1. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 1 Mandatory TSPEC Parameters and Reference Design of a Simple Scheduler Javier del Prado, Sai Shankar and Amjad Soomro (Philips) Yoshihiro Ohtani and John Kowalski (Sharp) Floyd Simpson (Motorola) Isaac Lim Wei Lih (Matsushita)

2. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 2 Outline Goal Mandatory TSPEC Parameters Simple Scheduler Flexible Admission Control Unit Summary

3. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 3 Goal Provide a reference design for a Simplified Scheduler and Admission Control unit that meets the Minimum Performance Requirements 1 –The reference design should be included as an informative annex Implementers may or may not use it –The Minimum Performance Requirements are normative Allow flexibility to implement different scheduling schemes 1 refer to 02/709r0 for the definition of Minimum Performance Requirements

4. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 4 TSPEC Mandatory Parameters

5. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 5 TSPEC Current TSPEC contains both rate and time based parameters –12 parameters –Allows for any scheduler implementation If polling service is required, few parameters need to be specified –Only 3 mandatory parameters so the scheduler can schedule (see next) –The rest of parameters are optionally specified May be ignored by the scheduler

6. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 6 Mandatory TSPEC Parameters Minimum Set of Parameters to generate a schedule –Mean Data Rate –Maximum Service Interval | Delay Bound –Nominal MSDU Size These parameters shall be different than 0 in the AddTS QoS action response frame when a stream is admitted –If any of the parameters have a value of 0 in the AddTS QoS action request frame sent by the WSTA the HC may reject the stream, Otherwise, the HC shall provide alternative TSPEC parameters to the WSTA in the AddTS QoS action response frame

7. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 7 Mandatory TSPEC Parameters (cont.) The scheduler shall understand this set of parameters –The scheduler may ignore the rest of parameters, even if they are specified Admission Control Unit and Scheduler may use the User Priority value in the TS Info field –If the User Priority is not specified, a default value of 0 shall be used

8. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 8 Who Generates the Mandatory TSPEC Parameters in the WSTA? The parameters in the TSPEC can be set by some entity above the MAC or… They can be generated autonomously by the MAC if polling service is required and the TSPEC parameters are not available from higher layers

9. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 9 A Simple Scheduler

10. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 10 Scheduler Scheduler can be sophisticated or as simple as desired by the implementer –In any case, the scheduler shall meet the Minimum Performance Requirements In this submission we propose the design of a simple scheduler that meets the Minimum Performance Requirements (as defined in a separate presentation)

11. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 11 A Simple Scheduler The simple scheduler uses the minimum set of Mandatory TSPEC Parameters to generate a schedule –Mean Data Rata, Maximum Service Interval and Nominal MSDU Size –Any scheduler may ignore other parameters in the TSPEC for the generation of a schedule

12. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 12 The Simple Scheduler Two parameters need to be calculated to generate a schedule for a stream: 1)Service Interval (SI) 2)TXOP Duration

13. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 13 The Simple Scheduler 1)Service Interval (SI) –Same for all stations –Calculated in two steps: 1.Calculate the Minimum of the Maximum Service Intervals (D) specified for all the admitted TSPECs. Lets call this minimum m 2.Choose a number lower than m that it is a submultiple of the beacon interval Ex: Three streams with Maximum Service Intervals = 60, 65 and 70 ms. The beacon interval is 100 ms. Choose: Service Interval (SI) = 50 ms

14. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 14 Simple Scheduler 2)TXOP Duration –Calculated using Service Interval: SI Mean Data Rate: Nominal MSDU Size: L Physical Transmission Rate: R MSDU of maximum size: M = 2304 bytes Overheads in time: O (PHY + MAC Headers, Interframe spaces, ACKs and Poll*) (see next slide) * Definition of TXOP does not include time for QoS (+) Cf-Poll, however to simplify these slides we consider QoS (+) Cf-Poll within TXOP. TXOP is the complete time spent for transmission from one station TSPEC Parameters

15. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 15 Simple Scheduler 2)TXOP Duration 1.Calculate number of frames N i that arrived during current SI: 2.Calculate TXOP duration: maximum of (1) time to transmit N i frames at R i and (2) time to transmit one maximum size MSDU at R i (plus overheads)

16. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 16 Simple Scheduler - Example First Stream: Stream from QSTA i admitted –Beacon Interval = 100 ms –Maximum Service Interval (D i ) = 60 ms Using steps of slide 12, scheduler calculates SI= 50 ms –Calculate N i and TXOP i during SI TXOP i SI=50ms TXOP i SI

17. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 17 Simple Scheduler - Example Stream from QSTA j admitted –Maximum Service Interval (D j ) = 90 ms (D j SI ) –Calculate N j and TXOP j in SI = 50 ms SI=50ms TXOP i SI TXOP j

18. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 18 Simple Scheduler - Example TXOP k TXOP l Repeat the same process while D new SI E.g.: D k SI and D l SI TXOP j SI=50ms TXOP i SI

19. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 19 Simple Scheduler - Example New stream from QSTA m is admitted and D m < SI –D m = 30 ms –Using steps of slide 12, the scheduler calculates SI = 25 ms (submultiple of beacon interval) –Recalculate TXOP durations for the rest of stations using the new SI (see next slide)

20. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 20 Simple Scheduler - Example TXOP k TXOP l TXOP j TXOP k TXOP l TXOP j TXOP k TXOP l TXOP j SI=50ms TXOP i SI TXOP j SI=25 ms TXOP i TXOP I SI TXOP k TXOP l TXOP m TXOP j TXOP k TXOP l TXOP j TXOP k TXOP l TXOP m

21. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 21 Simple Scheduler - Example If QSTA j finishes service: –Move the TXOPs (k, l …) that come after the removed QSTA: may need to announce schedule again –Or do nothing ( resume contention during that slot, or use that slot for multicast/broadcast …) TXOP k TXOP l TXOP k TXOP l TXOP k TXOP l SI TXOP i SI TXOP k TXOP l TXOP j TXOP k TXOP l TXOP j TXOP k TXOP l TXOP j SI TXOP i SI

22. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 22 Improving the Simple Scheduler This is an informative reference design that meets the Minimum Performance Requirements –An implementation may use different scheme Different modifications can be implemented to improve the performance of the minimum scheduler. E.g: –The scheduler may generate different Service Intervals (SI) for different QSTAs –The scheduler may consider a sandbag factor when calculating the TXOP duration in slide 14 to accommodate for retransmissions –…

23. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 23 Admission Control Unit

24. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 24 Admission Control Unit Use the same parameters –Service Interval - SI –Mean Data Rate - i –Nominal MSDU Size – L i –Physical Transmission Rate - R i –Maximum Size MSDU – M = 2304 –Overheads in Time – O 1)Compute, N i, the number of frames that arrive for the above stream in current SI

25. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 25 Admission Control Unit 2) TXOP i allocated to this Stream in SI is: Beacon Interval Time for EDCF Where k+1 stands for the newly arriving stream and the summation index counts for the streams already admitted and undergoing service from the HC 3) Admission Control Algorithm is:

26. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 26 Admission Control Unit Other Considerations for Admission Control: –Need to respect dot11CAPlimit –Optional % time for retransmissions

27. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 27 Admission Control Unit All admitted streams have guaranteed access to the channel Priority based admission control unit is possible: –Admission Control Unit can examine User Priority Field in TSPEC to decide whether to admit, retain or drop a stream If the User Priority is not specified, a default value of 0 will be used If a higher priority stream needs to be serviced, an admission control unit may drop lower priority streams

28. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 28 Admission Control Unit Vendors choose flavors of the admission control unit –Based on usage scenario enterprise, home, other… –Several approaches allowed

29. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 29 Summary

30. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 30 Summary Proposed informative reference design for a scheduler and admission control unit –Standard should not specify a normative scheduling algorithm or admission control unit –Vendors decide the scheduling algorithm and admission control unit – Based on deployment scenario Minimum performance requirements shall be normative –Allow for testability and compliance Flexible scheduling and admission control unit possible

31. doc: IEEE 802.11-02/705ar0 Submission Javier del Prado et. al November 2002 Slide 31 Motions Move to instruct the editor to incorporate the text in 02/709r0 into the TGe draft Move to instruct the editor to incorporate the text in 02/705r0 into the TGe draft