Subject: [Sipping] 488 vs 606

From: [email-masked]
Date: Wed, 10 Mar 2004 01:02:33 -0600

Hi,

I have a question on the usage of 488 vs 606 response. Kindly let me know
in the situation explained below which one is more appropriate.

Two UA's (A & B) establish a voice session, but after a while one of them
(say B) decides to change to FAX mode and hence sends a
Re-INVITE with T38 SDP. But User Agent 'A' does not support incoming T38
Re-INVITE (FAX SDP) for any call or any user and hence needs to
respond with a 488 or 606 response. In this situation, what response would
be more appropriate to reject the Re-INVITE. Please note that the request
sent by UA 'B' cannot be serviced by any other UAs as the fax data is
available only on 'A'.

Thank you,
Srini

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 11 Mar 2004 00:36:29 -0500

If the invite is rejected because fax is an unknown media type, send a 
488. Generally 6xx is not a great idea since you can never really know 
for sure that a request won't succeed elsewhere. For re-invite one could 
argue you do know, since re-invites dont fork, but I dont think you want 
different response codes for the same error condition, just because its 
inside vs. outside a dialog.

If the invite is rejected just because some kind of policy forbids 
re-invites (NOT A GOOD IDEA!) - use 403.

Ranjit writes:
> Hi Srini
> 
> If A does not support T.38 then it should send 415 Media Not Supported. 
> 
> Regards
> Ranjit

This is not correct. 415 means that the MIME media type (application/sdp 
in this case) in the body is not known. That is not the error condition 
we are talking about.

-Jonathan R.

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