SubmissionJoe Kwak, InterDigital1 BSS Load: AP Loading Metric for QOS Joe Kwak InterDigital doc: IEEE /0079r1May 2005

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 2 TGe Load Metric: QBSS Load Actually provides three elements all relating to load: Station Count Field, unsigned 16 bit integer indicating total number of STAs associated Channel Utilization, 8 bit percentage of time the QBSS detects the medium as busy Available Admission Capacity, 16 bit integer representing amount of medium time (32usec units) available via explicit admission control

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 3 Problems with TGe Metrics Three metric components make comparative loading evaluations difficult/impossible. No agreed way to combine the three variables into a summary metric for comparison purposes among QAPs and between APs and QAPs. Three metric components not sensitive to traffic assymetry: High downlink loads do not affect uplink access delays since dowlink traffic is “collsion free” within AP. Three metric components not sensitive to distribution of traffic among prioritized access categories: Access delay for BE not indicative of load and delay expected for VO traffic.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 4 New Metric Definition The Medium Access Delay (MAD) metric is defined as the average delay incurred from the time that any packet is ready for transmission (i.e. begins CSMA/CA access) to the actual packet transmission start time. MAD is defined for each Tge access category and indicates the current loading in terms of the expected delay for any new EDCF traffic in that category. For nonQAPs, MAD is defined for DCF traffic and indicates a summary loading in terms of the expected delay for any new DCF traffic. AP Service Load (APSL) is defined as a summary laoding metric for either APs or QAPs. For QAPs, APSL is the same as the MAD for the lowest priority BE access category.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 5 MAD Timing for Single Access Packet from head of MAC Queue TxRequest to PHY Tx Process CSMA/CA Transmit Access Delay == MAD Packet Transmission & ACK Time ( T packet _ TxAck ) Optional ACK ACK Received Next Packet from head of MAC Queue CSMA/CA.... MAD timing calculated by MAC = Total Time - T TxAck

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 6 MAD Timing with RTS/CTS Access Packet from head of MAC Queue TxRequest for RTS to PHY Tx Process CSMA/CA Transmit Access Delay == MAD RTS/CTS & Packet Transmission & ACK Time ( T packet _ TxAck ) Optional ACK ACK Received Next Packet from head of MAC Queue CSMA/CA.... MAD timing calculated by MAC = Total Time - T TxAck RTS CTS

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 7 MAD Timing for Packet ReTransmissions

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 8 MAD Measurement Implemented by MAC MAD is easily calculated for any measurement duration and for each access category. Separate MAC queues exist for traffic in each access category. MAC logs and timestamps queue status for each access category MAC logs Tx/Ack time for each PHY access. InterDigital has coded this to work in MAC using Brand A (theros) chipset.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 9 MAD Timing and Priority Queues AC = VI AC = VO AC = BE AC = BG MT logDefer log Access cntr MT logDefer log Access cntr MT logDefer log Access cntr MT logDefer log Access cntr HI LO Access counter counts number of accesses in this access category. TxAck Sum accumulates total time for transmit/ack of each access in this access category. When first packet enters access category queue: MT logs “not empty” timestamp. Defer logs “deferred” timestamp for all lower priority queues. When last packet leaves access category queue: MT logs “empty” timestamp. Defer logs “not deferred” timestamp for all lower priority queues. TxAck Sum Priority

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 10 MAD Calculation for AC where TQ mt = time during which queue for this access category is empty and where TQ def = time during which queue for this access category is deferred to to higher priority queue

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 11 MAD Detects Loads at all TGe Priorities MAD measurement at each access category include traffic loading effects from higher priority access categories which impact the performance of the measured access category. The access delay experienced by BE traffic is impacted by the loading of higher priority access categories. Since BE packets are lower priority than VO, VI or BG packets, the BE access delay values are sensitive to all VO, VI or BG channel loads. While channel is busy for VO, VI or BG, BE backoff is deferred while higher priority accesses continue and thus affects the MAD measurement.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 12 MAD Detects Loads at all TGe Priorities Each beacon interval example yields same MAD result for BE traffic BE BE load with 20 users at rate A 1. 3msec Access Delay BE VI BE load with 10 users at rate A 2. 50% 3msec Access Delay BE HCF 3. 75% 3msec Access Delay VI load with 10 users at rate A BE load with 5 users at rate A VI VO load with 5 users at rate A VO

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 13 New BSS Load IE Similar to TGe QBSS Load but modified for Radio Measurement capable APs Four component elements: New AP Service Load (total load metric for AP) New Access Category Service Load (MAD for each of 4 ACs) Station Count Field, same as TGe Channel Utilization, same as TGe Included in Beacons and Probe Response, like TGe Conditional inclusion of Station Count and Channel Utilization in Beacon and Probe Response to prevent redundant information Included as new Statistics Group in Statistics Report to provide upper layer MIB interface and radio interface

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 14 New AP Service Load Properties Quantized to 8 bits like RSSI & RCPI Based on MAD measurements in AP downlink during contention periods. logarithmic scaling over meaningful range Scaled so min value 1 represents 50usec (DIFS), and max value 253 represents 5.5msec covering a 20.4 db range Special values: 0 = All capacity available (no STAs associated) 254 = no capacity available (not accepting new associations) 255 = AP Service Load not available AP measures MAD over thirty second window; accuracy of +/-200 usec specified with minimum of 200 packets in average Combines AP loading effects of #STAs, Channel Utilization at all priorities and traffic assymetry into SINGLE metric to permit comparison of BSS loading.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 15 New AP Service Load Definition " The AP Service Load shall be a scalar indication of the relative level of service loading at an AP. A low value shall indicate more available service capacity than a higher value. The value 0 shall indicate that this AP is not currently serving any STA. The value 255 shall indicate that the AP Service Load is not available.  If dot11QoSOptionImplemented is true: the values between 0 and 254 shall be set equal to the subfield value for the Average Access Delay for the Best Effort (AADBE) within the Access Category Service Load field.  If dot11QoSOptionImplemented is false: the values between 0 and 254 shall be a logarithmically scaled representation of the average medium access delay for DCF transmitted packets measured from the time the DCF packet is ready for transmission (i.e. begins CSMA/CA access) until the actual packet transmission start time. A value of 1 shall represent a 50 us delay while a value of 253 shall represent a 5.5 ms delay or any delay greater than 5.5 ms. The value 254 shall indicate that DCF services are currently blocked. The AP shall measure and average the medium access delay for all transmit packets using DCF access mechanism over a continuos thirty second measurement window. The accuracy for the average medium access delay shall be +/- 200 usec or better when averaged over at least 200 packets.”

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 16 New Access Category Service Load Definition “The Access Category (AC) Service Load field shall be included in the BSS Load only if dot11QoSOptionImplemented is true. The AC Service load field is formatted as four subfields as shown in Figure kx-2. The AC Service Load shall be a scalar indication of the Average Access Delay (AAD) at a QAP for services for each of the indicated Access Categories. A low value shall indicate shorter access delay than a higher value. If the QAP is not currently providing services at the indicated AC, the AAD for this AC shall be set equal to the AAD of the following AC (located adjacent and to the right) within the Access Category Service field. The value 0 shall indicate that this QAP is not currently providing services of the indicated AC or of any higher priority AC. The values between 0 and 254 shall be a logarithmically scaled representation of the average medium access delay for transmitted packets in the indicated AC measured from the time the EDCF packet is ready for transmission (i.e. begins CSMA/CA access) until the actual packet transmission start time. A value of 1 shall represent a 50 us delay while a value of 253 shall represent a 5.5 ms delay or any delay greater than 5.5 ms. The value 254 shall indicate that services at the indicated AC are currently blocked. The value 255 shall indicate that the AC Service Load is not available. The QAP shall measure and average the medium access delay for all transmit packets of the indicated AC using EDCF access mechanism over a continuos thirty second measurement window. The accuracy for the average medium access delay shall be +/- 200 usec or better when averaged over at least 200 packets.”

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 17 Conclusions TGe QBSS Load does not provide adequate information for comparative load evaluation among neighbor APs. Meda Access Delay measurement does provide useful, comparative metric for traffic loading for each TGe Access Category and for all AP traffic. MAD calculation in MAC is straightforward and does not affect PHY implementations. TGk should incorporate this new BSS Load information into TGk draft.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 18 Motion for Improved Normative Text Move to instruct the editor to incorporate text from document k-BSS_Load_norm_text.doc into next TGk draft specification document Moved by Joe Kwak Seconded by: _______________ Vote YEA _______ Vote NEA _______ ABSTAIN _______ Vote Passes/Fails at ___%

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 19 Background: MAD Simulations Simulation results show how AP Service Load metric relates to Channel Utilization, number of STAs associated and traffic asymmetry. New AP Service load metric permits AP loads to be compared between APs operating under different conditions.

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 20 Simulation Results 1

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 21 Simulation Results 2

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 22 Simulation Results 3

doc: IEEE /0079r1May 2005 Submission Joe Kwak, InterDigital 23