CIT 513: Introduction to Computer Communication

Mohammed A. Salehhttp://ifm.ac.tz/staff/msaleh/CIT513.html

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Module Description Provides the student with knowledge

of fundamentals of how computers communicate.

Provides the student with an understanding of how computers interact with different computers systems

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Prerequisites There is no prerequisites before

undertaking this course.

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Plagiarism Policy Plagiarism is a serious offense Plagiarism is presenting somebody else's work

as your own. It includes: Copying information directly from the Web or books without

referencing the material Submitting joint coursework as an individual effort copying

another student's coursework Stealing coursework from another student and submitting it as

your own work.

Suspected plagiarism will be investigated and if found to have occurred will be dealt with accordingly.

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Cont … All material copied or amended from any source

(e.g. internet, books) must be placed in quotation marks and in italics, with a full reference to the source directly underneath the material

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Cont … All material copied or amended from any source

(e.g. internet, books) must be placed in quotation marks and in italics, with a full reference to the source directly underneath the material

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Instructor There is only one lecturer responsible for this course,

both lectures and tutorials. Find out about my contact details from my personal

website http://ifm.ac.tz/staff/msaleh If you need to see me in my office please book an

appointment by writing me an email m.saleh030@gmail.com

My office number is Block D, room 016 All notes will be uploaded on the CIT 513 web page,

http://ifm.ac.tz/staff/msaleh/CIT513.html A hardcopy will be submitted to the class representative

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Basic Rules Try to attend ALL lectures Sign against your name on the register Try not to be late, if you have to be late, come in

quietly. If you miss a class find out what was covered Material covered in lectures is examinable The course notes are not meant to be

exhaustive, read the recommended books; Read critically, point out any errors in the lecture notes.

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Assessment This module will be assessed by a

combination of tests, tutorials, unannounced quizzes and the final exam.

Both the tests will be written tests and the extent of coverage will be announced in due time.

There will also be unannounced quizzes, which will contribute to your coursework.

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Cont … And finally the Final Exam, which will

cover all contents of the course taught during the semester.

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Final Mark Calculation

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Assessment Marks (%)

Test I 15

Test II 15

Tutorials 5

Unannounced quizzes 5

Total 40

Final Exam 60

Grand Total 100

Required Readings

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Author Year Title Publisher

Hermachandran L.

2003 Computer Communications Network

Charulatha

Tanenbaum A. S. 2005 Computer Networks Prentice-Hall

Galo M. A. 2002 Computer Communications and Networking Technologies

Pacific Grove

Rowe S and Schuch

2005 Computer Networking Pearson

Recommended Readings

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Author Year Title Publisher

Kurose J. F 2001 Computer Networking a top down approach

Pearson

Halsall 2005 Computer Networking and Internet

McGraw-Hill

Madhulika J. 2002 Computer Networks BPB

Prescribed Materials If you have issue with getting hold of the book then it will

made it available in a CD with other additional material at a little fee, not more than TZS 2000/-

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How to survive this course Materials sound simple and easy, but they

are not. Do not leave everything to the exam

night!. Not to copy others work!, try them by

yourself. You can read the course by yourself, but

the class makes the life for you easier.

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IntroductionWhat is a Computer Network?

A network is nothing more than two or more computers connected to each other so that they can exchange information, such as e-mail messages or documents, or share resources, such as disk storage or printers.

These computers may be interconnected in the same building or different buildings.

In most cases, this connection is made via electrical cables that carry the information in the form of electrical signals.

The cables transmitting the information are commonly known as transmission media.

The transmissions media are classified as wired or wireless transmission media. 

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Cont … Examples of wired transmission medias are Unshielded

Twisted Pair (UTP), Coaxial Cable or Fiber Optic Cable

(a) Coaxial

(b) Fiber Optic (c) UTP

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Cont … Wireless transmission medias include radio waves,

infrared and Bluetooth

(a) Bluetooth icon (b) Radio signals

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Cont … When a computer is turned on and can be visible by all

other computers, then that computer is said to be online. If a computer is not turned on and it is not visible by

other networked computers, it is then said to be offline.

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Why Computer Networks? Networks are all about sharing. are about sharing three

things: information, resources, and applications. Sharing information: allow users to share information in several

different ways. The most common way of sharing information is to share individual files. For example, two or more people can work together on a word-processing document.

Sharing resource: certain computer resources, such as printers or hard drives, can be set up so that network users can share them. Sharing these resources can result in significant cost savings. For example, it is cheaper to buy a single high-speed printer with advanced features that can be shared by an entire workgroup than it is to buy separate printers for each user in the group.

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Cont … Sharing applications: several users can work together on a

single business application, For example, an accounting department may have accounting software that can be used from several computers at the same time.

Other uses High reliability: All data can be copied on two or three

machines, so if one of them is unavailable then other two copies could be used.

Communication: A computer network can provide a powerful communication medium along widely separated employees.

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Networks building blocks All networks, large or small, require specialized network

hardware to make them work. Small networks will have less network hardware than

large networks. Small or large, all networks are built from the following

basic building blocks: Client computers

computers that end users use to access the resources of the network. located on users’ desks. usually run a desktop version of Windows such as Windows Vista, Windows

XP, Ubuntu or Open Suse, along with application soft- ware such as Microsoft Office.

sometimes referred to as workstations.

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Cont … Server computers

Computers that provide shared resources, such as disk storage and printers, as well as network services, such as e-mail and Internet access.

run a specialized net- work operating system such as Windows Server 2008 or 2003, Ubuntu Server, Leopard (OS X) Server along with special software to provide network services.

Network interface card (NIC) An interface that’s installed in a computer that enables the computer to

communicate over a network. Every client and every server computer must have a NIC in order to be a

part of a network.

Cable Computers in a network are usually physically connected to each other using

a cable

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Cont … Switches

Network cable usually doesn’t connect computers directly to each other Instead, each computer is connected by cable to a device known as a switch Each switch contains a certain number of ports, typically 8 or 16

Wireless networks computers to communicate via radio signals radio transmitters and receivers take the place of cables main advantage of wireless net- working is its flexibility main disadvantage of wireless networking is that it is inherently less secure

than a cabled network.

Network software As important as network hardware. Server computers typically use a special network operating system (also

known as a NOS) in order to function efficiently.

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Clients and Servers The network computer that contains the hard drives,

printers, and other resources that are shared with other network computers is called a server

Any computer that’s not a server is called a client. Differences between the two computers:

The most powerful and expensive computers in a network are the servers

every user on the network shares the server’s resources.

The cheaper and less powerful computers in a network are the clients

clients’ resources don’t have to be shared

Most networks have more clients than servers A network with ten clients can probably get by with one server.

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Types of Computer Networks Networks are classified according to their geographical

coverage and size Network classifications include:

1. Personal Area Networks (PANs)

2. Local Area Networks (LANs)

3. Metropolitan Area Networks (MANs)

4. Wide Area Networks (WANs)

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Personal Area Networks (PANs) Introduced by the presence of wireless technologies. It is also referred to as Wireless Personal Area Networks

(WPAN). WPAN refers to the technologies involved in connecting

devices in very close proximity to exchange data or resources.

An example of this can be seen through connecting a mobile device with a mobile device to exchange files (music, photos or documents)

Connecting a laptop with a PDA.

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Cont … Because of the close proximity of WPAN networking, short-

range wireless technologies are typically used. This includes Bluetooth and Infrared

A laptop sending a file to a Personal Digital Assistant (PDA).

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Cont …

Mobile devices that can form a PAN

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Local Area Network (LAN) A network that is restricted to a single geographical

location. Encompasses a relatively small area such as an office

building or school The function of the LAN is to interconnect workstation

computers for the purposes of sharing files and resources.

It is typically high speed and cheaper to set up than a WAN

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Cont …

Local Area Network31

Cont …Major Characteristics of LANsEvery computer has the potential to communicate with any other computers of the networkHigh degree of interconnection between computersEasy physical connection of computers in a networkInexpensive medium of data transmissionHigh data transmission rate

AdvantagesThe reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers.

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Cont … Addition of new computer to network is easy. High rate of data transmission is possible. Peripheral devices like magnetic disk and printer can be

shared by other computers.

Disadvantages If the central device fails, the entire network system

breaks down.

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Cont …Use of LANFollowings are the major areas where LAN is normally used:

1.File transfers and Access

2.Word and text processing

3.Electronic message handling

4.Remote access

5.Digital voice transmission and storage

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Wide Area Network (WAN) It is used to describe a computer network spanning a

regional, national or global area. For example, for a large company the head quarters

might be at Dar Es Salaam and regional branches at Dodoma, Arusha, Mwanza and Morogoro

They are built so that users from one location can communicate with users from another location

WANs are slower than LANs Often require additional and costly hardware

Routers Dedicated leased line Complicated implementation procedures

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Example of WAN

Wide Area Network

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Cont … Followings are the major characteristics of WAN.1. Communication Facility: For a big company spanning over

different parts of the country the employees can save long distance phone calls and it overcomes the time lag in overseas communications. Computer conferencing is another use of WAN where users communicate with each other through their computer system.

2. Remote Data Entry: Remote data entry is possible in WAN. It means sitting at any location you can enter data, update data and query other information of any computer attached to the WAN but located in other cities. For example, suppose you are sitting at Dar and want to see some data of a computer located at Arusha, you can do it through WAN.

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Cont …3. Centralised Information: In modern computerised

environment you will find that big organisations go for centralised data storage. This means if the organisation is spread over many cities, they keep their important business data in a single place. As the data are generated at different sites, WAN permits collection of this data from different sites and save at a single site.

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Difference between LAN and WAN1. Coverage: LAN is restricted to limited geographical

area of few kilometers. But WAN covers great distance and operate nationwide or even worldwide.

2. Connectivity: In LAN, the computer terminals and peripheral devices are connected with wires and coaxial cables. In WAN there is no physical connection. Communication is done through telephone lines and satellite links.

3. Cost: Cost of data transmission in LAN is less because the transmission medium is owned by a single organisation. In case of WAN the cost of data transmission is very high because the transmission medium used are hired, either telephone lines or satellite links.

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Cont …4. Speed: The speed of data transmission is much higher

in LAN than in WAN. The transmission speed in LAN varies from 0.1 to 100 megabits per second. In case of WAN the speed ranges from 1800 to 9600 bits per second (bps).

5. Transmission Errors: Few data transmission errors occur in LAN compared to WAN. It is because in LAN the distance covered is negligible.

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Metropolitan Area Network (MAN) A network that usually spans across the city or a large

campus Interconnects several local area networks It uses a high-speed cable for the interconnections

between different LANs It might be owned or operated by a single organization Its geographical scope falls between a WAN and a LAN MANs provides internet connectivity for LANs in the

same metropolitan area

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Cont …

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Network Models There are two basic wired network models from which to

choose:

1. Peer-to-peer network model

2. Client/ server network model The model used for a network is determined by several

factors how the network will be used how many users will be on the network budgetary considerations

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Peer-to-peer Network Model This is a decentralized network model offering no

centralized storage of data or centralized control over the sharing of files or resources.

All systems on a peer-to-peer network can share the resources on their local computer as well as use resources of other systems.

Advantage: They are cheaper and easier to implement than client/server

networks, making them an ideal solution for environments in which budgets are a concern

It does not work well with large numbers of computer systems

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Cont … Disadvantages:

As a peer-to-peer network grows, it becomes increasingly complicated to navigate and access files and resources connected to each computer because they are distributed throughout the network.

The lack of centralized data storage makes it difficult to locate and back up key files

Typically found in small offices or in residential settings where only a limited number of computers will be attached and only a few files and resources shared.

Rule of Thumb: Have no more than 10 computers connected to a peer-to-peer network.

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Client/ server Network Model It is the most widely implemented model and the one you

are most likely to encounter when working in real-world environments.

Advantages: It allows for centralized network management of all network

services user management, security and backup procedures.

Disadvantages: It requires technically skilled personnel to implement and

manage the network Adds the cost of a dedicated server hardware and software

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Questions