Telecommunication

What is NSS Network Switching Subsystem

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NSS (Network Switching Subsystem) Explained Technically in Detail

The Network Switching Subsystem (NSS) is a core component of the GSM (Global System for Mobile Communications) architecture, playing a vital role in managing calls and mobility for mobile subscribers. Here's a breakdown of its technical aspects:

Function of the NSS:

The NSS acts as the central control point for call routing, subscriber authentication, and mobility management within a GSM network. It ensures seamless communication between mobile subscribers and other fixed or mobile network users, as well as external networks like the Public Switched Telephone Network (PSTN).

Key Components of the NSS:

The NSS consists of several key functional entities:

  • Mobile Switching Center (MSC): The MSC serves as the heart of the NSS. It performs call routing, handovers (when a mobile phone switches between base stations), and other switching functionalities within the mobile network.
  • Visitor Location Register (VLR): The VLR stores temporary location information for mobile subscribers currently roaming within the network area covered by a specific MSC. This allows the network to efficiently route calls and messages to these roaming subscribers.
  • Home Location Register (HLR): The HLR acts as a central database that stores permanent subscriber information, including their mobile station identity (IMSI), subscription details, and home network information. When a mobile phone connects to the network, the HLR is queried to authenticate the subscriber and retrieve relevant information for call routing.
  • Authentication Center (AUC): The AUC is a secure element responsible for generating temporary authentication keys used during the subscriber authentication process. This ensures only authorized devices can access the network.
  • Gateway Mobile Switching Center (GMSC): The GMSC acts as an interface between the mobile network and external networks like the PSTN. It routes calls to and from mobile subscribers and fixed-line users on the PSTN.

NSS Operations:

Here's a simplified overview of how the NSS operates:

  1. Call Origination: When a mobile subscriber initiates a call, the call request is sent to the nearest base station.
  2. MSC Involvement: The base station forwards the call request to the MSC responsible for that area.
  3. HLR and VLR Interaction: The MSC queries the HLR for subscriber information based on the received IMSI. It might also interact with the VLR if the subscriber is roaming.
  4. Authentication: The HLR and AUC participate in the subscriber authentication process.
  5. Call Routing: If authentication is successful, the MSC determines the appropriate call routing based on the dialed number and subscriber information. This might involve routing the call to another mobile subscriber within the network, a fixed-line user on the PSTN, or another network.
  6. Mobility Management: The VLR and MSC work together to manage handovers during a call when a mobile subscriber moves between different base station coverage areas.

Benefits of NSS:

The NSS provides several advantages for a GSM network:

  • Efficient Call Routing: Enables efficient routing of calls and messages to mobile subscribers, both within the network and to external networks.
  • Subscriber Authentication: Ensures only authorized devices can access the network, enhancing security.
  • Mobility Management: Facilitates seamless handovers as mobile subscribers move between different base stations, maintaining call continuity.
  • Integration with External Networks: Allows mobile subscribers to communicate with users on other networks like the PSTN.

Evolution beyond GSM:

While the NSS remains a core component of traditional GSM networks, its role has evolved with the introduction of newer mobile network technologies like UMTS (Universal Mobile Telecommunications System) and LTE (Long-Term Evolution). In these networks, the NSS functionalities are often integrated within a broader evolved Packet Switching Gateway (E-PSGW) architecture.

Conclusion:

The NSS (Network Switching Subsystem) plays a critical role in the smooth operation of GSM mobile networks. By managing call routing, subscriber authentication, and mobility, the NSS ensures seamless communication and network access for mobile subscribers. Although its form might change with newer network technologies, understanding the core functionalities of the NSS remains valuable in comprehending the overall architecture of mobile communication systems.

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