6.17 Study for Robust Call Setup for VoLTE subscriber in LTE (FS_RobVoLTE)
TD S2 160221 LS from TSG RAN: LS on introduction of new establishment cause for mobile originating calls. (TSG RAN)
Abstract: RAN#70 agreed to define the VoLTE establishment cause for AS with SIB solution to avoid backward compatibility problems in the legacy network, i.e., eNB rejecting a call with unknown cause value. The agreed CR for this can be found in RP-152056. RAN plenary also agreed that RAN WG2 should specify a general guidance and clarification for the eNB behaviour receiving unknown establishment cause.
RAN WG2 should work on providing a clarification to specification concerning the handling of spare values for establishment cause (including the release from which to introduce the clarification) and provide a CR capturing that for RAN#71. Since the mapping between AS and NAS establishment causes is specified in TS 24.301, CT WG1 should also check whether any modifications are required to NAS specification TS 24.301 Annex D.
Therefore, RAN would like to ask CT WG1 to check whether the agreed CR RP-152056 warrants any modifications would be required to the NAS specification, specifically to the mapping between AS and NAS establishment causes in TS 24.301 Annex D, and implement the identified changes from Rel 12 onward. Additionally, the RRC establishment cause values are used in S1AP specification.
Therefore, RAN would ask RAN WG3 to introduce the new establishment cause value into the S1AP specification TS 36.413 in accordance with the agreed CR RP-152056.
