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Re: [AVT] comments on section 10 ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
Hi Roni,
Perhaps the start of section 6.2 can be rewritten as follows:
<START>
6.2. Message Flows
Figure 2 shows the main entities involved in rapid acquisition:
o Multicast Source
o Feedback Target (FT)
o Burst/ Retransmission Source
o RTP Receiver (RR)
(fig 2)
The feedback target (FT) is the entity as defined in [rtcpssm draft], to
which the RR sends its RTCP FB messages, indicating packet loss in the
ssm primary stream by means of a NACK or indicating the RR's desire to
have rapid acquisition of the ssm primary stream (by means of an RTCP FB
message as defined in this document). While the burst/retransmission
source is responsible for responding on these messages and, in the case
of rapid acquisition, further RTCP interaction with the RR during this
acquisition process, it is assumed in the remainder of the document that
these two logical entities (FT and burst/retransmission source) are
combined in a single physical entity and share state. In the remainder
of the text, the term retransmission server is used whenever
appropriate, to refer to the combined functionality of the FT and
retransmission/burst source. However, it must be noted that only the FT
is involved in the primary ssm RTP session, whereas the
burst/retransmission source transmits unicast RTP burst and RTP
retransmissions packets (both formatted as RTP retransmission packets
[RFC4585]) in a single separate unicast RTP retransmission session to
each RR.
Note also that the same method (with the identical message flows) would
also apply in a scenario where rapid acquisition is performed by a
feedback target co-located with the media source.
(...)
<END>
Tom: As we mandate the retransmission source and burst source to be in
the same session, I think it is no longer required to split-up among
these two logical entities. I invite other people, including the
co-authors to comment on this new text proposal.
With respect to your comments on the RTP/RTCP port muxing support
indication by the RR inside the RAMS-R message. That would be needed,
but is not sufficient as, if only declarative SDP is used, and we want
to have the possibility that the RTP/RTCP packets in the retransmission
session can be received by the RR on the same port the RR issues the
RTCP RAMS-R, we need also a way by which the RR can signal this too. We
provided a possible solution in the draft, but I understood that you
think such a solution should be proposed in a separate draft proposal?
But I guess that would also apply then to the signaling of support for
RTP/RTCP port muxing by the RR?
Tom
-----Original Message-----
From: Roni Even [mailto:Even.roni at huawei.com]
Sent: woensdag 17 juni 2009 13:24
To: VAN CAENEGEM Tom; avt at ietf.org
Subject: RE: [AVT] comments on section 10
ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
Tom,
I understand the RAMS-R and RAMS-T, the text is not clear enough in
section
6.2
It still leaves open the issue of the addresses for the RR in the case
of declarative SDP when there is no answer SDP from the RR.
About RTP/RTCP multiplexing, the declarative SDP can show that the RS
supports it and I still think that some information about the addressing
(like support for RTP/RTCP mux) should be supplied in the RAMS-R for the
declarative case.
Roni
> -----Original Message-----
> From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On Behalf Of
> VAN CAENEGEM Tom
> Sent: Wednesday, June 17, 2009 11:17 AM
> To: avt at ietf.org
> Subject: Re: [AVT] comments on section 10 of draft-ietf-avt-rapid-
> acquisition-for-rtp-01
>
> Hi Roni,
>
> I think your understanding was indeed different from the general
>assumptions in this draft. Previously we agreed to only consider the
>case where there is only one physical entity involved (called the
>Retransmission Server in the draft), which allows us to NOT consider
>and discuss cases where for instance the feedback target (which is
>defined in the rtcpssm draft/RFC) is not in the same box as the
>retransmission source or burst source, the entities sourcing
>retransmision/burst packets. In that case we then would also need to
>describe how these separate entities communicate.
> The fact that these different entities are now in the same box does
>not necessarily mean that all interactions and data exchange with the
>RRs is part of the same RTP session, which is in this case the SSM
>RTP session.
> As Ali explained, the NACK and RAMS-R RTCP FB messages are directed to
>the FB target, where we do not defer from the rtcpssm draft. The RTP
>retransmission/burst packets that are sent as a response to the NACK
>and the RAMS-R can be either session multiplexed with respect to the
>original SSM RTP session or SSRC muxed (same session), following RFC
>4588.
>As the retransmission packets in this case are addressing the RR in
>unicast, we obviously have a dedicated RTP session for the
>retransmission/burst packets. We had some internal discussion on
>whether considering the use case of having a separate session between
>RS and RR for RTP retransmission packets triggered by an RTCP FB NACK
>and a separate session for RTP burst packets triggered by an RTCP
>RAMS-R made sense, but we ended up agreeing that allowing a single
>session was the easiest way out, without imposing serious limitations
>to the general architecture.
>
> This means that the ports used by the (single) RTP
> retransmission/burst session are in principle decoupled from the
> primary SSM session. Hence if an RR wants to receive the
> burst/retransmission packets and associated RTCP messages on the same
> port the RR sent out the RTCP RAMS-R/ NACK FB messages, this should
> either be signaled by the RR, OR such port usage scheme is considered
> the "default" case -which also means the RR supports RTP/RTCP port
> muxing for the retransmission/burst session-, and then the RR needs to
> signal the ports for receiving the RTP and RTCP packets in the
> retransmission session when it requires dedicated ports.
>
> The RAMS-I (RS-> RR) and RAMS-T (RR-> RS) messages are only relevant
> to a specific RR requesting the RTP burst stream and the RS, and carry
> information/signaling related to the retransmission/burst session and
> have nothing to do with the SSM session. Hence the FB target as
> logical entity is not involved here.
>
> I hope this clarifies rather than it contributes to your confusion.
> But we may need to rephrase the part you quoted, as your
> interpretation was different from its intended meaning. We also tried
> to be more explicit in which session which RAMS or other RTCP (e.g.
> Bye) messages needed to be exchanged compared to a previous version of
> the draft, but we are open of course to any other suggestions from
> your side if this is not clear enough in your opinion.
>
> Tom
>
>
>
>
>
>
> " A Retransmission Source may equally act as a Burst Source. The
> Retransmission Source may also incorporate the Feedback Target
> ([I-D.ietf-avt-rtcpssm] permits the feedback target to be a
> retransmission server, since it is a logical function to which RRs
> send their unicast feedback), and we will use the term
> Retransmission
> Server (RS) in the remainder of the document to refer to a single
> physical entity comprising these three entities that share state.
> Note that the same method (with the identical message flows) would
> also apply in a scenario where rapid acquisition is performed by a
> feedback target co-located with the media source."
>
> I assumed that we are only dealing with the case that the RS is a
> single entity and not three different entities with different
> addresses
>
> I also thought that this was agreed in previous discussions
>
> If my understanding is not correct I will review the draft since the
> current text is not explicit enough to specify which part is doing
> each message. I saw that RAMS-R is going to feedback target but RAMS-T
> is going to RS which is not specifying a specific address according to
> you.
>
> Roni
>
> -----Original Message-----
> From: Ali C. Begen (abegen) [mailto:abegen at cisco.com]
> Sent: Tuesday, June 16, 2009 10:00 PM
> To: Roni Even; avt at ietf.org
> Subject: RE: [AVT] comments on section 10
> ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
>
> Remember that the RAMS-R (RR->RS) message is NOT on the retransmission
> (unicast) session, it's on the primary session since it is sent to the
> feedback target of the primary SSM session. Thus, the source port RR
> uses to send RAMS-R "cannot" be assumed to be the destination port it
> wishes to receive the unicast burst on.
>
> If you agree with this statement, it is clear why we need port
> signaling.
> Muxing will not help much here. It will just reduce the number of
> signaled ports from 2 to 1.
>
> -acbegen
>
>
> > -----Original Message-----
> > From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On Behalf
> > Of Roni
> Even
> > Sent: Tuesday, June 16, 2009 10:08 AM
> > To: avt at ietf.org
> > Subject: [AVT] comments on section 10
> ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
> >
> > Hi,
> >
> > I looked at section 10 and have some comments
> >
> >
> >
> > 1. If RTP/RTCP multiplexing is used, there is no need for any
> specific operation
> > from the RR side. The RR sends the RAMS-R message to the RS from the
> > port
> it wants to
> > receive the RAMS-I and RTP payload. The RS just sends the
> > information to
> the port from
> > which it received the RAMS-R and not to the one in the SDP
> >
> > 2. In the case where there is no RTP/RTCP multiplexing, the
> RAMS-R
> RTCP message will
> > go to the RS and the RAMS-I will go to the port on the RR from where
> > the
> RAMS-R was
> > received. For the RTP, the RR does not know if it has a NAT on the
> way
>
> > to
> the RS and
> > should try to get a routable address (using STUN for example) and
> providing the port to
> > the RS ( we still need to agree on how to do it)
> >
> > 3. If the above two points are correct than the RR receive
port
> in
> the SDP is not
> > really useful
> >
> >
> >
> > Roni Even
>
>
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