1. ICOM 6115©Manuel Rodriguez-Martinez ICOM 6115 – Computer Networks and the WWW Manuel Rodriguez-Martinez, Ph.D. Lecture 1

2. ICOM 6115©Manuel Rodriguez-Martinez Course Objectives Introduction to computer networks –Design –Implementation –Performance Characterization –Application Development … Computer Science perspective –Design tradeoffs –Software organization –Hardware/Software Interface –Application requirements on the network

3. ICOM 6115©Manuel Rodriguez-Martinez This course is not about … Putting Cat 5 cables together Cutting fiber Hacking a Linux kernel Configuring routers and workstations Setting up Web servers Troubleshooting networks cards Writing applets, cgi scripts or servlets Reading packet formats

4. ICOM 6115©Manuel Rodriguez-Martinez This course is about … Understanding how networks work and how can they be used –Hardware issues –Software organization and implementation –Application development –Network services –Performance trade-offs

5. ICOM 6115©Manuel Rodriguez-Martinez Why do we need networks? To share data and computing resources Network

6. ICOM 6115©Manuel Rodriguez-Martinez Rationale Avoid centralization of resources –Early days One big computer with disk(s) and printers Terminals attached to this mainframe –Today Machine powerful machines with disk, fast CPU, memory and printer(s) Share these resources among the pool of users

7. ICOM 6115©Manuel Rodriguez-Martinez Key benefits Share resources –Make data, programs, hardware and other stuff available to everyone else High reliability –Many sources to supply services (disk or CPU) –Reduce down times In a company, computer down time is money lost Save Money ($$$) –Get performance and throughput via commodity computers connected in a network

8. ICOM 6115©Manuel Rodriguez-Martinez Networks for Enterprises Interconnect office buildings –In a country and between countries –Exchange data between Company dependencies Business partners –Form teams across geographical regions Leverage on expertise world wide –Keep assets spread and diversified

9. ICOM 6115©Manuel Rodriguez-Martinez Networks for people Access remote information –Journals and books –Software Personal communication channels –ICQ, e-mail, newsgroups, videoconferencing Entertainment –Music, Video, newspapers and magazines –Games : Half-life

10. ICOM 6115©Manuel Rodriguez-Martinez Building networks of computers UPRM UCLA

11. ICOM 6115©Manuel Rodriguez-Martinez Sounds cool but how do I build one? Need to create a bit pipe!!! –Move bits from one computer to another Ingredients: –Communication medium –Signaling scheme –Hardware to inject bits into the medium –Software to manipulate the hardware –Software to control data movement –Programming model to build applications

12. ICOM 6115©Manuel Rodriguez-Martinez Communications Medium Provides a channel to carry the bits between machines Example –Cooper Use voltage or current to encode bits –Fiber Use light to encode bit –Air Use Radio waves or microwaves to encode bits

13. ICOM 6115©Manuel Rodriguez-Martinez Signaling Scheme Provides a mechanism to convert bits into signals propagated by the medium and vice-versa –Bits voltage –Bits radio signals –Bits light pulses –Bits microwave signal Specifies possible error conditions on medium

14. ICOM 6115©Manuel Rodriguez-Martinez Network Hardware Has circuit logic to: –convert chunks of bytes into bits that get injected into the network –Read groups of bit from medium and make them into chunks of bytes –Implements the signaling scheme Has other logic to –Detect error and other conditions on the medium Diagnostic information

15. ICOM 6115©Manuel Rodriguez-Martinez Networking Software Device drivers are needed to manipulate the networking hardware –Network card Driver implement the logic to control the card –Read/write operations Protocols to –recover from error in bit transmission –arbitrate access to the medium

16. ICOM 6115©Manuel Rodriguez-Martinez More Networking Software Many networks might have different pieces –Cooper-based and wireless Need software to move data between machines on these segments –Identify data packets Sender Receiver –Finds paths for packets over the segments –Control traffic of the packets –Support for Quality of Service (QoS)

17. ICOM 6115©Manuel Rodriguez-Martinez Moving packets over networks Network 1 Network 2 This is called forwarding

18. ICOM 6115©Manuel Rodriguez-Martinez More on Networking Software Data packets can be lost on transit –Error on media Bent wire –Error on network hardware Faulty card –Error on network software Buggy code Need to software to make sure data gets to its destination

19. ICOM 6115©Manuel Rodriguez-Martinez Reliable data movement Software needs to monitor data movement –Keep timers to determine timeouts –Resent lost packets –Keep track of packet sequences To put packet in the proper order –Control the rate of packet movement To prevent error due to overloaded

20. ICOM 6115©Manuel Rodriguez-Martinez Application Software You programs need to have an API to deal with the network –Find other computer to send/receive data to –Invoke the routines provides by the OS to use the network –Determine the way in which data will be exchanged Characters Binary code –Specify operations to exchange data Control commands

21. ICOM 6115©Manuel Rodriguez-Martinez Application Software The API software must deal with errors and inform them to the application –Computer not found –Illegal operation –Network is not reachable –File is too big …

22. ICOM 6115©Manuel Rodriguez-Martinez Network Design Networks are designed and implemented in terms of layers –Each layer deals with specific communication issue –Provide a service (some kind of useful operation) A given layer: –Leverages on services provided by lower- level layer –Provides services to upper level layers

23. ICOM 6115©Manuel Rodriguez-Martinez Internet Networking Layers Application Layer Transport Layer Network Layer Data Link Layer Physical Layer

24. ICOM 6115©Manuel Rodriguez-Martinez Communication based on this model Application Layer Transport Layer Network Layer Data-Link Layer Physical Layer Application Layer Transport Layer Network Layer Data-Link Layer Physical Layer Physical Medium Bit Pipe