Question: In a Voice Group Call Service (VGCS) scenario, when a listener's mobile station (MS) needs to send application-specific data and the network indicates the uplink as busy, but another listener is currently using the group call channel uplink for talking, which channel should the MS use for sending the application-specific data?
Option 1: Group Call Channel Uplink
Option 2: Random Access Channel (RACH) to request a Standalone Dedicated Control Channel (SDCCH)
Option 3: Downlink Shared Channel (DSCH) with priority scheduling
Option 4: RACH to establish a new connection for the data transmission
Explanation: According to VGCS protocol, since the group call channel uplink is occupied and the network doesn't indicate it as free, the MS must use an alternative. The correct approach is for the MS to leave the group call, send a CHANNEL REQUEST on the RACH, and establish a new layer 2 connection on an SDCCH to send application-specific data without interfering with the ongoing voice group call.