What is TAC and TAI in LTE?
Today, we’ll explore two key concepts in LTE networks: TAC (Tracking Area Code) and TAI (Tracking Area Identity). If you’ve been following our previous articles, you know that LTE networks are designed to provide fast and efficient mobile data services, but the way devices are managed and tracked in the network is essential for maintaining seamless connectivity. TAC and TAI play an important role in this.
TAC (Tracking Area Code) is a unique identifier used to distinguish a tracking area within the LTE network. The tracking area is a defined geographic area that is managed by the eNodeB (evolved NodeB). These areas are crucial for tracking the location of a mobile device without the need for it to constantly communicate with the core network. TAC is essentially a way to group a set of eNodeBs (base stations) to form a tracking area that helps in the management of mobile devices as they move within the network.
The LTE network is divided into multiple tracking areas, and each tracking area is assigned a unique TAC. When a user equipment (UE), such as your mobile phone, connects to the LTE network, it registers within a specific tracking area. This is important because it enables the network to keep track of where the UE is, which helps optimize the delivery of services like voice calls, SMS, and data usage. Essentially, the TAC helps the network know the general location of the UE, but without the need to know the exact position down to the level of a single cell tower.
TAI (Tracking Area Identity), on the other hand, is a unique identifier that represents a combination of multiple TACs. TAI is used to identify a group of TACs that belong to a specific area within the network. In simple terms, while the TAC identifies a particular tracking area, the TAI identifies a broader area consisting of several TACs. It’s used to handle mobility management in the network, particularly when the UE is moving from one tracking area to another.
Let me break it down for you: The TAC is more granular, representing a specific area within a network, while the TAI represents a larger region consisting of multiple tracking areas. This distinction is important when the network needs to manage handovers, paging, and mobility events.
Here’s how TAC and TAI are used:
- Tracking Area Update (TAU): When a UE moves from one tracking area to another, it performs a Tracking Area Update procedure to inform the network about its new location. This procedure ensures that the network can manage the UE’s connectivity efficiently as it moves between different tracking areas.
- Paging: When the network needs to page a device (for example, for an incoming call or message), the paging request is sent to all eNodeBs in the relevant TAI. The TAI ensures that the network is aware of the user’s approximate location, so paging can be more efficient.
- Mobility: As the UE moves between different tracking areas, the TAC helps to identify which area the device is located in, allowing for smoother handovers and more efficient management of active sessions.
Why does this matter? The use of TAC and TAI improves the network’s efficiency by allowing it to manage and track the movement of users in large areas without requiring detailed location information for each individual device. This reduces the signaling load on the network while still providing accurate tracking and connectivity.
In previous articles, we’ve talked about how mobility is handled in LTE networks. TAC and TAI are key elements of that mobility management, ensuring that users maintain a seamless experience as they move between different network areas. This concept ensures that even if you’re moving across multiple tracking areas or cities, the network can keep track of your device, optimizing performance and connectivity.