What is MSRN Mobile Station Roaming Number

Technical details of the Mobile Station Roaming Number (MSRN) in mobile communication systems:

1. Definition:
   • The MSRN is an E.164-defined telephone number used within a mobile network.
   • It serves as a temporary identifier assigned to a roaming mobile station (MS).
   • The primary purpose of the MSRN is to facilitate efficient call routing for incoming calls to the roaming MS while it is outside its home network.
2. Routing Calls:
   • When someone initiates a call to a roaming MS, the Gateway Mobile Switching Centre (GMSC) in the caller’s network needs to route the call to the correct location.
   • The GMSC queries the home network (where the subscriber’s account is registered) to obtain the MSRN associated with the roaming MS.
   • The MSRN acts as a directory number temporarily assigned to the MS for the specific call.
3. Signaling Exchanges:
   • The process involves several signaling exchanges between different network elements:
     • Caller’s Network: Initiates the call and queries the home network.
     • Visited Network: The network where the roaming MS is currently located.
     • Home Network: The network where the subscriber’s account is registered.
   • These exchanges ensure that the call is correctly routed to the MS’s current location.
4. MSC and VLR Interaction:
   • Although many vendors’ Visitor Location Registers (VLRs) are integrated with the Mobile Services Switching Center (MSC), the GSM specification allows them to be separate entities.
   • The MSC and VLR are considered two different nodes, each having its own routing addresses.
   • The MSRN plays a crucial role in this interaction, allowing efficient call setup even when the MSC and VLR are not co-located.
5. SRI Response Message:
   • The MSRN is one of the parameters returned in the Send Routing Information (SRI) Response message.
   • This message is part of the Mobile Number Portability (MNP) scenario, where the MSRN can be modified as ‘RgN + MSISDN’ (Roaming Number + Mobile Subscriber ISDN Number).