CSE5345_Lecture11

CSE5345_Lecture11 - Last Class WLAN MAC CSE 5345...

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1 CSE 5345 – Fundamentals of Wireless Networks Yonghe Liu Yonghe@cse.uta.edu 2/16/12 Last Class WLAN MAC NAV DCF Multi-rate support 3 Calculation RTS:SIFS+CTS+SIFS+DATA+SIFS+ACK CTS: RTS duration – (CTS+SIFS) DATA: CTS duration – (DATA+SIFS) ACK: Data duration – (ACK+SIFS) 4 Distributed Coordination Function (DCF) Distributed random access Carrier sense and virtual carrier sense • NAV Exponential backoff for collision avoidance • Double Contention Window if retransmission • Fallback to CWmin if success • CWmin (e.g. 31 )<= CW <= Cwmax (e.g. 1023) Ack to increase reliability • Local retransmission • Short retry (e.g.4) and long retry (e.g., 7)
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2 Today PHY 6 Some Terminology MSDU: MAC Service Data Unit Link layer frame Received at MAC via MAC SAP MPDU: MAC Protocol Data Unit Mac layer frame Send to PHY through PHY SAP MMPDU: MAC Management Protocol Data Unit 7 Three Types of Frames Data frames Control frames Ack, RTS/CTS Management frames (re)Association, beacon, probe 8 General Frame Format General frame format Some frame types may omit some fields Frame control field
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3 9 Type Field Type and subtype identify the function of the frame: Type=00 Management Frame Type=01 Control Frame Type=10 Data Frame Data frame subtypes: data+ack, data+poll, etc Poll is a data frame Type=11 Reserved 10 To/From DS Field Addr. 1 = All stations filter on this address.
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CSE5345_Lecture11 - Last Class WLAN MAC CSE 5345...

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