Computer Communication Networks

1. Computer Communication Networks Data Transmission, Media Signal Encoding Techniques Data Communication Techniques Data Link Control, ATM Multiplexing, Switching, Routing Spread Spectrum, Wireless Networks Local and Wide Area Networks Introductory Lecture

2. Course Overview • Data Communication Networks and Open System Standards • Data Transmission • Data Link Controls • Technologies of Local Area Networks and Wide Area Networks • Communication Architecture and Protocols

3. Course Objectives The aim of this course is to provide a unified overview in the basic principles of data communications and computer networks. The lectures emphasize basic principles and topics of fundamental importance concerning the technology and architecture of this field, as well as providing the state of the art topics.

4. Course Objectives Followings are the basic objectives : To provide a conceptual foundation for the study of data communications using the Open Systems Interconnect (OSI) model for layered architecture To develop an understanding in basic hardware and software environments for data communications and computer networks

5. Text Books • Data and Computer Communications, 7th Edition, Prentice Hall, 2004 by William Stallings • Data Communication and Networking, 3rd Edition, McGraw-Hill, 2004 by Behrouz A. Forouzan

6. Course Website http://web.uettaxila.edu.pk/cms/teCCNmsAU09/

7. Class Schedule [Tuesdays 4~6 / 6~9]

8. Overview

9. Simplified Communications Model 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

10. Simplified Communications Model - Diagram

11. Simplified Data Communications Model

12. 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 Wide Area Network (WAN) Local Area Network (LAN) A B

13. Connecting N users: Directly ... Bus: broadcast, collisions, media access control Full mesh: Cost vs simplicity . . . Bus Full mesh • Address conceptneeded if we want the receiveraloneto consume the packet!

14. Connecting N users:Indirectly Star: One-hop path to any node, reliability, forwarding function “Switch” S canfilter and forward! Switch may forward multiple packets in parallel for additional efficiency! Star S

15. Connecting N users:Indirectly … Ring: Reliability to link failure, near-minimal links All nodes do “forwarding” and “filtering” Ring

16. Topologies: Indirect Connectivity S Ring Star Tree

17. Inter-Networks: Networks of Networks … … Internet = … … Our goal is to design this black box on the right

18. Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)

19. Circuit Switching Dedicated communications path established for the duration of the conversation e.g. telephone network

20. Packet Switching Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications

21. Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out

22. Asynchronous Transfer Mode ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to many Gbps Constant data rate using packet switching technique

23. Local Area Networks Smaller scope Building or small campus Usually owned by same organization as attached devices Data rates much higher Usually broadcast systems Now some switched systems and ATM are being introduced

24. LAN Configurations Switched Switched Ethernet May be single or multiple switches ATM LAN Fibre Channel Wireless Mobility Ease of installation

25. Metropolitan Area Networks MAN Middle ground between LAN and WAN Private or public network High speed Large area

26. NetworkingConfiguration

27. Further Reading Stallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, Chapter 1 Web site for Stallings book http://williamstallings.com/DCC7e.html

28. Protocols and Architecture

29. Need For Protocol Architecture E.g. File transfer Source must initiate communications. Find Path or inform network of destination Source must check destination is prepared to receive File transfer application on source must check destination file management system will accept and store file for his user May need file format translation Task broken into subtasks Implemented separately in layers in stack Functions needed in both systems Peer layers communicate

30. Key Elements of a Protocol Syntax Data formats Signal levels Semantics Control information Error handling Timing Speed matching Sequencing

31. 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

32. Simplified File Transfer Architecture

33. A Three Layer Model Network Access Layer Transport Layer Application Layer

34. 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.)

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

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

37. Protocol Architectures and Networks

38. Addressing Requirements Two levels of addressing required Each computer needs unique network address Each application on a (multi-tasking) computer needs a unique address within the computer The service access point or SAP The port on TCP/IP stacks

39. Protocols in Simplified Architecture

40. Protocol Data Units (PDU) At each layer, protocols are used to communicate Control information is added to user data at each layer Transport layer may fragment user data Each fragment has a transport header added Destination SAP Sequence number Error detection code This gives a transport protocol data unit

41. Protocol Data Units

42. Network PDU Adds network header network address for destination computer Facilities requests

43. Operation of a Protocol Architecture

44. Standardized Protocol Architectures Required for devices to communicate Vendors have more marketable products Customers can insist on standards based equipment Two standards: OSI Reference model Never lived up to early promises TCP/IP protocol suite Most widely used Also: IBM Systems Network Architecture (SNA)

45. OSI Open Systems Interconnection Developed by the International Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard

46. OSI - The Model A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers

47. OSI Layers

48. The OSI Environment

49. OSI as Framework for Standardization

50. Layer Specific Standards