3GPP IMS provides an IP-based session control capability based on the SIP protocol. IMS can be used to enable
services such as push-to-talk, instant messaging, presence and conferencing. It is understood that "early"
implementations of these services will exist that are not fully compliant with 3GPP IMS. For example, it has been
recognized that although 3GPP IMS uses exclusively IPv6, as specified in clause 5.1 of TS 23.221
, there will exist
IMS implementations based on IPv4 (TS 23.981
Non-compliance with IPv6 is not the only difference between early IMS implementations and fully 3GPP compliant
implementations. In particular, it is expected that there will be a need to deploy some IMS-based services before
products are available which fully support the 3GPP IMS security features defined in TS 33.203
with TS 33.203 security features is expected to be a problem mainly at the UE side, because of the potential lack of support of the USIM/ISIM interface (especially in 2G-only devices) and because of the potential inability to support IPsec on some UE platforms.
Although full support of TS 33.203 security features is preferred from a security perspective, it is acknowledged that early IMS implementations will exist which do not support these features. Therefore, there is a need to ensure that simple, yet adequately secure, mechanisms are in place to protect against the most significant security threats that will exist in early IMS implementations.
ThiS TR documents an interim security solution for early IMS implementations that are not fully
compliant with the IMS security architecture specified in TS 33.203. For security reasons, the provisions in this TR only apply to IMS procedures used over the 3GPP PS domain.