LTE中位置更新

协议中如下规定的情况需要进行TAU：5.5.3 Tracking area updating procedure (S1 mode only)
5.5.3.1 General
The tracking area updating procedure is always initiated by the UE and is used for the following purposes: 


- normal tracking area updating to update the registration of the actual tracking area of a UE in the network; 


- combined tracking area updating to update the registration of the actual tracking area for a UE in CS/PS mode 1 or CS/PS mode 2 of operation; 


- periodic tracking area updating to periodically notify the availability of the UE to the network; 


- IMSI attach for non-EPS services when the UE is attached for EPS services. This procedure is used by a UE in CS/PS mode 1 or CS/PS mode 2 of operation; 


- in various cases of inter-system change from Iu mode to S1 mode or from A/Gb mode to S1 mode (for details see subclauses 5.5.3.2.2 and subclause 5.5.3.3.2);


- S101 mode to S1 mode inter-system change; 


- MME load balancing; 


- to update certain UE specific parameters in the network (for details see subclauses 5.5.3.2.2 and subclause 5.5.3.3.2); 


- recovery from certain error cases (for details see subclauses 5.5.3.2.2 and subclause 5.5.3.3.2); 


- to indicate that the UE enters S1 mode after CS fallback or 1xCS fallback; 


- to indicate to the network that the UE has selected a CSG cell whose CSG identity and associated PLMN identity are not included in the UE's Allowed CSG list or in the UE's Operator CSG list; and 


- to indicate to the network that the UE's availability for voice calls in the IMS has changed to "available".

在LTE中只有TAU(跟踪区)更新;UE进行位置更新是其回落到2/3G后,其LAC区与此前的TAC区不一致时才进行的....

单卡单待的手机当联合位置更新失败的情况下，手机10秒后会发起TAU更新，直至联合位置更新成功。