L21_channel_access_protocols

L21_channel_access_protocols - Channel Access Protocols...

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1 Channel Access Protocols Lecture 21 6.02 Fall 2008 April 25, 2008 How to share a radio channel Time-Division Multiple Access Contention protocols (Aloha, CSMA) Analysis of utilization (throughput) Channel Access • Broadcast networks: assume everyone can hear everyone else • Examples of broadcast networks: • Most wireless networks incl. WiFi (802.11) • Ethernet (but not 1 Gbit/s or higher) • Goal: Want to share channel efficiently
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2 What Does “Efficiently” Mean? • Want high channel utilization • Throughput = Useful data rate (in bits/s or pkts/ s) Utilization = Throughput/Channel Rate • Example: If node i gets n_i bits through in time T, over channel of rate R bits/s, then utilization = ( ! n_i /T) / R • Easy to achieve: just allow one node to send all the time • So… want fairness also • Example: All nodes with data to send should get equal share over time (this is a simplification…) Many Channel Access Protocols • Aka “multiple access” protocols • Time Division Multiple Access (TDMA)
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This note was uploaded on 08/23/2009 for the course EECS 6.02 taught by Professor Terman during the Spring '08 term at MIT.

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L21_channel_access_protocols - Channel Access Protocols...

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