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Network Architecture & Protocols Lecture Notes

Explore network architecture and protocols with a focus on Internet fundamentals, switching types, delay sources, and service views, including TCP, UDP, and core networking concepts.

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Network Architecture & Protocols Lecture Notes

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  1. CS 5565Network Architecture and Protocols Godmar Back Lecture 2

  2. Announcements • Created Lectures Page • Created CS5565 Forum • Use this to find a project partner • All projects will be done in groups of up to 2. • Do Wireshark Lab 1/Intro • Either follow old link to Ethereal lab, or, if you have a textbook website subscription, download from website CS 5565 Spring 2009

  3. Outline for today • Internet: • “nuts and bolts” view • Service view • Network edge view • Network core view • Types of switching • Sources of Delay CS 5565 Spring 2009

  4. millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets router workstation server mobile local ISP regional ISP company network The Internet: “nuts and bolts” view CS 5565 Spring 2009

  5. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” loosely hierarchical public Internet versus private intranets Internet vs internet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force The Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network CS 5565 Spring 2009

  6. Network Virginia Source: Sean Gillespie CS 5565 Spring 2009

  7. communication infrastructure enables distributed applications: Web, email, games, e-commerce, file sharing communication services provided to apps: Connectionless unreliable Connection-oriented reliable The Internet: a service view CS 5565 Spring 2009

  8. a human protocol and a computer network protocol: TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection req Hi CS 5565 Spring 2009

  9. human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt CS 5565 Spring 2009

  10. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: CS 5565 Spring 2009

  11. end systems (hosts): run application programs e.g. Web, email at “edge of network” 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. Gnutella, KaZaA The network edge: CS 5565 Spring 2009

  12. 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 Connection-oriented service CS 5565 Spring 2009

  13. Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data transfer no flow control no congestion control TCP-friendliness App’s using TCP: HTTP (Web), ssh (remote login), SMTP (email),Bittorrent (file-sharing), XMPP (instant messenging) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony Connectionless service CS 5565 Spring 2009

  14. the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” How are the network’s resources shared? The Network Core CS 5565 Spring 2009

  15. End-end resources reserved for “call” (or session) link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching CS 5565 Spring 2009

  16. network resources (e.g., link bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) Network Core: Circuit Switching • multiplex different calls • frequency division multiplexing (FDM) • time division multiplexing (TDM) • synchronous vs. asynchronous (aka statistical) TDM CS 5565 Spring 2009

  17. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM CS 5565 Spring 2009

  18. S(ynchronous) TDM Suppose m slots Total bandwidth is R L bit packet takes Lm/R seconds L/R seconds if packet fits into slot (but next packet must wait m-1 slots) FDM Suppose m channels Total bandwidth is R Per channel bandwidth is R/m L bit packet takes Lm/R seconds Computing transmission delay CS 5565 Spring 2009

  19. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed no dedicated allocation no resource reservation Network Core: Packet Switching • resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • Node receives complete packet before forwarding CS 5565 Spring 2009

  20. Sequence of A & B packets does not have fixed pattern  statistical multiplexing. D E Packet Switching: Statistical Multiplexing 10 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B Note: transmission delay is L/R queue of packets waiting for output link CS 5565 Spring 2009

  21. 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active less than .0004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link CS 5565 Spring 2009

  22. Great for bursty data resource sharing simpler, no call setup Excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Challenge: How to provide circuit-like behavior where needed? bandwidth guarantees needed for audio/video apps Is packet switching a “slam dunk winner?” Packet switching versus circuit switching CS 5565 Spring 2009

  23. Circuit Switching Dedicated link bandwidth Dedicated switch capacity Low link utilization Low overall utilization Packet Switching Better link utilization Better overall utilization Need for congestion control Need to identify to which “call” a packet belongs Circuit vs. Packet Switching (1) CS 5565 Spring 2009

  24. Goal: move packets through routers from source to destination we’ll study several path selection (i.e. routing) algorithms Note distinction between routing & forwarding datagram network: (aka dynamic routing) destination address in packet determines next hop routes may change during session analogy: driving, asking directions virtual circuit network: (aka virtual circuit routing) each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintainper-call state Packet-switched networks: forwarding CS 5565 Spring 2009

  25. Packet Packet Packet Message vs. Packets vs. Cells • Message • Entity with some application/protocol defined meaning • Packets • Chunks of data into which messages are split • Can be further decomposed, e.g., into smaller packets or cells (small packets, ATM-cell: 53 bytes) Message CS 5565 Spring 2009

  26. Telecommunication networks Packet-switched networks Circuit-switched networks FDM TDM Datagram Networks Networks with VCs Network Taxonomy CS 5565 Spring 2009

  27. Summary • Terminology: hosts (end systems), communication links, routers, transmission rates, packets, internet vs. intranet vs. the Internet • Protocols: protocols define format, order of messages sent and received among network entities, and actions taken on msg transmission, receipt • View from network edge: • Client/server, peer2peer, other models • Service view • Communication infrastructure provide connection-oriented + connectionless service • View from network core: • Circuit-switching vs packet-switching • Datagram network vs. virtual-circuit networks CS 5565 Spring 2009

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