The combination of CS and IMS services (CSI) is the parallel operation of a CS service and an IMS session between the same two users. It does not require a specific subscription and a specific charging correlation.
This TS provides architectural details to combine CS services and IMS services for using them in parallel between the same two users in a peer-to-peer context. The document provides a detailed description of how capabilities and identities are exchanged to enable the combination of CS and IMS services between the same two UEs.
This TS includes the following capabilities that enable the combination of CS and IMS services:
Radio capability exchange.
SIP based UE terminal capability exchange.
MSISDN number exchange in SIP.
Establishing an IMS session in parallel to an ongoing CS call between the same two UEs.
Establishing a CS call in parallel to an ongoing IMS session between the same two users UEs.
Network support for establishing multimedia sessions between a UE that uses IMS origination and a UE that
uses CSI termination.
The individual CS call or IMS service that are combined are described in their respective specifications.