4 UE – network protocols
24.3223GPPRelease 17Stage 3TSTunnelling of IP Multimedia Subsystem (IMS) services over restrictive access networks
4.1 General
In order to access to IMS via restrictive non-3GPP access network, the UE and the EFTF shall establish a firewall traversal tunnel to IP network of IMS (FTT-IMS) using the UE requested FTT-IMS establishment procedure according to subclause 5.2.
The UE and the EFTF shall send the IP packets using the IP packet transport FTT-IMS procedure according to subclause 5.3.
The UE and the EFTF shall use the IP protocol according to clause 6.
When FTT-IMS is no longer needed (e.g. if the UE deregistered from IMS), the UE shall perform the UE requested FTT-IMS release procedure according to subclause 5.4.
When FTT-IMS is no longer needed, the EFTF can perform the EFTF requested FTT-IMS release procedure according to subclause 5.5.
NOTE: Keep-alive functionality is not defined in this document. Keep-alive functionality defined in 3GPP TS 24.229 [2] can be used to maintain the FTT-IMS between the UE and the EFTF.