To be able to later use the CONF service, when the UE sends an INVITE request to a second user, the UE shall use the same identity as the UE used when setting up the first communication.
When creating the conference with an INVITE request the UE shall use the same identity as the UE used in the communications now on HOLD. If the UE uses identity C or identity D for the established sessions, the UE shall add the Addditional-Identity header field containing this identity. The UE sets the Request-URI to the same conference factory URI as the UE uses for the native identities.
When the UE adds a conference participant using the procedures in
clause 5.3.1.5.3 in TS 24.147, the UE shall set the Referred-By header field in the REFER request to the same identity as the one used when creating the original session(s). If this identity is a non-registered identity (identity C or identity D) the UE adds the Additional-Identity header field containing this identity.
If the AS receives an INVITE request with a Request-URI to a conference factory used in the serving network and an Additional-Identity header field, the AS in addition to the procedures in
clause 4.5.3.2.1 replaces the Request-URI with a default conference factory URI for MMTel (as specified in
TS 23.003) valid in the home network of the identity in the Additional-Identity header field.
If the AS receives an INVITE request, addressed to a default conference conference factory URI for MMTel as specified in
TS 23.003, including an Additional-Identity header field the AS may in additon to the procedures in
clause 4.5.3.3 modify the Request-URI to include any conference factory URI of the serving network.
If the AS receives a REFER request containing an Additional-Identity header field, the AS shall in additon to the procedures in
clause 4.5.3.3 verify that the identity in the Referred-By header field is consistent with the Additional-Identity header field, and if necessary replace the Referred-By header field value with the identity in the received Additional-Identity header field. The AS then forwards the REFER request following normal procedures.