csma_ca

csma_ca - 802.11 Medium Access Control 4050-403 Concepts of...

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1 802.11 Medium Access Control 4050-403 Concepts of Wireless Networks bxyics 2 802.3 CSMA/CD ± Carrier Sense: Listen before talk ± Collision Detection: Stop if collision occurs ± How to sense the medium? bxyics 3 CSMA/CA ± Carrier Sense Multiple Access with Collision Avoidance ± Physical carrier sense ± Virtual carrier sense ± RTS/CTS mode ± Different types of delays
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2 bxyics 4 CSMA/CA NAV=0? Sense the medium Medium Idle Transmit Frame Collision? Start yes yes no Success Random Back-off Time yes no no bxyics 5 Binary Exponential Backoff ± Backoff time = Random()*aSlotTime ± Random() is a pseudo-random integer between 0 and CW ± CW is called collision window which is between CW min and max ± = 7 slot time ± = 255 slot time bxyics 6 Inter-Frame Spacing ± SIFS (Short Inter Frame Spacing) ± PIFS (PCF IFS) ± DIFS (DCF IFS) t medium busy SIFS PIFS DIFS DIFS next frame contention direct access if medium is free DIFS
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3 bxyics 7 Inter-Frame Spacing 8 μ s 50
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This note was uploaded on 04/21/2008 for the course VNSA 403 taught by Professor Yuan during the Winter '07 term at RIT.

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csma_ca - 802.11 Medium Access Control 4050-403 Concepts of...

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