In the case where the Request-URI of the incoming INVITE request to S-CSCF contains a
TEL-URL, it has to be translated to a globally routable SIP-URL before applying it as
Request-URI of the outgoing INVITE request. For this address translation the S-CSCF uses
the services of an ENUM-DNS protocol according to RFC 2916, or any other suitable
As S-CSCF1 does not know whether the I-CSCF at home2.net is a loose router or not,
it does not introduce a Route header.
S-CSCF1 inserts the corresponding TEL URL to the P-Asserted-Identity header in
order that the TEL URL is known to the destination network in case the INVITE is forwarded
to a MGCF.
S-CSCF1 adds the identifier of its own
network to the originating Inter Operator
Identifier (IOI) parameter of this header.
I-CSCF2 sends a query to the HSS (the public user identity is provided in the Request-URI)
to find out the S-CSCF of the called user. The HSS responds with
the address of the current S-CSCF for the terminating subscriber.