Re: [MMUSIC] Trickle ICE for SIP Questions

[Paul Kyzivat <[e-mail]>]

How is this better than PRACK?

	Thanks,
	Paul

On 7/21/13 2:56 PM, Emil Ivov wrote:
> 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
>