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ECA Overview (Enhanced Contention Access)
Jin-Meng Ho TI Khaled Turki TI Sid Schrum TI Wim Diepstraten Agere Systems Mathilde Benveniste AT&T Menzo Wentink Intersil Maarten Hoeben Intersil Greg Chesson Atheros Harold Teunissen Lucent Technologies
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History DCF DQOS vDCF pDCF TCMA ECA Contention window […CW…]
Multiple CWs [..CW0..] [… CW1 …] [… CW2 …] Internal collisions COffset [..CW0..] CO[.. CW1 ..] CO2..[… CW2 …] TCPP -> backoff time full updates, full adaptation UAT (non-decrementing offset) Unified controls
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Robust Differentiation
Goodput overlay with offered load
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Adaptive Control
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UAT-Enhanced MAC Priority TCMA V-DCF 30 90 5.0 Mbps 2.5 Mbps 150
Time (sec) 30 90 5.0 Mbps 2.5 Mbps 150 Priority UAT-Enhanced MAC TCMA TCMA A7 VDCF B7 V-DCF
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EAP Control Parameters in Beacon or Management Frame
flags NDO Offset[0-7] TCPP[0-7] Bscale Flags: Fast update flag: disable autonomous backoff Other bits reserved NDO Mask (non-decrementing offset) Enables UAT-like offset per TC, delta=1 after PIFS Autonomous backoff exponent: 1 bit per traffic class Flags, NDO mask, Offsets, TCPPs: 8-bits each Default parameters defined for IBSS use
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Station Capabilities Station may implement any internal queue frame-dropping method.
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Sending Frames Frame arrives in TC Get TxOP On collision/failure:
Apply offset and/or NDO if indicated; then do either: Select random backoff from CW[TCPP]; countdown. Compare random number to PP[TC] threshold at every slot; transmit from TC as indicated by comparison. On collision/failure: If CW method, double window size (unless disabled) Perform local fast backoff adaptation If TCPP method, divide TCPPs by two (unless disabled)
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Summary Controls Compatibility, Transparency Implementation Options
TxOP probabilities, contention offsets, non-decrementing offsets, centralized and autonomous adaptation IBSS: default parameters, local adaptation of CO/CW Compatibility, Transparency With legacy, HCF, bursting techniques Implementation Options Scheduler, Tx selection method
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References Pdcf: 467r1 TCMA: 456, 457, 01-002, 003, 004
Vdcf: 412r1, 429, 399
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