Here's a report that I did in December 1991 on Mobile Data Terminals for a Data Communications class I was in at the time. I think it's a good overview of Mobile Data Terminals (MTDs), and thought some of you out there in scanner land might enjoy it, especially if you're new to the hobby.

Update 8/26/97

I read your article on North Richland Hills PD's MDT system from 1991. I was the Captain you referred to at that time and have been the Assistant Chief since 1993. I thought you might be interested to see how much the system has grown since 1991. Hurst, Euless, Bedford and Grapevine all joined us after having to abandon an Electrocom system.

The overall success of the Motorola system has been overwhelming and we now support two separate channels and two different protocols. We have over $1 million invested in the system and none of it came from tax dollars.

Thanks for the article and I hope you find the "up to date" information interesting.
Auto Theft Task Force6 9
Haltom City12
NRH Municipal Court2
North Richland Hills32 3
Richland Hills7
Southlake112 4
Tarrant County SO29
Totals173 184

I believe VRM is an acronym for Vehicle Radio Modem but I'm not absolutely sure. The VRM is part of a model number (ex. VRM600) for a radio modem that is installed in the patrol car and allows a personal computer to attach and be used along with "TX" application (or other) software so the personal computer becomes an MDT capable device.

It is certainly permissible for you to utilize the information that I sent to you. We have seen great success with the system and the cities have a capability of inter operability that has caused many a "bad guy" to get caught. That's what we're here for.

Thank you again for the kind words about our agency and I appreciate your response to my message.

Best regards,

Tom Shockley

Assistant Chief of Police

Operations Bureau

Copyright © 1991 Ben Saladino

Networks on Wheels

Public Safety Mobile Data Terminals


Ben Saladino

December 10, 1991

Public safety departments depend on their communication systems to provide us with the best possible service when we need it. This system includes telephone lines to answer our calls, two-way radios to dispatch police, fire, and ambulance personnel, and long distance links (microwave and telephone) to connect municipal computers to state and federal databases. In the past few years a new means of communicating has been gaining in popularity among public safety departments. Mobile Data Terminals (MDTs) now connect police officers in cars and on foot to other officers, dispatch, and those far-away databases by way of radio. MDTs are small microcomputers that are connected by FM two way radio forming a network that is very flexible. The span of the network is typically equal to the coverage of voice FM channels used by city and county public safety departments, but it could span the country. MDTs have many advantages over traditional voice radio channels namely access to an enormous amount of information, speed, and security. The MDTs discussed here are not limited to just public safety agencies. There are probably many more businesses that are using MDTs to communicate between service and sales fleets and base computers. Of the public safety agencies, police departments make up most of the MDT users, but more and more often fire departments are taking advantage of MDTs. They access pre-fire plans, and hazardous materials databases, and are dispatched by way of MDTs.

Before the introduction of MDTs police voice channels were congested with dispatching, officer to officer messages, routine status changes ( en route, on scene, etc.), and licenses checks. Most of this traffic is non-emergency. By implementing an MDT system a police department can free up voice channels for emergency use and unusual traffic that can't be relayed effectively over the MDTs. An officer can now bypass the dispatcher for information that he needs. What's more, he can get the information faster and more accurately because there is no repeating the spellings of names back and forth between the dispatcher, and he doesn't have to wait for the dispatcher to finish taking a higher priority call. Often police and fire departments are using Computer Aided Dispatching (CAD) and 911 call taking. When an emergency call comes in on 911 the caller's location and phone number are displayed immediately on a 911 system screen, and then transferred to the CAD system where the dispatcher adds the type and details to the call. The dispatcher uses the CAD to decide which units to send on the call, and then sends the officer the call over the MDT. Within seconds of the phone call the officer's MDT beeps alerting him to the call. He responds by reading his terminal and acknowledging the dispatcher by hitting an "en route" button. When the officer arrives at the address displayed on his MDT he presses an "on scene" button signally the dispatcher via the CAD of the officer's status. Once the officer is finished on that call he can place himself back in service by pressing another button. Because an officer may not always be in his car or be by an MDT, voice channels will always remain a crucial link in the communication system.

According to a North Richland Hills police captain, information access accounts for about eighty percent of their MDT channel usage. In only eight seconds an officer can pull up driver's license, license plate, registration, or stolen property information from databases stored on computers in Dallas, Austin, and Washington D. C.. An officer can enter a vehicle's plate numbers and get information that may save his life. If the vehicle was involved in a crime the officer can call for assistance before making a traffic stop. Once the vehicle is stopped the officer can type in the suspect's name or driver's license number to get his record, that may show outstanding warrants or prior arrests. Should an officer recover stolen property he can enter the serial number of the item to locate the rightful owner. Gun registrations also can be retrieved via the MDTs. Most of the databases described above are found on a statewide network call Texas Law Enforcement Telecommunication System (TLETS). TLETs forms the physical connections between local police departments and the databases. When an officer types a request it travels to an MDT controller, to a network control processor, to a front end computer, which then routes the request to the proper database. The Federal Bureau of Investigations maintains the National Crime Information Center (NCIC) in Washington, the Texas Department of Public Safety handles the Texas Crime Information Center (TCIC) in Austin, and a regional database is also located in Dallas.

Mobile data terminals are also used for informal messages between officers and for sensitive information that may be easily eavesdropped over voice channels. Officers can arrange to meet with each other or discuss a case without tying up the dispatcher. MDTs are used to protect victim's identities or other details of a crime from being overheard by radio monitors outside the police force. Anyone tuned into a data channel will only hear short bursts of static when a message is sent by an MDT.

The short burst of data allows a large number of units to be on the same channel. The North Richland Hills Police Department is currently using twenty-two terminals. Up to 100 may be used with their current hardware. As you might expect much planning goes into designing an MDT system. North Richland Hills had their system planned so that several surrounding cities will be able to take part in the network. Currently only one other city is set up. Each city is grouped so that messages can be easily exchanged between officers within the same city. When necessary one city can route messages to another. For example an officer who has just received suspect information from a victim can type in a suspect and vehicle description and send that to all other units on the MDT system, whatever city. The suspect information is repeated fewer times so it will be more accurate and more timely.

Other features of MDTs are street maps, distress buttons, status timers, printers, and bar code/magnetic strip readers. Don't be surprised to see bar codes or magnetic strips on your driver's license soon!

Portable Data Terminals (PDTs) are scaled down versions of MDTs, which can be used by officers on foot or bike patrols and away from the car. PDTs are well suited for performing search warrants inside houses, where suspects, stolen property or guns can be efficiently processed. The distress button when pressed by an officer alerts all other MDT users that are signed on to the network that an officer needs help. It even provides his last location and status. There are even acoustic coupler modems available that will extend the MDT coverage area past normal radio coverage area by using phone lines. One disadvantage of today's MDTs is size. Most squad cars today are already packed with shotguns, radar equipment, light & siren controls, voice radios, and even video cameras occasionally. Future MDTs will no doubt become smaller and more functional.

The police officer's interaction with the MDT is simplified by electronic forms that he fills out to send messages and retrieve information, but in the background lies a complex computerized communication

system. The North Richland Hills MDT system initially cost about $300,000 that included the radio system, individual MDTs, and the necessary computer controllers. The entire system was funded by drug task force money not taxpayers. Their system includes a personal computer that controls a microwave link between the dispatch center and a radio tower, a second PC that controls the MDT traffic, and a third that interfaces the MTDs with the CAD. The MDTs are microcomputers that typically have up to sixty-four kilobytes of RAM. They can emulate IBM 3278 screens to access existing databases without special software being written. Motorola 9100-11 MDTs can be programmed using their C Language Applications Development System.

Communications wise, data is transmitted at 4800 bits per second over VHF, UHF, or 800 Mhz FM channels. The protocol and transmission speed will vary from vendor to vendor, so special software and hardware must be developed to connect two different brand MDT systems. For example Hurst, Euless, Bedford, and Grapevine use ElectroComm MDTs and the North Richland Hills system is Motorola, so communication between the two systems is done manually by a dispatcher.

When I visited the North Richland Hills Police Department I was very impressed with the technological advances that the department has made. They were also testing some crime fighting devices still in development stages like car mounted video cameras and vehicle tracking systems. Mobile data terminals are proven and here to stay, and they will allow public safety departments to serve their communities more effectively. The huge databases that police and fire units now have available by MDTs will let them make more informed decisions. The information they need is available more quickly than if they voiced their request to the dispatcher, and it is more accurate. The dispatcher is relieved from sorting though the requests of dozens of officers, and the officers are safer because the channel is open for emergencies. Sensitive information travels in an unreadable format to unauthorized listeners. These features are the reasons MDTs have become such a valuable tool for progressive police and fire departments.

4/3/96 Note, Hurst and Bedford are now using the North Richland Hills MDT system.

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