Hello everyone!
Today, I'd like to introduce some information about the TAU (Tracking Area Update).
What is TAU?
When a UE moves from a TA list to another TA list, the UE must perform location registration on the new TA to notify the network to change the location information of the MS. This process is called tracking area update.
1. The UE initiates a TA update when any of the following conditions is met. The UE sends a TA update request and starts a TA update. For details, see 3GPP TS 23.401.
When the UE detects that the TAI in the system information is different from the TAI stored in the USIM, the UE enters a new TA.
The timer for periodic tracking area update expires. The timer length is configured by the core network (CNS) to the UE through NAS messages.
The UE reselects an E-UTRAN cell from a cell of another RAT.
When an RRC connection is released due to load balancing, the tracking area needs to be updated.
UE capability information stored in the EPC changes.
2. The UE notifies the EPC of its TA through a tracking area update. The EPC sends paging messages to all eNodeBs of the TA to which the UE belongs based on the TA to which the UE belongs.
What is TA?
1. To determine the location of the MS, the LTE network coverage area is divided into multiple tracking areas (TAs). TA functions similar to LA and RA in 3G and is a basic unit of location update and paging in LTE systems.
2. TAs are identified by TA codes. A TA can contain one or more cells. TACs are broadcast in SIB1 of these cells, similar to LACs and RACs.
3. During network operation, a TAI is used as the unique identifier of a TA. The TAI = MCC + MNC + TAC. The TAI consists of six bytes in total.
Figure 1 EPS TA and UMTS RA
In the EPS system, a similar concept of location area is applied. This location area is called tracking area. Similarly, the EPC manages the TAs registered by the UEs in both idle and connected states. When the TA changes, the UEs change the TA registration information in the EPC.
Figure 1 shows TA in EPS and RA in UMTS. In the EPS, each eNodeB may contain cells belonging to different TAs, or cells under multiple eNodeBs may belong to the same TA, but each cell belongs to only one TA. In UMTS, all cells under an eNodeB must belong to the same RA.
TAU procedure
The TAU procedure consists of the following three steps:
Random Access
RRC connection setup
TAU Update
Generally, the TAU procedure does not require authentication or bearer setup. The connection is released immediately after the TAU is updated.
That's all the information I've shared about TAU.
You're welcome to read and comment.
