This article by Mike Fraser, General Manager Global Sales and Marketing at Tait Electronics was first published in the April edition of Radio Resource magazine.

Beets in hamburgers. Right-hand drive cars. As an American who has recently settled in New Zealand I can attest that things are done differently in different parts of the world. Take trunked radio. In many parts of the world MPT 1327, a technology developed in Europe, is the most widely used protocol. There are more than 30 suppliers of MPT 1327 equipment and because it's an open standard there is ample choice of terminal suppliers.

But as with cars, jeans and fast food, we Americans have become very focussed on locally developed mobile radio technologies, making MPT 1327 about as common as beets in a Big Mac. That is changing, however, as many open-minded US dealers and end users, after weighing up all the alternatives, are opting for MPT 1327 trunked radio solutions.

So what is MPT 1327? The technology was conceived in Europe in the early 1980s by a group comprising manufacturers, Government agencies and user representatives. They were looking to improve on the early trunked radio technologies that had emerged in the US. In particular the new standard would be non-proprietary, frequency transparent, suitable for networks of all sizes, and support a wide range of voice and data call types. The group obviously lacked creative marketing people because they settled on the unimaginative name, MPT 1327 - the British Ministry of Post and Telecom standard number.

Let's compare MPT 1327 with other commonly used North American technologies. Think trunked radio and most people think LTR (Logic Trunked Radio). This was designed for one-way despatching communications. It uses transmission trunking, which means that a new channel needs to be allocated every time a call participant presses the PTT switch, so two-way conversations strain the resources of an LTR system.

MPT 1327, on the other hand, uses message trunking, the traffic channel is allocated to all call participants for the duration of the conversation, making it more suitable for two-way conversations.

The call types on an MPT 1327 system include private one-to-one, fleet and group calls, broadcast, priority and emergency calling. Users can belong to many different talk groups and the composition of groups can be changed over-the-air from a despatcher or network terminal. As well as offering a superior range of closed group calls, MPT 1327 caters for calls outside your work group. This includes inter-fleet calls (subject to the approval of both parties), and PABX and PSTN interconnect, so you can place and receive telephone calls.

LTR is typically for single-site coverage, although technologies such as Passport are starting to cater for larger networks. MPT 1327 supports wide area networks. You can start out with a single-site system with full functionality and, if necessary, grow it to hundreds of sites.

One of the key differences with MPT 1327 is that each system has a dedicated control channel for managing the allocation of traffic channels and for several forms of data communications. In the frequency scarce USA we are accustomed to every channel being used for call traffic. But you have to consider the extra functionality provided by that control channel. You get faster call set-up, emergency calling (the control channel can be used to link all users in an emergency), the ability to queue calls when the called party is not available, and some forms of data communication take place over the control channel.

SmartNet, SmartZone and SmartTrunkII are more advanced forms of trunked radio than LTR but unlike MPT 1327 they are proprietary technologies and all have size limitations. SmartTrunkII is a scan-based trunking system which relies on the radio scanning for a vacant channel before placing a call. This can take up to three seconds, depending on the number of channels on the system, and if extra channels are added to a system all the radios must be reprogrammed.

Of all the trunked radio technologies commonly used in North America, EDACS is the most similar to MPT 1327, with a continuously available control channel, advanced calling options, wide area coverage and fast call set-up. But again EDACS is a proprietary technology, it uses message trunking for the majority of calls, is limited to 16,000 users per network and is likely to be less cost-effective than an MPT 1327 solution.

iDEN is a proprietary digital technology offering cellular-like communications with some despatch features such as group calls, and text messaging and data transfer. It offers three times more voice capacity than a standard 12.5KHz analogue voice channel but at the expense of voice quality. Also up to six times as many base station sites are required to provide coverage comparable to a single MPT 1327 site on the same frequency. Most iDEN users are connected to public access systems as the cost of implementing a network is prohibitive to most organisations.

One of the key advantages of MPT 1327 is that the protocol was designed from the outset for the communication of data. There are four types of data communication, Status Messaging (up to 32 predetermined messages conveyed over the control channel), Single Segment Transmissions (SST), Multi Segment Transmissions (MST) and Open Channel Data. MPT 1327 also has a data interface called MAP27 which is commonly used in applications like automatic vehicle location, e-mail connection, text messaging and access to a database.

In addition to all the user features, MPT 1327 offers significant network management benefits. It has flexible user validation and billing features enabling a network provider to block access for unauthorised users, provide different levels of system access, arrange inter-fleet calling and charge users.

Ultimately different trunked radio protocols are suited to different applications. But, as with most things in life, to make the best decisions it pays to keep an open mind about all the options, well, most options. I wouldn't recommend beets in your hamburger!

Read more about Tait and MPT 1327.