MO sms signaling flow

Short message mobile origination (SMMO) refers to the process that an UE/MS sends a short message to the short message center (SMC), and the SMC returns a report to the UE/MS, notifying whether the short message is sent successfully or not.

The SMMO signaling flow is as follows:

1. The UE/MS sends a connection management (CM) service request message carrying the cell information, service type, called number, user ID, and authentication parameters about the UE/MS to the MSC.
2. The authentication and encryption flow is started. For details, see Security Management.
3. After the MSC accepts the CM service request, the UE/MS sends a CP DATA message carrying the short message data and related address information to the MSC through the Iu/A interface.
4. Upon receipt of the CP DATA message, the MSC returns a CP ACK message to the UE/MS, notifying that the CP DATA message has been received (which does not mean that the SMC has received the short message).
5. The MSC requests user data from the VLR, and checks the subscription data about the UE/MS and whether the local MSC supports the short message service (SMS).
   • If the local MSC does not supportSMMOor the UE/MS subscribes to the Call Restriction SS, the MSC directly returns a message to notify the UE/MS that the SMMO request is rejected.
   • If the local MSC supports SMMO or the UE/MS does not subscribe to the Call Restriction SS, the MSC obtains the SMC address from the short message, and then transparently transmits the short message to the SMC through the MAP_MO_FORWARD_SHORT_MESSAGE_REQ message.
6. After receiving the request, the SMC checks the data validity. If the check is passed, the SMC returns a MAP_MO_FORWARD_SHORT_MESSAGE_CNF message to the MSC.
7. The MSC returns a CP DATA message to the UE/MS, notifying that the short message has been sent to the SMC successfully.
8. The UE/MS returns a CP ACK message to the MSC, notifying that the CP DATA message has been received.
9. If the length of the short message exceeds the limit, the UE/MS divides the short message into several parts, and send them through the CP DATA message.