doc: ieee 802.11-02/705ar0 submission javier del prado et. al november 2002 slide 1 mandatory tspec...
TRANSCRIPT
November 2002
Slide 1
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Mandatory TSPEC Parameters and Mandatory TSPEC Parameters and Reference Design of a Simple SchedulerReference 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)
November 2002
Slide 2
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
OutlineOutline
• Goal• Mandatory TSPEC Parameters• Simple Scheduler• Flexible Admission Control Unit• Summary
November 2002
Slide 3
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
GoalGoal• Provide a reference design for a Simplified
Scheduler and Admission Control unit that meets the Minimum Performance Requirements1
– 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
1refer to 02/709r0 for the definition of Minimum Performance Requirements
November 2002
Slide 4
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
TSPECTSPECMandatory Parameters
November 2002
Slide 5
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
TSPECTSPEC• 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
November 2002
Slide 6
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Mandatory TSPEC ParametersMandatory 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
November 2002
Slide 7
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Mandatory TSPEC Parameters (cont.)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
November 2002
Slide 8
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Who Generates the Mandatory Who Generates the Mandatory TSPEC Parameters in the WSTA?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
November 2002
Slide 9
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
A Simple SchedulerA Simple Scheduler
November 2002
Slide 10
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
SchedulerScheduler
• 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)
November 2002
Slide 11
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
A Simple SchedulerA 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
November 2002
Slide 12
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
The Simple SchedulerThe Simple Scheduler
• Two parameters need to be calculated to generate a schedule for a stream:
1)Service Interval (SI)2)TXOP Duration
November 2002
Slide 13
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
The Simple SchedulerThe Simple Scheduler1) 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. Let’s 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
November 2002
Slide 14
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple SchedulerSimple 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
November 2002
Slide 15
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple SchedulerSimple Scheduler2) TXOP Duration
1. Calculate number of frames Ni that arrived during current
SI:
2. Calculate TXOP duration: maximum of (1) time to transmit Ni frames at Ri and (2) time to transmit one
maximum size MSDU at Ri (plus overheads)
ii
i
SIN
L
max ,i ii
i i
N L MTXOP O O
R R
November 2002
Slide 16
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple Scheduler - Example
• First Stream: Stream from QSTA “i” admitted– Beacon Interval = 100 ms
– Maximum Service Interval (Di) = 60 ms • Using steps of slide 12, scheduler calculates SI= 50 ms
– Calculate Ni and TXOPi during SI
TX
OP
i
TX
OP
i
SI=50ms
TX
OP
i
SI
November 2002
Slide 17
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple Scheduler - Example
• Stream from QSTA “j” admitted– Maximum Service Interval (Dj) = 90 ms (Dj SI )
– Calculate Nj and TXOPj in SI = 50 ms
SI=50ms
TX
OP
i
TX
OP
i
TX
OP
i
SI
TX
OP
j
TX
OP
j
TX
OP
j
November 2002
Slide 18
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple Scheduler - ExampleTX
OP
k
TX
OP
k
TX
OP
k
TX
OP
l
TX
OP
l
TX
OP
l
• Repeat the same process while Dnew SI • E.g.: Dk SI and Dl SI
TX
OP
j
TX
OP
j
TX
OP
j
SI=50ms
TX
OP
i
TX
OP
i
TX
OP
i
SI
November 2002
Slide 19
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple Scheduler - Example
• New stream from QSTA “m” is admitted and Dm<
SI– Dm = 30 ms
– Using steps of slide 12, the scheduler calculatesSI = 25 ms (submultiple of beacon interval)
– Recalculate TXOP durations for the rest of stations using the new SI
(see next slide)
November 2002
Slide 20
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple Scheduler - ExampleTX
OP
k
TX
OP
l
TX
OP
j
TX
OP
k
TX
OP
l
TX
OP
j
TX
OP
k
TX
OP
l
TX
OP
j
SI=50ms
TX
OP
i
TX
OP
i
TX
OP
i
SI
TX
OP
j’
SI’=25 ms
TX
OP
i’
TX
OP
I’
TX
OP
I’
SI’
TX
OP
k’
TX
OP
l’
TX
OP
m
TX
OP
j’
TX
OP
k’
TX
OP
l’
TX
OP
j’
TX
OP
k’
TX
OP
l’
TX
OP
m
TX
OP
m
November 2002
Slide 21
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Simple Scheduler - ExampleSimple 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 …)
TX
OP
k
TX
OP
l
TX
OP
k
TX
OP
l
TX
OP
k
TX
OP
l
SI
TX
OP
i
TX
OP
i
TX
OP
i
SI
TX
OP
k
TX
OP
l
TX
OP
j
TX
OP
k
TX
OP
l
TX
OP
j
TX
OP
k
TX
OP
l
TX
OP
j
SI
TX
OP
i
TX
OP
i
TX
OP
i
SI
November 2002
Slide 22
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Improving the Simple SchedulerImproving 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
– …
November 2002
Slide 23
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission Control Unit
November 2002
Slide 24
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission Control Unit• Use the same parameters
– Service Interval - SI– Mean Data Rate - i
– Nominal MSDU Size – Li
– Physical Transmission Rate - Ri
– Maximum Size MSDU – M = 2304– Overheads in Time – O
1) Compute, Ni, the number of frames that arrive for the above stream in current SI
ii
i
SIN
L
November 2002
Slide 25
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission Control Unit
2) TXOPi allocated to this Stream in SI is:
max ,i ii
i i
N L MTXOP O O
R R
1
1
kk i CP
i
TXOP TXOP T T
SI SI T
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:
November 2002
Slide 26
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission Control Unit
• Other Considerations for Admission Control:– Need to respect dot11CAPlimit– Optional % time for retransmissions
November 2002
Slide 27
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission 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
November 2002
Slide 28
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
Admission Control UnitAdmission Control Unit
• Vendors choose flavors of the admission control unit– Based on usage scenario
• enterprise, home, other…
– Several approaches allowed
November 2002
Slide 29
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
SummarySummary
November 2002
Slide 30
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
SummarySummary• 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
November 2002
Slide 31
doc: IEEE 802.11-02/705ar0
Submission
Javier del Prado et. al
MotionsMotions
• 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