Bothway Through Connection Indicator

Dears,

I wanted to ask about the BothwayThroughConnectionIndicator  in Connect To Resource message.
what this parameter for ?? and what should happen when CTR sent including it ??

actually while testing:
1- Required: when sending CTR without this parameter, then the default value which is Required, the Announcement was heard normally.
2- Not Required: when sending CTR with this parameter, "NotRequired", the Announcement wasn't heard !!!

BR,