1. What Is Trunking?
An Introduction to Trunked Radio Communication Systems
In a world of increasing competition, communication becomes more and more important in order to stay on the scene. It is commonly understood that enhanced communication is the key to smooth processes, efficiency, and job satisfaction: In other words - optimization of a company or an organization's assets, and more productivity.
Technology is constantly on the move. In the following pages we will give you an introduction to TRUNKING IN RADIO COMMUNICATION using the MPT 1327 protocol , a technology that makes communication not only easier but also more efficient.
In traditional non-trunked radio communication systems the different user groups have been operating on separate radio frequencies or radio channels. Often the number of user groups using a system exceeds the number of channels that it provides. As a consequence several user groups have to share the same single channel.
As a radio user, have you ever tried to gain access to a busy radio channel? Nothing is more frustrating than waiting. Waiting for the channel to become free - only to get blocked out by another user with a stronger signal!.
Even if more channels are available in the system to be shared among the user groups, instructing all users to change channels is often difficult in practice. This leads to frustration among the users and lack of confidence in the radio communication system.
2. Trunking Systems
In a Trunked radio communication system the system intelligence takes care of guiding the users to a free channel. The user does not have to worry if a channel is free or not, but can concentrate on the essence of radio communication: Bringing the message across!
In two-way radio communication, Trunking is defined as: The automatic and dynamic allocation of a small number of channels among a large number of radio users.
Let's take a closer look at the techniques behind Trunking. Almost everybody has used the principle of trunking without realizing it. Trunking has been used in the public telephone network for many years. If you place a telephone call to a subscriber in another city, your call is transferred by an arbitrary line. You, as a subscriber, do not have to select that line. All you have to do is to request one by dialing, and the city exchange will automatically allocate you a free line. When your conversation is over you hang up, and the line is released for other users.
In other words, the system handles the allocation of a limited number of lines among a large number of subscribers.
In telephone Trunking, the subscriber just dials a number and the switching station assigns a line on which the conversation can take place.
In radio Trunking, the subscriber just requests permission to talk, and the Trunking controller assigns a channel on which the conversation can take place. You simply request a call to another user, or group of users, and the system allocates a free channel for your call. When you finish the conversation, the channel is released for other users. The above principle is called Trunking.
Trunking in radio systems became possible with the introduction of the microprocessor. this made it possible to bring enough computing power to mobile and portable radios, as well as the Trunking controller of the system. The Trunking controller is the heart of the Trunked radio system. It is the housekeeper of all activity within the system. It receives your request for communication, processes it, and establishes the contact. It keeps records of all calls, and provides important information to maximize the efficiency of the system during operation.
3. Benefits of Trunking
Applying Trunking techniques to radio communication gives a number of user benefits. We have already touched upon the user friendliness that is provided. But Trunking certainly offers you more than that:
4. Spectrum Efficiency
The grade of service is an indication of the time that the subscriber has to wait for access during the busy hours.
Radio Trunking is spectrum efficient. Two factors give major contribution to the Trunking spectrum efficiency. First, all radio users share all channels. Secondly, no channel stays unused when a need for communication exists. The Trunking controller immediately allocates a free channel when requested. Radio frequencies and spectrum management are an absolute criteria in today's business world. By optimizing spectrum availability, more users have access to the system and are provided an increased level of service.
IN MANY COUNTRIES, GOVERNMENTAL AGENCIES HAVE MANDATED THAT NEW ALLOCATIONS OF SPECTRUM WILL ONLY BE GRANTED IF TRUNKING TECHNOLOGY IS UTILIZED. THIS BRINGS US TO ANOTHER ADVANTAGE OF TRUNKING:
With a Trunked radio communication system, users only hear the conversation intended for them because they have exclusive use of the channel. At all other times, their radio is silent. Since communication in a Trunked radio communication system happens on an arbitrary channel selected by the system, it becomes difficult for unauthorized users to monitor the voice communication of a particular group of users. The degree of privacy can be even further enhanced on a Trunked system by adding digital voice encryption, if supported by the system architecture.
6. System Reliability
Consider communicating on a particular channel in a conventional system and you have a channel fault. The users on that channel are prevented from communicating unless they all know in advance what channel to switch to if another is available. This situation never occurs in a Trunked radio system. If a repeater station falls out, the Trunking controller registers the fallout and does not assign the repeater as a voice channel, until it has been repaired or the disturbance has disappeared.
Since channels are allocated as needed, and no user group is dependent on any one channel for communications, the failure of a single channel will most likely not be noticeable by the user.
7. System Control
The Trunking controller and the portable and mobile radios are microprocessor powered. This intelligence makes it possible to control the radios working in the system. All channels in the system are shared by all radio users, and no channel is ever left idle when there is a need for communication, therefore, more users have access to the system. More access to the system means more efficiency in money terms and a higher grade of service. (Win / Win situation). More users per channel means less demand for additional channels.
In order to make the Trunking controller and the individual mobile and portable radios talk to each other, and understand each other, they must speak a common language. This occurs by exchanging sets of information telegrams. The language that rules the telegrams is called the Trunking protocol . Several Trunking protocols are on the market today. Some of these are ruled by authorities, and some by the manufacturers of the trunked radio communication system. The authority ruled ones are "open", whereas the manufacturer ruled ones may be "proprietary".
An example of an open protocol is the UK standard MPT 1327, which has been adopted in many others areas of the world including, Europe (Eastern and Western), Africa, Middle East, Latin American, and the United States.
A manufacturer provided proprietary protocol is not country specific.
Radio Products used in a Trunked System are typically GP600, GM600, GP1200, GM1200 and Key Base Stations and Zetron 827 Controller.