Question: In a Voice Group Call Service (VGCS) for dispatcher-originated calls, what is primarily used by the Gateway Mobile Switching Center (GMSC) for routing the call to the group call anchor Mobile Switching Center (MSC)?
Option 1: MSISDN number received in the Initial_Address_Message
Option 2: Group Call Reference extracted from a dedicated signaling message
Option 3: IMSI retrieved after querying the Home Location Register (HLR)
Option 4: Cell ID of the originating User Equipment (UE)
Explanation: In VGCS, for dispatcher-originated voice group calls, the GMSC utilizes the MSISDN number contained within the Initial_Address_Message to derive routing information, enabling direct routing to the anchor MSC without an HLR query.