1. Spring 2004 EE4272 EE4272: Computer Networks Instructor: Dr. Tricia Chigan Dept.: Elec. & Comp. Eng.

2. Spring 2004 EE4272 Introduction of Computer Networks Communication & Computer/Data Networks Applications of Computer Networks Requirements Network Architectures Implementing Network Software Network Performance

3. Spring 2004 EE4272 Communication & Computer/Data Networks What are the differences between…  Applications  Underline technologies

4. Spring 2004 EE4272 Applications of Computer Networks (e.g. …) Surfing the Web  of Client/Server Streaming Audio & Video  Video-on-demand: ( )  Video Conference: ( ) Different requirements for various applications .

5. Spring 2004 EE4272 Requirements from Perspectives… Application programmer: services that their applications need, e.g., Network designers: cost-effective design e.g., Network providers: system that is easy to administer and manage e.g.,

6. Spring 2004 EE4272 High-level Major Requirements - Network Designers’ Perspectives Connectivity Cost-Effective Resource Sharing Reliability

7. Spring 2004 EE4272 Nodes: PC, special-purpose hardware…  Host: edge node for.  Switch: node to.  Router/Gateway: node connects two/more different. Links: coaxial cable, … Direct connectivity  point-to-point  multiple access Building Blocks & Connectivity (a) (b)

8. Spring 2004 EE4272 Indirect Connectivity  Switched networks switch  Internetworks router gateway

9. Spring 2004 EE4272 Switching Strategies  circuit switching ( ): dedicated circuit; send/receive.  packet switching ( ): store-and-forward; shared channel; send/receive. Addressing and Routing  address: byte-string that a node; usually unique  routing: process of messages towards the destination node based on its  types of addresses cast: node-specific cast: all nodes on the network cast: some subset of nodes on the network Issues Related to Connectivity

10. Spring 2004 EE4272 Cost-Effective Resource Sharing Must share (multiplex) network resources (nodes and links) among multiple users

11. Spring 2004 EE4272 Conventional Multiplexing Strategies Synchronous Time-Division Multiplexing (STDM) Frequency-Division Multiplexing (FDM)

12. Spring 2004 EE4272 Statistical Multiplexing On-demand (not predetermined) time-division Schedule link on a basis (fairness): FIFO, Round-robin…. Packets from different sources on link  What about if only one source has data? Why is needed?  Buffer packets that are contending for the link:.  Buffer (queue) overflow is called. ■ ■ ■

13. Spring 2004 EE4272 What Goes Wrong in the Network? -Reliability Issue (light, power, microwave interference -> error detection/correction): single or burst error  depend on transmission med.: coaxial cable, optical fiber? (congestion control) (network survivability)

14. Spring 2004 EE4272 Client Server process-to-process Network Architecture Use abstractions (unified model). Abstraction naturally lead to. Can have at each layer

15. Spring 2004 EE4272 Layering & Protocols Advantages of Layering  Manageable  Modular design Protocols  building blocks of a network architecture layer  Each protocol object has two different interfaces service interface: operations. peer-to-peer interface: messages exchanged with.  Term “protocol” is overloaded Module (various) that implements this interface:. specification of peer-to-peer interface ( )

16. Spring 2004 EE4272 Interfaces Host 1Host 2 High-level object High-level object Protocol

17. Spring 2004 EE4272 Host 1Host 2 File application Digital library application Video application File application Digital library application Video application Protocol Machinery Protocol Graph  most peer-to-peer communication is.  peer-to-peer is only at hardware level

18. Spring 2004 EE4272 Host 1Host 2 Application program Application program RRP Data HHP RRP HHP Application program Application program RRP Data HHP RRP Data Protocol Machinery (cont) Encapsulation ( : control infor., e.g. seq. num) Multiplexing & Demultiplexing ( ): share logical channel at each protocol layer

19. Spring 2004 EE4272 /aggregation OSI (open systems interconnection) Architecture

20. Spring 2004 EE4272 Ethernet, ATM, FDDI… ■ ■ ■ FTP TCP UDP IP NET 1 2 n HTTPNVTFTP Application TCPUDP IP Network Internet Architecture Defined by ( ) Design Application vs Application Protocol (e.g.,HTTP)

21. Spring 2004 EE4272 Some Protocols in TCP/IP Suite Source: book by William Stallings

22. Spring 2004 EE4272 Software Protocol Implementation Service Interface (e.g. Socket API)  socket: the point where a local applications process attaches to the network  built in most of the Unix OS, common library routines (socket, listen, accept, client, server, connect, send, recv…)  reference: W. Richard Stevens, Unix Network Programming, 2 nd edition, Prentice Hall 1998 Protocol Implementation Issues (difference between Socket & protocol- protocol interface)  Process Model  Message Buffers

23. Spring 2004 EE4272 Performance Metrics Bandwidth (throughput) :  data transmitted per time unit  link vs. end-to-end Latency (delay)  time to send message from point A to point B  one-way versus round-trip time (RTT)  components Latency = Propagation + Transmit + Queue  Propagation =.  Transmit =. Throughput (end-to-end) = TransferSize / TransferTime TransferTime = RTT + 1/Bandwidth x TransferSize (w/o queue)

24. Spring 2004 EE4272 Delay x Bandwidth Product Amount of data “in flight” or “in the pipe” Example: 100ms x 45Mbps = 560KB Application Needs  requirements ( ): burst with peak rate  : variance in latency ( )