In GSM (Global System for Mobile Communications), the MSRN (Mobile Station Roaming Number) plays a crucial role in call routing and mobile communication. The primary use of MSRN is associated with the process of call setup and call routing for mobile devices within the GSM network. Here’s a detailed explanation of the use of MSRN in GSM:
1. Call Routing and Mobile Termination:
- Location Update: When a mobile device is powered on or moves to a new location area, it performs a location update procedure to inform the network of its current location.
- HLR Query: During the location update, the Home Location Register (HLR) of the subscriber’s home network is queried to retrieve information about the subscriber, including the MSRN.
- Assignment of Temporary MSRN: The HLR assigns a temporary MSRN to the mobile device. This temporary MSRN is used during call routing while the mobile device is in the visited location area.
2. Mobile Originating Call:
- Call Setup: When a mobile device initiates an outgoing call (mobile-originating call), the MSC (Mobile Switching Center) queries the HLR for the destination subscriber’s MSRN.
- Routing Information: The HLR provides the MSC with the MSRN associated with the called subscriber’s current location.
- Call Routing: The MSRN is used by the MSC to route the call to the visited MSC or VLR (Visitor Location Register) serving the called subscriber.
3. Mobile Terminating Call:
- Incoming Call Routing: When a call is directed to a mobile subscriber (mobile-terminating call), the call is routed to the MSC or VLR associated with the current location of the called subscriber.
- HLR Query for MSRN: The HLR is queried to obtain the MSRN associated with the called subscriber’s current location.
- Routing to Temporary MSRN: The MSC uses the MSRN to route the call to the temporary MSRN assigned to the mobile device in the visited location area.
4. Temporary Routing for Roaming:
- Roaming Scenarios: MSRN is particularly crucial in roaming scenarios where a mobile device is in a location area different from its home network.
- Efficient Call Routing: The use of MSRN allows for efficient call routing to the temporary MSRN associated with the current location, ensuring that the call is correctly directed to the visited network.
5. Privacy and Security:
- Temporary Identifier: The temporary MSRN adds a layer of privacy and security by not revealing the actual subscriber’s MSISDN (Mobile Station ISDN) to the visited network. MSRN acts as a temporary identifier for call routing purposes.
In summary, the MSRN in GSM is primarily used for efficient call routing and setup, especially in roaming scenarios. It serves as a temporary identifier associated with the current location of the mobile device, ensuring that calls are correctly directed to the visited network’s MSC or VLR.