1. EDCF TCID, Queues, and Access Parameters Relationship
Month 1998
doc.: IEEE /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
Atul Garg
Philips Semiconductors
San Jose, California
S. Choi, Philips

2. Problem Statement per 802.11e/D1.2
October 2001
Problem Statement per e/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

3. 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

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

5. 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.”
: “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

6. Questionable Descriptions in D1.2
October 2001
Questionable Descriptions in D1.2
: “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

7. October 2001
Proposed Solutions
S. Choi, Philips

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

9. 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

10. 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

11. 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

12. 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