Re: [MMUSIC] Trickle ICE for SIP Questions

[Emil Ivov <[e-mail]>]

Hey Christer,

On 21.07.13, 19:49, Christer Holmberg wrote:
> Hi,
>
> As I've been on vacation,

Hope you had a good one!

> I tried to go through this thread in one
> sweep. I may have missed/misunderstood some parts, and my apologies
> if my comments below have already been dealt with.
>
> First, regarding 180, no matter if we use PRACK or not, SIP requires
> the SDP to be identical in all 180 responses. That means you can't
> add new candidates in subsequent 180 responses (eventhough vanilla
> ICE uses 180s without PRACK, the SDP is identical in all 180s,
> AFAIR).

Good point!

> Second, I get a little confused when we talk about the UAS sending
> INFO before it knows that the dialog is established, and that we
> would define some new handling rules when an error response is
> received. Now, IF we want the UAC to inform the UAS that the dialog
> has been established, we don't need PRACK for that. The UAC could
> send an INFO when it receives the 180, and when the UAS receives the
> INFO it knows the dialog has been established. I haven't thought so
> much about it, so I am not suggesting such mechanism at this point, I
> am only saying that it would be a possible solution from a SIP
> protocol perspective :)

This could indeed work! It would also make a lot of sense in cases where 
both agents are doing full trickle.

Of course it does mean that, especially in half trickle scenarios, we 
basically have one full end-to-end signalling RTT (180 + INFO) during 
which trickling will be completely blocked. This could take a while.

Still, if we don't come up with a better alternative, the worst case 
(i.e. half trickle + slow signalling) shouldn't be much worse than 
vanilla ICE.

Emil

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