Course EC-321: Computer Networks Credits 3(2, 1)

1. Course EC-321:Computer NetworksCredits 3(2, 1)

2. Introduction • Name : Mr. Liaqat Ali • Title / Role : Assistant Professor • Education : MS (Telecommunications), BE (Electrical), MCSE, MCITP, CIW, MCDBA, MCTS, MCT • Experience : 12 Years, 7 years on the job, 5 years teaching • Company : NUST, TEG Australia, Macquaire Telecomm Australia • Email : liaqat5@hotmail.com

3. Course Materials • Text Book : Computer Network by Andrew S. TanenbaumPrentice Hall Fourth Edition • Reference Books: Computer Networks, a top down approach by Keith Ross • Course Evaluation: Midterm – 30% Quizzes --- 10% Labs work - 20% Final Exam – 40% No credit for work that is not your own.

4. Focus • Intro to data networks from an engineering perspective. • Broad coverage. • Network architectures. • Network protocols, • Layered design. • Protocol stack. • TCP/IP and the Internet, • Hands-on aspect

5. Topics Covered • Introduction and Overview. • Physical Layer. • Medium Access Control (MAC). • Link Layer. • Network Layer. • Routing. • Internetworking and IP. • IP Routing and Control. • Transport Layer. • Application Layer. • Putting It All Together!

6. Course Outline. • Introduction • History, basic concepts, terminology. • More, “not-so-basic” concepts:protocols, layering,, etc. • Physical layer • Transmitting data. • Data link layer • Reliable transmission. • Accessing the communication medium • Medium access control protocols. • LANs • Ethernet, token ring, wireless LANs.

7. Course Outline. • Transport layer • E2E communication.. • Types of transport service. • Connectionless versus connection-oriented. • UDP.and TCP. • Application layer • DNS, telnet, ftp, news, e-mail. • The Web. • HTTP, HTML. • Search engines, Proxy and caches • Peer-to-peer, and Security.

8. What’s a network? • Merriam-Webster Dictionary: • “|A fabric or structure of cords or wires that cross at regular intervals…” • “A system of computers, terminals and databases connected by communication lines” • “A computer network is defined as the interconnection of 2 or more independent computers.” [Ramteke,”Networks”, pg. 24].

9. Why network? • Before networks: • One large computer (mainframe) used for all processing in businesses, universities, etc. • Smaller, cheaper computers… • Personal computers or workstations on desktops. • Interconnecting many smaller computers is advantageous! Why?

10. Why network? • Computers everywhere. • Also means ubiquitous communication. • Users connected anywhere/anytime. • PC, laptop, cell phone. • Networking computers together is critical!

11. Why network? • Provide access to local and remote resources. • Collection of interconnected end systems: • Computing devices (mainframes, workstations, PCs) • Peripherals (printers, scanners, terminals).

12. Why network? • Resource sharing! • Hardware: printers, disks, terminals, etc. • Software: text processors, compilers, etc. • Data. • Robustness. • Fault tolerance through redundancy. • Load balancing. • Processing and data can be distributed over the network. • Location independence. • Users can access their files, etc. from anywhere in the network.

13. Problems? • Security! • It’s much easier to protect centralized resources than when they are distributed. • Network itself as the target..

14. POTS or PSTN • For over 100 years, the POTS (Plain Old Telephone System) a.k.a. PSTN (Public Switched Telephone Network) handles voice-band communications. • The PSTN is well designed and engineered for the transmission and switching of voice • Real-time. • Low latency. • High reliability. • Moderate fidelity.

15. Communication Model • Source Network • Destination

16. Simplified Communication Model

17. Components • End systems (or hosts), • Routers/switches/bridges, and • Links (twisted pair, coaxial cable, fiber, radio, etc.).

18. Components (cont’d) • 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

19. Networking • Point to point communication not usually practical • Devices are too far apart. • Large set of devices would need impractical number of connections. • Solution is a communications network.

20. Simplified Network Model

21. Key Tasks in Computer Networking • Application (User Interface) • Encoding/Decoding, Encryption. • Transmission. • Signal Generation. • Error detection and correction. • Addressing and routing • End-to-end Recovery. • Security.

22. Key Tasks in Computer Networking Physical Layer • Transmission. • Signal Generation. • Error detection and correction. • Addressing and routing • End-to-end Recovery. • Security. Data Link Layer Network Layer Transport Layer Application Layer

23. Connecting End Systems Dedicated link Multiple access / shared medium

24. Connecting End Systems

25. Shared Communication Infrastructure A stream of packets from sender to receiver.

26. Types of Data Networks • Several ways to classify data networks. • For example, according to “coverage”. • Local Area Networks (LANs) typically provide networking capabilities within a building, campus. • Typically within 5-mile radius. • Wide-Area Networks (WANs) span greater geographic distances (e.g., world-wide). • Metropolitan Area Networks (MANs) span more restricted distances, e.g., geographic regions.

27. Types of Data Networks (cont’d) • Classification according to topology… • What is network topology? • The way network elements are interconnected. Ring Bus Star Mesh

28. Network Protocols • Diplomats use rules, called protocols, as guides for formal interactions. • A communication protocol is a set of rules that specify the format and meaning of messages exchanged between computers across a network. • A set of related protocols that are designed for compatibility are called protocol suite.

29. Human Protocol Computer Protocol Hi Hi Got the time? 2:00 <data> time Human and Computer Protocols Web client Web server

30. Layering • What is it? • Building complex systems is hard! • Approach: “Divide and conquer”. • Split job into smaller jobs, or layers. • Analogy to other fields. • Building a house: digging, foundation, framing, etc. • Car assembly line… • Basic idea: each step dependent on the previous step but does not need to be aware of how the previous step was done.

31. Analogy: Air Travel • The problem: air travel. • Decomposed into series of steps: Departure from airport Baggage claim Deplane Landing Arrival at airport Check-in Boarding Takeoff

32. Departure Baggage claim Deplane Landing Arrival Check-in Boarding Takeoff Arriving airport Departing airport Traveling Airplane routing Airplane routing intermediate air traffic sites Analogy: Air Travel

33. Protocol Architecture • Task of communication broken up into modules • For example file transfer could use three modules • File transfer application • Communication service module • Network access module

34. Simplified File Transfer Architecture

35. A Three Layer Model • Application Layer • Transport Layer • Network Access Layer

36. Network Access Layer • Exchange of data between the computer and the network • Sending computer provides address of destination • May invoke levels of service • Dependent on type of network used (LAN, packet switched etc.)

37. Transport Layer • Reliable data exchange • Independent of network being used • Independent of application

38. Application Layer • Support for different user applications • e.g. e-mail, file transfer

39. Layered Protocol Design • Layering model is a solution to the problem of complexity in network protocols • The model divides the network protocols into layers, each of which solves part of the network communication problem • Each layer has its own protocol! • Each layer implements a service to the layer above • Relying on services provided by the layers below.

40. Layers • Layers are the different components that need to be designed/implemented when designing/implementing networks. • Each layer responsible for a set of functions. • Top layer relies on services provided by bottom layer. • Layer makes it service available to higher layer through an interface.

41. Network/Protocol Architecture • Set of layers, what their functions are, the services each of them provide, and the interfaces between them. • Examples: • ISO-OSI 7 layer architecture. • TCP-IP architecture (Internet).

42. Example 1: ISO OSI Architecture • ISO: International Standards Organization • OSI: Open Systems Interconnection. Application Presentation Session Transport Network Data link Physical

43. TCP/IP Protocol Architecture • What is it? • Building complex systems is hard! • Approach: “Divide and conquer”. • Split job into smaller jobs, or layers. • Analogy to other fields. • Building a house: digging, foundation, framing, etc. • Car assembly line… • Basic idea: each step dependent on the previous step but does not need to be aware of how the previous step was done.

44. TCP/IP Protocol Architecture