Date: 28th September 2000


LONDON BUSES FIRST TO USE ISDN D-CHANNEL IN REAL TIME PASSENGER INFORMATION SYSTEM

London Bus Services' Countdown real time passenger information system has become the first to use the ISDN D-Channel for communicating data from the company's central computers to a network of LED signs in bus shelters all over London, thanks to a specially designed ISDN terminal adapter from Symicron. The £20million project to provide signs at all major bus stops, keeping passengers informed about exactly how long they will have to wait for buses and where they are going, was started in 1992 and now has 1000 signs operational, expanding rapidly to 4000 on 200 routes throughout the capital.

It is the biggest passenger information system in the world. The Countdown system draws its information from Automatic Vehicle Location beacons located at the roadside. As a bus passes it detects the beacon and sends information, by radio, to Communications Systems in Chingford, the network operator and service provider. The computers at Communications Systems calculate where the bus is and, mapping the information with historical and current data on traffic patterns, makes an accurate prediction of how long it will take to reach each stop along the route. That information is communicated to each sign by ISDN, using the D-Channel into a Symicron terminal adaptor.

The system requires a permanent virtual circuit, although only small bursts of traffic in the form of short text messages are transmitted, whenever timings deviate from the initial predictions. The original Countdown system used BT's EPS42 analogue multi-drop service for communicating with telephone exchanges near each stop and branching panels had spurs for up to 12 signs. EPS42 is, however, not a managed service and will soon be obsolescent. The decision has now been taken to install only ISDN communications via the BT Connect service. So far 60 ISDN-based signs have been installed and another 600 will be in use by March 2001.

According to Dave Mastin, Technical Manager at London Buses Communications Systems, "We asked SLE, our software supplier, to adapt the Countdown software to the X.25 protocol and Symicron refined the interface into the sign and the BT network and provided X.25 cards for our workstations. The software is now installed in the central system and we are rolling out ISDN as quickly as we can."

"The terminal adaptors have to be extremely robust and Symicron were very responsive to our requests and were able to produce a highly reliable product, specially designed for the sign industry, that goes on working in harsh conditions. Symicron have also added a stored charge to the terminal adaptors. If the adaptor detects a power failure in the sign it sets up a call via the B channel of ISDN to a remote monitoring terminal in Chingford and communicates the exact nature of the problem, enabling us to send the right people to the site more quickly."

Symicron Computer Communications are on 020 8857 5577 or www.symicron.com