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ENCRYPTED SIDEBAR – THE P25 STANDARD


January 11, 2013
By Morley Lymburner

Is it security or brevity

by Morley Lymburner

One of the questions oft asked by the public is why police use codes in communications. Is it to thwart the casual snooper, conserve air time or simply sound professional? The best answer I could come up with after some brief research is “all of the above.”

Development on the 10-codes began in 1937, when police radio channels were limited. With more and more calls for service they were used to reduce radio time.

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Credit for inventing the codes goes to Charles “Charlie” Hopper, communications director for the Illinois State Police. Hopper had been involved in radio for years and realized there was a need to abbreviate transmissions on state police bands.

Experienced radio operators knew the first syllable of a transmission was frequently not understood because of quirks in early electronics technology. Radios up the 1960s used vacuum tubes powered by a small motor-generator called a dynamotor. It took from 1/10 to 1/4 of a second to “spin up” to full power. Police officers were trained to push the microphone button, then pause briefly before speaking but sometimes they would forget to wait. Preceding each code with “ten-” gave the radio transmitter time to reach full power.

Ten-codes, especially “ten-four”, first reached public recognition in the mid- to late-1950s through the popular television series with Broderick Crawford. Crawford would reach into his patrol car to use the microphone to answer a call and precede his response with “10-4”.

The “cool factor” with 10-codes came about during the CB radio craze in the late 1970s. The hit 1975 song “Convoy” by C. W. McCall depicting conversation among CB-communicating truckers put phrases like 10-4 and what’s your twenty? (10-20) into common use in American English. A 1978 movie Convoy, loosely based on the song, further entrenched 10-codes in casual conversation.

The transition from the necessities of older technology to simple tradition was inevitable and most communications bureaus hold on to the ten codes for no apparent reason. Worse still is the dangers inherent in a lack of common rules of use from agency to agency.

As an example I checked in with some New York State police agencies and focused on one code (10-10) to determine how it is used.

Monroe Country Police 10-10 = Fight
Nassau County Police 10-10 = Call your Command
New York City Police 10-10 = Possible crime in progress
Poughkeepsie Police 10-10 = Go to scrambler
Suffolk County Police 10-10 = Auto accident
Amherst Police 10-10 = Sexual assault

Tonawanda, New York (suburb of Buffalo)
Code 8 = Out of Service – Investigating
Code 11 = Out of service
Code 12 = Out of service – Can take call
Code 14 = Lunch
Code 15 = Coffee break
Code 50 = Request beverage
Code 100 = Gassing vehicle

(Canadian cops need not apply).

Many agencies today have more air time due to the digital communication era and the migration to common language usage is becoming more common.


P25 – Saving lives through improved communications

by Morley Lymburner

Some police and other emergency services across North America began reviewing their communications needs post September 11. This singular watershed event displayed a wide variety of shortcomings in emergency communications both within house and while intercommunicating with other agencies. These problems were also compounded by a digital/analog changeover period which saw serious problems with transitional hardware incompatibilities.

The Association of Public Safety Communications Officials (APCO) has come to the rescue by helping to initialize and institute Project 25. This project sets up standards for all manufacturers of emergency communications equipment. Although not legally binding all companies interested in marketing to the emergency communications industry must seriously consider the marketability of their technology if they choose not to comply.

Project 25 (P25) or APCO-25 refers to a suite of standards for digital radio communications for use by federal, state/province and local public safety agencies in North America to enable them to communicate with other agencies and mutual aid response teams in emergencies.

Although developed primarily for North American services, P25 technology and products are not limited to public safety alone and have also been selected and deployed in other private system application, worldwide. P25 equipment has also been selected for a railroad system, including rolling stock, personnel, and transportation vehicles.

P25-compliant systems are being increasingly adopted and deployed. The largest advantage is that compliant radios can communicate in analog mode with legacy radios, and in either digital or analog mode with other P25 radios. Additionally, the deployment of P25-compliant systems will allow for a high degree of equipment interoperability and compatibility.

P25 standards use the Improved Multiband Excitation (IMBE) vocoders which were designed by DVSI to encode/decode analog audio signals.

P25 may be used in “talk around” mode without any intervening equipment between two radios, in conventional mode, where two radios communicate through a repeater or base station without trunking, or in a trunked mode, where traffic is automatically assigned to one or more voice channels by a repeater or base station.

P25’s Suite of Standards specify eight open interfaces between the various components of a land mobile radio system:

<> Common Air Interface (CAI) standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer.

<> Subscriber Data Peripheral Interface standard specifies the port through which mobiles and portables can connect to laptops or data networks.

<> Fixed Station Interface standard specifies a set of mandatory messages supporting digital voice, data, encryption and telephone interconnect necessary for communication between a fixed station and P25 RF subsystem.

<> Console Subsystem Interface standard specifies the basic messaging to interface a console subsystem to a P25 RF subsystem.

<> Network Management Interface standard specifies a single network management scheme which will allow all network elements of the RF subsystem to be managed.

<> Data Network Interface standard specifies the RF Subsystem’s connections to computers, data networks, or external data sources.

<> Telephone Interconnect Interface standard specifies the interface to Public Switched Telephone Network (PSTN). supporting both analog and ISDN telephone interfaces.

<> Inter RF Subsystem Interface (ISSI) standard specifies the interface between RF subsystems, which will allow them to be connected into wide area networks.

Resources:

Project 25 Technology Interest Group (PTIG) home page: http://www.project25.org/

Motorola Project 25 portable radios and information: http://www.project25.us/

APCO International Project 25 page: http://www.apcointl.org/frequency/project25/ –

APCO-25 control channel information: http://www.aeroflex.com/products/commtest/pmr/appnotes/p25cc.pdf

Daniels’ P25 Radio System Training Guide: http://www.p25.com/resources/P25TrainingGuide.pdf


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