Channel Priority

[andy404ns]

Hi all,

Question regarding trunking in general... It's clear that the vast majority of municipalities have enough channels in their trunking systems to handle day to day traffic and even one or two big incidents. I would guess that most major cities can easily accomodate major incidents. However, I live in a small town that utilizes a MOT II system with 5 channels. I got to thinking at drill last night about channel allocation.

Suppose that we were on scene of a regular motor vehicle accident and had to divert traffic. The traffic pepole would be on one fireground channel, command would be on fire dispatch, EMS would be on scene, and the PD would also be there. PD would most likely be utilizing two channels to coordinate additional traffic efforts. In the unlikely event that all 5 channels were used at once, the computer would allocate a separate frequency to each talk group without a problem. Now lets say by our bad luck that public works also decided to open a mic. Now there's six talk groups active. How would the computer handle this? Do some talk groups have "priority" over others (i.e. would PD take priority over public works?) or would the last user to key up simply be out of luck and receive some sort of error tone?

Obviously this situation would be very rare and would remedy itself quite quickly once one of the users stopped transmitting. I'm just curious as to how the computer would handle this.

Thanks, Andy

 

[N4DES]

First of if you have a 5 channel system you only have 4 talk paths unless you have voice over control, which I doubt you have.

To answer your question on priority, the highest one gets first crack when one becomes available unless someone pushes the emergency button and they go right to the top of the que. It's a system manager decision as to who has the highest priority (police or fire) but in my experience they are usually equal.

I have one agency attached to the smartzone syetm that I mange that is 5 channels and they go into the que quite often, but the typical busy que grant is less than 2 seconds when they do go into the que unless something really big is going on like a hurricane where everyone comes out to play at once.

Being a traffic crash isn't usually a high voice traffic incident once someone goes on scene you can usually set operational protocols so there is talk-group management per incident.

 

[Grog]

Having people go to a simplex or repeater "interop" or fireground frequency would do much to take the stress off of a trunked system.


As an example of a statewide recommendation, look at SCs palmetto 800 system page.

http://www.cio.sc.gov/cioContent.asp?pageID=764&menuID=413

Disaster Operations - To help manage system loading and to increase agency interoperability during local or state disasters, all Palmetto 800 Users should include the utilization of the statewide 800 MHz conventional repeater (ITAC's & SCTAC's) system as part of their communications plans. See the Coverage Maps link for additional information.

 

[WayneH]

One other thing to remember about trunking and efficiency is that a majority of all conversations only last seconds. Even with your hypothetical situation I don't see there being much of an issue.

 

[andy404ns]

One other thing to remember about trunking and efficiency is that a majority of all conversations only last seconds. Even with your hypothetical situation I don't see there being much of an issue.

Yeah I didn't think it would be an issue for more than a few seconds, I was just curious as to how the computer would handle the situation.

Grog, you're right about the interop frequencies. In most larger scale incidents we would utilize the statewide tactical channels.

Thanks for the responses.

 

[N4DES]

Yeah I didn't think it would be an issue for more than a few seconds, I was just curious as to how the computer would handle the situation.

Grog, you're right about the interop frequencies. In most larger scale incidents we would utilize the statewide tactical channels.

Thanks for the responses.

The controller handles all calls as "First In, First Out" unless there are other circumstances such as when all channels are busy which would be an Emergency Call, user/talk-group priorities, private calls, etc. These are parameters set by the System Admin. and usually decided in a user group setting.