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CIT 513: Introduction to Computer Communication Mohammed A. Saleh 1.

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1 CIT 513: Introduction to Computer Communication Mohammed A. Saleh 1

2 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 2

3 Prerequisites There is no prerequisites before undertaking this course. 3

4 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. 4

5 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 5

6 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 6

7 Instructor There is only one lecturer responsible for this course, both lectures and tutorials. Find out about my contact details from my personal website If you need to see me in my office please book an appointment by writing me an My office number is Block D, room 016 All notes will be uploaded on the CIT 513 web page, A hardcopy will be submitted to the class representative 7

8 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. 8

9 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. 9

10 Cont … And finally the Final Exam, which will cover all contents of the course taught during the semester. 10

11 Final Mark Calculation 11 AssessmentMarks (%) Test I15 Test II15 Tutorials5 Unannounced quizzes5 Total40 Final Exam60 Grand Total100

12 Required Readings 12 AuthorYearTitlePublisher Hermachandran L. 2003Computer Communications Network Charulatha Tanenbaum A. S.2005Computer NetworksPrentice-Hall Galo M. A.2002Computer Communications and Networking Technologies Pacific Grove Rowe S and Schuch 2005Computer NetworkingPearson

13 Recommended Readings 13 AuthorYearTitlePublisher Kurose J. F2001Computer Networking a top down approach Pearson Halsall2005Computer Networking and Internet McGraw-Hill Madhulika J.2002Computer NetworksBPB

14 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/- 14

15 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. 15

16 Introduction What 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 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. 16

17 Cont … Examples of wired transmission medias are Unshielded Twisted Pair (UTP), Coaxial Cable or Fiber Optic Cable (a) Coaxial (b) Fiber Optic (c) UTP 17

18 Cont … Wireless transmission medias include radio waves, infrared and Bluetooth (a) Bluetooth icon (b) Radio signals 18

19 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. 19

20 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. 20

21 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. 21

22 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. 22

23 Cont …  Server computers Computers that provide shared resources, such as disk storage and printers, as well as network services, such as 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 23

24 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. 24

25 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. 25

26 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) 26

27 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. 27

28 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). 28

29 Cont … Mobile devices that can form a PAN 29

30 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 30

31 Cont … Local Area Network 31

32 Cont … Major Characteristics of LANs Every computer has the potential to communicate with any other computers of the network High degree of interconnection between computers Easy physical connection of computers in a network Inexpensive medium of data transmission High data transmission rate Advantages The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers. 32

33 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. 33

34 Cont … Use of LAN Followings 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 34

35 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 35

36 Example of WAN Wide Area Network 36

37 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. 37

38 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. 38

39 Difference between LAN and WAN 1. 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. 39

40 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. 40

41 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 41

42 Cont … 42

43 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 43

44 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 44

45 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. 45

46 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 46

47 Questions


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