There are chances that operators local number portability databases(NPDB) are not synchronized with each other. So if an MSISDN X is considered ported to operator B in the NPDB of operator A while at the same time MSISDN X is considered to be still with operator A in the NPDB of operator B we have a LOOP CONDITION.
In this case if a call is dialled to X by another subscriber of operator A, the call will be treated as ported out call (based on information received from NPDB-A) and call is routed to operator B. Operator B upon querying its NPDB -B route the call back to operator A. However operator A upon querying its NPDB will route the call again to operator B and so on, cauing a continous loop. This loop may cause the fluctuation or complete outage in signallling links, therefore a solution needs to be in place to avoid this situation.
In order to avoid this loop condition, a mechanism to detect this loop needs to be implemented on GMSC in the form of software patch. This solution will consist of following logic.
- Operator-A recieves the IAM on interconnect links at its GMSC.
- GMSC-A will now append operator’s own RN(MNP Routing Number) in the called party number .e.g. if RN of operator A is D0355 then GMSC-A will convert the called number from 03335100068 to D03553335100068 .
- GMSC-A will send an SRI of 0333 5100068(original called number) to NPDB.
- NPDB will send SRI-Resp back to GMSC. if the number is ported out then the RN of other operator will be returned in the MSRN field of SRI_resp message.
- GMSC will compare the modified called number (generated by appending operator’s own RN in called number as in step 2) with the MSRN field. If the numbers are same then the call will be processed further. If numbers are different call will be dropped immediately in order to avoid loop.
