Re: [MMUSIC] New Version Notification for draft-reddy-mmusic-ice-happy-eyeballs-02.txt

Ari Keränen <ari.keranen@ericsson.com> Thu, 07 November 2013 01:11 UTC

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From: Ari Keränen <ari.keranen@ericsson.com>
To: "Tirumaleswar Reddy (tireddy)" <tireddy@cisco.com>
Thread-Topic: [MMUSIC] New Version Notification for draft-reddy-mmusic-ice-happy-eyeballs-02.txt
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Date: Thu, 07 Nov 2013 01:11:31 +0000
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Cc: "mmusic@ietf.org" <mmusic@ietf.org>
Subject: Re: [MMUSIC] New Version Notification for draft-reddy-mmusic-ice-happy-eyeballs-02.txt
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Hi Tiru,

On Nov 6, 2013, at 1:56 AM, Tirumaleswar Reddy (tireddy) wrote:
>> Have you done an exercise (or better, implementation?) on how the candidate
>> pairs would then look like? Since ICE uses MAX/MIN sorting of the pairs (see
>> http://tools.ietf.org/html/rfc5245#appendix-B.5) simply having high priority
>> on the other side may not give the results you want.
> 
> MAX/MIN logic used for calculating candidate-pair priority ensures that for a particular agent, a lower-priority candidate is never used until all higher-priority candidates have been tried. So even if the remote peer does not support Happy Eyeballs Extension algorithm, the ICE agent would start ICE connectivity checks based on the local prioritization and if IPv4 ICE connectivity is received by the remote peer then it would cause Triggered Checks for IPv4 candidate-pair. Hence IPv4 candidate-pair will be tested earlier even if remote peer does not Happy Eyeballs Extension algorithm. So effectively even if just one of the end points supports the algorithm, connectivity checks are optimized and should see better results. 

I'm afraid that still wouldn't work like that. As you said, "a lower-priority candidate is never used until all higher-priority candidates have been tried". You would not start checks based on a local high priority for an IPv4 candidate since a *pair* with that candidate would not have high priority (due to the "2^32*MIN(G,D)" part of the formula -- it's the smaller priority of the candidates that counts).

That said, I remember getting this wrong in my own implementation the first time so as I said you may want to do this exercise with real numbers and see where you end up.


Cheers,
Ari