traverses the application layer.
Rank the layers of the OSI model in the order in which encapsulation occurs, after the application layer.

Options
Option Description
A Data Link
B Network
C Physical
D Presentation
E Session
F Transport
Answerxv
(See Endnotes).
When the remote device receives a sequence of bits, the physical layer at the remote device passes the bits
to the data-link layer for manipulation.
The data-link layer performs the following tasks:
 Task 1
 Task 2
 Task 3
 Task 4
Task 1
Task 1: It checks the data-link trailer (the FCS) to see if the data is in error.

Task 2
Task 2: If the data is in error, it may be discarded, and the data-link layer may ask for the data to be
retransmitted.
Task 3
Task 3: If the data is not in error, the data-link layer reads and interprets the control information in
the data-link header.
Task 4
Task 4: It strips the data-link header and trailer, and then passes the remaining data up to the
network layer based on the control information in the data-link header.

This process is referred to as de-encapsulation. Each subsequent layer performs a similar de-encapsulation
process. Think of de-encapsulation as the process of reading the address on a letter to see if it is for you or
not, and then removing the letter from the envelope if the letter is addressed to you.
So that data packets can travel from the source to the destination, each layer of the OSI model at the source
must communicate with its peer layer at the destination.
This form of communication is referred to as peer-to-peer communication. During this process, the protocols
at each layer exchange information, called protocol data units (PDUs), between peer layers.
Data packets on a network originate at a source and then travel to a destination. Each layer depends on the
service function of the OSI layer below it.
To provide this service, the lower layer uses encapsulation to put the PDU from the upper layer into its data
field. It then adds whatever headers the layer needs to perform its function. As the data moves down
through Layers 7 through 5 of the OSI model, additional headers are added. The grouping of data at the
Layer 4 PDU is called a segment.
The network layer provides a service to the transport layer, and the transport layer presents data to the
internetwork subsystem.
The network layer moves the data through the internetwork by encapsulating the data and attaching a
header to create a packet (the Layer 3 PDU). The header contains information required to complete the
transfer, such as source and destination logical addresses.

The data-link layer provides a service to the network layer by encapsulating the network layer packet in a
frame (the Layer 2 PDU).
The frame header contains the physical addresses required to complete the data-link functions, and the
frame trailer contains the FCS.
The physical layer provides a service to the data-link layer, encoding the data-link frame into a pattern of 1s
and 0s (bits) for transmission on the medium (usually a wire) at Layer 1.
Network devices such as hubs, switches, and routers work at the lower three layers. Hubs are at Layer 1 –
the physical layer, switches are at Layer 2 – the data-link layer, and routers are at Layer 3 – the network
layer.

Quiz
Match the communication process with its definition.
Options:
1. Encapsulation
2. De-encapsulation
3. Peer-to-peer communication
Targets:
a. This is the process that wraps data with the necessary protocol information before network transit.
b. This is the process that checks for errors, and begins the process of stripping the header and trailer
from received data.
c. This is the process that facilitates the communication between OSI peer layers during data transfer.
Answerxvi
(See Endnotes).
4. The TCP/IP protocol stack
Although the OSI reference model is universally recognized, the historical and technical open standard of the
Internet is the TCP/IP protocol stack.
The TCP/IP protocol stack has four layers – the application layer, the transport layer, the Internet layer, and
the network access layer.
It is important to note that although some of the layers in the TCP/IP protocol stack have the same names as
layers in the OSI model, the layers have different functions in each model.
The following are the TCP/IP protocol stack layers.
 Application
 Transport
 Internet
 Network access

Application
The application layer handles high-level protocols, including issues of representation, encoding, and
dialog control. The TCP/IP model combines all application-related issues into one layer and ensures
that this data is properly packaged for the next layer.
Transport
The transport layer deals with quality-of-service issues of reliability, flow control, and error
correction. One of its protocols, the Transmission Control Protocol (TCP), provides for reliable
network communications.
Internet
The purpose of the Internet layer is to send source packets from any network on the internetwork
and have them arrive at the destination, regardless of the path they took to get there.
Network access
The network access layer is also called the host-to-network layer. It includes the LAN and WAN
protocols, and all the details in the OSI physical and data-link layers.
There are similarities and differences between the TCP/IP protocol stack and the OSI reference model.
The main similarities between the TCP/IP protocol stack and the OSI reference model are
 application layers
 packet-switched technology
 transport and network layers
application layers
Both have application layers, though they include different services.
packet-switched technology
Both assume packet-switched technology, not circuit-switched. (Analog telephone calls are an
example of circuit-switched.)
transport and network layers

Both have comparable transport and network layers.
The main differences between the TCP/IP protocol stack and the OSI reference model are
 data-link and physical layers
 implementation of standards
 presentation and session layers
data-link and physical layers
TCP/IP combines the OSI data-link and physical layers into the network access layer.
implementation of standards
TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP protocol
stack gains credibility just because of the widespread implementation of its protocols. In contrast,
networks are not typically built on the OSI model, even though the OSI model is used as a guide.
presentation and session layers
TCP/IP combines the OSI presentation and session layers into its application layer.
Quiz
In the TCP/IP protocol stack, which layer deals with reliability, flow control, and error correction?
Options:
1. Application
2. Internet
3. Network access
4. Transport
Answerxvii
(See Endnotes).
Summary
The advent of LANs, WANs, and MANs in the 1980s and 1990s was largely unregulated and no standard for
network communication was available. As a result it became more difficult for networks using different
specifications and implementations to communicate with each other. To resolve this, the ISO created and
released the OSI reference model in 1984 to provide vendors with a set of standards to ensure greater
compatibility and interoperability between various types of network technologies.
The OSI reference model comprises seven layers – the application, presentation, session, transport, network,
data-link, and physical layer. Each layer has its own function. The application layer provides network services
to the user applications. The presentation layer presents the data in a format that will be understood by the
receiving application. The session layer regulates the session between the communicating hosts. The
transport layer ensures reliable transport of the data. The network layer routes the packets through the
network. The data-link layer controls access to the network. The physical layer sends the data along the
physical wire.

Encapsulating wraps data with the necessary protocol information before sending it across the network. De-
encapsulation strips the protocol information when the data is received. Each OSI layer at the source
communicates with its peer layer at the destination – this is called peer-to-peer communication.
The TCP/IP protocol stack has four layers – the application layer, transport layer, internet layer, and network
access layer. There are both similarities and differences between the TCP/IP protocol stack and the OSI
reference model. The TCP/IP protocol stack is widely implemented whereas the OSI reference model is
widely used for reference.

F. Working with the OSI model
After completing this topic, you should be able to distinguish between basic computer and networking
terms, and between the principles of the OSI reference model and the TCP/IP protocol stack.
Exercise overview
Task1: Networking terms and functions
Task 2: Functions of the OSI model
Task 3: The data encapsulation process
Exercise overview
In this exercise, you are required to identify networking terms and functions, and the functions of the OSI
reference model. You will also examine data communication methods.
This involves the following tasks:
 identifying networking terms and functions
 defining the functions of each OSI layer
 examining the data encapsulation process
Task1: Networking terms and functions
The topology of a network describes the layout of the wire and devices as well as the paths used by data
transmissions.
Match the schematic description with its function.
Options:
1. Logical topology
2. Physical topology
Targets:
a. This defines the structure of the paths that the signals take within a network
b. This describes the physical layout or structure of the network
Result
The logical topology is the structure of the paths that the signals take within a network and the physical
topology refers to the physical layout or structure of the network.

The logical topology defines the structure of the paths that the signals take within a network. Although the
logical topology does not have to correspond to the physical topology, it is often the same as the physical
topology.
The physical topology is the actual physical shape of the network. Networks can be arranged in a bus, star,
ring, or mesh format.
Network applications are software programs that run between different computers connected on a network.
Each application type has an associated protocol depending on the function of the application.
Step 2 of 3
Which application transfers files between remote computers?
Options:
1. FTP
2. HTTP
3. POP3
4. SMNP
Result
File transfer protocol (FTP) is used to transfer files between remote computers.
Option 1 is correct. FTP is a simple file utility program used for transferring files between remote computers.
Option 2 is incorrect. Hypertext Transfer Protocol (HTTP) establishes a connection between a browser and a
web server allowing the client to view web pages in the web browser.
Option 3 is incorrect. When you send an email it is usually Post Office Protocol version 3 (POP3) that will
hold the mail in a storage container until the receiver is ready to download it.
Option 4 is incorrect. Simple network monitoring protocol (SNMP) is used for monitoring network device
status and activities.

A LAN covers a smaller geographic area than a MAN or a WAN.
Step 3 of 3
Home office users are most likely to connect to the main office LAN using what WAN technology?
Options:
1. Frame Relay
2. ADSL
3. Leased lines
4. X.25
Result
Home office users are most likely to connect to the main office LAN using an ADSL connection.
Option 1 is incorrect. Frame Relay provides a permanent serial connection. Due to the cost of such
connections, this is not an effective solution for home office users
Option 2 is correct. An ADSL connection is a dial-up connection, and is often used by home office users to
connect to a LAN.
Option 3 is incorrect. A WAN connection to the remote branch office requires a permanent connection such
as a leased line. Home office users will most often use a dial-up technology.
Option 4 is incorrect. X.25 is an older form of permanent serial connection, not used very often in modern
networks. Due to the cost of such connections, this is not an effective solution for home office users.
Task 2: Functions of the OSI model
The OSI reference model has seven layers, each illustrating a particular network function. This separation of
networking functions is called layering.

1 of 1
What layer defines voltage levels, timing of voltage changes and maximum transmission distances?
Options:
1. The data-link layer
2. The network layer
3. The physical layer
4. The session layer
5. The transport layer
Result
The physical layer defines voltage levels, timing of voltage changes and maximum transmission distances.
Option 1 is incorrect. The data-link layer controls network access and formats data before it is transmitted to
ensure that it will be properly received.
Option 2 is incorrect. The network layer provides connectivity and path selection for data when moving
between different network locations.
Option 3 is correct. The physical layer defines the hardware specifications required for end-system
communications.
Option 4 is incorrect. The session layer regulates the communication processes of conversations between
hosts.
Option 5 is incorrect. The transport layer is responsible for the reliable transfer of data between network
hosts.
Task 3: The data encapsulation process
Data packets are packaged in a process known as encapsulation before they travel safely across a network.

Step 1 of 1
Which of the following describes the first step of data encapsulation?
Options:
1. A data-link header is stripped from the message
2. The frame is converted into binary format
3. The data-link layer checks the data-link trailer to see if the data is in error
4. The user data is sent from an application to the application layer
Result
The first step of data encapsulation is when the user data is sent from an application to the application layer.
Option 1 is incorrect. This occurs during de-encapsulation. When a message arrives at the data-link layer, it is
checked for errors. If no errors exist, it is then stripped of its data-link header and trailer, and passed on up
to the network layer.
Option 2 is incorrect. Conversion to binary is one of the last processes that occurs before the data frame is
transmitted onto the network media.
Option 3 is incorrect. The FCS trailer is checked after the data has been received from the network and has
been passed from the physical layer to the data-link layer. This is actually a part of the de-encapsulation
process.
Option 4 is correct. When data is sent from an application for transmission on the network, the
encapsulation process begins. Encapsulation begins at the application layer and wraps data with the
necessary protocol information before network transit.

G. Glossary
ABR
Acronym for available bit rate. See UBR.
access list
List kept by Cisco routers to control access to or from the router for a number of services (for
example, to prevent packets with a certain IP address from leaving a particular interface on the
router).
acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example,
receipt of a message) has occurred. Sometimes abbreviated ACK.
active hub
Multiport device that amplifies LAN transmission signals.
adapter
An adapter is a physical device that allows one hardware or electronic interface to be adapted
(accommodated without loss of function) to another hardware or electronic interface. In a
computer, an adapter is often built into a card that can be inserted into a slot on the computer's
motherboard. The card adapts information that is exchanged between the computer's
microprocessor and the devices that the card supports.
adaptive routing
See dynamic routing.
address
Data structure or logical convention used to identify a unique entity, such as a particular process or
network device.
Address Resolution Protocol
Abbreviated to ARP.
administrative distance
A rating of the trustworthiness of a routing information source. In Cisco routers, administrative
distance is expressed as a numerical value between 0 and 255. The higher the value, the lower the
trustworthiness rating.
ADSL
Acronym for asymmetric digital subscriber line. One of four DSL technologies. ADSL is designed to
deliver more bandwidth downstream (from the central office to the customer site) than upstream.
Downstream rates range from 1.5 to 9 Mbps, while upstream bandwidth ranges from 16 to 640
kbps. ADSL transmissions work at distances up to 18,000 feet (5,488 meters) over a single copper
twisted pair.
algorithm
Well-defined rule or process for arriving at a solution to a problem. In networking, algorithms are
commonly used to determine the best route for traffic from a particular source to a particular
destination.
American National Standards Institute
See ANSI.
American Standard Code for Information Interchange
See ASCII
ANSI
Acronym for American National Standards Institute. Voluntary organization comprised of corporate,
government, and other members that coordinates standards-related activities, approves U.S.
national standards, and develops positions for the United States in international standards
organizations. ANSI helps develop international and U.S. standards relating to, among other things,
communications and networking. ANSI is a member of the IEC and the ISO.
API

Acronym for application programming interface. Specification of function-call conventions that
defines an interface to a service.
application layer
Layer 7 of the OSI reference model. This layer provides services to application processes (such as
electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The
application layer identifies and establishes the availability of intended communication partners (and
the resources required to connect with them), synchronizes cooperating applications, and
establishes agreement on procedures for error recovery and control of data integrity. Corresponds
roughly with the transaction services layer in the SNA model.
application programming interface
See API.
ARP
Acronym for Address Resolution Protocol. Internet protocol used to map an IP address to a MAC
address. Defined in RFC 826. Compare with RARP.
ASCII
Acronym for American Standard Code for Information Interchange. 8-bit code for character
representation (7 bits plus parity).
asymmetric digital subscriber line
Abbreviated to ADSL.
asynchronous timedivision multiplexing
See ATDM
Asynchronous Transfer Mode
See ATM.
asynchronous transmission
Term describing digital signals that are transmitted without precise clocking. Such signals generally
have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate
individual characters in control bits (called start and stop bits) that designate the beginning and end
of each character.
ATDM
Acronym for asynchronous time-division multiplexing. Method of sending information that
resembles normal TDM, except that time slots are allocated as needed rather than preassigned to
specific transmitters. See FDM.
ATM
Acronym for Asynchronous Transfer Mode. International standard for cell relay in which multiple
service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length
cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to
take advantage of high-speed transmission media such as E3, SONET, and T3.
attachment unit interface
See AUI.
attenuation
Loss of communication signal energy.
attribute
Configuration data that defines the characteristics of database objects such as the chassis, cards,
ports, or virtual circuits of a particular device. Attributes might be preset or user-configurable.
AUI
Attachment unit interface. IEEE 802.3 interface between an MAU and a NIC (network interface card).
The term AUI can also refer to the rear panel port to which an AUI cable might attach, such as those
found on a Cisco LightStream Ethernet access card. Also called transceiver cable.
autonomous system

Collection of networks under a common administration sharing a common routing strategy.
Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique
16-bit number by the IANA. Sometimes abbreviated AS.
back end
Node or software program that provides services to a front end. Usually transparent to the user.
backbone
The part of a network that acts as the primary path for traffic that is most often sourced from, and
destined for, other networks.
backbone cabling
Cabling that provides interconnections between wiring closets, wiring closets and the POP, and
between buildings that are part of the same LAN. Also known as vertical cabling.
backplane
The backplane is a large circuit board that contains sockets for expansion cards.
backward explicit congestion notification
See BECN.
bandwidth
The difference between the highest and lowest frequencies available for network signals. The term is
also used to describe the rated throughput capacity of a given network medium or protocol.
baseband
Characteristic of a network technology where only one carrier frequency is used. Ethernet is an
example of a baseband network. Also called narrowband.
Basic Rate Interface
See BRI.
baud
Unit of signaling speed equal to the number of discrete signal elements transmitted per second.
Baud is synonymous with bits per second (bps), if each signal element represents exactly 1 bit.
B-channel
The name for a bearer channel. DS0 time slot that carries analog voice or digital data over ISDN. In
ISDN, a full-duplex, 64-kbps channel used to send user data.
BECN
Acronym for backward explicit congestion notification. Bit set by a Frame Relay network in frames
traveling in the opposite direction of frames encountering a congested path. DTE receiving frames
with the BECN bit set can request that higher-level protocols take flow control action as appropriate.
Compare with FECN.
BGP
Acronym for Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP
exchanges reachability information with other BGP systems. It is defined by RFC 1163.
BGP4
BGP Version 4. Version 4 of the predominant interdomain routing protocol used on the Internet.
BGP4 supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables.
Bit
The smallest unit of data in a computer. A bit equals 1 or 0, and is the binary format in which data is
processed by computers.
Border Gateway Protocol
See BGP.
BPDU
Acronym for bridge protocol data unit. Spanning-Tree Protocol hello packet that is sent out at
configurable intervals to exchange information among bridges in the network.
BRI
Acronym for Basic Rate Interface. ISDN interface composed of two B channels and one D channel for
circuit-switched communication of voice, video, and data.

bridge
Device that connects and passes packets between two network segments that use the same
communications protocol. Bridges operate at the data-link layer (Layer 2) of the OSI reference
model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC
address of that frame.
bridge protocol data unit
See BPDU.
broadband
Transmission system that multiplexes multiple independent signals onto one cable. In
telecommunications terminology, any channel having a bandwidth greater than a voicegrade
channel (4 kHz). In LAN terminology, a coaxial cable on which analog signaling is used. Also called
wideband.
broadcast
Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast
address. Compare with multicast and unicast.
broadcast address
Special address reserved for sending a message to all stations. Generally, a broadcast address is a
MAC destination address of all ones.
broadcast domain
The set of all devices that will receive broadcast frames originating from any device within the set.
Broadcast domains are typically bounded by routers because routers do not forward broadcast
frames.
broadcast storm
Undesirable network event in which many broadcasts are sent simultaneously across all network
segments. A broadcast storm uses substantial network bandwidth and, typically, causes network
time-outs.
buffer
Storage area used for handling data in transit. Buffers are used in internetworking to compensate for
differences in processing speed between network devices. Bursts of data can be stored in buffers
until they can be handled by slower processing devices. Sometimes referred to as a packet buffer.
bus
A bus is a collection of wires through which data is transmitted from one part of a computer to
another. The bus connects all the internal computer components to the CPU. The ISA and the PCI are
two types of buses.
bus topology
Linear LAN architecture in which transmissions from network stations propagate the length of the
medium and are received by all other stations.
byte
A byte is a unit of measure used to describe the size of a data file, the amount of space on a disk or
other storage medium, or the amount of data being sent over a network. One byte equals eight bits
of data.
cable
Transmission medium of copper wire or optical fiber wrapped in a protective cover.
Canadian Standards Association
See CSA.
carrier sense multiple access collision detect
See CSMA/CD.
catchment area
Zone that falls within area that can be served by an internetworking device such as a hub.
Category 1 cabling

One of five grades of UTP cabling described in the EIA/TIA-568B standard. Category 1 cabling is used
for telephone communications and is not suitable for transmitting data. Compare with Category 2
cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling.
Category 2 cabling
One of five grades of UTP cabling described in the EIA/TIA-568B standard. Category 2 cabling is
capable of transmitting data at speeds up to 4 Mbps. Compare with Category 1 cabling, Category 3
cabling, Category 4 cabling, and Category 5 cabling.
Category 3 cabling
in 10BASE-T networks and can transmit data at speeds up to 10 Mbps. Compare with Category 1
Category 4 cabling
in Token Ring networks and can transmit data at speeds up to 16 Mbps. Compare with Category 1
Category 5 cabling
for running CDDI and can transmit data at speeds up to 100 Mbps. Compare with Category 1 cabling,
Category 2 cabling, Category 3 cabling, and Category 4 cabling.
CDDI
Acronym for Copper Distributed Data Interface. Implementation of FDDI protocols over STP and UTP
cabling. CDDI transmits over relatively short distances (about 100 meters), providing data rates of
100 Mbps using a dual-ring architecture to provide redundancy. Based on the ANSI Twisted-Pair
Physical Medium Dependent (TPPMD) standard. See FDDI.
CDP
Acronym for Cisco Discovery Protocol. Media- and protocol-independent device-discovery protocol
that runs on all Cisco-manufactured equipment by default including routers, access servers, bridges,
and switches. Using CDP, a device can advertise its existence to other devices and receive
information about other devices on the same LAN or on the remote side of a WAN. Runs on all
media that support SNAP, including LANs, Frame Relay, and ATM media. CDP is a Layer 2 multicast
technology.
cell
The basic unit for ATM switching and multiplexing. Cells contain identifiers that specify the data
stream to which they belong. Each cell consists of a 5-byte header and 48 bytes of payload.
cell switching
Network technology based on the use of small, fixed-size packets, or cells. Because cells are fixed-
length, they can be processed and switched in hardware at high speeds. Cell relay is the basis for
many high-speed network protocols including ATM, IEEE 802.6, and SMDS.
Challenge Handshake Authentication Protocol
See CHAP.
channel service unit
See CSU.
channelized T1
Access link operating at 1.544 Mbps that is subdivided into 24 channels (23 B-channels and 1 D-
channel) of 64 Kbps each. The individual channels or groups of channels connect to different
destinations. Supports DDR, Frame Relay, and X.25. Also referred to as fractional T1.
CHAP
Acronym for Challenge Handshake Authentication Protocol. Security feature supported on lines
using PPP encapsulation that prevents unauthorized access. CHAP does not itself prevent
unauthorized access, it merely identifies the remote end. The router or access server then
determines whether that user is allowed access.

checksum
Method for checking the integrity of transmitted data. A checksum is an integer value computed
from a sequence of octets taken through a series of arithmetic operations. The value is recomputed
at the receiving end and compared for verification.
CIR
Acronym for committed information rate. The rate at which a Frame Relay network agrees to
transfer information under normal conditions, averaged over a minimum increment of time. CIR,
measured in bits per second, is one of the key negotiated tariff metrics.
circuit switching
Switching system in which a dedicated physical circuit path must exist between sender and receiver
for the duration of the call. Used heavily in the telephone company network. Circuit switching can be
contrasted with contention and token passing as a channelaccess method, and with message
switching and packet switching as a switching technique.
Cisco Discovery Protocol
See CDP.
classful network
Network that uses traditional IP network addresses of class A, class B, and class C. The network
boundary is defined by using a prefix value that indicates the number of bits used for the network
portion.
classless network
Network that does not use the traditional IP network addressing (class A, class B, and class C). The
network boundary is defined by the use of a network mask or subnet mask and a logical "AND"
operation between the subnet mask and IP address. Classless networks are more pervasive in
today's networks because of flexibility and less wasted IP addresses.
CLI
Acronym for Command Language Interpreter. The basic Cisco IOS configuration and management
interface.
client
Node or software program (front-end device) that requests services from a server.
client-server model
Common way to describe network services and the model user processes (programs) of those
services. Examples include the nameserver/nameresolver paradigm of the DNS and fileserver/file-
client relationships such as NFS and diskless hosts.
CN
Acronym for Content Network. A collection of devices that optimizes the delivery of Internet content
(such as HTML documents and MPEG files) by caching content near clients, by proactively pushing
content into those caches, and by routing each client request to the best device available at that
moment to serve the particular content requested.
coaxial cable
Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor.
Two types of coaxial cable are currently used in LANs: 50-ohm cable, which is used for digital
signaling, and 75-ohm cable, which is used for analog signal and highspeed digital signaling.
collapsed backbone
Nondistributed backbone in which all network segments are interconnected by way of an
internetworking device. A collapsed backbone might be a virtual network segment existing in a
device such as a hub, a router, or a switch.
collision
In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device
impact and are damaged when they meet on the physical media.
Command Language Interpreter
See CLI

committed information rate
See CIR.
communication
Transmission of information.
compression
The running of a data set through an algorithm that reduces the space required to store or the
bandwidth required to transmit the data set.
computer
A device that computes. More recently, a device that can solve billions of equations per second.
concentrator
Any device that enables multiple physical or logical connections to be made at or to a single point. A
hub is an example of a device that allows multiple physical connections into that single hub.
conductor
Any material with a low resistance to electrical current. Any material capable of carrying an electrical
current.
configuration register
In Cisco devices, a 16-bit, user-configurable value that determines how the router functions during
initialization. The configuration register can be stored in hardware or software. In hardware, the bit
position is set using a jumper. In software, the bit position is set by specifying a hexadecimal value
using configuration commands.
congestion
Traffic in excess of network capacity.
connectionless
Term used to describe data transfer without the existence of a virtual circuit, error detection, and
acknowledgments.
connection-oriented
Term used to describe data transfer with the existence of a virtual circuit, error detection, and
acknowledgments.
console
DTE through which commands are entered into a host. The functionality can be provided for through
a terminal device or application such as Telnet.
Content Network
See CN.
contention
Network media access method in which network devices compete for permission to access the
physical medium.
convergence
The speed and ability of a group of internetworking devices running a specific routing protocol or
Spanning-Tree Protocol to agree on the topology of an internetwork after a change in that topology.
Copper Distributed Data Interface
See CDDI.
cost
Arbitrary value, typically based on hop count, media bandwidth, or other measures, that is assigned
by a network administrator and used to compare various paths through an internetwork
environment. Cost values are used by Layer 2 and Layer 3 protocols, such as STP and routing
protocols respectively, to determine the most favorable path to a particular destination: the lower
the cost, the better the path. Sometimes called path cost.
cps
Acronym for cells per second.
CPU

Acronym for central processing unit. The CPU is the "brains" of the computer, where most of the
calculations and processing take place.
CRC
Acronym for cyclic redundancy check. Error-checking technique in which the frame recipient
calculates a remainder by dividing frame contents by a prime binary divisor and compares the
calculated remainder to a value stored in the frame by the sending node.
CSA
Acronym for Canadian Standards Association. Agency within Canada that certifies products that
conform to Canadian national safety standards.
CSMA/CD
Acronym for Carrier sense multiple access collision detect. Contention based Media-access
mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier
is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a
collision occurs and is detected by all colliding devices. This collision subsequently delays
retransmissions from those devices for some random length of time. CSMA/CD access is used by
Ethernet and IEEE 802.3.
CSU
Acronym for channel service unit. Digital interface device that connects end-user equipment to the
local digital telephone loop. Often referred to together with DSU, as CSU/DSU.
cyclic redundancy check
See CRC.
data circuit-terminating equipment
See DCE.
data communications equipment
See DCE
Data Encryption Standard
See DES.
data service unit
See DSU.
data terminal equipment
See DTE.
data-link layer
Layer 2 of the OSI reference model. This layer provides reliable transit of data across a physical link.
The data-link layer is concerned with physical addressing, network topology, line discipline, error
notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two
sublayers: the MAC sublayer and the LLC sublayer. Sometimes simply called link layer. Roughly
corresponds to the data-link control layer of the SNA model.
DCE
Data communications equipment (EIA expansion) or data circuit-terminating equipment (ITU-T
expansion). The devices and connections of a communications network that comprise the network
end of the user-to-network interface. The DCE provides a physical connection to the network,
forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE
and DTE devices. Switches, modems and interface cards are examples of DCE.
D-channel (data channel)
Full-duplex, 16-kbps (BRI), or 64-kbps (PRI) ISDN channel used for call setup (BRI), control, and
protocol negotiations.
DDR
Acronym for Dial-on-demand routing. Technique whereby a Cisco router can automatically initiate
and close a circuit-switched session as transmitting stations demand. The router spoofs keepalives
so that end stations treat the session as active. DDR permits routing over ISDN or telephone lines
using an external ISDN terminal adaptor or modem.

DECnet
Group of communications products (including a protocol suite) developed and supported by Digital
Equipment Corporation. DECnet/OSI (also called DECnet Phase V) is the most recent iteration and
supports both OSI protocols and proprietary digital protocols. Phase IV Prime supports inherent MAC
addresses that allow DECnet nodes to coexist with systems running other protocols that have MAC
address restrictions.
decryption
The reverse application of an encryption algorithm to encrypted data, thereby restoring that data to
its original, unencrypted state.
default route
Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the
routing table.
demarc
Demarcation point between carrier equipment and CPE. The point at which the service provider's
local loop ends and the customer's network begins.
demodulation
Process of returning a modulated signal to its original form. Modems perform demodulation by
taking an analog signal and returning it to its original (digital) form.
demultiplexing
The separating of multiple input streams that have been multiplexed into a common physical signal
back into multiple output streams.
DES
Acronym for Data Encryption Standard. Standard cryptographic algorithm developed by the U.S.
NBS.
dial-on-demand routing
See DDR.
DNS
Acronym for Domain Naming System. System used in the Internet for translating names of network
nodes into IP addresses.
domain
In the Internet, a portion of the naming hierarchy tree that refers to general groupings of networks
based on organization-type or geography. Also can be generally used to describe a logical grouping
of networked devices that exhibit the same characteristics or use the same protocols.
dot address
Refers to the common notation for IP addresses in the form <a.b.c.d> where each number
represents, in decimal, 1 byte of the 4-byte IP address. Also called dotted notation or four-part
dotted notation.
dotted decimal notation
Syntactic representation for a 32-bit integer that consists of four 8-bit numbers written in base 10
with periods (dots) separating them. Used to represent IP addresses.
DRAM
Acronym for dynamic random-access memory. RAM that stores information in capacitors that must
be periodically refreshed. DRAMs are less complex and have greater capacity than SRAMs.
DS0
Digital signal level 0. Framing specification used in transmitting digital signals over a single channel at
64 kbps on an ISDN facility.
DS1
Digital signal level 1. Framing specification used in transmitting digital signals at 1.544 Mbps on a T1
facility (in the U.S.) or at 2.048-Mbps on an E1 facility (in Europe).
DS3

Digital signal level 3. Framing specification used for transmitting digital signals at 44.736 Mbps on a
T3 facility and 34.368 on an E3 facility.
DSU
Acronym for data service unit. Device used in digital transmission that adapts the physical interface
on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for such
functions as signal timing. Often referred to together with CSU, as CSU/DSU.
DTE
Acronym for data terminal equipment. Device at the user end of a user-network interface that
serves as a data source, destination, or both. DTE connects to a data network through a DCE device
(for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such
devices as computers, routers, protocol translators, and multiplexers.
dynamic random-access memory
See DRAM.
dynamic routing
Routing that adjusts automatically to network topology or traffic changes. Also called adaptive
routing. Requires that a routing protocol be run between routers.
E1
Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of
2.048 Mbps. E1 lines can be leased for private use from common carriers.
E3
Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of
34.368 Mbps. E3 lines can be leased for private use from common carriers.
EBCDIC
Acronym for extended binary coded decimal interchange code. Any of a number of coded character
sets developed by IBM consisting of 8-bit coded characters. This character code is used by older IBM
systems and telex machines.
EEPROM
Acronym for Electrically Erasable Programmable Read-Only Memory. EPROM that can be erased
using electrical signals applied to specific pins.
EGP
Acronym for Exterior Gateway Protocol. Internet protocol for exchanging routing information
between autonomous systems. Documented in RFC 904. Not to be confused with the general term
exterior gateway protocol. EGP is an obsolete protocol that has been replaced by BGP.
EIA/TIA-232
Common physical-layer interface standard, developed by EIA and TIA, that supports unbalanced
circuits at signal speeds of up to 64 kbps. Closely resembles the V.24 specification. Formerly known
as RS-232.
EIA/TIA-449
Popular physical-layer interface developed by EIA and TIA. Essentially, a faster (up to 2 Mbps)
version of EIA/TIA-232 capable of longer cable runs. Formerly called RS-449.
EIA/TIA-568
Standard that describes the characteristics and applications for various grades of UTP cabling.
EIA/TIA-606
Administration standard for the telecommunications infrastructure of commercial buildings. It
includes the following administration areas: terminations, media, pathways, spaces, bounding, and
grounding.
EIA-530
Refers to two electrical implementations of EIA/TIA-449: RS-422 (for balanced transmission) and RS-
423 (for unbalanced transmission).
EIGRP

Acronym for Enhanced Interior Gateway Routing Protocol. Advanced version of IGRP developed by
Cisco. Provides superior convergence properties and operating efficiency, and combines the
advantages of link state protocols with those of distance vector protocols.
EISA
Acronym for Extended Industry-Standard Architecture. 32-bit bus interface used in PCs, PC-based
servers, and some UNIX workstations and servers.
Electrically Erasable Programmable Read-Only Memory
See EEPROM
electromagnetic interference
See EMI.
electromagnetic pulse
See EMP.
electrostatic discharge
See ESD.
EMI
Acronym for electromagnetic interference. Interference by electromagnetic signals that can cause
reduced data integrity and increased error rates on transmission channels.
EMP
Acronym for electromagnetic pulse. Caused by lightning and other high-energy phenomena. Capable
of coupling enough energy into unshielded conductors to destroy electronic devices.
encapsulation
Device or software that modifies information into the required transmission format.
encoding
Process by which bits are represented by voltages.
encryption
The application of a specific algorithm to data so as to alter the appearance of the data making it
incomprehensible to those who are not authorized to see the information.
end of transmission
See EOT.
Enhanced Interior Gateway Routing Protocol
See EIGRP.
enterprise network
Large and diverse network connecting most major points in a company or other organization. Differs
from a WAN in that it is privately owned and maintained.
EOT
Acronym for end of transmission. Generally, a character that signifies the end of a logical group of
characters or bits.
EPROM
Acronym for erasable programmable read-only memory. Nonvolatile memory chips that are
programmed after they are manufactured, and, if necessary, can be erased by some means and
reprogrammed. Compare with EEPROM and PROM.
erasable programmable read-only memory
See EPROM.
ESD
Acronym for electrostatic discharge. A flow or spark of electricity that originates from a static source
such as a carpet and arcs across a gap to another object.
Ethernet
Baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and
Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable
types at 10 Mbps. Ethernet is similar to the IEEE 802.3 series of standards.
expansion card

The expansion card is a printed circuit board that can be inserted into a computer to give the
computer added capabilities.
expansion slot
The expansion slot is an opening in a computer where a circuit board can be inserted to add new
capabilities to the computer.
extended binary coded decimal interchange code
See EBCDIC.
Extended Industry- Standard Architecture
See EISA.
Exterior Gateway Protocol
See EGP.
Fast Ethernet
Any of a number of 100-Mbps Ethernet specifications. Fast Ethernet offers a speed increase ten
times that of the 10BASE-T Ethernet specification while preserving such qualities as frame format,
MAC mechanisms, and MTU. Such similarities allow the use of existing 10BASE-T applications and
network management tools on Fast Ethernet networks. Based on an extension to the IEEE 802.3
specification.
fast switching
Cisco feature whereby a route cache is used to expedite packet switching through a router. Contrast
with slow switching.
FCS
Acronym for frame check sequence. Refers to the extra characters added to a frame for error control
purposes. Used in HDLC, Frame Relay, and other data-link layer protocols.
FDDI
Acronym for Fiber Distributed Data Interface. LAN standard, defined by ANSI X3T9.5, specifying a
100-Mbps token-passing network using fiber-optic cable, with transmission distances of up to 2 km.
FDDI uses a dual-ring architecture to provide redundancy. Compare with CDDI and FDDI II.
FDDI II
ANSI standard that enhances FDDI. FDDI II provides isochronous transmission for connectionless
data circuits and connection-oriented voice and video circuits. Compare with FDDI.
FDM
Acronym for frequency-division multiplexing. Technique whereby information from multiple
channels can be allocated bandwidth on a single wire based on frequency. Compare with ATDM,
statistical multiplexing, and TDM.
FECN
Acronym for forward explicit congestion notification. Bit set by a Frame Relay network to inform DTE
receiving the frame that congestion was experienced in the path from source to destination. DTE
receiving frames with the FECN bit set can request that higher-level protocols take flow-control
action as appropriate. Compare with BECN.
Fiber Distributed Data Interface
See FDDI.
fiber-optic cable
Physical medium capable of conducting modulated light transmission. Compared with other
transmission media, fiber-optic cable is more expensive, but is not susceptible to electromagnetic
interference, and is capable of higher data rates. Sometimes called optical fiber.
field-replaceable unit
See FRU.
File Transfer Protocol
See FTP.
firewall

Router or access server, or several routers or access servers, designated as a buffer between any
connected public networks and a private network. A firewall router uses access lists and other
methods to ensure the security of the private network.
firmware
Software instructions set permanently or semi permanently in ROM.
flash memory
Technology developed by Intel and licensed to other semiconductor companies. Flash memory is
nonvolatile storage that can be electrically erased and reprogrammed. Allows software images to be
stored, booted, and rewritten as necessary.
flash update
Routing update sent asynchronously in response to a change in the network topology. Compare with
routing update.
flat addressing
Scheme of addressing that does not use a logical hierarchy to determine location.
flooding
Traffic passing technique used by networking devices such as routers and switches in which traffic
received on an interface is sent out all of the interfaces of that device except the interface on which
the information was originally received.
flow
Stream of data traveling between two endpoints across a network (for example, from one LAN
station to another). Multiple flows can be transmitted on a single circuit.
flow control
Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving
entity with data. When the buffers on the receiving device are full, a message is sent to the sending
device to suspend the transmission until the data in the buffers has been processed. In IBM
networks, this technique is called pacing.
forward explicit congestion notification
See FECN.
fractional T1
Access link operating at 1.544 Mbps that is subdivided into 24 channels (23 B-channels and one D-
channel) of 64 Kbps each. The individual channels or groups of channels connect to different
destinations. Supports DDR, Frame Relay, and X.25. Also referred to as channelized T1.
fragment
Piece of a larger packet that has been broken down to smaller units.
frame
Logical grouping of information sent as a data-link layer unit over a transmission medium. Often
refers to the header and trailer, used for synchronization and error control, that surround the user
data contained in the unit. The terms datagram, message, packet, and segment are also used to
describe logical information groupings at various layers of the OSI reference model and in various
technology circles.
frame check sequence
See FCS.
Frame Relay
Industry-standard, switched data-link layer protocol that handles multiple virtual circuits using HDLC
encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for
which it is generally considered a replacement.
frequency
Number of cycles, measured in hertz, of an alternating current signal per unit time.
frequency-division multiplexing
See FDM.
front end

Node or software program that requests services of a back end. Usually is the user interface.
FRU
Acronym for field-replaceable unit. Hardware component that can be removed and replaced by
Ciscocertified service providers. Typical FRUs include cards, power supplies, and chassis components.
FTP
Acronym for File Transfer Protocol. Popular network application that allows files to be moved from
one network device to another. Part of the TCP/IP protocol stack, used for transferring files between
network nodes. FTP is defined in RFC 959.
full duplex
Capability for simultaneous data transmission between a sending station and a receiving station.
full mesh
Term describing a network in which devices are organized in a mesh topology, with each network
node having either a physical circuit or a virtual circuit connecting it to every other network node. A
full mesh provides a great deal of redundancy, but because it can be prohibitively expensive to
implement, it is usually reserved for network backbones.
gateway
In the IP community, an older term referring to a routing device. Today, the term router is used to
describe nodes that perform this function, and gateway refers to a specialpurpose device that
performs an application layer conversion of information from one protocol stack to another.
Compare with router.
GB
Acronym for gigabyte.
Gb
Acronym for gigabit.
GBps
Acronym for gigabytes per second.
Gbps
Acronym for gigabits per second.
GHz
Acronym for gigahertz
gigabit
Abbreviated to Gb.
Gigabit Ethernet
An extension of the IEEE 802.3 Ethernet standard, Gigabit Ethernet increases speed tenfold over Fast
Ethernet, to 1000 Mbps, or 1 gigabit per second (Gbps). Two IEEE 802.3 standards, IEEE 802.3z and
IEEE 802.3ab, define Gigabit Ethernet operations over fiber-optic and twisted-pair cable.
gigabits per second
Abbreviated to Gbps.
gigabyte
Abbreviated to GB.
gigabytes per second
Abbreviated to GBps.
gigahertz
Abbreviated to GHz.
gigahertz (GHz)
A gigahertz is one thousand million, or 1 billion (1,000,000,000), cycles per second.
graphical user interface
See GUI.
GUI(
Acronym for graphical user interface. User environment that uses pictorial as well as textual
representations of the input and output of applications and the hierarchical or other data structure

in which information is stored. Conventions such as buttons, icons, and windows are typical, and
many actions are performed using a pointing device (such as a mouse). Microsoft Windows and the
Apple Macintosh are prominent examples of platforms utilizing a GUI.
half duplex
Capability for data transmission in only one direction at a time between a sending station and a
receiving station. Compare with full duplex and simplex.
handshake
Sequence of messages exchanged between two or more network devices to ensure transmission
synchronization.
hard disk drive
A drive device that reads and writes data on a hard disk, and is completely and internally self-
contained. A hard drive allows for larger data storage capacity than floppy drives, and is non-
removable.
hardware address
MAC address.
HDLC
Acronym for high-level data link control. Bit-oriented synchronous data-link layer protocol
developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous
serial links using frame characters and checksums.
hertz (Hz)
A hertz is a unit of frequency. It is the rate of change in the state or cycle in a sound wave,
alternating current, or other cyclical waveform. It represents one cycle per second and is used to
describe the speed of a computer microprocessor.
hexadecimal
Base 16. A number representation using the digits 0 through 9, with their usual meaning, plus the
letters A through F to represent hexadecimal digits with values of 10 to 15. The right-most digit
counts ones, the next counts multiples of 16, then 16^2=256, etc.
hierarchical routing
Routing based on a hierarchical addressing system. For example, IP routing algorithms use IP
addresses, which contain network numbers, subnet numbers, and host numbers.
hierarchical star topology
Extended star topology where a central hub is connected by vertical cabling to other hubs that are
dependent on it.
high-level data link control
See HDLC.
holddown
State into which a route is placed so that routers will neither advertise the route nor accept
advertisements about the route for a specific length of time (the holddown period). Holddown is
used to flush bad information about a route from all routers in the network. A route is typically
placed in holddown when a link in that route fails.
hop
Term describing the passage of a data packet between two network nodes (for example, between
two routers).
hop count
Routing metric used to measure the distance between a source and a destination. RIP uses hop
count as its sole metric.
host
Computer system on a network. Similar to the term node except that host usually implies a
computer system, whereas node generally applies to any networked system, including access servers
and routers.
HTTP

Acronym for Hypertext Transfer Protocol. The protocol used by Web browsers and Web servers to
transfer files, such as text and graphics files.
hub
Generally, a term used to describe a device that serves as the center of a startopology network. 2.
Hardware or software device that contains multiple independent but connected modules of network
and internetwork equipment. Hubs can be active (where they repeat signals sent through them) or
passive (where they do not repeat, but merely split, signals sent through them). 3. In Ethernet and
IEEE 802.3, an Ethernet multiport repeater, sometimes referred to as a concentrator.
hypertext
Electronically-stored text that allows direct access to other texts by way of encoded links. Hypertext
documents can be created using HTML, and often integrate images, sound, and other media that are
commonly viewed using a WWW browser.
Hypertext Transfer Protocol
See HTTP.
Hz
See hertz.
ICMP
Acronym for Internet Control Message Protocol. Network layer Internet protocol that reports errors
and provides other information relevant to IP packet processing. Documented in RFC 792.
IDF
Acronym for Intermediate distribution facility. Secondary communications room for a building using
a star networking topology. The IDF is dependent on the MDF.
IEEE 802.2
An IEEE LAN protocol that specifies an implementation of the LLC sublayer of the datalink layer. IEEE
802.2 handles errors, framing, flow control, and the network-layer (Layer 3) service interface. Used
in IEEE 802.3 and IEEE 802.5 LANs.
IEEE 802.3
An IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of
the data-link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical
media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet. Physical
variations of the original IEEE 802.3 specification include 10BASE2, 10BASE5, 10BASE-F, 10BASE-T,
and 10Broad36. Physical variations for Fast Ethernet include 100BASE-TX and 100BASE-FX.
IGP
Acronym for Interior Gateway Protocol. Internet protocol used to exchange routing information
within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP.
IGRP
Acronym for Interior Gateway Routing Protocol. IGP developed by Cisco to address the problems
associated with routing in large, heterogeneous networks. Compare with Enhanced IGRP.
in-band signaling
Transmission within a frequency range normally used for information transmission. Compare with
out-of-band signaling.
Industry Standard Architecture
See ISA.
infrared
Electromagnetic waves whose frequency range is above that of microwaves, but below that of the
visible spectrum. LAN systems based on this technology represent an emerging technology.
insulator
Any material with a high resistance to electrical current.
Integrated Services Digital Network
See ISDN.
Interface

1.Connection between two systems or devices. <br /> 2. In routing terminology, a network
connection. <br /> 4. The boundary between adjacent layers of the <a href="#"><span
class="crossref">OSI</span></a>model.
Interior Gateway Protocol
See IGP.
Interior Gateway Routing Protocol
See IGRP.
Intermediate distribution facility
See IDF.
Intermediate System-to-Intermediate System
See IS-IS.
internet
Short for internetwork. Not to be confused with the Internet.
Internet
Term used to refer to the largest global internetwork, connecting tens of thousands of networks
worldwide and having a "culture" that focuses on research and standardization based on real-life
use. Many leading-edge network technologies come from the Internet community. The Internet
evolved in part from ARPANET. At one time, called the DARPA Internet. Not to be confused with the
general term internet.
Internet Control Message Protocol
See ICMP.
internetwork
Collection of networks interconnected by routers and other devices that functions (generally) as a
single network. Sometimes called an internet, which is not to be confused with the Internet.
Internetwork Packet Exchange
See IPX.
internetworking
General term used to refer to the industry that has arisen around the problem of connecting
networks together. The term can refer to products, procedures, and technologies.
IPX
Acronym for Internetwork Packet Exchange. NetWare network layer (Layer 3) protocol used for
transferring data from servers to workstations. IPX is similar to IP and XNS.
ISA
Acronym for Industry Standard Architecture. An older standard for connecting peripherals to a
personal computer. Used primarily in AT-style IBM compatibles.
ISDN
Acronym for Integrated Services Digital Network. Communication protocol, offered by telephone
companies, that permits telephone networks to carry data, voice, and other source traffic.
IS-IS
Acronym for Intermediate System-to-Intermediate System. OSI link-state hierarchical routing
protocol based on DECnet Phase V routing whereby ISs (routers) exchange routing information
based on a single metric to determine network topology. Compare with Integrated IS-IS.
jabber
Error condition in which a network device continually transmits random, meaningless data onto the
network. 2. In IEEE 802.3, a data packet whose length exceeds that prescribed in the standard.
jitter
Analog communication line distortion caused by the variation of a signal from its reference timing
positions. Jitter can cause data loss, particularly at high speeds.
jumper

Term used for patchcords found in a wiring closet. 2.)Electrical switch consisting of a number of pins
and a connector that can be attached to the pins in a variety of different ways. Different circuits are
created by attaching the connector to different pins.
KB
Acronym for kilobyte. Approximately 1000 bytes.
Kb
Acronym for kilobit. Approximately 1000 bits.
kBps
Acronym for kilobytes per second.
kbps
Acronym for kilobits per second.
keepalive interval
Period of time between each keepalive message sent by a network device.
keepalive message
Message sent by one network device to inform another network device that the virtual circuit
between the two is still active.
kilobit
Abbreviated to kb.
kilobits per second
Abbreviated to kbps. This is a standard measurement of the amount of data transferred over a
network connection.
kilobyte
Abbreviated to KB.
kilobytes per second
Abbreviated to kBps. This is a standard measurement of the amount of data transferred over a
network connection.
LAN
Acronym for local-area network. High-speed, low-error data network covering a relatively small
geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals,
and other devices in a single building or other geographically limited area. LAN standards specify
cabling and signaling at the physical and data-link layers of the OSI model. Ethernet, FDDI, and Token
Ring are widely used LAN technologies.
LAN switch
High-speed switch that forwards packets between data-link segments. Most LAN switches forward
traffic based on MAC addresses. This variety of LAN switch is sometimes called a frame switch. LAN
switches are often categorized according to the method they use to forward traffic: cut-through
packet switching or store-and-forward packet switching. Multilayer switches are an intelligent subset
of LAN switches. An example of a LAN switch is the Cisco Catalyst 5000. Compare with multilayer
switch.
LAPB
Acronym for Link Access Procedure, Balanced. Data-link layer protocol in the X.25 protocol stack.
LAPB is a bit-oriented protocol derived from HDLC.
LAPD
Acronym for Link Access Procedure on the D channel. ISDN data-link layer protocol for the D
channel. LAPD was derived from the LAPB protocol and is designed primarily to satisfy the signaling
requirements of ISDN basic access. Defined by ITU-T Recommendations Q.920 and Q.921.
laser
Light amplification by stimulated emission of radiation. Analog transmission device in which a
suitable active material is excited by an external stimulus to produce a narrow beam of coherent
light that can be modulated into pulses to carry data. Networks based on laser technology are
sometimes run over SONET.

latency
Delay between the time a device requests access to a network and the time it is granted permission
to transmit. 2. Delay between the time when a device receives a frame and the time that frame is
forwarded out the destination port.
leased line
Transmission line reserved by a communications carrier for the private use of a customer. A leased
line is a type of dedicated line.
LED
Acronym for light emitting diode. Semiconductor device that emits light produced by converting
electrical energy. Status lights on hardware devices are typically LEDs.
light emitting diode
See LED.
line of sight
Characteristic of certain transmission systems such as laser, microwave, and infrared systems in
which no obstructions in a direct path between transmitter and receiver can exist.
link
Network communications channel consisting of a circuit or transmission path and all related
equipment between a sender and a receiver. Most often used to refer to a WAN connection.
Sometimes referred to as a line or a transmission link.
Link Access Procedure on the D channel
See LAPD.
Link Access Procedure, Balanced
See LAPB.
link-state routing algorithm
Routing algorithm in which each router broadcasts or multicasts information regarding the cost of
reaching each of its neighbors to all nodes in the internetwork. Link-state algorithms create a
consistent view of the network and are therefore not prone to routing loops, but they achieve this at
the cost of relatively greater computational difficulty and more widespread traffic (compared with
distance vector routing algorithms). Compare with distance vector routing algorithm.
LLC
Acronym for Logical Link Control. Higher of the two data-link layer sublayers defined by the IEEE. The
LLC sublayer handles error control, flow control, framing, and MAC-sublayer addressing. The most
prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented
variants.
local loop loop
Line from the premises of a telephone subscriber to the telephone company CO. Route where
packets never reach their destination, but simply cycle repeatedly through a constant series of
network nodes.
loopback test
Test in which signals are sent and then directed back toward their source from some point along the
communications path. Loopback tests are often used to test network interface usability.
MAC
Acronym for Media Access Control. Lower of the two sublayers of the data-link layer defined by the
IEEE. The MAC sublayer handles access to shared media, such as whether token passing or
contention will be used.
MAC address
Standardized data-link layer address that is required for every port or device that connects to a LAN.
MAC addresses are six bytes long and are controlled by the IEEE. Also known as a hardware address,
MAC layer address, and physical address.
main distribution facility
See MDF.

MAN
Acronym for metropolitan-area network. Network that spans a metropolitan area. Generally, a MAN
spans a larger geographic area than a LAN, but a smaller geographic area than a WAN.
MDF
Acronym for main distribution facility. Primary communications room for a building. Central point of
a star networking topology where patch panels, hub, and router are located.
Media Access Control
See MAC.
megabit (Mb)
A megabit is approximately 1 million bits.
megabits per second (Mbps)
A standard measurement of the amount of data transferred over a network connection during a
time period of one second.
megabyte (MB)
A megabyte is approximately 1 million bytes (1,048,576 bytes exactly). A megabyte is sometimes
referred to as a "meg."
megabytes per second(MBps)
A standard measurement of the amount of data transferred over a network connection during a
time period of one second.
megahertz (MHz)
A megahertz is one million cycles per second. This is a common measurement of the speed of a
processing chip, such as a computer microprocessor.
metropolitan-area network
See MAN.
microprocessor
A microprocessor is a silicon chip that contains a CPU.
modulation
Process by which the characteristics of electrical signals are transformed to represent information.
Modems perform modulation by taking a digital signal and altering it to an analog signal.
mouse port
This port is designed for connecting a mouse to a PC.
multicast
Single packets copied by the network and sent to a specific subset of network addresses. These
addresses are specified in the destination address field. See broadcast.
multicast address
Single address that refers to multiple network devices in a group. Synonymous with group address.
multiplexing
Scheme that allows multiple logical signals to be transmitted simultaneously across a single physical
channel.
NAK
Acronym for negative acknowledgment. Response sent from a receiving device to a sending device
indicating that the information received contained errors.
narrowband
See baseband.
negative acknowledgment
See NAK.
network
Collection of computers, printers, routers, switches, and other devices that are able to communicate
with each other over some transmission medium. 2. Command that assigns a NIC-based address to
which the router is directly connected. 3. Command that specifies any directly connected networks
to be included.

network card
The network card is an expansion board inserted into a computer so that the computer can be
connected to a network.
network interface card
See NIC.
network layer
Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two
end systems. The network layer is the layer at which routing occurs. Corresponds roughly with the
path control layer of the SNA model.
NIC
Acronym for network interface card. Board that provides network communication capabilities to and
from a computer system. Also called an adapter.
nonvolatile RAM
See NVRAM.
NVRAM
Acronym for nonvolatile RAM. RAM that retains its contents when a unit is powered off.
OIR
Acronym for online insertion and removal. Feature that permits the addition, the replacement, or
the removal of cards without interrupting the system power, entering console commands, or causing
other software or interfaces to shut down. Sometimes called hot swapping or power-on servicing.
online insertion and removal
See OIR.
Open System Interconnection
See OSI.
OSI
Acronym for Open System Interconnection. International standardization program created by ISO
and ITU-T to develop standards for data networking that facilitate multivendor equipment
interoperability.
out-of-band signaling
Transmission using frequencies or channels outside the frequencies or channels normally used for
information transfer. Out-of-band signaling is often used for error reporting in situations in which in-
band signaling can be affected by whatever problems the network might be experiencing. Contrast
with in-band signaling.
packet
Logical grouping of information at Layer 3 that includes a header containing control information and
a PDU from the same or upper layer. Packets are used to refer to network layer units of data. The
terms datagram, frame, message, and segment are also used to describe logical information
groupings at various layers of the OSI reference model and in various technology circles.
PAP
Acronym for Password Authentication Protocol. Authentication protocol that allows PPP peers to
authenticate one another. The remote router attempting to connect to the local router is required
to send an authentication request. Unlike CHAP, PAP passes the password and host name or
username in the clear (unencrypted). PAP does not itself prevent unauthorized access, but merely
identifies the remote end. The router or access server then determines if that user is allowed access.
PAP is supported only on PPP lines.
parallel port
The parallel port is an interface capable of transferring more than one bit simultaneously through a
single cable containing multiple conductors. It is used to connect external devices, such as printers
and internal devices to hard drives.
Password Authentication Protocol
See PAP.

patch panel
An assembly of pin locations and ports that can be mounted on a rack or wall bracket in the wiring
closet. Patch panels act like switchboards that connect workstation cables to each other and to the
outside.
path cost
See cost.
PCB
Acronym for printed circuit board. The PCB is a thin plate on which chips (integrated circuits) and
other electronic components are placed.
PCI
Acronym for peripheral component interconnect. A standard for connecting peripherals to a
personal computer. Used primarily in Pentium- and AMD-based systems, it is processor
independent, therefore can work with other processor architectures.
PCMCIA
Acronym for Personal Computer Memory Card International Association. PCMCIA is an organization
that has developed a standard for small, credit-card sized devices, called PC cards. Originally
designed for adding memory to portable computers, the PCMCIA standard has been expanded
several times and is now suitable for many types of devices.
PDU
Acronym for protocol data unit. OSI term for a layer-specific grouping of data.
peripheral component interconnect
See PCI.
Personal Computer Memory Card International Association
See PCMCIA.
physical layer
Layer 1 of the OSI reference model. The physical layer defines the electrical, mechanical, procedural,
and functional specifications for activating, maintaining, and deactivating the physical link between
end systems. Corresponds with the physical control layer in the SNA model.
ping
Acronym for packet internet groper. ICMP echo message and its reply. Often used in IP networks to
test the reachability of a network device.
power cord
The power cord is used to connect an electrical device to an electrical outlet in order to provide
power to the device.
presentation layer
Layer 6 of the OSI reference model. This layer ensures that information sent by the application layer
of one system will be readable by the application layer of another. The presentation layer is also
concerned with the data structures used by programs and therefore negotiates data transfer syntax
for the application layer.
PRI
Acronym for Primary Rate Interface. ISDN interface to primary rate access. Primary rate access
consists of a single 64-Kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data.
Primary Rate Interface
See PRI.
printed circuit board
See PCB.
process
A single thread of computation to achieve a specific goal performed within a microprocessor or
software.
PROM

Acronym for programmable read-only memory. ROM that can be programmed using special
equipment. PROMs can be programmed only once. Compare with EPROM.
propagation delay
Time required for data to travel over a network, from its source to its ultimate destination.
protocol
Formal description of a set of rules and conventions that govern how devices on a network exchange
information.
protocol data unit
See PDU.
QoS
Acronym for quality of service. Measure of performance for a transmission system that reflects its
transmission quality and service availability.
QoS parameters
Acronym for quality of service parameters. Parameters that control the amount, performance, and
reliability of traffic on a transmission device on a network.
query
Message used to inquire about the value of some variable or set of variables.
queue
Generally, an ordered list of elements waiting to be processed. 2. In routing, a backlog of packets
waiting to be forwarded over a router interface.
queuing delay
Amount of time that data must wait before it can be transmitted onto a statistically multiplexed
physical circuit.
RAM
Acronym for random-access memory. Also known as read-write memory, RAM can have new data
written into it as well as stored data read from it. If the computer is turned off or loses power, all
data stored in RAM is lost unless the data was previously saved to disk.
random-access memory
See RAM.
RARP
Acronym for Reverse Address Resolution Protocol. Protocol in the TCP/IP stack that provides a
method for acquiring an IP address based on MAC addresses.
Reverse Address Resolution Protocol
See RARP.
ring topology
Network topology that consists of a series of repeaters connected to one another by unidirectional
transmission links to form a single closed loop. Each station on the network connects to the network
at a repeater. While logically a ring, ring topologies are most often organized in a closed-loop star.
RIP
Acronym for Routing Information Protocol. IGP supplied on many UNIX systems. The most common
IGP in the Internet. RIP uses hop count as a routing metric.
RJ connector
Acronym for registered jack connector. Standard connectors originally used to connect telephone
lines. RJ connectors are now used for telephone connections and for 10BASE-T and other types of
network connections. RJ-11, RJ-12, and RJ-45 are popular types of RJ connectors.
ROM
Acronym for read-only memory. ROM is computer memory on which data has been prerecorded.
ROM
Acronym for read-only memory. Nonvolatile memory that can be read, but not written, by the
microprocessor.
route

Path through an internetwork.
routed protocol
Protocol that can be routed by a router. A router must be able to interpret the logical internetwork
as specified by that routed protocol. Examples of routed protocols include AppleTalk, DECnet, and
IP.
router
Network layer device that uses one or more metrics to determine the optimal path along which
network traffic should be forwarded. Routers forward packets from one network to another based
on network layer information. Generally called a gateway when used by a device to forward traffic
off a local network and that does not participate in routing or multiple networks.
routing
Process of finding a path to a destination host. Routing is very complex in large networks because of
the many potential intermediate destinations a packet might traverse before reaching its destination
host.
Routing Information Protocol
See RIP.
routing metric
Method by which a routing algorithm determines that one route is better than another. This
information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop
count, load, MTU, path cost, and reliability. Sometimes referred to simply as a metric.
routing protocol
Protocol that accomplishes routing through the implementation of a specific routing algorithm.
Examples of routing protocols include IGRP, OSPF, and RIP.
routing table
Table stored in a router or some other internetworking device that keeps track of routes to
particular network destinations and, in some cases, metrics associated with those routes.
RS-232
Popular physical-layer interface. Now known as EIA/TIA-232.
RS-422
Balanced electrical implementation of EIA/TIA-449 for high-speed data transmission. Now referred
to collectively with RS-423 as EIA-530.
RS-423
Unbalanced electrical implementation of EIA/TIA-449 for EIA/TIA-232 compatibility. Now referred to
collectively with RS-422 as EIA-530.
RS-449
Popular physical-layer interface. Now known as EIA/TIA-449.
SAN
Acronym for storage area network. An emerging data communications platform that interconnects
servers and storage at gigabaud speeds. By combining LAN networking models with the core building
blocks off server performance and mass storage capacity, SAN eliminates the bandwidth bottlenecks
and scalability limitations imposed by previous SCSI busbased architectures.
SDLC
Acronym for Synchronous Data Link Control. SNA data-link layer communications protocol. SDLC is a
bit-oriented, full-duplex serial protocol that has spawned numerous similar protocols, including
HDLC and LAPB.
serial port
This interface can be used for serial communication in which only one bit is transmitted at a time.
server
Node or software program that provides services to clients.
session layer

Layer 5 of the OSI reference model. This layer establishes, manages, and terminates sessions
between applications and manages data exchange between presentation layer entities. Corresponds
to the data-flow control layer of the SNA model.
Simple Network Management Protocol
See SNMP.
slow switching
Packet processing performed at process level speeds, without the use of a route cache. Contrast
with fast switching.
SNMP
Acronym for Simple Network Management Protocol. Network management protocol used almost
exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and
to manage configurations, statistics collection, performance, and security.
sound card
A sound card is an expansion board that handles all sound functions.
SRAM
Type of RAM that retains its contents for as long as power is supplied. SRAM does not require
constant refreshing, like DRAM. Compare with DRAM.
star topology
LAN topology in which end points on a network are connected to a common central switch by point-
to-point links. A ring topology that is organized as a star implements a unidirectional closed-loop
star, instead of point-to-point links.
statistical multiplexing
Technique whereby information from multiple logical channels can be transmitted across a single
physical channel. Statistical multiplexing dynamically allocates bandwidth only to active input
channels, making better use of available bandwidth and allowing more devices to be connected than
with other multiplexing techniques. Also referred to as statistical time-division multiplexing or stat
mux.
storage area network
See SAN.
STP
Acronym for shielded twisted-pair. See UTP.
Synchronous Data Link Control
See SDLC.
synchronous transmission
Term describing digital signals that are transmitted with precise clocking. Such signals have the same
frequency, with individual characters encapsulated in control bits (called start bits and stop bits) that
designate the beginning and end of each character.
T1
Digital WAN carrier facility. T1 transmits DS-1-formatted data at 1.544 Mbps through the telephone-
switching network, using AMI or B8ZS coding.
TDM
Acronym for time-division multiplexing. Technique in which information from multiple channels can
be allocated bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to
each channel regardless of whether the station has data to transmit. See FDM.
terminal
Simple device at which data can be entered or retrieved from a network or device. Generally,
terminals have a monitor and a keyboard, but no processor or local disk drive.
TFTP
Acronym for Trivial File Transfer Protocol. Simplified version of FTP that allows files to be transferred
from one computer to another over a network, usually without the use of client authentication (for
example, username and password).

time-division multiplexing
See TDM.
token passing
Network media access method by which network devices access the physical medium in an orderly
fashion based on possession of a small frame called a token. Contrast with circuit switching and
contention.
Token Ring
An IEEE 802 LAN that makes use of token passing on a physical or logical ring topology.
transport layer
Layer 4 of the OSI reference model. This layer is responsible for reliable network communication
between end nodes. The transport layer provides mechanisms for the establishment, maintenance,
and termination of virtual circuits, transport fault detection and recovery, and information flow
control. Corresponds to the transmission control layer of the SNA model.
Trivial File Transfer Protocol
See TFTP.
UART
Universal Asynchronous Receiver/Transmitter. Integrated circuit, attached to the parallel bus of a
computer, used for serial communications. The UART translates between serial and parallel signals,
provides transmission clocking, and buffers data sent to or from the computer.
UBR
Acronym for unspecified bit rate. QoS class defined by the ATM Forum for ATM networks. UBR
allows any amount of data up to a specified maximum to be sent across the network, but there are
no guarantees in terms of cell loss rate and delay. Compare with ABR (available bit rate), CBR, and
VBR.
UDP
Acronym for User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol
stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed
delivery, requiring that error processing and retransmission be handled by other protocols. UDP is
defined in RFC 768.
UL
Acronym for Underwriters Laboratories. Independent agency within the United States that tests
product safety.
unicast
Message sent to a single network destination. Compare with broadcast and multicast.
unicast address
Address specifying a single network device.
uninterruptible power supply
See UPS.
Universal Asynchronous Receiver/Transmitter
See UART.
unshielded twisted-pair
See UTP.
unspecified bit rate
See UBR.
UPS
Acronym for uninterruptible power supply. Backup device designed to provide an uninterrupted
power source in the event of a power failure. They are commonly installed on all file servers and
wiring hubs.
User Datagram Protocol
See UDP.
UTP

Acronym for unshielded twisted-pair. Four-pair wire medium used in a variety of networks. UTP does
not require the fixed spacing between connections that is necessary with coaxial-type connections.
There are five types of UTP cabling commonly used: Category 1 cabling, Category 2 cabling, Category
3 cabling, Category 4 cabling, and Category 5 cabling. Compare with STP.
V.32
ITU-T standard serial-line protocol for bidirectional data transmissions at speeds of 4.8 or 9.6 kbps.
V.34
ITU-T standard that specifies a serial line protocol. V.34 offers improvements to the V.32 standard,
including higher transmission rates (28.8 kbps) and enhanced data compression. Compare with V.32.
V.35
ITU-T standard describing a synchronous, physical-layer protocol used for communications between
a network access device and a packet network. V.35 is most commonly used in the United States and
in Europe, and is recommended for speeds up to 48 kbps.
VBR
Acronym for variable bit rate. QoS class defined by the ATM Forum for ATM networks. VBR is
subdivided into a real time (RT) class and non-real time (NRT) class. VBR (RT) is used for connections
in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in
which there is no fixed timing relationship between samples, but that still need a guaranteed QoS.
See UBR.
vertical cabling
Backbone cabling.
virtual circuit
Logical circuit created to ensure reliable communication between two network devices. A virtual
circuit is defined by a VPI/VCI pair, and can be either permanent (a PVC) or switched (an SVC). Virtual
circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.
Sometimes abbreviated VC.
Virtual LAN
See VLAN.
Virtual Private Network
See VPN.
virtual terminal
Software driven terminal emulation to provide the same functionality of a local terminal or console
to a remote location or device.
VLAN
Acronym for virtual LAN. Group of devices on a LAN that are configured so that they can
communicate as if they were attached to the same wire, when in fact they are located on a number
of different LAN segments. Because VLANs are based on logical instead of physical connections, they
are extremely flexible.
VPN
Acronym for Virtual Private Network. A logical network created through the use of encapsulation or
tagging techniques.
WAN
Acronym for wide-area network. Data communications network that serves users across a broad
geographic area and often uses transmission devices provided by common carriers. Frame Relay,
SMDS, and X.25 are examples of WANs.
wideband
See broadband.
wildcard mask
32-bit quantity used in conjunction with an IP address to determine which bits in an IP address
should be ignored when comparing that address with another IP address. A wildcard mask is
specified when setting up access lists.

window
Number of octets that the receiver is willing to accept.
window size
Refers to the number of messages that can be transmitted while awaiting an acknowledgment.
wire map
Feature provided by most cable testers. Used to test twisted-pair cable installations, it shows which
wire pairs connect to which pins on the plugs and sockets.
wiring closet
Specially designed room used for wiring a data or voice network. Wiring closets serve as a central
junction point for the wiring and wiring equipment that is used for interconnecting devices.
workgroup
Collection of workstations and servers on a LAN that are designed to communicate and exchange
data with one another.
workgroup switching
Method of switching that provides high-speed (100-Mbps) transparent bridging between Ethernet
networks and high-speed translational bridging between Ethernet and CDDI or FDDI.
X terminal
Terminal that allows a user simultaneous access to several different applications and resources in a
multivendor environment through implementation of X Windows.
X Windows
Distributed, network-transparent, device-independent, multitasking windowing and graphics system
originally developed by MIT for communication between X terminals and UNIX workstations.
X.25
ITU-T standard that defines how connections between DTE and DCE are maintained for remote
terminal access and computer communications in PDNs. X.25 specifies LAPB, a data-link layer
protocol, and PLP, a network-layer protocol. Frame Relay has to some degree superseded X.25.
10 Mbps
Approximately 10 million bits per second, an information transfer rate.
100BASE-FX
100-Mbps baseband Fast Ethernet specification using two strands of multimode fiberoptic cable per
link. To guarantee proper signal timing, a 100BASE-FX link cannot exceed 1312 feet (400 meters) in
length. Based on the IEEE 802.3 standard.
100BASE-T
100-Mbps baseband Fast Ethernet specification using UTP wiring. Like the 10BASE-T technology on
which it is based, 100BASE-T sends link pulses over the network segment when no traffic is present.
However, these link pulses contain more information than those used in 10BASE-T. Based on the
IEEE 802.3 standard.
100BASE-T4
100-Mbps baseband Fast Ethernet specification using four pairs of Category 3, 4, or 5 UTP wiring. To
guarantee proper signal timing, a 100BASE-T4 segment cannot exceed 328 feet (100 meters) in
length. Based on the IEEE 802.3 standard.
100BASE-TX
100-Mbps baseband Fast Ethernet specification using two pairs of either UTP or STP wiring. The first
pair of wires is used to receive data; the second is used to transmit. To guarantee proper signal
timing, a 100BASE-TX segment cannot exceed 328 feet (100 meters) in length. Based on the IEEE
802.3 standard.
100BASE-X
100-Mbps baseband Fast Ethernet specification that refers to the 100BASE-FX and 100BASE-TX
standards for Fast Ethernet. Based on the IEEE 802.3 standard.
10BASE2

10-Mbps baseband Ethernet specification using 50-ohm thin coaxial cable. 10BASE2, which is part of
the IEEE 802.3 specification, has a distance limit of 185 meters per segment.
10BASE5
10-Mbps baseband Ethernet specification using standard (thick) 50-ohm baseband coaxial cable.
10BASE5, which is part of the IEEE 802.3 baseband physical layer specification, has a distance limit of
500 meters per segment.
10BASE-F
10-Mbps baseband Ethernet specification that refers to the 10BASE-FB, 10BASE-FL, and 10BASE-FP
standards for Ethernet over fiber-optic cabling.
10BASE-FB
10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BASE-FB is part of the IEEE
10BASE-F specification. It is not used to connect user stations, but instead provides a synchronous
signaling backbone that allows additional segments and repeaters to be connected to the network.
10BASE-FB segments can be up to 2000 meters long.
10BASE-FL
10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BASE-FL is part of the IEEE
10BASE-F specification and, while able to interoperate with FOIRL, is designed to replace the FOIRL
specification. 10BASE-FL segments can be up to 1000 meters long if used with FOIRL, and up to 2000
meters if 10BASE-FL is used exclusively.
10BASE-FP
10-Mbps fiber-passive baseband Ethernet specification using fiber-optic cabling. 10BASE-FP is part of
the IEEE 10BASE-F specification. It organizes a number of computers into a star topology without the
use of repeaters. 10BASE-FP segments can be up to 500 meters long.
10BASE-T
10-Mbps baseband Ethernet specification using two pairs of twisted-pair cabling (Category 3, 4, or
5): one pair for transmitting data and the other for receiving data. 10BASE-T, which is part of the
IEEE 802.3 specification, has a distance limit of approximately 328 feet (100 meters) per segment.

H. Quizzes’ Answers
i
Answer
The backplane is a part of the computer that allows external devices to be connected, the bus connects all the internal
computer components to the CPU, the CPU is where most of the calculations take place, expansion slots are openings
in a computer into which you can insert a circuit board, and the floppy drive is a disk drive that can read and write to
floppy disks.
The backplane is a part of the computer that allows external devices to be connected. It contains components such as a
power cord, a serial port, a mouse port, and a parallel port.
The bus connects internal components to the CPU. Data is transmitted through the computer via its collection of wires.
The CPU is the computer's "brain". It uses a silicion-based microprocessor that performs calculations and is contained
inside the CPU.
You can insert a circuit board or NIC into expansion slots.
A floppy drive can read and write to floppy disks, whereas CD-ROMs and hard disks require a different type of drive
(rarely used nowadays).
ii
Answer
Laptops generally use less power than PCs, the components are smaller, and the slots you connect devices to are called
PCMCIA slots instead of expansion slots.
Option 1 is incorrect. It is more difficult to remove the components from a laptop than those from a PC because laptop
components are designed to fit together in a smaller physical space.
Option 2 is correct. Laptops generally use less power than PCs as they are designed to operate using a battery.
Option 3 is correct. Laptop components are smaller than those in a PC because they need to fit into a smaller physical
space.
Option 4 is correct. The slots you connect devices to are called expansion slots in a PC and PCMCIA slots in a laptop. For
example, you can connect NICs, modems, and hard drives.
iii
Answer
When selecting a NIC for a network, you should take into account the type of media, network, and expansion slot.
Option 1 is incorrect. The type of CPU is not relevant when selecting a NIC for a network. A NIC is designed to work with
a specific type of expansion slot, regardless of the CPU type.
Option 2 is correct. The type of media is important when selecting a NIC because it determines the type of port or
connector needed.
Option 3 is correct. The type of network is important when selecting a NIC. For example, if the network is an Ethernet
LAN, then you need an Ethernet NIC. For a Token Ring LAN, you need a Token Ring NIC.
Option 4 is correct. The type of expansion slot is important when selecting a NIC. For example, PCI slots are faster than
ISA slots. Using a faster slot means the data from the network is received and processed faster by the computer.
iv
Answer
Before you install a NIC, you must know how to configure the network card, how to use the network card diagnostics,
and be able to resolve hardware resource conflicts.

Option 1 is correct. You must be able to resolve hardware resource conflicts such as IRQ, I/O base address, and DMA.
Option 2 is incorrect. You don't need to be familiar with all types of network cards because some have specialized
functions in networks and are not commonly used, or require specific technical expertise.
Option 3 is correct. You need to know how the network card is configured. You should use the vendor-supplied
diagnostics and loopback test.
Option 4 is correct. You need to know how to use the network card diagnostics by using jumpers, "plug-and-play"
software, and EPROM.
v
Answer
A bit equals 1 or 0 in binary format, a byte is equal to 8 bits, a GB is equal to approximately one billion bytes, a KB is
equal to approximately 1000 bytes, an Mb is equal to approximately one million bits, and an MB is equal to
approximately one million bytes.
A bit is the smallest unit of data in a computer.
A byte is equal to eight bits and represents one character of alphanumeric data.
A gigabyte is also equal to one thousand megabytes.
A kilobyte is 1024 bytes exactly.
A megabit is equal to 1,048,576 bits exactly.
A megabyte is equal to 1,048,576 bytes exactly.
vi
Answer
The binary equivalent of 197 is 11000101.
Option 1 is incorrect. 10000101 is actually the binary equivalent of 133.
Option 3 is correct. 11000101 is the binary equivalent of 197. From right to left, the values are as follows: the first 1 is
represented by the place value "1", the second 1 is "4", the third 1 is ""64", and the fourth 1 is "128". Therefore, you
add 1+4+64+128 to give a result of 197.
vii
Answer
The decimal equivalent of 11011000 is 216.
viii
Answer
5689F1EC and 0x5689F1EC are both hexadecimal equivalents of 1010110100010011111000111101100.
Option 1 is incorrect. 1451880940 is the decimal equivalent of 1010110100010011111000111101100.
Option 2 is correct. 5689F1EC is the hexadecimal equivalent of 1010110100010011111000111101100. Add a 0 to the
left to make groups of 4. (0)101 is 5, 0110 is 6, 1000 is 8, 1001 is 9, 1111 is F, 0001 is 1, 1110 is E, and 1100 is C.
Option 3 is incorrect. AD13E3D4 is not the hexadecimal equivalent of 1010110100010011111000111101100. You
should be careful not to divide the groups up into bits of four from right to left. They should be divided left to right.
Option 4 is correct. 0x5689F1EC is the hexadecimal equivalent of 1010110100010011111000111101100. 0x is
commonly used in front of the hexadecimal number by computers and software.

ix
Answer
The binary equivalent of 52AC45123 is 10100101010110001000101000100100011, 589FE is 1011000100111111110,
56ED45 is 10101101110110101000101, and 63AC2 is 1100011101011000010.
10100101010110001000101000100100011 is the binary equivalent of 52AC45123. 0101 is the binary equivalent of 5,
0010 is 2, 1010 is A, 1100 is C, 0100 is 4, 0101 is 5, 0001 is 1, 0010 is 2, and 0011 is 3.
10101101110110101000101 is the binary equivalent of 56ED45. 0101 is the binary equivalent of 5, 0110 is 6, 1110 is E,
1101 is D, 0100 is 4, and 0101 is 5.
1011000100111111110 is the binary equivalent of 589FE. 0101 is the binary equivalent of 5, 1000 is 8, 1001 is 9, 1111 is
F, and 1110 is E.
110 0011 1010 1100 0010 is the binary equivalent of 63AC2. 0110 is the binary equivalent of 6, 0011 is 3, 1010 is A,
1100 is C, and 0010 is 2.
x
Result
xi
Result
xii
Result
xiii
4. Answer

The OSI reference model defines the network functions that occur at each layer and describes how data makes its way
from one application program to another throughout a network. It also specifies how information travels through
networks.
Option 1 is correct. The OSI reference model is divided into seven layers, and each layer carries out a clearly defined
function.
Option 2 is correct. In order to standardize the way data travels over a network, the OSI reference model specifies the
process by which data should be transmitted.
Option 3 is correct. The OSI reference model makes it easier for vendors to educate customers on how data is
transmitted throughout a network.
Option 4 is incorrect. The OSI reference model was developed in order to help companies move away from proprietary
networking systems toward open systems that would ensure greater compatibility.
xiv
Answer
The session layer manages the communication processes and data exchange between hosts.
Option 1 is incorrect. The network layer is concerned with connectivity and the routes selected for packets.
Option 2 is incorrect. The transport layer ensures data transport reliability.
Option 3 is incorrect. The presentation layer ensures that the data format is acceptable to the receiving application.
Option 4 is correct. The session layer establishes and manages sessions between hosts.
xv
Answer
Correct ranking
Option Description
D
Presentation
The presentation layer adds the Layer 6 header to the data and passes it to the session layer.
E
Session
The session layer adds the Layer 5 header to the data and passes it to the transport layer.
F
Transport
The transport layer adds the Layer 4 header to the data and passes it to the network layer.
B
Network
The network layer adds the Layer 3 header to the data and passes it to the data-link layer.
A
Data Link
The data-link layer adds the Layer 2 header and the frame check sequence trailer to the data and passes it to
the physical layer.
C
Physical
The physical layer transmits the data onto the physical connection.
xvi
Answer

Encapsulation is the process that wraps data with the necessary protocol information before network transit. When this
information is received it is checked for errors and stripped of its header and trailer in a process known as de-
encapsulation. Peer-to-peer communication is the process that facilitates the communication between OSI peer layers
during data transfer.
The process of encapsulation begins when data leaves the sender's pc. This data then travels through the seven layers
of the OSI reference model, where each layer adds a header to the data. These headers ensure that the data is properly
transmitted, and dealt with at the appropriate layer by the receiver.
The process of de-encapsulation begins when data is received. Firstly the information is passed to the data-link layer to
see if there is an error in the data. Once no errors are detected, it is stripped of its header and sent on up into the
network layer, and the headers are then stripped off by each subsequent layer.
Peer-to-peer communication is necessary so that packets can travel from the source to the destination. During this
process, each layer communicates to its peer layer and exchanges information called PDUs.
xvii
Answer
The transport layer deals with reliability, flow control, and error correction.
Option 1 is incorrect. The application layer handles high-level protocols and ensures that all data is properly packaged
for the next layer.
Option 2 is incorrect. The Internet layer is responsible for the delivery of source packets from any network on the
internetwork.
Option 3 is incorrect. Sometimes known as the host-to-network layer, the network access layer handles the details in
the OSI physical and data-link layers.
Option 4 is correct. The transport layer provides for reliable network communications, ensuring the reliability of
transmitted data.

Building a Simple Network - Study Notes

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