MSRN-Mobile Subscriber Roaming Number
It is similiar to MSISDN in STructure.Used for Providing the Routing during MT Calls.
When Ruting requested by HLR to MSC…MSC assigns one of the free (IF ANY) MSRN to that IMSI (if in ACTIVE STATE) then returns that MSRN via MAP .Which inturn forwarded to GMSC by HLR.GMSC Uses ISUP/TUP (18TH CENTURY COUNTRIES )
to route the call to MSC.
When the call reaches the MSC with that MSRN , MSC knows that the call is for the assigned IMSI and delivers the call and releases the MSRN.