Short Message Service technical realisation (GSM)

[1] These MAP messages may be transported using "traditional" TDM based signalling, or over IP using SIGTRAN and an appropriate adaptation layer.

This service sends the mo-ForwardSM[Note 1] MAP operation to the SMSC identified in the SM Submission from the handset, embedded within a Transaction Capabilities Application Part (TCAP) message, and transported over the core network using the Signalling Connection Control Part (SCCP).

[1] The Interworking MSC of the SMSC, on receipt of the MAP mo-ForwardSM message, passes the SMS-PP[2] Application Protocol Data Unit (APDU) containing the text message to the actual Service Centre (SC) of the SMSC for storing, and subsequent "forwarding" (delivery) to the destination address and the SC returns an acknowledgement indicating success or failure.

[2] The GMSC, on receipt of this Short Message, needs to discover the location of the B-Party in order to be able to correctly deliver the text to the recipient (the term Gateway MSC, in this context, indicating an MSC that is obtaining routing information from the Home Location Register (HLR)).

The HLR performs a database lookup to retrieve the B-Party's current location, and returns it in an acknowledgement message to the SMSC's GMSC entity.

Since a typical deployment sees the VLR being co-located with the MSC, this message flow is usually internal to the platform.

[Note 4] Should the page or search for the subscriber fail, the VLR will indicate the failure cause to the VMSC, which will abort the Short Message delivery procedure and return the failure to the SMSC (see the Failed Short Message delivery section below).

When the VMSC/SGSN indicates a Short Message delivery failure, the SMSC may send a message to the HLR, using the MAP_REPORT_SM_DELIVERY_STATUS procedure, indicating the reason for the delivery failure and requesting that the SMSC be put on a list of service centres wanting to be notified when the destination party becomes available again.

The TCAP_BEGIN has TCAP related information that would otherwise cause the limit to be exceeded due to the additional fields added by MAP phase 2.

This segmentation procedure is also increasingly followed, and optionally enforced, by carriers to avoid SMS spoofing impacting their customers.