NBS

PUBLICATIONS

A 1 1 1 0 4 DSlbbB

NBSIR 84-2991

Guide to Computer-Aided

Dispatch Systems

David J. Brenner

Marilyn A. Cadoff

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Manufacturing Engineering

Mechanical Production Metrology Division

Gaithersburg, MD 20899

Prepared by the

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Law Enforcement Standards Laboratory

Gaithersburg, MD 20899

March 1985

Final Report

(

QC

100

.1156

85-2991

1985

c. 2

Prepared for the

National Institute of Justice

U.S. Department of Justice

Washington, DC 20531
V
NATIONAL BUREAU

OF STANDARDS

LIBRARY

NBSIR 84-2991

GUIDE TO COMPUTER-AIDED

DISPATCH SYSTEMS

aw

i

David J. Brenner

Marilyn A. Cadoff

U S DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Manufacturing Engineering

Mechanical Production Metrology Division

Gaithersburg, MD 20899

Prepared by the

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Law Enforcement Standards Laboratory

Gaithersburg, MD 20899

March 1985

Final Report

Prepared for the

National Institute of Justice

U.S. Department of Justice

Washington, DC 20531

z

o

<•<

c

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director
ACKNOWLEDGEMENTS

This guide was prepared by the Law Enforcement Standards Laboratory of the National

Bureau of Standards under the direction of Marshall J. Treado , Program Manager for

Communications Systems and Lawrence K. Elia son. Chief of LESL. Comments and suggestions

were received from the reviewers listed in appendix C. Its preparation was sponsored by

tne National Institute of Justice, Lester D. Shubin. Standards Program Manager.

ii
FOREWORD

The application of advanced technology by law enforcement and criminal justice

agencies continues to grow, driven by both the desire to enhance capabilities and

tne need to improve operational efficiency resulting from increasing demands upon

limited resources. The Law Enforcement Standards Laboratory (LESL) was established

at the National Bureau of Standards to conduct research that will assist criminal

justice agencies in the cost effective procurement of quality equipment. To

accomplish this objective, LESL conducts research and subjects commercial equipment

to laboratory testing to develop voluntary national equipment standards, technical

reports, and user guides.

This guide is directed primarily toward police departments that are contemplating

the acquisition of a computer-aided dispatch (CAD) system or are in the planning

phase in advance of procuring such a system. The information contained in this

guide will provide a basic understanding of CAD svstems and operations including

equipment components, software, and information storage and display. The guide

draws heavily upon the experience of many departments that have installed CAD

systems to highlight those factors that are critical to svstem design, equipment

selection, procurement, installation, and training.

Additional reports and guides as well as other documents are being issued under the

LESL proqram in the areas of protective equipment, communication systems, security

systems, weapons, emergency equipment, investigative aids, vehicles, and clothing.

A list of all LESL publications is available upon request.

Technical comments and suggestions concerning this guide are invited from all

interested parties. They may be addressed to the Law Enforcement Standards

Laboratory, National Bureau of Standards, Gaithersburg, MD 20899.

iii

CONTENTS

Page

FOREWORD iii

INTRODUCTION 1 BENEFITS PROVIDED BY A CAD SYSTEM 2

HOW A CAD SYSTEM OPERATES 3 COMPONENTS OF A COMPUTER-AIDED DISPATCH SYSTEM

Haruware 7 CRT Terminal 8 Terminal -to- Computer Data Channel . . 10

The Computer 11

Mass Storage (External Memory) 14

Printers 16

Power Sources 17

Sizing the Hardware System 18

Software 19

Operating System 19

Real-Time Dispatch System Package 20

Applications Program 20

Modification to a CAD System Software Package 20

Software Maintenance 20

Maintenance and Repair of a CAD System 21

CAD SYSTEM PROCUREMENT PROCESS 22

Acquiring a Medium- or Large-Sized Commercial System 22

Acquiring a Small-Sized Commercial System 25

Custom Design of a CAD System Using In-House Capability 25

GENERAL OBSERVATIONS 25

SUMMARY 27

REFERENCES 28

APPENDIX A—GLOSSARY 31

APPENDIX B—DETERMINATION OF THE NUMBER OF COMPLAINT OPERATOR AND DISPATCH

TERMINALS REQUIRED FOR A CAD 33

APPENDIX C —LIST OF REVIEWERS 37

v

Guide to Computer-Aided Dispatch Systems

David J. Brenner and Marilyn A. Cadoff*

National Bureau of Standards

Gaithersburg, MD 20899

This guide provides current information on computer-aided dispatch (CAD)

systems as they are used by law enforcement and other public-safety agencies and is

intended to serve as a procurement aid to those persons who are or will be involved

with the planning and acquisition of a CAD system. Topics such as the improvements

in operations that may result from installation of a CAD system, a description of

the system components, various considerations that will require resolution when the

decision is made to purchase a CAD system, and provision of sufficient background to

enable a knowledgeable purchasing decision to be made are addressed. A general

purchase implementation plan is included also.

Key words: command and control; communications: complaint operator; computer-aided

dispatch; dispatcher; hardware; software.

INTRODUCTION

Prior to the 1970 's the dispatching facility for police, fire, and other public-safety

agencies almost always used manual methods. Where the population base being served was

small- to-medium in size, say less than a population of 100,000, this worked and still

may work well. But for larger populations, the ability of the dispatching personnel to

be familiar with the increased number of street locations or to keep up with the

increased amount of record-keeping had become progressively more difficult. Thus, when

computer systems of sufficient capability and affordable price became available, they

began to be employed to automate some parts of the dispatching operation.

Computer-aided dispatch (CAD) systems were first used in law enforcement operations in

the early 1970's and their implementation, and use has increased steadily since.

Whereas in 1975 only about 10 percent of the 135 police departments in jurisdictions of

more than 100,000 population had a CAD system [1]-*-, by 1930 a little over 50 percent of

these departments had operational CAD systems, and at least nine municipalities with

populations under 100,000 had installed them [2]. A recent listing of 64 jurisdictions

with operational CAD systems or systems under test included 13 serving populations of

100,000 or less [3]. This extraordinary growth seems to have occurred because a CAD

system utilizes the special abilities of the computer to service calls from the public

rapidly and efficiently and, in so doing, provides several significant dispatch

operation improvements, e.g., improved information exchange within the dispatching

system, automatic verification of certain information, and generation of case reports.

An excellent and wide-ranging document on CAD systems was prepared in 1975 by the Jet

Propulsion Laboratory for the Law Enforcement Assistance Administration [lj. This

publication is intended to summarize, supplement, and update the information given in

that report as an aid to those persons who are or will be involved in the planning and

acquisition of a CAD system. This planning involves such topics as the improvements in

operations that may result from installation of a CAD system, a description of the

system components, various considerations that will require resolution when the decision

is made to purchase a CAD system, and sufficient background to enable a knowledgeable

purchasing decision to be made. The reader should note that this reoort assumes that

tne major components of the overall system, such as a satisfactory communicat in:/:;

system, telephone system, and information system already exist. A general ;r •

. i

• implementation plan is given and a glossary of frequently used terms is attn • : i appendix A.

*Fabrication Technology Division, Center for Manufacturing Engineering.

iNumbers in brackets indicate the literature references at the end of this report.

1
BENEFITS PROVIDED BY A CAD SYSTEM

A CAD system that has been well planned and designed for the jurisdiction it is intended

to serve can provide many improvements to the complaint-taking and dispatching

operations of a police or fire department, and thereby to the public it serves. However, it should be clearly understood that a CAD system cannot and is not intended to

take the place of the human aspect of the command and control operations * rather . it is

intended to supplement it by performing certain routine and repetitive tasks quickly and

without error, storing the information for future reference, and retrieving it

essentially instantaneously.

Specifically, one benefit which should accrue from use of a CAD system is improvement of

the accuracy of the information handled between the complaint taker and the dispatcher,

and between the dispatcher and the officer on patrol. The computer is capable of

analyzing information as it is put into or transferred within the system, and the

computer will automatically signal for errors such as an incorrect case number or an improper patrol unit designation. Some systems, if equipped with the appropriate

software, can compare an address with an address file to check for its validity and

correctness . Use of a CAD system, over the long run, should improve operator performance by providing

relief from many tedious tasks. For example, when an address is entered into the

system, the computer can automatically determine which police precinct it is in and

display this information on the complaint operator's screen. Or when a complaint is

telephoned in. the computer can automatically determine whether a case file has already

been set up for this particular complaint. Thus, the complaint operator and dispatcher

are better able to concentrate on the more critical decision-making aspects of their

jobs . Another advantage of a CAD system is that the properly-designed system is capable of

responding quickly and accurately: thus, certain tasks can be added to the complaint

operator’s and dispatcher's routines with little or no loss in response time t4] . For

instance, the computer in a CAD system can be used to quickly check its file to

ascertain whether any previous incidents have occurred at the address where the current

report is coming from. If a number of incidents have occurred at this location, it

would be beneficial to a police officer's safety to have tnis information prior to

arrival on the scene. Such a check would probably not be carried out using a manual

system, because it would clearly increase the response time required to handle a complaint as well as decrease the number of calls a dispatcher could handle. Note that

a CAD system cannot substantially reduce the time it takes an operator or dispatcher to

process a complaint from an individual. There is a minimum amount of time needed to

simply exchange information between two persons, and no computer is capable of reducing

the time needed to accomplish this task, however, a well-designed CAD system can assist

the operator by organizing questions to limit the time spent querying each caller.

Use of a CAD system is an efficient way to keep track of incidents and their status and

tne numoer of patrol cars available ana their current status (i.e., those responding to an incident, on the scene, on patrol, etc.). Sucn information gives a dispatcher almost

instantaneous knowledqe of the events taking place witnin a jurisdiction and of

available resources. Thus, as new complaints come in. the dispatcher is capable of

accommodating them more efficiently and effectively.

Finally, a CAD system can generate certain reports thereby resulting in a decrease in

paperwork for almost all groups in a police department [5]

.

Because it stores records of

all cases. it is capable of eitner generating case reports on routine cases or generating the routine portions of a case report which require additional details from

the patrol unit officer(s). The dispatch unit supervisor can use the CAD system to

generate activity reports for each shift, and management can use it to generate

statistical reports, sorting incidents by type, area, patrol unit, time of day. date, or any other useful classification. These accumulated data can tnen be used to balance

workloads, redesign beats, and better manage manpower and financial resources [4]

.

In fairness, CAD systems are not without disadvantages. Complaint board operators and

dispatchers require extra training to learn the skills necessary to operate the CAD

system [6], Additionally, significant initial funding and careful planning is needed to

procure and initiate operations. Additional physical facilities and maintenance

2
agreements may be required before a CAD system can be installed and become operable.

The computer may need a special uninterruptible power supply or a back-up power source

in case of a power failure. Also, any problems which may arise with the computer and/or

the software systems often can be resolved only with professional help. This

complication was highlighted in reference 7. But it would appear from the growth in use

of CAD systems since their inception that their benefits far outweigh their

disadvantages. In fact, many jurisdictions are already in the process of purchasing a second-generation system, primarily because of increased demand for service.

HOW A CAD SYSTEM OPERATES

The operation of a CAD system can best be understood by following a hypothetical call

for assistance through the complaint and dispatch phase of the police operation. The

telephone call is forwarded to the police communications center and is routed to an available complaint board operator, whose responsibility it is to obtain from the caller

all of the information needed to enable the police to respond to the complaint. This

information will include items such as names, addresses, and a description of the

problem. It is here, at the complaint board operator’s position, that the CAD system

begins its functions.

When a telephone call for assistance comes in to the complaint operator's work station

(see fig. la), the complaint operator will press a special-function key on the keyboard.

This action will cause the computer to display a questionnaire on the screen of the

cathode-ray tube (CRT) display terminal. A typical screen display is shown in figure lb

and, as can be seen, the operator simply needs to fill out the "form" in the top third

of the screen by asking the caller for the information needed. The CAD system provides

assistance here and automatically supplies some of the information based on other

information provided by the caller; for example, when the caller gives a street address,

the computer will automatically search its geographic file to see if such an address

actually exists. If not found, it will signal the operator to ask for a correct

address. Once a valid street address is typed into the system, the computer will

determine what police precinct, beat, or other appropriate designation covers that

address and display this information on the complaint board operator's screen.

CARD

SLOTS CRT

PUNCH

CLOCK

INSTANT

RECALL

INSTANT

RECALL

KEYBOARD

CALL

ORECTOR

Figure la. Complaint board operator work station [1],

3
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*** ***

** ***A13 INVALID STREET TXPE/PIRECTIQE * MW SELECTION **

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**  VALID TYPE/DIRECTION - CHOOSE ONE **

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** D 1 1321 ALARM 1316 CEDAR ST Q 3 1316 VANDAL 5200 31ST AV **

** P 3 1320 THEFT 3550 QUEEN AV SO P 3 1315 PARTY 59 7TH AV **

** A 2 1319 BRGLRY 6115 FRANCE SO D 1 1314 FIRE 15111 AV/HIAWATHA ST **

** P 2 1318 PRWLER 425 5TH AV SO D 1 1313 CRDIAC 257 ADAMS ST NE **

 MP**  QUERY ** *** *** A**************************************************************************.*.** ****************************************************************************

Figure lb. forrnat of complaint board operator's CRT screen. (Note the fill-in- the-blanks information-gathering form shown on the top third of the screen ^f110 type ^ and the list of recently entered incidents on the bottom

If a street address acceptable to the CAD system cannot be provided, then the complaint board operator is able to override the computer's response and proceed. (This override feature is very desirable in a CAD system, since it enables the operator to correct for errors and omissions in the CAD system programs and data base, and to supply updated information.) After having obtained all (or most) of the information needed from the telephone caller, the complaint board operator pushes another special-function key on the keyboard which commands the computer to create an event file complete with the operator's data, with the current date and time automatically added. Since the CAD system now "knows" the street address, it will also automatically transfer the event data to the dispatcher handling the area where the event occurred.

The dispatcher's work station, shown in figure 2a, generally has two CRT screens, as he/she needs more information available at one time than does the complaint board

operator. The dispatcher's primary screen is the one on the left (fig. 2b) and is used

for the actual dispatching process. The screen on the right (fig. 2c) shows the status

(available, enroute to the scene, at the scene, or out of service) of all of the field

units for which the dispatcher is responsible. The CAD system also keeps track of how

long each responding unit remains in the active status, and can alert the dispatcher if

the time is unreasonably long, a possible indication of trouble.

4
CALL

CHRECTOR

CRT CRT

C(

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wo

moL

KEYBOARD

Figure 2a. Dispatcher work station [1]

.

****************************************************************************

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AT: 16:52

ZONE: 504

AD:

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VICTIM BLEEDING—BURNING ODOR

HAZ: KNOWN DRUG USER HANGOUT IN APT 6 3RD FLR

DSPTCH STATUS: POLICE/ /

RECOMMENDED DISPATCH: 540

FROM: C04

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MAP: 1234

EE/16: 53/327

MORE UE/16 : 55/579

05/09/79 MORE

FIRE/DPCH/16:54 EMS/ARRV/16 : 56

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** 2 07:33 1255 BRGLRY P 6115 FRANCE S **

** 3 06:41 1238 PARTY Q 5200 31ST AV **440   PEND TOT: P0=0 Pl=2 P2=2 P3=3 P9=0 MORE ** MP** *MDT* QUERY OVERDUE ** *** *** ******************************************************************************

****************************************************************************

Figure 2b. Dispatch screen of the dispatcher, (Note that the upper third of the s c r < < n displays the information for the incident currently being dispatched (in italic type]., and that the bottom third of the screen displays a list nf

incidents waiting to be dispatched.

5
* ******* .<*************************;. *************************************** ******************************************************************************

to** ***

to* UNIT NATURE STAT LOCATION UNIT NATURE STAT LOCATION to*

to* 302 560* to*

to* 304 570* ACC-PI A10 2931 W 58TH ST to*

to* 305 571 to*

to* 307* 592 to*

to* 310* AS SALT A0 2 LAKE ST/40TH AV 602 to*

to* 311 604 to*

to* 320A* 605 to*

to* 330 607* to*

toto 340F 610A* INFOR A0 2 3636 FRANKLIN E to*

to* 350 611 to*

to* 360 620* toto to* 370* HDQTS D12 630* to*

toto 371A* 640* to*

toto 382 641 to*

toto 392 650* to*

toto 504 660* to*

toto 505 670* to*

toto 510* 671 to*

toto 520* DOMES E02 XERXES AV S 672 to*

to* 530 935 to*

toto 540* 1280 to*

toto 550* 1902 to*

toto 551 000 ADDITIONAL UNITS FOR THIS AREA toto

tototo tototo ******************************************************************************

****************************************************************************

Figure 2c. Status screen of dispatcher.

The dispatcher's primary screen shows all known information about the incident now

waiting for the dispatcher's attention. This includes the information that was obtained

by the complaint board operator, plus additional information that the computer added

from various data files that are part of the system. Also, the incident record now

includes a computer -selected recommendation of several field units that are suitable for

responding to the incident. The dispatcher either may select one of these or may act on

his own judgment and send a different unit (another example of human judgment being

allowed to override the computer system) . The actual dispatching is done either by

voice over police radio or by a computer -controlled digital message that is sent over a radio channel allocated specifically for digital transmissions.

When a field unit has been assigned to respond to an incident, the primary job of the

CAD system is almost done. All that remains is for it to update the status of the

responding field unit as events progress from "enroute" to "at the scene" to. "incident

closed" and back to "available." It also will add to the incident's record any

additional information and may perform any follow-up activities required by the

particular jurisdiction. This might include requests for warrants, vehicle information,

and travel details.

A possible physical layout of a CAD dispatch center is shown in figure 3. The number of

personnel and equipment shown is only illustrative and is not meant to imply this is the

typical number required. These needs are determined by the requirements of the

individual department procuring the system. The main determining factors seem to be

average waiting time before a caller is connected to an operator, average processing

time per call, peak number of calls per hour, and actual time spent by the operator

processing calls during the peak hour. A more detailed discussion of the considerations

of sizing a CAD system is given in appendix B to this report. Due to the noise levels

produced by processors, disk drives, and printers, several departments have decided to

physically separate the hardware components from the room where communications

operations are being performed.

6
Figure 3. Typical computer-aided dispatch center [1]

.

COMPONENTS OF A COMPUTER-AIDED DISPATCH SYSTEM

Hardware

The major hardware components of a CAD system are:

1) Cathode-ray tube (CRT) terminal

a) keyboard

b) CRT display

2) terminal-to-computer data channel

3 ) computer

a) central processor unit (CPU)

b) memory

4) mass storage (external memory)

5) printers

6) power source

The following discussion will focus on each of these elements. A simple block : . i ; : e of the hardware elements of a CAD system is given in figure 4.

7
Figure 4. Simple block diagram of the hardware components of a CAD system.

CRT Terminal

Basically, a CRT terminal consists of a typewriter-like keyboard for entering

information and a television- like screen which displays the information being entered

into the CAD system by the complaint board operator and also transmitted by the

dispatcher to the field unit. The only major consideration for the buyer is that the

CRT terminal must be compatible with the particular hardware and software being used.

Keyboard

The purpose of the keyboard of a CRT terminal is to enter commands and information into

the CAD system. The keyboard consists of a standard typewriter keyboard plus a number

of additional keys, called function keys, which make it easier to give commands to the

computer. Thus, while an ordinary typewriter has approximately 50 keys, the keyboard of

the CRT terminal will have, in addition to these 50 keys, anywhere from less than a dozen to three dozen function keys. The alternative to using a function key is for the user to type an appropriate command code into the system via the standard typewriter

keyboard. For example, if the desired command were NEXT PAGE, the correct code might be

the character-string NP. After typing these two characters, the user would then press

the RETURN key, and the computer would perform the task requested. If the function key were not used, the user would have to memorize (or look up) the command code as well as use three key strokes instead of just one. Obviously, dependence on an operator's

memory can introduce a source of error and result in lost time.

8
There is no standard rule or practice governing the number of function keys that should

be employed. At a minimum, each of the more important and/or frequently used commands

snould be assigned a special key in order to save time and reduce errors. The decision

as to which commands will merit a function key will depend upon the specific CAD system,

the system designers, and user preference. It should also be noted that an excessively

large number of function keys may be self-defeating, because it then becomes difficult

and time-consuming to locate the desired key.

Another important consideration concerning the keyboard is the presence or lack of

tactile or audible feedback when a key is pressed. Tactile feedback means that the

finqers can sense a distinct change in the key force as they "break through" the

transition region during the keystroke. Audible feedback, which might annoy some

people, is usually a short beep that is used to indicate that a keystroke has been

accepted by the terminal. The benefit of some form of feedback is that it provides a positive indication to the user that the terminal has "recognized" the keystroke.

Tactile feedback is generally recommended; audible feedback is an option that is a matter of personal preference.

Most keyboards on a CRT terminal have a long life if not abused. The most common

hazards seem to be striking the keys too forceably and spilling liquid or ashes on and

into the keyboard and its mechanisms.

CRT Display

Just as the keyboard is the means by which instructions and information are entered into

the computer system, the CRT display is the quickest means to get information from the

system. A monochrome (single color) CRT display is generally used in a CAD system.

Full-color displays are seldom used in a CAD system or in any other situation where it

is necessary to display a large amount of text. The reasons for this appear to be

twofold. First, the spatial resolution of a monochrome CRT display is much better than

that of a full-color variety. Second, the cost of a full-color display has been more

than double that of a monochrome display. However, it should be noted that at least one jurisdiction effectively uses color displays to indicate unit status and emergency

situations. In this case, use of several colors saves valuable text space on the screen

and interpretation of the meanings of the colors becomes automatic for well-trained

operators

.

The typical CAD system terminal has a 30 or 37.5 cm (12 or 15 in) screen (diagonal

measurement) . The display usually produces 24 lines of text of 80 characters each

(24x80 = 1920 characters) . This is the industry standard at present, and represents the

accepted trade-off between price and performance. However, the use of 24-line disdays

is definitely a handicap because abbreviations and space-saving screen formats must be

freely used in order to display the amount of information that the users need. In

addition to this, the dispatcher's work station requires the use of two display screens

in order to display the minimum amount of information needed to ensure optimum

performance. Terminals are available where the screen can displav more than twice this

number of characters, but their cost is higher.

Monochrome CRT displays have been found to be relatively free of technical and safety

problems. With respect to safety, there are almost no problems. X-ray radiation (from

the high voltage electron beam striking the phosphor screen) has proved to be

negligible, provided that the high-voltage supply does not exceed the voltage soecified

by the CRT manufacturer (for a 12-in screen, usually between 11,090 and 14,000 V). Th"

high-voltage components are well insulated, and a person would have to make a positive

effort to create an electrical shock hazard.

Nearly all health-related complaints about CRT displays have nothing to do with the

display itself, but rather are problems that develop from the way that it is used. The

problems, when they occur, are usually caused by the combined stresses of sitting for

hours at a CRT terminal and having an unsatisfactory work environment or work habit.

For example, complaints of eye strain or back pain might actually be caused by improper

display contrast or poor posture, respectively. Most eyestrain problems would be

minimized if satisfactory choices were made for the following:

9
1) Eye-to-screen distance such that the eyes can focus comfortably;

2) Contrast of the display set at a comfortable level —not too high or too low;

3) Reflections from the screen minimized; and

4) Work sessions set up such that adequate rest periods are provided for

personnel.

With respect to eye-to-screen distance, it is only necessary that each user find out the

distance at which his/her eyes can comfortably focus on the screen. It may be useful to

be aware that the characters on the screen are larger than those on an ordinary

typewritten page, so it is not desirable to sit too close to the screen.

The contrast of the CRT display (i.e., the relative brightness of the characters with

respect to the brightness of the background) should be set to a visually comfortable

value. It is common to find that users set the contrast and/or brightness controls to

produce very bright characters. This not only shortens the life of the CRT display but

also promotes user eyestrain. When the contrast is too low or too high, eye comfort is

likely to be affected at some point. As a guide, the contrast provided by an ordinary

printed page is about right for minimum eye strain.

Minimizing the amount of glare and other reflections from the face of the screen requires several steps. The first step is to make the room brightness fairly low (this

is commonly done at CAD system installations) , and check to see which lights or other

bright or shiny objects produce too much interference with the CRT display. If

reflections cannot be prevented by appropriate positioning of the trouble source or the

CRT screen, then an optically diffusing CRT faceplate- an optical filter, or a shading

hood can do much to reduce the problem. Anti-reflective coatings and polarizing films

also are now available and are quite effective. Use of a diffusing faceplate is quite

common, and is effective because it scatters the unwanted light in all directions, so that only a small amount reaches the viewer's eyes. A diffusing faceplate tends to

reduce the sharpness of the CRT display slightly, but the loss is small and the CAD

system user is unlikely to notice it. Manufacturers also can produce diffusing surfaces

by lightly etching the front of the cathode-ray tube, by applying a diffusing coating,

or by bonding a diffusing plate to the front of the CRT display.

Some users feel that green display characters are easier on the eyes than white ones,

and in some European countries, orange characters are used for the same reason. Again,

this is a matter of personal preference, but the user would be advised to observe and

try CRT displays with different colors in order to choose the one which seems to be the

most comfortable.

Number of CRT Terminals Required

The minimum number of terminals required will be determined by the number of complaint

board operators and dispatchers employed in the command and control center. The

procedures to make this determination, presented in appendix B, were extracted and

summarized from a previous study conducted for the U.S. Department of Justice [1]. Some

departments provide remote (nondispatch) terminals that can access the system from

locations other than the command center. As more applications programs are provided

(see table 1) , access becomes more attractive and other groups within the department may

want terminals.

Terminal-to-Computer Data Channel

The terminal-to-computer data channel is an important link because it, in part,

determines how rapidly the computer can respond to the information and commands it is

receiving from the complaint board operator. In a typical CAD system, the exchange rate

between the terminal and the computer is usually 9600 or 4800 baud. Expressed in other

terms, at a rate of 9600 baud, it would take 2 s to completely fill the screen of the

usual CRT terminal display (24 lines with 80 characters/line) . Or, expressed in terms

of typing speed, this is about 10,000 words per minute.

The extent to which the CRT terminal and data channel meet the user's needs depend on how they are used and on how long the user is willing to wait for new data to appear on

the screen. When typing into the terminal, there is no contest as the system is a hundred times faster than an operator. On the other hand, although a screen-full of

information can be obtained from the computer in a couple of seconds, this might not be

fast enough. Fortunately, the vast majority of computer- to- terminal transactions need

10
to transfer only a small amount of data to the CRT screen. Thus, the typical

transmission time falls closer to a 1/2 s than 2 s.

This would be an acceptable situation if each terminal was served by its own data

channel. However, in a typical CAD system, several terminals are usually served by a single data channel because it is a much less expensive way to connect multiple

terminals to the computer. Channels serving multiple users are more complex because it

is necessary to provide additional circuitry and communications protocol so that the

desired terminal, and only that terminal, will be connected to the computer at any one

moment. The drawback is that too many terminals on a channel will cause excessively

long delays for its users, because only one terminal at a time can use the channel. As

an extreme example, suppose that a dozen terminals are served by a data channel and that

each terminal needs to be sent a screen-full of text. At 2 s per screen, it would be

almost 30 s before the last terminal got its message. The usual solution is for a medium or large CAD system to have several channels, with each of them serving several

terminals, out even here, it is possible for noticeable delays to occur.

An actual CAD system is likely to use several of the communications techniques just

described. As an example, consider three dispatching positions, each provided with its own dedicated 9600-baud channel, while the six complaint board operator positions are

served by a single 4300-baud channel. The dispatcher is provided with the faster

channel because this job requires a relatively large amount of information from the

computer and requires relatively little manual (i.e., slow) typing. The operators make

fewer demands on their data channel because their activities require much more typing

time as well as time to obtain information from the incoming caller.

This data channel arrangement has one drawback. The computer itself is being used to

directly control the data channel, and this, in itself, consumes an unreasonably large

amount of computer time. This arrangement can be used effectively only if there are very few CRT terminals. When there are many, a data-channel controller may have to be

placed between the computer and the CRT terminals, as shown in figure 5. Computer time

is saved because the computer now can transfer messages to or from the controller at a very fast rate, while the controller takes over the entire process of transferring data

to and from the CRT terminals at a slower rate. The controller is equipped with a buffer memory that temporarily stores the message to be sent to the terminals, or stores

the message received from the terminal until the computer has read it. Except for the

snort time that the computer uses for its high-speed data transfers to or from the

controller, it is free to work on other tasks.

The Computer

There are two parts that make up a computer: the hardware (what most people think of as the computer) and the software. By hardware is meant the electronic circuits, the

cables, and connectors that join the various parts. By software is meant the computer

programs that provide a sequence of instructions that tell the hardware what to do.

Without hardware. there would be no wav to carry out the software's instructions.

Without software, there would be no way to control the operation of the hardware so that

useful results could be obtained. This section will discuss only the hardware aspect of

a computer (the software will be taken up in a later section)

.

The essential hardware components of a simple computer are:

1) Central Processing Unit

2) Memory

3) Input/Output

4) Power Supply

Central Processing Unit

The central processing unit (CPU), the function of which is to read, decode, and ex,.-.*,

machine-language instructions automatically, is the heart of the computer. There will

be anywhere from a few hundred to over a thousand such instructions in the repertoire

the CPU. These instructions are designed and placed into the CPU memory :,y th-- manufacturer and cannot be changed by the user. Each manufacturer usually c; •. designs the machine- language instruction set in order to best meet the ne<- is of • >.<• market for which the computer is aimed.

11
OO50.DI-11JDC

12

Figure

5.

Using

a

communications

controller

to

assist

the

computer.
H amor

y

The memory is used to store the program instructions and data which the CPU requires to

perform its tasks. The storage capacity of a computer's memory is one of the factors

that determine the speed at which a CAD system can respond to a user's request. The reason for this is that the capacity of the memory determines the amount of data which

can be processed at one time. The greater the capacity of the memory, the faster the

computer will be able to respond to requests from the users.

Tne memory will be used for a wide range of purposes, but in order to prevent conflict

between the various tasks, it is necessary to reserve a separate block of memory for

each. A memory map provides the best way to clearly document these assignments, and an

eicamole is given in figure 6. By givina each task its own block of memory, the designer

is assured that one task will not destroy the memory contents needed by another task.

32767

DDOS 30720

30719

TRANSIENT

PROGRAM

AREA

19968

19967

RESIDENT

AREA

11776

11775 TERMINAL

TABLES 9728

9727

UNIT AND INCIDENT

STATUS REPORT

2048

2047 AGENCY

TABLES 1216

1215 DINOS 0

This memory map will support: 20 terminals

240 status entries (in any mix of

units and incidents)

26 agencies from one central

dispatch point

Figure 6. Shown here is a memory map for an actual commercial CAD system. Tne numi- r-. on the map give the highest and lowest address for each functional lo

*

memory

.

13
The partitioning and use of memory is an important task because it can have a large

effect on the speed with which a computer system accomplishes its tasks. System speed

is strongly influenced by the characteristics of the computer, the characteristics of

the mass storage devices (see section on Mass Storage (External Memory)) used with it,

and the type of work the system is to do. No single choice is best for all situations.

This brings us to the most important limitation of memory; no matter how well the system

is designed and implemented, tnere never seems to be enough memory to accomplish all the

tasks. Note that the memory map of figure 6 shows that the entire memory is used.

Actually, most of the useful information in a CAD system is not kept in memory, but is

stored externally in a mass storage device. This means tnat the computer must send a great deal of data to the mass storage device, and must retrieve it again when needed.

It typically takes more than a hundred times longer for the CPU to retrieve a few lines

of text from mass storage than is needed to retrieve it from memory. This continual

swapping between mass storage and memory is perhaps the major bottleneck of a CAD

system. Therefore, the more fast memory, the better. The more information kept in

memory, the fewer accesses of the mass storage device needed.

Other things being equal, the larger the word size, the faster the computer can process

data. In general, a 16-bit word size is adequate for most CAD systems, although very

large dispatch systems may prefer the increased soeed and other performance enhancements

that are provided by the 32-bit word size computers which are now available. The

present memory capacity for a typical CAD system is roughly 100,000 bytes.

Interestingly, a 64k byte memory that, in 1975, was fairly expensive and considered to

be maximum capacity for a CAD system is now relatively low in cost and is considered to

be minimal capacity. In some new or upgraded CAD systems, 123k and 256k byte memories

are being used, and it can be expected that even larger capacity memories—say 1-2M

bytes--will be utilized soon.

One point should be made about the construction of a memory. For many years, computers

used magnetic-core memories. This kind of memory has the reassuring trait of not

forgetting anything, even if its power supply failed, as the magnetic cores do not need

electricity to maintain their magnetization. But, beginning about 1975, electronic

memory became less expensive than core memory and the former is now used in almost all new equipment. These memories, however, forget everything the instant their supply

voltage fails. This is not a major catastrophe since the CAD programs and data can be

replaced from a backup mass storage device when power is available. However, to combat

momentary power failures. some type of auxiliary or uninterruptible power supply is

needed. Batteries are usually used to supply the necessary energy.

Mass Storage (External Memory)

Storing and retrieving information is one of the major functions of a CAD system.

However, it is not possible to store in its own memory even a hundredth of the

information needed by the system. Instead, the information is stored in a mass storage

medium, two basic types of which are commonly used with a CAD system. These are the

hard disk and magnetic tape. The information held by both types is stored in a thin

coating of magnetic material. The data are reasonably permanent provided that the disk

or tape remains clean, blemish free, and is kept away from extreme temperatures and

magnetic fields. The data can be erased quickly, either intentionally or accidently, by

external magnetic fields. Hard disks are always used; tape may or may not be used.

Tape is less expensive to use than a hard disk, but is also slower and less convenient.

This discussion is limited to the hard disk type of storage.

The capacity of mass storage devices is very large, and dwarfs that of the memory. It

is not unusual for a CAD system to be able to hold roughly 1000 times more data in its mass storage devices than in its memory. As prices continue to drop, newer systems are being procured that have more of both kinds of memory than do the older systems. At the

present, 100,000 bytes of memory and 100,000,000 bytes of mass storage are typical

figures for a CAD system. The price structure for memories is interesting. From

information published in November 1981, one manufacturer was offering 1M (1 million)

bytes of memory for $16,000 or a 64M-byte hard-disk device for about the same price. In

disk devices there are substantial economies of scale, causing the cost-per-byte to drop

sharply as capacity goes up. The same manufacturer, for example, also offered a 16Mbyte hard-disk system for approximately $10,000, and a 404M-byte system for about

$28,000. In this last case, a 25-fold increase in capacity is obtained for less than a 3-fold increase in price.

14
Essential ly all CAD systems use hard-disk storage systems as their real-time mass

storage device. Thus, all information acquired by the system during its minute-to- minute operation must ultimately be stored on a hard disk. In comparison to the internal memory, disk-storage (external memory) has both benefits and drawbacks:

Benefits Drawbacks

1) Almost unlimited storage capacity.

2) Nonvolatile data storage.

3) Much lower cost per byte.

4) Portable (except for fixed disks).

1) Much slower operation.

2) More sensitive to air pollutants

,

temperature changes, etc.

3) More maintenance is required.

The four major components of a disk-storage system are:

1) Disk (the storage medium)

.

<-) uisk arive (spins aisk, moves read/write head).

3) Controller for disk drive (formats data for the disk).

4) Software for computer (tells the controller what to do).

Tue nard disk used in CAD systems is a flat, precision-machined aluminum disk 35 cm (14

in) in uiameter ana about .1 cm (.04 in) thick. Its top and bottom surfaces are coated

with a uniform thin, mirror- smooth layer of magnetic material like that used on magnetic

recording tape. This layer is approximately .025 cm (.01 in) thick and is the medium

tnat actually stores the digital data. The disk drive is the device that performs the

mechanical operations needed to store information on the disk and retrieve it. The

drive rotates the disk at a constant speed, usually either 2400 or 3600 rpm. The disk

drive contains one or more read/write heads that can move to any of several hundred

positions located along a radial path from the disk's center. When the disk is rotating

at operating speed, the read/write head is lowered to the disk surface, where it is

supported by a thin layer of air created by the spinning disk. This air layer provides

a low-friction, low-wear interface between the head and the disk. When the data are to

be written or read, tne head is placed at one of the positions, and the data transferred

as the disk spins past the nead . The data are written onto the narrow, circular path of

tne spinning disk that passes next to the stationary read/write head. This circular

path is called a track, and a different track is accessed at each of the hundreds of

possible positions of the read/write head.

Each disk surface holds approximately 400 to 800 tracks. Each track can store between

6000 and 40,000 bytes of data, with 20,000 bytes being typical for new disk-drive

designs. Tnese data are not written as a continuous unbroken string of data, nowever

.

Instead, each track is divided into sectors. Usually. the sectors have a storage

capacity of either 256 or 512 bytes of data. This range of sizes usually produces the

most efficient overall performance of tne computer system. It is large enough to hold a sufficient amount of information, while also minimizing both the amount of wasted space

on tne disk and tne time needea for data transfers. Data are written into or read out

in one-sector groups.

Botn the top and the bottom surfaces of the disk have a magnetic coating , and the disk

drive proviaes a read/write head for each. However, only one of the surfaces is used to

store aata from the computer. The otner surface is used to record information that

tells the drive wnere the data tracks are located. The very close track -to-track

spacing makes it very difficult to accurately position the read/write nead over the

desired track. Mechanical imperfections of the positioning mechanism ana ther oi i expansion and contraction of the aluminum disk are just two of tiie dif f icuI 1 i

< •: encounterea . But by patting the tracK-locating information onto tne dis,. , thus-.- proolems are reduced or eliminated. Although this means tnat only one of the two

surfaces is useu for storing data from the computer, the improveu reliability makes t;.is a reasonaole choice. Also, tne resulting improvement in nead-oosi tioning accuracy n. that more tracks per inch can oe placed on tne surface tnat is used to store iata.

It was mentioned earlier tnat a typical modern disk arxve will store around 20, (hh : u i bytes on each track, ana that it must move the head to another track if more :it i

• neeaed. Moving tne nead always uses up a significant amount of time, so so. <• disk

urives provide more tnan one read/write head for tne disk surface. If. f r < -x i-.t there were five neads on the surface, then 100.000 bytes of data coui . i

15
without moving the head. When more data storage is needed than a single disk can provide, the most economical way to obtain greater capacity is to employ a disk drive

that uses a multidisk assembly. This consists of up to 12 hard disks, usually referred

to as platters, mounted on a common shaft.

In order to obtain accurate data transfers, the magnetic coating on the disk must be

kept blemish-free and clean. Thus, disks are always protected by one of three packaging

arrangements. One of these is the disk cartridge, which consists of a single disk that

is permanently mounted in a portable protective case. The manufacturer mounts the disk

in the case and that is where it stays. Even when in use, the whole cartridge is placed

in tne user's disk drive. The major attribute of the disk cartridge is its portability.

It can be easily removed from the disk drive and either stored on a shelf or installed

in another compatible disk drive. This makes it suitable for archival storage and for

transferring data from one computer to another, in addition to providing real time

storage. Another benefit is that damaged disk cartridges can be easily replaced.

Another arrangement is a multiplatter assembly, also called a disk pack. This is

sonewnat similar to a aisk cartridge, except that there may be up to 12 platters in the

pack , all mounted on the same shaft. A disadvantage of this type of assembly is that

tne protective cover of the disk pack must be removed before the disks can be used in a disk drive, thus exposing them to damage from external sources. Disk packs store

between 25M and 400M bytes of data. Like the disk cartridges, the disk packs are removable and have the benefits that this brings.

Tiie tnird method of protecting disks is to permanently seal the disk inside a disk drive

at the time of manufacture. This provides the best possible protection for the disk and

results in more reliable performance. In this kind of design, the disk is in a compartment through which only highly-filtered air passes.

Printers

In a CAD system, one of the most important uses of printers is to produce a permanent

record of each dispatching event. This is vitally important because, should the system

fail, this becomes tne only available record of the current status of in-progress

dispatching incidents. This printed information also ensures that in-progress events

will not be overlooked when reverting to manual dispatching techniques. Another

customary use of printers is to provide printouts of reports or other useful information

that the CAD system has collected, because, frequently, it is much more convenient to

have the information on paper than to read it from the CRT display screen. A CAD system is likely to use both medium- and high-speed printers. Medium-speed

printers are appropriate for printing the record stream as the dispatching events

unfold. They are also suitable for printing reports and general information if there is

not an overwhelming amount. When the amount of information to be printed is very great,

then a hign-speed printer becomes desirable. Medium-speed printers print between 30 and

120 characters per second, which usually amounts to less than one line per second,

high-speed printers print anywhere from 2 to 10 or more full lines per second, but

the performance and price of the fastest printers are both probably higher than is

needeu in a typical CAD system. Conversely, the purchase of a printer even slightly

inferior to the rest of the system can result in unnecessary slowdowns and the

elimination of beneficial printed information.

Printers tend to be noisy, so it may be desirable to place them at a distance from

communications center personnel, or even in a room not ordinarily used by people. On

the average, the faster the printing speed, the noisier the printer. The print quality

of printers used with a CAD system is usually inferior to that of an ordinary

typewriter, but this is one of the tradeoffs made in order to obtain both high speed and

lower cost. Although exceptions can readily be found, it is also customary for higher- speed printers to give poorer print quality than the medium speed ones. Printers

require more repairs and routine maintenance than any other CAD system component. Paper

and ribbons must be supplied periodically, and the mechanical wear on its mechanisms

cause them to have a shorter life than other system components.

16
r’-'wer Sources

Normally a CAD system obtains its power from the local electric company. Although

reasonably reliable, this external source is subject to three problems that can disrupt

t;ie system. These are electrical interference, high voltage transients, and power

outages

.

Systea Interrupts

Because the electric lines used by the power company are often long and may be connected

to a wide range of users, there is ample opportunity for them to pick up additional

electrical signals, some of which can interfere with a CAD system. As the length of a line increases, the likelihood of it acting as a receiving antenna for interference

sources such as lightning and radio waves also increases. The more users served by any

-articular electric line, the more opportunity exists for this type of interference.

Llectric motors, radio transmitters, and high-power equipment being turned on or off are also sources of interference. If the interference is strong enough, it can cause the

CAD system to become temporarily inoperative. This does no permanent damage, and merely

requires that the CAD system be restarted. Restarting the system is usually done

manually and takes roughly from 5 to 15 min, although in some systems, the restart is

accomplished automatically and without human intervention. Several jurisdictions

suggested that the ability to restart the system from the control center, rather than

from tne computer room, would be a nice feature.

,'nen failure from electrical interference occurs, it is usually because a strong

interfering signal is somehow coupled into the computer circuits and overrides the

normal signals. Once inside the computer, a 1-V transient lasting less than a millionth

of a second may be sufficient to cause failure. Because troublesome transients tend to occur infrequently, and because of their short duration, it can be very difficult to

tell wnetlier a computer problem is being caused by them. The best way to minimize tne

problem is to purchase computer equipment that has been tested and found to be

reasonably immune to electrical interference.

A second problem is high-voltage transients, which are simply a more extreme case of

electrical interference. In addition to being able to render a CAD system temporarily

inoperative, they can sometimes be strong enough to permanently destroy computer

equipment . Lightning is the most potent source of high-voltage transients, but

transients can also be produced by other means, such as high-powered electrical

equipment. As was the case for electrical interference, it is usually difficult to

prove whether or not high-voltage transients are responsible for computer failure.

Prevention is again the best way to deal with the problem. In addition to the steps taken to protect the system from ordinary electrical interference, it may be necessary

to ado components to limit the magnitude of the high-voltage transients before they reach the computer equipment.

^ne last problem, a power outage, is very easy to recognize. In a computer system the

effect of a power loss is felt quickly, since complete loss of power from the pui.lic utility

^ even a fraction of a second is likely to render the computer system inoperative unless some kind of backup power source had been incorporated into the

system. In urban areas, power failures are usually of short duration, probably rarelv

more than 2 s long. Battery-powered backup supplies are available that can keep tr.’- entire CAD system (including the room lights) operating during short duration outa jos (roughly 15 min or less). The high cost and large size of batteries make it undesirable

to use them as a long-term power source. When outages of long duration can be expect!- : to occur, gas- and diesel-powered generators are the standard power source. As lc: : a . there is fuel, they can power the CAD system indefinitely.

j-.ie need to provide uninterrupted power to the computer system

L nin uerruptible power supplies are available from several companies, and theri than one type c. design approach tnat can be used. As an example, consider shown in the block diagram in figure 7. This is the design which provides posoiole protection to the CAD system, but it is also the most expensive to : most costly to operate. In its favor is the fact that the transfer fro- n<d ;

i

bo batteries is so smooth tnat the CAD system cannot even sense that • . »- a change. Another benefit is that this kind of system inherently -rotocts an tne computer equipment from all three of the problems introduce! •

y

electric power

is vital.

is more

the method

the best

uy and the

c utility

c has boon

d shields

17
BATTERY

PACK

Electric

power from

public utility .

AC-to- DC

CONVERTER DC

POWER

DC~to—AC

INVERTER

AC power

for the

CAD system

Figure 7. Block diagram of an AC-DC-AC uninterruptible power supply.

Otner circuit arrangements can be used in an uninterrupted power supply, and they have

their own sets of strengths and weaknesses. An uninterrupted power supply can be

expected to give reliable service with the batteries being the component likely to have

the shortest life expectancy. Batteries that have a long life may be expensive, so it

is worthwhile to ask manufacturers about battery life expectancy and replacement cost.

Siting the hardware System

Determining the quantities of hardware components and their individual capacities is

normally done when the system is designed in detail. It is important to note that a CAD

system docs not reciuire very advanced or large-scale data processing equipment. h

standard minicomputer is usually more than adequate and, if peripherals are added, the

capability of the system to handle a larger load can be expanded. Many departments

require a high system "on-line'' time, resulting in the need for redundant hardware

components. Dual recording of data is often done, esDecially in larger systems, to ensure against loss of data due to system interrupts (see previous section). A back-up

computer may be required, with automatic switchover to maximize "up time."

The minimum equipment requirements for a medium-size department would be as follows:

Computer Standard 16-byte minicomputer

Integrated-circuit memory 64k bytes minimum: 1/4 megabyte is better

Disk storage One 25-megabyte unit

Peripherals One line printer (600 lines per minute)

One typewriter- typepr inter

One microfiche file and viewer per console (optional)

18
Sof tware

Tne term software' is used to refer to a set of instructions executed by the computer

to perform its tasks, plus the data in machine-readable form that is used by the

conDuter in carrying out these tasks [1] . The software for a CAD system is usually

supplied by the system vendor although, in larger law enforcement agencies, it may be

possible (although it seldom seems to be done) to develop the necessary programs inhouse if the agency has software support groups [8] .

The overall package of software and files that would be needed in a CAD system is shown

in taole 1 and consists o* the following three major parts:

1) Operating system General purpose utility programs

2) Real-time dispatch system Provides all dispatch canabilities

3) Applications programs Provide additional capabilities

Table 1. Software and file structure for a CAD svstem (adapted from reference 1)

Operating system Real-time disnatch system Applications programs

‘System generation ‘Access authorization Data base query

‘Job scheduler * Sign-on/Sign-off Management reports

‘Communication control ‘Incident log-in Deployment schedule

‘Executive services ‘Incident file Radio-telephone statistics

‘System recovery ‘Incident summary file

‘Dispatch log-in

‘Patrol unit status

‘Patrol unit file

‘Deployment schedule

‘Data logging

*Geograpnic File

Unit Recommendation Algorithm

Operator activitv file

Patrol unit activitv file

Address verification

Telephone directory

Address intelligence file

‘Basic elements- remaining elements are optional.

Operating System

The operating system software consists of a large collection of utility programs that

provide a wide range of useful and commonly-used services. It is the core of the CAD

system software, for the other two software components depend uoon and use its

capabilities. It handles such tasks as controlling the communications between the

computer and the CRT terminals, providing a way to get data to or from a hard disk, and

providing diagnostic messages when it detects problems. A CAD system reguires a realtime multiuser (i.e., many CRT terminals) operating system: its response to a command

typed into a CRT terminal must be quick. The operating system of at least one jurisdiction did not meet this latter criterion, and it became the fatal flaw that made

the system almost useless.

3ecause the detailed structure of an operating system is greatly influenced by the

design of its computer and the peripherals furnished with it. it is usually develop : and supplied by the manufacturer of the computer. Althouoh it is a complicate^. i:.,; expensive undertaking to write these programs, it is sometimes done by a C^D svstvendor or user.

19
Real-Time Dispatch System Package

A real-time dispatch system package is a large collection of closely integrated and

specialized programs that are the essence of a CAD system. These are the programs that

perform such tasks as accepting information from the complaint board operator, sending

that information to the dispatcher, automatically maintaining a file for each complaint

event, querying remote data bases, responding to the commands of the dispatch personnel

and, in general, controlling the entire disDatch operation. Each dispatch-related

command and capability possessed by the CAD system is made possible by programs

contained in this package. If it were necessary to add a new command, or modifiy an old

one, the changes would be made in this package. Before a contract is signed, the vendor

and users should develop a detailed list of every command and task that the proposed CAD

system will be required to perform, as listed items will have to be implemented by the

Drograms in the real-time dispatch system package. This package like the operating

system package, is costly and is usually written by a vendor or a user. Apnlications Programs

Applications programs are those that generate reports based on the information processed

through the CAD system or provide the system with additional informational capability.

These usually can be added to a CAD system at anv time, and will provide the system with

many additional features. Capabilities not provided when the system was originally

ourenased can be added by acquiring additional applications programs. Because these

programs are not intricately interwoven with the internal complexities of the system

software package, they are relatively easy to implement. They can be written in any

convenient computer language, by either in-house or outside programmers, and are not

very likely to have problems with speed of execution or other limiting factors. An

example of an amplications program would be one that generates crime statistics from the

event records that the dispatch operation has already stored in the CAD system.

Modification of a CAD System Software Package

The cost of a CAD system software package is high because it is the result of several

person-years of programming effort. Only by using the same software package for several

CAD systems can the costs be recovered, which is a primary reason why the vendors of CAD

systems prefer to sell a standard system.

Some vendors are willing to make major changes in their software package in order to

meet the requirements of the purchaser, but this increases the cost of the system.

Minor changes will sometimes be made by the vendor at no additional charge. It is

important to realize that "major changes" means that it will take a programmer a significant amount of time to make the revisions. Some changes which appear to be

trivial ones are actually very difficult to implement, whereas other changes may be much

easier to implement than might be expected. Clearly, any changes contemplated should be

reviewed by a relevant expert.

In the past, some vendors have been much more willing to modify their standard software

package than others. If a new CAD system will require that the standard software be

modified significantly, only those vendors who can demonstrate their ability to

competently complete this task should be considered.

Software Maintenance

Software maintenance, rather than referring to the repair of software packages, actually

refers to the ongoing develonment of new software and the correction of errors that have

been discovered in old software. These errors mav have been uncovered by the user, by users of other computer systems that employ the same software, or by the companv that

originally develooed the software. After a software product has been used extensively,

most of its errors will have been detected and corrected, but a new software product is

quite likely to have some errors and shortcomings, and the users may initially have to

devote a substantial amount of time to resolvina these problems. To prevent nrogranming

problems from jeopardizing the functioninn of the svstem, self-checks that detect when

the program is in trouble can be incorporated that will enable the system to recover

automatically. The CAD system may be inoperative during the recovery, a period lasting

perhaps 20 s. One estimate is that this might occur about once in 24 h, making this a very minor problem.

20
v " ally, software develoners will ke >p their customers informed about corrections and

nancements to their product. Also, a knowledgeable user mav be able to make his/her

own corrections and write supDlementary new programs. It is almost universal to find

tnat software packages do not give the CAD system all of the features that its users would like. Quite often, this is because the user was not aware of the feature

initially but, usually, this is due to a recent increase in the number of proqrans made

available to the user by the software developer. Also contributing to this is the

unwi 1 1 ingness of the user to nay the high orice that a very thorough and comnlete

software product would command, and partly because the user's needs also change.

Occasionally, users must respond to changes not under their control, e.g., those

prompted by change in a state or national data base. So, for one reason or another,

there tends to be a continuous process of upgrading and expanding the software of CAD

systems

.

Maintenance and Repair of a CAD System

The owner of a CAD system can expect to encounter one problem with regard to the upkeep

of the system. This is an unexpected hardware failure. Unless some provision has been

made for this eventuality, the dispatch operation may be forced to revert to a manual

mode for an extended period. The system should receive routine maintenance on a regular

basis to reduce the possiblity of an unexpected failure.

During the planning for a CAD system, choices are made that have a direct and permanent

effect on the maintenance and repair of the system. For example, will all of the major

computer related equipment, such as the computer and disk drives, be purchased from the same manufacturer? Some manufacturers will provide service only if the answer to this

is YES. This policy is a reasonable one, because it protects the comnany from the

expense of having to work with a wider range of equipment and from the expense of

attempting repairs when the problem is not the fault of its own equipment. To exnlain

the latter item more clearly, assume that a computer system is composed of equipment

from two manufacturers and that each had agreed to provide renair service for their own equipment. A serious problem occurs if the computer system fails in such a way that it

is not known whose equipment is at fault. Obviously, a company does not want to spend

time on a problem for which they are not responsible, and the user does not want to lose

time waiting for the CAD system to be returned to operation. If it should happen that

different manufacturers supply the major computer-related equipment, then maintenance

and repair can still be done by a third-party maintenance contractor or, in some agencies, by the agency's own personnel.

In return for the substantial sum a user pays for a CAD system maintenance contract (the

annual cost of a maintenance contract will be roughly 10 to 15 percent of the purchase

price of the svstem hardware) . the contractor provides important services. The

maintenance company can provide routine maintenance, guarantee to have a repair person

arrive within a specified reasonable time after being notified that the svstem has

failed, and maintain a stock of spare parts. Generally, the shorter the guaranteed

response time, the higher the cost of the contract. Also, the contractor's stock of

spare parts can be a tremendous timesaver. This is especially true for older equipment

or for any scarce item. For example, the CAD system of the Police Department of Las

Vegas, Nevada, needed a new motor for an old taoe drive for which parts were becoming

difficult to obtain. There was no service contract in effect at the time, and the

manufacturer planned to construct a replacement tape drive with a delivery time of L weeks. It took much negotiation before the department was allowed to purchase one fro:-

existing, but reserved, stock.

21
There are several ways to obtain maintenance and repair services for the computerrelated portion of a CAD system:

1) Maintenance and Repair Contract With an Outside Company: Depending upon

circumstances, a maintenance contract might be held by either the equipment

manufacturer, the company that suoolied the CAD system package, or a third party

company. Good results can be obtained from any of these, but to obtain the best

satisfaction, the following information should be known before signing a contract. Does the company maintain an ample stock of spare parts and have

capable service people available on short notice? A typical agreement will ask

for help to arrive within 4 h if a breakdown occurs during normal working hours.

A shorter response time can usually be agreed to, though at additional cost. The

closer the CAD system is to the contractor's local service office and to the

spare parts depot, the shorter can be the response time. When there is a large

amount of equioment to be maintained, the contractor will usually station a service person at the user's site.

2) Repairs "On Demand" By An Outside Company: Agencies that have used this approach

have generally not had good experiences. Without a contract, agencies are going

to receive the lowest priority, generally. Help will be provided AFTER the

company has satisfied its contract customers, and you might have no claim to

reserved scarce parts. The other side of the story is that when the company is

not busy and has an adequate supply of the replacement parts needed, good service

is obtained at a low yearly cost.

3) Maintenance By The User's Own Personnel: When the maintenance work load is large

enouqh this a rranger.ient usually works well , except that obtaining scarce replacement parts quickly may be a problem. In some police departments the radio

repairman may be able to provide the maintenance for the computer equipment. If

hard- to- diagnose problems occur, it might be necessary to obtain outside help,

because intimate knowledge of computer equipment is needed, as well as specialized and expensive diagnostic equipment. An example of this approach is

given in reference 9.

4) Combinations of the above, i.e., in-house technician and backup contract with an outside company.

CAD SYSTEM PROCUREMENT PROCESS

Once a decision has been made to acquire a CAD system, typical steps which have to be

followed include those listed below. Most jurisdictions suggest that you select a project leader early in the process, someone who will be able to guide the project

through to completion. Give that person the authority, within some set of guidelines,

to make the necessary day-to-day project decisions without having to consult a large

decision-making group that takes valuable time to assemble.

Acquiring a Medium- or Large-Sized Commercial System

A) Obtain funding approval. The money to buy a CAD system is usually provided by the

local government, although in the past some police departments have obtained grants from

the Law Enforcement Assistance Administration (LEAA) of the U.S. Department of Justice.

An example in which there was mixed funding was for the CAD system purchased by Prince

George's County, Maryland. County funds paid for the hardware, and an LEAA grant paid

for the software. However. LEAA grants are no longer available. For agencies which are unable to obtain the funds to purchase a system, there is the option of leasing one

(oerhans with a bargain purchase option included) . This has the advantage of spreading

the costs over a more extended period (although the rentals will almost certainly exceed

the purchase price in the end) . Leasing is also the least hazardous way to acquire a CAD system, for the users need not renew the lease if they consider the system to be

unsatisfactory. Normally the lessor also provides the maintenance and repair for the

CAD system.

22
>) Outside consultants. The importance of the design of the CAD system cannot be

•veremphasized. If you have CAD experts on your staff, use them. If not. or if the new

. /stem is to be an expensive one, it may be desirable to hire an independent consultant

*-o guide the planning. The vendors of CAD systems usually do not provide this service,

because they would then not be allowed to compete for the system procurement. The

vendors can, however, recommend independent consultants. Since the acquisition of a new

system usually results in restructuring the entire disnatch operation, it would be a lus if the consultant had a background that extended beyond an expertise in commuter

systems. One agency warns that the hiring of consultants does not, by itself, ensure

that your CAD objectives will be met. Be prepared to work with them, on a daily basis,

to prenare a specification that will meet your needs.

C) Become familiar with the capabilities provided by a CAD system. This requires

reading about them talking to both users and vendors, and visiting an operational

,acility. Different users and vendors tend to offer different viewpoints and

capabilities, so it is desirable to obtain information from a variety of sources. If

you have engaged a consultant, be sure that he/she attends all meetings and is

aole to obtain answers to all questions.

D) Identify and justify what the proposed CAD system will be required to do. There is

much to consider here. Some CAD systems provide basic dispatching functions only, while

some others also include report generators, mobile digital terminals, automatic Querying

of remote data bases, etc. It is important that the planned-for system have enough

capability to make it satisfying to use. If funding cannot be obtained for such a system, then the wisest decision may be to postpone the acquisition until funds for an adequate system become available. Develop a functional specification that fully

satisfies the needs of your department. Use appendix B to assist in the determination

of the number of terminals needed. Be sure to tailor your specification to provide a CAD transaction response time fast enough to keep pace with other disoatch center

renuirements . The need for an accurate geographic file, produced in a timely fashion,

should also be stressed. Include a reauirement for maintenance and repairs to the

system (see I below) if not maintained in-house, and any necessary training (see J

below) and the services of a qualified programmer, who will probably be needed through

the hardware warranty period and beyond.

E) Develop a Request for Proposal. Using the information gained from items B, C, and D,

write a formal request for proposal (RFP) and distribute it to interested vendors. The

RFP may specify a requirement for a turnkev system, i.e., one in which the vendor

supplies a total hardware and software packape to meet user design requirements, or it

may specify any portion thereof.

F) Select a vendor and draw um a contract. Based upon the responses to the request for

proposal, choose a vendor. Because the vendors may suagest capabilities that differ

from those requested by the department, the selection process should have the

flexibility to evaluate the merits of each offering, and to give competing vendors the

opportunity to respond to any new requirements that differ significantly from the

original request. Develop specific acceptance criteria and procedures at this time.

The vendor must know what the user will consider to be acceptable Derformance and be

able to verify compliance at a later date. It is imperative that the user and the C’.h

vendor agree on all aspects of the system before installation is begun. T'fter a vendor

is chosen, the contract must be drawn up.

G) Monitor the contract and all other related presvstem installation activities. As

stated earlier, one person should be given the authority, responsibility, and the time

to handle the multitude of details and problems that occur during the installation and

start up of the system [4]. This person would oversee the remaining items on this •

.

and deal with unforeseen problems.

II) Prepare the area where the system will be installed. Fnsure that sufficient " ri - power, with backup, will be available at start-up time. If possible, physically

separate the noise-making equipment, such as disk drives and printers, from the- c :d r : center area to improve the working environment. Provide temperature control an i

' r:- * area lighting. You miqht even want to select an architect who understands the ;!>«• . ‘

: sound proofing and a quiet environment [10].

23
I) Follow through on maintenance and repairs for the system. The vendor should be

developing a maintenance plan and designating thoso spare narts that should be suoplied with the system.

J) Train the personnel who will use the system. Work with the vendor on a training

plan, than implement it. Personnnel must be trained prior to the operational use of the

system. For complex systems, training is especially critical.

K) Contractor installs the system and it is tested in accordance with the acceptance

criteria specified in F above.

L) Maintain the ability to operate the dispatch system manually. It has happened that

this item was overlooked in the implementation of a new CAD system. It is almost

inevitable that the computer system will experience temporary failure, but the

dispatching operation must not be rendered helpless. In order to keen their personnel

competent in manual dispatch techniques (i.e., with no computer), many agencies revert

to manual techniques for a few hours each month.

A timetable showing the overall schedule of activities to acquire and place a CAD system

into operation is shown in figure 8. Individual times will vary based on the type of

system selected, amount of customization, number of peripherals, preparation of space, use of consultants and possible funding delays.

MILESTONES

MONTHS AFTER APPROVAL

1 2 3 4 5 6 7 8 8 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1 FUNDING APPROVAL /_ 2 PRECONTRACT ACTIVITY

3 FUNCTIONAL REQTS

4 PREPARE RFP

S APPROVAL TO RFP L \

6 PROPOSALS RECEIVED A

7 CONTRACTOR SELECTION

8 CONTRACT SIGNED L

0 SYSTEM DESIGN

10 PRELIM. DESIGN REVIEW L

1 1 FACILITY PREPARATION

12 EQUIPMENT INSTALLATION

13 EQUIPMENT TEST

14 SYSTEM TEST

15 SYSTEM ACCEPTANCE L

16 PERSONNEL TRAIN

17 OPERATIONS TRANSFER

18 MAINTENANCE CONTRACT

Figure 8. Overall schedule of activities to acquire a CAD system [1]

.

24
Acquiring a Small-Sized Commercial System

rach of the stems discussed above apply eaually to the procurement of a smaller-sized

system, albeit on a smaller scale. However, where the total amount to be paid to the

vendor will be less than roughly $100,000, the cost of hiring a consultant and designing

a functional specification may be an unreasonably large percentage of the total

expenditure. Thus these steps are sometimes omitted and the system acquired directly

from a vendor whose system meets the basic performance requirements. In other resoects

the stens listed above would apply to procurement of a small-sized system also. An

example of how one very small department provided 24-h service to its citizens is given

in reference 11.

Custom-Oesinn of a CAD System Using In-House Capability

There are agencies large enough to have in-house expertise that can be used to design,

implement, and install a CAD system of their own custom design. This is a verv

ambitious project, requiring many man-years of work, but it has been done by a few

nolice departments. The main benefit is that the system can be tailored to the specific

needs of its users, rather than having to accept a standard packaae from a system

vcnuor. Two of the drawbacks to this approach are:

1) A one-of-a-kind system is much more expensive than a standard nackaae, whose

development costs can be spread over several systems.

2) Much more time will elanse before a custom in-house CAD system is installed and

ready for routine operation.

The era of the in-house-built CAD system may have already passed. Several CAD

system vendors now offer competently packaged systems that are relatively inexpensive

and can be installed quickly. Different vendors produce different types of systems, so prospective users will probably find at least one that is well-suited to their

requirements. Another major benefit of the packaged systems is that they have already

been used by others, so most of their nroblems will have already been discovered and

corrected. Most of the vendors are willinp to add custom features to their standard

packages, but will charge extra for this.

Still another variation of the custom-design approach used occasionally is for the user agency to plan its own system and then purchase the hardware, software, maintenance,

etc. , from various suppliers. This will work if the planners really understand the

complexities of computer systems. Otherwise this can be a very risky approach. A good

consultant may be a valuable asset when this approach is used.

Additional discussion of the ramifications of procuring a CAD system is given in

reference 12.

GENERAL OBSERVATIONS

In the course of writing this report, the authors submitted preliminary drafts to a group of interested users and vendors of CAD systems for comment and constructivecriticism. In return, many sugaestions were received that were used to improve th<- topics covered in this document. The respondents who took time from their busy

schedules to review the draft document and provide comments are listed in appendix C.

For the most part, those departments with operational CAD systems wor*3 enthusiastic

about the benefits of CAD. For example, one reviewer stated, "Our system is on iv ) months old and we wonder how we even got along without it. We are running about 3,,0

events per month with 8 complaint operators and 6 dispatch positions. We feel it is i success." Nonetheless, virtually all of the reviewers encountered problems at v.ir:< :

•

stages of planning, implementation and operational use. The comments and opinions

summarized in the paragraphs that follow represent topics that those contemnla 1 1 n : t acquisition of a CAD system should keep in mind.

25
Most of the reviewers stressed the importance of comprehensive planning, with at least

two citing interface requirements as potential problems. Typical comments were:

A. One consistent area of deficiency is inadequate planning. Too many times

contractors find themselves in the situation of being forced to automate a poor

operational process.

B. In order to achieve a high level of success, the system must be designed by publicsafety personnel with assistance from data processing professionals and/or

consultants. If the system is designed without proper input from the public-safety

sector, it is doomed to fail.

C. System design stages are very critical. Decisions made at these points will be with

you for a long time.

D. It is imperative that system specifications dictate that the vendor is responsible

to design the proper interfaces with other state or local information systems to

prevent overlooking the requirement.

E. The subject of interfaces was almost swept under the rug by the vendor and

overlooked by the purchaser.

F. Separate independent environmental control system is very critical.

G. The system, as designed, should be as idiot-proof as possible. System designers

must anticipate that operators are creative and will spend their idle time looking

for ways to beat the system.

H. There is a need to develop specific acceptance criteria and procedures. The vendor

must know what the user will consider to be acceptance performance and be able to

verify compliance.

I. Make the work area comfortable for dispatchers. Control the temperature and provide

correct area lighting. Need accurate geographic file.

J. Serious problems with system acceptance will result if users must unreasonably

change their procedures to satisfy the system design.

K. It is mandatory that the complaint board operator have the capability to override

any system generated parameter. Do not be so rigid in your design as to not allow

the operator freedom to correct design mistakes.

L. Costs are far less apparent when a system is being developed in-house. Advocates of

developing systems in-house thus have a political advantage, even though the actual

cost may be higher.

M. Having a real-time CAD system expert design the system cannot be overemphasized.

N. Early identification of a qualified project leader is essential.

O. The hiring of consultants by an agency does not, in and of itself, ensure that the

objectives of C7\D will be met.

P. The importance of the functional specification cannot be overemphasized. It is

imperative that the CAD vendor and the user agree on all aspects of the final system

before installation.

Q. CAD generates data for law enforcement models. Work load and performance can be

measured and modeled. Dispatch data play a vital role in the Patrol Operations

Budget

.

26
s a nart of the planning process, it is also important to recognize the critical need

training. Two reviewers commented as follows:

depending on comnlexity of the system, there is a monumental training program needed

to utilize system to full capacity.

n. Consideration for training on the new system must be made. Vendors who supDlv

fantastic systems may not be fantastic trainers.

Finally, there were a number of cases in which the reviewers identified potential

technical and operational problems. It should be noted that many of the following

comments also support the need for prooer planning.

One problem area is CAD transaction response time. Law enforcement communications

is a very dynamic environment and the system must be fast enough to keep pace. The

geographic file must be completed early in order to be folded in at the right time.

B. The multi-function nature of a CAD system is likely to lead to conflicts over its

objectives, particularly between ooerations and management information points of

view. The fact that reports and modeling often result in more or better utilized

field resources gets lost in the scuffle. A shared backup or mainframe computer

presents further contentions.

C. Inefficiently written programs, added on to a heavily-loaded system, can seriously

degrade system response time.

D. Tne language issue needs to be addressed with reference to memory, compute power,

system load and speed requirements. Not all departments can use BASIC on a microcomputer for a CAD system. The County's CAD svstem is so slow that they enter

the barest minimum of information for calls for service and have very limited

capabilities

.

E. It is totally unrealistic to assume that no software maintenance or enhancements to

the system will be needed or desired. It is also doubtful to exoect that an anencv

will have in-house, a qualified programmer that can be assigned to learn the CAD

system.

F. Ooerations personnel often do not understand the importance of record keeping and

modeling. Management information personnel may not realize the need for real-time

data and information.

G. CRT compatibility and obsolescence has been a problem.

H . One of our greatest problems has been printers slightly inferior to our system.

This has resulted in unnecessary slow down periods and the necessity of eliminatir. : beneficial printed information.

I. Do not forget that the ooeration, software maintenance and subsequent enhancement of

a CAD system will require the services of a qualified programmer, usually beyond the

hardware warranty period.

J. A major problem area was the coordination of svstems development and innlerontat : or. with dispatch personnel. Console manufacturer necessitated equipment changes.

SUMMARY

Computer-aided dispatch systems are having a major inoact in the solution of so-' f * l ..? chronic problems of command and control of law enforcement agencies, both ir.si : outside of the United States [13,14]. Use of a CAD system has resulted i- f • • • response time in emergency situations, greater accuracy of communication, a- r p

improved utilization of existing mannower [4-5.13-18]. Use of CAD with : •• .* P

terminals in police cars has substantially improved resoonse tine and accmi f communications as well as providing imnroved security of transmissions, acccr ! i r.

• • agencies [9,14]. Further, two departments cited a need for increasing r. c f :

• if. • a?

a reason for implementing a CAD system [4,19].

27
Additionally, the CAD system has proven to be cost beneficial in that it provides a more

efficient return on the investment of tax dollars [4,5,13]. One department projected

that their savings in the first year of operation would amount to more than $29,000,

with the benefits accruing almost equally between hours saved by officers in the field

and those manning the communication center [16] . Another locality estimated that even if

it hired four additional people per shift, it was doubtful that they could perform the

work of the computer, and further, it was unlikely that the work would be done as completely and as accurately [19].

Finally, a benefit which many departments viewed as significant was the generation, by

the computer, of a wide variety of meaningful management reports [5,9,15-18,20]. The

system's ability to provide department management with the kind of data they need to do

their job efficiently and thoroughly would seem to be impressive. Included in this

would be the ability to provide data crucial to criminal investigations [5 18].

It seems inevitable that the demand for computer-aided dispatch systems will continue to

increase. They are becoming indispensable to communications control systems, and it is

reasonable to expect that soon CAD systems will come within the reach of all but the

very smallest localities and jurisdictions.

REFERENCES

[1] Sohn R. L. ; Ourfielu, R. M. ; Garcia. E. A. : Fielding. J. E. Application of

computer-aided disnatch in law enforcement -- an introductory planning guide.

Lav; Enforcement Assistance Administration, U.S. Department of Justice, Doc. No.

JPL 5040-16; 1978 September. 81 p.

[2] Colton, K. W. , et al. National assessment of police command, control, and

communications systems. National Institute of Justice. U.S. Department of

Justice; 1980 September.

[3] Search Group, Inc. National Clearinghouse for Criminal Justice Information

Systems. Automated index. 1983 August.

[4] Henrico County, VA. Computer-aided communications improve police service. Law

and Order; 72-75; 1981 November.

[5] Roy, Samit. Computer dispatch system breaks three-minute barrier. Law and Order:

60-65; 1982 August.

[6] Guthrey, Thomas and Guthrey, Jean. Dispatching should not be a problem. Law and

Order: 56-59; 1982 Aupust.

[7] Rosen, M. Daniel. Police and computers: the revolution that never happened.

Police Magazine; 9-18; 1982 September.

[8] Sohn, R. Computer-aided dispatch for police operations, computers in local

government: police and fire. Auerbach Publishers: 1-19; 1930.

[9] Rodrigues, Matt L. Links field to records via mobile terminal system. The

Police Chief; 19-23; 1982 September.

[10] Williams. Travis. Combined solutions solve communications challenges. Law and

Order. 49-52; 1984 October.

[11] Klein, William G. The automated dispatch system for the very small department.

The Police Chief: 22-23; 1978 February.

[12] Richards, Tony. CAD in your future? APCO Bulletin: 20-22; 1983 August.

[13] Advanced computerized command and control system. The Police Chief: 16-19; 1981

September

.

[14] Bocklet, Richard. Computers linked to patrol aid German operations. Law and

Order: 22-27; 1983 April.

28
lij] Fortier, K. San Diego: computer-aided dispatch. APCO Bulletin 40(11): 20; 8;

1974 November.

ixo] Huntington Beach; computer-aided dispatch. APCO Bulletin 40(11): 20; 1974

November.

1 17) Scully, D. P. Los Angeles County: computer-aided disnatch. APCO Bulletin

40(11); 12- 1974 November.

(18) Kelly, Robert T. The Kansas City, Missouri Police Denartment information systems

plan. The Police Chief: 44-45- 1980 Aoril.

[19] .The future is now. Communications: 68-72; 1979 December.

[ 2u ] McCormick, J. A. Computer-aided disnatch: the digital patrolman. APCO Bulletin

10(11): 16; 1974 November.

29

APPENDIX A- -GLOSSARY

American Standard Code for Information Interchange (ASCII) - A digital code widely

employed with terminals, commuters, and printers. It is a 7-bit (i.e., has 128

different characters) number that represents upper- and lower-case letters, the digits 0 through 9, punctuation marks, and control characters.

Baud - Measure of the speed of digital transmission, in units of bits Der second.

For example, a transmission rate of 9800 bits per second is the same as 9800 baud.

Bit, b - From b (inary + dig) it. A single, basic unit of information used in

connection with computer and communication theory. A binarv number system uses only two

digits -- 0 and 1.

Hvte. B - A unit of information for orocessing in certain computers, equal to one character of eight bits.

Cathode-Ray Tube (CRT) Terminal - Consists of at least a typewriter-like keyboard

that is used to enter information into a computer system, and of a CRT screen that the

system can use to display information.

Central Processor Unit (CPU) - The part of a computer incorporating its machine

language instruction set and responsible for essential control and computational

functions

.

Disk Drive - The mechanical portion of a disk storage system. The drive contains

tne read/write head(s) and their positioning mechanism, a motor to spin the disk, and a nrotective case. Geoqraphic File - A computer file that contains the street names, street numbers,

common place-names, and perhaps other geographic information about the area served by a CAD system. It can serve a variety of uses, from automatically verifying the existence

of addresses given to complaint operators, to helping choose the souaa cars that

respond.

Hard Copy - Any permanent copy that can be directly read by people. Usually, this

is simply the paper output from a Printer.

Hard Disk - Mass storage medium commonly used to store data for a computer. The

hard disks used in most CAD systems are made of aluminum approximately .1 cm (.04 in)

thick and 35 cm (14 in) in diameter, with a thin magnetic coating on both sides. A

single disk can hold several million alphanumeric characters.

Hardware - The actual electronic and mechanical eouipment used in association with

data processing; distinct from software. For example. a disk and its associated

electronics are hardware; on the disk may be stored the programmed instructions--the

software —for particular computer operations.

K - The number 1024 (2^). For example, a 2k-byte segment of memory contains 204 , bytes

.

Line Printer - A high speed printer used by a computer svstem. High sneer! in this

instance, means that a minimum of 150 lines of text per minute (each line havir ; 1

' ~ * characters) is produced.

Mass Storage - Any means by which very large amounts of computer data cas be

economically stored. In a CAD system hard disks, and sometimes magnetic tape, ar- u •• for mass storage.

Microcomputer - A member of the smallest and least expensive family of com r iters

.

Microcomputers are presently available that have 1, 2, 4, 8, and 16-bit word si7.«-s. nr 32-bit word sizes will soon be available. Some of the more pownrf il K 1 >i

t

microcomputers have been successfully used in smaller CAD svstems, instead of t minicomputer.

31
Minicomputer - A member of the family of middle-sized computers. These usually have

a 16-bit word size, although 32-bit sizes also are available.

Real Time - By "real time" is meant that a computer system promptly performs the

tasks given to it. For a CAD system this usually means that dispatching personnel need

wait no longer than 2 s for the system to respond to a command

.

Software - Anotner name for computer programs. It is the set of instructions put

into the computer memory which enables it to perform the proper sequence of operations

to accomplish a designated task.

Word - A sequence of bits that may be interpreted by the computer as an instruction

or as data.

Word Size - The greatest number of bits that a computer's CPU can handle as a single

group

.

32
APPENDIX B—DETERMINATION OF THE NUMBER OF COMPLAINT OPERATOR

AND DISPATCH TERMINALS REQUIRED FOR A CAD SYSTEM

In a study [1] conducted in 1975 by the Jet Propulsion Laboratory (JPL) for the Law

Enforcement Assistance Administration, a model was developed for determining the number

of complaint board operator and dispatcher terminals required for a CAD system. The

model was developed from information obtained by direct observation of the CAD system

operations of two police departments--IIuntinqton Beach and San Diego. At Huntington

Beach, the researchers obtained voice tanes of the dispatchers along with the

corresponding case logs. The taped voice messages were timed with stop watches and

elansea time clocks and compared with the case logs to establish correlations between

cases, cars on patrol, message rates, and operator utilization. In San Diego, the voice

channel was recorded and videotapes v/ere made of the dispatcher's incident display.

These were analyzed for relationships between the keyboard and screen operations and the

voice messages. The discussion below is a summary of the calculations which were developed from the observations of the JPL studv.

Primary Complaint Board Operator Position

Tne key criteria for determining the number of primary complaint board operator

positions are the number of calls which must be Processed, before a caller waiting in the

queue is connected to a primary operator (delay unit) and the number of calls Per hour

during the peak hour(s). The delay unit is obtained from:

delay unit mean waiting time in seconds

mean operator service time in seconds

The mean waiting time is the average time it takes for a caller to be connected with an operator and is an optimum value based both on the observations discussed earlier and

the kind of service which the department would like to provide the public. Mean

operator service time is the average time it takes to process a call and pass it along

to the dispatcher, and is based on the observations.

The operator workload units, based on the peak call rate per hour, are then calculated:

operator

workload

units

peak call rate [calls per hour during the peak hour(s)] x mean service time, s

3 g 00

The intersection of these two parameters on figure Bl will indicate how many primary

operators will be required. For example, consider the following information and

performance requirements:

1) Average waiting tine in the queue shall not exceed 2.5 s2) average service time per call is 100 s; and

3) peak call rate is 200 calls per hour.

The number of delay units is:

2.5 s/100 s = 0.025 unit.

The operator workload units are:

(200 x 100)/3600 = 5.56 workload units.

It can be seen from figure Bl that where these two values intersect indicates that 11

operators would be required to handle the complaint board under the conditions • r: . 1 above

.

33
o Primary complaint board operators

Secondary complaint board operators

Figure Bl . Complaint board operator position design (from Sohn, et al.).

Secondarv Como laint Board Operator Position

The duty of a secondary complaint board operator is to handle longer incoming calls and

calls which do not require dispatching. Although not all departments use them. it has

been found to be an efficient way to improve service to the public and reduce the work

load of the primary operators. The number of secondary operators needed is calculated

in the same way as described in the Primary Complaint Board Operator Position section,

except the data used would be different due to the different nature of the job. As an example, the following information applies:

1) Maximum average waiting in the queue is 20 s;

2) average service time per call is 300 s: and

3) number of "long" calls during the peak call rate time is 10.

The number of delay units is:

20 s/300 s = 0.066 unit.

The operator workload units are:

(10 x 3Q0)/3600 = 0.83 workload units.

In figure Bl, the intersection for these two values is between two and three operators.

This would indicate that three secondary operators are needed if the average call

waiting time is not to exceed 20 s.

34
Disnatcher Positions

The dispatcher is the heart of the command and control center operations as it is his

r ?sponsibility to coordinate the patrol force to meet the many and varying demands for

police service. Dispatcher duties fall into five main areas:

1) messages involving initial assignment of cases,

2) messages supporting cases in progress,

3) messages supporting units on patrol,

4) messages involving case dispositions, and

3) messages relaying emeries to remote data banks (e.g., Department of Motor

Vehicles, National Crime Information Center) and the answers to these queries.

In observations made of tne dispatch activities of the San Diego Police Department, the

following distribution of activities was found:

Type of activity Percent of total

Initial assignment 26

In-progress case support 44

Patrol support 15

Case dispositions 15

In addition, queries to data bases were added in proportion to the number of patrol

units deployed at a rate of one query per 2 h per on-duty patrol unit. From the

observations, two things are especially worthy of mention. First, when dispatchers have

to handle remote data base queries in addition to their other duties, it significantly

reduces the number of cases each dispatcher can handle. Secondly, it was observed that

when the dispatcher is busy 60 percent or more during the peak call time, the stress

becomes severe and he/she begins (1) to defer action on calls perceived to be of low

priority, (2) to shorten messages, (3) waiting times become excessive, and (4) patrol

units cannot communicate with the dispatcher satisfactorily. The stress results because

the dispatcher is faced with simultaneous and conflicting demands that cannot all be met

at once and with which he/she must make critical decisions. The observers felt that

when the dispatchers were busy 65 percent or more of the time, the peak limit of the

system has been exceeded. They drew the conclusion that sufficient terminals and

operators should be provided to keep the busy time to approximately 30-50 percent during

peak periods.

Based on the observations, a computer simulation of a dispatcher work station under

three different conditions was conducted. These conditions were:

1) separate complaint board operator and dispatcher: dispatcher does not handle

queries to remote data bases (System A)

;

2) separate complaint board operator and disnatcher; dispatcher handles emeries to

remote data bases (System B) ; and

3) dispatcher takes calls from public, but does not handle queries to remote lata

bases (System C)

.

To determine the number of dispatchers needed under each system is a relatively sit 1-- matter. The system should be sized to handle the heaviest load--that is, the nunbnr of cases in progress during one or more of the busiest hours should be counted. Then th<> maximum allowable case load per dispatcher is determined. From these, the total number

of dispatcher stations is determined as follows:

Number of dispatchers needed = ?^1 .case load during peak hour (s)

Case load per dispatcher

35
Based on the observations made at the San Diego Department, it was determined by

computer simulation (in which the dispatcher's channel utilization rate during the peak

hour(s) was 30 percent,* and the type of case handled was varied according to the

percentages given above) the critical case loads for each system were:

System Cases per hour

A 21

B 11

C 8 With this information, it is then an easy matter to determine the number of dispatchers

needed. For example, under System A, assume the peak case load is 80 cases per hour.

The number of dispatchers needed would be:

Q A Number of dispatchers needed (System A) = = 3.8,

which means four dispatcher stations will be required. Similar calculations can be done

for System B and C.

Based on the results of the observations, the following general conclusions were confirmed

:

1) Separating the complaint board operator position from the dispatcher position

increased the capacity of the dispatcher position; and,

2) removing remote data base queries from the dispatcher position increases

dispatcher capacity.

For a more detailed discussion of the calculations and simulations referred to and

summarized above, the reader is referred to reference 1 of the basic report.

*lTTthe channel' utilization rate was above 30 percent, it was found that the waiting

time to use a channel became too high

.

36
APPENDIX C—LIST OF REVIEWERS

Mr. Robert J. Benson

Executive Director

South Bay Regional Public Communications Authority

Hawthorne California

CaDtain Herman R. Campbell

Communications Bureau

Viriginia Beach Police Department

Virginia Beach, Virginia

Captain Dave Crow

San Jiego Police Department

San Diego, California

Cantair. J. W. Hilliard

Greensboro Police Department

Greensboro North Carolina

Mr. 3. V. Iiuahes

Management Information System

Memphis Police Department

Memphis Tennessee

Captain Larry husemann

Computer Services

Pnoenix Fire Department

Phoenix. Arizona

Major H. V. Johnson

Inspectional Services Division

Seattle Police Department

Seattle. Washington

Mr. Tom McKinney

PRC Public Management Services

McLean, Virginia

Mr. James A. Munson

Manager Special Projects

PRC Public Management Services

Huntington Beach, California

Mr. Jimmy D. Patty

Director of Communications & Information Services

Boone County/Columbia Disaster Preparedness

Columbia, Missouri

Mr. Thomas F. Sawyer

Assistant Chief

Phoenix Fire Department

Phoenix, Arizona

Mr. Steve Smith

Communications Supervisor

Public Works Department

Des Moines, Iowa

37
N BS-H4A (rev. 2 »sc ) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See in struction s)

4.

TITLE AND SUBTITLE

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NBSIR 84 - 2991 March 1985

Guide to Computer-Aided Dispatch Systems

5. AUTHOR(S)

David J. Brenner and Marilyn A. Cadoff

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Institute of Justice

U.S. Department of Justice

Washington, DC 20531

10.

SUPPLEMENTARY NOTES

QJ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200~word or less factual summary of most sign ificant information. If document includes a significant

bi bliography or literature survey, mention it here) This guide provides current information on computer-aided dispatch (CAD)

systems as they are used by law enforcement and other public safety agencies and is intended to serve as a procurement aid to those persons

who are or will be involved with the planning and acquisition of a CAD

system. Topics such as the improvements in operations that may result

from installation of a CAD system, a description of the system components, various considerations that will require resolution when the

decision is made to purchase a CAD system, and provision of sufficient

background to enable a knowledgeable purchasing decision to be made

are addressed. A general purchase implementation plan is included also.

12. KEY WORDS (Six to twelve entries; alphabetical order; capilali ze only proper names; and separate

command and control* communications; complaint operator;

dispatch; dispatcher; hardware; software

key words by semicolon s) computer -a ided

13. AVAILABILITY 14. NO. OF

[ Uni i mi ted

[ J For Official Distribution. Do Not Release to NTIS

PRINTED PAGES

42

"] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

[ X) Order F rom National Techn ical Information Service (NTIS), Springfield, VA. 22161 $8.50

USCOMM-DC 6043-P80