Alert SMSC

     Alert SMC is often referred as Alert SC. Whenever SMSC unable to deliver a SMS to MS then it will keep try to send that to the corresponding MS till the expiry time of the SMS. (Expiry time is defined by the operator).

Here some cases..

o   Alert SMC-MS Reachable

o   Alert SMC-Memory Available

o   Alert SMC-Short Message Delivery Successful

Note: third case is not a failure case

Alert SMC-MS Reachable signaling flow:

If the MS is not-reachable when the SMC tried to send SMS that corresponding SMS will be resent to the customer once the customer gets coverage i.e customer back to reachable state. 

Once the customer back to reachable state, HLR of the corresponding operator will intimate to the respective SMC. Here the flow for that.

1.            The MS/UE makes or receives a call or performs a location update.

2.            The MSC server sends a Process_Access_Request message to the VLR when the MS/UE makes or receives a call. Or the MSC server sends an Update_Location_Area to the VLR when the MS/UE updates the location area.

3.            The VLR checks the subscriber data. If the VLR detects that the MNRF of the subscriber is set to Mobile Subscriber Reachable, the VLR removes the MNRF and sends a Ready_For_SM message to the HLR. The VLR directly sends an Update_Location request to the HLR in the case of a location update flow.

4.            If the HLR receives a Ready_For_SM message, it checks the dynamic data of the subscriber. If the MNRF is set, the HLR removes the MNRF and sends an Alert_Service_Centre message to the SMC and a Ready_for_SM_Ack message to the VLR. If the HLR receives an Update_Location request and the MNRF in the dynamic data of the subscriber is set, the HLR removes the MNRF, sends an Alert_Service_Centre message to the SMC, and continues the location update flow.

5.            The SMC returns an Alert_Service_Centre_Ack message to the HLR and attempts to resend the short message

Alert SMC-MS Memory Available signaling flow

If the Memory Capacity of the MS full i.e inbox is full,  when the SMC tried to send SMS that corresponding SMS will be resent to the customer once the customer gets available space in inbox.

Once the customer gets available space in inbox, HLR of the corresponding operator will intimate to the respective SMC. Here the flow for that.

1.            The MS/UE sends an SM Memory Capacity Available message to the MSC server over the A/Iu interface.

2.            The MSC server sends a READY_FOR_SM message to the HLR.

3.            The HLR checks the dynamic subscriber data. If the MCEF of the subscriber is set, the HLR removes it and then sends an Alert_Service_Centre message to the MSC server and a READY_FOR_SM_ACK message to the VLR.

4.            The MSC server sends an SM Memory Capacity Available message to the MS/UE.

5.            On receiving the Alert_Service_Centre message, the SMC sends an Alert_Service_Centre_Ack message to the HLR and tries to resend the short message.

Signaling flow for alert SMC-Short Message Delivery Successful

If the SMS is successfully delivered to a MS that will also be informed to the SMC and here the flow for that and this will be sent to the originator as SMS delivery report.

1.            The GMSC server sends a REPORT_SM_DELIVERY_STATUS message to the HLR.

2.            The HLR returns a REPORT_SM_DELIVERY_STATUS_ACK message to the GMSC server.

3.            The HLR sends an Alert_Service_Centre message to the SMC.

4.            The SMC returns an Alert_Service_Centre_Ack message to the HLR.

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.