Computer Communication & Networks

1. Computer Communication & Networks Lecture 1 Introduction http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp Waleed Ejaz waleed.ejaz@uettaxila.edu.pk

2. Overview • Administrative • Networking: An Overview of Ideas and Issues

3. Who’s Who • Instructor • Engr. Waleed Ejaz • 2006 -2008 MS (Computer Engineering) from NUST • Area of Specialization: Communication & Computer Networks • 2003-2006 BE (Computer Engineering) from UET Taxila • Lab Engineer • Engr. Noshina Ishaq

4. Web Resources • Course web • http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp • This website and email will serve as a communication medium between you and me besides the lecture timing. • Do visit the course website regularly and see Recent Announcements for updates.

5. Grading Policy • Final Exam: 100 • Grand Quiz 10 • Assignments 5 • Quizzes: 10 • Labs 25

6. Answers to FAQs • All home works are due at the beginning of the class indicated on the course calendar • After that 10% penalty: only if submitted before solutions are posted. • Exams are closed-book and extremely time limited. • Exams consist of design questions, numerical, maybe true-false and short answer questions. • More about Exams you can see Past Exams from WEB.

7. Reading • Text book: • Data Communications and Networking, 4/e • B.A. Forouzan, McGraw-Hill, 2003, ISBN 0-07-292354-7. • Reference books: • Computer Networking, a top-down approach featuring the Internet (3rd edition), • J.K.Kurose, K.W.Ross, Addison-Wesley, 2005, ISBN 0-321-26976-4. • Computer Networks, A Systems Approach L. Peterson & Davie

8. Required Skills • The course does not assume prior knowledge of networking.

9. My Requirement from YOU • I require YOU to take active part during lectures • Which means Lot of Questioning in the class – (Interactive session)

10. Aim of the Course • Aim of the course is to introduce you to the world of computer networks, so that you could • know the science being used in running this network • Use this knowledge in your professional field

11. Network design Before looking inside a computer network, first agree on what a computer network is

12. Computer network ? • Set of serial lines to attach terminals to mainframe ? • Telephone network carrying voice traffic ? • Cable network to disseminate video signals ? Specialized to handle: Keystrokes Voice Video

13. What distinguishes a Computer network ? • Generality • Built from general purpose programmable hardware • Supports wide range of applications

14. Information, Computers, Networks • Information: anything that is represented in bits • Form (can be represented as bits) vs • Substance (cannot be represented as bits) • Properties: • Infinitely replicable • Computers can “manipulate” information • Networks create “access” to information

15. Networks • Potential of networking: • move bits everywhere, cheaply, and with desired performance characteristics • Network provides “connectivity”

16. What is “Connectivity” ? • Direct or indirect accessto every other node in the network • Connectivity is the magic needed to communicate if you do not have a direct pt-pt physical link. • Tradeoff: Performance characteristics worse than true physical link!

17. … Building Blocks • Nodes: PC, special-purpose hardware… • hosts • switches • Links: coax cable, optical fiber… • point-to-point • multiple access

18. Why not connect each node with every other node ? • Number of computers that can be connected becomes very limited • Number of wires coming out of each node becomes unmanageable • Amount of physical hardware/devices required becomes very expensive • Solution: indirect connectivity using intermediate data forwarding nodes

19. Switched Networks • two or more nodes connected by a link • white nodes (switches) implement the network • colored nodes (hosts) use the network • A network can be defined recursively as...

20. Switched Networks • two or more networks connected by one or more nodes: internetworks • white nodes (router or gateway) interconnects the networks • a cloud denotes “any type of independent network” • A network can be defined recursively as...

21. A Network A network can be defined recursively as two or more nodes connected by a physical link Or two or more networks connected by one or more nodes

22. Switching Strategies • Packet switching: store-and-forward messages • operates on discrete blocks of data • utilizes resources according to traffic demand • send/receive messages at variable rate • example: Internet • Circuit switching: carry bit streams • establishes a dedicated circuit • links reserved for use by communication channel • send/receive bit stream at constant rate • example: original telephone network

23. What next ? • Hosts are directly or indirectly connected to each other • Can we now provide host-host connectivity ? • Nodes must be able to say which host it wants to communicate with

24. Addressing and Routing • Address: byte-string that identifies a node • usually unique • Routing: forwarding decisions • process of determining how to forward messages to the destination node based on its address • Types of addresses • unicast: node-specific • broadcast: all nodes on the network • multicast: some subset of nodes on the network

25. Wrap-up • A network can be constructed from nesting of networks • An address is required for each node that is reachable on the network • Address is used to route messages toward appropriate destination

26. What next ? • Hosts know how to reach other hosts on the network • How should a node use the network for its communication ? • All pairs of hosts should have the ability to exchange messages: cost-effective resource sharing for efficiency

27. L1 R1 L2 R2 Switch 1 Switch 2 L3 R3 Multiplexing • Physical links and nodes are shared among users • (synchronous) Time-Division Multiplexing (TDM) • Frequency-Division Multiplexing (FDM) Multiple flows on a single link Do you see any problem with TDM / FDM ?

28. What Goes Wrong in the Network? Reliability at stake • Bit-level errors (electrical interference) • Packet-level errors (congestion) • distinction between lost and late packet • Link and node failures • distinction between broken and flaky link • distinction between failed and slow node

29. What Goes Undesirable in the Network? Required performance at stake • Messages are delayed • Messages are delivered out-of-order • Third parties eavesdrop • The challenge is to fill the gap between application expectations and hardware capabilities

30. Research areas in Networking • Routing • Security • Ad-hoc networks • Wireless networks • Protocols • Quality of Service • …

31. Readings • Chapter 1: 1.1, 1.2 • Computer Networks, A Systems Approach L. Peterson & Davie