[Asterisk-Dev] SIP codes/behaviors

[Kevin P. Fleming]

Mark Willis wrote:
> I have two SIP issues. In one case we're dealing with Level3, who always 
> require a 100 Trying in response to an INVITE. Problem is this is for an 
> unprovisioned number. So I want to send a 100 then a 404. I can't find a 
> way to do this, since asterisk just sends the 404. If there was an 
> NotFound application I could just call that and asterisk would send the 
> 100 followed by a 404 in the NotFound app.

This is completely unreasonable on their part; there is no legitimate 
reason to require a '100 Trying' response to an INVITE before sending a 
final response. We have other users successfully interoperating with 
Level3 with Asterisk CVS HEAD that don't have this issue.

> In the second case, we're terminating calls. If we run out of lines the 
> customer wants a SIP 603, rather than the 503 asterisk sends on 
> Congestion().

Quoting from RFC3261:

21.6.2 603 Decline

    The callee's machine was successfully contacted but the user
    explicitly does not wish to or cannot participate.  The response MAY
    indicate a better time to call in the Retry-After header field.  This
    status response is returned only if the client knows that no other
    end point will answer the request.

A 603 response would be inappropriate here, since the callee was not 
contacted and did not decline the call. There could also be other paths 
that would answer the request (since you are only out of channels), so 
again 603 would be inappropriate.