TMSI 重配置流程

TMSI  重配置流程

                    Figure: TMSI allocation(33.102-a00[6.1.2])

TMSI重配置流程的目的：提供身份保密，防止用户被窃听者识别和定位。

TMSI 的重配置一般是在RR链接已经建立的情况下进行，它总是由网络侧来发起。

   ①.            VLR/SGSN 向MS发送MSI REALLOCATION COMMAND 消息，消息中带有新的TMSI(IMSI)和LAI 

   ②.            VLR/SGSN启动 计时器 T3250

   ③.            MS接收到MSI REALLOCATION COMMAND 消息后把LAI 和TMSI存储在 SIM/USIM中

   ④.            MS向VLR/SGSN发送ALLOCATION COMPLETE 消息

   ⑤.            VLR/SGSN停止计时器 T3250，使新的TMSI合法

 

 

Abnormal cases

Mobile station side:

        The mobile station shall consider the new TMSI and new LAI, if any, as valid and the old TMSI and old LAI as deleted as soon as a TMSI REALLOCATION COMMAND or another message containing a new TMSI (e.g. LOCATION UPDATING ACCEPT) is correctly received. Any RR connection failure at a later stage shall not have any impact on the TMSI and LAI storage.

Network side:

(a)  RR connection failure:

        If the RR connection is lost before the TMSI REALLOCATION COMPLETE message is received, all MM connections (if any) shall be released and both the old and the new TMSIs should be considered as occupied for a certain recovery time.

        During this period the network may:

-      use the IMSI for paging in the case of network originated transactions on the CM layer. Upon response from the mobile station the TMSI reallocation is restarted;

-      consider the new TMSI as valid if it is used by the mobile station in mobile originated requests for RR connection;

-      use the Identification procedure followed by a new TMSI reallocation if the mobile station uses the old TMSI.

Other implementations are possible.

(b)  Expiry of timer T3250:

        The TMSI reallocation is supervised by the timer T3250 in the network. At the first expiry of timer T3250 the network may release the RR connection. In this case, the network shall abort the reallocation procedure release all MM connections if any, and follow the rules described for RR connection failure above.