Batboard

With P25 trunking systems starting to pop up here and there, and not a lot of information yet posted on them, I'd like to suggest that
anyone who has good information on how P25 trunking systems are set up should post that information for our benefit.

I have a good understanding of the essential data needed for a radio to operate on a Motorola trunking system,
and also what's needed and how to set it up for other trunking systems including various flavors of EDACS.

Motorola systems require, at the minimum, the frequencies of the control channels, the system ID, and the connect tone. Then talkgroups can be added.
EDACS systems require all system control channels in the correct order, a site number, and then talkgroups.

Of course, these are VERY oversimplified examples.

What do P25 systems require?


Elroy

It sounds to me like you covered the jist of it.

1 thing that isn't a requirement but is probably a good thing for all radios to have in common is a fresh DSP. Nothing like the crappy sound of mixed/old DSP's. Yuck.

I haven't covered ANY of the P25 trunking requirements. It's what I'm asking for.

So I guess that real data on them is, at the moment, sparse.

I'd like to know, at the very least, if P25 trunking relies on a Motorola-stye collection of only control channel frequencies,
with the radios assigned the working voice channels by the central controller, or a M/A-Com style collection of system
frequencies that have to be entered in a specific order, or some other scheme.

Elroy

I went through the Astro 25 Repeater site training a while back, Its more or less just smartzone, with digital voice and control channels.

Elroy Jetson wrote:I'd like to know, at the very least, if P25 trunking relies on a Motorola-stye collection of only control channel frequencies,
with the radios assigned the working voice channels by the central controller, or a M/A-Com style collection of system
frequencies that have to be entered in a specific order, or some other scheme.
Elroy

The APCO-25 control channel tells the mobiles how to map channel numbers used in the protocol into frequencies, so all the radio needs to know to start with is a list of one or more frequencies to listen for a control channel on. When the radio hears a control channel, it can then glean from that control channel the channel's receive frequency (i.e. the frequency the mobile should transmit on to be heard by the control channel), the identification numbers for the control channel (what system ID and such it belongs to, so that the radio can then determine if "these are the droids I am looking for'), and what conversations are currently going on elsewhere in the system (in case the group to which the radio belongs in already in a call the radio can then join the call already in progress).

It depends - there are two modes I have read about, implicit and explicit P25 control channels...

I see...so the setupis a more advanced variation on the traditional Motorola school of setting up a trunking system, rather than the EDACS way.


That's good. But I'd imagine that there's a lot more data to go through to fully set up an Astro 25 personality than there is for any previous type of trunking system, or at least, there CAN be. Right?


Elroy

MattSR wrote:It depends - there are two modes I have read about, implicit and explicit P25 control channels...

The only difference between implicit and explicit is whether the TX frequency is specified explicitly, or as an offset from the RX frequency. In the latter case, the TX offset given in the IDEN_UP or IDEN_UP_VU messages is used, in the former case the messages which specify a channel (e.g. RFSS_STAT_BCST, NET_STAT_BCST, GRP_V_CH_GRANT, etc.) specify both the RX and TX channel ID and number, instead of only specifying the RX ID and number, and the TX offset field of the IDEN_UP messages is ignored.

However, in both cases, as I said, the control channel provides the mobile with all the information it needs to operate on the system.