1. COMP361 by M. Hamdi1 COMP 361, Fall 2000 Computer Communication Networks I Dr. Mounir Hamdi hamdi@cs.ust.hk

2. COMP361 by M. Hamdi2 How Important is COMP 361? Computer Networking is the backbone of the information technology Information technology is having and will be having a tremendous impact on our social lives, the economy, and the way we work The knowledge of this class, COOMP 361, is a key factor to be an active and productive member of the information technology

3. COMP361 by M. Hamdi3 You Will Learn Networking Terminology Communication basics –Media and signals –Data transmission characteristics asynchronous and synchronous communication serial and parallel transmission bandwidth, throughput and noise multiplexing

4. COMP361 by M. Hamdi4 You Will Learn [continued] Networking and Network Technologies –Packet Switching, Circuit/virtual Switching –Protocols and Layering –Network Addressing –Interconnection (bridges, switches, routers) –Local Area Networks (star, ring, bus, mesh) –Routing –Flow, Error and Congestion Control –State-of-the-art in networks

5. COMP361 by M. Hamdi5 You Will Learn [continued] Applications and Network Services –Network Programming –Client-server communications –Hierarchical naming (DNS) –File transfer (FTP) –Remote login (TELNET) –Email (SMTP, POP, IMAP) –Web technologies (HTTP, HTML, Java) –Network Security

6. COMP361 by M. Hamdi6 I’ll Do My Part Help you learn and enjoy the course Answer email promptly Be fair and impartial Encourage discussion and questions

7. COMP361 by M. Hamdi7 You Do Your Part Have the drive to learn and work hard Be present and attentive Don’t wait until the last minute Contribute in discussions Ask questions

8. COMP361 by M. Hamdi8 Grading Homework/Quiz 20% –2 homeworks and 2 quizes (best 3 out 4) Midterm Exam25% Final Exam30% Labs programming/project25%

9. COMP361 by M. Hamdi9 Tentative Schedule - Lecture Week 1:Introduction Week 2:Physical Layer Week 3-4:Data Link Layer Week 5-7:Local Area Networks Midterm Exam Week 8-10:Network Layer Week 11:Transport Layer Week 12:Application Layer Week 13-14:State-of-the-art in Networking

10. COMP361 by M. Hamdi10 Tentative Schedule - Lab Week 1:No lab Week 2:General Introduction Week 3:Introduction to Network Application Programming Interface (API) Week 4:Introduction to Socket Programming Week 5-6:Example Application of Socket programming Week 7:Advanced Concepts of Socket Programming Week 8-12:More Advanced Concepts of Socket Programming and the start of a more advanced network programming project Week 13:Presentation/Demonstration of Projects

11. COMP361 by M. Hamdi11 Lecture/Lab Time/Venue Lecture: T-Th: 9:00 - 10:20 LTE Labs: 1A - Wed: 9 - 9:50 Lab: 4214 1B - Wed: 10 - 10:50 Lab: 4214

12. COMP361 by M. Hamdi12 FAQ for this Class Grade depends on the rest of the class (there is a curve) Late homework must be pre-approved No copying on homework/labs please Midterm/final sample exam will be available one week prior Watch course home page for latest material and announcement

13. COMP361 by M. Hamdi13 How to Contact Us Instructor: Mounir Hamdi hamdi@cs.ust.hk Office Hours –Mondays 10:00 - 12:00 p.m. –Wednesdays: 11:00 - 12:00 p.m. –...and by appointment

14. COMP361 by M. Hamdi14 How to Contact Us Lab TA: Pun Kong Hong - konghong@cs.ust.hk Course TA: Zhang Lei - zhanglei@cs.ust.hk Office Hours –To be given later

15. COMP361 by M. Hamdi15 Textbook Andrew Tanenbaum, “Computer Networks” Prentice Hall, 1996, ISBN: 0-13-349945-6 W. R. Stevens, UNIX Network Programming Vol. 1, 2nd ed., Prentice-Hall, 1998. See course home page for other recommended texts –Computer Networks - Peterson and Davie –Computer Networks and Internets - Comer –An Engineering Approach to Computer Networks - Keshav –TCP/IP Illustrated - Stevens –Interconnections - Perlman –Internetworking with TCP/IP - Comer –Data and Computer Communications - Stallings –Routing in the Internet - Huitema

16. COMP361 by M. Hamdi16 Who Am I? Associate Prof. Of Computer Science and Co-Director of Computer Engineering –Have been at HKUST since 1991 –Spent last year at Stanford University Current interests: High-Speed Switching and Routing, Optical Networks, Network Management, Quality-of-Nervice Networking, Network Application (VoIP and Video Conferencing)

17. COMP361 by M. Hamdi17 Who Are You? Computer Engineers/Scientist –You’re very familiar with computers and the Internet –Very interested in networking –Eager to learn new things What else?

18. COMP361 by M. Hamdi18 Introduction

19. COMP361 by M. Hamdi19 Communication Networks Problem: Given a set of devices that want to exchange information. (Device = telephone, computer, terminals, etc.) Simple Solution: Connect each pair of devices by a dedicated point-to-point link

20. COMP361 by M. Hamdi20 Communication Networks The simple solution is sufficient if the number of devices is small. With large number of devices it is not practical to connect each pair of devices.

21. COMP361 by M. Hamdi21 Communication Networks A communication network provides a general solution to the problem of connecting many devices: –Connect each device to a network node –Network nodes exchange information and carry the information from a source device to a destination device –Note: Network nodes do not generate information

22. COMP361 by M. Hamdi22 Communication Networks A generic communication network: Other names for Device: station, host, terminal Other names for Node: switch, router, gateway

23. COMP361 by M. Hamdi23

24. COMP361 by M. Hamdi24

25. COMP361 by M. Hamdi25 HKUST Campus Network

26. COMP361 by M. Hamdi26 Classification of Communications Communication networks can be classified based on the way in which the nodes exchange information: Communication Network –Switched Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network –Datagram Network –Virtual Circuit Network –Broadcast Communication Network

27. COMP361 by M. Hamdi27 Broadcast Communication Networks Broadcast Communication Networks do not have intermediate switching nodes: –Each station has a transmitter/receiver that communicates over a medium shared by other stations –Transmission from any station is received by all other stations

28. COMP361 by M. Hamdi28 Broadcast Network Examples Packet Radio Network Satellite Network Bus Local Network

29. COMP361 by M. Hamdi29 Switched Communication Network A switched communication network consists of an interconnected collection of nodes. Data are transmitted from source to destination by being routed through the nodes The switching method describes how data are processed and routed in the network The basic switching methods are: –Circuit Switching –Packet Switching Datagram Packet Switching Virtual-Circuit Packet Switching

30. COMP361 by M. Hamdi30 Circuit Switching In a circuit-switched network, a dedicated communication path is established between two stations through the nodes of the network The dedicated path is called a circuit-switched connection or circuit A circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuits Data is not delayed at the switches Circuit Switching

31. COMP361 by M. Hamdi31 Circuit Switching Circuit-switched communication involves three phases: –1. Circuit Establishment –2. Data Transfer –3. Circuit Termination Busy Signal if capacity for a circuit not available. Most important circuit-switching networks: –Telephone networks –ISDN (Integrated Services Digital Networks)

32. COMP361 by M. Hamdi32 Circuit Switching A node in a circuit-switching network:

33. COMP361 by M. Hamdi33 Circuit Switching

34. COMP361 by M. Hamdi34 Timing in Circuit Switching

35. COMP361 by M. Hamdi35 Packet Switching Data are sent as formatted bit- sequences, so-called packets. Packets have the following structure: Header and Trailer carry control information

36. COMP361 by M. Hamdi36 Packet Switching Each packet is passed through the network from node to node along some path (Routing) At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and- Forward Networks) No capacity is allocated for packets

37. COMP361 by M. Hamdi37 Packet Switching

38. COMP361 by M. Hamdi38 Datagram Packet Switching Packets are called datagrams The network nodes process each packet independently: If Host A sends two packets back- to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together. In fact, the two packets can take different routes. Implications of processing packets independently: –A sequence of packets can be received in a different order than it was sent –Each packet header must contain the full address of the destination

39. COMP361 by M. Hamdi39 Exercise: Datagram Packet Exercise: Most network applications (think of email and file transfer) require that data is received in sequence. For such applications a datagram network appears to be inappropriate, since packets may need to get reordered. Question: What are advantages of datagram networks? The main example of a datagram packet- switching network is the Internet

40. COMP361 by M. Hamdi40 Datagram Packet Switching

41. COMP361 by M. Hamdi41 Timing of Datagram Packet Switching

42. COMP361 by M. Hamdi42 Virtual-Circuit Packet Switching As the name suggests: Virtual-circuit packet switching is a hybrid of circuit switching and packet switching All data is transmitted as packets All packets from one packet stream are sent along a pre-established path (=virtual circuit) Guarantees in-sequence delivery of packets However: Packets from different virtual circuits may be interleaved

43. COMP361 by M. Hamdi43 Virtual-Circuit Packet Switching Communication with virtual circuits (VC) takes place in three phases: –1. VC Establishment –2. Data Transfer –3. VC Disconnect Note: Packet headers don't need to contain the full destination address of the packet

44. COMP361 by M. Hamdi44 Examples X.25 –X.25 networks have been around since the 1970s –It is used in many public packet switching networks ATM (Asynchronous Transfer Mode) –Developed in the 1980s –For transmission of voice, video, and data in a single network Others –SNA (Systems Network Architecture) by IBM

45. COMP361 by M. Hamdi45 Virtual-Circuit Packet Switching

46. COMP361 by M. Hamdi46 Timing of Virt. Circ. Packet Switching

47. COMP361 by M. Hamdi47 Comparison