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