TD在G网掉话分析不是太明白

如题。
出现这种掉话是什么情况，看服务小区是空的，邻区倒是有的，请大家帮我分析下：
Outgoing Call Connected
Handover Start from TDD to GSM
RAT Measurement Stop in TD mode
Handover Failure from TDD to GSM
RAT Measurement Start in TD mode
Cell update Start
cell reselection start in TDD Mode
RAT Measurement Stop in TD mode
Cell reselection Failure in TDD Mode
cell reselection start in TDD Mode
Cell reselection Failure in TDD Mode
cell reselection start in TDD Mode
Read new SIB on new cell
Drop Call

这种掉话是不是TD切换2G为成功后，TD上小区更新后在TD模式中小区重选失败导致的掉话啊！！！但是通话状态唉，能重选么？TD知识匮乏，请大家帮我解释下，谢谢！！

楼上正解!

系统间切换后小区更新失败所致!