Re: [Dart] RTP and non-RTP traffic on same UDP 5-tuple

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 11 June 2014 20:42 UTC

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Date: Thu, 12 Jun 2014 08:42:56 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Subject: Re: [Dart] RTP and non-RTP traffic on same UDP 5-tuple
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On 11/06/2014 07:59, Black, David wrote:
> In another message, Ruediger Geib asked (>), and I responded:
> 
> --------------------
> 
>> Is the following correct:
>>
>> UDP_5-tuple-+--transport protocol 1-----
>>             |
>>             +--RTP session 1-----
>>             |
>>             +--RTP session 2-----+---RTP_stream_2.1
>>                                  |
>>                                  +---RTP_stream_2.2
>>                                  |...
> 
> Yes, that matches my understanding, although the author team would like to
> see discussion of whether it's a good idea to mix RTP and non-RTP protocols
> on the same 5-tuple - I'll copy your useful diagram into a separate message
> to start that discussion.
> 
> --------------------
> 
> This is that message, and I want to thank Ruediger for drawing that useful
> diagram.
> 
> The author team for draft-york would like input on whether the draft should
> discuss mixing of RTP and non-RTP traffic on the same UDP 5-tuple, vs. using
> separate 5-tuples (probably separate UDP ports) for RTP and non-RTP traffic.

One observation is that we should be thinking about a 6-tuple these
days (see RFC 6437). I don't think it makes much difference to the argument.

Another observation is when load balancing is in play, things get a bit
more complicated, but to a first approximation using the same 5-tuple
or 6-tuple will usually ensure that all the packets reach the same
load-balanced destination, which is probably a good thing.

Third, reverting to the diffserv discussion, the same 5-tuple
should ensure that all the packets would be classified the same
(if they cross a diffserv domain boundary and get reclassified).

    Brian

> 
> RTCWEB clearly intends to mix SCTP (via DTLS) and RTP traffic on the same
> 5-tuple see the last paragraph of Section 3.5 of draft-ietf-rtcweb-transports-04:
> 
>    RTCWEB implementations MUST support multiplexing of DTLS and RTP over
>    the same port pair, as described in the DTLS_SRTP specification
>    [RFC5764], section 5.1.2.  All application layer protocol payloads
>    over this DTLS connection are SCTP packets.
> 
> OTOH, concerns have been expressed about whether the not-exactly-elegant
> demux processing specified in the reference (RFC 5764, Section 5.1.2) ought
> to be recommended as a good way of doing this multiplexing.
> 
> Please comment, including whether mixing SCTP and RTP on the same UDP
> 5-tuple is a good idea (some rationale for doing this sort of multiplexing
> onto a single 5-tuple can be found in Section 3 of draft-york-dart-dscp-rtp-00).
> 
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> +1 (508) 293-7953             FAX: +1 (508) 293-7786
> david.black@emc.com        Mobile: +1 (978) 394-7754
> ----------------------------------------------------
> 
> 
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