[Asterisk-Users] unsolicited NOTIFY messages from Asterisk

[Olle E. Johansson]

Chris A. Icide wrote:
> Olle E. Johansson wrote:
> 
>>Chris A. Icide wrote:
>>  
>>
>>>Note however, that in the unsolicited NOTIFY that Asterisk sends for
>>>MWI, it includes a ;tag= as part of the NOTIFY.  This will break some
>>>devices as they will not accept the NOTIFY because the tag doesn't match
>>>any transaction that is open.  The correct way to send an unsolicited
>>>NOTIFY would be without the tag altogether.
>>>    
>>That's interesting. Any suggestions on such a device? I haven't seen that.
>>
>>I guess if they do that, it's ok, since sending unsolicited NOTIFY is
>>theoretically wrong anyway. If the phone software wants to support it,
>>they wouldn't bother with the tag, I guess.
> 
> Yes, a Metaswitch softswitch (and I suspect some other softswitches
> would as well).  It returns a 403 error if you send a NOTIFY for MWI to
> it with a tag attached.
> 
> This is a little different implementation.  The Metaswitch is providing
> the end user (over PSTN) service, and when a phone goes unanswered, it
> sends a the call to asterisk over sip.  I extract the phone number that
> was originally dialed from the SIP Header using the dialplan command for
> reading sip header messages, and send the call to voicemail.  Now I have
> to send back indication that a message exists.
> 
> Since the Metaswitch isn't sending a subscribe for every single line, we
> have a push model.  So we push out MWI, but Asterisk tags the push, and
> the Metaswitch rejects it since it has no previous transaction with a
> matching tag.
> 
> I patched the code so it won't send a tag on an MWI Notify for my own
> use, but it's specific to this implementation and would cause problems
> where a subscribe has been sent.
Chris,
Thanks for the feedback. I don't think that would cause problems, since
Asterisk doesn't relate the subscription for MWI with the NOTIFY,
another chan_sip error... We just happily accept the subscription, but
do not react to it at all.

So the Metaswitch accepts NOTIFY without TAG and any relationship to
anything else, but do not accept NOTIFY with a tag? That's odd.
SIP is kind of odd in itself, so it makes sense ;-)

/O