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Re: [AVT] comments on section 10ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
Tom/Roni-
We need to clarify the text to make the port relationships more clear.
We are still getting reader confusion when considering the relationship
between the ports associated with the primary multicast flow, the ports
associated with the RTCP feedback on the initial flow, and the ports
associated with the acceleration flow.
These proposed words are an improvement. I will start with your new
words and make further clarifications for consideration. I hope to have
some words tonight.
bvs
-----Original Message-----
From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On Behalf Of
VAN CAENEGEM Tom
Sent: Thursday, June 18, 2009 7:45 AM
To: Roni Even; avt at ietf.org
Subject: Re: [AVT] comments on section
10ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
Hi Roni,
I 100% agree with your remarks, and in fact I had proposed additional
text for step 2 and step 8 that clarified which message was sent in
which session and/or to/by whom, but now I notice these clarifying text
fragments seem to have been missed by the main editor in the last draft
release. Bill, can you add these phrases in a subsequent release?
Step 2:
Add text: "Both the unicast burst and the RAMS-I message are transmitted
by the burst/retransmission source logical entity that is part of the
RS."
Step 8:
Replace "Note that RR MUST send at least one RAMS-T message" by
"Note that RR MUST send at least one RAMS-T message, and the RAMS-T
message MUST be addressed to the Burst source logical entity that is
part of the RS."
On step 4, I took it kind of for granted that, as RAMS-R update messages
are the same as RAMS-R messages, the RAMS-R update message has to be
sent towards the FT... But you are right, that this should be explicitly
mentioned in the draft. One could even argue this message should be sent
to the Burst/Retransmission Source entity as it services the purpose of
controling the RTP burst (similar as an RAMS-T message), but I would
suggest that this message is addressed to the FT, based on my previous
reasoning.
So for Step 4, I'd propose to change the current sentence "RR MAY send
a new RAMS-R message with a different value for one or more fields of an
earlier RAMS-R message." to "RR MAY send a new RAMS-R message to the
FT entity of the RS, with a different value for one or more fields of an
earlier RAMS-R message."
Tom
-----Original Message-----
From: Roni Even [mailto:Even.roni at huawei.com]
Sent: donderdag 18 juni 2009 11:47
To: VAN CAENEGEM Tom; avt at ietf.org
Subject: RE: [AVT] comments on section 10
ofdraft-ietf-avt-rapid-acquisition-for-rtp-01
Hi Tom,
My comment about the text was more about the steps described later in
section 6.2
In step 2 the RS will send the RAMS-I from the RTCP port for the
burst/retransmission stream. This will help the RR to learn his address
In step 4 - update RAM-R, will it be sent to the FT target or to the
burst/retransmission.
In step 8 - specify where to send the RAMS-T not to the RS but to the
burst/retransmission address.
As for the RTP/RTCP port multiplexing, I do not think that this is a
separate draft. We need to discuss the solution and decide where to it
should go. If the declarative SDP will include RTP/RTCP mux the RAM-R
should acknowledge that it is supported by the RR.
The need for a separate draft discussion is if the RR wants to offer
different ports for receiving the RTP and RTCP, and this needs to be
discussed. The major question is if we need a general mechanism which
requires a new RTCP message or is it just for this case and we can add
the information to the RAMS messages..
Roni
> -----Original Message-----
> From: VAN CAENEGEM Tom [mailto:Tom.Van_Caenegem at alcatel-lucent.be]
> Sent: Wednesday, June 17, 2009 3:23 PM
> To: Roni Even; avt at ietf.org
> Subject: 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
> >
> >
> > _______________________________________________
> > Audio/Video Transport Working Group
> > avt at ietf.org
> > https://www.ietf.org/mailman/listinfo/avt
_______________________________________________
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