23.1533GPPOut of band transcoder controlRelease 17Stage 2TS
Figure 6.1/1: Configuration during Call Setup of a Mobile to Mobile Call
Following network and protocol entities are involved in the scenario, outlined in Figure 6.1/1:
RNC-T, RNC-O: terminating/originating RNCs.
MSC Server-T, MSC Server-O: MSC Servers, performing service, i.e. codec negotiation.
MGW-T, MGW-O: terminating/originating MGWs with the optional capability to insert/remove so called.
TrFO break equipment: (TBEs), i.e. contexts containing an UTRAN- and a CN side IU Framing termination (T1 – T4), inter-working in a distinct manner on control level. [Note: context is meant to be the H.248 specific throughout the document]. It is aimed to design protocols for TrFO in a way, that these pieces of HW can be removed after call setup phase to allow to revert to "simple" AAL2 switching in case of ATM transport.
IU FP term.T, IU FP term.O: Terminating- and originating-side TrFO peers (IU Framing terminations in RNC’s in Figure 6.1/1).
RANAP, TICC:C-plane protocol incarnations, responsible for codec negotiation, controlling the respective interfaces (IU, NC), creating, modifying, removing etc. terminations and contexts.
The final configuration is (at least logically) an end to end TrFO relation between RNC-T and RNC-O with the option to remove the TBEs from the user data path, i.e. to revert to pure AAL2 switching in case of ATM Transport.
Figure 6.1/2: Call Setup. Mobile to Mobile Call. Message Flow part 1
Figure 6.1/3: Call Setup. Mobile to Mobile Call. Message Flow part 2
Figure 6.1/4: Call Setup. Mobile to Mobile Call. Message Flow part 3
Steps 1. to 6. give the codec negotiation phase. The mobiles inform the network about their capabilities (1. and 4.). Afterwards the MSC-Server performs codec negotiation according to clause 5.6.
Network side bearer establishment
MSC-T/MSC-O shall request seizure of network side bearer terminations with IuFP properties (see steps 5. and 7.). Intermediate CN nodes that may perform certain service interactions (e.g. IN nodes) have to seize terminations with IuFP properties as well.
RAN side terminations with IuFP property have to be seized (9. and 17.) before sending RAB Assignment (steps 10. and 18.), that contains RAB parameters according to the selected codec and the negotiated ACS. In addition, the respective NAS synchronisation indicator shall be included.