Re: [MMUSIC] Draft new version: draft-holmberg-mmusic-sdp-dtls-01

Paul Kyzivat <pkyzivat@alum.mit.edu> Sat, 20 June 2015 17:47 UTC

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Date: Sat, 20 Jun 2015 13:47:11 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [MMUSIC] Draft new version: draft-holmberg-mmusic-sdp-dtls-01
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I have a few comments on this version:

* Section 2.1:

    When a new DTLS association is established, an endpoint MUST use a
    new set of transport parameters (IP address and port combination).

The above seems slightly ambiguous: does "an endpoint" mean "each 
endpoint" or "one (of the two) endpoints"?

IIUC we have established that the important point is that the 5-tuple 
must change. So at least one side must change the address or port. But 
if one side is known to do so, then the other side need not do so. So I 
suggest changing the above to:

    When a new DTLS association is established, one of the endpoints
    MUST use a new set of transport parameters (IP address and port
    combination).

But there may be more to sort out about the o/a protocol for 
guaranteeing this. I can see a few:

- if the offer has connection:new then the offer must have new
   transport parameters. Else, if the offer has connection:existing
   but the answer has connection:new then the answer must have new
   transport parameters.

- if the answer has connection:new and the offer didn't have new
   transport parameters, then the answer must have new ones.

Something about the above should probably go into section 6.

* Section 5.1

    A 'connection' attribute value of 'new' indicates that a new DTLS
    association MUST be established.  A 'connection' attribute value of
    'existing' indicates that a new DTLS association MUST NOT be
    established.

I think this is wrong - that the answerer is permitted to answer with 
connection:new.

* Section 6.3

    If an answerer receives an offer that contains an SDP 'connection'
    attribute with a 'new' value, the answerer MUST insert a 'new' value
    in the associated answer.  The same applies if the answerer receives
    an offer that contains an SDP 'connection' attribute with a 'new'
    value, but the answerer determines (based on the criteria for
    establishing a new DTLS association) that a new DTLS association is
    to be established.

I think I previously commented on this: the 2nd sentence "The same 
applies if ... attribute with 'new' value ...". *That* 'new' should be 
'existing' - it is covering an alternative to the first sentence. And 
this aligns with my comment above about section 5.1.

	Thanks,
	Paul