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1. Data Communications and Computer Networks
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2. Basics of Data Communication
• Data communication: is the process of sharing ideas,
information and messages with others in a particular time
and place.
• It is exchange of data between two or more parties.
• It includes :
– Writing and talking
– Nonverbal communication (such as facial expressions, body
language or gestures)
– Visual communication (the use of images of pictures such as
painting, photography, video or film)
– Electronic Communication
– Such as telephone calls, electronic mail, cable television,
satellite broadcasts.
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3. Communications Model
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4. A Communications Model
• Source
– generates data to be transmitted
• Transmitter
– Converts data into transmittable signals
• Transmission System
– Carries data
• Receiver
– Converts received signal into data
• Destination
– Takes incoming data
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5. Simplified Data Communications
Model
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6. Mode of transmission
• Simplex
– One direction
• e.g. Television
• Half duplex
– Either direction, but only one way at a time
• e.g. police radio
• Full duplex
– Both directions at the same time
• e.g. telephone
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7. Continuous & Discrete Signals
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8. Analog and Digital Data Transmission
• Data
– Entities that convey meaning
• Signals
– Electric or electromagnetic representations of
data
• Transmission
– Communication of data by propagation and
processing of signals
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9. Types of signals
• Analog
– Continuous values within some interval
– e.g. sound, video
• Digital
– Discrete values
– e.g. text, integers
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10. Data and Signals
• Usually use digital signals for digital data and
analog signals for analog data
• Can use analog signal to carry digital data
– Modem
• Can use digital signal to carry analog data
– Compact Disc audio
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11. Analog Signals Carrying Analog and
Digital Data
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12. What is a Network ?
• A network is a system that links
computers and computer resources.
The resource may be a printer,
plotter, or storage device.
• A network is a collection of
computers and other devices that
are interconnected & communicate
to share data, hardware, and
software.
– Networks allow users to share
resources
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13. Goal of a Network
• The main goals of network computing is to make it
easy to connect with another network resource,
whether that resource is in the same building or the
other side of the globe.
• Networks minimize distance and communications
problems and give users access to information
anywhere on the network.
– With proper licensing, many network users can use the same
applications and data files simultaneously and share other
resources, such as storage space or a printer.
• Is a single PC attached to a printer considered a
network?
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14. Importance of Networking/
The Need for Computer Networks
•Program and File Sharing/To share databases
–The program and its data files can be stored on the file server for
access by any network user. A database program is an ideal
application for a network.
•Resource sharing:
–Resources include printers, plotters, storage devices, and other
computing systems like minicomputers & mainframes.
•Personal Communication (like Electronic Mail):
–Users can easily communicate with one another. Messages are
dropped in “mailboxes” for the recipient to read at a convenient
time. Meetings can be arranged and schedules can be managed..
•Ability to use Network Software :
–Software such as electronic mail, groupware is becoming available.
–Groupware is designed for groups of users who have a need to
interact with each other over the network.
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15. The Need for Computer Networks …
• Creation of work groups:
–Groups of users may work in a department or be assigned to
a special project. Messages and electronic mail can be sent
to each member of the group by referencing the group
name.
• Centralized management:
–Because most of the resources of a network are centered
around the server, management becomes easy. Backups and
file system optimization can be handled in one location.
• Security:
–Diskless workstations can be used to prevent sensitive data
from being downloaded to disk.
–Managers can prevent users from working outside their own
assigned directories, and login restrictions can be applied.
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16. • To share application programs
• To undertake parallel processing
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17. Components of a Network
• All types of networks require special networking hardware and
software to allow different computers to communicate with each
other.
• Network hardware components include:
– Workstations
– Servers
– Network Interface Cards/Network Adapter Card
– Hubs/switches
– Cables
• Network software
–A network operating system (NOS) is the group of programs that
manages the resources on a network.
• Novell NetWare
• Ms Windows NT Server
• Ms Windows 2000
• Linux (SOLARIS, RedHat..)
• UNIX
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18. Components of a Network
• Clients/Workstations:
– a stand-alone individual computer attached to a network is
called a client or a workstation on a network.
– A workstation provides access to:
• Your computer’s local resources
• Network resources
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19. Components of a Network
• A server
–Server is a computer connected to a network that
distributes and stores resources for other network
users.
–Server offers network services to workstations including file
storage, user management, security, common network
commands, system manager commands, and much more.
– A server is a computer
connected to a network
that distributes and stores
resources for other
network users.
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20. Components of a Network
• Network Interface Card (NIC):
– Each computer to be attached to the network
requires an interface. An interface may be built-in, or
it must be added as an optional item.
– The interface card must match the type of network
being used. The network cable attaches to the back
of the NIC.
– A network interface card (NIC) – a key hardware
component that connects a workstation to the
network.
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21. Components of a Network
• Cabling System:
– It may be wired or wireless
• The biggest difference between these two types of networks
is one uses network cables and the other uses radio
frequencies.
– The network cabling system is the wire used to connect
the server and nodes together, Ethernet cables.
– Ethernet cables may be coaxial cable, shielded and
unshielded twisted pair cable, high-speed fiber optic
cable.
– Wireless transmission include radio, microwave,
infrared, satellite, ..
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22. A wired or wireless network, Which is better?
• Which is better? That depends on your situation and your priorities.
• Wired Network
– A wired network uses Ethernet cable to connect the computers to the
network router. Wired networks are less expensive, faster, and more secure
than wireless networks.
– All computers on a wired network must be connected by Ethernet cable.
Running Ethernet cables between rooms or floors can be a significant
challenge.
• Wireless Network
– A wireless network provides the flexibility to connect your computers to the
network using wireless network devices. Data is sent and received using
radio waves that eliminate the need for Ethernet cables.
– Connecting to the network is possible from anywhere within range of the
wireless router. Wireless networks trade speed and some loss of security for
greater flexibility and ease of use.
• It is another option to combine Wired and Wireless Components
• Which option do you think is suitable for health sector?
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23. Hub and Switch
• Hubs & switches are types of network equipment that connect devices.
They differ in the way they pass on the network traffic that they receive.
• Hubs: refers to any piece of network equipment that connects PCs together, but it actually
refers to a multi-port repeater. This type of device simply passes on (repeats) all the
information it receives, so that all devices connected to its ports receive that information.
– Hubs repeat everything they receive & can be used to extend the network. However, this
can result in a lot of unnecessary traffic being sent to all devices on the network. Hubs
pass on traffic to the network regardless of the intended destination; the PCs to which the
packets are sent use the address information in each packet to work out which packets are
meant for them.
– In a small network (less than 30 users) repeating is not a problem but for a larger, more
heavily used network (more than 50 users), switch networking device may be required to
help reduce the amount of unnecessary traffic being generated.
• Switches: control the flow of network traffic based on the address information in each
packet. A switch learns which devices are connected to its ports (by monitoring the packets it
receives), & then forwards on packets to the appropriate port only. This allows simultaneous
communication across the switch, improving bandwidth.
– This switching operation reduces the amount of unnecessary traffic that may occur if the
same information had been sent from every port (as with a hub).
• Switches & hubs are often used in the same network; the hubs extend the
network by providing more ports, & the switches divide the network into
smaller, less congested sections. 26

24. Types of Computer Networks
• Networks come in all sizes. Such networks may
exist
– within a single office,
– throughout a building,
– span cities & countries, or
– all over the world
• The major categories of networks are:
– Local area networks (LANs)
– Metropolitan Area Network(MAN)
– Wide area networks (WANs)
– Internetwork
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25. Local Area Network (LAN)
•LAN is owned by the same organization that owns the
attached devices.
–In contract, for WANs at least a significant fraction of the
network assets are not owned.
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• An interconnected group of
computers and devices that
are located in a limited
geographic area.
–A small network (3 to 50
nodes) usually located within a
single building or group of
buildings belonging to an
organization.

26. • Characteristics of LAN:
– Physically limited
– High bandwidth
– Inexpensive cable media (Co-axial or twisted pair)
– Used for data and hardware sharing
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27. • Metropolitan Area Network (MAN)
– Covers large geographic areas
– Uses Fiber Optics cables
– For example: Colleges, Universities, banks etc.
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28. Wide Area Network (WAN)
• A network that covers a large geographical area, requires public
right-of-ways, and rely at least in part on circuits provided by a
common carrier.
–WANs are characterized by some form of remote communications, such as high-
speed phone lines, microwave dishes, or satellites.
• It is a network that spans countries and the globe.
• Large corporations that have regional or worldwide offices may
interconnect their local area networks into wide area networks.
–The airline reservation system is a good example.
WAN
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29. Internetwork
•The Internet
– is largest of all networks.
– The Internet is a network between networks; or it is a
worldwide connection of networks
– It is a network owned by the world, not by specific
organization
•Intranets
–are LANs or WANs within a building or organization.
• Communication standards called protocols allow for global
exchange of information using Internet/ Intranet.
–Transmission Control Protocol (TCP)
–Internet Protocol (IP)
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30. • Based on the architecture, networks are
divided into two broad categories or
• Depending on the role of the participating
computers we have two types of networks
1. Peer-to-peer Networks
2. Server –based Networks
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31. • Peer-to-peer Networks
– Type of network where all the computers are
equal and therefore are known as peers.
– Normally, each computer functions as both a
client and a server, and there is no one assigned to
be an administrator responsible for the entire
network.
– The user at each computer determines what data
on their computer gets shared on the network
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32. Peer-to-peer Networks
• No dedicated server
• Every computer acts as both a client and a server
• Good for 10 or few users
• Less security
• User at each computer determines what data on that computer is
shared on the network., also called work groups
• all computers on the network belong to users and are equal as far
as the network is concerned
• Computers simply connect with each other in a workgroup to share
files, printers and Internet access.
• This is most commonly found in home configurations and is only
practical for workgroups of a dozen or less computers
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33. Client server networks:
• Type of network in which particular computers
— servers — are responsible for resources and
providing these resources for other computers
— clients. There can be many clients and one
server, or vice versa. Servers can have one
specific type of resource to control.
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34. • Server can provide various services, including
– centrally routed Internet Access,
– mail (including e-mail),
– file sharing and printer access,
– ensuring security across the network.
• Supports large number of users
• Needs dedicated server (acts only as a server, but not
as a client)
• Security is an issue
• Size is limited by a server and network hardware
• Requires at least one professional administrator.
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35. • The type of network you choose to implement
depends on
– Size of the organization
– Level of security required
– Level of administrative support available
– Amount of network traffic
– Needs of the networks use
– Network budget
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37. Network Topologies
• Network topology refers to the physical layout of
the network, especially the locations of the
computers and how the cable is run between
them.
• The most common network topologies include:
– bus
– star
– ring
– Mesh
– Hybrid
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38. Bus Topology
• In a bus configuration, all computers are connected to a
single shared communication link through interface units
and cables.
– Messages are broadcast along the whole bus. In order to
receive a transmission, the computers must be able to
recognize their own address.
• The bus topology is often used when a network
installation is smaller, simple, or temporary.
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40. • The linear network consists of a number of
nodes that are attached to a common cable or
bus
• This common cable is known as a trunk line, a
segment or a bus.
• Each end of the trunk line terminated so when
network traffic reaches the end of the cable it
is removed the network.
• The signal on the bus travels in both
directions from the workstations or nodes.
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41. • Advantages:
1. It uses the least amount of cable / Low cost
2. The wiring layout is simple / Easy to implement
4. It is very easy to extend
Disadvantages:
1. Limited cable length and workstation
2. Fault diagnosis and isolation is difficult
3. The trunk can be a bottle neck to the network
when network traffic is very heavy.
4. Cable fault affects all workstations
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42. Star Topology
• most common network topologies found in
most offices and home networks
• The star network has a central device to
which all the workstations, or nodes, and
servers are attached via some kind of
transmission media.
• The hub is the focal point of the star, and all
network traffic must pass through the hub.
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43. 46

44. Star Topology
• In a star topology all
cables run from the
computer to a central
location, where they are
all connected by a
hub/switch.
• In a star configuration,
messages are passed
from a computer to the
hub. Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
Central Server
Star Topology Network
Hub
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45. • Hub - is a device that processes and switches
the messages from one incoming line to
another.
– Signals are transmitted from the sending
computer through the hub to all computers on
the network.
– Failure of one computer doesn’t affect the
network
– Failure of the hub affects the network
– Cabling cost is high
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46. Advantages to a star topology
• It is easy to modify and add new computers to a star
network without disturbing the rest of the network.
• The center of the star is a good place to diagnose
network problems.
• Single computer failures do not necessarily bring down
the whole star network.
Disadvantages to a star topology:
• If the central hub fails, the whole network stops.
• It costs more to cable a star network because all
network cables must be pulled to one central point,
requiring more cable than other network topologies.
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47. Ring Topology
• In a ring or loop
topology, each
computer is connected
to only two
neighboring nodes.
• Data travels in only one
direction, from node to
node around the ring.
Token-ring
Workstation
Workstation
Workstation Server
Laser printer
ASCII Printer
Ring Topology Network
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49. • Unlike the bus topology, there are no terminated ends.
• Each node on the cabling acts as a repeater, boosting the
signal between transmissions.
• A token is a special series of bits that contains control
information
• Each computer acts as a repeater to boost the signal and
send it to the next computer.
• Failure of one computer can have an impact on the
entire network.
• Allows signals to travel farther by regenerating signals
• Cable failures affect limited users.
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50. • Advantages:
1. The overall cable length is short
2. The shorter cable means lower cabling costs
3. No wiring closet space is required
Disadvantages:
1. A single node failure causes network failure
2. It is more difficult to diagnose faults
3. Network modifications/recognition is more
difficult and disrupts network operation.
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51. Physical Mesh Topology
• A mesh topology is a network
where computers are linked
to each other through
intermediate nodes with
redundant paths.
• Between any two computers
are a number of other nodes
not arranged in a straight
line.
• The Internet is an example of
a large mesh topology.
Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
Mesh Topology Network
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52. • Each computer is connected to every other
computer by a separate cable.
• Provides redundant paths through the new
work
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53. Advantages
1. even multiple link failure doesn’t
mean that the network will fail
Disadvantages
1. Wiring is expensive
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54. Hybrid Topology Types
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56. • Transmission Media
• Transmission Medium is the physical path
between transmitter and receiver in a data
communication system.
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57. • Media of data transmission:
1) Guided Transmission media- Data
transmission is through solid medium
(wired system).
2) Unguided Transmission media– Data
transmission through air /space (i.e wireless
system)
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58. Commonly used guided media:
· Twisted pair
· Coaxial cable
· Optical fiber
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59. • Twisted Pair
– Is a copper wire similar to the common telephone line
– each of the pair of wire are twisted
– Insulated copper wires arranged in regular spiral pattern.
– The oldest, least expensive, and most commonly used
media
– reduce susceptibility to interference than straight pair
wires (two straight parallel wires tend to act as an antenna
and pick up extraneous signals when compared to twisted
pairs)
– Highly susceptible to electrical noise, interference, and
‘tapping’ of the signal as compared to the other guided
media
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60. 63

61. Types of Twisted pairs
-UTP (unshielded twisted pair )
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62. • Unshielded twisted pairs (UTP)
– UTP is highly subjected to external
electromagnetic interference.
– made up of up to four twisted pairs enclosed in a
plastic jacket
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63. • -STP (shield twisted pair)
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64. • Coaxial Cable
• Most versatile medium used in LANs, Cable TV,
VCR-to-TV connections
• Noise immunity is better than twisted pair
• Less susceptible to interference and cross talk
but there still is attenuation and thermal noise
problem
• Can go up to 185m(10Base2) or 500m(10Base5)
without the need for an amplifier/repeater
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65. • Coaxial cable details
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66. • Optical Fiber
– Flexible, thin (maximum of a hundred of mm), made of
very pure glass / plastic fiber capable of conducting optical
rays
– Extremely high bandwidth: capable of ³ 2Gbps
– Very high noise immunity, resistant to electromagnetic
interference
– Does not radiate energy/cause interference
– Very difficult to tap
– Better security but multipoint not easy
– Need optical-electrical interface (more expensive than
electrical interface) Fiber
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69. • Unguided (wireless transmission)
• In unguided media transmission and reception
are achieved by means of an antenna. There are
two types of configuration for wireless
transmission namely, directional and
omnidirectional.
• Wireless transmission can of the following types
• Terrestrial Microwave
• Satellite Microwave
• Infrared
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