[sr-dev] PATCH: use correct to-tag in 302 redirects following early dialog creation

[Andrew Mortensen]

Hi all. We've recently been experimenting with 302 redirects as the vehicle for call-forwarding, and ran into an issue with call-forward no answer. A small patch against (see below) fixed things.

Caller and callee are Polycom 550s. The caller sends an INVITE to the callee, and the callee returns a 180 with a to-tag, establishing an early dialog. When sip-router's fr_inv_timer fires and sends the fake 408 reply to the INVITE, we handle enter the failure route and redirect to the forwarding address:

	# ... set URI to forwarded target here ...
	t_reply("302", "Call Forwarded");
	exit;

This should have worked, but in our testing the caller would completely ignore the 302. I tracked it down to sip-router returning a new to-tag in the 302, not the to-tag used in the early dialog. The Polycoms were evidently rejecting the 302 from sip-router as not matching any known dialog because of the unrecognized to-tag. [1]

My patch simply stores forwarded to-tags for early dialogs, making the winning to-tag available for the 302 reply. We've tested it with 3.0.3; the patch below is against git head. I'm happy to revise it to get it into acceptable form. Please let me know.

Best,
andrew

[1] Oddly, our Cisco gateways don't care about the new to-tag from sip-router, and will happily redirect regardless of the tag value in the 302. Perhaps it's the result of a looser interpretation of RFC 3261 12.1 and 12.3.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: sr-t_reply-302-totag.patch
Type: application/octet-stream
Size: 4085 bytes
Desc: not available
URL: <http://lists.sip-router.org/pipermail/sr-dev/attachments/20110915/bd0259e7/attachment-0001.obj>