scope:

The present document contains the result from the study of introduction of support for A-interface over IP. High level areas that are studied are e.g. potential placement of transcoders in the core network, effective bandwidth utilisation at the A-interface, impact on call related messages, payload formats.

The following items shall be covered in the study:

• In the target solution it is wanted to transfer compressed speech as far as possible end-to-end to achieve efficient transport and speech quality. The possibility to free GERAN from handling all kind of transcoders shall be studied, and the architecture might place Codecs in the core network. 

• Impacts/changes on current A-interface procedures resulting from placing transcoders in the core network as well as in the BSS shall be studied, e.g. impacts on the assignment and handover procedures.

• In addition to allow compressed speech over the A-interface the study shall provide further solution for effective bandwidth utilisation at the A interface, which means it shall describe multiplexing of RTP flows and how this will be negotiated between the BSS and CN nodes.

• The study shall describe a solution for "true end-to-end Codec negotiation", which considers on a call basis the preference/situation of the radio network.

• It shall be studied how call related messages have to be adapted, e.g. transfer of Codec related information, identification of calls/sessions.

• The study shall describe the wanted payload formats and other relevant user plane parameters like packetization time etc.