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G-MSC (Gateway Mobile Switching Center)

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Introduction:

In modern telecommunication networks, Gateway Mobile Switching Center (GMSC) is an important component that serves as the interface between the mobile network and the Public Switched Telephone Network (PSTN). The GMSC is responsible for handling incoming calls to mobile subscribers from the PSTN and routing them to the correct destination within the mobile network. The GMSC is also responsible for routing outgoing calls from mobile subscribers to the PSTN.

In this article, we will explain in detail the architecture, functions, and operation of the GMSC.

Architecture:

The GMSC is a network element that is located at the edge of the mobile network and provides a point of interconnection between the mobile network and the PSTN. The GMSC is connected to the PSTN via one or more trunk lines, and to the mobile network via a signaling interface, such as the Signaling System No.7 (SS7) network.

The GMSC is designed to handle both voice and data traffic. It is also equipped with various interfaces, such as the Home Location Register (HLR), Visitor Location Register (VLR), and the Short Message Service Center (SMSC), to support the delivery of various services.

Functions:

The GMSC performs several important functions in a mobile network. Some of these functions are as follows:

  1. Call handling: The GMSC is responsible for handling incoming calls from the PSTN to mobile subscribers. It receives the call from the PSTN and identifies the destination mobile subscriber using the Mobile Subscriber Integrated Services Digital Network Number (MSISDN). The GMSC then routes the call to the appropriate destination within the mobile network.
  2. Routing: The GMSC is responsible for routing outgoing calls from mobile subscribers to the PSTN. It receives the call from the mobile subscriber and identifies the destination number. The GMSC then routes the call to the appropriate destination within the PSTN.
  3. Address resolution: The GMSC is responsible for resolving the mobile subscriber's address when it receives a call from the PSTN. It queries the HLR for the subscriber's current location and routing information.
  4. Number translation: The GMSC is responsible for translating the incoming PSTN number to the appropriate mobile network number format.
  5. Service access control: The GMSC is responsible for controlling access to various services offered by the mobile network. It checks the subscriber's authorization and authentication before allowing access to the requested service.

Operation:

The operation of the GMSC involves several steps, as described below:

  1. Call setup: When a call is initiated from the PSTN to a mobile subscriber, the call is received by the GMSC. The GMSC then queries the HLR for the subscriber's location information.
  2. Address resolution: The HLR returns the current location and routing information for the subscriber to the GMSC. The GMSC then routes the call to the appropriate MSC.
  3. Call routing: The MSC routes the call to the appropriate Base Station Controller (BSC), which in turn routes the call to the appropriate Base Transceiver Station (BTS). The BTS then delivers the call to the mobile subscriber.
  4. Call termination: When the mobile subscriber answers the call, the call is routed back to the GMSC. The GMSC then terminates the call by releasing the resources used by the call.

Conclusion:

In conclusion, the Gateway Mobile Switching Center (GMSC) is a vital component of modern mobile networks. It provides the interface between the mobile network and the PSTN and is responsible for handling incoming calls from the PSTN to mobile subscribers and routing outgoing calls from mobile subscribers to the PSTN. The GMSC performs several important functions, such as call handling, routing, address resolution, number translation, and service access control. Its operation involves several steps, including call setup, address resolution , call routing, and call termination. The GMSC is an essential element of the mobile network architecture and is necessary for providing seamless connectivity and services to mobile subscribers.

However, with the advent of IP-based networks and the migration towards all-IP networks, the role of the GMSC is evolving. In all-IP networks, the GMSC functionality is being integrated into the Media Gateway Control Function (MGCF), which provides a single point of interconnection between the mobile network and the PSTN. The MGCF is responsible for handling all types of traffic, including voice, video, and data, and provides a standardized interface between the mobile network and the PSTN.