This document provides an introduction to data communication and computer networks. It discusses the basics of networking including: 1. The key components of a data communication system including the message, sender, receiver, transmission medium, and protocols. 2. Different types of networks including LANs, WANs, MANs, WLANs, and VPNs. 3. Network topologies such as mesh, star, bus, and ring. 4. Common network cabling including twisted pair, coaxial, and fiber optic cables.

1. Chapter 2
Basics of Networking
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2. Introduction to Data communication:
 Data Communication:
 Data communication are the exchange of data between two devices via some form of
transmission medium such as a wire cable.
#Data: The word ‘data’ refers to information presented in whatever form is agreed upon the parties
creating and using the data.
#Telecommunication: The term telecommunication, which includes telephony, telegraphy and
television, means communication at a distance (Tele is Greek for ‘far’).
 The effectiveness of a data communication system depends on four fundamental characteristics:
Delivery, accuracy, timeliness and jitter.
 Delivery:
o The system must deliver data to the correct destination.
o Data must be received by the intended device or user and only by that device or user.
 Accuracy:
o The system must deliver the data accurately.
o Data that have been altered in transmission and left uncorrected are unusable.
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3.  Timeliness:
o The system must deliver data in timely manner.
o Data delivered late are useless.
o Incase of video and audio, timely delivery means delivering data as they are produced, in the same order
that they are produced, and without significant delay. This kind of delivery is called real- time transmission.
 Jitter:
o Jitter refers to the variation in the packet arrival time.
o It is the uneven delay in the delivery of audio or video packets.
o For example, let us assume that video packets are sent every 30ms. If some of the packets arrive with
30ms delay and other with 40ms delay, an uneven quality in the video is the result.
 Components:
 A data communication system has 5 components.
Protocol
Medium
Sender Receiver
Message
Rule 1:
Rule 2:
….
Rule n:
Rule 1:
Rule 2:
….
Rule n:
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4.  Message:
o The message is the information (data) to be communicated.
o Popular forms of information include text, numbers, pictures, audio and video.
 Sender:
o The sender is the device that sends the data message.
o It can be computer, telephone handset, video camera, etc.
 Receiver:
o The receiver is the device that receives the message.
o It can be computer, telephone handset, television, etc.
 Transmission medium:
o The transmission medium is the physical path by which a message travels from sender to receiver.
o Some examples of transmission medium include twisted-pair wire, coaxial cable, fiber-optic cable
and radio waves.
 Protocol:
o A protocol is a set of rules that govern data communications.
o It represents an agreement between the communicating devices.
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5. o Without a protocol, two devices may be connected but not communicating.
 Data Representation:
 Text
 Number
 Image
 Audio
 Video
 Data Flow:
 Communication between two devices can be simplex, half-duplex, or full-duplex.
 Simplex:
o The communication is unidirectional.
o Only one of the devices on a link can transmit; the other can only receive.
o Example: Keyboards and traditional Monitors.
Direction of Data
Fig: Simplex.
Station Station
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6. o The simplex mode can use the entire capacity of the channel to send data in one direction.
 Half-Duplex:
o In half-duplex mode, each station can both transmit and receive, but not at the same time.
o When one device is sending, the other can only receive, and vice versa.
o In this mode of transmission, the entire capacity of a channel is taken over by whichever of the
two devices is transmitting at the time.
o Walkie - talkies and CB (Citizen Band) radios are half- duplex system.
o The entire capacity of the channel can be utilize for each direction.
Direction of data at time 1
Direction of data at time 2
Fig: Half Duplex.
Station Station
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7.  Full-Duplex mode:
o In full-duplex mode, both stations can transmit and receive simultaneously.
o One common example of full-duplex communication is the telephone network (When two
people are communicating by a telephone line, both can talk and listen at the same time).
o The capacity of the channel, however must be divided between the two direction.
Direction of data all the time
Fig: Full-Duplex.
Station Station
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8. Introduction to Computer Networks:
 A network is a collection of independent computers that communicate with one another over a
shared network medium.
 A network is a set devices (often referred to nodes) connected by communication links. A node can
be a computer, printer, or any device capable of sending and/or receiving data generated by other
nodes on the network.
 As companies rely on applications likes e-mail and database management for core business
operations, computer networking becomes increasingly more important.
 Network criteria:
 A network must be able to meet a certain number of criteria. The most important criteria includes
performance, reliability and security.
 Performance:
o It can be measured base on transit time and response time (Transit time is the amount of time
required for a message to travel from one device to another and response is the elapse time between
an inquiry and a response).
o It depends on number of factors, including the number of user, the type of transmission medium, the
capacities of the connected hardware and the efficiency of the software.
o Performance is often evaluated by two networking metrics: Throughput and delay.
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9. o We often need more throughput and less delay. However, these two criteria are often contradictory.
We may increase throughput but delay will also increase because of traffic congestion in the
network.
 Reliability:
o Network reliability is measured by the frequency of failure, the time it takes a link to recover from a
failure, and the network’s robustness(quality/condition being strong) in a catastrophe(suddenly
damage/failed).
 Security:
o Network security issues include protecting data from unauthorized access, protecting data from
damage and development, and implementing policies and procedures for recovery from breaches
(failing to observed agreement) and data losses.
Every network includes:
o At least two computers (Server or client workstation).
o Networking interface card (NIC).
o A connection medium, usually a wire or cable or in form of wireless.
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10. Types of Networks:
 Network are usually classified by distance of coverage.
 LANs (Local Area Networks)
o A LAN is usually privately owned and links the devices in a single office, building or campus.
o The size of the LAN may be determined by licensing restrictions on the number of users per copy
of software or by restrictions on the number of users licensed to access the operating system.
o In addition to size, LAN are distinguished from other types of networks by the transmission media
and topology.
o The most common topology used in LAN are Bus, Ring and star.
o Early LANs had data rates in the range of 4 to 16 Mbps, however today’s speeds are normally in
the range of 100 to 1000 Mbps.
o Wireless LANs are the newest evolution in LAN technology.
 WAN (Wide Area Network)
o A WAN provides long distance transmission of data, image, audio and video information over
large geographic areas that may comprise a country, a continent or even the whole world.
o Wide area networks are often established with leased telecommunication circuits.
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11. o Example: Internet is the largest WAN.
o The Internet is a system of linked networks that are worldwide in scope and facilitate data
communication services such as remote login, file transfer, e-mail, the world wide web and
newsgroup.
o The Internet provides a communications highway for millions of users.
 MAN (Metropolitan area Networks):
o MAN is a high speed network that consists of LAN in metropolitan area such as a city or town and
handled the bulk of communication acting across that region.
o A MAN is a network with a size between a LAN and a WAN.
o It is normally covers the area inside a town or a city.
o Example1: The cable TV network that originally was designed for cable TV.
o Example2: MAN is the part of the telephone company network that can provide a high speed DSL line
to the customer.
 WLAN (Wireless LAN):
o A wireless local area network (WLAN) is a wireless computer network that links two or more devices
using wireless communication within a limited area such as a home, school, computer laboratory, or
office building.
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12. o WLAN gives users the ability to move around within a local coverage area and yet still be
connected to the network.
o Example: Bluetooth and Wi-Fi (Wireless Fidelity).
 VPN (Virtual Private Network):
o A virtual private network (VPN) extends a private network across a public network, and enables
users to send and receive data across shared or public networks as if their computing devices were
directly connected to the private network.
o VPN technology was developed to allow remote users and branch offices to securely access
corporate applications and other resources.
 Categories of Network:
 Network can be divided into two main categories:
1. Peer-to-Peer.
2. Server-Based.
 Peer-to-Peer:
o In Peer-to-Peer networking there are no dedicated servers or hierarchy among the computers.
Normally each computer serves as Client/Server and there is no responsible for the entire network.
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13. o All of the computers are equal and therefore known as Peers.
o Peer-to-Peer networks are good choices needs of small organizations where the users are in the
same general area, security is not an issue and the organization and the network will limited
growth within the foreseeable future.
 Server-Based:
o The client/server network is the most efficient way to provide:
• Databases management of applications such as spreadsheets, accounting, communications
and document management.
• Networking Management.
• Centralized file storage.
o The client/server model is basically an implementation of distributed or cooperative processing.
o The capacity of the channel is shared, either spatially or temporary.
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14.  Network Topology:
 The topology of a network is the geometric representation of the relationship of all the links and
linking devices (nodes) to one another.
 There are four basic topologies: Mesh, Star, Bus, Ring.
 Mesh:
o In mesh topology, every devices has a dedicated point-to-point link to every other devices. The
term dedicated means that the link carries traffic only between the two devices it connects.
o To accommodate that many links, every device on the network must have (n-1) I/O ports to be
connected to other (n-1) stations.
o Advantages over other network topology:
 The use of dedicated links guarantees that each connection can carry its own data load,
thus eliminating the traffic problems.
 A mesh topology is robust (healthy).
 There is the advantage of privacy and security.
o The main disadvantages of a mesh are related to the amount of cabling and the number of I/O
ports required.
o Example: The connection of telephone regional offices in which each regional office needs to be
connected to every other regional office.
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15. Fig: Mesh Topology.
Station 1
Station 2 Station 5
Station 3 Station 4
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16.  Star Topology:
o In star topology, each device has a dedicated point-to-point link only to a central controller,
usually a hub. The devices are not directly linked to one another.
o If one device wants to send data to another, it sends the data to the controller, which then relays
the data to the other connected device.
o Advantages:
 A star topology is less expensive than a mesh topology.
 Easy to install and configure.
 Robustness.
 As long as the hub is working, it can be used to monitor link problems and bypass defective
link.
o Disadvantages:
 The dependency of the whole topology on one single point, the hub.
 If the hub goes down, the whole system is dead.
o The star topology is used in local area networks (LANs). High speed LANs often use a star
topology with a central hub.
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17. Hub
Fig: A star Topology connecting four stations.
 Bus Topology:
o A Bus Topology is multipoint. One long cable acts as a backbone to link all the devices in a network.
o Nodes are connected to the bus cable by drop lines and taps.
o Advantages:
 Ease(make less severe) of installation.
 Only the backbone cables stretches through the entire facility. Each drop line has to reach only
as far as the nearest point on the backbone.
Station 1 Station 2 Station 3 Station 4
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18. o Disadvantage:
 Difficult reconnection and fault isolation.
 A fault or break in the bus cables stops all transmission, even between devices on the same
side of the problem.
o Ethernet LANs can be use Bus topology.
Cable end Cable end
Drop line Drop line Drop line
Tap Tap Tap
Fig: A bus topology connecting three stations.
Station 1 Station 2 Station 3
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19.  Ring Topology:
o In a ring topology, each device has a dedicated point-to-point connection with only the two devices on
either side of it.
o A signal is passed along the ring in one direction, from device to devices, unit it reaches its destination.
o Each device in the ring incorporates a repeater.
o A ring is relatively easy to install and configure.
Repeater Repeater
Repeater Repeater Repeater
Repeater
Repeater Repeater
Fig: A ring topology connecting six stations
Station 2 Station 3
Station 4
Station 5
Station 6
Station 1
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20.  Network Cables:
 Network cables provide a conduit from one device to another, include twisted-pair cable, coaxial
cable and fiber-optic cable.
 Twisted cable and coaxial cable use metallic (copper) conductors that accept and transport signals
in the form of electric current.
 Optical fiber is a cable that accepts and transports signals in the form of light.
 Twisted-Pair Cable:
o A twisted pair consists of two conductors (normally copper), each with its own plastic insulator,
twisted together.
o One of the wires is used to carry signals to the receiver and the other is used only as a ground
reference.
o Twisted-pair cables are of two types: Unshielded and shielded twisted-pair cable.
 Unshielded twisted-pair cable:
 The most common twisted-pair cable used in communications is referred to as Unshielded
twisted-pair(UTP).
 The most common UTP connector is RJ45 (RJ-Register Jack). The RJ45 is a keyed, meaning the
connector can be inserted in only one way.
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21.  Shielded Twisted-pair cable:
 STP cable has a metal foil or braided mesh covering that encases each pair of insulated
conductors.
 Metal casing improves the quality of cable by preventing the penetration of noise or
crosstalk, it is bulkier and more expensive.
o Twisted-pair cable are used in telephone lines to provide voice and data channels.
Fig: Twisted Pair cable.
Fig: UTP &STP. Fig: RJ-45 connector.
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22.  Coaxial cable:
o Coaxial cable carries signals of higher frequency ranges than those in twisted-pair cable.
 Coaxial has a central core conductor of solid or stranded wire (usually copper) enclosed in an
insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a
combination of the two.
 The outer metallic wrapping serves both as a shield against noise and as the second conductor,
which completes the circuit.
 This outer conductor is also enclosed in an insulating sheath and the whole cable is protected
by a plastic cover.
o Coaxial cable standards:
 Coaxial cables are categorized by their radio government(RG) ratings. Each RG number denotes
a unique set of physical specification, including the wire gauge (diameter of the wire) of the
inner conductor, the thickness and type of the inner insulator, the construction of the shield,
and the size of the outer casing.
 Each cable defined by an RG rating is adapted for a specialized function, as mentioned below:
Categories Use
RG-59 Cable TV
RG-58 Thin Ethernet
RG-11 Thick Ethernet 22

23. o Coaxial Cable connectors:
 The most common type of connector used today is the Bayone-Neill-Concelman (BNC).
 The three popular types of connectors includes, BNC connector, the BNC T connector, and
the BNC terminator.
 The BNC connector is used to connect the end of the cable to a device, such as a TV set. The
BNC T connector is used in Ethernet networks to branch out to a connection to a computer or
other device. The BNC terminator is used at the end of the cable to prevent reflection of the
signal.
o Coaxial cables are widely used in telephone network and Cable TV network.
Fig: Coaxial Cable. Fig: BCN connectors.
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24.  Fiber-Optical Cables:
o A fiber-optic cable is made of glass or plastic and transmits signals in the form light.
o Fiber optics are pretty darn cool and not cheap.
o This cable is really smaller and can carry a vast amount of information fast and over long
distance.
o There are three types of connectors for fiber-optic cables which includes Subscriber Channel (SC)
connector, Strip-tip (ST) connector and MT-RJ (Mechanical Transfer Registered Jack)connector.
 The SC connector is used for cable TV. It uses a push/pull locking system.
 The ST connector is used for connecting cable to networking devices.
 The MT-RJ provides Housing two fibers and mating together with locating pins on the plug.
o Fiber optical cable is often used as in backbone networks because its wide bandwidth is cost-
effective.
Fig: Fiber-Optical Cables.
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25. Fig: Fiber optic connectors.
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