This document discusses computer networks and their classification. It defines the goals of computer networks as resource sharing without regard to physical location. It classifies networks into personal, local, metropolitan and wide area networks. The document then discusses how computer networks enable communication and collaboration between employees through technologies like email, video conferencing, desktop sharing and e-commerce. It explains how networks allow businesses to place electronic orders and enhance efficiency.

1. 1. What is computer Network? Give the classification and goals of computer network.
A computer network is a set of computers connected together for the purpose of sharing
resources. The most common resource shared today is connection to the Internet. Other shared
resources can include a printer or a file server.
Types of networks:
I. Personal Area Network (PAN)
II. Local Area Network (LAN)
III. Metropolitan Area Network (MAN)
IV. Wide Area Network (WAN)
The main goal of networking is "Resource sharing". And this goal is to make all programs,
equipment, and especially data available to anyone on the network without regard to the physical
location of the resource or the user. An obvious and widespread example is having a group of
office workers share a common printer.
A second goal of setting up a computer network has to do with people rather than
information or even computers. A computer network can provide a powerful communication
medium among employees. Virtually every company that has two or more computers now has
email (electronic mail), which employees generally use for a great deal of daily communication.
Telephone calls between employees may be carried by the computer network instead of
by the phone company. This technology is called IP telephony or VoIP when Internet technology is
used. In modern times, Video can also be added to audio so that employees at distant locations
can see and hear each other as they hold a meeting. This technique is a powerful tool for
eliminating the cost and time previously devoted to travel.
Desktop sharing lets remote workers see and interact with a graphical computer screen.
This makes it easy for two or more people who work far apart to read and write a shared
blackboard or write a report together. When one worker makes a change to an online document,
the others can see the change immediately, instead of waiting several days for a letter.
A third goal for many companies is doing business electronically, especially with customers
and suppliers. This new model is called e-commerce (electronic commerce) and it has grown
rapidly in recent years. Airlines, bookstores, and other retailers have discovered that many
customers like the convenience of shopping from home. Consequently, many companies provide
catalogs of their goods and services online and take orders online. Manufacturers of automobiles,
aircraft, and computers, among others, buy subsystems from a variety of suppliers and then
assemble the parts. Using computer networks, manufacturers can place orders electronically as
needed. This reduces the need for large inventories and enhances efficiency.
2. What is point- to- Point subnet? Draw the possible topologies for point- to- Point subnet.
Point-to-point links connect individual pairs of machines. To go from the source to the
destination on a network made up of point-to-point links, short messages, called packets in
certain contexts, may have to first visit one or more intermediate machines. Often multiple

2. routes, of different lengths, are possible, so finding good ones is important in point-to-point
networks.
Point to point Subnet
3. Write the principles for designing the layered architecture of a network.
Reliability is the design issue of making a network that operates correctly even though it is
made up of a collection of components that are themselves unreliable. Finding errors in received
information, finding a working path through a network are the segments of reliability.
A second design issue concerns the evolution of the network. Over time, networks grow larger
and new designs emerge that need to be connected to the existing network.
A third design issue is resource allocation. Networks provide a service to hosts from their
underlying resources, such as the capacity of transmission lines. To do this well, they need
mechanisms that divide their resources so that one host does not interfere with another too
much.
The last major design issue is to secure the network by defending it against different kinds of
threats. One of the major threats is eavesdropping on communications.
Ref: CN, Tanenbaum (page-33)

3. 4. Write short note on: NSFNET, ARPANET, and Internet.
NSFNET: A wide-area network developed under the auspices of the National Science Foundation
(NSF). NSFnet replaced ARPANET as the main government network linking universities and
research facilities. In 1995, however, the NSF dismantled NSFnet and replaced it with a
commercial Internet backbone. At the same time, the NSF implemented a new backbone
called very high-speed Backbone Network Service (vBNS), which serves as a testing ground for the
next generation of Internet technologies.
ARPANET was the network that became the basis for the Internet. Based on a concept first
published in 1967, ARPANET was developed under the direction of the U.S. Advanced Research
Projects Agency (ARPA). In 1969, the idea became a modest reality with the interconnection of
four university computers.
ARPANET was the network that became the basis for the Internet. Based on a concept first
published in 1967, ARPANET was developed under the direction of the U.S. Advanced Research
Projects Agency (ARPA). In 1969, the idea became a modest reality with the interconnection of
four university computers. The initial purpose was to communicate with and share computer
resources among mainly scientific users at the connected institutions. ARPANET took advantage of
the new idea of sending information in small units called packets that could be routed on different
paths and reconstructed at their destination. The development of the TCP/IP protocols in the
1970s made it possible to expand the size of the network, which now had become a network of
networks, in an orderly way.
INTERNET: A means of connecting a computer to any other computer anywhere in the
world via dedicated routers and servers. When two computers are connected over the Internet,
they can send and receive all kinds of information such as text, graphics, voice, video,
and computer programs.
No one owns Internet, although several organizations the world over collaborate in its functioning
and development. The high-speed, fiber-optic cables (called backbones) through which the bulk of
the Internet data travels are owned by telephone companies in their respective countries.
The Internet grew out of the Advanced Research Projects Agency's Wide Area Network (then
called ARPANET) established by the US Department Of Defense in 1960s for collaboration in
military research among business and government laboratories. Later universities and other
US institutions connected to it. This resulted in ARPANET growing beyond everyone’s expectations
and acquiring the name 'Internet.'
The development of hypertext based technology (called World Wide web, WWW, or just the Web)
provided means of displaying text, graphics, and animations, and
easy search and navigation tools that triggered Internet's explosive worldwide growth.

4. 5. Define layer, protocol, interfaces. Show how communication is provided to the top layer in
the layer based network?
Layers: To reduce network design complexity, most networks are organized as a stack of layers or
levels, each one built upon the one below it. The number of layers, the name of each layer, the
contents of each layer, and the function of each layer differ from network to network. The
purpose of each layer is to offer certain services to the higher layers while shielding those layers
from the details of how the offered services are actually implemented. In a sense, each layer is a
kind of virtual machine, offering certain services to the layer above it.
Protocol: a protocol is an agreement between the communicating parties on how communication
is to proceed. In another word, Protocol is set of some rules and regulations that govern data
communication over network.
Interface: Between each pair of adjacent layers is an interface. The interface defines which
primitive operations and services the lower layer makes available to the upper one. When
network designers decide how many layers to include in a network and what each one should do,
one of the most important considerations is defining clean interfaces between the layers. Doing
so, in turn, requires that each layer perform a specific collection of well-understood functions.
A five-layer network is illustrated in below fig. The entities comprising the corresponding layers on
different machines are called peers. The peers may be software processes, hardware devices, or
even human beings. In other words, it is the peers that communicate by using the protocol to talk
to each other.
In reality, no data are directly transferred from layer n on one machine to layer n on another
machine. Instead, each layer passes data and control information to the layer immediately below
it, until the lowest layer is reached. Below layer 1 is the physical medium through which actual
communication occurs. In Fig. 1-13, virtual communication is shown by dotted lines and physical
communication by solid lines.

5. 6. Define connection oriented and connectionless networks. Explain how packets are sent in
a simple client serverinteraction on connection oriented network?
 Connection-oriented Requires a session connection (analogous to a phone call) be
established before any data can be sent. This method is often called a "reliable" network
service. It can guarantee that data will arrive in the same order. Connection-oriented
services set up virtual links between end systems through a network, as shown in Figure 1.
Note that the packet on the left is assigned the virtual circuit number 01. As it moves
through the network, routers quickly send it through virtual circuit 01.
 Connectionless Does not require a session connection between sender and receiver. The
sender simply starts sending packets (called datagram’s) to the destination. This service
does not have the reliability of the connection-oriented method, but it is useful for
periodic burst transfers. Neither system must maintain state information for the systems
that they send transmission to or receive transmission from. A connectionless network
provides minimal services.

6. 7. Name and define services of data link layer. Show the environment of data link layer.
Explain how data link layer work in Internet with diagram.
The data link layer can be designed to offer various services. The actual services that are offered
vary from protocol to protocol. Three reasonable possibilities that we will consider in turn are:
1. Unacknowledged connectionless service.
2. Acknowledged connectionless service.
3. Acknowledged connection-oriented service.
Unacknowledged connectionless service consists of having the source machine send independent
frames to the destination machine without having the destination machine acknowledge them.
When reliability service is offered, there are still no logical connections used, but each frame sent
is individually acknowledged. In this way, the sender knows whether a frame has arrived correctly
or been lost.
In Acknowledged connection-oriented service, the source and destination machines establish a
connection before any data are transferred. Each frame sent over the connection is numbered,
and the data link layer guarantees that each frame sent is indeed received. Furthermore, it
guarantees that each frame is received exactly once and that all frames are received in the right
order.
Fig: Internal Environment of Data Link Layer
Fig: The Data Link Layer in the Internet

7. 8. Name and define key assumptions for dynamic channel allocation protocol. Define CSMA/
CD protocol with algorithm.
Independent Traffic: The model consists of N independent stations (e.g., computers, telephones),
each with a program or user that generates frames for transmission. The expected number of
frames generated in an interval of length Δt is λΔt, where λ is a constant (the arrival rate of new
frames). Once a frame has been generated, the station is blocked and does nothing until the
frame has been successfully transmitted.
Single Channel Assumption: A single channel is available for all communication. All stations can
transmit on it and all can receive from it. The stations are assumed to be equally capable, though
protocols may assign them different roles (e.g., priorities).
Collision Assumption: If two frames are transmitted simultaneously, they overlap in time and the
resulting signal is garbled. This event is called a collision.
Continuous time: Frames transmission can begin at any instant of time.
Slotted Time: Time is divided into discrete intervals which are called slots and frame transmission
can always begin at start of a slot.
Carrier sense: stations can tell if the channel is in use. If busy, no other station can use it until it is
idle. The term ‘carrier’ here refers to an electrical signal on the cable.
No Carrier Sense: Stations cannot sense the channel’s status. They just transmit the data. Only
later they can determine whether the transmission was successful or not. For example, satellite
networks.

8. 9. What is error control? Error correction and detection using hamming code (odd/ even
parity for the given code).
Network is responsible for transmission of data from one device to another device. The end to
end transfer of data from a transmitting application to a receiving application involves many
steps, each subject to error. With the error control process, we can be confident that the
transmitted and received data are identical. Error control is the process of detecting and
correcting both the bit level and packet level errors.
Error correction and detection using Hamming code (Check Assignment).
10. Name and define the fields of Ethernet frame format.
Preamble & Start of Frame: The format used to send frames is shown in Fig. 4-14. First comes a
Preamble of 8 bytes, each containing the bit pattern 10101010 (with the exception of the last
byte, in which the last 2 bits are set to 11). This last byte is called the Start of Frame delimiter for
802.3.

9. Destination address: Hardware address (MAC address) of the destination station (usually 48 bits
i.e. 6 bytes).
Source address: Hardware address of the source station (usually 48 bits i.e. 6 bytes).
Type: Specifies the protocol sending the packet such as IP or IPX (only applies to DIX frame).
Length: Specifies the length of the data segment, actually the number of LLC data bytes, (only
applies to 802.3 frame and replaces the Type field).
Data: This block contains the data and it may be up to 1500 bytes long.
Pad: If the length of the field is less than 46 bytes, then padding data is added to bring its length
up to the required minimum of 46 bytes.
Checksum: The final field is the Checksum. It is a 32-bit CRC to detect transmission errors. If the
receiving host detects a wrong CRC, it will throw away that packet.
11. Draw a typical ADSL arrangement and explain the function of its.
A typical ADSL arrangement is shown in Fig. 2-35. In this scheme, a telephone company technician
must install a NID (Network Interface Device) on the customer’s premises. This small plastic box
marks the end of the telephone company’s property and the start of the customer’s property.
Close to the NID (or sometimes combined with it) is a splitter, an analog filter that separates the
0–4000-Hz band used by POTS from the data. The POTS signal is routed to the existing telephone
or fax machine. The data signal is routed to an ADSL modem, which uses digital signal processing
to implement OFDM. Since most ADSL modems are external, the computer must be connected to
them at high speed. Usually, this is done using Ethernet, a USB cable, or 802.11.
At the other end of the wire, on the end office side, a corresponding splitter is installed. Here, the
voice portion of the signal is filtered out and sent to the normal voice switch. The signal above 26
kHz is routed to a new kind of device called a DSLAM (Digital Subscriber Line Access Multiplexer),
which contains the same kind of digital signal processor as the ADSL modem. Once the bits have
been recovered from the signal, packets are formed and sent off to the ISP.

10. 12. What is Bluetooth technology? Define the goals of Bluetooth. Explain the Bluetooth
architecture. Name five Bluetooth profiles. Define different types of multiplexing.
Bluetooth is a wireless standard for interconnecting communication and computing devices and
accessories using short-range, low-power, inexpensive wireless radios.
Goals of Bluetooth:
• Open spec.
• Low cost.
– In order to replace cables, should have similar cost.
– Cell phone cable is ~ $10.
• Power efficiency.
• Lightweight and small form factor.
• Easy to use.
• Reliable and resilient to failures.
•
Bluetooth Architecture:
The basic unit of a Bluetooth system is a piconet, which consists of a master node and up to seven
active slave nodes within a distance of 10 meters. Multiple piconets can exist in the same (large)
room and can even be connected via a bridge node that takes part in multiple piconets, as in Fig.
4-34. An interconnected collection of piconets is called a scatternet.
In addition to the seven active slave nodes in a piconet, there can be up to 255 parked nodes in
the net. These are devices that the master has switched to a lowpower state to reduce the drain
on their batteries. In parked state, a device cannot do anything except respond to an activation or
beacon signal from the master.
Bluetooth Profiles:
01. Intercom profile allows two telephones to connect as walkie-talkies.
02. The headset and hands-free profiles both provide voice communication between a headset
and its base station.
03. The human interface device profile is for connecting keyboards and mice to computers.

11. 04. Some profiles let a mobile phone or other computer receive images from a camera or send
images to a printer.
05. One profile uses a mobile phone as a remote control for a (Bluetooth-enabled) TV.
Frequency-Division Multiplexing (FDM) is a technique by which the total bandwidth available in a
communication medium is divided into a series of non-overlapping frequency sub-bands, each of
which is used to carry a separate signal. The mostnatural example of frequency-divisionmultiplexingis
radioand television broadcasting.
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals
over a common signal path by means of synchronized switches at each end of the transmission
line so that each signal appears on the line only a fraction of time in an alternating pattern. TDM is
used widely as part of the telephone and cellular networks.
Code Division Multiplexing (CDM) is a technique in which each channel transmits its bits as a coded
channel-specific sequence of pulses.
13. Define the characteristic properties of twisted pair and coaxial cables with diagrams?
Twisted Pair: A twisted pair consists of two insulated copper wires, typically about 1 mm thick.
The wires are twisted together in a helical form, just like a DNA molecule. When the twisted pair
cable is more twisted then it reduces electromagnetic interference. Twisted pairs can be used for
transmitting either analog or digital information. The bandwidth depends on the thickness of the
wire and the distance traveled, but several megabits/sec can be achieved for a few kilometers in
many cases.
A category 5 twisted pair consists of two insulated wires gently twisted together. Four such pairs
are typically grouped in a plastic sheath to protect the wires and keep them together. This
arrangement is shown in Fig. 2-3.
Different LAN standards may use the twisted pairs differently. For example, 100-Mbps Ethernet
uses two (out of the four) pairs, one pair for each direction. To reach higher speeds, 1-Gbps
Ethernet uses all four pairs in both directions simultaneously; this requires the receiver to factor
out the signal that is transmitted locally.
Coaxial cable: It has better shielding and greater bandwidth than unshielded twisted pairs, so it
can span longer distances at higher speeds. Two kinds of coaxial cable are widely used. One kind,
50-ohm cable, is commonly used when it is intended for digital transmission from the start. The
other kind, 75-ohm cable, is commonly used for analog transmission and cable television.

12. A coaxial cable consists of a stiff copper wire as the core, surrounded by an insulating material.
The insulator is encased by a cylindrical conductor, often as a closely woven braided mesh. The
outer conductor is covered in a protective plastic sheath. A cutaway view of a coaxial cable is
shown in Fig. 2-4.
14. What are the major components of an optical system? Write the working principles of
fiber optic. Explain the ways of connecting a fiber.
An optical transmission system has three key components: the light source, the transmission
medium, and the detector. Conventionally, a pulse of light indicates a 1 bit and the absence of
light indicates a 0 bit. The transmission medium is an ultra-thin fiber of glass. The detector
generates an electrical pulse when light falls on it. By attaching a light source to one end of an
optical fiber and a detector to the other, we have a unidirectional data transmission system that
accepts an electrical signal, converts and transmits it by light pulses, and then reconverts the
output to an electrical signal at the receiving end.
When a light ray passes from one medium to another—for example, from fused silica to air—the
ray is refracted (bent) at the silica/air boundary, as shown in Fig. 2-6(a). Here we see a light ray
incident on the boundary at an angle α1 emerging at an angle β1. The amount of refraction
depends on the properties of the two media (in particular, their indices of refraction). For angles
of incidence above a certain critical value, the light is refracted back into the silica; none of it
escapes into the air. Thus, a light ray incident at or above the critical angle is trapped inside the
fiber, as shown in Fig. 2-6(b), and can propagate for many kilometers with virtually no loss.
Fibers can be connected in three different ways. First, they can terminate in connectors and be
plugged into fiber sockets. Second, they can be spliced mechanically. Third, two pieces of fiber can
be fused (melted) to form a solid connection.

13. 15. Define cabling & cable topologies for Ethernet?
Point to point Topology: The network consists of a direct link between two computers.
Bus Topology: Bus topology uses one main cable to which all nodes are directly connected. The
main cable acts as a backbone for the network.
Star Topology: In star topology, each computer is connected to a central hub using a point-to-
point connection.

14. Ring Topology: In ring topology, the computers in the network are connected in a circular fashion,
and the data travels in one direction.
Mesh Topology: In mesh topology, every node has a direct point-to-point connection to every
other node.
16. Write short note on Gigabit, Switched Ethernet & Bluetooth technology?
Gigabit Ethernet:
Gigabit Ethernet increase performance tenfold while maintaining compatibility with all existing
Ethernet standards. In particular, gigabit Ethernet offer unacknowledged datagram service with
both unicast and broadcast, use the same 48-bit addressing scheme already in use, and maintain
the same frame format, including the minimum and maximum frame sizes. The final standard met
all these goals.
Like fast Ethernet, all configurations of gigabit Ethernet use point-to-point links. In the simplest
configuration, illustrated in Fig. 4-20(a), two computers are directly connected to each other. The
more common case, however, uses a switch or a hub connected to multiple computers and
possibly additional switches or hubs, as shown in Fig. 4-20(b). In both configurations, each
individual Ethernet cable has exactly two devices on it, no more and no fewer.
Also like fast Ethernet, gigabit Ethernet supports two different modes of operation: full-duplex
mode and half-duplex mode. The ‘‘normal’’ mode is fullduplex mode, which allows traffic in both
directions at the same time.
The other mode of operation, half-duplex, is used when the computers are connected to a hub
rather than a switch. A hub does not buffer incoming frames. Instead, it electrically connects all
the lines internally, simulating the multidrop cable used in classic Ethernet.
Gigabit Ethernet supports both copper and fiber cabling, as listed in Fig. 4-21.
Switched Ethernet:

15. 19. How DNS works? Define DNS name space with diagram.
To map a name onto an IP address, an application program calls a library procedure called the
resolver, passing it the name as a parameter. We saw an example of a resolver, gethostbyname, in
Fig. 6-6. The resolver sends a query containing the name to a local DNS server, which looks up the
name and returns a response containing the IP address to the resolver, which then returns it to
the caller. The query and response messages are sent as UDP packets. Armed with the IP address,
the program can then establish a TCP connection with the host or send it UDP packets.
For the Internet, the top of the naming hierarchy is managed by an organization called ICANN
(Internet Corporation for Assigned Names and Numbers). The Internet is divided into over 250
top-level domains, where each domain covers many hosts. Each domain is partitioned into sub
domains, and these are further partitioned, and so on. All these domains can be represented by a
tree, as shown in Fig. 7-1. The top-level domains come in two flavors: generic and countries. The
generic domains, listed in Fig. 7-2
20. What are resource records? Explain with example.
Every domain, whether it is a single host or a top-level domain, can have a set of resource records
associated with it. These records are the DNS database. A resource record is a five-tuple.

16. The format we will use is as follows:
Domain_name Time_to_live Class Type Value
The Domain name tells the domain to which this record applies.
The Time to live field gives an indication of how stable the record is.
The third field of every resource record is the Class. For Internet information, it is always IN.
The Type field tells what kind of record this is. There are many kinds of DNS records. The
important types are listed in Fig. 7-3.
Finally, we have the Value field. This field can be a number, a domain name, or an ASCII string.
An entry like this one might do the job:
cs.mit.edu 86400 IN CNAME csail.mit.edu
21. What is name server? Explain with example how a resolver look-up a remote name in DNS
name space.
In theory at least, a single name server could contain the entire DNS database and respond to all
queries about it. In practice, this server would be so overloaded as to be useless. Furthermore, if it
ever went down, the entire Internet would be crippled.
To avoid the problems associated with having only a single source of information, the DNS name
space is divided into nonoverlapping zones. One possible way to divide the name space of Fig. 7-1
is shown in Fig. 7-5. Each circled zone contains some part of the tree.

17. Where the zone boundaries are placed within a zone is up to that zone’s administrator. This
decision is made in large part based on how many name servers are desired, and where. For
example, in Fig. 7-5, the University of Washington has a zone for washington.edu that handles
eng.washington.edu but does not handle cs.washington.edu. That is a separate zone with its own
name servers. Such a decision might be made when a department such as English does not wish
to run its own name server, but a department such as Computer Science does.
What happens when the domain is remote, such as when flits.cs.vu.nl wants to find the IP address
of robot.cs.washington.edu at UW (University of Washington)? In this case, and if there is no
cached information about the domain available locally, the name server begins a remote query.
This query follows the process shown in Fig. 7-6. Step 1 shows the query that is sent to the local
name server. The query contains the domain name sought, the type (A), and the class(IN).
24. What is flow control? Name and define different types of flow control?
Flow control is the process of managing the rate of data transmission between two nodes to
prevent a fast sender from overwhelming a slow receiver.
Stop-and-wait
Stop-and-wait flow control is the simplest form of flow control. In this method, the message is
broken into multiple frames. The sender waits for an ACK (acknowledgement) from receiver after
every frame for specified time (called time out). It is sent to ensure that the receiver has received
the frame correctly. It will then send the next frame only after the ACK has been received. If a
frame or ACK is lost during transmission then it has to be transmitted again by sender. This
retransmission process is known as ARQ (automatic repeat request).
Sliding Window
A method of flow control in which a receiver gives a transmitter permission to transmit data until
a window is full. When the window is full, the transmitter must stop transmitting until the receiver
advertises a larger window.

18. 27. What is CRC? Explain CRC method using Modulo-2 arithmetic. Give example.
A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks
and storage devices to detect accidental changes to raw data. Blocks of data entering these
systems get a short check value attached, based on the remainder of a polynomial division of their
contents.
28. Name different types of modulation with necessary diagram. Explain switching techniques.
Circuit Switching:
Conceptually, when you or your computer places a telephone call, the switching equipment within
the telephone system seeks out a physical path all the way from your telephone to the receiver’s
telephone. This technique is called circuit switching. It is shown schematically in Fig. 2-42(a). Each
of the six rectangles represents a carrier switching office (end office, toll office, etc.). In this
example, each office has three incoming lines and three outgoing lines. When a call passes
through a switching office, a physical connection is (conceptually) established between the line on
which the call came in and one of the output lines, as shown by the dotted lines.
Packet Switching:
The alternative to circuit switching is packet switching, shown in Fig. 2- 42(b). With this
technology, packets are sent as soon as they are available. There is no need to set up a dedicated
path in advance, unlike with circuit switching. It is up to routers to use store-and-forward
transmission to send each packet on its way to the destination on its own.