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Unformatted text preview: 1 CSE 5345 – Fundamentals of Wireless Networks Yonghe Liu [email protected] 2/14/12 Last Class WLAN Various standards:802.11* Network architecture: BSS and ESS MAC • Exposed/Hidden terminal problems • CSMA/CA Today Continue on 802.11 MAC 4 802.11 Solutions for Collision Avoidance Random backoff Backoff coutner uniformly drawn from [0, CW] • In terms of number of slots • Slot time PHY dependent, 802.11b DSSS: 20 s Decrement backoff counter per idle time slot Transmit when zero reached Double CW if collision/error CW=2 CW+1 (31, 63, 127, …) CW<=CWmax Fallback to CWmin if success For RTS or Data 2 5 802.11 Backoff Procedure DIFS Contention Window Slot time Defer Access Backoff-Window Next Frame Select Slot and Decrement Backoff as long as medium is idle. SIFS PIFS DIFS Free access when medium is free longer than DIFS Busy Medium 6 Inter-frame Space DIFS = DCF inter-frame space Used for backoff SIFS + 2 Slot time...
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This note was uploaded on 03/22/2012 for the course CSE 5345 taught by Professor Youngheliu during the Spring '12 term at UT Arlington.
- Spring '12