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MAC layer solutions IEEE 802.11e (1)

MAC layer solutions IEEE 802.11e (1). Enhanced Distributed Coordination Function The frames from higher layer carries its User Priority (UP) MAC layer maps it into an Access Category (AC) Each AC has different parameters, such as CWmin, CWmax, TXOP, AIFS

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MAC layer solutions IEEE 802.11e (1)

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  1. MAC layer solutionsIEEE 802.11e (1) • Enhanced Distributed Coordination Function • The frames from higher layer carries its User Priority (UP) • MAC layer maps it into an Access Category (AC) • Each AC has different parameters, such as CWmin, CWmax, TXOP, AIFS • TXOP is defined as an interval of time when a station has the right to initiate transmissions • when detecting a channel is idle, each AC starts a back-off counter after AIFS (Arbitration Inter-Frame Space) AIFS[i] = SIFS + AIFSN[i] * slottime • AIFSN[i] is the AIFS slot count for priority class i. • For high priority classes, low AIFSN values are assigned. • After waiting for AIFS, back-off counter is select from a random number: [1, CW[i]+1] for each class i with AIFSN[i] = 1 [0, CW[i]] for other classes i with AIFSN[i]>1

  2. MAC layer solutionsIEEE 802.11e (2) 本圖取自"Ad Hoc Wireless Networks", by C. Siva Ram Murthy and B. S. Manoj, published by Prentice Hall, 2004

  3. MAC layer solutionsIEEE 802.11e (3) • Hybrid Coordination Function • Conbines features of EDCF and PCF • Only in infrastructure-based BSSs that provides QoS (QBSS) • HCF uses a QoS-aware point coordinator, called HC • HC can start contention-free controlled access periods (CAPs) at any time in CP • During CAP, HC may transmit frames and polls to stations which grant them TXOPs • A superframe can be divided into CFP, CP, CAP

  4. MAC layer solutionsIEEE 802.11e (4) • During the CP,each TXOP begins • When the channel is determined available by EDCF • When a station receives a QoS CF-poll frame form HC 本圖取自"Ad Hoc Wireless Networks", by C. Siva Ram Murthy and B. S. Manoj, published by Prentice Hall, 2004

  5. MAC layer solutionsIEEE 802.11e (5) 本圖取自"Ad Hoc Wireless Networks", by C. Siva Ram Murthy and B. S. Manoj, published by Prentice Hall, 2004

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