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.