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How does the Network Switching Subsystem (NSS) contribute to GSM networks?

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The Network Switching Subsystem (NSS) is a critical component of GSM (Global System for Mobile Communications) networks, responsible for handling the call and mobility management functions. NSS comprises several key elements, including Mobile Switching Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR), Authentication Center (AUC), and Equipment Identity Register (EIR). Let's delve into the technical details of how NSS contributes to GSM networks:

  1. Mobile Switching Center (MSC):
    • The MSC is the central component of the NSS and serves as the gateway between the mobile network and other networks, such as the Public Switched Telephone Network (PSTN) or another mobile network.
    • MSC performs call routing and switching functions, establishing and releasing connections, and managing handovers between different cells as a mobile device moves.
  2. Visitor Location Register (VLR):
    • VLR is responsible for temporarily storing subscriber information when a mobile device roams into a new location area. It retrieves necessary data from the HLR when a call is initiated or received for a roaming subscriber.
    • VLR maintains a subset of the subscriber information from the HLR, including the current location area, so that call setup and handovers can be efficiently managed.
  3. Home Location Register (HLR):
    • HLR is the central database that stores permanent subscriber information, including subscriber profiles, current locations, and subscription details.
    • When a call is initiated, the HLR is queried to retrieve subscriber information, such as the subscriber's current location, allowed services, and supplementary service information.
  4. Authentication Center (AUC):
    • AUC is responsible for ensuring the security of the GSM network by authenticating mobile devices and preventing the use of stolen or cloned devices.
    • AUC generates a random number, which is sent to the mobile device and the authentication key stored in the SIM card. The mobile device uses this key to encrypt the random number, and the result is sent back to the AUC for verification.
  5. Equipment Identity Register (EIR):
    • EIR is responsible for maintaining a database of International Mobile Equipment Identities (IMEIs). IMEI is a unique identifier for each mobile device.
    • EIR helps in preventing the use of stolen or unauthorized mobile devices by checking the IMEI against a list of blacklisted or barred devices.

In summary, the NSS in GSM networks plays a crucial role in call management, subscriber authentication, and ensuring the security and integrity of the network. It involves a combination of databases and switching functions to facilitate the seamless operation of mobile communication services.