1. Computer Communication & Networks Lecture # 01 Introduction Course Instructor: Engr. M.Zeeshan Sarwar

2. Grading Policy Final Exam: 40% Mid term Exam20% Assignments5% Quizzes:10% Labs25%

3. Quizzes may be announced or unannounced. Exams are closed-book and extremely time limited. Exams consist of design questions, numerical, maybe true-false and short answer questions.

4. 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  Data and Computer Communication by William Stallings (7th Edition) Prentice Hall.

5. Data Communications term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.

6. Fundamental Characteristics The effectiveness of a data communication system depend on four fundamental characteristics:  Delivery  Accuracy  Timelines  Jitter

7. Five Components of Data Communication 1.Message 2.Sender 3.Receiver 4.Medium 5.Protocol

8. Direction of data flow Simplex Half Duplex Full Duplex

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

10. 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

11. What distinguishes a Computer network ? Generality Built from general purpose programmable hardware Supports wide range of applications Not optimized for special purpose application like making phone calls or delivering television signals

12. 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

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

14. 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!

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

16. 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

17. 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

18. 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...

19. 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...

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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 ?

26. 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

27. 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

28. Networks: key issues Network criteria  Performance Throughput Delay  Reliability Data transmitted are identical to data received. Measured by the frequency of failure The time it takes a link to recover from a failure  Security Protecting data from unauthorized access

29. Terminology The throughput or bandwidth of a channel is the number of bits it can transfer per second The latency or delay of a channel is the time that elapses between sending information and the earliest possible reception of it

30. Network topologies Topology defines the way hosts are connected to the network

31. Network topology issues 1.high throughput (bandwidth) 2.low latency a goal of any topology

32. Bandwidth and Latency 1. telecommunications: range of radio frequencies: a range of radio frequencies used in radio or telecommunications transmission and reception 2. computing: communications capacity: the capacity of a communications channel, for example, a connection to the Internet, often measured in bits per second 3. a data transmission rate; the maximum amount of information (bits/second) that can be transmitted along a channel Latency A synonym for delay, is an expression of how much time it takes for transmission from one designated point to another Bandwidth

33. Categories of Topology

34. Mostly used network topologies mesh star bus ring

35. A hybrid topology: a star backbone with three bus networks

36. Hierarchical organization of the Internet

37. LAN, WAN & MAN  Network in small geographical Area (Room, Building or a Campus) is called LAN (Local Area Network)  Network in a City is call MAN (Metropolitan Area Network)  Network spread geographically (Country or across Globe) is called WAN (Wide Area Network)

38. Layering & Protocol Stacks

39. What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols

40. Protocol protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

41. Standard Essential in creating and maintaining an open and competitive market for equipment manufacturers Guaranteeing national & international interoperability of data & telecommunication technology & process.

42. Layered Tasks An example from the everyday life Hierarchy? Services

43. Why layered communication? To reduce complexity of communication task by splitting it into several layered small tasks Functionality of the layers can be changed as long as the service provided to the layer above stays unchanged  makes easier maintenance & updating Each layer has its own task Each layer has its own protocol

44. Reference Models OSI reference model TCP/IP

45. OSI Reference model Open System Interconnection 7 layers 1. Crate a layer when different abstraction is needed 2. Each layer performs a well define function 3. Functions of the layers chosen taking internationally standardized protocols 4. Number of layers – large enough to avoid complexity

46. Seven layers of the OSI model

47. Exchange using OSI Model

48. Issues, to be resolved by the layers Larger bandwidth at lower cost Error correction Flow control Addressing Multiplexing Naming Congestion control Mobility Routing Fragmentation Security....

49. Applications  E-mail  Searchable Data (Web Sites)  E-Commerce  News Groups  Internet Telephony (VoIP)  Video Conferencing  Chat Groups  Instant Messengers  Internet Radio

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

51. Readings Chapter 1: 1.1, 1.2  Computer Networks, A Systems Approach L. Peterson & Davie Chapter 1 (B. A Forouzan)  Section 1.1, 1.2, 1.3,1.4 Chapter 2 (B.A Forouzan)  Section 2.1