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Chapter 9 Local Area Network Technology

Chapter 9 Local Area Network Technology. LAN Protocols – Basics. LAN Protocols – Media Access Control (MAC). Govern access to transmission medium Not found in traditional layer 2 data link control Assembly of data into frame with address and error detection fields Disassembly of frame

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Chapter 9 Local Area Network Technology

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  1. Chapter 9 Local Area Network Technology

  2. LAN Protocols – Basics

  3. LAN Protocols –Media Access Control (MAC) • Govern access to transmission medium • Not found in traditional layer 2 data link control • Assembly of data into frame with address and error detection fields • Disassembly of frame • Address recognition • Error detection • For the same LLC, several MAC options may be available

  4. LAN Protocols – In Context

  5. LAN Topologies – Overview

  6. LAN Topologies –Frame Transmission, Bus LAN

  7. Topologies – Frame Transmission,Ring LAN

  8. Media Access Control (MAC) – Basics • Where? • Central • Distributed • How? • Synchronous • Asynchronous • Asynchronous • Round robin • Reservation • Contention

  9. Media Access Control–Typical Frame Format

  10. Logical Link Control (LLC) – Basics • Transmission of link level PDUs between two stations • Must support multi access, shared medium • Relieved of some link access details by MAC layer • Addressing involves specifying source and destination LLC users • Services and protocol based on HDLC • Unacknowledged connectionless service • Connection-mode service • Acknowledged connectionless service

  11. Bridges – Basics Why? Reliability, performance, security, geography

  12. Bridges – Level of Operation Bridge operates on MAC level; unaware of LLC level

  13. Bridges – Fixed Routing • Complex large LANs need alternative routes • Load balancing • Fault tolerance • Bridge must decide whether to forward frame • Bridge must decide which LAN to forward frame on • Routing selected for each source-destination pair of LANs • Done in configuration • Usually least-hop route • Only changed when topology changes

  14. Bridges – Multiple LANs

  15. Bridges – Spanning Tree • Bridge automatically develops routing table • Automatically update in response to changes • Frame forwarding • Address learning • Loop resolution

  16. Bridges – Frame Forwarding • Maintain forwarding database for each port • List station addresses reached through each port • For a frame arriving on port X: • Search forwarding database to see if destination MAC address is listed for any port except X • If address not found, forward to all ports except X • If address listed for port Y, check port Y for blocking or forwarding state • Blocking prevents port from receiving or transmitting • If not blocked, transmit frame through port Y

  17. Bridges – Address Learning • Can preload forwarding database • Can be learned • When frame arrives at port X, it has come from the LAN attached to port X • Use the source address to update forwarding database for port X to include that address • Timer on each entry in database • Each time frame arrives, source address checked against forwarding database

  18. Bridges – Loop of Bridges

  19. Bridges –Spanning Tree Algorithm • Address learning works for tree layout, but loops cause problems • For any connected graph there is a spanning tree that maintains connectivity but contains no loops • Each bridge assigned unique identifier • Data exchange between bridges to establish spanning tree

  20. Summary • LAN architecture • LAN topologies • Bus • Tree • Ring • Star • Media Access Control (MAC) • Logical Link Control (LLC) • Bridges

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