GSM测试异常掉话，求解！！！

难得糊涂110

路测中层3信令中出现disconnect之后就出现dropped call或Block call 是什么原因？
MS1
Disconnect
MS Tick: 1315961
Time: 10:10:35.28
Transaction identifier : 8
Protocol discriminator : (3) Call control; call related SS messages
Message type : 37
Cause
  Coding standard : (3) Standard defined for the GSM PLMNS
  Location : (2) public network serving the local user
  cause value : (27) Destination out of order

Message dump (Hex):
    83 25 02 E2 9B

MS1
Time: 10:10:35.28
Dropped Call
  Drop type: Abnormal network
  CC Causeestination out of order
  Call duration: 24516 ms