In Long-Term Evolution (LTE) networks, TAC stands for Tracking Area Code, while TAI stands for Tracking Area Identity. These are important concepts related to mobility management in LTE, providing information that helps User Equipments (UEs) and the network manage tracking areas and track the location of UEs as they move within the network.
Tracking Area Code (TAC) in LTE:
1. Definition:
- The Tracking Area Code (TAC) is a numerical identifier used in LTE networks to distinguish different tracking areas. A tracking area is a group of cells that share the same identity for tracking and paging purposes. TAC is an essential parameter for the UE to determine its location within the LTE network.
2. Purpose and Function:
- Location Area Identifier (LAI):
- The TAC, along with the PLMN Identity (PLMN ID), forms part of the Location Area Identifier (LAI). The LAI is used to identify the location of a UE within the LTE network.
- Tracking Area (TA) Identification:
- The TAC helps UEs identify and register with the correct tracking area. It is broadcasted by the eNodeB (evolved NodeB) in System Information Block Type 2 (SIB2), allowing UEs to determine the tracking area they are currently located in.
- Mobility Management:
- TAC plays a crucial role in mobility management. As UEs move within the LTE network, the TAC assists in tracking their location changes, allowing for efficient handovers and paging.
3. TAC Structure:
- Numerical Representation:
- TAC is represented as a numerical value typically ranging from 0 to 65535. Each tracking area within a PLMN is assigned a unique TAC.
- Broadcasted by eNodeB:
- The eNodeB broadcasts the TAC as part of the system information, enabling UEs to read and identify the tracking area they are currently within.
Tracking Area Identity (TAI) in LTE:
1. Definition:
- The Tracking Area Identity (TAI) is a broader identifier that encompasses both the PLMN Identity (PLMN ID) and the Tracking Area Code (TAC). It serves as a globally unique identifier for a tracking area in the LTE network.
2. Components of TAI:
- PLMN Identity:
- The TAI includes the PLMN Identity, which consists of the Mobile Country Code (MCC) and the Mobile Network Code (MNC). The PLMN Identity identifies the PLMN to which the tracking area belongs.
- Tracking Area Code (TAC):
- The TAI also includes the Tracking Area Code (TAC), which is the specific code identifying a tracking area within the PLMN.
3. Purpose and Function:
- Global Identification:
- TAI provides a globally unique identification for a tracking area within the LTE network. It helps in avoiding ambiguity and ensuring that each tracking area is uniquely identified on a global scale.
- Mobility Management:
- Similar to TAC, TAI is crucial for mobility management. UEs use TAI to determine their location within the network, facilitating efficient handovers and paging procedures.
- Broadcasted by eNodeB:
- Like TAC, TAI is also broadcasted by the eNodeB in the system information. UEs can read this information to determine the tracking area and PLMN they are currently located in.
4. TAI Structure:
- Combined Identifier:
- TAI is a combined identifier that consists of the PLMN Identity and the Tracking Area Code. The structure ensures that each TAI is unique across different PLMNs.
- Numerical Representation:
- The numerical representation of TAI combines the numerical values of the PLMN Identity and the TAC.
5. Dynamic Nature of TAI:
- Network Configuration Changes:
- TAI may change dynamically in response to network reconfiguration, expansion, or optimization. Changes in TAI are communicated to UEs through system information broadcasts.
- UE Monitoring:
- UEs periodically monitor the system information broadcast channel to keep track of changes in TAI. This allows UEs to adapt to alterations in tracking areas within the LTE network.
6. Interplay with Mobility Procedures:
- Handovers:
- During handovers, UEs use information from TAI to optimize the handover process. Efficient handovers contribute to seamless communication as UEs move across different tracking areas.
- Paging:
- TAI is used in the paging process, where the network sends paging messages to UEs within specific tracking areas. UEs need to be reachable within the identified tracking area.
7. Evolution to 5G (NR):
- Continuity of Concepts:
- As LTE evolves to 5G (NR – New Radio), the concepts of tracking areas, TAC, and TAI continue to be fundamental for mobility management. The specifics of implementation may evolve, but the need to efficiently manage UE mobility remains.
- Enhancements in NR:
- In 5G NR, enhancements may be introduced to support increased data rates, lower latency, and improved connectivity. The principles of tracking areas and identifiers remain relevant in ensuring effective mobility management.
8. Network Planning and Optimization:
- TAI Planning:
- Network operators plan and optimize the configuration of TAI based on factors such as coverage requirements, capacity planning, and network performance goals.
- Efficient Paging and Handovers:
- Proper configuration and management of TAI contribute to efficient paging procedures and handovers, enhancing the overall performance and user experience in the LTE network.
In summary, Tracking Area Code (TAC) and Tracking Area Identity (TAI) are key components in LTE networks, providing identifiers for tracking areas and facilitating mobility management. TAC specifically represents the numerical code for a tracking area, while TAI combines the PLMN Identity and TAC to form a globally unique identifier. These parameters play a crucial role in location tracking, handovers, and paging procedures within LTE networks, ensuring seamless communication as UEs move across different tracking areas.