Trunking Vs. Conventional - What would you do?

[Wile E. Coyote]

What would you do?

I’m looking to start a little debate here. I know everyone has a strong opinion on the matter, and here is your moment to shine:

I currently represent a public safety center that currently uses UHF conventional for both Police and Fire. It works just fine for our needs, but our new Police Chief is getting a lot of flack from other Chiefs in the area. They say that our system is old and out of date. In fact, most of our infrastructure is quite new, just the design is a little less than cutting edge. They are all using trunking of various makes, and think their systems are the shi... stuff. =)

What do you think? Are we being a stick in the mud for not upgrading to P25 Trunking, or should we stand our ground and stick to what works?

[Tom in D.C.]

Your neighbors have been influenced by salesmen who have convinced them that
they "can't live without" a trunked system. You and I both know how such statements
bear no relation to the true state of the world without an honest wants and needs
discussion taking place. The salesmens' objective is to sell equipment, even IF what
you're now running is only a few years old, works fine, meets your needs, gives excellent
coverage, and rarely if ever fails in its mission. Let's just leave it at the fact that there are
an awful lot of analog FM public safety and fire department systems still operating in the
country that work fine. I take nothing away from a company that works hard to improve
its product and sell a lot of it to users, but when they tell you it's "new and improved" you
should probably get some good technical advice from a consultant to see if it is indeed
new, and then exactly how it's been improved over what you now are using.

[Grog]

If it works for you, tell them to screw off. Even better, see if they will pay 100% of the cost for trunking and keep your conventional too

[WB6DGN]

It's hard to improve on Tom in DC's answer to your question. His answer is well thought out and he exhibits considerable experience in the field. After reviewing your post, I suspect your "neighbors'" main objection is the lack of interoperability between your system and theirs in the event of an area-wide emergency. While an area-based trunking system can, indeed, address this issue with varying degrees of success, the point should be made that this type of approach is, indeed, putting "all of your eggs in one basket". Interoperability ceases to be an attribute when the area-wide system is taken down due to some natural or man-made disaster. I would echo other suggestions of obtaining the services of a competent consultant to analyze your jurisdiction's needs but would add the caveat to examine carefully this consultant's past recommendations and loyalties before commissioning a detailed and costly survey
Tom

[RKG]

If you take a look at most police or fire dispatch channels, you will find that their duty cycle (i.e., how many seconds of the day the transmitter is keyed up) is hardpressed to get much above 1-2%. The channel is idle (but waiting for traffic) all the rest of the time. Putting aside the motives of the manufacturers and salesmen (as to which Tom in D.C. is quite correct), this is the technical argument for trunking.

On the plus side, a trunked system allows one to take 5-10 voice channels and create upwards of 100-200 "logical" channels, and, if the system is designed properly, few if any users (and no PD or FD users) will ever see a busy signal.

On the negative side, the entire system is dependent upon a complex and, sometimes, fragile, infrastructure (much of it powered by Microsoft Windows!), and when it goes down, it does so in a spectacular way. In addition, the cost threshold simply to get a trunked system off the ground (i.e., first PTT by any user) can be staggering. There are other issues: trunking does not accomodate "direct," which is critical for firefighters at a fireground and could be important for other services as well; this is why trunking is forbidden for fireground use by NFPA 1221.

Any municipality seriously considering a trunked system should investigate the system (which includes trunked and non-trunked aspects) employed by the City of Cambridge, Massachusetts, which is perhaps the best designed and implemented system anywhere.

[alex]

On the negative side, the entire system is dependent upon a complex and, sometimes, fragile, infrastructure (much of it powered by Microsoft Windows!), and when it goes down, it does so in a spectacular way. In addition, the cost threshold simply to get a trunked system off the ground (i.e., first PTT by any user) can be staggering. There are other issues: trunking does not accommodate "direct," which is critical for firefighters at a fireground and could be important for other services as well; this is why trunking is forbidden for fireground use by NFPA 1221.

I know all the console software itself is based off of windows, but I thought the site controllers actually ran unix as opposed to some sort of MS based operating system.

The consoles that I have seen which do run windows (aka centracom gold elite) do seem to have a solid uptime when combined with proper hardware / software that is tested/approved for the software. I'm not saying that it's perfect, but I know that the console the agency I used to work with had 99.9% uptime on their system. We also did a lot of PM on the system as well, but should be no different than any larger public safety system.

Properly maintained and implemented systems will always work great.

-ALex

[Ford]

If you have the coverage needed, the equipment provides the safety required and can handle the incidents, then stick with what works. The question you asked is kinda vague, as I don't know what the requirements for the system are. If you could use multiple talkgroups, want to tie into a zone, then go with trunking. Trunking also has the capability of being somewhat resistant to interference, as it doesn't rely on one specific frequency. Upgrading to P25 will also give you the potential for communicating with alternate resources that are already using it.

[PETNRDX]

I worked in Law Enforcement for 27 years in a LARGE department in a high popluation area.
We had a UHF conventional system that worked just fine.
Also had a multi-band/freq conventional mutual aid repeater system, also worked just fine.
We were pretty much forced by a large city to go 800 trunking.
With out question, it was the worst thing for my juridiction, and most of the 30 some agencies that went to it.
Worked good enuf for the LE people in the large city, bad for the FD of that same city.
So, as many above listed, if you have the capacity and the system you have works, I would stay with it.
Analog FM is interoperable.

[Ford]

If you take a look at most police or fire dispatch channels, you will find that their duty cycle (i.e., how many seconds of the day the transmitter is keyed up) is hardpressed to get much above 1-2%. The channel is idle (but waiting for traffic) all the rest of the time. Putting aside the motives of the manufacturers and salesmen (as to which Tom in D.C. is quite correct), this is the technical argument for trunking.

On the negative side, the entire system is dependent upon a complex and, sometimes, fragile, infrastructure (much of it powered by Microsoft Windows!), and when it goes down, it does so in a spectacular way. In addition, the cost threshold simply to get a trunked system off the ground (i.e., first PTT by any user) can be staggering.

How many people can you put on a conventional channel simultaneously? The 1-2% duty cycle doesn't matter that much, it's what's going on in that 1-2% that matters.

As for the fragile system, most systems have redundancy, and any lack of redundancy is the choice of the end user. Dual links, dual site controllers, backup master sites. If a conventional channel goes down, you have no communications. Trunking, not a concern. Granted, failure rate isn't that high.

What infrastructure are you talking about? I don't know of any infrastructure (ASTRO, SmartZone, Smartnet) that relies on Windows at all.

[fineshot1]

On the negative side, the entire system is dependent upon a complex and, sometimes, fragile, infrastructure (much of it powered by Microsoft Windows!), and when it goes down, it does so in a spectacular way. In addition, the cost threshold simply to get a trunked system off the ground (i.e., first PTT by any user) can be staggering. There are other issues: trunking does not accommodate "direct," which is critical for firefighters at a fireground and could be important for other services as well; this is why trunking is forbidden for fireground use by NFPA 1221.

I know all the console software itself is based off of windows, but I thought the site controllers actually ran unix as opposed to some sort of MS based operating system.

The consoles that I have seen which do run windows (aka centracom gold elite) do seem to have a solid uptime when combined with proper hardware / software that is tested/approved for the software. I'm not saying that it's perfect, but I know that the console the agency I used to work with had 99.9% uptime on their system. We also did a lot of PM on the system as well, but should be no different than any larger public safety system.

Properly maintained and implemented systems will always work great.

-ALex

Alex - you are correct. The console work stations and CDM server run on MS XP these days but the zone controllers and servers run on Solaris(Sun version of unix) and there is much redunancy built in to the smart zone system. Even if you loose both zone controllers the system resorts to "site trunking" before it resorts to "failsoft". The weakest link in the chain is the link transport that is chosen(Terrestrial T1, Microwave) to the simulcast and IR sites. If there is already a robust microwave network in place that would be the obvious choice for link transport. Terrestrial T1's are sometimes unstable as the providers can do maint on them un-announced and repair support is sometimes slow response.

[psapengineer]

Like dad and grandpa always said: "If it's working don't mess with it". I think the same applies here. If you need interoperability with the surrounding communites accomplish it in some other manor than changing your cost effective working system. Regards, Bob

[akardam]

The real problem I see with trunking in public safety is the fact that the unit in the field has to wait for the little bleebily-boop before he can send his traffic. With a conventional repeater, if properly designed to provide good coverage in all service areas, at minimum you'll have some hetrodyne and know you had multiple units.

I don't have a problem with a trunking system for administrative/non priority traffic, to help address the bandwidth utilization issue. I think pushy salesmen aside, many agencies are under the impression that it's one or the other, not both. What's wrong with working on a band of your choice, appropriate for the terrain, and having dispatch on a conventional and everything else on a trunking system?

That's how we do it at the agency I do part time work for. We're fortunate to have a small enough coverage area that one repeater site does the trick. We have several conventional repeaters for dispatch and operations, etc, and everything else goes on the trunking system. We have redundancy and spares across the board, and if we were to loose either a conventional or trunked repeater we'd be back up on the air in whatever time it took to swap out the affected unit (less than 5 minutes for someone who's handy with a screwdriver) as all the repeaters are programmed identically - just rotate the knob to the channel you need for that slot.

In the grand scheme of things I really get the feeling that those pushing for and mandating these large complex trunking systems for public safety by and large have little or no experience using such a system in the field...

[RKG]

The City of Cambridge (MA) is similar:

Well-designed trunked system for PD, FD and virtually everyone else in the City.

One conventional tac channel for PD and two conventional channels for FD fireground.

[mruwave]

Several questions I haven't seen asked or answered thus far....
Is LE looking for additional operational functions (in-the-field computers)?
Is the municipality thinking about adding additional users (buses, garbage trucks, school buses, meter maids)?
Is there a real danger of jamming the analog system?
Is there a need for additional security (encryption) in dispatching?
What are the REAL reasons you are considering moving to trunking? Additional capability or outside pressure?

Seriously answer these questions and your answer will be apparent. Trunking will give you a lot of advantages at the cost of complexity. Analog truly is a workhorse and is cheap, simple and reliable. RKG may have the best answer for you, a hybrid system.

[Wile E. Coyote]

Sorry I havent had a chance to reply to some of these. It's been a busy winter around here! I tought I would try to clear things up a little with where I stand, and what our system looks like.

Several questions I haven't seen asked or answered thus far....
Is LE looking for additional operational functions (in-the-field computers)?

We already have a wireless computer system on 800. Although the interference from Nextel is horrible, the rest of the time it works OK. No real need to upgrade here.

Is the municipality thinking about adding additional users (buses, garbage trucks, school buses, meter maids)?

The need for growth is always there. However, all of the entities listed above have their own independent frequencies and repeaters. Adding users usually does not mean adding frequencies. They all wait their turn.

Is there a real danger of jamming the analog system?

Not likely. But if someone had the means, they could jam any system – Trunking or conventional.

Is there a need for additional security (encryption) in dispatching?

Not with our department. We believe in an open-door policy when it comes to radio transmissions. The chief thinks that the people in scanner land are more of a help than a nuisance.

What are the REAL reasons you are considering moving to trunking? Additional capability or outside pressure?

A little of both. Trunking does have its advantages, but for whatever reason we could never justify the cost after calculating the long term care and feeding of a trunking system. Now that everyone else around us has jumped on to a trunking island, they are preaching the benefits. For some reason, they never talk about the added cost of maintenance. On top of that, The FCC is about to force us all to go through several steps of narrow banding – Eventually ending up at 6.25 channel spacing. Since (almost) no radios today support that, why pay extra money for trunking radios when they will all have to be replaced by a certain date?

I hope that clears things up a little.

WEC

[Ford]

On top of that, The FCC is about to force us all to go through several steps of narrow banding – Eventually ending up at 6.25 channel spacing. Since (almost) no radios today support that, why pay extra money for trunking radios when they will all have to be replaced by a certain date?

Not sure I agree with that statement, even Sabers support 6.25, unless you're referring to the radios that were purchased?

[Wile E. Coyote]

On top of that, The FCC is about to force us all to go through several steps of narrow banding – Eventually ending up at 6.25 channel spacing. Since (almost) no radios today support that, why pay extra money for trunking radios when they will all have to be replaced by a certain date?

Not sure I agree with that statement, even Sabers support 6.25, unless you're referring to the radios that were purchased?

Sorry, the saber only goes down to 12.5 channel spacing.
http://www.motorola.com/governmentanden ... csheet.pdf

The ONLY radio that I am aware of that will support 6.25 is the Icom IC-F4029SDR... But they don't count. It's Motorola we are after.
http://www.icom.co.jp/world/products/pd ... 029sdr.pdf

[edit] I almost forgot. MOTOTRBO is only 6.25 compliant, not true 6.25 channel spacing. Only when you use 2 co-located 6.25 channels by using "TDMA technology for narrowband 12.5 KHz (6.25 equivalent-6.25e)". But this is getting a little off topic.
http://www.jancommunications.com/downlo ... L_3_07.pdf

[Ford]

I stand corrected sir, and I do apologize. I was looking at the user manual, which indicates that the value 2 represents 6.25 KHz, and assumed that since it was shown in the Saber manual, that it was capable of it. Portables is not my strong-suit; I shall try to refrain from being "helpful" in that area. There are some things shaking up in the portables area. I've heard that the previous radios have to be capable of being upgraded to APCO standards, so it may be the case that down the road they can be upgraded to it.

[RKG]

In all events, channel spacing (i.e., what channel value will the radio accept for the center frequency?) is not the relevant issue for narrow-banding, but rather channel width (i.e., what maximum deviation will the radio program for?).

None of the Sabers are programmable for narrow-band channels.

The FCC has not (yet) mandated a shift to 6.25 KHz wide channels. This is primarily because it appears that it will be difficult, if not impossible, to manufacture field-use capable equipment that can achieve this standard. If you think about, that isn't all that surprising.

The rough rule of thumb for the amount of spectrum occupied by a channel operating in conventional analog FM for passing voice audio with a width of 3 KHz is: 2MD+6, where "MD" equals max. deviation. Ergo, a "wideband" (i.e., 25 KHz) channel occupies about 16 KHz (or 8 KHz on either side of the center freq.), while a "narrowband" (i.e., 12.5 KHz channel) occupies about 11 KHz. As it is, the wider footprint of narrowband channels relative to their nominal spacing is already causing some problems.

Even if you could do FM voice with a MD of 1.25 KHz, the occupied spectrum under the rule of thumb would be about 7.5 KHz, and the channels already overlap (even assuming everyone is spot on assigned center freq.)

Enter Motorola, with its notion of "effective 6.25 KHz channel width," achieved by TDMA'ing two voice channels on an RF 12.5 KHz data channel.

MotoTRBO has its plusses and minuses. As a general substitute for analog FM, however, it will not (in this man's opinion) ever fly or ever be mandated by the FCC.

Which is where trunking enters the picture. Take Cambridge as just one example. It employs 4 data channels and 6 voice channels, for a total occupation of 125 KHz (looking only at the outputs, for analytical consistency). The Cambridge system produces (or is capable of producing) something on the order of 100-150 logical channels (with only the dog catcher and the Muni Course Greenskeeper at risk of a rare busy signal). This works out to the effective equivalent of less than 0.83 to 1.25 KHz per "channel," or five times more efficient than 6.25 would be in a perfect world.

The problem with trunking, of course, is that only works for (a) bigger systems or (b) subscription systems. This is what the SMRSs were supposed to be, but the Commission sat back while the SMRSs were gobbled into extinction by Nextel.

All of which might cause one to pause and reflect on whether the notion of spectrum congestion is real. Certainly at one time it was. Given HDTV, however, and couple that with a more realistic administration of Sub-part L, and I'll bet that spectrum congestion goes away overnight, even in such metropolises as Boston.

Oh, dear; that's enough philosophy for one day.

[ai4ui]

There are 11,000 members of this board, so it's safe to say that you could get as many as 10,999 answers. At my agency we went from a 6 channel VHF conventional system to a 5 site, simulcasted 800 MHz Smartzone system. It works at least as well as our conventional system did. The only thing is, operationally nothing has changed. Before we usually utilized one of the six channels for dispatch & two of the channels (assigned in real time) for operations, and many simplex frequencies for tactical channels. When there was a large incident, we would open up another channel. Even though there was only four channels available for incidents, we would run out of dispatchers before we would run out of channels. Now we use one talkgroup for dispatch & two talkgroups for operations. We can open up seven more talkgroups to support incidents, plus a bunch of special event talkgroups. There are many more talkgroups available than operating positions in dispatch or dispatchers to manage them.

We don't use any of the features of trunking except for the emergency call button and unit ID, but that was something that we did on the conventional system.

There was no major change operationally, but a huge change in cost. Where we were using $800 portables, now we have $3000 subscriber sets. $1000 Mobiles now cost more like $4000. Annual budgeted operating costs quadrupled.

So what it boils down to, unless all your local gov't. agencies are needing their radio systems replaced at the same time, you need additional "channels" but there are no more frequencies available, or you are looking for a system to support a bunch of features like man down, select call, SMS, etc., then trunking may not be the best utilization of your communications budget or tax dollars.

YMMV

Robert