The procedures for SMS in this annex apply only if the UE is 1xRTT CS Registered and the CS access domain is chosen by the UE and/or the home PLMN for delivering short messages.
This clause describes both the mobile originating and mobile terminating SMS over S102 which uses 1xCS procedures in EPS. SMS support is based on the S102 reference point between the MME and the 1xCS IWS, use of RRC Information Transfer message between the UE and the E-UTRAN, and use of S1 cdma2000 Tunnelling message between the E-UTRAN and the MME.
A mobile originating short message is triggered. If the UE is in idle state, the UE performs the UE triggered Service Request procedure, which is defined in TS 23.401.
The MME sends an S102 Ack message to the 1xCS IWS. This occurs immediately after step 9 if the MSC has not requested an acknowledgement from the 1xCS IWS.
The 1xMSC receives the SMS message from the MC and sends an ADDS Page message to the 1xCS as defined in 3GPP2 A.S0008 [16] and 3GPP2 A.S0009 [17]. The ADDS Page contains the SMS message.
If the UE is in idle state, the MME performs the network initiated Service Request procedure to bring the UE to active state prior to tunnelling of the SMS message toward the UE.
The MME sends an S102 Ack message to the 1xCS IWS. This occurs immediately after step 3 if the MSC has not requested an acknowledgement from the 1xCS IWS.
When UE is performing CS fallback procedure to 1xRTT for the purpose of emergency call, it shall indicate to the MME that this CS fallback request is for emergency purpose. MME also indicates to the E-UTRAN via the appropriate S1-AP message that this CS fallback procedure is for emergency purpose.
Emergency call with enhanced 1xRTT CS fallback procedure shall be executed without the concurrent PS handover procedure.