[Dart] IPv6 Flow labels? (Re: RTP and non-RTP traffic on same UDP 5-tuple)

Harald Alvestrand <harald@alvestrand.no> Thu, 12 June 2014 11:40 UTC

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Date: Thu, 12 Jun 2014 13:40:33 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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Subject: [Dart] IPv6 Flow labels? (Re: RTP and non-RTP traffic on same UDP 5-tuple)
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you mentioned 6-tuples - with the link you gave, I assume you're talking 
about IPv6 flow labels.

Apart from the issues with remapping, the use of flow labels should have 
many of the same aspects as the use of DSCP codepoints.

Can you give us some idea of how the use (or not) of multiple flow 
labels within a 5-tuple has been thought about in the IPv6 context?


On 06/11/2014 10:42 PM, Brian E Carpenter wrote:
> 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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