Friday, October 14, 2016

Roaming Call Flow

Hi All,

   Greeting from TelecomTigers Team,

As per request from many of our readers,
Here is a MT Call Flow, When Subscriber is in Roaming,
Following parameters are not taken here for simplicity i.e. Authentication, Ciphering, Paging, etc.

Postpaid Subscriber MT Call Flow :-

  • Mobile (MS A) dials Mobile (MS B) Number (which is of Circle 2 but currently in roaming at Circle 1).
  • "Connect" msg is sent from MS A to MSC A, which analyse B-Number & found it's of different circle, so it route the call to GMSC A.
  • After receiving IAM from GMSC A, GMSC B initiates the SRI request to HLR B.
  • In Normal Scenario, i.e. Postpaid MT call flow, GMSC B will initiate the SRI query to HLR B & HLR B will ask for PRN from MSC B (in which MS B currently present), & MSC B will respond to that query by providing MSRN number to GMSC B via HLR B, but here,
  • Since MS B is in Roaming at Circle 1, so HLR B will ask for PRN from MSC C, via GMSC B & GMSC C.
  • MSC C provides the MSRN to GMSC A via GMSC C & GMSC B
  • After receiving MSRN by GMSC A, MSC A routes the call to MSC C.
  • Now, ISUP msgs (IAM, ACM, ANM, REL, RLC) is sent from MSC A to MSC B, to complete the call.

Comments are most Welcomed,

Telecom Tigers Team
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