Hi Rubayet,
Thanks for your questions, please see my response below in-line.
Regards,
Yunbo
发件人: Rubayet Shafin [mailto:r.shafin@xxxxxxxxxxx]
发送时间: 2022年4月12日
22:04
收件人: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx; Liyunbo <liyunbo@xxxxxxxxxx>
主题: Re: [STDS-802-11-TGBE]
答复: [STDS-802-11-TGBE] 答复: [STDS-802-11-TGBE] 11-22-0349-02-00be-cr-discussion-of-nstr-and-emlsr
Hi Yunbo,
Thank you for the contribution.
A couple of quick questions--
-
What is the "Blindness period" (5.484ms) in the simulation parameters in slide 6?
[Yunbo] the number is default value of MediumSyncDelay timer in the spec, please see below
text.
“The MediumSyncDelay timer is a single timer, shared by all EDCAFs within a non-AP STA, which is initialized to aPPDUMaxTime defined
in Table 36-70 (EHT PHY characteristics).”
-
What is the definition used for traffic load (%) in slide 7?
[Yunbo] The traffic load = the time occupied by frame transmission / the total simulation time. Please notice that these are rough estimated values which assumes no collision happens and there are certain number of
MPDUs in each A-MPDU.
Best
Rubayet
From: Liyunbo <00001846a2e5e0c1-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Sunday, March 27, 2022 9:40:15 PM
To: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-11-TGBE] 答复: [STDS-802-11-TGBE]
答复: [STDS-802-11-TGBE]
答复: [STDS-802-11-TGBE] 11-22-0349-02-00be-cr-discussion-of-nstr-and-emlsr
Hi Shubho,
Thanks for your further discussion. I still don’t agree with your opinion.
You are saying that although non-AP MLD can not transmit or receive, but it may still capable of “listen”, so it can still perform CCA. I think “listen”
is a type of receive with limited functions, so “no receive” means “no listen”. “shall not transmit or receive on the other EMLSR link(s)”
in the spec clearly means no CCA on the other EMLSR link(s).
Regards,
Yunbo
发件人: Shubhodeep Adhikari [mailto:00000c144a46bcee-dmarc-request@xxxxxxxxxxxxxxxxx]
发送时间: 2022年3月26日
16:12
收件人:
STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
主题: Re: [STDS-802-11-TGBE]
答复: [STDS-802-11-TGBE] 答复: [STDS-802-11-TGBE] 11-22-0349-02-00be-cr-discussion-of-nstr-and-emlsr
Hi Yunbo,
Thanks for the discussion. I have embedded comments.
[Yunbo] I think “no receive” means blind. Firstly no receive means the EMLSR STA can not do PD at all, if you argue that it still may do ED at this stage. I don’t agree
ED equals to CCA.
[Shubho] A non-AP in EMLSR mode can transmit and receive on one link at a time. If “no receive” means blind as you interpret, then such a non-AP will be blind all the time on all
but a single link. Clearly this is not the case, as the non-AP, in addition to transmit and receive, can “listen” on all EMLSR links and the spec states that “The listening operation
includes CCA”.
So, the non-AP is not blind whenever it can listen.
[Yunbo] The spec already clearly say it can not do CCA during the transition delay period. From below sentences, you can see the listening operation happens after transition
delay.
[Shubho] The spec says the following “The non-AP MLD shall be switched back to the listening operation on the EMLSR links after the time indicated
in the EMLSR Transition Delay”
This sentence refers to the
entire “non-AP MLD”
switching back to listening i.e. a state where all its affiliated STAs on EMLSR links go back to listen operation. This clause (of which the above sentence is a part) defines 3 phases of EMLSR operation:
?
Phase 1: The non-AP MLD is in listen mode i.e. all its affiliated STAs on EMLSR links are listening on their respective links.
?
Phase 2: When one of the STAs affiliated to the non-AP MLD receives an initial control frame directed to it, that particular STA switches from listen
to transmit/receive. The spec only mentions that the other affiliated STA(s) cannot transmit/receive, but does not rule out listen.
?
Phase 3: The non-AP MLD switches back to listen on EMLSR links i.e. the same mode as in Phase 1.
[Yunbo] Can you explain the difference of EMLSR STA’s capability in DL procedure (with initial control) and untriggered UL transmission. Why
a EMLSR MLD can not transmit and receive on link 2 after receiving an initial control in link1, but it suddenly can transmit and receive on link2 when it initial a transmission on link1 by itself?
[Shubho] What I said is that the clause/section that you had cited does not apply for untriggered UL transmissions. For such transmissions, the following
clauses apply:
?
“When a STA of the non-AP MLD initiates
a TXOP the following applies: The non-AP MLD shall switch back to the listening operation on the EMLSR links after the time duration indicated in the EMLSR Transition Delay subfield after the end of the TXOP.”
?
“NOTE 3―A STA affiliated with a non-AP MLD operating in the EMLSR mode does not need to transmit an initial Control frame to initiate frame
exchanges with the AP MLD …”
The key difference here is that the non-AP may not need an initial control frame (and so only
EMLSR Transition Delay and no EMLSR Padding Delay). Further, there will be non-APs in EMLSR mode that will set
EMLSR Transition Delay to 0 us. If this happens, untriggered UL transmissions will have no additional control overhead at all.
Regards,
Shubho
On Sat, Mar 26, 2022 at 8:55 AM Liyunbo <00001846a2e5e0c1-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:
Hi Shubho,
Thanks for your discussion. Please see my response below in-line.
Regards,
Yunbo
发件人: Shubhodeep Adhikari [mailto:00000c144a46bcee-dmarc-request@xxxxxxxxxxxxxxxxx]
发送时间: 2022年3月26日 3:28
收件人: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
主题: Re: [STDS-802-11-TGBE] 答复: [STDS-802-11-TGBE] 11-22-0349-02-00be-cr-discussion-of-nstr-and-emlsr
Hi Yunbo,
Thanks for your response.
The EMLSR spec text that you have quoted specifies “shall not transmit or receive”. So, this allows a non-AP in EMLSR mode to listen on one link during frame exchanges on the other link, depending on the non-AP architecture. It also allows a non-AP to declare 0 us for one or both of EMLSR Padding Delay and EMLSR Transition Delay. Even if they are > 0 us, the specification doesn’t say that the non-AP isn’t able to perform CCA during the entire duration of the EMLSR Padding Delay and EMLSR Transition Delay.
[Yunbo] I think “no receive” means blind. Firstly no receive means the EMLSR STA can not do PD at all, if you argue that it still may do ED at this stage. I don’t agree ED equals to CCA. It will be unfair to say that an STA only do ED is sync with the medium. BTW, the spec also not clarify whether ED can be done in link2 while link 1 is in TX/RX mode.
The spec already clearly say it can not do CCA during the transition delay period. From below sentences, you can see the listening operation happens after transition delay.
The non-AP MLD shall be switched back to the listening operation on the EMLSR links after the time indicated in the EMLSR Transition Delay subfield of the EML Capabilities subfield in the Common Info field of the Basic Multi-Link element if any of the following conditions is met and this is defined as the end of the frame exchanges
The non-AP MLD shall switch back to the listening operation on the EMLSR links after the time duration indicated in the EMLSR Transition Delay subfield after the end of the TXOP.
Further, the clause “shall not transmit or receive” is conditional on “After receiving an initial Control frame”. So, it does not apply for untriggered UL transmissions.
[Yunbo] Can you explain the difference of EMLSR STA’s capability in DL procedure (with initial control) and untriggered UL transmission. Why a EMLSR MLD can not transmit and receive on link 2 after receiving an initial control in link1, but it suddenly can transmit and receive on link2 when it initial a transmission on link1 by itself?
On blindness, the specification mentions only the following for a non-AP in EMLSR mode: If it loses medium synchronization due to a) not being able to perform CCA on an EMLSR link during frame exchanges on another EMLSR link and b) if this duration of loss of medium synchronization is longer than aMediumSyncThreshold, it shall perform medium sync recovery. So, if a non-AP is able to do CCA on a link for all durations > aMediumSyncThreshold, it is not considered blind.
[Yunbo] it can not perform CCA during the frame exchanges (include both TX and RX) not only TX, and any frame exchange will larger than aMediumSyncThreshold. So link 2 will always enter blindness mode once link1 is switch to TX/RX mode.
When a non-AP MLD is operating in the EMLSR mode, a STA affiliated with a non-AP MLD that is operating on one of the EMLSR links is considered to have lost medium synchronization if it is not able to perform CCA during frame exchanges that includes the link switch delays between an AP affiliated with an AP MLD and one of the other STAs operating on the other EMLSR links, which are affiliated with the same non-AP MLD.
Given the above, the EMLSR specification is flexible enough to allow non-AP architectures that have the same blindness behavior as NSTR.
Regards,
Shubho
On Fri, Mar 25, 2022 at 9:02 AM Liyunbo <00001846a2e5e0c1-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:
Hi Shubho,
Thanks for your questions. Please find my response below in-line.
Regards,
Yunbo
发件人: Shubhodeep Adhikari [mailto:00000c144a46bcee-dmarc-request@xxxxxxxxxxxxxxxxx]
发送时间: 2022年3月24日 22:20
收件人: STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
主题: Re: [STDS-802-11-TGBE] 11-22-0349-02-00be-cr-discussion-of-nstr-and-emlsr
Hi Yunbo,
Thanks for initiating the email discussion.
I think there is a difference of understanding among us on the capabilities of an EMLSR non-AP.
You seem to be assuming the following for an EMLSR non-AP:
・ It requires a switching delay for all of the following transitions.
o (Listen -> Receive) and (Receive -> Listen)
o (Listen -> Transmit) and (Transmit -> Listen)
・ It becomes blind on one link during all of the above transitions and also during either Receive or Transmit.
This is a very conservative assumption. The EMLSR specification too does not mandate such blindness. I have explained my understanding below.
Untriggered UL transmissions: It is very much possible to have EMLSR architectures where the non-AP will not require any switching delay, either for (listen -> transmit) or (transmit->receive). So, there is no blindness unless the UL PPDU duration is > 72us. Note that the EMLSR specification too does not define any switching delay for untriggered UL transmissions.
[Yunbo] I don’t agree with you. Below text in the spec shows that when a link 1 is in TX/RX mode, link 2 will be blind until the frame exchanges finished and switch back finished. It means that in your below figure, link2 will be in blind from t1 to t6, and also the switch back period.
After receiving the initial Control frame of frame exchanges (#7336)(#5933)and transmitting an immediate response frame as a response to the initial Control frame, a STA affiliated with the non-AP MLD that was listening on the corresponding link shall be able to transmit or receive frames on the link in which the initial Control frame was received and shall not transmit or receive on the other EMLSR link(s) until the end of the frame exchanges, and subject to its spatial stream capabilities, operation mode, and link switch delay, the STA affiliated with the non-AP MLD shall be capable of receiving a PPDU that is sent using more than one spatial stream (#6658)on the link in which the initial Control frame was received a SIFS after the end of its response frame transmission solicited by the initial Control frame.
The non-AP MLD shall be switched back to the listening operation on the EMLSR links after the time indicated in the EMLSR Transition Delay subfield of the EML Capabilities subfield in the Common Info field of the Basic Multi-Link element
The non-AP MLD shall switch back to the listening operation on the EMLSR links after the time duration indicated in the EMLSR Transition Delay subfield after the end of the TXOP
DL transmissions: It is very much possible and allowed by the specification to have EMLSR architectures where the non-AP will not have any blindness during DL, except for transmissions of CTS/BA which can typically be <72us. As an example, I have drawn below a DL frame exchange and marked the instances where an EMLSR non-AP may require switching delays and EMLSR blindness.
[Yunbo] see my response above, you can not only count CTS and ACK period for blind.
From the above it is observed that the EMLSR non-AP,
・ Is blind on link2 only during transmission of CTS and BA. However, since both of these can be < 72us, the EMLSR non-AP need not perform any blindness recovery.
[Yunbo] don’t agree. Link 2 will be blind from t1 to t6.
・ Requires a delay (t2-t1) to switch from (listen->receive), but is not blind on any link (either link1 or link2) during the switch.
[Yunbo] how link2 could still receive packet during switch period (from t1 to t2)? it is hard to understand.
o In a less capable non-AP architecture, the EMLSR non-AP may become blind for a sub-interval of [t1, t2], but it does not have to perform blindness recovery if this sub-interval is < 72us and the non-AP is able to listen on link2 during [t2, t3].
[Yunbo]below sentence shows that link 2 shall not receive frames during [t2 t3]
After receiving the initial Control frame of frame exchanges (#7336)(#5933)and transmitting an immediate response frame as a response to the initial Control frame, a STA affiliated with the non-AP MLD that was listening on the corresponding link shall be able to transmit or receive frames on the link in which the initial Control frame was received and shall not transmit or receive on the other EMLSR link(s) until the end of the frame exchanges, and subject to its spatial stream capabilities, operation mode, and link switch delay, the STA affiliated with the non-AP MLD shall be capable of receiving a PPDU that is sent using more than one spatial stream (#6658)on the link in which the initial Control frame was received a SIFS after the end of its response frame transmission solicited by the initial Control frame.
・ Does not require any delay to switch from (receive->listen) at the end of DL frame exchanges.
[Yunbo] yes, a switch delay is needed from receive to listen.
The non-AP MLD shall be switched back to the listening operation on the EMLSR links after the time indicated in the EMLSR Transition Delay subfield of the EML Capabilities subfield in the Common Info field of the Basic Multi-Link element
The non-AP MLD shall switch back to the listening operation on the EMLSR links after the time duration indicated in the EMLSR Transition Delay subfield after the end of the TXOP
Triggered UL transmissions: Is similar to DL, except that if the UL PPDU duration > 72us, the EMLSR non-AP will become blind and has to perform blindness recovery. This will be applicable for NSTR too.
That is why I had mentioned during the call yesterday that since an EMLSR non-AP has 2 receive chains it is very much possible to have EMLSR architectures where the non-AP does not have any additional blindness over what is present for an NSTR non-AP.
[Yunbo] I think we have very different understanding about EMLSR mode, please see my above response. Further discussions are welcome.
Regards,
Shubho
On Thu, Mar 24, 2022 at 4:34 AM Minyoung Park <mpark.ieee@xxxxxxxxx> wrote:
Hello Yunbo,
As I commented during the call, you are not doing apple to apple comparison. A NSTR MLD has two fully capable radios (two independent PHY/MAC blocks) whereas a single radio non-AP MLD operating in EMLSR has one fully capable radio. The NSTR MLD is close to double the complexity/cost of the non-AP MLD that has the EMLSR capability. The complexity/cost has to be considered in the comparison.
Another observation is that a NSTR non-AP MLD with two 1x1 radios is actually less spectral efficient than 2x2 non-AP MLD in EMLSR mode since the NSTR non-AP MLD is using two 80 MHz links with 1ss on each link whereas the non-AP MLD in EMLSR mode is using one 80 MHz link with 2ss. For a busy network environment with many OBSSs that are not synchronized on both links (i.e. busy/idle are not synchronized on both links), this becomes a bigger problem to the NSTR non-AP MLD since most of time the two links are not idle at the same time and only 1ss can be used on one idle link whereas for the non-AP MLD in EMLSR mode it can still use 2ss on one idle link.
I also couldn't understand clearly why delay results are so high. There will be many cases where a STA can sync to the medium by receiving a frame from its own BSS or OBSS, by transmitting an RTS based on the current 11be spec, perform CCA if a STA is not doing 2ss tx, soliciting uplink traffic with a trigger frame, etc.
Regards,
Minyoung
On Wed, Mar 23, 2022 at 9:48 AM Liyunbo <00001846a2e5e0c1-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:
Dear all,
Thanks for your discussion during the presentation. I initiate this email thread to further discussion for doc 22/349. Please let me know your questions and comments if you don’t have time to express them during the call.
Here are some response to Minyoung and Shubho’s questions.
Q1: Whether switch delay of EMLSR affect the blindness in UL short PPDU transmission?
A1: when EMLSR MLD do UL transmission on link1, whether link 2 will enter blindness mode depends on the total duration of switch delay period and UL PPDU length. Assuming the UL PPDU length is 50 us, a 22 us switching delay (22+50=72us, which is the duration of MediumSyncThreshold) will trigger link 2 enter blindness mode. So you can see that link 2 will enter blindness mode even it is a small switching delay and short UL PPDU.
Q2: For blindness, can EMLSR be same as NSTR?
A2: No. For DL data transmission, NSTR will not enter blindness mode because most BA will shorter than 72us. But EMLSR will enter blindness for sure, because the initial control frame exchange already larger than 72us. For UL short packet transmission, NSTR will enter blindness when UL PPDU length >=72us, while EMLSR will not enter blindness when UL length >= (72-swithing delay). Consider the PHY preamble and switching delay, you can see that EMLSR will very easy to enter blindness even for short UL packet.
Q3: Why complexity is not considered in the presentation?
A3: The main purpose of this presentation is to show the performance of EMLSR and NSTR. Because performance is a very important factor for people to judge a feature. For complexity, I don’t think it is an easy to compare, it relates to a lot of implementation details. Here I want to point out one more benefit of NSTR. There are full radios on both links for NSTR, so it is very flexible for a non-AP MLD to operate as STR (when AP MLD set up two links with enough frequency gap) or NSTR (when AP MLD set up two links very close). But EMLSR MLD can not switch between STR and EMLSR even AP set up two links with enough frequency gap.
Regards,
Yunbo
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