7 Interworking requirements

22.1733GPPIP Multimedia Core Network Subsystem (IMS) Multimedia Telephony Service and supplementary servicesRelease 17Stage 1TS

7.1 Interworking with CS domain

Standardisation of interworking between the IMS domain and the CS domain for multimedia telephony communications is provided as specified in [4].

7.2 Interworking with external networks

General interworking requirements with external networks as specified for IMS services in [4] apply.

7.3 Media Aspects on Interworking

End to end codec negotiation shall be supported. When the codec negotiation fails, transcoding should be provided as an operator option.

When transcoding applies, the quality degradation and additional latency due to decoding/encoding operation shall be minimized.

When the media plane is locally broken-out and/or locally broken-in within a visited network, the home network may instruct the visited network to perform transcoding.

To optimize the end-user experience, during the codec negotiation and subject to operator policy, a wideband codec should be preferred over a narrowband codec, subject to the capabilities of both ends.