This document provides an overview of computer networks. It begins by defining a network as two or more connected computers and describes the main types as local area networks (LANs) and wide area networks (WANs). LANs are confined to a limited geographical area while WANs cover a larger area and are often composed of multiple connected LANs. The document then discusses specific network types like LANs, WANs, MANs, and PANs. It also outlines the benefits of networks like information sharing, hardware sharing, software sharing, and collaborative environments. However, it notes networks also face risks from equipment malfunctions, system failures, computer hackers, and virus attacks. The document concludes by discussing network

1. 1
Dr. Shahinaz. M. Al-tabbakh
Lecturer of Computer Networks
Faculty of Women for Arts, Sciences and
Edu. Ain Shames university
WHAT IS A NETWORK?
 A network is simply two or more computers
that are linked together.
 The most common types of networks are:
○ Local Area Networks (LANS) and
○ Wide Area Networks (WANS).
 The primary difference between the two is
that a LAN is generally confined to a limited
geographical area, whereas a WAN covers a
large geographical area. Most WANs are
made up of several connected LANs.
TYPES OF NETWORKS
 Local Area Network (LAN) – a network that spans
a small area such as a building or an office.
 Software applications and other resources are stored on a
file server.
 Print servers enable multiple users to share the same
printer.
 Wide Area Network (WAN) – a network that spans a
wide geographical area city or country
 there are several types of networks
 Metropolitan area network (MAN)
 Public access network (PAN)
4
 Metropolitan Area Networks (MANs)
 A metropolitan area network (MAN) is a network
designed for a town or city. MANs are generally not
owned by a single company or organization and are
commonly used to connect multiple LANs.
 Personal Area Networks (PANs)
 A personal area network (PAN) is a network of all
devices in a person’s life. PANs can keep portable
devices synchronized with a desktop PC and
coordinate Internet access and e-mail.
Other Types of Networks
Benefits Of a Computer Network
 Information sharing: Authorized users can use other
computers on the network to access and share information and
data. This could include special group projects, databases, etc.
 Hardware sharing: One device connected to a network,
such as a printer or scanner, can be shared by many users.
 Software sharing: Instead of purchasing and installing a
software program on each computer, it can be installed on the
server. All of the users can then access the program from a single
location.
 Collaborative environment: Users can work
together on group projects by combining the power and capabilities
of diverse equipment.
RISKS OF NETWORK
COMPUTING
 The security of a computer network is
challenged everyday by:
 Equipment malfunctions
 System failures
○ Note: equipment malfunctions and system failures may be
caused by natural disasters such as floods, storms, or fires,
and electrical disturbances
 Computer hackers
 Virus attacks

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NETWORK ARCHITECTURE
 Network architecture – refers to the way a network is
designed and built. The two major types are:Peer-to-1-
1-peer architecture – Computers connect with each other in a
workgroup to share files, printers, and Internet access. This is
used to connect a small number of computers.
2-With client-server
 Each workstation getting network service is called a client,
while the computers managing the requests for facilities within
the network are called servers.
 There can be several different servers, such as a mail server,
Web server, print server, etc.
 Sending data to a server is called uploading; retrieving data
from a server is called downloading
NETWORK ARCHITECTURE
 Network architecture – refers to the way a network is
designed and built. The two major types are:Peer-to-1-
1-peer architecture – Computers connect with each other in a
workgroup to share files, printers, and Internet access. This is
used to connect a small number of computers.
2-With client-server
 Each workstation getting network service is called a client,
while the computers managing the requests for facilities within
the network are called servers.
 There can be several different servers, such as a mail server,
Web server, print server, etc.
 Sending data to a server is called uploading; retrieving data
from a server is called downloading
COMMUNICATIONS MEDIA
 Communications Channel
 To transfer data from one computer to another
requires some type of link through which the data
can be transmitted. This link is known as the
communications channel.
 To send data through the channel requires some
type of transmission media, which may be either
physical or wireless.
PHYSICAL MEDIA
 Twisted-pair cable – consists of two independently
insulated wires twisted around each other (least
expensive type of cable—the kind that is used in many telephone
systems)(UTP,STP)
 Coaxial cable – consists of an insulated center wire
grounded by a shield of braided wire (the primary type of
cabling used by the cable television industry; it is more expensive than
twisted pair) Coax cables are used to attach antennas to wireless
devices
 Fiber-optic cable – contains hundreds of clear
fiberglass or plastic fibers (threads) (made from thin,
flexible glass tubing; bandwidth is greater, so it can carry more data; it
is lighter than metal wires and is less susceptible to interference; it is
expensive)
Assignment
WRITE A RHREE PAGES FOR DATA
TRANSMISSION IN OPTIC FIBERS
STRUCTURE+MECHNISM.
Coaxial cable
Twisted-pair cable
Shielded Twisted-pair cable

3. 3
WIRELESS MEDIA
 Microwave system – transmits data via high-frequency
radio signals through the atmosphere.Satellite system
 Radio wave cellular communication,wireless LAN
 Infrared technology – transmits data as infrared light
waves from one device to another, providing wireless
links between PCs and peripherals. WI-FI
Note: The type selected is determined by the type of
network, the size of the network, and the cost.
Fuller, Floyd, Computers: Understanding Technology: EMC Paradigm, 2003.
HOW ARE NETWORKS
CATEGORIZED?
 Networks are usually classified using three
properties:
○ Topology
○ Protocol
○ Architecture
NETWORK
TOPOLOGIES
 Network Topology (or layout) – refers to the
way computers and peripherals are
configured to form networks
 Bus topology – all computers are linked by
a single line of cable
 Star topology – multiple computers and
peripheral devices are linked to a central
computer, called a host
 Ring topology – each computer or
workstation is connected to two other
computers, with the entire network forming
a circle
 Hybrid topology – combine network layout
types to meet their needs
NETWORK
TOPOLOGIES
NETWORK/COMMUNICATION PROTOCOLS
A protocol is simply an agreed-on set of rules and procedures
for transmitting data between two or more devices.
PROTOCOL SUIT
 Successful communication between hosts on a network
requires the interaction of many different protocols.
 A group of inter-related protocols that are necessary to
perform a communication function is called a protocol
suite.
 These protocols are implemented in software and hardware
that is loaded on each host and network device.
ROLE OF THE COMM PROTOCOLS
 The format or structure of the message.
 The process by which networking devices share information
about pathways with other networks(routing).
 How and when error and system messages are passed between
devices.
 The setup and termination of data transfer sessions.
TCP/IP and OSI models are the primary models
used when discussing network functionality.
Ultimately, designers of network protocols, services, or devices
are required to communicate to the industry by relating their
product or service to either the OSI model or the TCP/IP model,
or to both.

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A complete communication process for TCP/IP
includes these steps:
1. Creation of data at the application layer of the originating
source end device
2. Segmentation and encapsulation of data as it passes down
the protocol stack in the source end device
3. Generation of the data onto the media at the network access
layer of the stack
4. Transportation of the data through the internetwork, which
consists of media and any intermediary devices
5. Reception of the data at the network access layer of the
destination end device
6. Decapsulation and reassembly of the data as it passes up the
stack in the destination device
7. Passing this data to the destination application at the
Application layer of the destination end device
•Layer seven, is the top layer of both the OSI and four
for TCP/IP suit.
•It is the layer that provides the interface between the
applications we use to communicate and the underlying
network over which our messages are transmitted.
•Provide services that directly support user application
such as data base , email and file transfer.
•Application layer protocols are used to exchange data
between programs running on the source and
destination hosts.
Application layer
•There are many Application layer protocols and
new protocols are always being developed.
•Hypertext Transfer Protocol (HTTP) is used to transfer Web
pages files of the World Wide Web.
•Simple Mail Transfer Protocol (SMTP) is used for the transfer
of mail messages and attachments.
Application layer
Presentation Layer
The Presentation layer has three primary functions:
•Coding and conversion of Application layer data to ensure that
data from the source device can be interpreted by the appropriate
application on the destination device.
•Compression of the data in a manner that can be decompressed
by the destination device.
•Encryption of the data for transmission and the decryption of data
upon receipt by the destination.
•Among the well-known graphic image formats are Graphics
Interchange Format (GIF), Joint Photographic Experts Group
(JPEG), and Tagged Image File Format (TIFF). GIF and JPEG are
compression and coding standards for graphic images, and TIFF
is a standard coding format for graphic images.
The Session Layer
As the name of the Session layer implies create and exchange
of information to maintain dialogs between source and
destination applications.
Allows addition of check points i.e. synchronization points in to
stream of data . In the case of crash the transmission of data can
be retransmitted from the check point in spite of retransmitting it
from the start.
The Session layer handles the exchange of information to initiate
dialogs, keep them active, and to restart sessions that are
disrupted or idle for a long period of time.

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Transport layer(TCP LAYER)
1- creating a sessions between the applications. These
connections prepare the applications to communicate with
each other before any data is transmitted.
2-It divides each message into packets at the source and
reassembles them at the destination.(segmentation and
multiplexing)
3- port number is used in the transport layer header to indicate to
which application that piece of data is associated.
4-transport layer guarantee transmission of data from one end to
another without error
5-Ordered data reconstruction, Connection-oriented conversations
Reliable delivery
EACH FUNCTION IS SUPPORTED BY CERTAIN PROTOCOL
TCP AND UDP
 The two most common Transport layer
protocols of TCP/IP protocol suite are
Transmission Control Protocol (TCP)
and User Datagram Protocol (UDP).
Both protocols manage the
communication of multiple applications.
The differences between the two are the
specific functions that each protocol
implements.
THE NETWORK LAYER (IP LAYER)
1. It encapsulates the segments (adding headers) to becomes a
packet and splitting it to smaller packets if the packet is
larger than largest data frame.
2. The network layer is concerned with controlling the
operation of the subnet.
3. A ROUTER is used to determining how packets are routed
from source to destination.(path selection)
4. If one path is busy, then the router will select another path for
the packets to travel. So really, the packets can all have
different paths and find their way to the final destination.
5. decapsulation
THE NETWORK LAYER(IP LAYER)
The router has millions of IP addressing built into the
software, and knows where to send the packets.
IP stands for Internet Protocol and is basically an address
that the packets will be sent to.
An example would be 216.27.61.137
THE NETWORK LAYER
If you look at the IP Address, the number are broken
into different categories.
216. 27.61.137
Classification Hosts
216. 27.61.137
Octets

6. 6
Every machine on the Internet has a unique
identifying number, called an IP Address.
A typical IP address looks like this:
216.27.61.137
But computers communicate in binary form.
The same IP address in binary:
11011000.00011011.00111101.10001001
216.27.61.137
If you add all the positions together, you get 32,
which is why IP addresses are considered
32-bit numbers
Combine the four octets and you get 232 or a possible
4,294,967,296 unique values.
11011000.00011011.00111101.10001001
Subnetting
•Network administrators need to devise the
internetwork addressing scheme to accommodate
the maximum number of hosts for each network.
The number of hosts in each division should allow
for growth in the number of hosts.
Data link layer
•The OSI Data Link layer prepares Network layer packets for
placement onto the physical media that transports data. be it
copper, fiber, or the atmosphere.
•Interface between above layers and physical layers
•It divides the data packets received from the N.L into
manageable data units called frames
•Adds header to the frames to define the physical address of
the sender and receiver of the frame.
•Error control by adding a trailer at the end of the frame . It
uses mechanism to prevent duplication of frames.
Data link layer
Media Access control
•Putting frames on to the media
•Regulating the placement of data frames onto the media is
known as media access control .
•These methods are defined by sophisticated protocols,
which require mechanisms that introduce overhead onto the
network.
•The method of media access control used depends on:
•Media sharing - If and how the nodes share the media
•Topology - How the connection between the nodes appears
to the Data Link layer
DLL
•There are two basic media access control methods for shared
media:
•Controlled - Each node has its own time to use the medium
•Contention-based - All nodes compete for the use of the
medium
•In point-to-point connections, the Data Link layer has to
consider whether the communication is half-duplex or full-
duplex.

7. 7
EXAMPLE OF AN ETHERNET BUS
 Ethernet LANs use a bus
topology.
 All stations are connected to
a single long cable.
 Any station can send a
signal along the cable,
which all other stations will
receive. Unlike ring
topologies, the cable doesn't
close a loop.
Networks for Beginners: http://compnetworking.about.com/
TOKEN RING NETWORK
 A token passing ring LAN is a
group of computers connected in a
loop. The group uses a token
passing access mechanism.
 A computer wishing to send data
should first receive
permission. When it gets control
of the network it may transmit a
frame. Each frame transmitted on
the ring is transmitted from one
computer to the next, until it
ultimately returns to the initiator of
the transmission.
Networks for Beginners: http://compnetworking.about.com/
Encapsulation
Data
Segmen
tsPacket
Frame
Bits
Data
Data
PHYSICAL LAYER
The three fundamental functions of the Physical layer are:
1. Data encoding
2. Signaling
3. The physical components
•Encoding is a method of converting a stream of data bits
into a predefined "code. Codes are groupings of bits used
to provide a predictable pattern that can be recognized by
both the sender and the receive
•The Physical layer must generate the electrical, optical, or
wireless signals that represent the "1" and "0" on the
media. The method of representing the bits is called the
signaling method.
Physical Layer
Describe the role of signaling in the physical media
 Explain that network communication at this
layer consists of individual bits encoded onto
the Physical layer and describe the basic
encoding techniques

8. 8
PHYSICAL COMPONENTS
•Identify several media characteristics defined by Physical layer
standards
•Describe the impact interference has on throughput and the role
of proper cabling in reducing interference
•Identify the basic characteristics of UTP cable, STP,FIBER
Physical layer
 Identify the characteristics used to categorize
connectors, describe some common uses for the
same connectors, and identify the consequences
for misapplying a connector in a given situation
• Identify the basic characteristics of STP and Coaxial
cable
• Identify the characteristics used
to categorize connectors
•Describe the role of radio waves when using air as the media
and the increased need for security in wireless communications
INTERNET PROTOCOLS
Networks for Beginners: http://compnetworking.about.com/
 Hubs Hub provide connection to all ports (i.e. in one
port and out all other ports).
 Passive hub – no signal regeneration
 Active hub – provide signal regeneration(physical layer)
 Switches are similar to hubs, but send data to only
the appropriate output node, not all network nodes.
This increases the efficiency of the network.(good
band width utilization) (DLL)
 Routers are used in large WANs—like the Internet—
to pass packets along to their destinations. They
decide the most efficient path to send the packets
over the network.(Network layer)
depend on the knowledge of ip address, protocol
dependent. tcp/ip---------router----------tcp/ip
Network devices

9. 9
49
Gateways and Bridges
 Gateway
is a collection of hardware and software resources that
enables devices on one network to communicate
with devices on another, dissimilar network.
Bridge
 When the two networks being linked are based on
similar technology—such as a LAN in one city and a
LAN in another—a device called a bridge is used to
connect them.
 Repeaters
are devices that amplify signals along a network.
Network devices, cont’d
Hub versus Switch