WO2003015052A1

WO2003015052A1 - System of exchanging information between vehicles and a control centre

Info

Publication number: WO2003015052A1
Application number: PCT/FR2002/002836
Authority: WO
Inventors: Roland Mermoz
Original assignee: Sofide
Priority date: 2001-08-09
Filing date: 2002-08-08
Publication date: 2003-02-20

Abstract

The invention relates to a system of exchanging information between a vehicle (C1 to C7) and a control centre within a geographical area (1) which is located around the control centre and which contains the vehicles (C1 to C7). Each vehicle (C1 to C7) comprises a very short-range emitting/receiving terminal that is used to emit and receive route establishment requests with a view to transmitting data to a central terminal (B5 to B8) of the control centre along a route using the vehicle terminals (C1 to C7) as relays.

Description

SYSTEM FOR EXCHANGING INFORMATION BETWEEN VEHICLES AND A SURVEILLANCE CENTER

The present invention relates to an information exchange system between vehicles and a monitoring center assigned to them.

It applies in particular, but not exclusively, to communication between transport vehicles, for example trucks, and the management center of the company to which these vehicles belong, when the latter are in the vicinity of a center depending on this management center.

In general, we know that at present trucks used for the transport of goods and which make daily delivery rounds are more and more frequently fitted with on-board processors (on-board computers). These processors receive information before their departure from the company such as for example the list of customers to deliver, the nature of the deliveries. They then memorize, during the tour, information such as for example the time at which the delivery was made, the duration of the delivery, etc. When the truck returns to the management center, the information stored at the course of the tour are transmitted for processing to the computer system of the management center.

Usually, the information to be transferred is voluminous and requires specialized procedures. For this purpose, the company has different solutions, consisting for example of using: a smart card system involving on the one hand, a read / write terminal installed in the monitoring center connected to the computer system of the management center and, on the other hand, a terminal of the same type forming part of the computer system on board the truck, - a portable computer, of the PDA type, a cellular telephone device, for example of the GSM type, means of transmission by radio wave, for example high frequency waves, these means being able to involve, at the level of the monitoring center, an HF transmitter / receiver terminal, connected to the management center for example by wire connection and arranged at a fixed point, for example at the fuel distribution station; in this case, the trucks are fitted with HF transmitters / receivers or equivalent, the driver will then temporarily stop the truck to allow automatic transfer of information to the management center via the terminal of the monitoring center, networks wireless, for example, conforming to the "BLUE TOOTH" standard in which the entities of the network can be successively master or slave.

It turns out that these different solutions have many drawbacks such as fragility, cost, lack of flexibility.

In particular, HF radio transmission involves the use of a fixed device at the surveillance center, the HF terminal (s) constituting the only entry point (s) / output to the computer system of the management center. A drawback of this solution is that, when an HF terminal of the monitoring center is mobilized by an exchange with a truck, the other trucks must wait for the end of the exchange to communicate in turn. This limit is not lifted by the simple installation of other HF terminals in the monitoring center. Indeed, using current techniques the presence of a large number of trucks communicating in the same perimeter causes (using current techniques) interference disrupting the system.

Another drawback of this solution consists in that in the event of a breakdown of the terminal of the monitoring center and / or of the link system which connects it to the computer system of the management center, communications are permanently interrupted.

Another drawback of this solution is that loading the data, in the management center / vehicle direction, requires that the vehicle park near a terminal of the surveillance center before leaving this center. This is an important constraint for drivers and therefore a random solution in terms of efficiency.

In the case of HF radio transfers, increasing the range of emissions is also not a satisfactory solution.

In fact, unlike what happens with a wired network (where when a communication between two points is established to perform a transfer, this communication cannot be disturbed by other transfer requests) in a network wirelessly, a receiver remains subject to any radio signal reaching it in its frequency range, so that an established communication can be disturbed permanently. The "anti-collision" or multi-frequency systems which could be used to reduce, or even eliminate these drawbacks, remain for the moment too expensive.

With regard to systems using the "BLUE TOOTH" standard, these systems which involve networks which are simpler to implement than the usual systems, have the following drawbacks: - before being used, an element must be declared beforehand to the other elements of the system, which permanently memorize its identity,

- the number of elements of a given network is limited, - the distance between two elements which transfer information between them is limited.

The invention therefore more particularly aims to eliminate all these drawbacks.

To this end, it offers a system for exchanging information between a vehicle and a computer system for the management and processing of a surveillance center, within a specific geographical area situated around the surveillance center. and in which a plurality of vehicles are usually present at varying locations.

According to the invention, this system is characterized in that:

the vehicles each comprise an on-board radio transmission / reception terminal of deliberately limited range much smaller than the dimensions of said zone, this terminal comprising means of identification and / or positioning, composition of requests and constitution of the route, with a view to establishing connections with the surveillance center, these requests containing vehicle identification and positioning data, as well as vehicle-specific data transmission means when a connection has been established,

the surveillance center comprises a plurality of central terminals directly connected to the computer system of the surveillance center, these central terminals comprising transmission / reception means matched to those of the vehicle terminals, - Said zone comprises a plurality of peripheral terminals of the same type as the on-board terminals, but arranged in fixed locations suitably chosen from said zone.

Exchanges between a vehicle terminal, hereinafter called "requesting terminal", and a destination terminal, in principle a central terminal, are then carried out according to the following protocol:

- In order to obtain a connection with the destination terminal, the requesting terminal issues a connection request with the aim of finding a data transfer path to the destination terminal.

- If the destination terminal is within radio range of the requesting terminal and is able to connect (for example if it is not in communication) the destination terminal acknowledges receipt of the request, then the requesting terminal validates this route and performs data transfer along this route.

- If the destination terminal is not directly accessible but if another terminal, for example a peripheral terminal or an on-board terminal, receives the request, this terminal, hereinafter referred to as "relay terminal", acknowledges receipt of the request at the requesting terminal at the same time as it retransmits the request, indicating its own identification and positioning data to the destination terminal and, by default, to a new relay terminal.

This process is repeated until the destination terminal is reached. The requesting terminal reconstitutes the route taken by the request to reach the destination terminal using the acknowledgments of receipt which have been forwarded to it (from relay terminals to relay terminals), then performs a data transfer along this route. Once the transfer has been made, the requesting terminal transmits an "end of transfer" message which can selectively erase in all relay terminals the data relating to the transfer made.

It can be seen that, in the system described above, all the elements used (terminals) are not necessarily specialized, each of them being able to alternately fulfill all the roles necessary for establishing and carrying out a data transfer . In addition, these elements are not permanently hierarchized (master / slave).

This system operates without any specific structure linked to data transfers and without a pre-established network plan.

In fact, when a data transfer must take place, the system begins an initial phase of discovery of the network (which varies over time). During this discovery phase, only the elements likely to intervene are identified. This discovery is made in successive stages of transmission of search requests for possible routes. When the transfer ends, the means for storing the elements erase the trace of the elements discovered.

Thus, thanks to these features, the system according to the invention has the following advantages:

- a relatively low economic cost, the transfer distances, the simultaneous number of transfers and the number of network elements, at a given time, being limitless in the context of use,

- an operation which does not impose any constraint on the drivers of the vehicles, such as the obligation of a stop station in front of an HF terminal, for data loading, before the departure of the company for example; these constraints can be difficult to enforce, - great robustness and high reliability of the network obtained: apart from a malfunction on an element of the network originating or receiving a data transfer, a failure on any element does not disturb the system, unlike what can occur in a fixed structure wireless network; here, the network is built for each transfer need, by automatically detecting what are the means of the moment that are actually available; due to the lack of hierarchy, a transfer route may be established even in the case where a part of the terminals located in the geographical area is faulty (provided that there is a sufficient number of valid terminals),

- simplicity of implementation of a new terminal, the system does not require prior declaration to the other terminals present.

Embodiments of the invention will be described below, by way of nonlimiting examples, with reference to the appended drawings in which:

Figure 1 is a schematic representation for illustrating the principle of the system according to the invention.

FIG. 2 is a block diagram of the circuits for circulating data by HF radio transmission or by the GSM telephone network, between a vehicle, a peripheral terminal and a central terminal.

Figure 3 shows the processing and storage means available at a terminal fitted to a vehicle.

Figures 4 and 5 are schematic representations of the processing and storage means available at a peripheral terminal and a central terminal. FIG. 6 illustrates the operating principle of the storage means, for a vehicle terminal, for a peripheral terminal and for a central terminal.

FIG. 7 illustrates a variant of the system in which the path search area is reduced.

In the example illustrated in FIG. 1, the rectangular block 1 represents the perimeter of a determined geographical area surrounding a surveillance center (block 2), equipped with a computer processing system (block 3) to which terminals are connected fixed central units B ₅ , B ₆ , B ₇ , B ₈ .

In this geographical area, which may consist of a parking lot for the surveillance center, vehicles or vehicles, here trucks Ci to C ₇ , equipped with mobile terminals connected to the vehicle's on-board computer can circulate or park.

Furthermore, fixed terminals, called peripheral devices B] to B ₄ are arranged at predetermined locations in the geographic area 1.

Each of the terminals Bi to B ₈ and of the terminals of the vehicles Cj to C ₇ comprises a transmitter / receiver module capable of ensuring transmission by HF waves and is provided with data storage and processing means.

Thus, as illustrated in FIGS. 3, 4 and 5, these data storage and processing means could include:

- measurement means: 30, 50, 56,

- calculation means: 31, 51, 57,

- position notification means: 32, 52, 58, - journey request notification means: 33, 53, 59,

- means of monitoring and steering transfers: 34, 54.60, - data storage means: 35, 55, 61.

In these figures, the transmitter modules are represented by blocks 13, 15 and

17.

Of course, certain means such as the calculation, measurement, etc. means can be grouped together within a computer indicated by blocks 12, 14 and 16.

The mobile terminals assigned to trucks C] to C ₇ may also include:

a means of monitoring the geographical position using for example a system of the GPS 10 (Global Positioning System) type or the like, a means of transfer, by cellular network for example, of the GSM 22 type.

Similarly, the central terminals B ₅ to B ₈ may also contain:

a cellular network transfer system, for example of the GSM 23 type, a data transfer system 18 with the processing system 3 of the monitoring center 2.

The range of the transmitter / receiver modules is deliberately limited so as to avoid interference and interference phenomena as much as possible.

Consequently, in most cases, data transfers between the mobile terminals assigned to the trucks Ci to C ₇ and the central terminals B ₅ to B ₈ can only be carried out via relay terminals which may consist of mobile truck terminals Ci to C ₇ or to peripheral terminals Bi to B ₄ . Between each requesting terminal (who wants to make a transfer) and the destination terminal, usually a central terminal B ₅ to B ₈ , the path taken by the data is called "the path". The distance between two successive terminals of a path will always be less than or equal to the range of their transmitter / receiver.

By way of example, it will be assumed that the vehicle Ci enters geographical area 1 (to go to the parking lot) and has data to be transferred to the computer system of the surveillance center. Vehicles C ₂ to C ₇ are already present in this area.

The entry of the vehicle into the zone can be detected by means of positioning means 11 and means 30 for measuring the distance between the vehicle and position 36 of the monitoring center, stored in the means of storage 35 of the same vehicle, or by any other system.

As soon as it enters zone 1, the vehicle can connect to the computer system of the surveillance center to warn it of its arrival and carry out the transfer of the digital data stored in the memory 35 of its on-board system. This information transmission takes place by wireless transfer means 13 (or GSM type transfer means 22).

Through the transfer means 13, the path request notification means 33 send a transfer request R. The purpose of this request is to discover, in the vicinity of the vehicle Ci, a data transfer path to the processing center 3.

If one of the central terminals B] to B ₈ is within the range of the transfer means 13 and is usable for a new communication, then the route is immediately established. In the example shown in Figure 1, this path may pass through the central terminal B ₅ which is the closest. The path could then consist of path 20 indicated in FIG. 2.

If no central terminal B ₅ to B ₈ is accessible, but at least one peripheral terminal Bi to B ₄ or a vehicle terminal C to C ₇ can be reached, a process of requests by successive waves is established. Thus, in the example of FIG. 1, the peripheral terminal Bj is reached by the request Ri from the vehicle C. The means of notification of the terminal Bj in turn send a transfer request to the attention of any terminal (vehicle or peripheral) present and available within the range of action of the terminal Bi. If a central terminal is reached, the route is established, otherwise the process continues step by step with each step a new terminal. In the example illustrated in FIG. 1, a path has been indicated connecting the vehicle terminal Cj to the central terminal B ₇ and passing successively through the peripheral terminal B ,, the peripheral terminal B ₂ and the vehicle terminals C ₄ , C ₅ and C ₆ .

On the one hand, it can be seen that the system according to the invention does not involve memory means permanently storing the characteristics of the various transmitter / receiver systems (central terminals, peripheral terminals, vehicle terminals) present in zone 1 and, on the other hand, that there is no pre-established transfer network.

Furthermore, the means for memorizing the terminals used by the system, namely, the means 35 for the vehicle terminals, the means 55 for the peripheral terminals and the means 61 for the central terminals store the following permanent data only (FIG. 6):

- An identifier 70, 90, 110, installed during the installation of the terminals. - Longitude / latitude pairs 71/72 - 91/92 - 111/112. On fixed terminals (peripheral terminals, central terminals) they are permanently installed during their installation. For vehicle terminals, it is the vehicle positioning system that permanently determines these torques.

- Priority information 73, 93 or 113, installed during installation and easily modifiable. This information can be used by the computing means to define the optimum path.

Initially, all the other storage locations are empty and, in particular:

- locations 74, 94, 114 which are spaces intended to store information concerning the terminals located downstream of the terminal in question, on the transfer path,

- the locations 81, 101, 121 which are spaces intended to store information concerning the terminals located upstream of the terminal considered, on the transfer path.

The process of establishing the route from the vehicle terminal C] to the central terminal B ₇ will be described more precisely below.

At the time of the issuance of a request R _ls by the terminal of the vehicle Ci, the availability indicator 88 of this terminal is set to a value representative of a "origin / unavailable terminal" state. Similarly, the indicator 108 of the peripheral terminal Bj is positioned on the "unavailable" state at the time of receipt of the notification sent by the terminal of the vehicle C].

Following this reception, the notification means 53 of the peripheral terminal B] return to the vehicle terminal Ci an acknowledgment message containing its coordinates 90, 91, 92 and its priority characteristic. These data are stored by the storage means 35 of the terminal of the vehicle C] in a list 75 of the terminals 76 of the journey in progress. The coordinate 90 is stored in the box labeled 77, coordinate 91 in box 78, coordinate 92 in box 79 and coordinate 93 in box 80.

Then, the peripheral terminal Bi transmits in its turn, via its path request notification means 53, a request intended to find a terminal located downstream, in the direction of the final objectives constituted by the central terminals B _s to B ₈ .

In this example, it is the peripheral terminal B ₂ which receives the request and which, by a process similar to the previous one, transmits to the peripheral terminal B], thanks to its wireless transfer means 15, the characteristics 90, 91, 92, 93 of this terminal B ₂ . The indicator 108 of terminal B ₂ is then positioned on the "unavailable" state.

The characteristics 90 to 93 of the terminal B ₂ are stored in a list 95 of the storage means 55 of the peripheral terminal B] which includes all the terminals 26 downstream of the terminal Bj. The characteristic 90 of the terminal B ₂ is stored in the box labeled 97, the characteristic 91, in the box 98, the characteristic 92 in the box 99 and the characteristic 93 in the box 100.

The wireless transfer means 15 of the terminal B] transmit in turn to the terminal which is located upstream, here the vehicle terminal, the characteristics of the terminal B ₂ which have just been stored in the list 95 of the points 96 which have just been stored. In the terminal of the vehicle Ci, this data is stored in the list 75 of the points 76 of the journey in progress.

It therefore turns out that at each terminal, the system implemented stores the permanent characteristics of all the terminals located downstream in the current route. Thus, the vehicle terminal stores the characteristics of terminals B], B ₂ , C ₄ , C ₅ , C ₆ , and B ₇ . Terminal B] stores that of terminals B ₂ , C ₄ , C ₅ , C ₆ , B ₇ etc ...

Several lists 75 of path terminals 76 are provided because the establishment method used can construct, from the terminal considered, several downstream paths.

These downstream paths are grouped into homogeneous storage blocks 74, 94, 114, storage means 35, 55, 61 of the vehicle terminals, peripheral terminals and central terminals.

Furthermore, the storage means 35, 55, 61 comprise storage blocks 81, 101, 121 in which are stored in an analogous manner all the upstream paths 82, 102, 122 which end at a determined terminal. These journeys are recorded in lists 83, 103 and 123.

The previously described process leads to three possible solutions, at the terminal of the vehicle Ci which has taken the initiative in the search for a transmission path:

- n possible routes are found,

- only one route is found,

- no route was found.

If n paths have been found, the means of calculating the terminal Ci determine the optimum path. To this end, these calculation means may take into account criteria such as the length of the paths or the priority characteristics 73, 93, 113. The vehicle terminal C] then notifies all the downstream terminals concerned that they have been retained and releases the others who become available again for the construction of another route. Their storage spaces are erased.

When a terminal of the route being set up does not find a response to its request for setting up a route, it notifies the upstream terminal of a failure alert which, step by step, leads to the vehicle terminal.

The request transmission means of the vehicle terminal Ci can then launch various actions, such as the transmission to the downstream terminals that the request phase is completed, that they must eliminate from their storage means all the stored data and become available again. for other requests (the availability indicators 88, 98, 108 being positioned on an "available" state) or on the contrary that they must remain mobilized by the journey in progress, the most downstream terminal receiving from the terminal, by the route already established, the notification to continue to search for a downstream terminal for the route, in the direction of one of the central terminals.

When a complete route has been established, the transfer tracking means 34 of the terminal of the vehicle Ci control the progress of the transfer. If an interruption occurs, they are able to restart the transfer to the terminal where this process was interrupted.

At the end of the transfer, the notification means 33 of the vehicle terminals notify an end of transfer to each terminal of the journey. Each terminal erases all the data in blocks 74, 81, 94, 101, 114, 121 and returns the availability indicators to the "available" state (88, 98, 108).

All the terminals of the route (Ci, B _t , B ₂ , C ₄ , C ₅ , C ₆ , B ₇ ) then become available again to participate in the construction of another route, initiated by example by the terminal of the vehicle C ₄ which must carry out a data transmission.

The request transmission means for making up the route of the terminal of the vehicle C ₄ (which therefore constitutes the original route terminal) had been temporarily deactivated by the request Ri of the terminal Cj (by a process leading to the setting of indicator 108 in the unavailable state). As soon as this indicator changes value, the request transmission means of the vehicle terminal C ₄ again has the possibility of playing the same role as those of the vehicle terminal Ci. When sending a request of type Ri, the indicator 88 can switch to the "origin / unavailable terminal" state.

Of course, the invention is not limited to the communication protocol previously described. Thus, this protocol can provide for a transmission process allowing the surveillance center to transmit data to a vehicle located in geographic area 1.

By way of example, the vehicle Ci which has just entered the surveillance zone and whose presence in this zone has been reported to the surveillance center will be chosen.

The monitoring center selects an available central terminal, preferably but not necessarily the closest central terminal to the vehicle and transmits a trip establishment request to peripheral terminals or vehicle terminals possibly available within its range , it being understood that the objective to be reached is the terminal of the vehicle.

If the vehicle terminal C] is immediately accessible, then the route is found and the monitoring center can transmit the data it intends to this terminal. If not, a network discovery process occurs. sets up similar to the previous one but in which the respective role of the requesting terminal and the destination terminal is reversed.

The invention is not limited to the embodiment described above. Thus, for example, the management and processing computer system could be located at a distance from the monitoring center with which it is associated, the data transfers between this management and monitoring system and the monitoring center could be ensured by any means classic (Modem, Internet).

Likewise, the system according to the invention may have means making it possible to delimit a region within which the transfer paths must be made, in order to limit the number of terminals requested for each search for a transfer path.

These means take into account the fact that each vehicle terminal has a GPS or similar location device which permanently provides its geographical position.

They imply that the fixed terminals (whether central or peripheral terminals) keep their respective geographic positions in memory.

Thus, as illustrated in FIG. 7 when a vehicle terminal Ci wants to establish a communication with a terminal Bj, for example a central terminal, before starting the protocol described above, the system determines a direct (geographic) path (here a rectilinear path) between the points Ci and Bj, then determines around this path a transmission zone outside of which the bomes whatever they are will not be retained during the determination of the transmission path. In this example, the transmission zone is delimited by two straight lines Δj, Δ ₂ passing through the terminal Ci and extending symmetrically with respect to the path Ci, Bj, forming an angle α therebetween. This angle could constitute a parameter managed in the same way as the parameters previously mentioned.

In this example, two routes have been identified within the area, namely:

- a first path Ci-X X ₃ -X -X ₅ -X ₇ -X ₉ , Bj, - a second path Ci-X ₂ -X ₆ -X ₈ -Xιo, Bj.

Boundaries such as the bollards X _{] 2} , X _{] 3} , X ₁₄ , which answered the call of Ci, are excluded from the constitution of the possible paths because they are located outside the zone.

The system can then select one of the identified routes on the basis of predetermined criteria, for example the route consuming the fewest terminals, ie Ci-X ₂ -X ₆ -X ₈ -X ₁₀ , Bj.

If no path can be found in the area, this can be enlarged for example by giving the angle α a larger value (maximum 180 °) until a path is found.

A particularity of the systems previously described consists in that the networks which they make it possible to obtain can be qualified as "destructured", "fugitive" and "volatile" for the following reasons:

- No network construction pre-exists, when either a vehicle terminal or a central terminal issues an initial request Rj for network establishment. - The only permanent data that pre-exists are the characteristics 70 to 73, 90 to 93, 110 to 113 of the different terminals, including their unique identifier 70, 90, 110. They are only stored in the terminal that they characterize. - No mapping of the terminals present is used. No terminal, in the absence of a transfer path in progress, has data stored concerning the other terminals. No terminal, or equivalent entity, is pre-designated to play a role of master in transfers. This role is temporarily assigned to the requesting terminal, vehicle or central, which takes the initiative for the transfer (origin terminal).

- The identification of the possible elements to constitute a route is only done through successive waves of requests, produced and processed by the means 33, 53, 59 of the terminals. Each request in return causes a transfer, by the downstream means, of the data characterizing these downstream terminals, with successive feedbacks until a destination terminal is reached, or the process is interrupted.

This is the reason why the network can be described as "unstructured".

In addition, a route is only constructed for the desired transfer, at a given time. As soon as the transfer is completed, or definitively interrupted, a notification is transmitted by the requesting terminal at the origin of the journey, which causes the emptying of all the storage means used. Each mobilized terminal becomes available again to establish another route. The current route has disappeared, hence the qualifier of "fugitive network".

Finally, a vehicle can move, causing the exit of its terminal from the action radii of the upstream and downstream terminals, on a path in which the vehicle terminal participates. The transfer is temporarily or permanently interrupted, so the "volatile network" management is justified.

Claims

claims

1. Information exchange system between a vehicle and a computer system of a management center, within a geographical area (block 1) located around a monitoring center (block 2) depending on the management center and in which vehicles are usually present in variable locations, characterized in that:

- The vehicles (Ci to C ₇ ) each include an on-board radio transmission / reception terminal with a range much smaller than the dimensions of said zone (block 1), this terminal comprising identification and / or positioning means, of composition requests and route creation, with a view to establishing connections with the monitoring center (block 2), these requests containing vehicle identification and positioning data, as well as data transmission means specific to the vehicle when a connection has been established,

- the surveillance center (block 2) comprises a plurality of central terminals (B ₅ to B ₈ ) directly connected to the computer system (block 3) of the surveillance center (block 2), these central terminals (B ₅ to B ₈ ) comprising transmission / reception means matched to those of the vehicle terminals (Ci to C ₇ ).

2. System according to claim 1, characterized in that said zone comprises a plurality of peripheral terminals (B] to B ₄ ) of the same type as the on-board terminals, but arranged in fixed locations suitably chosen from said zone (block 1) .

3. System according to one of claims 1 and 2, characterized in that the exchanges between a vehicle terminal (Ci to C ₇ ), hereinafter called "requesting terminal" and a destination terminal are carried out according to the following protocol :

- with a view to obtaining a connection with the destination terminal, the requesting terminal issues a connection request with the aim of finding a data transfer path to the destination terminal,

- if the destination terminal is within radio range of the requesting terminal and is able to connect (for example if it is not in communication) the receiving terminal acknowledges receipt of the request then the requesting terminal validates this route and performs a data transfer along this route,

- if the receiving terminal is not directly accessible but if another terminal, for example a peripheral terminal or an on-board terminal, receives the request, this terminal designated hereinafter "relay terminal" acknowledges receipt of the request to the requesting terminal at the same time as it retransmits the request by indicating its own identification and positioning data to the destination terminal and, by default, to a new relay terminal, this process repeating itself until the destination terminal is reached

- when the destination terminal is reached the requesting terminal reconstitutes the route taken by the request to reach the destination terminal thanks to the acknowledgments of reception which have been retransmitted to it (from relay stations to relay terminals), then performs a data transfer according to this path.

4. System according to claim 3, characterized in that once the transfer has been carried out, the requesting terminal transmits a message "end of transfer" which erases in all the relay terminals the data relating to the transfer carried out.

5. System according to one of the preceding claims, characterized in that each of the terminals comprises an availability indicator (88), this indicator passing to the "origin home unavailable" state when it issues a request for establishment of path.

6. System according to claim 5, characterized in that the availability indicator (88) of a boom goes to the "unavailable" state when the boom receives a path establishment request from another boom.

7. System according to one of the preceding claims, characterized in that the storage means (35, 55, 61) of the bomes that it uses contain the following permanent data:

- an identifier (70, 90, 110) installed during the installation of the terminals,

- longitude / latitude pairs (71/72 - 91/92 - 111/112) permanently installed on fixed bollards and permanently determined by a positioning system in the case of vehicle bollards,

- priority information (73, 93, 113) installed during installation and usable to define an optimum route in the case where several routes have been determined.

8. System according to one of the preceding claims, characterized in that the storage means (35, 55, 61) comprise initially empty locations, namely:

- the locations (74, 94, 114) which are spaces intended to store information concerning the bomes located downstream of the terminal in question, on the transfer path, - the locations (81, 101, 121) which are spaces intended to store information concerning the terminals located upstream of the terminal considered, on the transfer path.

9. System according to one of the preceding claims, characterized in that the aforesaid acknowledgment message sent by a terminal contains the coordinates (90, 91, 92) of this terminal and its priority characteristic.

10. System according to one of the preceding claims, characterized in that, following the emission of a request, each terminal carries out a storage of the permanent characteristics of all the terminals located downstream in the current path.

11. System according to one of the preceding claims, characterized in that the above storage means are capable of storing the permanent characteristics of several lists of terminals corresponding to different routes.

12. System according to one of the preceding claims, characterized in that in the case where several paths have been found, the requesting terminal selects an optimum path, notifies all the terminals of this selected path that they are retained and releases the other booms which become available again for the construction of another route.

13. System according to one of the preceding claims, characterized in that when a bome of a route being formed does not find a response to its request for constituting a path, it notifies the upstream boom an alert of failure which, step by step, leads to the requesting boom.

14. System according to one of the preceding claims, characterized in that it comprises means making it possible to signal the entry of a vehicle carrying a boom in the said zone.

15. The system as claimed in claim 14, characterized in that, in order to transmit information to the destination vehicle terminal present in the above zone (block 1), it selects a central terminal (B ₅ to B ₈ ) available and transmits a request to establish a route to the bomes available within its range, in that, in the case where the bome of this vehicle (C to C ₇ ) is immediately accessible, the monitoring center (2) transmits the data it intends for this receiving terminal, and in that, if this is not the case, it initiates a discovery process using the aforementioned protocol.

16. System according to one of the preceding claims, characterized in that it comprises means making it possible to delimit a region inside which the transfer paths must be carried out.

17. System according to claim 16, characterized in that, prior to the implementation of the above protocol, it determines a direct path (Ci - Bj) connecting the requesting terminal (Ci) and the receiving terminal (Bj) and then determines around of this path a transmission zone outside of which the terminals are not retained when determining the transmission path.

18. The system as claimed in claim 17, characterized in that the aforesaid zone is delimited by two straight lines (Δ _l5 Δ ₂ ) passing through the request terminal and extending symmetrically with respect to the path, forming between them a determined angle (α) .

19. System according to one of the preceding claims, characterized in that, if no path is found in the above zone, this zone is enlarged until a path is found.