Re: [MMUSIC] Comments onhttp://tools.ietf.org/html/draft-begen-avt-ports-for-ucast-mcast-rtp-01
"Jean-Francois Mule" <jf.mule@cablelabs.com> Fri, 30 October 2009 16:08 UTC
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From: Jean-Francois Mule <jf.mule@cablelabs.com>
To: mmusic@ietf.org
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Cc: VAN CAENEGEM Tom <Tom.Van_Caenegem@alcatel-lucent.com>
Subject: Re: [MMUSIC] Comments onhttp://tools.ietf.org/html/draft-begen-avt-ports-for-ucast-mcast-rtp-01
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As an FYI, and thanks to Ali who suggested it, we have also added this draft on the agenda for the MMUSIC WG session in Hiroshima. Jean-François > -----Original Message----- > From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On > Behalf Of Ali C. Begen (abegen) > Sent: Friday, October 30, 2009 9:48 AM > To: VAN CAENEGEM Tom; avt@ietf.org > Cc: mmusic@ietf.org > Subject: Re: [MMUSIC] Comments onhttp://tools.ietf.org/html/draft- > begen-avt-ports-for-ucast-mcast-rtp-01 > > Hi Tom, > > Thanks for reading the revised draft. > > > Hi Ali, > > > > When reading through the draft http://tools.ietf.org/html/draft- > begen-avt-ports-for-ucast- > > mcast-rtp-01 <http://tools.ietf.org/html/draft-begen-avt-ports- > for-ucast-mcast-rtp-01> , > > including your editor comments, I understand that despite the > cookie exchange solution, it > > does not allow to have a "stateless" server (that is, the server > needs to remember the > > ports). You indeed correctly pointed out that RTCP SR messages > are unsollicited, so they > > cannot be linked to a received cookie. I do not think it makes > sense to "forbid" the > > server (RS in the considered use cases) to send RTCP SR at any > moment in time. Hence, as > > Yes, sender reports pose a problem at this time (the server needs > to remember the port). There may be a nice solution to it, but we > don't have any for now. > > > the RS needs to remember anyhow the ports and thus must keep > state, the cookie would no > > longer be needed from that perspective. Is that an appropriate > conclusion? Port mapping > > That is where we are now. But I am not sure whether the WG will > make that conclusion. > > > response message (exchange) is then no longer needed anymore, > although I understand this > > message is also a kind of confirmation of reception of the port > mapping request message. > > Yes, response serves as a confirmation of the request. > > > You also mention that NAT tolerance is a design criterium. How > was that taken into account > > in the proposed messaging flow? > > We have not gotten into its details yet. But, yes, nat friendliness > is desired/required. > > > The NAT friendly solution IMO is that the port mapping request > messages for RTP and RTCP > > is sent along with a RAMS-R FB by the RR to the RS whereas a port > mapping request for RTP > > But this message (since it includes RAMS-R) needs to go to port P2 > on RS (rtcp port for the primary mcast session) instead of port P3. > > > is sent along with a NACK FB by the RR to the RS. This is not to > inform the RS of the > > ports it should use each time -as it needs to remember that > anyhow and keep state based on > > the 1st received port maping request by the RR- but to open the > NAPT in between. The > > disadvantage is of course the higher messaging load for the RS > (and RR). > > > > I realise the draft wants to provide an answer on how an RR can > indicate the UDP ports it > > wishes to use for RTP unicast sessions without any session- > signaling protocol involved, > > but I do not think all design criteria can be met. I think we can > drop the cookie, and > > just keep the port mapping response/request message (without > cookie), meaning the RS needs > > to keep state of the port allocated to each RR based on > acknowledged port mapping request > > messages, and when receiving RTCP Byes in the retransmission > session, it can drop the > > "state". > > This is an interesting proposal but we are giving up from the > stateless server idea. Are we willing to do that? In order to keep > the server stateless, we might break another rule, if we have to, > and re-consider our earlier proposal - PubPorts (where port numbers > are directly transmitted in the RTCP message). That will satisfy > our requirements except that it introduces layer violation. > > > In my opinion, the ideal solution is still that we can make the > P2 and P3 ports on the RS > > equal, where a single message (RAMS-R or NACK) by an RR will > allow the response (RTP burst > > or RTP retransmission packet) to pass through NAT, provided the > RR supports the RTP/RTCP > > Yes, your proposal above requires this. > > > port muxing. I realise this would require the RS to use an SSRC > in the unicast > > retransmission session that is different from the one used in the > primary SSM session- > > allowing the RS to distinguish RTCP messages based on the media > SSRC in the RTCP messages. > > However, using a different SSRC when retransmission session > muxing is used, is forbidden > > Correct. > > > by RFC 4588. But there is no justification in RFC 4588 why this > was disallowed, and > > further inquiries have made me believe that there is really no > hard reason why this > > constraint was imposed. > > I believe the reason is to allow for easier monitoring and > processing of RTCP reports. If a session and its retransmission > session use different SSRCs, how do we correlate them at the > monitoring (RTCP processing) agent? There can be multiple primary > sessions and their retransmission sessions running on the same > client at the same time. > > > As you know, in the DVB retransmission solution for linear TV > (hence SSM sessions), it is > > allowed to use a different SSRC even though session muxing is > used (as the UNICAST > > retransmission session is associated with a SSM session), > "overruling" RFC 4588 on that > > aspect. This then allows making P2=P3, with no ambiguities for > the RS in resolving which > > incoming RTCP message belongs to which session (either the > unicast retransmission session > > or the unicast feedback channel of the SSM session). This > solution requires no port > > signaling at all and is NAT friendly. > > Yes, I am aware of that. I will try to get an answer from MMUSIC > folks, too. In fact, I cc'ed mmsuic hoping that someone will > clarify this requirement in RFC 4588. > > Thanks again, > -acbegen > > > Regards > > Tom > > > > > > > > > > > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic
- Re: [MMUSIC] Comments on http://tools.ietf.org/ht… Ali C. Begen (abegen)
- Re: [MMUSIC] Comments onhttp://tools.ietf.org/htm… Jean-Francois Mule
- Re: [MMUSIC] Comments on http://tools.ietf.org/ht… Ali C. Begen (abegen)
- Re: [MMUSIC] Comments on http://tools.ietf.org/ht… VAN CAENEGEM Tom
- Re: [MMUSIC] Comments on http://tools.ietf.org/ht… Ali C. Begen (abegen)