Ericsson This memo describes a private extension to SIP in the form of a P-Called-Party-ID header. A proxy inserts this header typically in an INVITE, en-route to its destination. The header is populated with the Request-URI received by the proxy in the request. The UAS identifies which ID out of several IDs the invitation was sent to (for example, the user may be using simultaneously a personal and a business SIP URI to receive invitation to sessions). The UAS may use the information to render different distinctive audiovisual alerting tones, depending on the ID used to receive the invitation to the session.