24.4033GPPIP Multimedia Call Control Protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP) Stage 3 [3GPP TS 24.229 (Release 7), modified]Release 7TISPANTS
Entities in the IM CN subsystem shall restrict cpc tel URI or SIP URI parameter to specific domains that are trusted and support the cpc parameter. Therefore for the purpose of the cpc parameter within this specification, a trust domain also applies. This trust domain is identical to that of the P-Asserted-Identity. If the communication is to be passed to an untrusted network or a network not supporting the cpc the cpc parameter shall be removed.