[0001] The present invention relates to urban transport systems, and more specifically an
audio, video and data communications network for an urban public transport system.
[0002] These days, the definition of new, efficient urban public transport systems cannot
exclude from consideration the functionalities offered by the technological evolution
in the computer and telecommunications sector.
[0003] Users require quality, efficiency and security in the latest generation of urban
transport systems and to this end there are provided, at the stations or stops of
the lines constituting an urban transport network, voice communication services via
telephones or intercom systems from the users to a management central unit, and from
the central unit to the users via sound diffusion systems, as well as video surveillance
services of the access entrances to the transport network, and remote control of the
station equipment, relative to stops and vehicles, in this latter case for application
to railway systems or similar restrained guide systems, in particular, among others,
tramways and urban railway systems.
[0004] The application of new communications technology to terrestrial urban transport systems
is hindered - by comparison, for example, to its application in the industrial automation
sector, or in the automotive sector - by the time taken to build works, by the high
reliability characteristics required, and by the necessity of having the same technology
available for a considerable number of years, specifically for the replacement of
components which might fail in the course of their working life, without it being
necessary to replace the whole apparatus or even the entire system with other more
up-to-date technology.
[0005] Infrastructure works traditionally have extremely long design and production times
as compared to those characteristic of the development of the computer sector. In
fact, whilst the design and production cycle (the so-called "Time-To-Market") of a
computer system, however complex, is limited to only 6-12 months, for the average
infrastructure of a metropolitan railway public transport system, even in the best
of cases, a design period lying between two and four years is needed and a subsequent
production period from two to five years, depending on the length of the line or lines
to be formed.
[0006] The necessary reliability is another determining factor. In traditional systems the
architecture and components adopted are based on preceding choices whose outcome has
been tested and evaluated by experience. Moreover, the use of traditional equipment
makes it possible to secure a long-term availability for any spare parts which may
become necessary.
[0007] Furthermore, in the specific case of metropolitan railway systems, it is often necessary
to utilise arrangements of the "railway" type, and this necessarily involves a design
approach which brings with it an excessive attachment to the choices and methodologies
derived from the railway sector itself. The application to metropolitan railway systems
of solutions which are suitable for national or regional railway lines is often unsatisfactory
bearing in mind the different type of transport and areas of use.
[0008] The object of the present invention is to provide a flexible and reliable integrated
communications network for the management of an urban transport system. In particular,
the object of the invention is the provision of an integrated communications network
for the management of the telecommunications equipment (sound diffusion system, telephone
and intercom systems), the surveillance and automation equipment at the stations (or
stops) of a metropolitan railway transport system of restrained guide type, such as
for example an underground metropolitan railway transport system.
[0009] A further object is to provide a communications network the future expansion of which,
such as the implementation of new functionalities, will be easy and inexpensive.
[0010] A further object is to provide a communications network the initial installation
and subsequent maintenance of which will present low costs in comparison with known
networks.
[0011] To this end the subject of the invention comprises a communications network having
the characteristics defined in Claim 1 and an urban transport system according to
Claim 11.
[0012] Particular embodiments are defined in the dependent Claims.
[0013] In summary, the communications network according to the invention is based on the
principle of considering the communications apparatus and systems at the stations
of an urban transport network as subsystems interfaced with one another and with a
control central unit by means of connections of universal type, utilising recognised
standards and via a single communications network of ring type operable to convey
the stream of audio, video and data signals for the services which it is desired to
provide.
[0014] The communications network is preferably formed as a packet switching network of
IP on Ethernet type, structured and dimensioned to adapt to the morphological characteristics
of the urban transport system. The streams of audio, video and data signals are encoded
by gateways at nodes of the network and transported on optical transmission means,
by means of a statistical multiplexing.
[0015] In view of the enormous diffusion of the worldwide telematic network Internet the
IP protocol has been adopted as the protocol of the network layer in the ISO/OSI reference
model, and the TCP/UDP protocol has been adopted as the protocol of the transport
layer. As far as the data connection layer is concerned, various arrangements have
been evaluated, including dedicated technologies (typical of various constructors
and non-standard types), technologies of synchronous type (SDH), asynchronous technologies
(ATM) and technologies of non-deterministic type (Ethernet), and of these Ethernet
is that which offers the lowest cost and perfect coupling with the IP network layer.
The apparent weak point of Ethernet, that is a high reconfigurability time in the
case of breakdown, is overcome by employing routing techniques at the IP layer, such
as OSPF or Fast Spanning Tree.
[0016] These considerations, together with the greater technical stability and availability
of widespread knowledge of Ethernet technology, and the perspective of a long survival
and future evolution of this technology, has inclined the choice towards an integrated
network of "IP on Ethernet" type.
[0017] Further characteristics and advantages of the invention will be explained in more
detail in the following detailed description given purely by way of non-limitative
example, with reference to the attached drawings, in which:
Figure 1 is a schematic representation of one line of an urban public transport network;
Figure 2 is a general diagram of a multi-service integrated communications network
for an urban public transport system the subject of the invention;
Figure 3 is a detailed diagram of the connections of the network of Figure 2 at a
control centre;
Figure 4 is a detailed diagram of the connections of the network of Figure 2 at station
nodes;
Figure 5 is a schematic representation of the system for signal processing of the
network of Figure 2; and
Figure 6 is a diagram of the redundancy layer architecture of a diagnostic and remote
control system accessory to the network.
[0018] Hereinafter the components of an urban public transport system provided with an integrated
communications network according to the invention are described in an exemplary manner
which is, however, not to be considered as a limitation on the possibilities of expansion
and adaptation of the proposed network architecture.
[0019] In particular, the following discussion is developed with reference to a restrained
guide urban transport system such as, for example, a tramway or urban metropolitan
railway transport system.
[0020] Such a system comprises a network of transport lines which cover an area or region
to be provided with the service. A line L of a metropolitan railway transport network
comprises a plurality of stations S1,... S15 (areas of access to the service) and
a control area called the Technical Area (CT) where the offices, the depot for the
transport means, and the maintenance works are located. S16-S21 are indicated in the
example as further stations of a subsequent section of the line, which can be designed
and subsequently built after formation of the first section.
[0021] Preferably, a metropolitan railway transport system will be considered the trains
of which make use of VAL technology and are therefore completely automated and have
no driver on board in normal service conditions. The stations are also automated and
the management of the entire system takes place via a single management centre called
the Central Command and Control Station, indicated PCC in the drawing, preferably
located at one end of the line in the Technical Area CT.
[0022] In such a system, all the data streams must be conveyed from the stations S1-S15
(and S16-S21 of the exemplary line possibly extended) to the management centre PCC
to allow operation of the entire system.
[0023] Typically, depending on the use of a telematic network, and on the disposition of
its nodes (corresponding to the stations S1-S15) and the requirements for reliability
and tolerance to breakdowns, the following network topologies and associated considerations
can be presented:
1) Star Network: is the most commonly utilised in local area communications networks, and is the base
of the idea of structured cabling; all the nodes of the network are connected to a
central node, the so-called star centre, which functions as a relay and/or switch.
Among the advantages of this configuration is the fact that interruption of one of
the connections does not compromise the functionality of the remainder of the network,
and only the device connected to the star centre by means of that connection remains
isolated; moreover, the bandwidth necessary for each connection depends only on the
bandwidth requirements of the node connected to it. The loss of the star centre isolates
all the nodes and the central apparatus therefore must be chosen with good characteristics
of reliability and redundancy; moreover, in the case of breakdown of an interface
to a peripheral node the information does not have any available alternative routes
to enable it to reach the remainder of the network and therefore the node actually
remains isolated. The central node must have a high switching capacity to manage and
sort the data coming from all the nodes. Finally, it is necessary to install a large
quantity of cables in order to be able to reach all the peripheral nodes from the
star centre with dedicated connections.
This is therefore a configuration of little interest for a metropolitan railway urban
transport system in which the route of the lines is for the most part linear.
2) Grid Network: each node is connected in a more or less complex manner to the other nodes of the
network. Advantageously the alternative paths which the information can follow in
the event of a breakdown of the connections are increased and therefore the tolerance
level against failure increases with an increase in the complexity of the network.
It is a disadvantage that it also increases the costs, given that the cabling and
the interfaces for the connection of the various nodes increase, the complexity of
the routing is very much increased, and, as the number of nodes increases, the number
of connections needed in order to maintain the level of tolerance against breakdowns
increases in a more than linear manner. Finally, it accentuates the problems of cabling
already encountered in the star topology, which makes this arrangement even more impracticable
for use in the relevant urban transport system. Consequently, it can only be utilised
in the case of a small number of nodes.
3) Ring Network: the individual devices of the network are connected together in such a way as to
form a ring. Advantageously, each node has two alternative paths in order to be able
to reach the remainder of the network, thereby increasing the level of tolerance to
breakdown, whereby to tolerate the loss of one connection without causing isolation
of any of the nodes. Moreover, with an increase in the nodes the number of connections
and interfaces increases in a linear manner and therefore the costs remain contained
even in the case of very complex networks. Finally, the cost of cabling is a minimum,
in particular for the construction of a transport network with the characteristic
linear arrangement of stations as in the case of a metropolitan railway transport
network.
[0024] In this configuration, with two alternative paths being available, it is necessary
to adopt strategies to redirect the data stream and to reconfigure the direction of
these stream in the event of a breakdown somewhere along the network ring.
[0025] Taking account of the fact that a metropolitan railway line of an urban public transport
system has a mostly linear topography, substantially rectilinear for the major part
of the route, with a control centre PCC typically located at one end, and the fact
that the individual nodes of the communications network are preferably located at
each station, for the purpose of:
- limiting as far as possible the quantity of cabling which runs from the PCC centre
to the stations in order to simplify the overall cabling and to reduce equipment costs;
- diversifying the paths followed by the cables so that damage to a backbone connection
does not prejudice the functioning of the entire network and so that, in the case
of a breakdown, this information shall have at least one alternative path to reach
the control centre; and
- limiting the time needed for a possible reconfiguration of the network with the consequent
redirection of the data streams,
the communications network according to the invention adopts the ring network topology.
[0026] In particular, along a linear line L, the transmission line (backbone) B of which
the ring is constituted can follow physically separated out and return paths (for
example to channels located on the two opposite sides of the route of the train) the
ring then being closed at the two ends of the path, that is at one end at the node
of the PCC central station and at the other end at the node of the furthest distant
station.
[0027] Advantageously, with this configuration, future extension of the network does not
involve modifications to the pre-existing network structure in that it is sufficient
to "open" the ring at one of the nodes without it being necessary to locate new cables
between the central station and the new stations.
[0028] In Figure 3 is shown in detail the node of the network at the control centre PCC,
respectively indicated N
PCC.
[0029] By this means a plurality of control apparatus access to the network (to the backbone
B), in particular a network supervision processor unit 10, an assembly 12 of processor
units for the management of telephone/intercom, video surveillance, sound diffusion
and video information equipment located at the stations of the transport line, and
recording units 14 for recording audio and video communications and images coming
from the stations.
[0030] To the node N
PCC are also directly connected apparatus 20 for encoding/decoding and management of
the signals for service telephony and intercom, apparatus 22 for encoding and management
of signals for sound diffusion of messages, and apparatus 24 for decoding and management
of video signals for remote surveillance, all communicating with terminals of the
control centre PCC such as, for example, operator posts 30 and monitor 32. A direct
connection for the transmission of video information signals between operator posts
30 and the communication node N
PCC without interface of an encoding or decoding apparatus is also envisaged.
[0031] The node N
PCC is, moreover, connected to a processor unit 40 of the SCADA type for supervision
and control of the electrical equipment of the line.
[0032] Finally, the node is coupled to a local network of control nodes (indicated LAN PCC)
for grouping together the N
PCC nodes of other lines of the transport system.
[0033] Figure 4 shows in detail a single station Si (i = 1,..., 15 in the example) of the
network.
[0034] It includes a pair of network nodes N
1 and N
2, each connected to the backbone B, both coupled to station apparatus such as the
encoding/decoding and signal management apparatus 20' for the service telephone and
the intercom, encoding and signal management apparatus 22' for sound diffusion of
messages, and video signal decoding and management apparatus 24' for remote surveillance,
all communicating with station terminals such as, respectively, for example, intercom
and service telephones 50, loudspeakers 52, video cameras 54. A direct connection
between monitor 56 and communication node N
1, N
2 without an encoding or decoding interface is also envisaged for the transmission
of video information signals.
[0035] The pair of nodes N
1, N
2 is further connected to a processor unit 40' of SCADA type for supervision and control
of electrical equipment of the line.
[0036] The architecture described satisfies the requirements for rapid and efficient transport
of the following signals:
- signals coming from the station video cameras for video surveillance;
- sound signals from intercoms and service telephones;
- audio signals for station public address systems, for the technical area and possibly
for the sections of track between stations (in particular in case of restrained ways,
as in tunnels);
- signals for a public video-information system;
- signals for an automation system for the electrical and technological devices.
[0037] These signals, collected at the PCC, are made available to the operators who manage
the service and the telecommunications from suitable control posts.
[0038] A brief description of each sub-system to which the said signals belong is given
hereinafter. A supervision post of the network allows monitoring, configuration and
maintenance operations on the components of the network itself.
Video-Surveillance
[0039] Surveillance of the stations and the technical area is effected by means of a plurality
of video cameras (a different number from station to station), preferably PAL standard
colour television; only a restricted number of video streams from the video cameras
are directed to the N
PCC simultaneously. The system envisages an enlargement of the number of video streams,
including those possibly coming from video cameras located on board the trains. The
operators at the PCC can display the chosen video streams on a monitor or can choose
a video camera from those available and display its images on a personal computer.
It is possible also to effect a selection "by groups" of the video cameras, for example
to display all the video cameras of a station platform. For this, there are functional
matrices present at the stations for selection of analogue input signals to associated
video encoders, whilst at the central station PCC similar selection matrices provide
for routing of the video signals coming from the decoders towards the monitors.
Telephony/Intercom
[0040] Telephone lines reserved for the service and line maintenance staff and for the station
maintenance rooms are provided for each station; further, in the areas open to the
public, there are a plurality of intercoms to allow calls from the users to the operators
at the central station PCC to be made. The intercom systems behave as house phones
and can be adapted for connection to the telephone line making them therefore substantially
equivalent to the telephone from the point of view of the transport of signals.
Sound Diffusion
[0041] The possibility of diffusing sound messages into the stations and possibly into the
sections of track between stations (for example restrained ways, in tunnels) is envisaged
via suitable loudspeakers. At the stations there are provided analogue selection stages
for selection of the zones to which the messages are to be sent and analogue amplification
stages, whilst in the control centre there is an analogue stage for selection of input
signals so as to allow, under control of the operators, the diffusion of background
music, pre-recorded messages or messages directed to the operators themselves. In
the stations and in the depot there are loudspeakers grouped by homogeneous zones
of relevance; from the PCC it is possible to deliver different messages to different
zones (for example; platforms and ticketing zones); moreover a local call post (located
in a technical area) can be utilised by authorised staff (for example firemen) to
diffuse priority messages directly from the station.
Video Information to the Public
[0042] A series of monitors spaced along the platforms and in the concourse or atrium of
each station delivers preliminarily stored text messages intended for the users of
the transport network. These messages are selectable by the PCC operators.
Remote Control Systems for Electrical and Technological Equipment
[0043] All the signals coming from the programmable station controllers which manage the
electrical equipment and supervise the technological equipment are received by a SCADA
system (Supervisory Control And Data Acquisition), located at the PCC, the functioning
of which will be described hereinafter.
[0044] In defining the technical characteristics of the integrated network forming the subject
of the invention the following two aspects are taken into account:
- the difference between the delay requirements in the transfer of information; and
- the differences between the bandwidth requirements.
[0045] Many applications, such as, for example, the display of messages for video information
or data streams from remote SCADA diagnostic systems are not affected by delay ("best-effort"
applications), but for these it is important to guarantee an adequate bandwidth availability
and to ensure that there are no data (packets) losses. Other applications, such as
the traffic in voice and video signals (closed circuit TV) require that the delay
introduced by the transmission system is maintained below a determined threshold and
that possible packets which exceed this threshold are discarded so as not to delay
the reproduction of samples contained in the subsequent packets. As opposed to voice
traffic, the video traffic is unidirectional and therefore is more tolerant to delays
and better supports degradation of the information due to packet losses.
[0046] The amount of bandwidth required by each application which utilises the integrated
network for the transport of information is very variable, a large part of the bandwidth
utilised relates to video-surveillance signals which are subject to an analogue-to-digital
conversion at the stations; consequently, the amount of digital video data is strongly
dependent on the type of compression algorithm utilised (MJPEG, MPEG1, MPEG2) (to
a first analysis it can be assumed that the bit rate is maintained below the value
of 8 Mb/s for each video stream). The traffic of the automation system, whilst not
being of continuous type and, more than that, being traffic limited to the transmission
of the variations of the state variables, can have stringent time constraints and
can require simultaneous transmission from all the stations; for this reason a significant
part of the bandwidth has been reserved to this type of traffic. The data of the telephone/intercom
and the sound diffusion systems have very much smaller bandwidth requirements.
[0047] In order better to explain the role of the apparatus of the subsystems which make
use of the integrated network the subject of the invention, Figure 5 schematically
illustrates the classic model of a generic digital telecommunications system.
[0048] A signal source 100 (for example an input transducer) at which is generated an analogue
input signal is coupled to a source encoder 110 at which analogue-to-digital conversion
of the signal takes place through a compression algorithm with the addition of redundancy
codes for recovery of encoded data and correction of possible encoding errors.
[0049] A channel encoder 120 downstream of the source encoder provides for optimisation
of the digital signal for transmission on the channel, for example by the addition
of bits for recovery of data possibly lost in transmission and data identifying the
destination.
[0050] A channel modulator 130 modulates the signal as a function of the chosen transmission
channel (that is to say the displacement to the assigned frequency band) and converts
it into the form of signal which the channel is able to transmit (for example: sound
wave, electromagnetic wave, light pulses, electrical pulses).
[0051] The signal reception chain associated with the transmission channel comprises a channel
demodulator 140 operable to reconvert into binary form the signals received by the
channel, returning the signal to the base band.
[0052] Downstream of the demodulator 140 is disposed a channel decoder 150 operable to reconstruct
the digital signal from the received packets. It is arranged to recover possible lost
data through the additional bits provided upon transmission and to remove any auxiliary
information of the transmission introduced artificially by the source encoder 110
and the channel encoder 120.
[0053] A source decoder 160 is coupled to the channel decoder 150 and is able to decode
the digital signal and reconstruct the original analogue signal possibly by removing
any transmission errors through the redundancy bits provided.
[0054] Finally, an output transducer 170 converts the analogue signal into a suitable form
to be presented to an operator by the terminal interface apparatus.
[0055] The nodes N
PCC of the control centre and N
1, N
2 of each station constitute the access points to the communications network of the
devices for processing different types of signals; these nodes are preferably implemented
by devices which combine in one apparatus the functionality of a router with those
of a switch, such as for example level 3 switches or L3-switch.
[0056] The transmission carrier is preferably formed by two single mode optical fibre cables
which connect the two network nodes N
1, N
2 at each station with those of the adjacent stations forming two parallel independent
rings connected together at the PCC node; to each pair of network nodes there are
in turn connected audio/video signal processing apparatus in numbers such as to part
the final utilisers (the station terminals) between the two optical backbones thus
constituted.
[0057] A redundant configuration of this type has two fundamental benefits;
- malfunction of one node of the network nevertheless makes it possible to have full
control on the half of the terminals connected to the other node;
- twice the bandwidth is available for transport
[0058] The optical fibre cables, in their outward path from the control centre PCC towards
the end of the line (S15 or, for the extended line, S21) and in their return path
from the end of the line (S15 or, for the extended line, S21) to the control centre
PCC are joined to alternate stations in such a way as to minimise attenuation of the
optical signal along all sections between two contiguous connections.
[0059] At the control centre PCC there is a single network node suitably dimensioned to
be connected to both the optical backbones. The purpose of this node is to receive
data from the stations and to transmit it to the signal decoder apparatus 140-160
to make it available to the operators in suitable form. On the other hand, the same
network node will receive from the operator posts data and commands suitably encoded
by the encoding apparatus 110-130, and will transmit them onto the network in order
to be transferred to the stations.
[0060] Since the control centre represents the most critical point of the network this node
will have to guarantee superior performance and therefore will be preferably completely
redundant to allow the maximum reliability and availability.
[0061] The multi-service communications network forming the subject of the invention is
preferably a network of the Gigabit Ethernet type on single mode optical fibre (1000BaseLX
or greater). The use of single mode optical fibre (transmission in the second window,
wavelength about 1300 nm) advantageously guarantees connections between nodes spaced
by about 2km with 1000BaseLX Gigabit Ethernet optical modules without the use of signal
regenerators.
[0062] The apparatus connected to the multi-service network are able to encode the audio/video
signals into formats transportable on an IP network; interface with the network nodes
is achieved according to the 10/100BaseT Ethernet standard.
[0063] The network uses standard TCP/IP and UDP transmission protocols and routing algorithms
(OSPF) such as to minimise the reconfiguration times in the case of malfunction of
the nodes.
[0064] Hereinafter the SCADA system mentioned above is analysed in greater detail.
[0065] The SCADA system makes it possible to provide a supervision, control and data acquisition
service, permitting diagnostics and remote control to be performed on all the electrical
and technological devices which do not have available a network interface and, therefore,
do not constitute an integral part of the network the subject of the invention. Such
devices are typically constituted by components dedicated to the civil infrastructure
(for example lifts, moving staircases, lights etc) and to the supply network (transformer
substations, UPS etc). From these the data necessary for the service are acquired
by means of Station Acquisition Units (hereinafter UAS) devices of the PLC type (Programmable
Logic Controller) provided with interfaces connected to the multi-surface integrated
network.
[0066] The analogue and digital variables detected by the terminals are pre-processed by
the PLC and sent to a redundant software module on server computers situated at the
control centre. The structure of this redundancy will become clearly apparent from
the explanatory diagram of Figure 6.
[0067] As is seen from this diagram, the UAS devices - which can be considered as generic
client computers C - are not directed to a single virtual IP address to achieve the
redundancy but see, at the network level, two separate machines, with two different
network addresses. Because, for the purpose of saving bandwidth on the data network,
the transmission of data from the periphery towards the centre takes place only "on
data change" in a "unsolicited" manner, on the initiative of the UAS (client) with
any protocol, it is necessary to inform these latter of the address of the master
server to which the data is to be sent.
[0068] Writing of the address by the master server at regular time intervals in a memory
location of all the configured clients is therefore programmed.
[0069] There is, however, a problem of a general nature related to the redundancy of the
two machines: in order to designate the master server, these need to exchange a signal
generally called a "heartbeat" which necessitates a dedicated connection. If this
connection is interrupted whilst that to the client remains active, both the servers
elect themselves as master causing a concurrent double writing of the address on the
UASs. These latter then do not have available a stable address to which to send the
acquired data.
[0070] The solution adopted, in this case, is to continue to communicate with the last individual
master server, thereby stabilising the address and maintaining as valid the last address
stable for a given minimum time interval. This interval must be greater than or equal
to the write period of the address by the servers, plus a safety margin which must
take into account the possible additional delays or skew effects between the two signals
due to transport on the network.
[0071] The algorithm for control of the stability of the address must be executed by the
side client and is set out by way of example hereinafter in pseudo code:
[0072] The variable STEADY signals the stability of the written address ADDR_NEW and is
set at 1. After this a cycle is commenced which repeats at each reading and which,
after the necessary time interval has passed, puts the read value of ADDR_NEW to ADDR_OLD
to re-set the comparison and, following a verification of the stability, saves this
latter in ADDR_DEF which constitutes the definitive address to which the information
is sent.
[0073] During normal master-slave switchings the new written address is validated by the
algorithm with a maximum delay equal to twice the stability interval calculated starting
from when the old master server ceases control of the clients, thereby stopping writing
its address.
[0074] This addressing procedure of the servers by the clients indicated MMAP (Multi Master
Addressing Procedure), makes it possible to realise a client-server communication
initiated by the client, with concurrent multiple servers.
[0075] The above-described principle is easily generalised to the case in which there are
more than two servers.
[0076] With respect to the solution based on "heartbeat" control this has the following
advantages:
- it is possible to have a generic number of concurrent servers to provide multiple
redundancy configurations, preventing each from knowing the addresses of the others
so as to control the activity thereof;
- it is not necessary to have a connection between the concurrent servers;
- it resolves the problem of disconnections between the servers which occurs if, for
any reason, they continue to be able to communicate with the clients but not with
one another.
[0077] From tests conducted it is possible to extrapolate estimates of the times that the
communication network the subject of the invention takes to reconstruct a topology
which recovers from a breakdown. From an experimental architecture it is derived that
the reconfiguration times of a network composed of 7 nodes is of the order of 3.5
seconds in the case of a breakdown of an interface immediately identified by the node.
In the very rare case in which the node of a station no longer participates in the
correct functioning, but maintains connections active, impeding the prompt identification
of the malfunction by the neighbour nodes the times will be influenced by the so-called
"dead interval" (time which must pass before declaring an OSPF node as out of service,
imposed by default as four times the "hello" interval or "hello time"). In this case,
with the "hello time" set at 2 seconds, the reconfiguration times are 10.5 seconds.
The formula deduced experimentally is:
[0078] Where:
Nnd The number of nodes of the ring network
Ht "Hello time" (which can be set on the apparatus, default = 2 seconds)
Trs Experimental reconfiguration time.
[0079] This, for a ring topology of a line layout of 16 stations, means about 12.5 seconds
in the worst case, that is to say when the connection between the two nodes most distant
from the management centre are interrupted.
[0080] Further experimental tests and the results obtained during the course of the development
of the design of the Turin automatic metropolitan (underground) system have indicated,
following a fine optimisation of the configuration parameters, results which are much
better than those previously obtained. This is achieved by technological updating
of the network apparatus utilised in the experimental architecture, which has made
it possible to record reconfiguration times both in the case of loss of a network
node and in the case of disconnection of a connection between the nodes, always less
than 3 seconds.
[0081] From the tests it is apparent that these reconfiguration times are proportional to
the number of nodes which constitute the ring of the network and, therefore, a reduction
in the diameter of the ring leads to a reduction in the maximum reconfiguration times.
[0082] Up to now, therefore, the transport of signals on an integrated IP on Ethernet network
is the best solution for the transmission of the audio/video/data information from
the point of view of the flexibility of the apparatus, standardisation of the protocols
and the data encoding algorithms, as well as the availability of these for the future
and the gradually falling costs of Ethernet network apparatus.
[0083] The choice of the IP on Ethernet protocol, moreover, opens the way to a whole series
of innovative services which can be implemented without particular problems on this
type of network, for example the possibility of using "dynamic" publicity posters
controlled by processors and programmed by the control centre in the night hours,
or the possibility of utilising video telephones.
[0084] Advantageously, the current possibility of integrating video, voice and data on a
single packet switching network greatly increases the flexibility and rationality
of the system. Moreover, it is possible to increase the reliability of this integrated
network by forming two unconnected networks and transporting on each of these a mixture
of all the services in such a way as to guarantee, in the case of a network breakdown,
the functioning, although degraded, of all the subsystems.
[0085] In brief summary the single integrated network according to the invention presents
the following advantages:
- extreme flexibility of the system from the point of view of extensions such as the
addition of stations, relocation of the management centre, addition of new services;
- rationality in the use of network resources which are dynamically shared by the various
services;
- reduction of cost in the long term;
- greater stability of the architecture with respect to technological evolutions;
- lower costs in the application program development which can utilise standard protocols
and interfaces.
[0086] By contrast, the choice of several separate networks dedicated to each type of traffic,
although based on confirmed technology of analogue type relevant to the world of audio/video
transmission at a professional level, would be more expensive in that these networks
would not be able to enjoy the economy of scale and reduction of costs achieved by
the still greater diffusion of computer networks.
[0087] Naturally, the principle of the invention remaining the same, the embodiments and
details of construction can be widely varied with respect to what has been described
and illustrated purely by way of non-limitative example, without by this departing
from the scope of protection of the present invention defined in the attached Claims.
1. A communications network for an urban transport system comprising at least one transport
line (L) including a plurality of stations (S1-S15; S16-S21) disposed along a substantially
linear route and a control centre (PCC),
characterised in that it comprises at least one communication node (N
PCC) associated with the said control centre (PCC) and one communication node (N
1; N
2) associated with each station (S1-515; S16-S21), which are arranged for:
- access to the network by respective apparatus for the management and processing
of audio, video and data signals;
- routing through the network of the said signals from each station (S1-S15; S16-S21)
to the control centre (PCC) and vice versa;
and in which the said nodes (N
PCC, N
1, N
2) are connected via a signal transmission backbone (B) which has a ring topology.
2. A network according to Claim 1, comprising a pair of communication nodes (N1, N2) associated with each station (S1-S15; S16-S21), each adapted for access to the network
by a subsystem of apparatus for the management and processing of audio, video and
data signals of the station (S1-515; S16-S21) and routing of the said signals through
the network.
3. A network according to Claim 1 or 2, characterised in that it is a packet switching network.
4. A network according to Claim 3, in which the communication nodes (NPCC, N1, N2) include equipment which combines the functionality of router with that of switch.
5. A network according to Claim 3 or 4, characterised in that it is based on an Ethernet standard for the data link layer.
6. A network according to Claim 5, in which the communication nodes talk by means of
the TCP/IP family of protocols at the network and transport layer.
7. A network according to any preceding Claim, in which the transmission backbone (B)
includes a optical fibre transmission channel.
8. A network according to Claim 7, in which the said transmission channel includes at
least one optical fibre cable which, along the route of the said transport line (L),
follows an outward path from the control centre (PCC) towards the station (S15; S21)
at the end of the line (L) and a return path from the station (S15; S21) at the end
of the line (L) to the control centre (PCC), the communication nodes (N1, N2) associated with the stations (S1-S15; S16-S21) being connected alternately to the
outward path or the return path of the channel.
9. A network according to any preceding Claim, in which the said apparatus for management
and processing of audio, video and data signals includes audio telecommunication equipment,
video surveillance equipment and automation equipment.
10. A network according to any preceding Claim, in which the said communication node (NPCC) associated with the control centre (PCC) is connected to an external local area
network (LAN PCC) for connection of nodes associated with the control centres of other
lines of the transport system.
11. An urban transport system comprising at least one transport line (L) including a plurality
of stations (S1-S15; S16-S21) disposed along a substantially linear route and a control
centre (PCC), including a communications network between at least one node (NPCC) associated with the said control centre (PCC) and one node (N1; N2) associated with each station (S1-S15; S16-S21) as defined in Claims 1 to 10.
12. A system according to Claim 11, including a plurality of apparatus associated with
the control centre (PCC) for the management and processing of audio, video and data
signals, the said apparatus including at least one of the following components:
- encoding/decoding and signal management apparatus (20) for service telephony and
intercom, communicating with a plurality of terminals (30, 32) of the control centre
(PCC);
- signal encoding and management apparatus (22) for sound diffusion of messages, communicating
with a plurality of terminals (30, 32) of the control centre (PCC);
- video signal and decoding management apparatus (24) for remote surveillance, communicating
with a plurality of terminals (30, 32) of the control centre (PCC);
- a processing unit (10) for supervision of the network;
- a processing unit (12) for management of sound diffusion, video surveillance, telephone/intercom
and video information equipment located at the stations (S1-S15; S16-S21) of the transport
line (L);
- a recording unit (14) for recording audio and video communications and images from
the stations (S1-S15; S16-S21); and
- a SCADA processing unit (40) for supervision and control of the electrical equipment
of the line (L).
13. A system according to Claim 11 or Claim 12, comprising a plurality of apparatus associated
with the stations (S1-515; S16-S21) for the management and processing of audio, video
and data signals, the said apparatus including at least one of the following components:
- signal and encoding/decoding management apparatus (20') for service telephony and
intercom, communicating with a plurality of terminals (50-56) at the stations (S1-S15;
S16-S21);
- signal and encoding management apparatus (22') for the sound diffusion of messages,
communicating with a plurality of terminals (50-56) at the stations (S1-S15; S16-S21);
- video signal and decoding management apparatus (24') for remote surveillance, communicating
with a plurality of terminals (50-56) at the stations (S1-S15; S16-S21);
- a SCADA processing unit (40') for supervision and control of the electrical equipment
of the line (L).