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Doc. :IEEE 802.11-02/314r0 Submission Sai Shankar et al., Philips ResearchSlide 1 May 2002 TXOP Request: in Time vs. in Queue Size? Sai Shankar, Javier.

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Presentation on theme: "Doc. :IEEE 802.11-02/314r0 Submission Sai Shankar et al., Philips ResearchSlide 1 May 2002 TXOP Request: in Time vs. in Queue Size? Sai Shankar, Javier."— Presentation transcript:

1 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 1 May 2002 TXOP Request: in Time vs. in Queue Size? Sai Shankar, Javier del Prado and Sunghyun Choi Philips Research USA Briarcliff Manor, New York

2 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 2 May 2002 Outline QoS Control Field - Overview Problem Statement: Making a TXOP Request TXOP Requests in time TXOP Requests in Queue Size Conclusions

3 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 3 May 2002 References Bobby Jose, “Contention Free TXOP Request and Allocation Issues,” IEEE /248r0 Bobby Jose, “Updated QoS Control Field,” IEEE /290r0 IEEE e QoS draft D2.0a

4 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 4 May 2002 QoS Control Field - Overview ·16 bit field Bits 0-8 represent either: –TXOP limit in the Poll Frame –TXOP duration request or queue size information (in QoS data, QoS Null and RR frames) Bit 9, 10, 11 identities FEC, non final and no Ack respectively Bits identifies TID

5 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 5 May 2002 Making a TXOP Request A QSTA can request for Bandwidth Allocation using the QoS control field: –Request can be in time: TXOP duration in units of 16  seconds –Or based on queue size (units of 128 octets) What are the advantages of each request method? Do we need both methods?

6 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 6 May 2002 TXOP Requests in Time Time requests simplifies the problem of the scheduler at the HC/QAP - just grant the bandwidth in time to QSTA if available May not be optimal as requests can be arbitrary However, an scheduling algorithm based on “time requests” can not be optimal

7 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 7 May 2002 TXOP Requests in Time Increases computational complexity at the QSTA as it has to determine the time required depending on the queue size. Need to consider: Data rate Frame length Fragmentation Additional problem: Is the TXOP duration requested for aggregated frames or for a single frame? If TXOP duration requests are for aggregated frames, how does one evaluate the minimum TXOP duration? Need mechanism to determine if the TXOP duration request is for a single frame Parameters that vary during time. Even within the same TXOP

8 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 8 May 2002 TXOP Requests in Time - Scales 9 bits available for the request. Bit 9 indicates if it is time or queue size. Only 8 available The maximum TXOP duration that can be requested up to day is milliseconds (very less) We need two scales: –Of the 8 bits 1 bit should set aside to clarify the scale of the request being made: If bit 8 equal to 0: scale of 32  sec (32  sec -> 4096  sec) If bit 8 equal to 1: scale of 256  sec (256  sec ->  sec)

9 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 9 May 2002 TXOP Requests based on Queue Length QSTA need NOT determine the time required, so simple at QSTA side. Scheduler at HC needs to determine the TXOP time to be allocated using the queue size information, so the complexity is passed to the HC/QAP side. An scheduling algorithm based on queue size may be optimal if the HC has some information regarding the traffic characteristics Main Problems at HC side are –Determining Rate (Transmission rate from QSTA to HC) –Determining Fragment Size (Based on Queue length as there may be more than one fragments. This may vary frame to frame)

10 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 10 May 2002 TXOP Requests based on Queue Length Problem for Prioritized QoS: –If Parameterized QoS, the HC knows information regarding the stream (minimum rate, nominal MSDU/MPDU size). This is necessary to compute TXOP duration based on queue size information –If Prioritized QoS, the HC does not know which is the nominal MSDU size - so difficult to determine TXOP duration. However the HC can “monitor” the traffic from a QSTA an easily determine the frame/fragment size and the data rate used.

11 doc. :IEEE /314r0 Submission Sai Shankar et al., Philips ResearchSlide 11 May 2002 Conclusions An scheduling algorithm based on “queue size” can be optimal. TXOP requests in time can be arbitrary. The scheduling algorithm will always be sub-optimal. Change all the requests to bytes. Having two methods to request a TXOP can be confusing and complicated to implement.


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