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

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

3. 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. 4 Web Resources Course web http://web.uettaxila.edu.pk/CMS/coeCCNbsS p09/index.asphttp://web.uettaxila.edu.pk/CMS/coeCCNbsS p09/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. 5 Grading Policy Final Exam: 100 Grand Quiz 10 Assignments5 Quizzes:10 Labs25

6. 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.Past Exams

7. 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(3 rd edition), J.K.Kurose, K.W.Ross, Addison-Wesley, 2005, ISBN 0-321-26976-4.  Computer Networks, A Systems Approach L. Peterson & Davie

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

9. 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. 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. 11 Network design Before looking inside a computer network, first agree on what a computer network is

12. 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. 13 What distinguishes a Computer network ? Generality Built from general purpose programmable hardware Supports wide range of applications

14. 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. 15 Networks Potential of networking:  move bits everywhere, cheaply, and with desired performance characteristics Network provides “connectivity”

16. 16 What is “Connectivity” ? Direct or indirect access to 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. 17 Building Blocks Nodes: PC, special-purpose hardware…  hosts  switches Links: coax cable, optical fiber…  point-to-point  multiple access …

18. 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. 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. 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. 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. 22 Switching Strategies Circuit switching: carry bit streams a. establishes a dedicated circuit b. links reserved for use by communication channel c. send/receive bit stream at constant rate d. example: original telephone network Packet switching: store- and-forward messages a.operates on discrete blocks of data b.utilizes resources according to traffic demand c.send/receive messages at variable rate d.example: Internet

23. 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. 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. 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. 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. 27 Multiplexing Physical links and nodes are shared among users  (synchronous) Time-Division Multiplexing (TDM)  Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3 Switch 1Switch 2 Multiple flows on a single link Do you see any problem with TDM / FDM ?

28. 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. 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. 30 Research areas in Networking Routing Security Ad-hoc networks Wireless networks Protocols Quality of Service …

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

32. 32