ETSI TS 123 292 specifies the architectural requirements for delivery of consistent services to the user regardless of the attached access type (e.g. CS domain access, or IP-CAN). This is achieved by implementing the services in the IP Multimedia Subsystem (IMS).

Consideration is given to how to access specified IMS-based services (see clause 22.4 of TS 22.101 [9]) whilst still allowing other, bespoke services to be offered by the home operator. IMS control of services related to those defined in clause 22.4 of TS 22.101 [9] are part of the present scope of this specification. However, IMS control of all other types of calls, including emergency calls that utilise TS12, are outside the scope of the present release of this specification.

The scope of the specification includes:

• Session establishment when using CS access for media transmission for an IMS service.
• Support of Service Continuity as specified in TS 23.237 [12].
• Support of Single Radio Voice Call Continuity as specified in TS 23.216 [36].
• Access Domain Selection (ADS).
• IMS control of services where the media is transported via the CS network (e.g. managing of mid-call services).
• Service data management.

The solution is applicable for UEs with or without ICS functionality, and is applicable for the following deployment scenarios:

• An operator who supports for their subscribers only UEs that have ICS functionality.
• An operator who supports for their subscribers only UEs that do not have ICS functionality.
• An operator who supports for their subscribers UEs which do and do not have ICS functionality (to different subscribers and the same subscribers) ensuring the coexistence of UEs that have and do not have ICS functionality.
• Inbound roaming subscribers on an operator's network that supports either the same or different ICS functionality that the inbound roaming subscriber is using, ensuring the coexistence of UEs that have and do not have ICS functionality.