You may notice that a user from operator A cannot send SMS to a user from operator B. SRI comes from A network to B side. CS STP is sending the SMSC the true IMSI and VLR information for the destination B user. Operator A's SMSC sends the MO-Forward SM towards operator B's SMSC. But B's SMSC is not sending correctly to the VLR GT on the SCCP side. Instead, it is using the GT from the SCCP sender side. The error that appears on the SCCP side is "(SCCP) No transl for spec addr".
That might happen several times, and the MO-Forward SM arrives in a different SMSC each time and fails the same way. Eventually, it is directed to a server that uses the VLR GT correctly, and the SMS is delivered successfully. The SRIs are the same when it fails and when it is ok.
The issue might happen when the SMSC is configured with Address Indicator (gtnatureofaddressind) set to International (default). If SCCP CdPA comes with the national format, it will result in UDTS.
You can find more details about that in the RTR Operator Manual, such as:
|Location||Host-specific or Common configuration files|
|Description||Type of address indicator used in the specific GT of an RTR|
|Valid Values||• unknown
Request the MO Originator to send the SMS with the Address Indicator set to International.