FR2556536A1 - Method of asynchronous communication of digital information in a ring, and distributed processing device using this method - Google Patents

Abstract

Ths subject of the present invention is an asynchronous device for distributed processing of information and for communication, having a ring structure. It includes a set of stations S, each centralising a certain number of items of equipment Eq; each station is joined to the next by at least one ring-like information transmission path A. Each station S provides for the processing of information, its transmission over the ring A, its routing and its distribution to the various items of equipment Eq to which it is connected. The opportunity for transmission is distributed among the stations; at any instant a single station is transmitting, the others receiving.

Description

ASYNCHRONOUS RING COMMUNICATION METHOD
DIGITAL INFORMATION, AND DEVICE FOR
DISTRIBUTED TREATMENT USING THIS PROCESS
The present invention relates to a method of asynchronous ring communication of digital information and a distributed information processing device using this method.

 When there is a plurality of equipment in one place, fixed or mobile, implemented within the framework of the same application, there is a problem of interconnection of this equipment and a problem of managing exchanges on the interconnection network, as well as that of the operational safety of the whole.

 It is known to solve these problems using a centralized structure system, in which there is a so-called "master" unit which controls the exchanges between the various pieces of equipment, generally called "slaves", and which checks their operation. The drawbacks of such a system are twofold: firstly, centralization causes a bottleneck effect limiting the flow of information over the entire system, then a breakdown of the single "master" unit leads to the breakdown of the entire system.

 The present invention relates to a method and a device ensuring both the communication of information between different pieces of equipment and their processing, which makes it possible to avoid the above drawbacks thanks to a decentralized structure.

 To this end, the device comprises a set of stations, the equipment being linked to the stations and each of the stations being joined to the next by one or more ring-shaped information transmission channels; each station ensures the processing of information, its transmission on the ring, its routing and its distribution to the various equipment to which it is finally connected, each station is capable of taking turns in transmitting function, the other stations then being all receptive.

 In the present description, the term "ring" means a transmission channel connecting the various stations in cascade, and closing in on itself.

More specifically, the subject of the invention is a distributed processing and information communication device, comprising a plurality of equipment, a plurality of stations to which the equipment is connected, each of the stations being connected to the next by at least one unidirectional ring-shaped information transmission channel, each station comprising:
- means of interface with the equipment;
- transmission means, ensuring a first formatting of the information provided by the equipment and its routing;
- Coupling means with the ring, ensuring a second formatting of the information provided by the transmission means and their transmission on the ring, as well as their reception;
means for receiving information circulating on the ring via the coupling means, ensuring their distribution inside the station and to the equipment to which it is connected.

The invention also relates to an asynchronous information communication method, the information being provided by a plurality of equipment, the equipment being connected to a plurality of stations, each of the stations being connected to the next by at least one channel. for unidirectional transmission of ring-shaped information the method comprises the following steps:
- the emission, by a first station having the right to transmit, of at least one set of information;
- the proposal by the first station for the right to transmit in the form of proposal information circulating on the ring;
- the reception of this information of proposal by a second station, which is in condition to transmit another set of information, and the transformation of this information of proposal into information of application for the right to transmit, having the effect of '' prohibit any transmission to any station in the ring other than the first or second;
- receipt by the first station of this application information and its transformation for the first station into transmission authorization at the address of the second station;
- the reception by the second station of the previous authorization and the transmission by the second station of its set of information.

Other objects, features and results will emerge from the following description, given by way of nonlimiting example and illustrated by the appended drawings, which represent:
- Figure 1, the general diagram of the device according to the invention;
- Figure 2, an embodiment of a station used in the device according to the invention;
- Figures 3, a and b, the operating process on transmission and reception of the station of Figure 2;
- Figure 4, a and b, examples of information formats usable in the device according to the invention;
- Figure 5, an embodiment of the device according to the invention;
- Figure 6, a, b, c and d, examples of service information formats usable in the device according to the invention
- Figure 7, a practical embodiment of a station used in the device according to the invention
- Figure 8, another embodiment of a station used in the device according to the invention
- Figure 9, another embodiment of the device according to the invention.

 In these different figures, the same references relate to the same elements.

 In Figure 1, there is therefore shown the general diagram of the device according to the invention.

 This concerns systems comprising a certain number of items of equipment marked Eq. This equipment can be, for example, computers, radar systems, command and control consoles for television cameras, laser viewfinders, etc. They are capable of transmitting and receiving information, possibly via sensors (not shown) in terms of reception.

According to the invention, these items of equipment Eq are combined with at least one of n stations S. By way of example, the stations S1 to S4, Si and Si + 1 are shown in the figure, as well as the last station sn equipment, such as for example the equipment marked EqO in the figure, can be combined at several stations (at stations S2 and S3 in this example). Stations can have a variable number of devices, some of which may not even be linked to any device, such as the station
S. in the figure.

 The different stations are linked together by a transmission channel A of any type, connecting each station unidirectionally to the next and thus forming a ring.

In an alternative embodiment, not shown in Figure 1, the stations can be connected by two (or more) transmission channels, always according to the same ring principle. It should be noted, as will be shown below, that the operations of the rings are completely independent of each other, the stations S may not even be in the same order from a ring to
The other.

 FIG. 2 shows an embodiment of a station S, connected to 2 pieces of equipment Eqa, Eq ... Eqp and, by way of example, two rings A1 and A2.

The station S proper comprises:
- a set of interfaces la, Ib ..lp ensuring the reception of the signals coming from the equipment Eqa ... Eq; there is generally an interface I per equipment Eq connected to the station S, but this is not compulsory; - a set of operators F (fl ... fi fk) fk) suscep to execute a certain number of predefined treatments on information or. data;
- transmitting means E;
- receiving means R;
- a circuit called transmission loop BE1 and a circuit called reception loop BR1 connected to each other and ensuring coupling with the ring A1
- CC1 short-circuit means, making it possible to short-circuit the station with respect to the ring A1;
- BE2 transmit loop and BR2 receive loop coupling circuits, as well as CC2 short-circuit means, relating to the ring A2.

 The operation of such a station for transmitting information in a ring (A1 for example) is explained below with reference also to FIG. 3a.

In a first step (marked 11 in FIG. 3a), the interfaces I acquire the "message (s)" coming from the equipment
Eq, either by periodic scanning or upon arrival of an event.

 In parallel, in a step marked 12 (FIG. 3a), the station S performs data processing by means of its set of operators F.

 All these results, coming from the equipment Eq or from the operators F, are supplied to the transmitter circuit E as indicated by arrows, 21 and 22 respectively, illustrating the movements of information relationship. Depending on whether the destination of the result of the processing or of information from the equipment is local or not, the rest of the processing in the station S differs (test marked 13 in FIG. 3a).

If the destination is local, that is to say that the information is intended for the set of operators F of the station or the equipment
Eq to which the station is connected, the message is transmitted to the receiver R (arrow 24) which ensures its local broadcast either to the ion of the set operators F (arrow 51), or to the interfaces I (arrow 50) intended for equipment Eq. This is step 14 in Figure 3a.

 If the message is not intended for the station but for the ring A1, the message or messages received by the transmitter E is transformed into one or more "packets" by this transmitter (step 15 in FIG. 3a).

 Figure 4a shows an example packet format.

A packet contains the data (area 59) constituting a fraction of a message, an entire message or several messages. They are for example expressed on a variable number of bytes and proceeded by:
a zone 54 making it possible to identify the origin of the data: an equipment or an operator of the set F, long for example of one byte;
a zone 55 indicating the number of the message to which the data of zone 56 belongs, number for example expressed on a byte;
an area 56, used when the message is divided into several packets, indicating the message element number and making it possible to reconstitute the entire message on arrival, this number can for example also be expressed on a byte;
- a zone 57 making it possible to number the successive packets (for example a byte) ;;
- a zone 58 containing a qualifier, allowing a classification in order of importance of the packets (packets to be repeated, single packets not to be lost, etc.) s the qualifier is possibly defined by default.

 In the case where the packet has a length which is not predefined, it is necessary to add to it a zone (not shown) containing the indication of its length.

The packet thus formed is transmitted to the transmission loop circuit
BE1, accompanied by the addresses of the destination stations determined by the transmitter E, in order to transform the packet into a "frame" (step 16, FIG. 3a).

 FIG. 4b represents an example of the format of such a data frame, of the HDLC type.

 This frame begins with a flag 41, expressed for example on a byte. Behind the flag 41 at the start of the frame is placed the address or addresses of the destination stations (area 42), expressed in one or more bytes. Behind the address, there is placed (area 43) a command indicating the nature of the frame considered, which can be a data frame as in the present case or a service frame as described below; this command is expressed for example on a byte. Then there is an area 44 reserved for the information itself, that is to say the packet, followed by an area 4i used for error detection, for example using a code called CRC ( cyclic redundant code) making for example two bytes. A flag 46 expressed for example on a byte ends the frame.

Such a frame is then likely to be transmitted on the ring
A1 on condition that the station considered then has the right to transmit on this ring what is represented by a test 17 in FIG. 3a.

This right to transmit is transmitted from station to station according to a process described below, in relation to FIG. 5. If so, the transmission takes place (step 18).

 The frame transmitted by the circuit BE1 is received (step 19) after the entire ring A1 has passed through the reception circuit BR1.

 It is then transmitted (arrow 25) to a control unit C1 which checks (step 20) the conformity of the received frame.

 The operation of a receiving station S is described in connection with FIG. 3b.

 The station S therefore receives a data frame from one of the rings, for example A2, which is illustrated by step 31 of FIG. 3b. At this time, two cases are possible the station S considered may or may not be the recipient of this frame, this is what is represented by test 32, corresponding to a decoding of the address appearing in the frame (area 42, Figure 4b) by circuit BR2.

 If the station S is not a recipient, the frame received is retransmitted as it is in the ring by the circuit Bye2, which is represented in FIG. 2 by an arrow 52 and constitutes step 35 of FIG. 3b.

 Otherwise, when the station S is the recipient of the frame, it is controlled by the reception loop BR2 (step 33 in FIG. 3b), then simultaneously transmitted to the transmission loop BE2 for the purpose of retransmission (arrow 52) and transmitted to the receiver R (arrow 53) for the purpose of local broadcasting, the receiver R determining the addresses of the equipment Eq, via the interfaces I, and of the operators of the set F (arrow 50 and 51) respectively.

 FIG. 5 represents an embodiment of the device according to the invention, comprising a certain number of stations such as S, for example six stations marked S1 to S6, connected in series by one or more rings, for example two marked A1 and A2 in the order S1, S2, S4, S3, Sg, S6 for the ring A2 and S1, 52 '54, S5, S6 for the ring A1 by way of example. Each station is connected to equipment Eq to EqpX index 1 to 6 respectively p for stations S1 to S6, it being understood that the number (p) of equipment is not necessarily the same from one statiDn to another . These stations have a general structure identical to that described in FIG. 2, it being understood that the number of interfaces is not necessarily the same from one station to another: it indeed depends on the number of devices and, moreover, a given piece of equipment can be connected to two stations7 as shown for example for the Eqal equipment connected both to station S1 (lal interface) and to station S2 (interface Ip2). Likewise, the number of functions capable of being executed by the sets F is variable from one station to another.

At a given instant, each of the stations of the device can be in one of the following four states, and this for each of the rings:
- the station can be a transmitter on a ring;
- the station can be a receiver on a ring;
- The station can be "on" for a ring, when the frame it receives in its reception loop circuit BR does not contain its address and is retransmitted by its transmission loop circuit BE without control or duplication;
- A station can be short-circuited by a ring when, following a decision and a failure, this station cannot use the ring considered, the frames then passing through the corresponding CC circuit.

In the example of FIG. 5, we have represented:
- the station S1 transmitting on the ring A2 and passing on the ring A1
- the station S2 passing on the ring A1 and receiving on the loop A2;
- the station S3 transmitting on ring A1 and receiving on ring A2;
- the receiving station S4 on the ring A1 and short-circuited on Panel A
- the receiving S5 station on the two rings
- the station S6 passing on the two rings.

 For each of the stations, the flow of information between these different units has been illustrated by arrows.

 The operation of the device of Figure 5 is as follows.

 The station Sj has for example the right to transmit on the ring A2.

The frame sent by the station S1 passes from station to station, each of them recognizing or not its own address. This frame returns to the transmitting station, in this case S1, which checks (circuit C21) that the frame has not been altered during circulation on the ring A2. A It should be noted that then only station S is a transmitter, the other stations being receivers.

 The operation of the device of FIG. 5, as regards the transmission of the right to transmit, is as follows.

 The right to transmit which owns a station is a right to transmit a maximum number of data frames. In one embodiment, this number is equal to one and the data frame is followed by a service frame, proposing the right to transmit to the other stations. An example of format for the proposal frame of the right to be transmitted is given in Figure 6a.

This proposal frame differs from the data frame in Figure 4b only in the following points:
the address zone 42 contains a particular code, expressed for example on a byte, signifying that the frame is of general broadcasting, all the stations being recipients thereof;
- the control area 43 indicates that it is a frame for proposing the right to be issued;
- the area 47, replacing the data area 44 of the frame of FIG. 4b, contains as many bits as there are stations in the system, possibly rounded up to the next byte; each station receiving this frame acknowledges receipt of the previous data frame by changing the state of the bit assigned to it in area 47.

 The first station after station S1, in the direction of circulation of information on the ring, which is ready to transmit a frame, for example station S4, modifies the proposal frame to transform it into an application frame. This modification consists in transforming the command area 43, which then indicates that it is an application frame, and in adding an additional area, for example before the error detection area 45, containing the address of the candidate station (S4), for example on a byte. Such an application frame is for example represented in FIG. 6b where the additional address area bears the reference 48. I1 appears as well as the stations located after the candidate station S4 can no longer apply for the right to broadcast, since they do not receive a proposal frame.

Any conflict is thus avoided.

 In order to make the transmission of the right to transmit from station S1 to station 54 more secure, and to avoid any incident in the event that one of these stations has a failure during transmission, in an alternative embodiment, a a number of additional steps are planned before the station S4 can actually transmit.

First of all, a monitoring station is defined which is the station which was a transmitter before station S12, for example station 56; station S1 then tracks another service frame at both stations S4 and S6, indicating that the right to transmit is transmitted to station S4. This last frame has for example the form indicated in FIG. 6c, where the general frame structure of FIG. 4b is found, but where
- the recipient address area 42 contains the addresses of the candidate station (S4) and of the monitoring station
- the data zone (44) is replaced by a zone 49 containing the addresses of the station S1 and of the monitoring station
- the control area 43 indicates the nature of the frame.

 After transmission of this last frame, station S1 becomes a monitoring station. On receipt of this frame, the previously monitoring station (S63 becomes again a simple receiving station.

 Finally, to cover certain possibilities of failure, on reception of this frame, the station S4 transmits to the former monitoring station (56) a frame indicating that it has become a transmitting station. This last frame has the form indicated in FIG. 6d: it is simplified compared to the previous ones by the fact that it does not include a given area, the control area 43, indicating the nature of the frame, being followed directly by the area 45 error detection.

 When no station has a frame ready to be transmitted and does not apply for the right to transmit, the corresponding proposal circulates permanently on the loop considered.

 According to the procedure described above, it appears that the right to transmit therefore passes from station to station, without possible conflict. In addition, it appears from the above that no blocking is possible, in fact, the number of data frames that a single station can transmit is limited, and the right to transmit is then systematically offered to the following stations on the ring: the transmission opportunity is thus equally distributed among all the stations. It should be noted that this right to transmit is not materialized by a signal held by the station which has this right.

 In the initialization phase, the device in FIG. 5 operates as follows.

 At power-up, each of the stations self-tests, tests the interfaces I of the equipment Eq, possibly acquires the results of the equipment tests and tests the BE and BR circuits for coupling on the rings. If the station considered considers itself incapable of operating on one or more rings, it does not connect to it.

If on the contrary it considers itself capable of operating on at least one ring, it prepares a frame for this ring, containing state information which represents the result of the previous tests, connects to the ring in question and waits for have the right to transmit to transmit its status information.

 In all the equipment to which the stations are connected, there is system supervision equipment, which is privileged and is connected to a station which itself becomes privileged. During initialization, this privileged station performs the following operations: as before, it self-tests, it gives its status to the supervision equipment and, after connection to the rings, sends a frame without destination on each of the rings.

 At that time, on the two rings, the other stations successively take the right to transmit according to the process described above, send the results of their tests to the preferred station and propose the right to transmit to the next station.

When, on a ring, the right to transmit has returned to the privileged station, the latter has received all the results of the tests of which it makes a summary which it transmits to the supervision equipment; finally, the privileged station sends on each of the rings, either a frame containing a useful message followed by a proposal for the right to transmit, or directly a proposal for the right to transmit.

 It should be noted that in this structure, from initialization, the rings are desynchronized: indeed, the frames without addressee are not necessarily transmitted at the same times, the circulation times on the two a. differ according to the state of the stations and the results of the tests do not necessarily return at the same time on the two a. ; finally, the useful traffic is not necessarily identical on the two a.

 FIG. 7 represents a practical embodiment of a station used in the system according to the invention.

The different interfaces Ia ... Ip of the station are all connected to a common bus 74, to which are also connected:
a central unit 70, for example produced using a microprocessor;
- a memory 71;
- as many access units, or couplings as there are rings in the system, namely here two units 72 and 73 for the rings
A1 and A2 respectively.

 The central unit 70, in relation to the memory 71, directs and controls the exchanges between interfaces and access units to the rings, the proper functioning of the various materials of the station, and ensures the management of priorities and interruptions.

Each of the ring access units has the following components:
- a microprocessor 81 and its memory 82, whose function in particular is to manage packets and frames, connected to bus 74;
a communication controller 83, having the function of creating the frames described above and of verifying them, on command from the microprocessor 81
- an encoder 85 and a decoder 84 of the information circulating on the ring respectively receiving the information and supplying it to the controller 83
a transmission circuit 87 and a reception circuit 86, transmitting or receiving the information propagating on the ring and respectively receiving it from the encoder 85 or supplying it to the decoder 84.

 Finally, the circuits CC1 and CC2 of FIG. 2 form an interface between the ring and the transmission 87 and reception 86 circuits.

 If we refer to the functional diagram of FIG. 2, the functions of the emitter E, receiver R units and of the assembly F are generally performed by the central unit 70, in relation to its memory 71, and the functions of the units BE , BR and C by the ur.i access to a ring, 72 or 73.

On the diagram of figure 7, one indicated the three possible ways for information coming from a ring
- path marked 1: the station is out of service on the ring in question and the DC circuit short-circuits the station;
- path marked 2: it is followed by all the frames which are not modified by the station, which can thus be retransmitted on the ring with a minimum of delay
- path marked 3: it is followed by the frames which are modified by the station.

 In order to improve the operational safety of the device according to the invention, a certain number of provisions are or can be taken, such as those which are described below.

 At the level of the message, it is possible to have the consistency of the message checked by the transmitting and / or receiving station and to make it report the inconsistencies. The station can also calculate an error code or error corrector.

 At the package level, as described above (Figure 4a), the qualifier (area 58) allows acknowledgments, repetition, etc.

 At the level of the frame, the transmitting station receives its frame after it has traversed the entire ring; it then checks it using the error control zone 45, of CRC type for example.

At the station level, each of them has a set of test processes implemented by the central unit 70 (FIG. 7) allowing, either periodically or on demand, internal or external to test:
- interfaces I and possibly Eq equipment;
- the central unit 70 and its memory 71
- access units to the rings.

Equipment failure is reported to other stations and system supervision equipment. An interface failure is equivalent to an equipment failure if the equipment is connected to only one interface; otherwise, the routes of the stations concerned are modified. A breakdown of the central organs of the station can put it out of service or authorize degraded operation. In the first case, it disconnects from the rings (DC circuits); the first station which notices the impossibility of communicating with the station in fault broadcasts the information to the other stations of the system. In the second case, the station concerned informs the supervision equipment of its state.

Figure 8 shows another embodiment of a
station S of the device according to the invention, in which this station is connected to two pairs of rings.

 To this end, the station includes, as before, the elements E, F, R, BE1, BR1, CC1, BE2, BR2, CC2, but does not have an interface and is not connected to equipment; on the contrary, it comprises two other series of elements BE, BR, CC, one towards a ring A3 and the other towards a ring A4 for example.

Such a station, capable of being connected to two pairs of rings, makes it possible to produce a communications node between two systems as described in FIG. 5, as shown in FIG. 7.

 In this FIG. 7, there are three networks 61, 62, 63, such as the network of FIG. 5, connected together by two stations respectively 64 and 65 as described in FIG. 6.

 A method and a device have thus been described making it possible to establish communication between different pieces of equipment and to carry out information processing in a decentralized manner: in fact, none of the stations is master by construction, the right to transmit passing from the 'to each other; they are also flexible and modular: it is in fact possible in particular to connect any number of equipment to any number of stations, to use any number of rings, to adapt transmission security to demand.

Claims (8)

 1. A method of asynchronous communication of information, the information being supplied by a plurality of equipment, the method being characterized in that, the equipment being connected to a plurality of stations, each of the stations being connected to the next by the minus a unidirectional ring-shaped information transmission channel, it includes the following steps, for the transmission of the emission right  - remission, by a first station having the right to transmit, of at least one set of information;  - the proposal by the first station for the right to transmit in the form of proposal information circulating on the ring;  - the reception of this signal by a second station, which is in a condition to transmit another set of information, and the transformation of this information of proposal into information of application for the right to transmit, having the effect of prohibiting any broadcast at any station in the ring other than the first or second;  - receipt by the first station of this application information and its transformation by the first station into authorization to send to the address of the second station;  - receipt by the second station of the previous authorization and Remission by the second station of its set of information.  2. Method according to claim 1, characterized in that it further comprises a step of transmission by the second station of information expressing the fact that it has the right to transmit, before the transmission of its entirety of information.  3. Method according to one of the preceding claims, characterized in that the sets of information, the proposal information, applications and authorization for transmission are expressed in the form of frames whose formats are similar.  4. Method according to claim 3, characterized by the fact that said frames are of HDLC format.  5. Method according to one of the preceding claims, characterized in that the station which held the right to transmit before the first station operates a monitoring and is recipient of the information exchanged during the transmission of the transmission right.  6. A distributed processing and information communication device for the implementation of the method according to one of the preceding claims, comprising a plurality of equipment (Eq), characterized in that it comprises a plurality of stations ( S) to which the equipment is connected, each of the stations being connected to the next by at least one channel (A) for unidirectional transmission of ring-shaped information, each station comprising:  - interface means (I) with the equipment;  - transmission means (E), ensuring a first formatting of the information provided by the equipment and its routing;  - coupling means (BE, BR) with the ring ensuring a second formatting of the information provided by the transmission means and their transmission on the ring, as well as their reception;  means for receiving information circulating on the ring, via the coupling means, ensuring their distribution inside the station and to the equipment to which it is connected.  7. Device according to claim 6, characterized in that each station further comprises means ensuring a short-circuiting of the station.  8. Device according to one of claims 6 or 7, characterized in that it comprises at least one station ensuring coupling with a second ring.