Question: In a network supporting validation of Priority Uplink Requests for Voice Group Call Service (VGCS), what is the primary purpose of the timer Tbb after a valid Priority Uplink Request has been received and accepted with a matching token?
Option 1: To delay the sending of an acknowledgement to the User Equipment (UE) that sent the Priority Uplink Request.
Option 2: To supervise the broadcast of a new token (Y) on the voice group call channels, ensuring other subscribers can receive it after a brief interval.
Option 3: To manage the handover process from one Base Station System (BSS) to another during an ongoing voice group call.
Option 4: To synchronize the uplink busy messages on the Fast Associated Control Channel (FACCH) with downlink transmissions for all subscribers in the voice group.
Explanation: The correct answer, Option 2, highlights the timer Tbb's role in ensuring that after a valid Priority Uplink Request is accepted and its token invalidated, a brief interval (defined by Tbb) is allowed before broadcasting a new token (Y). This interval enables other service subscribers who might have sent requests with the old token (X) to get back on the channel and receive the updated token, thus maintaining synchronization and access to the voice group call for all legitimate subscribers.