Tunnelling of IP Multimedia Subsystem (IMS) services over restrictive access networks; Stage 3
The present document specifies procedures and protocol elements for tunnelling of IMS traffic over restrictive access networks, specifically procedures and protocol elements for establishing, maintaining, and sending traffic via a firewall traversal tunnel between the UE and an enhanced firewall traversal function (EFTF) in the network. The present document is applicable to UE and EFTF.
The present document applies only to the case when the IMS traffic is not routed via EPC of a PLMN. Procedures for tunnelling of IMS traffic that is routed via EPC are specified in 3GPP TS 24.302 [3] annex F.