K.1 Scope

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

This annex describes the UE, P-CSCF, and S-CSCF procedures in support of UE managed NAT traversal. For ICE, the IBCF procedures are also described. In this scenario, both the media flows and the SIP signalling both traverse a NA(P)T device located in the customer premises domain. The term "hosted NAT" is used to address this function. This annex does not consider the case where the NAT is behind the P-CSCF as different NAT traversal procedures are necessary for this architectural scenario.

The procedures described in this subclause of this annex rely on the UE to manage the NAT traversal process. As part of the UE management process, the UE can learn whether it is behind a NAT or not, and choose whether the proceedures in this annex are applied or not.

The protection of SIP messages is provided by applying either UDP encapsulation to IPSec packets in accordance with RFC 3948 [63A] and as defined in 3GPP TS 33.203 [19] or by utilizing TLS as defined in 3GPP TS 33.203 [19].

NOTE 1: This annex describes the mechanism for support of UE managed NAT traversal scenario defined in 3GPP TS 23.228 [7]. This does not preclude other mechanisms but they are out of the scope of this annex.

NOTE 2: It is recognized that outbound can be useful for capabilities beyond NAT traversal (e.g. multiple registrations) however this annex does not consider such capabilities at this time. Such capabilites can require additional information elements in the REGISTER request so that the P-CSCF and S-CSCF can distinguish whether to apply procedures as of annex F or annex K.