Re: [Sip] 199: Staus and open issues after Dublin - support indicator

["Christer Holmberg" <christer.holmberg at ericsson.com>]

Hi, 

>>>>If UAC does not support 199, sending it might cause more harm than
good.
>>>A UAC should discard what it doesn't support.
>>>RFC 3261 section 8.1.3.2: "A UAC MUST treat any provisional response
>>>different than 100 that it does not recognize as 183 (Session
Progress)."
>>>The above requirement adds complication for devices (not supporting
>>>199) only maintaining a limited number of early dialogs or using 
>>>latest 1xx to recognize most likely active early dialog.
>>>The 199 could trigger them to forgot or not prefer a useful early
>>>dialog for the one associated with 199.
>> 
>>Wouldn't that mean that, if the UAC does not insert the indicator, 
>>proxies are not allowed to insert it either? Because, if they do, and 
>>receive 199 I guess they will simply forward the 199 towards the UAC, 
>>and you end up in the same situation. An intermediate B2BUA could of 
>>course terminate the 199, and not forward it towards a UAC not 
>>supporting it, but I don't think we want to define such behavior for 
>>normal proxies.
>
>If we postulate such an indicator, then why would a proxy *want* to
insert it? I agree it would be a bad thing.

I guess proxies would normally NOT insert it, since they normally don't
control media resources etc. However, I guess e.g. an P-CSCF could be
interested in inserting the indicator if not received from the UE. 

But, if we choose to define an indicator I guess a P-CSCF that wants to
do such thing would have to act as a B2BUA.

That also means we could use an option-tag.

Regards,

Christer

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