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802.11e Medium Access Control Enhancements for Quality of Service

802.11e Medium Access Control Enhancements for Quality of Service. HPMN lab. 용어의 정의 (1). AC : Access Category CAP :Controlled Access Period (HCF 또는 HC 에 의해서 station 들이 medium 에대한 access 를 control 받는 기간 ) CCI :Controlled Contention Interval

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802.11e Medium Access Control Enhancements for Quality of Service

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  1. 802.11eMedium Access Control Enhancements for Quality of Service HPMN lab.

  2. 용어의 정의(1) • AC : Access Category • CAP :Controlled Access Period (HCF 또는 HC에 의해서 station들이 medium에대한 access를 control받는 기간) • CCI :Controlled Contention Interval (CAP안에 포함되는 것으로 RR에 대하여 HC에 의해서 access를 control 받는 기간) • EDCF :Enhanced Distributed Coordination Function • HC :Hybrid Coordinator • HCF :Hybrid Coordination Function HPMN lab.

  3. 용어의 정의(2) • QAP :QoS Access Point • QBSS :QoS BSS • QSTA :QoS Station (in QBSS) • TC :Traffic Category(일반적인 traffic) • TS :Traffic Stream(periodic 또는 continuous한 traffic) • TID :Traffic Identifier(TCID와 TSID로 나뉨) • TSPEC :Traffic Specification • TXOP :Interval Time of Transmission Opportunity (QSTA이 전송할 수 있는 권리를 가지 고 있는 시간) • UP :User Priority HPMN lab.

  4. 2 2 6 6 6 2 6 2 n 4 Frame Control Duration / ID Addr Addr Addr Sequence Control Addr QoS Control Frame Body FCS Type value : Management, Ctrl, Data Type 구분 Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bit 8-15 Usage T I D FEC Ack Policy reserved TXOP limit, units of 32 microseconds QoS data type frames that include CF-Poll sent by the HC T I D FEC Ack Policy reserved TXOP limit, units of 32 microseconds QoS data type frames without CF-Poll sent by the HC T I D FEC Ack Policy reserved TXOP limit, units of 32 microseconds QoS data(non-null) frames sent by the WSTAs T I D FEC Ack Policy reserved TXOP limit, units of 32 microseconds QoS null frames sent by the WSTAs T I D 1 Ack Policy reserved Queue size, units of octets T I D 0 Reserved reserved TXOP duration requested, units of 32 microseconds RR frames T I D 1 Reserved reserved Queue size, units of 256 octets MAC frame format(1) HPMN lab.

  5. MAC frame format(2) - TID : Identify the TC or TS to which the corresponding MSDU - Ack policy : Followed upon the delivery of the MPDU ( Normal, No, Burst Ack ) - FEC : Set to 1 in those QoS data type frames. - TXOP An interval of time when a particular QSTA has the right to initiate transmissions onto the WM HPMN lab.

  6. 2 2 6 6 6 2 0 - 2312 4 Frame Control Dur / ID DA SA BSSID Seq. Ctrl Frame Body FCS MAC header 16 Bits 20 Bits 8 Bits 8 Bits 16 Bits 8 Octets 8 Octets 8 Octets Element ID Length Reserved QoS Parameter Set Count EDCF TXOP Limit CWmin[UP] Values AIFS[UP] Values CWP Factor [UP] Values < QoS Parameter Set Element > MAC management frame format(1) CP동안 QSTA에서 QoS facility의 적절한 동작을 위한 AIFS의 Update를 위해서 QoS Parameter Set Element 사용  QAP에서 Beacon frame 또는 Probe Response frame통해 전송 HPMN lab.

  7. MAC management frame format(2) - QoS parameter set count : 0 부터, parameter set 변화시 1씩 증가 (MIB value update위한, QoS parameter set의 변화여부 확인) - EDCF TXOP limit : Time limit on TXOPs that are not granted by QoS (+) CF-Polls - CWmin Value : TC (0-7)를 위한 8개의 CW 값. - AIFS Value : TC(0-7)를 위한 8개의 AIFS 값. HPMN lab.

  8. Bits 5-7 Bit 1 Bits 2,3 Bits 12-15 Bit 4 Bits 8-11 Bit 0 13 User Priority Traffic Type TSID FEC TS Info Ack Policy Reserved Element ID Reserved TSPEC element (For use by the HC and WSTA)(1) : TS의 characteristic, QoS expectation 정의 위한 parameter set 포함. 16 2 Octets 1 Octet 1 Octet 2 Octets 2 Octets 2 Octets 2 Octets 1 Octet 1 Octet 1 Octet Length TS Info Inactivity Interval Inter Arrival Interval Norminal MSDU Size Min Data Rate Mean Data Rate Max Burst Size Min Tx Rate Reserved Delay Bound 1 Octet Jitter Bound - Traffic type : Set to 1 (Continuous traffic or periodic traffic) - TS Info Ack Policy : MSDU에 사용할 Policy (Normal, No, Alternate, Burst Ack) - TSID : WSTA uses it for a TSPEC HPMN lab.

  9. TSPEC element (For use by the HC and WSTA)(2) - Inactivity Interval : Max time units that elapse without arrival or transfer of an MSDU - Interarrival Interval : Interval of MSDUs belong to TS and the MAC SAP - Delay Bound : Arrival of the MSDU at the local MAC sublayer from the MAC SAP - Jitter Bound : Acceptable max. delay difference in units of TU HPMN lab.

  10. 1 Octet 1 Octet L Octets reserved Element ID Search priority Classifier Type Frame Classifier 0 1 2 Classifier Type 4 5 - 255 3 TCP/UDP IP parameters Meaning 802.2 LLC parameters 802.1 D/Q parameters 802.3 MAC parameters Reserved TSID parameter TClas Element(1) : Contain the parameters necessary to identify incoming MSDUs with a particular TS to which they belong. 2+L Length HPMN lab.

  11. TClas Element(2) - Search priority : Search order for this frame classifier in a classification table above the MAC SAP - Classifier type : Type of frame classifier in this traffic classification - Frame Classifier : Parameter for the given classifier type • Type 0 : TSID of the TS (Determine the incoming MSDU’s signaling and multiplexing mechanism) • Type 1 : TCP/UDP Header parameters (Version, TOS, Protocol, source/destination address) • Type 2 : IEEE 802.2 LLC header (DSAP, SSAP address) • Type 3 : IEEE 802.1Q tag header : Reserved(1bit), IEEE 802.1D User Priority (3bits), and IEEE 802.1Q VLAN ID(12bits) • Type 4 : IEEE 802.3 MAC header(DA-6, SA-6, Type-2) • Type 5 – 255 : Reserved HPMN lab.

  12. MAC sublayer service architecture(1) HPMN lab.

  13. MAC sublayer service architecture(2) • Hybrid Coordinator • HCF contention-based channel access (EDCF) • provide differentiated, distributed access to the WM for 8 user priorities • 각각의 QSTA와 QAP는 8개 이하의 AC를 가지고 contention이 일어난다. • By using different AIFS, CWmin,CWmax values, • HCF polled channel access (HCF) : QoS-aware point coordinator • initiate frame exchange sequence • allocate TXOP to WSTA during CAP • By polling and controlled contention HPMN lab.

  14. EDCF –Inter-Frame Space(1) HPMN lab.

  15. EDCF –Inter-Frame Space(2) • Arbitration IFS (AIFS) Used by the QoS facility • data type frame(MPDU) 와 management type frame (MMPDU) 전송시 사용 • QSTA이 AC[i]에 대하여 transmission을 위한 channel 점유를 하려면 Carrier Sensing을 통해서 medium이 AIFS[i]동안 channel이 idle해야 한다. HPMN lab.

  16. Random backoff time • Medium이 busy인 경우 전송을 미루다가 AIFS[i]동안 medium이 idle한 경우 충돌을 피하기 위하여 random backoff를 수행하는데 이때 의 backoff time은 Backoff Time[i] = [Random(i)+ X] x aSlotTime 여기서 Random(i)는 Pseudo random integer로 0에서 CW[i]까지의 uniform distirution을 가지고 CW[i]는 dot11CWmin[i] <= CW[i] <= dot11CWmax[i]를 만족하는 정수의 값을 가진다. X = 0 : AIFS[UP] > PIFS X = 1 : AIFS[UP] = PIFS HPMN lab.

  17. Hybrid Coordination Function (HCF) • 특징 • CFP와 CP 모두에서 HCF frame exchage sequence가 사용될수있다. • CF Poll을 사용하여 마치 point coordiator와 같이 동작한다. HPMN lab.

  18. HCF – Contention Free Period with HC • HC 는 pointer coordinator와 같으므로 먼저 PIFS동안 medium이 idle하면 CF-Poll을 전송하게 된다. • CF-Poll을 받은 QSTA은 SIFS를 기다린 후 전송(=PCF) • CF-Poll을 받은 QSTA에서 channel을 점유 • Polled TXOP는 NAV값에 의해 보호 받는다. • NAV는 전송하는데 걸리는 시간으로 Duration/ID field를 set한다. HPMN lab.

  19. HCF – Controlled Contention Interval with HC(1) • HCF controlled contention mechanism : 특정 QSTA들이 contention을 하도록 제어한다. • HC만 CC frame을 보낼 수 있으며 CP 와 CFP모두에서 전송될 수 있다. • CC frame에는 Priority Mask, Ccop의 기간, Ccop의 수 등이 표현되어있다. HPMN lab.

  20. HCF – Controlled Contention Interval with HC(2) • 먼저 QSTA에서 HC로 RR(Reservation Request)를 요청한다. : 이때는 CC내의 priority mask에 맞는 TID를 가진 QSTA만 전송한다. • RR frame은 • Request를 받은 HC는 ack를 QSTA에 보낸다. : 이때 ack는 CC frame을 CCI length field를 ‘zero’ set해서 보낸다. • 먼저 QSTA에서 HC로 RR(Reservation Request)를 요청한다. : 이때는 CC내의 priority mask에 맞는 TID를 가진 QSTA만 전송한다. • RR frame은 • Request를 받은 HC는 ack를 QSTA에 보낸다. : 이때 ack는 CC frame을 CCI length field를 ‘zero’ set해서 보낸다. PIFS + ( R X Dccop) 후에 전송된다. R은 random integer로 [0,(Nccop-1)]사이에서 uniform distribution을 가진다. CC frame format RR frame format HPMN lab.

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