EDCF TCID, Queues, and Access Parameters Relationship Month 1998 doc.: IEEE 802.11-98/xxx October 2001 EDCF TCID, Queues, and Access Parameters Relationship Sunghyun Choi, Sai Shankar, and Javier del Prado Philips Research USA Briarcliff Manor, New York sunghyun.choi@philips.com Atul Garg Philips Semiconductors San Jose, California S. Choi, Philips

Problem Statement per 802.11e/D1.2 October 2001 Problem Statement per 802.11e/D1.2 TCID (from 0 to 7) = priority parameter in MA-UNIDATA.request 802.11e EDCF AP is required to implement at least 4 physical queues. 802.11e ESTA may implement fewer than 8 physical queues. Which queue each frame should be fed to, and how to access channel for each frame? S. Choi, Philips

8 EDCF Access Parameters (AIFS, CWmin, ...) October 2001 Three Mappings >8 Traffic Types M0 8 Priorities = TCID M1 <= 8 Physical Queues M2 8 EDCF Access Parameters (AIFS, CWmin, ...) S. Choi, Philips

October 2001 Goal M1 & M2 should be specified in 802.11e to achieve a fair access by ESTAs M0 is out of the scope of 802.11e Refer to other spec, e.g., 802.1d Annex H.2 S. Choi, Philips

Problematic Descriptions in D1.2 October 2001 Problematic Descriptions in D1.2 9.1.1: “A station may implement fewer than 8 physical queues and provide a mapping from traffic categories to the available queues.” 9.2.3.4: “An EDCF station that provides fewer than 8 output queues shall use the TxAIFS[TC] slot boundary for queue[i] where TC is the highest priority TC assigned to queue[i].” What happens if a STA assigns TC=0-7 to one queue when it knows that it will need to serve TC=0 frames only? TC=0 frames will be served using TC=7 parameters!!! S. Choi, Philips

Questionable Descriptions in D1.2 October 2001 Questionable Descriptions in D1.2 9.2.3.4: “A STA using the EDCF shall be allowed a transmit opportunity (TxOP) for a particular Traffic Class (TC) if its carrier sense mechanism (see 9.2.1) determines …” 9.10: “ESTAs may transmit multiple frame exchange sequences within these TXOPs, as well as in {E}DCF TXOPs under HCF, subject to the limit of TXOP duration.” What happens if you have frames of different TCs in one queue? Are you allowed to transmit these frames in one TXOP limit? S. Choi, Philips

October 2001 Proposed Solutions S. Choi, Philips

M1: TCID -> Queue Number October 2001 M1: TCID -> Queue Number Reference: 802.1d-1998 Table 7-2 S. Choi, Philips

M2: Queue -> Access Parameters October 2001 M2: Queue -> Access Parameters Use access parameters of the frame at the head of the queue. By using this mapping, we can make M1 a recommended practice. S. Choi, Philips

October 2001 EDCF TXOP Operation During an EDCF TXOP, ESTA may transmit multiple frames from the same physical queue. After the final frame within an EDCF TXOP, the post back-off for the queue will be done using: the access parameters, used for the TXOP acquisition, if the queue is empty, or the access parameters, corresponding to the frame at the head of the queue, if the queue is non-empty. S. Choi, Philips

October 2001 EDCF TXOP Operation During an EDCF TXOP, ESTA may transmit multiple frames from the same physical queue. After the final frame within an EDCF TXOP, the post back-off will be done using: the access parameters, used for the TXOP acquisition, if all the queues are empty, or the access parameters, corresponding to the next frame to be transmitted, if there is any non-empty queue. S. Choi, Philips

Number of Queues Comparison October 2001 Number of Queues Comparison Implementing smaller number of queues may degrade the performance of the high priority frames. It may upgrade the performance of the low priority frames though. S. Choi, Philips