EEC-484/584 Computer Networks

1. EEC-484/584Computer Networks Lecture 3 Wenbing Zhao wenbing@ieee.org

2. Outline • Network Bandwidth definition • Network Software • Connection-oriented and connectionless services • Circuit switched and packet switched networks • Reference models • Networking Standards EEC-484/584: Computer Networks

3. Network Bandwidth: Definition • Network bandwidth refers to the data rate that a network connection or interface can support • How many bits can be transmitted per second (bps)? EEC-484/584: Computer Networks

4. Connection-Oriented Services • Modeled after telephone system– establish connection before communication • Some service allows a negotiation among sender, receiver and subnet regarding the parameters to be used, such as max message size, etc. EEC-484/584: Computer Networks

5. Connectionless Services • Modeled after postal system– a message carries full destination address, and each one is routed through the system independent of all the others • Ordering of messages are not guaranteed EEC-484/584: Computer Networks

6. Quality of Services • Quality of service– characterize each service • Reliableservice– it does not lose data • Implemented by having the receiver acknowledge the receipt of each message • Possible for both connection-oriented and connectionless services • Connection-oriented service is not necessarily a reliable service! EEC-484/584: Computer Networks

7. Connection-Oriented and Connectionless Services First class mail EEC-484/584: Computer Networks

8. Switching • Circuit switching • Packet switching EEC-484/584: Computer Networks

9. Circuit Switching and Packet Switching (a) Circuit switching (b) Packet switching EEC-484/584: Computer Networks

10. Circuit Switching • Circuit switching –physical path set up from source to destination before any data transmitted, e.g., phone system • Adv: no congestion problem, only delay is propagation time • Disadv: unused bandwidth on allocated circuit is wasted • Will go back on this in lecture 9 (network layer) EEC-484/584: Computer Networks

11. Packet Switching • Packet switching – store-and-forward, one hop at a time, uses pipelining, each packet has limited size • Adv: no setup required, high utilization • Disadv: packets may be received out of order, packets may be lost due to buffer overflow • Will go back on this in lecture 9 (network layer) EEC-484/584: Computer Networks

12. Reference Models • The OSI Reference Model • ISO – International Standards Organization • OSI – Open Systems Interconnection • Open: open for communication with other systems • The TCP/IP Reference Model EEC-484/584: Computer Networks

13. The OSI Reference Model EEC-484/584: Computer Networks

14. Principles Applied in Deriving Layers • A layer should be created where a different level of abstraction is needed • Each layer should perform a well-defined function • The layer boundaries should be chosen to minimize info flow across interfaces • The number of layers should be • large enough to separate distinct functions • small enough to have a manageable architecture EEC-484/584: Computer Networks

15. TCP/IP Reference Model • TCP – Transmission Control Protocol • IP – Internet Protocol • Used in Internet and its predecessor ARPANET • TCP/IP invented by Cerf and Kahn in 1974, became official protocol of ARPANET in 1983 EEC-484/584: Computer Networks

16. TCP/IP Reference Model EEC-484/584: Computer Networks

17. TCP/IP Reference Model • Internet Layer • Connectionless (packet switched) • Injects packets into the network; delivers them to the destination • May be delivered out-of-order • Packet routing is a key issue • Uses Internet Protocol EEC-484/584: Computer Networks

18. TCP/IP Reference Model • Transport layer, two protocols • TCP – Transmission Control Protocol • Point-to-point • Connection-oriented • Reliable (no message loss or corruption) • Source ordered (sequenced) • Flow control • Byte stream, does not maintain message boundary EEC-484/584: Computer Networks

19. TCP/IP Reference Model • UDP – User Datagram Protocol • Point-to-point • Connectionless • Unreliable • Not source ordered • No flow control • Preserve message boundary EEC-484/584: Computer Networks

20. TCP/IP Reference Model • Application Layer – contains higher-level protocols • DNS – Domain Name Service • Maps host names onto their network addresses • HTTP – HyperText Transfer Protocol • Fetches pages on the World Wide Web • FTP – File Transfer Protocol • Allows user to transfer files efficiently from one machine to another EEC-484/584: Computer Networks

21. TCP/IP Reference Model • Host-to-Network Layer • Host has to connect to the network using some protocol so it can send IP packets to it • No protocol is defined EEC-484/584: Computer Networks

22. Network Standardization • Why standard? • Only way to achieve interoperability • Standards also increase the market for products adhering to them • Two kinds of standards • De facto – from the fact (standards that just happened) • De jure – by law (formal, legal standards adopted by authorized organization) EEC-484/584: Computer Networks

23. United Nations ITU - International Telecommunications Union CCITT/ITU-T – telephone and data communications Treaty Organization between Nations EEC-484/584: Computer Networks

24. ISO (International Standards Organization) issues standards on wide range of topics 200 TC (Technical Committees) TC97 – computers and info processing SC (Subcommittees) WG (Working Groups) ANSI (American National Standards Institute) Voluntary, Nontreaty Organization EEC-484/584: Computer Networks

25. IEEE 802 Standards EEC-484/584: Computer Networks

26. Internet Standard Body • Internet Society (used to be Internet Architecture Board) • Internet Research Task Force (IRTF) • Concentrate on long term research • Internet Engineering Task Force (IETF) • Deal with short term engineering issues • Standardization process • Proposed standard: request for comments (RFCs) • Draft standard: > 4 month test • Internet standard: if convinced the idea is sound EEC-484/584: Computer Networks