Sign in Subscribe

How does the Gateway Mobile Switching Center (GMSC) function in GSM networks?

Last updated on 


In GSM (Global System for Mobile Communications) networks, the Gateway Mobile Switching Center (GMSC) plays a crucial role in facilitating communication between mobile subscribers and other networks, such as the Public Switched Telephone Network (PSTN) or other mobile networks. The GMSC is responsible for routing calls to and from mobile subscribers, ensuring that the call reaches its intended destination. Here is a technical explanation of how the GMSC functions in GSM networks:

  1. Call Origination:
    • When a mobile subscriber initiates a call, the call setup process begins. The originating MSC (Mobile Switching Center) receives the call request from the mobile station (MS) and determines the appropriate GMSC to handle the call.
  2. Location Area Update:
    • Before routing the call, the MSC may perform a Location Area Update to determine the current location of the called party. This helps in optimizing the call routing process by ensuring that the call is directed to the appropriate MSC or GMSC serving the called party.
  3. Number Analysis:
    • The GMSC performs number analysis on the dialed number to determine the type of destination network. It checks whether the destination is a mobile subscriber within the same GSM network or a subscriber in another network, such as a fixed-line telephone or another mobile network.
  4. Routing Decision:
    • Based on the number analysis, the GMSC makes a routing decision on how to route the call. If the destination is within the same GSM network, the GMSC may route the call directly to the MSC serving the called party. If the destination is in an external network, the GMSC interfaces with the appropriate external network, such as the PSTN or another mobile network.
  5. Interconnection with External Networks:
    • If the destination is in an external network, the GMSC interfaces with the appropriate external network's MSC or switching center. This involves signaling exchanges and, if necessary, negotiation of call parameters and protocols to establish the call connection.
  6. Signaling Procedures:
    • The GMSC engages in signaling procedures, such as sending Initial Address Message (IAM) to the destination network or the PSTN. The IAM contains information about the call, including the called party number, calling party number, and other relevant details.
  7. Call Routing to Destination MSC:
    • Once the GMSC has established communication with the destination network, it routes the call to the MSC serving the called party. The destination MSC then processes the call setup and establishes the necessary connections to reach the called party.
  8. Call Establishment:
    • The call is established between the calling and called parties. This involves the allocation of voice channels, setting up the necessary connections in the network, and allowing the voice traffic to flow between the mobile stations.
  9. Billing and Call Management:
    • Throughout the call, the GMSC is involved in call management tasks, including call duration tracking, call termination handling, and signaling for the end of the call. Billing information is generated based on the call duration and other relevant parameters.
  10. Call Termination:
    • When the call is terminated, the GMSC and associated network elements release the allocated resources, update call records for billing purposes, and prepare for the next call setup.

In summary, the GMSC in GSM networks acts as a gateway for routing calls between mobile subscribers and external networks. It performs number analysis, routing decisions, interfaces with external networks, and manages signaling procedures to establish and terminate calls. The GMSC plays a pivotal role in ensuring the seamless communication of mobile subscribers with subscribers in other networks.