Re: [AVTCORE] Comments on draft-ietf-avtcore-feedback-supression-rtp-07
Roni Even <Even.roni@huawei.com> Mon, 24 October 2011 14:45 UTC
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Date: Mon, 24 Oct 2011 16:42:25 +0200
From: Roni Even <Even.roni@huawei.com>
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To: 'Magnus Westerlund' <magnus.westerlund@ericsson.com>, 'Qin Wu' <bill.wu@huawei.com>
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Cc: 'IETF AVTCore WG' <avt@ietf.org>, draft-ietf-avtcore-feedback-supression-rtp@tools.ietf.org
Subject: Re: [AVTCORE] Comments on draft-ietf-avtcore-feedback-supression-rtp-07
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Hi Magnus, Maybe we can add a recommendation for SSM to use the round trip sub report block specified in section 7.1.6 of RFC 5760 (http://tools.ietf.org/html/rfc5760 ) to distribute the RTT from the distribution source to the receivers. Roni > -----Original Message----- > From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] On Behalf Of > Magnus Westerlund > Sent: Wednesday, October 19, 2011 11:09 AM > To: Qin Wu > Cc: IETF AVTCore WG; draft-ietf-avtcore-feedback-supression- > rtp@tools.ietf.org > Subject: Re: [AVTCORE] Comments on draft-ietf-avtcore-feedback- > supression-rtp-07 > > Hi, > > Sorry for the delay in following up. > > I have removed the issues which don't need further discussion. > > > On 2011-10-11 03:40, Qin Wu wrote: > > Hi, Magnus, > > Thank for your valuable review, please see my replies belows. > > ----- Original Message ----- > > From: "Magnus Westerlund" <magnus.westerlund@ericsson.com > > > 2. Section 3. > > "The timer value shall be > > based on the observed round-trip time. A receiver should compute > an > > estimate of the round-trip time (RTT) to the sender of TPLR from > RTCP > > report round-trip time if available, or its reception time of the > > reflected RTCP FB message (e.g.,NACK), or any other means." > > > > We hade the discussion before but now that you clarified which RTT to > be > > used, I think it is worth having a discussion if that RTT is the > right > > one. So you suggest that the RTT between the sender of the TPLR and > the > > receiver of the message is the most appropriate to use when > suppressing > > the message. I am not certain that is the case. > > > > Lets consider the use cases. In the case of an intermediary in a > > distribution tree sending the TPLR and at the same time sending a > NACK > > upstream. Then the time until the retransmission reaches the > suppressed > > receiver is the time from the sending of the NACK up to the > > retransmitting entity and all the way down past the TPLR sender to > the > > suppressed receiver. The receiver may not have a true RTT to the > > original media sender as that source appears to live at the TPLR > sender, > > not further upstream. > > > > Yes, the sender of the TPLR and the receiver might at least have > mutual > > knowledge of each other, thus the TPLR sender is able to determine > the > > lowest RTT in the set of receviers thus determining how often to > repeat > > it to cover additional time requried for the upstream part of the > > request. But I do note that these times aren't matching what appear > to > > be the delays in the systems. > > > > Can we find a better solution? > > > > > > [Qin]: It looks to me the round trip time between media source and > > > > intermediary is trivial if we assume the intermediary is much > > > > closer to the source, that is why I put the last paragraph in the > > > > section 3 as follows: > > > > > > > > In order not to incur a lot of NACK requests due to additional TPLR > > > > described above, it is recommended that the RTP system sending > > > > TPLR should be implemented more closer to the source. Also when > > > > the loss was detected and repair initiated much closer to the > source, > > > > the delay for the receiver to recover from packet loss can be reduced > > > > through the combination of intermediary feedback to the source and > > > > Third Party Loss Report downstream. > > > > > > > > > > > > If we look for a better solution, I think we have two possible ways: > > > > The first way is to rely on sender report from media sender to > > > > calculate the more approximate RTT from media sender to the receiver. > > > > RTT measurement method follows the same way described in the > > > > figure 2 of RFC3550. > > > > > > > > The second way is to we can allow the intermediary tell the receiver > the > > > > RTT from media source to intermediary itself by sending a new message > > > > since the intermediary can measure such RTT based on past observation > > > > and estimation. However for the second way we need to define new > > > > message or extend TPLR message to carry such RTT. > > > > > > > > What do you think? > > > > From follow up email: > > Hi,Magnus: As regarding if there is better solution, I have some > > corrections and additional thoughts. > > I think If the media source is the repair server, the receiver should > > set timer to T1=max(the RTT from media source to middlebox sending > > TPLR, 1/2 of RTT from middlebox to receiver) when the receiver > > receives first TPLR. When the receiver receive addtional TPLR within > > T1, the receiver should reset the timer to the RTT from media source > > to middlebox sending TPLR. > > > > If the middlebox is the repair server, the receiver should set the > > timer to T2=1/2 of RTT from middlebox to receiver when the receiver > > receives first TPLR. When the receiver receive addtional TPLR within > > T2, the receiver should reset the timer to the T2. > > > > Can you express these rules for the receiver as something that is based > on what is observable from the RTP and RTCP traffic? Is when media > server being repair server equal to TPLR sender SSRC = Media SSRC the > TPLR applies on? And if they are not the same it is the second case? > > > > > > > > > 3. Section 3: > > "To increase the robustness to the loss of a TPLR or of a > transmission > > packet, a receiver is allowed to receive additional TPLR for the > same > > packet. In the case the first TPLR is lost and the additional > TPLR > > arrives at the receiver, the receiver should immediately refresh > the > > timer." > > > > In the second sentence I don't see how the receiver can know that it > is > > a retransmission. It is simply a TPLR from its perspective if that is > lost. > > > > Robustness reasons is only one reason for repeating them the other is > > clearly to renew the timer. Thus I think the formulation should be > more > > generic to make it clear that all receivers should upon reception of > a > > TPLR refresh the timer for the packets indicated. > > > > > > > > [Qin]: If the receiver does not keep state for the times the TPLR is > > > > retransmitted, we can add repetition count field in each FCI entry > > > > of TPLR feedback message to indicate the times TPLR is > retransmitted. > > > > Particularly in PSLEI Feedback Message, we can reuse seq nr. Field > to > > > > indicate if additional TPLR is retransmitted, which one you think > better? > > > > > > How, can the receiver keep state for something it has not seen due to > the initial packet not having been received? > > I don't think we need new packet extensions, just clarified rules that > correctly describe what the RTP end-point should do when it sees the > TPLR message. > > > > > > 7. Section 4.2: > > Seq nr:8bits Command sequence number. It is used by the Command > > receiver to check if the Command is repeated. The sequence > number > > space is unique for each pairing of the SSRC of command sender > and > > the SSRC of the command receiver. The sequence number SHALL > > increase by 1 modulo 256 for each new Command. A repetition > SHALL > > NOT increase the sequence number. The initial value is > arbitrary. > > > > Based on that it is defined that upon receiving one of the PSLEI > > request, one shouldn't send a FIR or PLI message for a time interval > > equal to the RTT between the receiver and the sender of the PSLEI > > message does the sequence number field have any meaning? From my > > perspective it doesn't matter if it is a new request or not. You are > > suppressed from the reception of the message, nothing else. > > > > [Qin]: I think we can use seq nr field to indicate the times the TPLR > is > > retransmitted, e.g., > > > > If the additional TPLR with the same SSRC and different Seq Number is > > received, the > > > > receiver knows that it is a retransmission if the receiver keeps > state > > for the previous > > > > TPLR with the same SSRC. > > > > Also we can replace seq nr. Field with Repetition count field to > > indicate how many time > > > > the TPLR is retransmitted. > > > > > > That is possible, but is the repetition count really providing > anything? > What is the simplest most straight forward that can work? I think that > is that one simple suppress the source for X time after having receives > a TPLR message indicate that source. So, as long as you get repeat > messages more often than X you continue to be suppressed. Will the > receiver work better to know that it is now suppressed for Y times in a > go because of the same event? > > cheers > > Magnus Westerlund > > ---------------------------------------------------------------------- > Multimedia Technologies, Ericsson Research EAB/TVM > ---------------------------------------------------------------------- > Ericsson AB | Phone +46 10 7148287 > Färögatan 6 | Mobile +46 73 0949079 > SE-164 80 Stockholm, Sweden| mailto: magnus.westerlund@ericsson.com > ---------------------------------------------------------------------- > > _______________________________________________ > Audio/Video Transport Core Maintenance > avt@ietf.org > https://www.ietf.org/mailman/listinfo/avt
- [AVTCORE] Comments on draft-ietf-avtcore-feedback… Magnus Westerlund
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Qin Wu
- Re: [AVTCORE] Comments ondraft-ietf-avtcore-feedb… Qin Wu
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Magnus Westerlund
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Qin Wu
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Roni Even
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Magnus Westerlund
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Magnus Westerlund
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Qin Wu
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Roni even
- Re: [AVTCORE] Comments on draft-ietf-avtcore-feed… Magnus Westerlund