regarding your question of “IMSI attach”. Here is the description of this parameter for Ericsson equipment “Attach and detach allowed”.
If this parameter is “NO” then “MSs in the cell are not allowed to apply International Mobile Subscriber Identity (IMSI) attach and detach.”
If “YES” – “MSs in the cell must apply IMSI attach and detach.”
In my previous post I’ve made mistake. Instead “And if someone calls to MS1 the call is successful.” you should read “And if someone calls to MS1 several minutes later then the call is successful.”