The To header is a cosmetic, purely logical commentary on the intended ultimate
destination of the call, and no routing should ever be done on it. The RURI of the INVITE
is the appropriate vehicle for that.
When dealing with proxies, however, one will encounter from time to time the grim reality
that there are user agents which expect the To URI and the INVITE RURI to be in alignment.
For that scenario, you can use ‘uac’ module’s stateful rewriting functionally
(uac_replace_to()) to modify To with Kamailio in a way that displays fidelity and esteem
for protocol formalities.
—
Sent from mobile, with due apologies for brevity and errors.
On May 21, 2019, at 9:32 AM, JR Richardson
<jmr.richardson(a)gmail.com> wrote:
Hey Folks,
I could use some feedback to see if my mind is right on this topic.I'm
in a discussion with a software Vendor (respectfully unnamed) with
terminal software routing on To: header info. It's my contention any
modern SIP software should use INVITE header to retrieve DID info and
route from there.
My reasoning is due to the To: header should contain the original
intended DID, Extension, Name, AoR or whatever else the original SIP
transaction wanted to contact, but being in a multi-carrier,
multi-hop, call forwarding environment, the INVITE header contains the
hop-to-hop true intention of where the call should route at any given
transaction. So in the case of terminal software the To: header could
likely be irrelevant where as the INVITE header is accurate.
My most recent response from the Vendor suggest I put a SIP Proxy in
front of the terminal software and transform the To: header to
whatever I need for this application. Although I can do this, I'm
concerned with breaking RFC for CANCEL and BYE transaction sent back
from the terminal software that may not be recognized by upstream
origination carriers.
Plus modifying To: header is widely frowned upon by most folks.
Thanks.
JR
--
JR Richardson
Engineering for the Masses
Chasing the Azeotrope
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