说下我的个人理解。虽然根据TS23060的MM状态转换图，MS侧的standby不能直接切换到idle。但即使小区信号不好，丢失了和SGSN的通信，MS也仍然会发起周期性的RA更新。这时候TS24.008定义了MS在发送RA更新后应遵守的流程，可以参考TS24.008的4.7.5 RAU Procedure章节。
在4.7.5.1.5 Abnormal cases in the MS就提到了RAU中不正常的case，本例就是因为丢失了无线信号不好，而收不到SGSN的RAU Accept的异常case。这个异常case在4.7.5.1.5共定义了a-j 10种情况。本例应该是属于case c。
c) T3330 time-out
The procedure is restarted four times, i.e. on the fifth expiry of timer T3330, the MS shall abort the procedure and, in Iu mode, release the PS signalling connection (see 3GPP TS 25.331 [23c]). The MS shall proceed as described below.
也就是MS将在T3330计时器超时后（T3330用于监管是否收到RAU Accept），重发5次。MS将放弃这个流程，并将按照后面描述的行为进行处理。这里说的The MS shall proceed as described below在稍后一点的文里有提到：
In cases b, c and d the MS shall proceed as follows:
If the routing area updating attempt counter is greater than or equal to 5:
- the MS shall start timer T3302, shall delete the list of equivalent PLMNs, shall set the GPRS update status to GU2 NOT UPDATED and shall change to state GMM-REGISTERED.ATTEMPTING-TO-UPDATE or optionally to GMM-REGISTERED.PLMN-SEARCH(see subclause 4.2.5.1.8) in order to perform a PLMN selection according to 3GPP TS 23.122 [14].
如果RAU尝试计数器达到5（重发了5次），MS将启动T3302，并删除等价的PLMN列表，并会将GPRS更新状态设置为GU2 NOT UPDATED。并且会进入到GMM-REGISTERED.ATTEMPTING-TO-UPDATE or optionally to GMM-REGISTERED.PLMN-SEARCH子状态。GMM-REGISTERED.ATTEMPTING-TO-UPDATE 和GMM-REGISTERED.PLMN-SEARCH都是GMM-REGISTERED的子状态。根据规范4.2.5 Behaviour in state GMM-REGISTERED的说明，前者只能进行RAU，shall initiate routing area update on the expiry of timers T3311, T3302 or T3346;后者将重新选择一个PLMN。
这样，当MS重新获得小区信号时，它将发送RAU Request给SGSN，但SGSN因为MM是Idle状态，因此会回RAU Reject并带上cause code #9，表示MS identity cannot be derived by the network。而在规范中也定义了MS在收到CC9的时候，应采取的行为：
# 9 (MS identity cannot be derived by the network);
The MS shall set the GPRS update status to GU2 NOT UPDATED (and shall store it according to subclause 4.1.3.2), enter the state GMM-DEREGISTERED, and shall delete any P-TMSI, P-TMSI signature, RAI and GPRS ciphering key sequence number. Subsequently, the MS may automatically initiate the GPRS attach procedure.
因此，MS最后将进入GMM-DEREGISTERED状态，并且最后将重新发起一个GPRS的附着流程。 作者: zglaojiang 时间: 2011-8-29 22:41:21
