Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-ietf-avtcore-multi-party-rtt-mix-18: Answer 4.
Gunnar Hellström <gunnar.hellstrom@ghaccess.se> Wed, 26 May 2021 07:40 UTC
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To: Benjamin Kaduk <kaduk@mit.edu>
Cc: The IESG <iesg@ietf.org>, draft-ietf-avtcore-multi-party-rtt-mix@ietf.org, avtcore-chairs@ietf.org, avt@ietf.org, bernard.aboba@gmail.com
References: <162139279927.706.12647899386073526674@ietfa.amsl.com> <db3446ad-b3c5-53b9-d8f6-f3480907999d@ghaccess.se> <20210526002319.GD32395@kduck.mit.edu>
From: Gunnar Hellström <gunnar.hellstrom@ghaccess.se>
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Date: Wed, 26 May 2021 09:39:53 +0200
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Subject: Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-ietf-avtcore-multi-party-rtt-mix-18: Answer 4.
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Hi Ben, Thank you for the kind words. The inserted words about packets out-of-order that you did not find in version -19 are there, but in the beginning of section 3.16.2, instead of in 3.16.3 where you expected to find them. Please see furthe comments inline. Den 2021-05-26 kl. 02:23, skrev Benjamin Kaduk: > Hi Gunnar, > > On Tue, May 25, 2021 at 12:29:51PM +0200, Gunnar Hellström wrote: >> Benjamin, >> >> Continuing the answers with the last part., > Thank you for going through them all. To be clear, I was not waiting for > you to finish before I started replying -- I just had a deadline earlier > today and did not have a chance to do much with my email sooner. Having > the content chunked up into multiple pieces can make it easier to manage. > > This is the only message I'm going to respond to, though, since I basically > have nothing further to say. (I've already updated my ballot position to > remove the Discuss.) I'm really impressed with how you took my comments > and turned them into improved text in the document, especially in the > places where I did not have a clear proposal. I also appreciate your > explanations in the places where my questions did not make sense or are > already covered by some of the fundamental documents in this space; the > gaps in my knowledge are slowly getting filled in. > >> Den 2021-05-19 kl. 04:53, skrev Benjamin Kaduk via Datatracker: > [...] >> [GH]Again, thanks for a thorough review and many good proposals for changes. > I must thank you again for your thorough responses; I feel like I am not > doing them justice by only sending this one short note, but do not want to > make you read through a repetitive set of "yes", "this sounds good", "thank > you", etc. > > I read through the changes in the already-uploaded -19 (thank you again!), > and there were only two items that might be worth following up on (both in > section 3.16.3 of the -19): > > You had proposed: > > [GH] Would it be sufficient to insert the words "and reordering" in the > first two sentences in the paragraph to read: "The receiver SHALL monitor > the RTP sequence numbers of the received packets for gaps and packets > out of order. If a sequence number gap appears and still exists after some > defined short time for jitter and reordering resolution, the packets in the > gap SHALL be regarded as lost." > > I don't think this made it into the -19; my preference is to use your > proposed text that includes mention of reordering, but I do not insist on > it. [GH] They are there, in 3.16.2, where basic packet reception and gap analysis is specified. it says: " The receiver SHALL monitor the RTP sequence numbers of the received packets for gaps and packets out of order. If a sequence number gap appears and still exists after some defined short time for jitter and reordering resolution, the packets in the gap SHALL be regarded as lost. " This is intended to require that packets are in order when they go to the loss analysis and data retrieval stages. Very late packets out-of-order would be regarded lost. When you said that you could imagine cases of duplication, did you then imagine a procedure which would recover text also from late coming packets after the short time mentioned in the paragraph above? It would be possible, but I do not think it should be part of the general document, because it would possibly mean manipulating display buffers already presenting earlier received text. I have created a paragraph for that, that can follow the first in 3.16.2, but I do not think it adds any value to insert it. What do you think? " Advanced procedures for recovering data from packets received out of order later than the short time for jitter and reordering resolution mentioned above MAY be implemented but are out of scope for this document. Such procedures would need to manipulate data in receive buffers and possibly also in presentation areas. The procedures MUST avoid duplication of already received data." > > There was also a mention about the procedures for extracing T140blocks with > the redundancy procedure, where we currently say "T140blocks SHALL be > extracted in the following way. The description is adapted to the default > redundancy case using the original and two redundant generations." While I > am inclined to agree that the extension to the generic case with other > levels of redundancy is something that the reader can be expected to > perform, it feels a little incomplete to say that something "SHALL be > [done] in the following way" but give a not-complete/not-generic procedure. > Only for that reason do I prefer to have an explicit indication that the > procedure might need to be adjusted for a different level of redundancy; as > for the previous point, I do not insist on any change, though. [GH] I have made a try to generalize the description. I think it can replace the current limited one. What do you think? " 3.16.3. Extracting text and handling recovery When applying the following procedures, the effects MUST be considered of possible timestamp wrap around and the RTP session possibly changing SSRC. When a packet is received in an RTP session using the packetization for multiparty-aware endpoints, its T140blocks SHALL be extracted in the following way. The source SHALL be extracted from the CSRC-list if available, otherwise from the SSRC. If the received packet is the first packet received from the source, then all T140blocks in the packet SHALL be retrieved and assigned to a receive buffer for the source beginning with the oldest available redundant generation, continuing with the younger redundant generations in age order and finally the primary. NOTE: The normal case is that in the first packet, only the primary data has contents. The redundant data has contents in the first received packet from a source only after initial packet loss. If the packet is not the first packet from a source, then if redundant data is available, the process SHALL start with the oldest generation. The timestamp of that redundant data SHALL be created by subtracting its timestamp offset from the RTP timestamp. If the resulting timestamp is later than the latest retrieved data from the same source, then the redundant data SHALL be retrieved and appended to the receive buffer. The process SHALL be continued in the same way for all younger generations of redundant data. After that, the timestamp of the packet SHALL be compared with the timestamp of the latest retrieved data from the same source and if it is later, then the primary data SHALL be retrieved from the packet and appended to the receive buffer for the source. " Regards Gunnar > > Thanks again, > > Ben -- Gunnar Hellström GHAccess gunnar.hellstrom@ghaccess.se
- [AVTCORE] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk via Datatracker
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Benjamin Kaduk
- Re: [AVTCORE] Benjamin Kaduk's Discuss on draft-i… Gunnar Hellström