Computer Communication Networks

1. Computer Communication Networks By Dr. Khalid H. Usmani dr.usmani@uaar.edu.pk

2. Books: • Data and computer communication By: William Stalling • Computer Networks A System Approach 3rd Edition. By: LARRY L. PETERSON and BRUCE S. DAVIE

3. Objectives: Principles and Concepts • At the end of this course, you should be able to: – identify the problems that arise in networked communication – explain advantages/disadvantages of existing solutions to these problems in different networking scenarios – evaluate novel approaches to these problems – understand the components of Internet protocol suite – understand the implications of a given solution for performance in various networking environments

4. What is Your Goal ? • Build a computer network which – Can grow to global proportions – Support diverse applications

5. Network Design • Before looking inside a computer network, first agree on what a computer network is? • Set of serial lines to attach terminals to mainframe ? • Telephone network carrying voice traffic ? • Cable network to disseminate video signals ? Specialized to handle: • Keystrokes • Voice • Video

6. What Distinguishes a Computer Network ? • Overview • Built from general purpose programmable hardware • Supports wide range of applications

7. Applications – Consumers of Networks • On a simple click, several messages may be exchanged over the Internet • In a web browser, 17 messages may be exchanged – up to six messages to translate the server name – three messages to set up a TCP connection – four messages to send HTTP “get” request + response – four messages to tear down the TCP connection • Moreover, millions of messages are exchanged each day by Internet nodes to make their presence and services known

8. Applications – the Driving Force • Streaming audio and video is an emerging application – Source generates and sends the video stream in messages across the Internet • Video-on-demand: reads a preexisting movie – One-way data transfer • Videoconferencing: interactive session – Very tight timing constraints • Diversity of applications that can be built on top of the Internet hint at the complexity of the Internet design • We will study that why networks are designed the way they are?

9. What is my Requirement

10. Selecting the research paper: Select the papers from a reputed journal Like ACM (Portal.acm.org), IEEE, Computer Communication or Computer Networks (sciencedirect.com). Should be published in 2008. Presentations will be in the 11th week. Email the following to me and to the class group • Paper title • Author, journal name, Publication date • Abstract and conclusion in points.

11. Critical Review of the Paper. • From which database? • Journal/conference • If conference, which? • Who has written paper? • Topic how much relevant to the material in the paper? • Abstract and conclusion? • Introduction of problem, statement of problem • Literature review • Assumptions if any? • Proposed solution?  Do you think any other possible solution? • Tools to verify the hypothesis? • Analysis of the results  comparison with previous published material? • Performance parameters  how many and which are those  validity? • Statistical analysis? • Conclusion and future work?

12. Network Overview • What must a network provide ? – connectivity – cost-effective sharing – functionality – performance • How are networks designed and built ? – layering – protocols – standards

13. Perspective • For network user – connectivity: for services required; error free delivery within acceptable time limits • For network designer – efficiency: cost-effective design, fair allocation and efficient use of resources • For network operator – maintenance: easy to administer, fault localization & isolation, usage accounting

14. BuildingBlocks • Nodes: PC, special-purpose hardware… – hosts – switches • Links: coax cable, optical fiber… – point-to-point – multiple access

15. Why not connect each nodewith every other node ? • Number of computers that can be connected becomes very limited • Number of wires coming out of each node becomes unmanageable • Amount of physical hardware/devices required becomes very expensive • Solution: indirect connectivity using intermediate data forwarding nodes

16. Introduction What is a Network? A collection of computers, display terminals, printers, and other devices linked either by physical or wireless means. • Computer Networking • Internet: A world-wide network connecting millions of computer networks for the purpose of exchanging data and communications using special rules of communication. • internet: (lower case i) Any network connecting two or more computer networks.

17. What do you need? Hardware 1. Network cards, modems (or ports) 2. Cables, phonelines (connection) Computer #1 ? Software 1. Operating system 2. Application- Browser Computer #2

18. Introduction: “Everything is Connected to Everything” • Seeds of Networking • 1966: ARPA (Advanced Research Projects Agency) State Defense Department’s research organization. • Focused major development effort on computer networking. • ARPA’s Goal: To promote research in advanced future technologies by funding university and industry research proposals. • Result: Thousands of databases became available to the public. • Minnesota . Gopher system

19. Communication Basics of Networks • Two Types of Network Connections: Physical versus Wireless connections • The first type: The Physical Connection. • Physically connect computers together. • wires or optical cables. • The connections are called network links. • Three most common physical links: • Twisted pair • Coaxial cable • Fiber-optic cable

20. Communication Basics of Networks • Twisted pair - INEXPENSIVE • Two wires twisted together. • Makes them less susceptible to acting like an antenna and picking up radio frequency information or appliance noise. • Telephone company uses twisted-pair copper wires to link telephones.

21. Communication Basics of Networks • Coaxial cable • Also two wires: • One of the wires is woven of fine strands of copper forming a tube. • The wire mesh surrounds a solid copper wire that runs down the center. • Space between has a non-conducting material. • Makes them more impervious to outside noise. Use this when 1. Long distances 2. Lots of interference

22. Communication Basics of Networks • Fiber-optic cable • (BIG JOBS + EXPENSIVE) • Light is electromagnetic. • Can transmit more information down a single strand. • It can send a wider set of frequencies. • Each cable can send several thousand phone conversations or computer communications.

23. Communication Basics of Networks • Second type of connections of computers into networks: Wireless connections • The link is made using electromagnetic energy that goes through space instead of along wires or cables. • Three types of wireless communications commonly used in networking: • Infrared • Radio frequency • Microwave

24. Communication Basics of Networks • Infrared • Commonly used in TV and VCR remote controls. • Use infrared frequencies of electromagnetic radiation that behave much like visible light. • Must be in the line of sight. • Often used to connect keyboards, mice, and printers.

25. Communication Basics of Networks • Radio frequency • Uses radio frequencies. • Function even though line of sight is interrupted. • Not commonly used because of the possible interference from other sources of electromagnetic radiation such as old electric drills and furnace motors.

26. Communication Basics of Networks • Microwave • Often used to communicate with distant locations. • Must be line of sight. • Satellite communications use microwaves.

27. Communication Basics of Networks • Five Basic Properties of Transmission: (of both the physical and wireless links:) 1. Type of signal communicated (analog or digital). 2. The speed at which the signal is transmitted (how fast the data travels). 3. The type of data movement allowed on the channel (one-way, two-way taking turns, two-way simultaneously). 4. The method used to transport the data (asynchronous or synchronous transmission). 5. Single channel (baseband) and multichannel (broadband) transmission.

28. Communication Basics of Networks • The type of data movement allowed on the channel. • Simplex transmission - One way transmission. • Half-duplex transmission - Flows only one way at a time. • Full-duplex transmission - Two-way transmission at the same time.

29. Communication Basics of Networks • The method used to transport the data. • Two types of data transmission, each requiring a different modem. • Asynchronous transmission - • Information is sent byte by byte. • Cheaper and more commonly used. • Synchronous transmission - • Data is sent in large blocks rather than in small pieces. • Preceded by special information, concerning error detection and block size.

30. Components of a Network

31. Addressing and Routing • Address: byte-string that identifies a node – usually unique • Routing: forwarding decisions – process of determining how to forward messages to the destination node based on its address • Types of addresses – unicast: node-specific – broadcast: all nodes on a network – multicast: some subset of nodes on a network

32. Multiplexing • Physical links/switches must be shared among users – Time-Division Multiplexing (TDM) – Frequency-Division Multiplexing (FDM)

33. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM

34. Statistical Multiplexing • On-demand time-division • Schedule link on a per-packet basis • Buffer packets in switches that are contending for the link • Packets from different sources interleaved on link

35. Packet-switched networks Circuit-switched networks FDM TDM Datagram Networks Networks with VCs Network Taxonomy Telecommunication networks Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

36. roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage treat each other as equals NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

37. Tier-1 ISP: e.g., Sprint Sprint US backbone network

38. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs NAP Tier-2 ISPs also peer privately with each other, interconnect at NAP • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet • tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

39. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

40. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

41. End of Today’s Lecture