Re: [MMUSIC] Adding a new candidate when ICE running

[Jonathan Rosenberg <jdrosen at cisco.com>]

A restart is a heavy-handed process really. There are cases where an 
agent doesn't want to wait to finish its gathering before sending the 
initial offer, in order to speed things up. And so it sends the initial 
offer and continues gathering and then sends an updated offer, all to 
make things go faster. If ICE needs to restart on the updated offer, any 
time savings are eliminated.

-Jonathan R.

Zingerle, Meinrad wrote:
> Hi Jonathan,
>  
> in my understanding,  section 9.1.2.1. and section 9.3.1.4. allow adding 
> new candidates without restarting ICE.
>  
>     9.1.2.1. Existing Media Streams with ICE Running
>     If an agent generates an updated offer including media stream that
>     was previously established, and for which ICE checks are in the
>     Running state, the agent follows the procedures defined here.
>     An agent MUST include candidate attributes for all local candidates
>     it had signaled previously for that media stream. The properties of
>     that candidate as signaled in SDP - the priority, foundation, type
>     and related transport address SHOULD remain the same. The IP
>     address, port and transport protocol, which fundamentally identify
>     that candidate, MUST remain the same (if they change, it would be a
>     new candidate). The component ID MUST remain the same. The agent
>     MAY include additional candidates it did not offer previously, but
>     which it has gathered since the last offer/answer exchange, including
>     peer reflexive candidates.
>  
>     9.3.1.4. ICE Continuing for Existing Media Stream
>     The valid list is not affected by an updated offer/answer exchange
>     unless ICE is restarting.
>     If an agent is in the Running state for that media stream, the check
>     list is updated (the check list is irrelevant if the state is
>     completed). To do that, the agent recomputes the check list using
>     the procedures described in Section 5.7. If a pair on the new check
>     list was also on the previous check list, and its state was Waiting,
>     In-Progress, Succeeded or Failed, its state is copied over.
>     Otherwise, its state is set to Frozen.
>         .....
>  
> If my understanding is correct, what's the reason behind it?
> Wouldn't it simplify ICE a little bit, if the ICE draft requests 
> restarting ICE wehn adding a new candidate to an existing media stream 
> for that ICE hasn't completed yet? At least the answerer would not have 
> to recompute the check list and in my opinion requesting an ICE restart 
> when adding a new candidate would make such scenarios more deterministic.
>  
> Thanks for your patience and regards,
>   Meinrad

--
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Cisco Fellow                                   Parsippany, NJ 07054-2711
Cisco Systems
jdrosen at cisco.com                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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