TAU (tracking area update)

Tracking Area Update (TAU) is a procedure in cellular networks that allows a mobile device to update its location information with the network. TAU is primarily used in Long-Term Evolution (LTE) and 5G networks to manage the mobility of mobile devices and ensure seamless connectivity as devices move between different tracking areas within the network coverage.

Here are the key aspects and features of the Tracking Area Update (TAU):

Tracking Area (TA):

In LTE and 5G networks, a tracking area is a geographic area that consists of multiple cells. Each tracking area is identified by a unique Tracking Area Identity (TAI) and is served by one or more base stations or eNodeBs (in LTE) and gNBs (in 5G). The network keeps track of the mobile devices within a particular tracking area for efficient call routing and management.

Location Update Requirement:

As a mobile device moves within the network coverage, it may enter a new tracking area. To maintain accurate location information and enable seamless connectivity, the mobile device needs to perform a Tracking Area Update. The TAU procedure is initiated by the mobile device to inform the network about its new tracking area.

Initiating TAU:

There are several events that can trigger a TAU, including the device's movement into a new tracking area, expiration of the TAU timer, or specific network conditions. When a TAU needs to be initiated, the mobile device sends a TAU request to the network.

Location Update Procedure:

The TAU procedure involves several steps between the mobile device and the network:

a. TAU Request: The mobile device sends a TAU request to the network, indicating its current tracking area and requesting an update.

b. TAU Accept: The network receives the TAU request, validates the device's identity and authentication, and sends a TAU accept message to the device, confirming the TAU procedure.

c. Location Update: The mobile device updates its location information with the network, including the new tracking area information. The network updates its location database accordingly.

d. TAU Complete: Once the location update is successful, the network sends a TAU complete message to the mobile device, indicating that the TAU procedure is completed.

Security and Authentication:

During the TAU procedure, security measures are employed to authenticate the mobile device and protect the integrity of the communication. The mobile device and the network exchange security parameters and verify each other's identities to ensure a secure connection.

Reducing Signaling Overhead:

TAU procedures are designed to optimize signaling overhead. Rather than performing a TAU for every cell change, the network groups multiple cells into a tracking area. This reduces the frequency of TAU requests and minimizes unnecessary signaling between the mobile device and the network.

Location Management and Paging Optimization:

By updating the location information through TAU, the network can efficiently manage the mobile device's location for call routing and paging purposes. The network knows which tracking area the device is in and can direct incoming calls and messages to the appropriate location.

TAU plays a crucial role in maintaining accurate location information and enabling seamless mobility in cellular networks. It ensures that mobile devices can efficiently update their location information as they move between tracking areas, allowing the network to deliver reliable connectivity and services.