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1 Chapter 9 Local Area Network Technology. 2 LAN Protocols – Basics.

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Presentation on theme: "1 Chapter 9 Local Area Network Technology. 2 LAN Protocols – Basics."— Presentation transcript:

1 1 Chapter 9 Local Area Network Technology

2 2 LAN Protocols – Basics

3 3 LAN Protocols – Media Access Control (MAC) Govern access to transmission medium 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 Assembly of data into frame with address and error detection fields Disassembly of frame Disassembly of frame –Address recognition –Error detection For the same LLC, several MAC options may be available For the same LLC, several MAC options may be available

4 4 LAN Protocols – In Context

5 5 LAN Topologies – Overview

6 6 LAN Topologies – Frame Transmission, Bus LAN

7 7 Topologies – Frame Transmission, Ring LAN

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

9 9 Media Access Control– Typical Frame Format

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

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

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

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

14 14 Bridges – Multiple LANs

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

16 16 Bridges – Frame Forwarding Maintain forwarding database for each port Maintain forwarding database for each port –List station addresses reached through each port For a frame arriving on port X: 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 17 Bridges – Address Learning Can preload forwarding database Can preload forwarding database Can be learned Can be learned When frame arrives at port X, it has come from the LAN attached to port X 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 Use the source address to update forwarding database for port X to include that address Timer on each entry in database Timer on each entry in database Each time frame arrives, source address checked against forwarding database Each time frame arrives, source address checked against forwarding database

18 18 Bridges – Loop of Bridges

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

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


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