29.1633GPPInterworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networksTS
The Interworking between Circuit switched multimedia telephony service, as described in 3GPP TS 26.110  and 3GPP TS 26.111 , and packet switched multimedia services, as described in 3GPP TS 26.114  is addressed.
NOTE: Examples in the present Annex assume that the ITU-T H.263  video codec is used at the CS side. However, in the present release of 3GPP TS 26.114 , the H,263 video codec is no longer recommended (although it has been mandated in previous releases).
Figure E.1.1.1 Overview of relevant CS-Domain Protocols (from TS 26.110 )