EPC网络中的EMM和ECM状态机

爱卫生

翻译自《LTE-Signaling&Protocol Analysis [E-UTRAN and UE》一书。该书原版也已上传至论坛城通网盘。

2.1.2.1 Relationship between EMM and ECM

In general, ECM relates to the presence of an S1-bearer plus RRC-connection. As long as both are present, the UE is in ECM-CONNECTED mode. Upon release, the UE switches to ECM-IDLE mode.

Therefore, the UE may well be EMM-registered but still be ECM-idle.

- While the UE is in ECM-CONNECTED state, the network is in charge to control the UE-mobility. While the UE is in ECM-CONNECTED mode, the location of the UE is known with the granularity of a cell inside an eNodeB.

- While the UE is in ECM-IDLE mode, the location of the UE is known with the granularity of a tracking area. Within ECM-IDLE mode, the UE shall perform autonomous cell reselection and tracking area update procedures.

2.1.2.1 EMM和ECM的关系

通常来说，ECM可以看成是存在一个S1的bearer加上一个RRC连接。只要上述两个都存在，UE就处于ECM-CONNECTED模式。一旦释放，UE将切换到ECM-IDLE模式。

因此，UE可能同时处于EMM-registered和ECM-idle状态。

- 当UE处于ECM-CONNECTED状态，网络侧来控制UE的移动性。当UE处于ECM-CONNECTED模式下，网络侧将知道UE位于的当前位置是处在哪个eNB的哪个小区下。

- 当UE处于ECM-IDLE模式，网络侧只知道UE处于哪个TA下。因此在ECM-IDLE模式下，UE应执行小区重选以及TAU流程。

参考：TS36.300(A.2)和,TS23.401(5.1.3.2.2.4)。