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Re: [AVT] comments on section 10 of draft-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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