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.
full Table of Contents for TS 23.279 Word version: 15.0.0