From: lockhart@mothra.nts.uci.edu (Jack C. Lockhart)
Subject: Re: 800MHz Trunked Radio System Signals
Newsgroups: alt.radio.scanner
Organization: University of California, Irvine
Keywords: The Control channel
Date: 30 Dec 92 21:55:49 GMT
Followup-To: alt.radio.scanner

In article <9212290333.AA10060@deepthought.cs.utexas.edu> PLAWS@UAFSYSB.UARK.EDU writes:
>On 28 Dec 1992 04:51:00 GMT you said:
>>In article <9212271908.AA21958@deepthought.cs.utexas.edu>
>>PLAWS@UAFSYSB.UARK.EDU
>>writes:
>>

>Speaking of E.F Johnson, I don't think that their system meets APCO specs
>for a public safety system.  Something about no emergency button.
>

The way I read the FCC/APCO 16 A&B NPSPAC standards: one of the
reasons why the E. F. Johnson trunked radio system does not meet
specified standards is because of the lack of a control channel.

Sets assume that all the channels of the trunked radio system are
busy.  A control channel allows the trunk radio system controller to
interrupt a conversation in progress when it receives an emergency
request and immediately assign the requestor (usually a police
officer, fire personnel, or anyone with emergency request
capabilities) to the captured channel.  The captured channel is
usually placed in the MESSAGE trunked mode to secure the channel for
the duration of the event or conversation.

Another option is for the trunked radio system controller to place the
emergency call at the top of the queue and assign the emergency call
to the NEXT available channel.

Speaking of queueing, another thing the control channel does is queue
all of the requestors (if all channels are busy) and assign these
channels requests based on the users predetermined priority.

Obviously, if all channels are busy on a EFJ trunked radio system, one
cannot access the radio system with an emergency call until a
conversation on one of the trunked radio channels is finished.  My
understanding of the EFJ radio system is that it keeps a log of who
requested a channel and when a channel is free, it notifies ALL of the
requesting radios to try again.  So, all requesting radios attempt to
access the SAME channel AT THE SAME TIME.  Sorry for the shouting;
just wanted to make my point!  The system does not build a priority
queue nor tell the requesting radios who is first, second, third ...
I think you get the picture.

This may not be a big deal to public works personnel and local
government radio user, however, in the Public-Safety sector, lives are
measured in fractions of a second and instant access to public-safety
channels is an absolute must.

~jack_

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