Basic SMS Flow

                

The below figure is the representation on 3G/UMTS architecture

3G/UMTS

  

Basic SMS Flow

The basic SMS flow consists of the following:

• ·         Short Message Mobile Originated (SMMO)
• ·         Short Message Mobile Terminated (SMMT)

·         

SMMO signaling flow: 

Mobile Originated SMS

1.       The MS/UE sends a short message to the MSC server over the A/Iu interface.

2.       On receiving the SMS request over the A/Iu interface, the MSC server sends a SEND_INFO_FOR_MO_SMS message to the VLR based on the MSISDN of the originating MS/UE.

3.       The VLR checks the subscription information and whether the MSC server supports the SMS, and then returns a SEND_INFO_FOR_MO_SMS_ACK message to the MSC server.

4.       The MSC server analyzes the SEND_INFO_FOR_MO_SMS_ACK message. If the MSC server does not support the SMMO service, or the MS/UE has subscribed to the outgoing call barring service, the MSC server directly sends a Short Message Error (RP_ERROR) message to the MS/UE. Otherwise, the MSC server obtains the address of the SMC from the short message and transparently transmits an MO_FORWARD_SHORT_MESSAGE message to the SMC.

5.       On receiving the MO_FORWARD_SHORT_MESSAGE request, the SMC checks whether the data is valid. If the data is valid, the SMC returns an MO_FORWARD_SHORT_MESSAGE_ACK message to the MSC server.

6.       The MSC server sends a Short Message Acknowledgement message to the MS/UE.

SMMT signaling flow

Mobile Terminated SMS

1.            On receiving a short message, the SMC obtains the called number from the short message, and then sends a SEND_ROUTING_INFO_FOR_SM message carrying the called number to request the HLR for the routing information.

2.            The HLR returns a SEND_ROUTING_INFO_FOR_SM_ACK message to the SMC.

3.            Based on the MSC server number, the SMC sends an MT_FORWARD_SHORT_MESSAGE to the MSC server.

4.            The MSC server requests the VLR to check the data of the SMMT subscriber.

5.            The VLR checks the subscription data and mobility management status, and performs one of the following operations based on the actual conditions:

·         If the subscriber cannot be paged because the SMMT service is not supported, the MS/UE is powered off, the MNRF is set, or the roaming is not allowed, the MSC server returns a failure response to the SMC.

·         If the location area of the MS/UE is known, the MSC server starts paging the MS/UE in the specific location area.

·         If the location area of the MS/UE is unknown, the MSC server starts paging the MS/UE in the coverage area of the MSC server.

6.            The MSC server pages the MS/UE.

7.            The MS/UE returns a paging response to the MSC server.

8.            The MSC server sends a PROCESS_ACCESS_REQUEST_ACK or SEARCH_FOR_MOBILE_SUBSCRIBER_ACK message, requesting that the VLR process the access request from the MS/UE.

9.            The VLR returns a SEND_INFO_FOR_MT_SMS_ACK to the MSC server.

10.          The MSC server sends the short message to the MS/UE.

11.          The MS/UE returns a Short Message Acknowledgement message to the MSC server.

12.          The MSC server sends an MT_FORWARD_SHORT_MESSAGE_ACK message to the SMC.