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IRAU (Inter SGSN routing area update)

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Introduction:

The Inter SGSN routing area update (IRAU) is a feature in the Global System for Mobile Communications (GSM) network that enables the transfer of a mobile device's location information from one Serving GPRS Support Node (SGSN) to another. This is a crucial function for mobile network operators (MNOs) because it helps to maintain the quality of service for mobile subscribers. This article will explain the concept of IRAU, its benefits, and the technical aspects that make it possible.

Understanding the Need for IRAU:

When a mobile subscriber moves from one routing area to another, their location information needs to be updated to ensure that incoming calls, messages, and data traffic are delivered to the right location. The routing area is a geographical area within a cellular network that determines which base station controller (BSC) manages the radio resources for the mobile device. Each SGSN is responsible for managing one or more routing areas, and when a mobile device moves from one routing area to another, the SGSN needs to be informed of the change so that it can continue to manage the device's connectivity and location information.

Before IRAU was introduced, the SGSN serving the mobile device would initiate the process of updating the location information with the new SGSN. This process was called the GPRS Tunnelling Protocol (GTP) Update. When the mobile device crossed the routing area boundary, it would initiate a location update procedure with the current SGSN. The current SGSN would then forward the location update request to the Home Location Register (HLR), which would check the subscriber's authentication and authorization status. The HLR would then send a location update response back to the current SGSN, which would update its location information and forward the update to the new SGSN.

The GTP Update process had several drawbacks. First, it was time-consuming, and it could take several seconds to complete, which could cause a delay in delivering incoming calls or messages. Second, it put a significant load on the SGSN and the HLR, which could impact network performance. Finally, it was not efficient in managing handovers between different types of radio access networks (RANs), such as from a 2G network to a 3G network or vice versa.

To overcome these challenges, the IRAU feature was introduced.

How IRAU Works:

IRAU is a network-level feature that enables the SGSN serving the mobile device to delegate the responsibility of location updating to the new SGSN. This means that when a mobile device moves to a new routing area, the new SGSN initiates the location update procedure with the HLR directly, without involving the old SGSN. This helps to reduce the load on the network and improve the efficiency of the location update process.

The IRAU procedure involves three main stages: the handover initiation, the forwarding of the IRAU request, and the completion of the IRAU procedure.

Handover Initiation:

When the mobile device moves to a new routing area, it triggers a handover procedure between the old SGSN and the new SGSN. The old SGSN sends a handover request to the new SGSN, which includes the mobile device's identity, the current location area code (LAC), and the old SGSN's identity. The new SGSN then acknowledges the handover request and sends a Routing Area Update Request (RUReq) to the HLR, indicating that it has taken over the responsibility of managing the mobile device's location information.

Forwarding of the IRAU Request:

The HLR sends an acknowledgment message (RUAck) back to the new SGSN, indicating that it has received the IRAU request. The HLR also updates its subscriber database with the new SGSN's identity and the mobile device's new location information. The new SGSN then sends a confirmation message (RUConfirm) to the old SGSN, indicating that the IRAU procedure is complete and that it has taken over the responsibility of managing the mobile device's location information.

Completion of the IRAU Procedure:

Once the IRAU procedure is complete, the new SGSN updates its location information for the mobile device, and any incoming calls, messages, or data traffic are directed to the new SGSN. The old SGSN then releases its resources and ends the handover procedure.

Benefits of IRAU:

IRAU provides several benefits to MNOs and mobile subscribers, including:

  1. Reduced Network Load: IRAU reduces the load on the network by delegating the responsibility of location updating to the new SGSN, which helps to improve the efficiency of the location update process.
  2. Faster Handover: IRAU enables faster handover between different routing areas and RANs, which helps to maintain the quality of service for mobile subscribers.
  3. Improved Network Performance: IRAU helps to improve the performance of the network by reducing the delay in delivering incoming calls, messages, and data traffic.
  4. Better Resource Management: IRAU enables better resource management by allowing the old SGSN to release its resources and the new SGSN to take over the management of the mobile device's location information.

Conclusion:

The Inter SGSN routing area update (IRAU) is a critical feature in the GSM network that enables the transfer of a mobile device's location information from one SGSN to another. IRAU helps to reduce the load on the network, improve the efficiency of the location update process, and maintain the quality of service for mobile subscribers. By delegating the responsibility of location updating to the new SGSN, IRAU enables faster handover between different routing areas and RANs, which helps to improve network performance and resource management.