Re: [MMUSIC] Trickle ICE for SIP Questions

[Emil Ivov <[e-mail]>]

On 22.07.13, 13:11, Christer Holmberg wrote:
> Hi,
>
>>>>> How is this better than PRACK?
>>>>
>>>> Well, you don't have to worry about supporting offers and answers in the PRACK (which could indeed be a pain).
>>>
>>> In my years of "PRACK experience", PRACK itself (for the purpose of acknowledging reliable 18x responses) has never been a
>>> problem. But, I agree there could be issues when it is used for O/A - especially if one wants to reject an offer. In my experience, however,
>>> offers in PRACK are normally used e.g. to change pre-condition state, and/or to remove codecs, so the likelihood of rejection based on the SDP content should be rather small.
>>>
>>> There are also implementations that don't accept offers in PRACK to
>>> begin with, but I think that goes under "bad implementation" :)
>>>
>>> Having said that, not specific to trickle ICE, if O/A is a show
>>> stopper for the community to use PRACK,
>>
>> Well, speaking as an implementor, I can completely see how many would feel uneasy about adding this to working implementations. It basically means adding some additional complexity with no actual benefit in return.
>>
>>> maybe that is something we need to look into on a more general level.
>>
>> You mean something like PRACK-lite that doesn't have offer answer? This sounds like something that could be relatively straightforward to specify. It would basically
>> have to mimic PRACK but remove the part that talks about the additional O/A possibilities.
>
> It could perhaps even be a request without a response, similar to ACK, which would make it even more "lite". When the UAS receives it, it simply ceases the transmission of the 18x.

Hmm ... this sounds like something that would make a lot of proxies and 
SIP stacks unhappy.

I actually think we could pull this off with simple PRACKs. Only, rather 
than using the "100rel" tag we go for something like "100rel-lite" which 
could be defined to indicate that a UA supports PRACK but only for 
reliability (and PRACK bodies are not allowed).

Emil


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