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.
And this is now in the project's tracker:
http://sip-router.org/tracker/index.php?do=details&task_id=152&project=1
Feedback is welcome.
andrew
On Sep 15, 2011, at 5:19 PM, Andrew Mortensen wrote:
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.
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Andrew Mortensen