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Re: [STDS-802-11-TGBE] [EXTERNAL] Re: [STDS-802-11-TGBE] [Suspected Marketing Mail] [STDS-802-11-TGBE] 11-20/1045: "prioritized EDCA channel access" discussion



Hi, John:

 

Sorry for the late reply. Thanks for your question. See inline.

 

Thanks.

Chunyu

 

From: Wullert, John R II <jwullert@xxxxxxxxxxxxxxxxx>
Sent: Thursday, August 27, 2020 10:45 AM
To: 'Chunyu Hu' <chunyuhu07@xxxxxxxxx>; STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
Subject: RE: [EXTERNAL] Re: [STDS-802-11-TGBE] [Suspected Marketing Mail] [STDS-802-11-TGBE] 11-20/1045: "prioritized EDCA channel access" discussion

 

Chunyu,

   Thanks for the presentation.  I also had some questions:

  • You describe the traffic as being bursty/periodic.  What type of traffic are you envisioning fits this model?  I can see where the downstream video portion of AR/VR would fit this model.  What about the upstream aspects of AR/VR? They would have similar latency requirements and be bursty, but I would not expect them to be so periodic?

 

[Chunyu:] we think majority of applications that requires low latency as well as small jitter can be well modelled as periodic, and bursty; or served so such that they can enjoy a more predictable latency performance. It also has additional power saving benefit

For the upstream of AR/VR applications, it also has such characteristics. E.g. IMU, camera, sensor captured data. They may not have exact the same period. But often, the application has to be designed at system level, and a system level of pipeline helps optimize overall performance. The multiple (DL/UL or within either direction) traffic streams can be grouped into one or two or few periodic streams as results.

There are quite some literatures online, e.g. [link].

 

  • Related question – Does the traffic really need to be periodic?  The AP is effectively allocating periodic resources to ensure that the a slot is available to meet the latency constraints.  It seems to me that non-periodic traffic would just tend to waste more of these slots. (not great to waste, but the approach would still help meet the latency objectives.)

 

[Chunyu:] agree not all traffic are periodic. The P-slots/schedule are intended for periodic/latency-sensitive traffic  that has non-trivial amount of bandwidth requirement.

The non-periodic doesn’t need to operate on slot boundary in a time zone where none of slots are P-slots.  Efficiency is sacrificed mostly at the R/P-slot boundaries.

 

  • Are you expecting that access to this capability would be restricted in any way?  Would any non-AP STA be allowed to invoke this, or would there be infrastructure to restrict this (e.g., make it a paid-for extra service in public Wi-Fi networks)?

 

[Chunyu:] yes, we can surely consider this and provide means for network operator/AP owners to configure in their deployment.

E.g. this can be achieved by AP announces maximum total time allocated to P-slots, and/or maximum # of slots assigned to each TC or STA.

Welcome for contributions discussing this aspect.

 

Thanks,

 

John

 

 

From: Chunyu Hu <chunyuhu07@xxxxxxxxx>
Sent: Thursday, August 27, 2020 11:41 AM
To: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] Re: [STDS-802-11-TGBE] [Suspected Marketing Mail] [STDS-802-11-TGBE] 11-20/1045: "prioritized EDCA channel access" discussion

 

Hi, Zhijie:

 

Thanks for the questions. See inline.

 

Chunyu

 

On Wed, Aug 26, 2020 at 7:20 PM Yang, Zhijie (NSB - CN/Shanghai) <zhijie.yang@xxxxxxxxxxxxxxx> wrote:

Hi Chunyu,

 

Let’s continue our discussion here.

 

Q1:  slide12: the current txop should end at the boundary. If retransmission happened during the TXOP, it means retransmission also need to be stopped even if it is not up to the max retransmission times?

 

A: correct. retransmission follows the same rule.

 

 

Q2: I remember Yonghong ask the question about the OBSS, I have a similar question on it. How do you consider the compatibility with legacy devices, including legacy AP and legacy STA?

      For instance, for the legacy AP, it can’t decode the new signaling sent from P-EDCA AP, and how the legacy STA connected to P-EDCA AP get the transition opportunity compared to P-EDCA STA?

 

 A: For the OBSS, it would have the requirement that the neighboring BSSs understand the same protocol however STAs within OBSS doesn't need to track every slot boundary. Additional OBSS coordination can be designed (see the slot information format design --> information bitmap that contains OBSS) such that BSS informs each other the protected time periods in its own TSF time domain. It's some work we can extend to. 

 

 

Q3: slide19, simulation results: What’s the SNR do you set? What’s the simulation results if set different SNR on each STA? Do you enable MPDU and MPSU aggregation for VO traffic? Because we don’t do any aggregation for VO traffic in practice because of low latency reason.

 

A: in this set of simulation, rate is fixed and every STAs can hear each other. No hidden terminal situation is simulated. We are mostly focusing on the protocol effectiveness here.

MSDU agg is ON: 2 MSDUs per A-MSDU. A-MPDU is on and BA window of 64 is used -- for all three schemes (VO uses txop limit 0). We set txop limit to 0 for VO for a fair comparison and mean to demonstrate that using an aggressive CW/AIFSN doesn't solely solve the problem.

 

 

Q4: If a STA has some higher priority traffic, How AP to allocate the time slot if AP find the RSSI of STA is very bad? If AP allocates too much time slot for it, it will harmful for the total TP.

How do you consider in such scenario?

 

A: the requester and granter need to take into account their link operating state: that includes their tx/rx capability, rssi, traffic, to request reasonable amount of time in slots. In practice, one can go through some probing stage to start the initial assignment. It may need to do so with some margin to tolerate traffic/channel dynamics. It may need to adjust assignment as traffic/channel vary over time but hopefully at slow pace.

 

 

 

 

 

 

Thanks

 

Best Regards

 

Jay Yang

 

From: Chunyu Hu <chunyuhu07@xxxxxxxxx>
Sent: 2020827 0:09
To: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
Subject: [Suspected Marketing Mail] [STDS-802-11-TGBE] 11-20/1045: "prioritized EDCA channel access" discussion

 

Hi, all:

 

Starting a thread for Q/A for the doc 11-20/1045r3 to cover remaining Q/As.

I captured Jay, Mohamed, Liangxiao, and Sharan. Other please also feel free to ask questions here or send me separate emails.

 

Thanks.

Chunyu


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