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Computer Networks BITS ZC481

Computer Networks BITS ZC481. Lecture 1. Grading Policy. EC1 : 3 Quizes of 5% Weightage Each (Closed Book). EC2: Mid Sem Test 35% on Sunday 08/09/2013 at 2 PM – 4 PM (Closed Book). EC3: Compre Exam 50 % on Sunday 10/11/2013 at 2 PM – 5 PM (Open Book). Required Textbook.

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Computer Networks BITS ZC481

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  1. Computer Networks BITS ZC481 Lecture 1

  2. Grading Policy • EC1 : 3 Quizes of 5% Weightage Each (Closed Book). • EC2: Mid Sem Test 35% on Sunday 08/09/2013 at 2 PM – 4 PM (Closed Book). • EC3: Compre Exam 50 % on Sunday 10/11/2013 at 2 PM – 5 PM (Open Book).

  3. Required Textbook • Text Book: Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, 2005. • R1: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Pearson Education, 2006. • R2: William Stallings, Computer Networking with Internet Protocols and Technology, Pearson Education, 2004 • L. Peterson and B. Davie, Computer Networks: A Systems Approach, Fourth Edition, Elsevier, 2007 (Book From 24x7 Online Book)

  4. Course Objectives • Learn how communication networks are put together • mechanisms, algorithms, technology components • Understand fundamental challenges • Learn about existing solutions • typically: no single dominant solution • What problems still need solving?

  5. Today’sAgenda • Introduction to Internet/computer networks • Uses of Computer Networks • Network Hardware: The Network Edge, The Network Core, Access Networks

  6. Internet :Nuts & Bolts View • Internet is hundreds of millions of connected computing devices (nodes). End Systems are the hosts. • Internet applications run on end system but don’t run in packet switches in network core. • All the nodes are connected via Communication links (fiber, copper, radio, satellite). • Transmission rate to transmit the data between the devices is measured in Bandwidth

  7. PC Mobile network server Global ISP wireless laptop cellular handheld Home network Regional ISP access points wired links Institutional network router Internet :Nuts & Bolts View(1) • Intermediate Nodes between two hosts forwards the packets (Packet Switching) from one node to other towards destination host can be routers or switches.

  8. Internet :Nuts & Bolts View(2) • Internet: “network of networks” • loosely hierarchical • public Internet versus private intranet • Internet standards • RFC: Request for comments • IETF: Internet Engineering Task Force

  9. Internet :Nuts & Bolts View(3) • End system attached to the Internet provides an API (Application programming interface). • API Specifies how a software piece running on one end system asks the internet infrastructure to deliver data to specific destination software piece running on other end system. • It is set of rules the sending software piece must follow.

  10. Internet: a service view • Most people know about the Internet (a computer network) through applications like • World Wide Web • Email • Online Social Network • Streaming Audio Video • File Sharing • Instant Messaging

  11. Internet: a service view(1) • Communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing. • Different Communication services provided to apps: • reliable data delivery from source to destination. • “best effort” (unreliable) data delivery.

  12. Protocol • All communication activity in Internet governed by protocols. • Define format, order of messages sent and received among network entities, and actions taken on messages transmission, receipt, or timeout. eg: TCP, IP, HTTP, Skype, Ethernet • Protocol defines the interfaces between the layers in the same system and with the layers of peer system.

  13. Protocol(1) • Each protocol object has two differentinterfaces: • service interface: operations on this protocol • peer-to-peer interface: messages exchanged with peer

  14. Protocol(2) • Except at the hardware level, where peers directly communicate with each other over a link, peer-to-peer communication is indirect—each protocol communicates with its peer by passing messages to some lower level protocol, which in turn delivers the message to its peer.

  15. Network Structure • Network edge: applications and hosts. • Access networks, physical media: wired, wireless communication links • Network core: • interconnected routers • network of networks (Internet)

  16. Network Edge • End systems (hosts): run application programs at “edge of network e.g. Web, email • client/server model • client host requests, receives service from always-on server e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers e.g. Skype, BitTorrent

  17. Network Edge: connection-oriented service Goal: data transfer between end systems • handshaking: setup (prepare for) data transfer ahead of time • Hello, hello back human protocol • set up “state” in two communicating hosts • TCP - Transmission Control Protocol • Internet’s connection-oriented service TCP service[RFC 793] • reliable, in-order byte-stream data transfer • loss: acknowledgements and retransmissions • flow control: • sender won’t overwhelm receiver • congestion control: • senders “slow down sending rate” when network congested

  18. Network Edge: connectionless service Goal: data transfer between end systems • UDP - User Datagram Protocol [RFC 768]: • connectionless • unreliable data transfer • no flow control • no congestion control App’s using TCP: • HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: • streaming media, teleconferencing, DNS, Internet telephony

  19. Access networks • How to connect end systems to edge router? • residential access nets • institutional access networks (school, company) • mobile access networks

  20. Access Network: Dial Up • User software actually dials a ISP Phone Number and makes a traditional phone connection with ISP. • Home Modem coverts digital output from PC to analog format and Modem in ISP converts back data from analog to digital format.

  21. Access Network: Dial Up(1) Drawback: • up to 56Kbps direct access to router (often less) • Can’t surf and phone at same time: can’t be “always on”

  22. Access networks: DSL

  23. Access networks: DSL(1) • Telephone lines carries both data and telephone signals encoded at different frequencies. • Splitter separates the data from telephone signals and transfers it to DSL Modem. • Upstream and downstream transmission rates are different (asymmetric).

  24. Access Network: Cable • Cable head end broadcast the television channels through distribution networks of coaxial cable and amplifiers to residence. • Hybrid Fiber-coaxial (HFC) access network makes use of both coaxial and fiber cables. • Shared broadcast Medium • asymmetric: up to 30Mbps downstream, 2 Mbps upstream

  25. Access Network: Cable(1)

  26. Access Network: Ethernet

  27. Access Network: Ethernet(1) • company/university local area network (LAN) connects end system to edge router. • Ethernet: • 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet • modern configuration: end systems connect into Ethernetswitch

  28. Access Network: Wireless Access • In wireless LAN, Wireless users transmit/receive packets to/from access point. Eg: 802.11b/g (WiFi): 11 or 54 Mbps. • In wide area wireless access network, packets are transmitted to the base station over same wireless infrastructure used for cellular telephony. • Wimax(10’s Mbps over wide area).

  29. Access Network: Wireless Access(1) router base station mobile hosts

  30. Physical Media • Bit: propagates betweentransmitter/reciver pairs • physical link: what lies between transmitter & receiver • guided media: • signals propagate in solid media: copper, fiber, coax • unguided media: • signals propagate freely, e.g., radio Twisted Pair (TP) • two insulated copper wires • Category 3: traditional phone wires, 10 Mbps Ethernet • Category 5: 100Mbps Ethernet

  31. Physical Media: coax, fiber Coaxial cable: • two concentric copper conductors • bidirectional • baseband: • single channel on cable • legacy Ethernet • broadband: • multiple channels on cable • HFC Fiber optic cable: • glass fiber carrying light pulses, each pulse a bit • high-speed operation: • high-speed point-to-point transmission (e.g., 10’s-100’s Gps) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise

  32. Physical media: radio • signal carried in electromagnetic spectrum • no physical “wire” • bidirectional • propagation environment effects: • reflection • obstruction by objects • interference Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., Wifi) • 11Mbps, 54 Mbps • wide-area (e.g., cellular) • e.g. 3G: hundreds of kbps • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus low altitude

  33. Next Lecture • Network Core • ISP • Delay & loss in packet-switched networks • Protocol layers, service models • OSI and TCP/IP reference models

  34. Thanks!!! Queries?

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