EDACS: Loss of control channel?

[GTR8000]

EDACS is not my forte, so I'm hoping one of you old school EDACS experts can explain what I observed earlier today.

One of the sites of a networked EDACS 9600 system lost its control channel for a number of hours earlier today. This particular site has 3 frequencies, however the control channel never rolled to another repeater, it simply went completely off the air.

The site continued to carry voice traffic on the remaining two traffic channels, as if everything were operating normally. Since this is a networked site part of a larger system, and this site is normally low local traffic, I assumed that even without a control channel on the air, hearing it carry voice traffic from the rest of the system was not that unusual.

However at one point a subscriber that would definitely be affiliated with that site was active, and it seemed like he was having no issues with getting inbound and getting the proper traffic channel LCN assignments.

How was this local subscriber 's radio able to function at that site with a lack of a control channel? Was the site in some sort of failsoft mode, and why would the site not have rolled over to another channel when the control channel repeater failed?

I should note that currently the control channel is back on the air, however on a different LCN. The LCN that was previously the control channel prior to the failure appears to no longer be active for voice traffic, instead all voice traffic is being carried over the same LCN. In other words, the three channel site is now operating as a two channel site; one control channel + one traffic channel.

 

[emtLarmy15]

Is it possible that there’s a fourth freq that you’re not aware of?

 

[GTR8000]

No, that was ruled out immediately.

 

[Bub]

The only way possible is the system is simulcast and the units were hearing control channel info from another site.

 

[GTR8000]

The only way possible is the system is simulcast and the units were hearing control channel info from another site.

Multicast system, not simulcast. While many sites often carry the same traffic, all frequencies are unique to each site.

In any event, the condition was corrected and the site is back to normal operation. Upon further research it was determined that all subscribers in the area of the affected site had roamed to adjacent sites during the event. What was being heard over the remaining operational traffic channels was the traffic from other talkgroups at other sites.

 

[Bub]

Multicast system, not simulcast. While many sites often carry the same traffic, all frequencies are unique to each site.

In any event, the condition was corrected and the site is back to normal operation. Upon further research it was determined that all subscribers in the area of the affected site had roamed to adjacent sites during the event. What was being heard over the remaining operational traffic channels was the traffic from other talkgroups at other sites.

Multicast programmed correctly... go figure..

 

[KevinC]

This one had me intrigued.

Since it was still passing wide-area traffic it obviously didn't lose the site link to the core and since it was still trunking it didn't lose the site controller (I'm using Motorola terms, but I'm sure EDACS has equivalent components). This leads me to believe the CC had an undetected PA fail or the power otherwise wasn't making it out of the antenna for the CC.

Troubleshooting systems I have absolutely no connection to...jeez I'm a nerd.

 

[GTR8000]

This one had me intrigued.

Since it was still passing wide-area traffic it obviously didn't lose the site link to the core and since it was still trunking it didn't lose the site controller (I'm using Motorola terms, but I'm sure EDACS has equivalent components). This leads me to believe the CC had an undetected PA fail or the power otherwise wasn't making it out of the antenna for the CC.

Troubleshooting systems I have absolutely no connection to...jeez I'm a nerd.

That was exactly the same hypothesis I arrived at. This site rotates control channels regularly, so it seemed very unusual for it not to force a roll for an apparent repeater issue...the repeater that was acting as the control channel at the time, no less. It seems that the site controller was completely oblivious to the fact that the repeater had some sort of failure.

It was certainly interesting hearing the wide-area traffic continuing to be passed on the other two repeaters, as if nothing was wrong at the site. Of course they had to be scanned conventionally, a little tough to track with no control channel on the air!