[Serusers] Tags, forwarding, redirects, and picky UACs

[Alistair Cunningham]

I'm trying to implement forwarding to voicemail with a UAC that's picky
about the tags in the To: headers it receives.

First, I tried the following:

failure_route [1] {
	rewritehostport("192.168.1.1:5060");
	append_branch();
	t_relay();
}

This failed because the UAC received a "180 Ringing" from the ringing
Grandstream phone via ser that contained a To: tag. After the timeout,
it received another 180 from Asterisk (the voicemail system) with a
different tag. Since it doesn't support forked INVITES, it dropped the call.

Then I tried:

failure_route [1] {
	rewritehostport("192.168.1.1:5060");
	t_reply( "302", "Moved Temporarily" );
}

This time it receives the 180 from the phone as before. Then it receives
the 302. Alas, SER has ignored the tag from the phone, and created a new
one of it's own, so the UAC again drops the call.

Does anyone know of a way round this? Can SER be persuaded to use a tag
it has already received? Can I strip the tag from the To: header in one 
or both of the responses? I'm willing to get my hands dirty with the SER 
source code if necessary.

-- 
Alistair Cunningham,
Integrics Ltd,
+44 (0)7870 699 479
http://integrics.com/