We agree on many points but I respectfully disagree on others.
My background: In my 'day job' I design/build/maintain RoIP infrastructure and IT systems, but am an old tip and ring RF guy from way back. I am also a long-time law officer turned Firefighter and Emergency Manager in predominantly rural environments, with academic credentials in public safety administration, technology, and interpersonal (non-radio) communications.
First I believe that communications planning is more art than science …
I would propose that communications planning is one quarter Art and one quarter Science, with the remainder being ego, politics and Dumb Luck.
With that said, I believe the only time simplex communications should be used is when a user is out of range of the system. For example a crew of firefighters entering a sub basement and they get the "Out of Range" tone on their radio. They should back out to where they are in range and report to command that they need to use a simplex channel in that situation.
Digital trunking radios are a networked computer with an antenna. The present OSI network model has eight layers (seven if you don't include the actual users). That translates to sixteen points of failure for any communication between users to fail. I contend that agency policy adds another layer on each end and brings that to eighteen points of failure, plus the inherent weirdness of radio itself. (I count users and policies twice each because of differing abilities and training levels of users, and interpretation of policies between users and agencies.)
In contrast, 'old fashioned' radios are a simple receiver/transmitter with a speaker/microphone. Analog simplex involves a user, transmitter, antenna, RF, antenna, receiver and user. That is seven points of failure, and still far less by any accounting.
On the top end of the model, policy is often driven by politics and manufacturer campaign donations that do not always make sound sense. The OSI physical layer (radio / RF) is an afterthought. Device selection is often made on the user interface and the bells and whistles the application layer provides the user.
Just below policy are the actual users. Training, complacency and a frequent don't-care attitude when it comes to communications have bitten many responders where it hurts. "It's a black box - push button to talk, let off to listen" is far too common. "It's always worked before so it will now" is not always true. To compound the problem, technical aspects of radio communications are a low mental priority when focused on the mission. To further compound the problem, remembering/figuring out how to change a radio to overcome failure is frequently difficult when things start going south.
Now let's jump to the bottom physical layer, in this case the actual RF signal. On the 'downlink' side for a mobile/portable receiver to operate reliably it really needs at least a -121db signal strength at the front end. If control channel signal is lost the portable will be off-line while searching or trying to re-associate with a new site. If the portable's location is between two or more sites it may spend more time trying to connect and less time being a usable radio. If you have an infrastructure that delivers usable RF everywhere including building interiors, congratulations. You are an exception to the norm. Reality: In the fine print of the builder's contract there is probably a specification that says the system will provide 95% coverage with exceptions for building interiors. Mr. Murphy says that life and safety problems will occur five seconds after the portable moved into a dead zone. That has been documented in multiple death and injury reports.
On the 'uplink' side infrastructure receivers must also have -121db of signal from the mobile/portable present at one of the associated or voting receive sites. Body attenuation, structure attenuation, interference and multipath issues make this uncertain. Toss portable antenna physical condition, water coated equipment and surfaces, and battery problems on top and conditions worsen.
Too many agencies put their budget into the bells and whistles, and next to nothing into properly sited and engineered RF components. They gloss over the simple fact that if the RF link fails, the bells don't ring.
My contention is that simplex operation will likely provide a minimum -109db signal over the hundred yard range required for most incident scene tactical operations. That is sixteen times the minimum required signal strength. Physical problems between the transmitter and receiver are less of an issue; a signal too weak to go from interior to infrastructure is still likely to go to an on scene receiver. None of the middle OSI layers are a factor. It's stupid old fashioned RF – and there is no site selection or association to add down time when seconds matter. You said yourself that simplex is a reliable backup to your trunking system.
If the RF from a portable doesn't receive an immediate confirmation, walk to the engine and pick up the microphone, or have the Engineer repeat it by policy and training. The -109db just turned into a -60db RF level. If interior can't hear that, they're not listening.
One of my hard and fast rules is that you should never require operational folks to switch channels while actively performing operations, and I like to preach that once you switch to a tactical channel you should never have to change. In your comments you mention 'out-of-range' situations. For that to work, first the end user must recognize that the situation exists and until they do their safety is in peril. They may not know until they yell MAYDAY and get 'bonked'. Next they must do something about it, breaking my hard and fast rule. And third, everyone affected must do the same 'something' or folks get lost off the grid. You have just added an unnecessary layer of complexity and confusion.
Any disaster you examine is made up of multiple failures, including the Hackensack incident. NFPA, IAFC, Nationalneariss.org and others detail scores of them, with trunking failures as a frequent significant contributing factor. The I-35 system crash, Detroit’s multiple failures and others are not isolated incidents; system wide failures are common and folks who rely on them are hard pressed to remember what to do when (not if) it happens. Any single component of the OSI model failing puts everyone in the dark. Fail-soft mode is proving to be helpful but not 100% reliable. Here again, Mr. Murphy holds that a system failure, even one lasting only a few minutes, will take place seconds before command calls for an evacuation or major tactical change. The folks on the wet end of the hose will be left in the dark until they realize the system has failed and remember what to do about it.
By not relying on infrastructure for tactical comms from the beginning, you have just cut the possible points of failure in half.
Without wanting to start an analog vs. digital discussion, I will offer this: With known issues considered, digital clarity is consistent out to the limits of the BER. Analog will be scratchy at lower RF levels. Interference originating from outside sources and nearby off-channel transmitters affects both but in different ways. Receiver de-sense is a greater issue with digital formats than with analog. Analog radios will play heterodyne noise, static or garbage, maybe discernible, maybe not, but
something will come out. If the digital codec cannot assemble a signal according to its software, it will do
nothing. Personally, I would rather hear something that maybe sounded like 'Evacuate' instead of blissful silence.
One of those bad situations involving communications was in Hackenshack New Jersey where 8 firefighters perished. They called for help on the radio, but no one on the scene heard them. Someone listening to a scanner heard the help call and called the dispatch center. So that's why I think it is so critical to responder safety for someone away from that hectic scene whose sole task is to be monitoring communications.
In my view, the primary life and safety oversight is the responsibility of the on scene IC and/or Safety Officer (NFPA-1561), not a remote dispatcher who may or may not be paying attention and has no idea what Bill or Charlie sounds like when they’re stressed. However, I have no disagreement that the more ears, the better
provided remote monitoring is
acknowledged as a tertiary backup.
An apparatus mounted system to broadcast simplex tactical traffic to a larger audience is simple and inexpensive, and should be standard for all agencies. Talkgroups are cheap and the apparatus configuration can be one-way or two-way. I use an apparatus mounted repeater over analog VHF to extend on scene tactical channel monitoring, but not for actual tactical use.
Also when "off" the system channels, the emergency button function on the radio no longer exists. When the emergency button is pressed, the dispatcher sees and hears someone might be in trouble. (Also, the way our radios are programmed, everyone else's radio alerts when the button is pressed.)
Even though P25 is supposed to be a standard across all platforms, manufacturer ‘enhancements’ have made that a joke. Emergency panic buttons DO work on simplex and the functionality is standard in EIA, MDC, NXDN and P25 formats. Many of the agencies I work with have them enabled on simplex and the reliability is excellent, including display of the radio ID on all units on the scene. If yours do not it is because they are programmed not to.
Another contributing factor to that incident was incidents were being dispatched on the same channel as fireground operations. The current best practice is to assign a separate channel for fireground operations which is different from the dispatch channel. With trunked systems, it is much easier to add more channels.
We are in total agreement that initial notification and wide area command and control should never take place on channels used for life and safety critical communications. Most suggest that any system having over 750 initial notifications a year use a dedicated channel for that purpose alone.
Combining command & control and tactical channels is
never a good idea. Traffic priority is never observed. A distant station may not hear on scene portables and will blindly walk over critical traffic without knowing any better. In Illinois (also WI, IN, IA and MO) MABAS provides six licensed standard
ten watt analog channels for simplex fireground operations. Harmful interference from other incidents or off-scene transmitters is never an issue, and as a statewide standard mutual aid can immediately be on the right channel.
