Proceedings 2002/2003 - IRSE

52
SIGNALLING CONTROL CENTRES TODAY AND TOMORROW
IECC uses its own real time operating system BRX
(British Rail real time executive) which is specifically
designed to support the networking and duplication
which delivers very high system availability.
To achieve predictable performance and high
availability, IECC was designed around two duplicated
networks, one for real time signalling data and
the other for less critical information exchange. With
the available technology at the time, a “register
insertion ring” network architecture running at 1.5
Mbits/second was chosen, because this could
achieve the required data throughput with a more
predictable time response than networks based on
“collision and recreate-try” strategies. Interfaces
between sub-systems and network nodes are 9,600
baud or 19,200 baud serial links. As with the processor
hardware, the network equipment has been very
reliable, and the same supplier of network nodes has
been used throughout. The only change has been
that the nodes are now rack mounted cards in place
of the original “black boxes”. The technology is now
obsolete, and it is envisaged that at some time in the
future there will be a move to a more modern
technology such as Ethernet, with predictable time
response achieved by installing a high speed
network used at a small fraction of its theoretical
capacity.
One of the most recent innovations has been to
move from EPROMs to CD-ROM as the means of
configuring IECC sub-systems with software and
data 2 . This has been made possible by using the
latest processor boards with Electrically Erasable
ROM memory. For security and to avoid installing
additional hardware, the CD-ROM is read using a
laptop PC, which is plugged directly into an Ethernet
interface on the VME processor board when an
update is required. This allows updates to take place
much more rapidly and without physical disturbance
to the IECC equipment.
SIGNALLER’S WORKSTATION
The VDU-based signaller’s workstation is the
critical human interface on the operating floor of the
control centre. The original design (SDS – signalling
display system) typically incorporated four colour
monitors built into a purpose-designed workstation
cabinet, with a trackerball and keyboard for operator
input. Normally two monitors provide an “overview”
which allows the signaller to see all main running
signals, points, track circuits and train descriptions
simultaneously. A third monitor allows selection of a
“close-up” view providing a more detailed view of
selected areas, including details such as shunting
signals and ground frames, and a fourth “general
purpose VDU” provides a number of text areas for
fault reporting and signaller interaction with train
describer and ARS. High availability was provided
for throughout the design, with a facility to switch
any view to another monitor if one should fail, all
critical functions accessible via both keyboard and
trackerball, and duplicated processors with hot
standby. Some of the later schemes incorporated
more monitors (up to six) to allow very large areas of
control.
The workstations were well-accepted by signallers
from the start, and there were few problems in
adapting from panel working to VDUs. However, the
monitors themselves and the VME graphics cards
which provide the interface to the processors were
amongst the first IECC components to become
unavailable. The chosen solution to the problem was
to replace these components with an industrial
quality PC and monitor, linked to the main VME
processors via a dedicated Ethernet link. This new
system (DIS – Flexible Display System) has allowed
much more choice in the size and style of monitors,
and for many new installations and upgrades the
customers now choose flat-screen monitors on a
desktop, instead of the original fully enclosed
cabinet. The old and new styles of workstation are
shown in Figure 3. The move to a PC does not
totally eliminate the obsolescence problem, as the
PC components change on an almost monthly
basis. A fast-track acceptance process has been
specified to enable minor changes to PC specification
to be tolerated without invalidating Railtrack’s
product acceptance of the system.
The colour VDU terminal providing the interface to
the IECC maintenance technician, the IECC System
Monitor (ISM), is also no longer available. This has
been replaced by a PC-based system, which
provides an improved Windows-based interface with
some additional facilities.
AUTOMATIC ROUTE SETTING
The sophistication of the automatic route-setting
function (ARS) of IECC is the feature which sets it
apart from similar signalling control systems in the
UK and overseas. Whilst automatic setting of routes
for trains running in normal timetable order is
commonplace, IECC uses train regulation algorithms
to maintain a full automatic route setting capability
during periods of service disruption, and the
signaller only needs to intervene in exceptional
circumstances. This contrasts with the approach
seen elsewhere, such as the network management
centres in Germany, where the automated system
provides warning of conflicts, but the decision to
change the timetabled order of trains is taken by the
human not the computer.
The IECC approach to automatic route setting was
based on fundamental research into route setting
algorithms undertaken by British Rail Research. The
ideas were validated first using a system which
simply provided advice to the signaller (a system
called JOT at Glasgow Central in the late 1970s),
and then by a full trial of ARS which took place from
1983 onwards at Three Bridges signalling control
centre, controlling the Haywards Heath area of the
London-Brighton line. The fully developed version of
ARS was active from the first day of IECC commissioning
at Liverpool Street in 1989, and immediately
demonstrated its versatility in handling traffic into
and out of this 18-platform terminus, despite major
disruptions to service caused by initial unreliability of
some of the SSI trackside equipment in a very
severe EMC environment.
The objectives of ARS were to reduce manning
requirements in signalling control centres, and to
improve punctuality by guaranteeing prompt route