Control Channel indicate Talkgroups active on site?

[danko139]

In realtime, does a P25 control channel stream indicate what talkgroups are currently active on the site, and can DSD+ or Unitrunker (or any other software for that matter) have a way to show that (in realtime)?

The reason is that I am curious to study what towers (sites) are best for monitoring certain talkgroups across our very big county. I can eyeball it geographically and by studying the log files I suppose, but I was wondering if the P25 control channel stream regularly spills its guts on this type of information.

I know that the site knows what talkgroups are active (as well as which ones to deny, etc.) but I was wondering if it in realtime broadcasts that info.

So far I haven't found anything to indicate it does; prior to digging into the logs and P25 specs, thought I'd ask here.

 

[mdulrich]

I've never used DSD+ so I can't tell you about that, but Unitrunker shows that information

Mike

 

[garys]

Yes, it does. I did a quick system set up on a P25 system near me using DSD+. Not only does it show talk groups, but it shows which voice channel is being used.

In DSD+, you only need to program the control channel frequency into FMP-24.CC and the program will do the rest for you.

 

[danko139]

How does Unitrunker or DSD+ show talkgroups on a site?

Thanks for your answers, but I may have asked my question poorly. Specifically:

1) Does a P25 CC stream contain the active talkgroups on the site in one of the stream fields, and

2) Does DSD+ or Unitrunker have some sort of updating display like this below in realtime:

WEST SITE TGs___EAST SITE TGs
------------------------------------------------------
0099_______________0122
9078_______________0123
0122_______________9079
0123
2001

If not, I was thinking of writing a little app to do this just for the heck of it. I know I can reassemble this from the TGs currently talking by looking at the logs, or looking at the JOINS in the stream; I wanted to see who is LOGGED IN at the site per TG, not necessarily talking.

 

[danko139]

Similar to what Pro96 Com does

By the way, what I am looking for is something in Unitrunker like Pro96Com has with its Affiliations screen, but current and in real time, not just showing what talkgroups have affiliated and unaffiliated over the history. I suppose I could just pick out the affiliations and unaffiliations and build my display this way and if the last of a TG unaffiliates, assume the site is not serving that talkgroup. So the reason for asking my question was to see if the CC stream routinely announces what TGs are affiliated with the site at the moment. I am reading through the P25 documentation but haven't found an answer yet.

 

[slicerwizard]

So the reason for asking my question was to see if the CC stream routinely announces what TGs are affiliated with the site at the moment.

No, it does not. As far as the system and the subscriber radios are concerned, such announcements would serve no purpose.

 

[Spitfire8520]

By the way, what I am looking for is something in Unitrunker like Pro96Com has with its Affiliations screen, but current and in real time, not just showing what talkgroups have affiliated and unaffiliated over the history. I suppose I could just pick out the affiliations and unaffiliations and build my display this way and if the last of a TG unaffiliates, assume the site is not serving that talkgroup.

In Pro96Com, the 'Affiliation List' tab is an attempt to build a real time list based on the method that you have described. The issue with this is that it appears that many radios tend to not cleanly unaffiliated from a site, or the control channel does not announce certain cases of unaffiliation. As a result, the 'Affiliation List' using this method tends to produce a large number of false affiliations over time.

 

[SCPD]

By the way, what I am looking for is something in Unitrunker like Pro96Com has with its Affiliations screen, but current and in real time, not just showing what talkgroups have affiliated and unaffiliated over the history.

The poor-mans way around this is to look at the Groups tab in Unitrunker. Sort by the "Last Seen" time stamp. If you monitor only one site - assume groups older than a few hours are probably not active on the site. There will be exceptions to this and as Andrew points out - there are no messages that specifically say site X currently serves groups Y and Z. It can only be inferred though activity - or the lack of activity.

 

[danko139]

Thanks everyone, these are the kinds of answers I was looking for and I understand now (especially that is serves no purpose in real-world operation). I appreciate it.