FR2695782A1 - Data transmission between networks with different protocols - having first frame with data fields and integrity check field for data fields, and converting bit by bit to second field - Google Patents

Abstract

The data transmission method involves sending data via an interface (10) from a first network (1), using a first protocol e.g. Ethernet and connected to receiving equipment (20, 32) across a second network (40) using a second protocol e.g. high data link control (HDLC). The protocol date is converted bit by bit between the two networks. The receiving equipment may include a second interface (20) for converting back to the first protocol for reception at the first network receiving equipment (32). The interface converter has a buffer memory, which is written to and read from at different rates according to the protocols. For Ethernet and HDLC protocols, a decoder receives fields according to Manchester codes, and transmits to the converter according to no return to zero (NRZ) codes. USE/ADVANTAGE - Interconnection of local networks. Simpler converter. Second network receiver can demand retransmission of data from partic. transmitter if fault is detected.

Description

Data transmission method between networks
with heterogeneous protocols and converters
protocol for implementing the method.

The present invention relates to a method of transmitting data between a transmitting device, connected to a first data transmission network according to a first protocol providing a frame comprising a first field of data bits and an associated field of integrity check bits data of the first field, and a receiving device connected to the first network through a second data transmission network according to a second protocol providing a frame comprising a second field of data bits, and, if necessary, the bit rates of transmission of the two networks.

Such a method is used to establish a logical gateway between local networks with incompatible protocols and thus allows communications between the devices connected to these local networks. Likewise, it makes it possible to connect remote local networks, with identical protocols, for example of the type of the registered mark.
ETHERNET, through a public network having a protocol incompatible with them, for example the HDLC protocol (High Data Link Control ").

In the latter case, it is known to convert the network data into "input" on the public network.
ETHERNET which are in packet mode and present them in circuit mode to the HDLC network.

To comply with the HDLC protocol standard, a control code word (CRC2) is calculated and transmitted, from all the bits of the packet, i.e. data to be transmitted, addresses of the sending and receiving devices. and a code word for checking the integrity of the packet (CRC1) which has been calculated by the sending device of the ETHERNET network.

This respect for the standard of the protocol used in the second network, HDLC in this example, seemed, until now, to be a sine qua non condition for correctly transmitting the data there, since the protocol provides for all possible situations and treats remedies for abnormal situations.

This "security" has the drawback, however, of requiring large and complex software which, in order not to slow down the transmission rate, must be implemented by specific rapid components, such as integrated circuits. However, although integrated, these circuits are, by their complexity, relatively expensive. In addition, in the event of a problem when connecting two networks, their hardware and software complexity does not make it easier to locate the problem.

The present invention aims to overcome these drawbacks.

To this end, the present invention firstly relates to a method of transmitting data between a transmitting device, connected to a first data transmission network according to a first protocol providing for a frame comprising a first field of data bits and a field associated with data integrity check bits of the first field, and a receiving device connected to the first network through a second data transmission network according to a second protocol providing a frame comprising a second field of data bits, and, the if necessary, the transmission rates of the two networks are adapted, a process characterized in that, at the interface between the two networks, the bits of the first field and of the associated control field are converted exclusively into bits of the second field which are recognized by the receiving device and from which it extracts the data bits of the first field.

Finally, the plaintiff realized that the calculation of the code word (CRC2) in the second network was a heavy constraint, as for the hardware and software complexity of the conversion, and that one could do without it. In this respect, it went against the prejudice mentioned. As there is already a code word (CRC1) protecting the transmission in the first network, the addition of another code word (CRC2) in the second network would only serve to locate a transmission fault in this second network . It is in fact more advantageous to transmit the data from the first network transparently, with the only conversion necessary but without protecting it again.

If the receiving device, connected to the second network, detects a fault by means of the control field of the first protocol, it can request a retransmission of the data from the sending device. In other words, the second protocol serves, with minimal adaptation, as an extension to the first protocol, the first network thus having an extension link.

Advantageously, the receiving device is connected to said second network through a third data transmission network according to the first protocol.

The advantage of this implementation is to be able to assimilate, in a set of networks of the same protocol, a different protocol network to an intermediate link of this set of networks with a single protocol.

Advantageously, an HDLC protocol network is integrated into a set of ETHERNET protocol networks.

The invention also relates to a protocol converter for implementing the method of the invention, designed to be connected to a first data transmission network according to a first protocol providing a frame comprising a first field of data bits and a associated field of data integrity control bits of the first field, and to a second data transmission network according to a second protocol providing a frame comprising a second field of data bits, characterized in that it comprises means arranged to convert the bits of the first field and the associated control field exclusively into bits of the second field.

The converter, having a relatively light task, can be made much more simply than those of the prior art and, in particular, can use sequentially single logic circuits, which would have to be duplicated if its task was heavier.

Finally, the invention relates, for the implementation of the method of the invention, to a data transmission protocol converter arranged to be connected to a data transmission network according to a protocol providing for a frame comprising a global field of bits of data containing, in known positions, a primary field of data bits as well as a data integrity control bit field of the primary field, characterized in that it comprises means arranged for routing, then storing, the bits from the global field to a control bit field or to another data bit field depending on whether the bits considered occupy said known positions or not.

Indeed, although the inventive concept of the invention is unique, the two converters according to the invention can be put on the market separately and used respectively in different numbers. This is for example the case if the data receiving device receives this data, coming from the type of converter of the invention mentioned first, according to the second protocol, but does not retransmit it which allows it to not use, of the first protocol, as the part concerning the position of the data received.

Similarly, the numbers of converters of each type will be different if the data from the first type of converter is broadcast to several converters of the second type.

The invention will be better understood by means of the following description of the preferred embodiment of two protocol converters for implementing the method of the invention, with reference to the attached drawing, in which - FIG. 1 schematically represents two networks
ETHERNET connected, through the two respectively
converters of the invention, to the same network at
modified HDLC protocol, - Figure 2 shows the bit fields of a packet
ETHERNET, - Figure 3 shows a field of transmitted data
according to HDLC protocol as well as a control field
data field integrity, provided for by the
HDLC protocol and, - Figures 4 and 5 are block diagrams
representing the converters of the invention,
performing an ETHERNET / HDLC conversion respectively
modified and a modified HDLC / ETHERNET conversion.

Two networks 1 and 31, here of the same type, ETHERNET, represented in FIG. 1, are respectively connected to the input of a converter 10 from ETHERNET protocol to modified HDLC protocol (as explained below) and to the output of a converter 20 of the HDLC protocol modified into the ETHERNET protocol. The output of converter 10 is connected to the input of converter 20 by a link 40 of a data transmission network according to the HDLC protocol.

To the networks 1 and 31 are respectively connected devices, here terminals, for transmitting data 2, 3, 4 and 32, 33, 34. In this example, it is not intended, by the clarity of the description, that '' a possibility of unidirectional transmission from network 1 to network 31.

It will be recalled that the ETHERNET protocol provides a frame 50, represented in FIG. 2, for the transmission of bit packets, at 10 Mb / s, which includes a field 51 of address of the recipient of the packet, a field 52 of address from the packet sender, a data field 53, containing the information usable by the recipient of the packet, and a field 54 for checking the integrity of fields 51, 52 and 53, containing a control code word CRC1. The package is identified by the presence of an electrical signal.

For its part, the HDLC protocol relates to a transmission in circuit mode, that is to say permanent, whether or not there is data to be transmitted. The data are transmitted in frames (60), one of which is shown very schematically in FIG. 3, comprising a field 61 of data usable by their recipient, and a field 62 of data integrity control, of field 61 , containing a CRC2 control code word. The absence of frame 60 is indicated by the presence of flags.

The modified ETHERNET / HDLC converter 10, shown in more detail in FIG. 4, has at its input an ETHERNET interface circuit 11, having the hardware and software elements of an ETHERNET interface circuit of the known type.

In response to the reception of an ETHERNET packet, the circuit 11 provides at its output the bits of the packet
ETHERNET received, here sent by terminal 2 to terminal 32, of which it has recognized the address of recipient 32.

The output of circuit 11 is only connected to the data input of a circuit 16 for managing the modified HDLC protocol, the output of which constitutes the output of circuit 10.

For the sake of simplicity of presentation, the service signals allowing the management of transmissions according to the ETHERNET and HDLC protocols, and in particular the flags for locating the limits of the bit fields, are not explained in detail here.

The circuit 16 includes the hardware and software elements of a known circuit managing the transmission of bits according to the HDLC protocol, except for the elements relating to the control field 61, the modification of the protocol.
HDLC relating to the fact that the presence of control field 61 is not foreseen. The bits of the packet, received at the input of circuit 16, are put in buffer memory 17 then sent to a circuit 18 where they are converted exclusively into bits of the data field 61 from where they are then emitted at the output of circuit 10 .

The buffer memory 17 ensures the bit rate adaptation between the bits coming from the ETHERNET network 1, at 10 Mb / s, and those sent on the HDLC network 40, here at 64 kb / s.

It will be understood that the conversion of bits received by the circuit 16 depends on the way in which each protocol plans to physically represent a bit in order, in particular, to allow or not to transmit, implicitly with the data bits, a clock signal facilitating the reception of these bits.

Likewise if, contrary to the present description, the bits were, in a protocol, coded by contiguous blocks, they could be converted into other blocks, with different coding and possibly of different length.

In the present example, the bits received by the converter 10 from the ETHERNET network 1 are coded according to the MANCHESTER code, which allows the transmission of a clock signal. Circuit 11 includes a transcoder 12 which receives the bits of the packet, coming from the input of circuit 11, and transforms each bit received into a bit presented according to the code No Return to Zero (NRZ), code according to which circuit 16 receives the bits of the ETHERNET packet.

The modified HDLC / ETHERNET converter 20, represented in FIG. 5, has at its input an interface circuit 21, consisting of the hardware and software elements of a known circuit managing the reception of bits according to the HDLC protocol, except the elements relating to the control field 62. The output of circuit 21 is connected to the input of circuit 22 which includes a buffer memory 23, here a shift register, receiving the data bits of field 61, coming from circuit 21, as well as 'a switching logic 24 connected to the output of the register 23. The role of the register 23 is to temporarily store the bits of a packet while waiting for their transmission to the network 31. Its capacity is adapted to the number of messages, more precisely of bits, which it is planned to store temporarily. In this example, the instantaneous speed on the ETHERNET network 31 is higher than that of the HDLC network 40, so that the register 23 allows the adaptation, here increase, of instantaneous speed by ensuring that the whole of a packet is available before its transmission on the network 31.

The switching logic 24 includes a comparator (not shown), having in memory the position of the fields
ETHERNET, which is connected as an input to the output of register 23 and directs the bits leaving register 23 to one of four memories 25, 26, 27 and 28 according to the last flag it recognized and which announced the start of one of the four fields 51, 52, 53 and 54.

The memories 25, 26, 27 and 28 respectively receive the ETHERNET fields 51, 52, 53 and 54, conveyed in the global field 61 HDLC, which are then transmitted on the ETHERNET network 31, by an interface circuit 29
ETHERNET of known type, to be received there by the destination terminal 32.

It will be understood that the size of the four ETHERNET fields 51, 52, 53 and 54 is in no way limited by that of the field 61 of HDLC data, since a set of data to be transmitted, here an ETHERNET packet, can occupy less than 'a field 61 or be distributed over several fields 61, the presentation of which adjoining the output of the circuit 21 restores the unity of all the data transported.

It will also be noted that the presence of memories 25, 26, 27 and 28, and not of a single memory containing all the bits of the ETHERNET packet originating from terminal 2, is only necessary in the case where the content of one or several of the four fields 51, 52, 53 and 54 must be used, which is the case if a data integrity check is carried out at this level of the transmission chain, starting from the code word CRC1 of field 54.

This would in particular be the case if the network 31 were non-existent, the receiving terminal 32 then comprising the transcoder 20, in this case devoid of the circuit 29 of the ETHERNET interface.

In the general case, where a possibility of transmission in one direction or the other is desired between the networks 1 and 31, it is then respectively added to the transcoders 10 and 20, preferably in an integrated manner with these, transcoders having the function of transcoders 20 and 10.

Claims (10)

1. Method of transmitting data between a device  transmitter (2), connected to a first network (1) of  data transmission according to a first protocol  providing a frame (50) comprising a first field  (51, 52, 53) of data bits and an associated field  (54) data integrity check bits of the  first field (51, 52, 53), and a receiving device  (20, 32) connected to the first network (1) through a  second data transmission network (40) according to  a second protocol providing a frame (60)  comprising a second field (61) of data bits,  and, if necessary, the flow rates of  transmission of the two networks, characterized process  by the fact that at the interface (10) between the two  networks (1.40), we convert the bits of the first  field (51, 52, 53) and the associated control field  (54) exclusively in bit of the second field (61) which  are recognized by the receiving device (20, 32) and at  from which it extracts the data bits from the  first field (51, 52, 53). 2. Transmission method according to claim 1,  in which the receiving device (32) is connected to said audit  second network (40) through a third network  (31) data transmission according to the first  protocol. 3. Method according to one of claims 1 and 2, in  which the first protocol is the ETHERNET protocol  and the second protocol, the HDLC protocol. 4. Transmission protocol converter (10)  data for the implementation of the process of  claim 1, designed to be connected to a first  data transmission network (1) according to a  first protocol providing a frame (50) comprising  a first field (51, 52, 53) of data bits and  an associated field (54) of integrity check bits  data from the first field (51, 52, 53), and to a  second data transmission network (40) according to  a second protocol providing a frame (60)  comprising a second field (61) of data bits,  characterized by the fact that it includes means  (10, 11, 12, 16) agencies to convert the bits of the  first field (51, 52, 53) and the control field  associated (54) exclusively in bits of the second field  (61). 5. Converter according to claim 4, in which  storage means (17) are provided arranged for  write and read buffer at speeds  different, respectively depending on the flow rates of  transmission of the first and second networks (1, 40)  to ensure a flow adaptation between said  networks (1, 40). 6. Converter according to one of claims 4 and 5,  in which the converting means (10, 11, 12)  are arranged to receive data according to the  ETHERNET protocol and to, in response, provide  data according to HDLC protocol. 7. Converter according to one of claims 4 to 6,  in which decoder means are arranged for  receive the bits of the first field (51, 52, 53) and of the  control field (54) according to the MANCHESTER code and  to transmit in response, to the means  converters (16), corresponding coded bits  according to the NRZ code. 8. Transmission protocol converter  data for the implementation of the process of  claim 1, designed to be connected to a network  (40) data transmission according to a protocol  providing a frame (60) comprising a global field  (61) of data bits containing, in positions  known, a primary field (51, 52, 53) of bits of  data as well as a field (54) of control bits  data integrity of the primary field (51, 52,  53), characterized in that it includes  means (21, 22, 23, 24, 25, 26, 27, 28) arranged for  direct, then memorize, the bits of the global field  (61) to a field (28) of control bits or to  another field (25, 26, 27) of data bits according to  whether or not the bits considered occupy said bits  known positions. 9. The converter of claim 8, wherein  storage means include a buffer memory  (23, 25, 26, 27, 28) arranged to receive the bits  of the global data field (61) and for  transmit to the referral means (21, 22, 23,  24), at their request. 10. Converter according to one of claims 8 and 9,  in which the switching means (21, 22, 23, 24)  are arranged to receive data according to the  HDLC protocol and to, in response, provide  data according to the ETHERNET protocol.