radio system maximum user

[harrycaul11]

Not being an expert on these radio systems and kind of new to them I have been following the NJ migration thread and wondering with all the new towns and agency's signing on to the system wouldn't it eventually max out. even with regionalization of resources throughout the state between tower sites I feel that the system is going to be maxed out. there is a predicted storm tomorrow and snow in the NW part of the state, what will happen if the system maxes out. this also assumes that every single thing at every single site is working properly. am i on track with my thinking?

 

[K2NEC]

What youre asking about happens occasionally and a capacity issue is a very real possibility. However each site has a rather sufficient amount of talk paths and subscribers are limited to only the sites that they are permitted to use.

Take passaic county simulcast for example, it has 1 active control channel at any time and 6 voice channels. Since its TDMA, voice channels are split into 2 talk paths. This means that at any given moment, 12 talkgroups can be active at those sites.

Of course this can be upgraded if more repeaters and frequency pairs are added.

Long story short, if the system is at capacity and a user tries to key up, they will get denied and put into a "queue" until a talk path opens up.

 

[cavmedic]

A system of that size was surely properly or even overly engineered. Look at each site and count the repeater pairs. Take that number and multiply it by 2, then subtract 1 and that will tell you how many talk paths are available at each site. Then take into consideration on how efficient trunking is.


Will there possibly be a time when subscribers get busy tones, maybe. Subscribers have priorities assigned to them. Some higher than others, so the system will allow for a higher priority user to get access before a lower priority user would.
If subscribers get busy tones, then they just wait for their turn. Typically when their turn in the cue comes around, their radio will chirp with a channel grant to let the user know they can now talk.

 

[mmckenna]

Not being an expert on these radio systems and kind of new to them I have been following the NJ migration thread and wondering with all the new towns and agency's signing on to the system wouldn't it eventually max out. even with regionalization of resources throughout the state between tower sites I feel that the system is going to be maxed out. there is a predicted storm tomorrow and snow in the NW part of the state, what will happen if the system maxes out. this also assumes that every single thing at every single site is working properly. am i on track with my thinking?

I don't know about that specific system, but I've been involved in others.

Active radio traffic is only routed to sites that have radios that are set to that specific talk group. Not all radio traffic gets routed to every radio site.

Agencies can be limited to certain radio sites so they can't tie up others.

Traffic engineering is a real thing. It's not too difficult to calculate channel loading based on the number of radio users, and design the system to support that. That's one of the beauties of a trunked radio system. This information would be known ahead of time and there's usually a considerably amount of excess capacity to support major events.

Talk groups can be assigned priority levels, so the resources go to those that need it most. PD, Fire, EMS would have priority over non-public safety users.

Users can be assigned priority levels, also.

There were situations were trunked sites could get overloaded (a major interstate bridge collapse many years back was a prime example) but that was due to poor talk group permissions on the system, as well as user discipline. Lessons were learned and changes adopted.

Not going to say it's impossible for a system to get completely bogged down, but it is something that is taken into consideration, designed for, and easily addressed.

Even if the system does get briefly maxed out, it's usually for a very brief period of time (seconds) and clears quickly. Users get the bonk and try again, and their call magically goes through….

 

[PhillyFireFeed]

We've talked about site RF resources, but what is the actual max limit of available talkgroups for an entire P25 system? Isn't it 65,535 or something like that? And what's the maximum number of radio IDs for a P25 system?

 

[Unitrunker2]

Group IDs are 16 bits. Subscriber IDs are 24 bits. Some IDs are reserved. Adds up to about 65535 groups and over 16 billion subscribers.

 

[bunangst]

User discipline should not be discounted either in the slightest. Directing traffic 100 yards apart for a dozen different tree/wires down incidents on one county simulcast should not be tying up trunking system resources...maybe generalizing a bit but it happens during big storms.

 

[K2NEC]

User discipline should not be discounted either in the slightest. Directing traffic 100 yards apart for a dozen different tree/wires down incidents on one county simulcast should not be tying up trunking system resources...maybe generalizing a bit but it happens during big storms.

Bold of you to assume users know what a direct channel is and how to switch to it

 

[kayn1n32008]

Bold of you to assume users know what a direct channel is and how to switch to it

Bold to assume the subscribers are even programmed with simplex or even non-trunked repeated channels.

3 places I worked had zero off network channels.

 

[cavmedic]

User discipline should not be discounted either in the slightest. Directing traffic 100 yards apart for a dozen different tree/wires down incidents on one county simulcast should not be tying up trunking system resources...maybe generalizing a bit but it happens during big storms.

Ever listen to Fire Police in Pa? They will use the system to talk to the person standing next to them.

 

[iamrftechnj]

Something else the OP said has to be factored in, that every channel is on the air and working properly. those 11 talkpaths might fill up quickly during an event especially one where statewide talkgroups might be in use.

 

[K2NEC]

Bold to assume the subscribers are even programmed with simplex or even non-trunked repeated channels.

3 places I worked had zero off network channels.

Not even ITacs? Nice

 

[KevinC]

Group IDs are 16 bits. Subscriber IDs are 24 bits. Some IDs are reserved. Adds up to about 65535 groups and over 16 billion subscribers.

Speaking for a MSI M3 core, the limit on subscriber ID's is 64,000 per zone.

 

[kayn1n32008]

Not even ITacs? Nice

They were not public safety jobs, but radio was a life safety device, I'm also not in the US.

One place did hold a simplex license in the same band the trunk system was on, but they never put it in their subscribers.

When I did volunteer, we used simplex regularly. I left before they transitioned to trunking, but I did 'spin the dial' on one of their trunking subscribers after I left and it didn't have simplex.

It's amazing how some places will become totally reliant on trunking/infrastructure.

 

[PhillyFireFeed]

Speaking for a MSI M3 core, the limit on subscriber ID's is 64,000 per zone.

I'm asking because I truly don't know, or maybe confused:

I've seen P25 systems with RIDs of 1, systems with RIDs of 16151, systems with RIDs of 4369123, etc. I'm assuming these numbers can go to 9,999,999, no?

And can you clarify what you mean by the term "zone"? Are you referring to site (either single or simulcast cell) or something else?

 

[GTR8000]

The valid range of subscriber ID's on a P25 system is 1-16777212, however that doesn't mean that the system is capable of 16,777,212 subscribers being registered. Those IDs are somewhat arbitrary, you can basically pick any valid ID you want for any subscriber and use it, up to the maximum number of subscribers the system supports.

Zone in ASTRO 25 parlance refers to the RFSS.

 

[PhillyFireFeed]

Ah, got it. Thank you.