VMSC (Visited MSC): Definition, Functions, and How It Works

telcomatraining.com – Visited MSC (VMSC) is a critical component in mobile communication networks. It stands for “Visited Mobile Switching Center,” and it refers to the MSC that serves a mobile subscriber when they are roaming outside their home network. The VMSC is responsible for handling call processing, location updates, and managing subscriber mobility.

The VMSC plays a vital role in ensuring seamless connectivity for mobile users as they travel between different regions or even countries. By coordinating with other network elements, it allows users to make and receive calls, send messages, and use mobile data services while roaming.

Functions of VMSC

The Visited MSC has several essential functions in mobile networks. These include:

1. Call Routing and Switching

One of the primary roles of the VMSC is to route and switch calls for subscribers who are currently in a different network than their home MSC. When a roaming subscriber initiates a call, the VMSC determines the best route for the connection and ensures seamless call delivery.

2. Subscriber Location Management

The VMSC constantly updates the Home Location Register (HLR) and the Visitor Location Register (VLR) with the current location of the roaming subscriber. This ensures that incoming calls and messages can be correctly directed to the subscriber’s temporary location.

3. Authentication and Security

When a mobile user enters a new network, the VMSC verifies their identity through the authentication center (AuC). This process helps prevent unauthorized access and protects both the subscriber and the network from potential fraud.

4. Billing and Charging

The VMSC records call data, including duration, destination, and type of service used by a roaming subscriber. This information is then sent to the home network for billing purposes. It ensures accurate charges are applied for roaming services.

5. Handover Management

When a subscriber moves from one cell to another within the visited network or back to their home network, the VMSC handles the handover process. This transition must be smooth to prevent call drops and maintain service continuity.

How VMSC Works

The VMSC operates as an intermediary between the roaming subscriber and their home network. Here’s how it functions step by step:

Step 1: Mobile Device Registration

When a mobile user enters a new network, their device automatically searches for an available signal. The VMSC detects the subscriber’s presence and registers their device in the Visitor Location Register (VLR).

Step 2: Authentication and Authorization

The VMSC contacts the subscriber’s Home Location Register (HLR) to authenticate the user. It verifies the SIM card credentials, subscriber identity, and security information before granting access to network services.

Step 3: Location Update

Once authenticated, the VMSC updates the HLR with the subscriber’s current location. This ensures that any incoming calls or messages can be correctly routed to the visited network.

Step 4: Call and Data Session Handling

When the roaming user initiates a call, the VMSC determines the best route and establishes a connection. It also facilitates data transmission for mobile internet usage by connecting the device to the appropriate network nodes.

Step 5: Charging and Billing

The VMSC records all network activities, including call duration and data usage, for billing purposes. These records are sent to the subscriber’s home network, where charges are applied based on the user’s roaming agreement.

Step 6: Handover Process

If the user moves to another region within the visited network or returns to their home network, the VMSC ensures a seamless handover. This prevents dropped calls and service interruptions.

Conclusion

The Visited MSC (VMSC) is a crucial element in mobile communication, allowing users to stay connected while roaming. It manages call switching, subscriber location updates, authentication, billing, and handovers to ensure a smooth mobile experience. By efficiently coordinating with other network components, the VMSC plays a vital role in global mobile connectivity. Understanding how it works helps in appreciating the complexity and efficiency of modern mobile networks.