At 08:44 PM 08-05-2017, gnorbury@bondcar.com [op25-dev] wrote:
Operationally, when a user keys the PTT button on a P25 radio, a series of messages are exchanged that either grants or denys access to the requested TGID. Typically the user hears a "beep" or a "bong" and at that point they can start speaking and this is transmitted over the uplink freq. The repeater then turns the data stream back around and retransmitts it on the downlink for other affiliated radios to receive.
This is not correct. You suggest that there is "a series of messages" followed by "turns the data stream around and retransmits it"; that's an odd way to describe a single inbound request and an outbound grant.
As a "fly on the wall" scanner user, OP25 can monitor for these messages and use them to determine where to tune, what tgid and timeslot etc. When the PTT key is released, more messages are passed and a message pops out on the control channel notifying client radios that the call has ended.
How would radios sitting on a voice channel see this message on the control channel? And why have we never seen evidence of such a "call is over" message on any P25 control channel?