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?