 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.
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. |
