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SMS MT During Handover

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SMS MT During Handover


I have a question regarding SMS MT during Inter MSC Handover.
If a subscriber is on Call and moves from MSC A to MSC B, now call will be still connected and VLR of this subscriber is still with MSC A. At this time if there is a SRI_SM comes to HLR it will provide the address of MSC A for SMS termination, but subscriber has been moved out to MSC B. Now my question is how this SMS will reach to subscriber.
In this case will VLR A will control the MSC B.

It might reach by this way...

Hi Tarun

Keeping the following things in mind:

1. Location update in HLR will not happen untill the call is ended.
2. MSC A will not send FSM_ACK to SMSC as it will not be able to deliver the SMS to Subscriber.
3. So a copy of SMS will be in the SMSC buffer untill it recieves FSM_ACK.
4. There is a limit for SMSC to keep the SMS . It depends whether it is 48 hours or something else. Also it depends upon the buffer of SMSC (if its full the msg will be discarded).
5. So, when call ends,location update happens in HLR .The HLR initiates the cancel location procedure when it receives an 'update location' message from a VLR (VLR B) other than the one in which the MS was located at the time when its location information was last updated in the HLR database.
6. Now if SMSC again does an SRI towards HLR it will get the updated information and the sms will be routed to subsciber via MSC B. (This I am not confident , SOMEONE PLEASE CONFIRM THIS).
But if this doesnt happen the SMSC will keep on sendinf FSM towards MSC A untill timer (there will be some timer) expires. So in this case also SMS will not reach the subscriber.

It will be good if u can send some traces.

Abhishek Bhardwaj