[Sip] RE: Defining new requests

["Christer Holmberg (JO/LMF)" <[e-mail]>]

Hi Gonzalo,

Thanks for your reply!

>it seems that some people in the ITU-T are having some issues 
>figuring out whether or not certain requests can be sent by the UAS within an 
>early dialog. The confusion comes from statements like this 
>one (taken from the INFO spec):
> 
> "     Unless stated otherwise, the protocol rules for the INFO request
>        governing the usage of tags, Route and Record-Route,
>        retransmission and reliability, CSeq incrementing and message
>        formatting follow those in [1] as defined for the BYE request."
> 
>Since a UAS does not send BYEs within an early dialog, but a non-2xx 
>final response instead, to terminate the dialog, people assume that INFO 
>cannot be sent in this situation either.
> 
>Let's try to keep this in mind and clarify this point when/if 
>we define new SIP methods.
> 
>In any event, the clarification to this issue can be found in 
>RFC 3398:
> 
>"From the callee to the caller, if a message is received by a gateway
>before the call has been answered (i.e., ANM is received) 
>it SHOULD be encapsulated in an INFO, provided that this will not 
>be the first SIP message sent in the backwards direction (in which 
>case it SHOULD be encapsulated in a provisional 1xx response)."

The problem is that the ITU-T interworking spec doesn't reference RFC3398. The spec reference the INFO RFC, and that is also where I think the usage rules should be defined (not in another spec, RFC3398 in this case, simply using the method).

The INFO RFC, as you said, currently says that INFO "follows the rules of BYE" (whatever that means is another question :), and the rules for BYE specifically says that it must not be sent backward before the INVITE has finished. If the INFO RFC would say "follow the rules of UPDATE" we would not have this problem, since the UPDATE spec specifically allows the use of the method before the INVITE has finished.

Thanks!

Christer Holmberg
Ericsson Finland

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