Robust Data Communications Solutions for the Rail Industry

Datacoms’ coming of age

It is now nearly 40 years since British Rail introduced the TOPS (Total Operations Processing System) into service. This was the first big application of IT and data networking to the UK rail sector, the genesis having been acquired from Union Pacific in the USA. Things have moved on a great deal in the intervening years but surprisingly datacoms is not a technology that features much at seminars and conferences. It was refreshing therefore to attend a recent event organised by Westermo entitled Robust Data Communications Solutions for the Rail Industry, held at the London Transport Museum. This was well supported by all sections of the industry, which is perhaps indicative of the need to acquire more knowledge on this now-vital sector.

Westermo is a Swedish-based company that has been in the business since 1975 and specialises in designing products suitable for harsh industrial environments. Its modems were acquired in the early days of TOPS and proved to be exceptionally reliable. Whilst the seminar was unashamedly aimed at promoting its own capabilities, Westermo arranged for three industry case studies to be presented so that attendees could learn some of the many and varied datacom applications that now exist to control difficult operational challenges.

Service continuity

Lars-Ola Lundkvist, Westermo’s Managing Director, and UK chief Alan Bollard gave an insight into the company’s approach to the problems often presented. The term datacoms covers a multitude of products these days: at the high level are routers, switches and Ethernet extenders; for radio connections come GSM/GPRS modems and 3G routers; at local level are local access fibre routers, media converters and field bus devices. So important is data networking that most designs have to incorporate redundancy and security protection with often triple paths to guarantee continuity of service.

In the industrial sector, temperature ranges of -40C to +70C can be experienced and finding equipment to work reliably within this range is a challenge. Fan cooling has its drawbacks owing to the moving parts, so is not used for equipment with a stated MTBF (mean time between failures) of >50 years. In the rail environment, multiple earth ground loops, other induced interference from electric traction and high transient voltages all impact adversely on datacom equipment. EC specifications EN50121-4 and EN50155 set down the requirements for trackside and on-board equipment respectively; shock and vibration limits are detailed in EN61373.

Input power supply is another difficult area: voltages can swing considerably with up to 40% over voltage being experienced; equally power gaps of up to 10ms must not cause system shutdown. Often the lines upon which datacom circuits are to be borne are old and out of specification. Installing new circuits is rarely an option so the datacom equipment has to work with lines having high noise and unbalanced characteristics. COTS (Commercial Off The Shelf) equipment designed for office and domestic environments will not last long in such conditions and, whilst the design principles are the same, firms such as Westermo have seen the need to produce something much better. The fact that they have survived in business for so long is indicative of their success.

Cooling the Tube

The first case study considered the problem of London Underground’s deep level tubes. As is well known, these are getting hotter and many people have been wracking their brains for a solution. On the Victoria Line, FirstCo has been given the task of inducing additional air movements through the mid-tunnel ventilation shafts. In basic terms, this means extracting air via powerful variable speed fans but this has to be done in conjunction with track isolation dampers, fan isolation dampers and bypass dampers to ensure acceptable conditions for routine maintenance and the avoidance of blowing air in a fire situation. All of these need a sophisticated and reliable control mechanism.

The core of this is a Rockwell PLC (Programmable Logic Controller)/SCADA-based system with a station control panel, a local control panel at the shaft, a secondary control panel at some shafts for diversity purposes and a firefighters’ override unit. The network to connect all these together is Ethernet-based using Westermo equipment with an ADSL interface from the shaft PLCs to the control office SCADA. At present the control of the fans is direct from mimic panels at the control points with the SCADA only used for monitoring, but eventually full control will come from the SCADA system. The initial trials were completed in December 2010 and full operation is expected this year.

Scottish IP networks

The creation of IP networks in Scotland was described in Issue 72 (October 2010) of the rail engineer and formed the basis of the second case study. Dr Robert Gardner, Network Rail’s expert on datacoms, explained how this now-extensive network had come about, initially to provide lineside access for the remote condition monitoring of signalling equipment on the Glasgow-Edinburgh main line and also for the Ayrshire LLPA system. The network has now grown to embrace all of the central belt from Perth and Dundee, through Glasgow and Edinburgh, to Gretna and Largs. The plan is to extend it to all of Scotland and will eventually be part of an all-UK network.

Central to the architecture are two Ethernet Layer 3 rings with 15 main nodes, intermediate locations being served by Layer 2 access nodes. The connecting in of mini rings and spurs enable places to be served away from the main ring routing. At the lowest level, remote devices can be linked via the legacy copper cable plant. The Ethernet network is connected direct to fibre without the need to use the SDH (Synchronous Digital Hierarchy) transmission. All of this has required a host of datacom equipment for which Westermo has been one of a number of suppliers. Many items are housed in trackside cabinets without heating and subject to the vibration of passing trains.

Having proved the capability, robustness and resilience of the network, Scotland is now testing its suitability for carrying safety-related and safety-critical traffic. Whilst the network itself is regarded currently as SIL 0 under the EN50129 requirements for safety-related information over transmission media, it may be possible to raise this if the network can be proved a closed system. Trials to carry Solid State Interlocking data and CCTV level crossing pictures have been successful. Maybe this is a foretaste of things to come.

Modular signalling

The need to reduce the cost of signalling projects has long been recognised but the means of achieving this remain elusive. In the third case study, Jon Clarke of Invensys described the idea of signalling designs made up of a number of standardised modules all connected by a common data network or ‘cloud’. A control centre would be the hub of this but interlockings, radio block centres, object controllers and all the usual signalling peripheral devices would be connected to the cloud. A total of 54 module types are envisaged, which is far fewer than would be found on a conventional project. The addition of ETCS Level 2 is part of the vision. The Westrace Mk 2 interlocking – itself based on PLC technology – has been designed to connect direct to an Ethernet and fibre cables. Factory testing can be made easy by plugging the design together, proving it works, then disassembling and taking to site.

This concept will mean a simplification of the rules and a challenge to existing signalling standards but without reducing safety. Whilst low-cost modules form the crux of the concept, having an industry standard data network to connect it all together is very much part of the overall plan. A trial on the Crewe-Shrewsbury line is now underway and the results will be watched with interest. Is it too much to hope that eventually similar standardised modules from different suppliers can connect into the cloud, thus creating true interoperability and interchangeability for signalling equipment?

The datacom vision

Ray Lock of Westermo was keen to promote the future role that data networking can play in the rail industry. Several examples of imaginative datacom use were given in Sweden, Poland, Italy and Singapore. The same usage can exist on trains and, in cooperation with Bombardier, the Viper switch is capable of running all on-board subsystems – heating, ventilation and aircon, CCTV, passenger counting, and platform detection amongst others.

Appreciating that railway cable plant is often old should not be a reason for not using modern datacom techniques. The ITU G991.2 standard for SHDSL (Symmetric High-bit-rate Digital Subscriber Loop) will give data rates of between 192Kbit and 15Mbit over a single twisted pair. Bonding two together can double the data rate. Forward Error Correction (FEC) and negotiation protocol that look at cable characteristics with tone pulses, and then spectrally shape the data rate to suit, are becoming commonplace techniques.

The biggest challenge is seen as the acceptability of using data networks and IP protocols for the transmission of rail signalling information and the Invensys development is seen as encouraging. The goal is to use data networking for SIL 4 applications but this is still some way off. When one looks back over the past 40 years and views the advances that have been made, it can only be speculation as to what the next 40 years will bring. Altogether, this event provided a fascinating exposé of a subject many of us take for granted.