Re: [Dart] Commentary on draft-york-00
"Black, David" <david.black@emc.com> Thu, 12 June 2014 15:57 UTC
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From: "Black, David" <david.black@emc.com>
To: Harald Alvestrand <harald@alvestrand.no>, Ben Campbell <ben@nostrum.com>
Date: Thu, 12 Jun 2014 11:57:16 -0400
Thread-Topic: [Dart] Commentary on draft-york-00
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References: <5399A1C8.7080407@alvestrand.no> <2996CB73-E2E5-4AE9-B602-A5466FD8C445@nostrum.com> <5399BB79.9010900@alvestrand.no>
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Cc: "dart@ietf.org" <dart@ietf.org>
Subject: Re: [Dart] Commentary on draft-york-00
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Harald, This explanation helps (thank you): > 3.4. Multiple RTP Sessions over one Media Transport > > [I-D.westerlund-avtcore-transport-multiplexing] describes a mechanism > that allow several RTP Sessions to be carried over a single > underlying Media Transport. [... snip ...] > The -westerlund- draft expired this April. I have not heard of anyone > pursuing it. I believe that the westerlund-avtcore draft was the indirect source of draft-york's assertion that multiple RTP sessions could be mixed on a single 5-tuple. In correcting that statement to say that RTP sessions cannot be mixed on a UDP 5-tuple, would it be reasonable to make note of that expired draft's proposal, possibly via a reference to the avtext-taxonomy draft? Thanks, --David > -----Original Message----- > From: Dart [mailto:dart-bounces@ietf.org] On Behalf Of Harald Alvestrand > Sent: Thursday, June 12, 2014 10:39 AM > To: Ben Campbell > Cc: dart@ietf.org > Subject: Re: [Dart] Commentary on draft-york-00 > > On 06/12/2014 04:25 PM, Ben Campbell wrote: > > Thanks Harald! I want to hit one particular comment: > > > > On Jun 12, 2014, at 7:49 AM, Harald Alvestrand <harald@alvestrand.no> wrote: > > > > [...] > > > >> "SCTP ... can be multiplexed with one or more RTP sessions". Actually we > can only multiplex SCTP with a single RTP session. There have been proposals > that would allow multiplexing of multiple RTP sessions (each containing > multiple media flows) over a single 5-tuple, but these were not accepted. > >> > >> > > [...] > > > >> In bullet 2, only one RTP session can be multiplexed with another transport > protocol (again). > > [...] > > > > Is this a matter of proper definitions of "RTP Session" vs "Media Flow"? > (i.e. properly naming the thing that can be multiplexed?) Or is there a > technical misunderstanding? > > > > Ben. > The word "session" is one of the most horrible words in the vocabulary..... > > RTP packet streams that are in the same RTP session can be multiplexed > over the same 5-tuple. > RTP packet streams that are from different RTP sessions cannot. > > A media flow as you've defined it here (="packet stream" from > -taxonomy-) is identified by its SSRC. > > About "RTP Session", -taxonomy- has this definition: > > 2.2.2. RTP Session > > An RTP session is an association among a group of participants > communicating with RTP. It is a group communications channel which > can potentially carry a number of Packet Streams. Within an RTP > session, every participant can find meta-data and control information > (over RTCP) about all the Packet Streams in the RTP session. The > bandwidth of the RTCP control channel is shared between all > participants within an RTP Session. > > Alternate usages: > > o Within the context of SDP, a singe m=line can map to a single RTP > Session or multiple m=lines can map to a single RTP Session. The > latter is enabled via multiplexing schemes such as BUNDLE > [I-D.ietf-mmusic-sdp-bundle-negotiation], for example, which > allows mapping of multiple m=lines to a single RTP Session. > > Characteristics: > > o Typically, an RTP Session can carry one ore more Packet Streams. > > o An RTP Session shares a single SSRC space as defined in RFC3550 > [RFC3550]. That is, the End Points participating in an RTP > Session can see an SSRC identifier transmitted by any of the other > End Points. An End Point can receive an SSRC either as SSRC or as > a Contributing source (CSRC) in RTP and RTCP packets, as defined > by the endpoints' network interconnection topology. > > o An RTP Session uses at least two Media Transports > (Section 2.1.13), one for sending and one for receiving. > Commonly, the receiving one is the reverse direction of the same > one as used for sending. An RTP Session may use many Media > Transports and these define the session's network interconnection > topology. A single Media Transport can normally not transport > more than one RTP Session, unless a solution for multiplexing > multiple RTP sessions over a single Media Transport is used. One > example of such a scheme is Multiple RTP Sessions on a Single > Lower-Layer Transport > [I-D.westerlund-avtcore-transport-multiplexing]. > > o Multiple RTP Sessions can be related. > > About the possibility of putting multiple sessions on a single media > transport, -taxonomy- says: > > 3.4. Multiple RTP Sessions over one Media Transport > > [I-D.westerlund-avtcore-transport-multiplexing] describes a mechanism > that allow several RTP Sessions to be carried over a single > underlying Media Transport. The main reasons for doing this are > related to the impact of using one or more Media Transports. Thus > using a common network path or potentially have different ones. > There is reduced need for NAT/FW traversal resources and no need for > flow based QoS. > > However, Multiple RTP Sessions over one Media Transport makes it > clear that a single Media Transport 5-tuple is not sufficient to > express which RTP Session context a particular Packet Stream exists > in. Complexities in the relationship between Media Transports and > RTP Session already exist as one RTP Session contains multiple Media > Transports, e.g. even a Peer-to-Peer RTP Session with RTP/RTCP > Multiplexing requires two Media Transports, one in each direction. > The relationship between Media Transports and RTP Sessions as well as > additional levels of identifiers need to be considered in both > signaling design and when defining terminology. > > This is, in my opinion, a very longwinded way of saying "this doesn't > exist". > > The -westerlund- draft expired this April. I have not heard of anyone > pursuing it. > > > > _______________________________________________ > Dart mailing list > Dart@ietf.org > https://www.ietf.org/mailman/listinfo/dart
- [Dart] Commentary on draft-york-00 Harald Alvestrand
- Re: [Dart] Commentary on draft-york-00 Dan York
- Re: [Dart] Commentary on draft-york-00 Ben Campbell
- Re: [Dart] Commentary on draft-york-00 Harald Alvestrand
- Re: [Dart] Commentary on draft-york-00 Black, David
- Re: [Dart] Commentary on draft-york-00 Harald Alvestrand
- Re: [Dart] Commentary on draft-york-00 Black, David
- Re: [Dart] Commentary on draft-york-00 Ruediger.Geib
- Re: [Dart] Commentary on draft-york-00 Black, David
- Re: [Dart] multiplexing different media types Paul E. Jones
- Re: [Dart] multiplexing different media types (wa… Paul E. Jones
- Re: [Dart] multiplexing different media types Harald Alvestrand
- Re: [Dart] multiplexing different media types Harald Alvestrand
- Re: [Dart] multiplexing different media types Paul E. Jones
- Re: [Dart] multiplexing different media types Paul E. Jones
- Re: [Dart] multiplexing different media types Paul E. Jones
- Re: [Dart] Commentary on draft-york-00 Ruediger.Geib
- Re: [Dart] multiplexing different media types Harald Alvestrand
- Re: [Dart] multiplexing different media types Eric Rescorla
- Re: [Dart] multiplexing different media types Eric Rescorla
- Re: [Dart] multiplexing different media types Eric Rescorla
- Re: [Dart] multiplexing different media types Eric Rescorla