Multimedia Telephony for IMS (MTSI) is a standardized service for conversational telephony, TS 22.173. The media handling and interaction are specified in TS 26.114. MTSI has been specified such that the user experience of multimedia telephony is equivalent to or better than corresponding circuit-switched telephony services while still having efficient resource usage. Multimedia telephony also exploits the richer capabilities of IMS where media components can be used symmetrically or asymmetrically in different directions.

TS 26.114 define media handling and interaction for the Multimedia Telephony Service for IMS (MTSI) including mechanisms for the negotiation of bandwidth using the SDP bandwidth modifiers. The present study investigates potential improvements for the end-to-end QoS handling with the purpose to improve the network resource allocation for variable bit-rate codecs, rate-adaptive codecs and asymmetric sessions (i.e. different bitrates for different directions). The study will focus on SDP extensions and the interaction with the policy control. The present document:

• Identifies high-level use cases
• Evaluates for these use cases the current limitations and the expected benefits
• Establishes recommended high-level functional requirements and related recommended technical requirements
• Discusses potential solutions
• Studies impact of potential solutions on networks and terminals