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
P-Charging-Vector: The S-CSCF adds the identifier of its own
network to the originating Inter Operator
Identifier (IOI) parameter of this header.