[Dart] WGLC: draft-ietf-dart-dscp-rtp-02

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Wed, 13 August 2014 20:33 UTC

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Date: Wed, 13 Aug 2014 21:33:06 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: The University of Aberdeen is a charity registered in Scotland, No SC013683.
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Subject: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02
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I can see good points raised on the details, instead I have some 
questions about the overall document strcuture:

(1) This statement appears at the end of section 2:

    "Multiplexing may reduce the complexity and resulting load on an
    endpoint.  A single instance of STUN/ICE/TURN is simpler to execute
    and manage than multiple instances STUN/ICE/TURN operations happening
    in parallel, as the latter require synchronization and create more
    complex failure situations that have to be cleaned up by additional

I suspect this is all true, but I'd like to ask that section 4 also 
makes a similar summary claim at the end - saying that using a single 5 
tuple and multiplexing multiple streams with *different* QoS expectation 
and therefore different DSCP markings can complicate the transport 
protocol design, by requiring a transport to disambiguate the congestion 
state for each network QoS category that is used. It will also result in 
increased complexity at the transport layer to validate path integrity, 
where a 5-tuple could result in a different routing/forwarding path in 
order to validate that the individual 5-tuples are reachable.  Of 
course, using DSCPs with an AF class can reduce some of the latter 
costs. etc according to what the draft says.

I don't suggest that the extra complexity and additional algorithms are 
as big a problem as being unable to get through a NAPT/Firewall, but it 
seems that this nonetheless extra stuff that I don't recall having been 
worked upon before in the IETF - and a challenge I guess for the RMCAT WG.

(2) I don't know if the document's goal is also to make transport 
recommendations for using multiple code points - i.e.things such as 
must be robust to the network changing a DSCP; needs to independently 
verify that a particular DCSP is not being black-holed, needs to not 
imply relative precedence when interpreting loss or marking of packets 
for a flow using multiple DCSPs etc. ???

If these are out of scope, then maybe the document should say that this 
particular document does not provide this sort of guidance.