Ethernet-Suppl

Ethernet-Suppl - Dr. Tracy Bradley Maples (Fall 2009)...

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CECS 474 Computer Network Interoperability Ethernet Overview LANs Local area networks(LANs) depend on multiple access protocols to regulate the sharing of the transmission medium. There are two primary categories of multiple access protocols: 1. Contention Access --> MANAGE COLLISIONS Examples: ALOHA, CSMA, CSMA/CD 2. Controlled Access --> COLLISION FREE Predetermined Assignment: Static Examples: FDMA, TDMA Demand Assignment: Based on Demand Examples: circuit-oriented assignment, packet-oriented assignment Dr. Tracy Bradley Maples (Fall 2009)
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Performance of Multiple Access Schemes 0 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 Traffic Intensity Contention Access Demand Assignment Predetermined Assignment Dr. Tracy Bradley Maples (Fall 2009)
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Contention Access Advantages: short delay for bursty traffic simple (do to distributed control) flexibility in number of users fairness Disadvantages: low channel efficiency not good for stream traffic (e.g., voice) cannot support priority function high variance in transmission delays
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Unformatted text preview: Dr. Tracy Bradley Maples (Fall 2009) CSMA/CD Most popular contention access scheme CSMA/CD stands for C arrier S ense M ultiple A ccess with C ollision D etection CSMA/CD Transmission Stations are attached to a bi-directional bus A C B CSMA/CD Transmission Algorithm Assemble Frame Is Channel Busy? Start Transmission Collision Detected? Transmission Done? Send Jam Increment Attempts Too Many Attempts? Wait Backoff Time Done: OK Done: Erro r Yes No Yes Yes Yes No No No Dr. Tracy Bradley Maples (Fall 2009) CSMA/CD Collision Detection A B (a) A begins transmission A B (b) B begins transmission A B (c) B detects collision; sends jam signal A B (d) A detects collision just before the end of transmission Conclusion: The amount of time it takes to detect a collision is twice the propagation delay. Dr. Tracy Bradley Maples (Fall 2009)...
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This note was uploaded on 04/11/2010 for the course CECS 474 taught by Professor Maples,t during the Spring '08 term at CSU Long Beach.

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Ethernet-Suppl - Dr. Tracy Bradley Maples (Fall 2009)...

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