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

[Brian E Carpenter <[e-mail]>]

On 12/06/2014 12:58, Black, David wrote:
>> What do you mean by 'all the packets would be classified the same'?  If you
>> mean all the packets in a 5-tuple would get the same differentiated treatment,
>> that is not desirable, because there are lots of folks wanting to send video
>> i-frames or packets with FEC or other stuff with lower drop precedence than
>> other packets.
> 
> That would most likely be within an AF class; the entire set of packets marked
> w/different drop precedences within an AF class should be classified the same.
> 
> Beyond that, one can hope that any AF remarker (e.g., for traffic shaping) is
> running in Color-Aware mode and hence tries to preserve source drop precedence
> distinctions, but this cannot be relied upon.

Indeed not, and that's on the assumption that the receiving domain
even operates an AF service class. The worst case assumption is
that everything reverts to best effort somewhere along the path.

For some of the reasons behind this situation, I suggest reading
http://tools.ietf.org/html/rfc2475#section-6.1

   Brian

> 
> Thanks,
> --David
> 
>> -----Original Message-----
>> From: Dan Wing [mailto:[e-mail]]
>> Sent: Wednesday, June 11, 2014 8:32 PM
>> To: Brian E Carpenter
>> Cc: Black, David; [e-mail]
>> Subject: Re: [Dart] RTP and non-RTP traffic on same UDP 5-tuple
>>
>>
>> On Jun 11, 2014, at 1:42 PM, Brian E Carpenter <[e-mail]>
>> 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).
>> What do you mean by 'all the packets would be classified the same'?  If you
>> mean all the packets in a 5-tuple would get the same differentiated treatment,
>> that is not desirable, because there are lots of folks wanting to send video
>> i-frames or packets with FEC or other stuff with lower drop precedence than
>> other packets.
>>
>> -d
>>
>>
>>>    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
>>>> [phone]             FAX: [phone]
>>>> [e-mail]        Mobile: [phone]
>>>> ----------------------------------------------------
>>>>
>>>>
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