NMCS Compatibility Testing

The Highways Agency has defined the National Motorway Communications Standard (NMCS), which all motorway communications systems must comply to. The aim is to allow the Highways Agency to procure equipment from a number of suppliers, without worrying about issues of mutual compatibility. This in turn leads to improved reliability, simple installation and the ability to mix equipment of different ages at the roadside. All of this ensures good value for money.

Key to this strategy is the Compatibility Testing undertaken by Cambridge Consultants. This ensures that the equipment's communications behaviour is well defined even in the presence of faults from other parts of the system. For example, if a device receives a message with a parity bit error it should not generate a spurious message in reply.

The Portable Standard

An important tool for the Highways Agency, their suppliers and Cambridge Consultants is the Portable Standard.

The Portable Standard is a combination of a protocol analyser and a test vector generator. It is able to analyse the communications between different types of roadside equipment and display the information in an application level format.

It is also able to simulate the communications interface of a piece of equipment at the roadside. This allows it to be used to test the behaviour of other devices and how they respond to messages including erroneous mesages. It is possible to construct complex test scripts that generate both normal and erroneous communications.

We continue to maintain and develop the Portable Standard to meet the evolving roadside environment, while maintaining the old legacy interfaces. This way the Highways Agency can be confident that fifteen year old equipment does not stop working when completely new equipment is installed next to it.