FR2524232A1 - MULTI-ACCESS DATA RECEIVER / TRANSMITTER DATA TRANSMISSION SYSTEM - Google Patents

Abstract

THE INVENTION RELATES TO A DIGITAL DATA TRANSMISSION ASSEMBLY. THIS SET INCLUDES A MODEM 20 CONNECTED TO TERMINAL DATA PROCESSING EQUIPMENT 12, 14, 16 AND 18 AND, BY A TRANSMISSION LINE 22, TO A REMOTE MODEM 24 WHICH, ITSELF, IS CONNECTED TO TERMINAL EQUIPMENT 26, 28, 30, 32 FOR DATA PROCESSING. DATA TRANSMISSION IS CARRIED OUT IN TIME-SHARED MODE. MEANS ARE INTENDED TO DETECT THE PRESENCE, IN THE DATA TRANSMITTED AND ASSIGNED TO THE RESPECTIVE TERMINAL EQUIPMENT, OF A REPETITIVE SUITE OF 1 OR 0 BINARY, AND THEN DETECT THE PRESENCE OF A PREDETERMINED CODE SEQUENCE OF BITS IN A CHOSEN NUMBER OF BITS BITS SUCCESSIVELY RECEIVED. FIELD OF APPLICATION: MODEMS FOR THE TRANSMISSION OF DIGITAL DATA.

Description

The invention relates to the field of modulators

  demodulators (modems) used for the transfer of digital data, and it relates more particularly to an improvement made to modems working in multiplexing, which transmit data by one or more selected channels, one or more of these channels

  may be periodically inactive while a transmission

  is performed by one or more of the other channels.

  It is known in the art to interface a terminal data processing equipment (EMTD) with a modem that has multiple accesses, for example four output ports, each connected to a transmission channel at the other end of which is connected a remote modem For saving time of data transmission, it is known to make work the channel of

  output in multiplexing on a time paging basis.

  This reduces the number of pieces of equipment required for several terminal processing equipment.

  data to be placed in communication with several

  modems, for example in several locations, which can be remote and with which telephone lines are communicated, or which can be placed in a central location with respect to the data terminal equipment with which it communicates via fixed cable connections Before the appearance of

  multi-access modems, the terminal equipment for

  The data set had to be connected to several modems, one for each corresponding access of the current multiple access modems. However, it has become apparent that, when multiple modems connected to the data terminal equipment are replaced by a multi-access modem connected to the same equipment, when access becomes inactive, it is no longer connected to a communication channel

  and the indication transmitted to the terminal processing equipment

  The channel is offline, that is, the channel indication is not in the transmit request mode (RTS) nor in the data carrier detection mode (DCD). This differs from previous use

  of several modems entered the terminal equipment-

  data and each transmission channel, used

  in which the communication link between this modem and a modem with which it communicates is not interrupted, despite a pause in the transmission of data from a first data terminal equipment to another terminal processing equipment data or another remote modem, connected to the remote modem on the channel In this case, the appropriate signals RTS and DCD remain in the appropriate state during the pauses of the data transmission, because the carrier remains present

  between modems, although no data is transmitted.

  Maintaining the application of the appropriate RTS and DCD signals to the data terminal equipment in the absence of data transmission has certain advantages. For example, U.S. Patent No. 4,044,307 discloses that the time lost to ensure the presence of this equalization after each apparent loss of the carrier can significantly impede the saving of data transmission time, enabled by modems

with multiple access.

  In addition, similar problems arise for the receiving modem if the latter consists of a null access modem connected to several terminal equipments.

  data processing or other remote modems.

  These terminal equipment or other remote modems indicate a loss of RTS or DCD signals, as appropriate, when the corresponding access to which one of them is

  connected becomes inactive during multiplexing.

  With the aid of a DCD / RTS simulator, a multi-access modem can be operated in a continuous carrier mode Normally, in a continuous carrier mode,

  the local terminal equipment for data processing,

  to communicate with a remote modem, transmits a broadcast request signal (RTS) to a connected local modem

  to the local terminal equipment for data processing.

  For this to happen, the data set (modem) must have its own power supply in operation, in which case it transmits to the data terminal equipment a ready data set signal (DSR) which enables the data set (DSR) to terminal equipment to transmit to this modem a signal Rr S. If the local modem detects the presence of a carrier on the transmission line to the remote modem, which transmission line may be, for example, a telephone line, a a four-wire half-duplex transmission line or a two-wire full-duplex transmission line, the modem can not generate and transmit to the data terminal equipment an erasure signal for CTS transmission, because data are in the process of receiving from a distant modem on

this channel.

  The detection of a carrier signal can be

  present in the form of a signal detection of

  delay (DCD) which is a modem output signal occurring during the detection of a carrier signal (CXR detection) with a given delay before

DCD signal generation.

  In a multi-access system, it is important to keep the appropriate DCD / RTS signals, even though access may become momentarily inactive. It is also important to prevent the means used to perform this function from interfering with the actual transmission of data. the data channels or cause a

  confusion with these real data Thus, various agencies

  In the past, coding schemes have been used to code the multi-access modem to simulate a DCD or RTS signal, as appropriate. These arrangements have the disadvantage that they can cause confusion with actual and useful transmitted data. typical codes include repeated sequences of bits, for example

  "0000 00", "1111 11" or "1010 10".

  The present invention relates to a new way of signaling a remote modem to abandon data carrier detection, which means an actual cessation of data transmission rather than a temporary cessation due to multiple-port operation of the transmitting modem. characteristic of the present invention is to use a coded signal which, when received by a remote modem, causes it to drop the data carrier detection and which must be received before

  the detection of data carrier is thus abandoned.

  The coded signal is such that it can hardly be reproduced by the transmitted user data, which prevents accidental abandonment or detection of the data carrier, and it can not be falsified in any way. the payload received by the remote modem or data terminal equipment. The problems listed above are not limiting, but rather part of those that tend to affect the efficiency of the operation of prior multiple access modems.

  may also exist; however, those indicated

  previously sufficient to demonstrate that prior art null access modems have

  which do not give complete satisfaction.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which FIG. 1 is a simplified diagram of a network.

  multi-access modem transmission system according to the invention.

tion; and

  FIG. 2 is a diagram of the times represented

  schematically the coded signal which, alone, is enough to cause the abandonment of the detection of the carrier of

-data to a remote modem.

  Figure t is a simplified diagram of a network

  multi-access modem transmission system according to the

  The transmission network comprises four sources

  data, for example terminal equipment for processing

  data A, B, C and D, 12, 14, 16 and 18, respectively.

  Each data terminal equipment 12, 14, 16 and 18 is connected to a modem 20 capable of producing an output signal multiplexed on a transmission line 22 which may be, for example, a telephone line. 20 to share in time the transmission of data via line 22, between data sources 12, 14, 16 and 18, in order to make maximum use of line 22

of transmission.

  A remote modem 24 is connected to the opposite end of the transmission line 22 and is also connected to data collectors A ', B', C 'and D' 26, 28, 30 and 32, respectively. The remote modem is also capable of transmitting by multiplexing the data it

  receives at the appropriate collector 26, 28, 30 or 32 of data.

  It should be noted that data collectors 26, 28

  30 and 32 may be, for example, terminal equipment

  Data processing or other remote modems for transmitting data to other locations

  It is assumed, for the description of the

  the present invention and for the sake of simplicity of explanation, that the data collectors 26, 28, 30 and 32 are data processing terminal equipment receiving the transmitted data for use thereof, and it is assumed

  20 and 24 multi-port modems

  put the data from terminal equipment A, B, C and D to the respective terminal equipment A ', B', C 'and D' It should be noted, however, that this is not necessarily the case and that For example, all terminal equipment A, B, C and D may transmit data intended for one or more, but not all, of terminal equipment A ', B', C 'and D'. Moreover, all equipment data processing terminal A, B, C and D can transmit data intended, during different transmission periods, to some, different terminal data processing equipment A ', B', C 'and D' Thus, for example, the terminal equipment A and B can transmit data while the equipment C and D are inactive, and this data can be intended, for example, only for the terminal equipment D '. Terminal A may issue data that is intended for terminating equipment nal A ',

  followed by data intended for the terminal equipment B '.

  The multi-access modems 20 and 24 serve to multiplex the data thus transmitted by the terminal equipment A, B, C and D on the transmission line 22 and to assign the received data to the appropriate collectors.

26, 28, 30 and 32.

  Referring now to FIG. 2, it can be seen that data processing terminals A, B, C and D can, at various times and in different periods, possess data to be transmitted, which is indicated by the presence of the RTS signal 34 (transmit request) The RTS signal is transmitted via the modems 20 and 24 to the appropriate remote data collector which in this case is assumed to be the designated data terminal equipment. by the corresponding letter

  accompanied by a prime sign, A ', B', C 'or D', this team

  sending a data carrier detection signal DCD to the corresponding transmitting terminal equipment A, B, C or D via the modems 24 and 22 This allows the sending equipment A, B, C or D to transmit its data, indicated respectively at 36, 38, 40 and 42, to the multi-access modem 20 so that they are multiplexed on the transmission line 22 to be received and distributed, by multiple accesses, to the collector

  appropriate data A ', B', C 'or D'.

  As a result of the operation performed by the multiple access modem 20 and 24, the respective data queues from the data processing terminal equipment A, B, C or D may not be transmitted in one sequence.

  continuous, but they can be interrupted and

  plexed with the data suites from other data terminal equipment A, B, C or D, in real time Thus, the appropriate data collector, for example the collector A ', can receive data 36 from of the terminal equipment A in two or more separate data suites, forming the total data queue 36 When the terminal equipment A 'does not actually receive a data queue from the remote modem 24, its data carrier detection must to be maintained

  for the reasons indicated above.

  The multi-access modem 20 detects when the corresponding terminal equipment A, B, C or D drops its RTS signal, indicating that there is no more data to come, and it adds at the end of the queue a coded signal that is transmitted to the remote modem 24 as part of the data destined to the appropriate collector A ', B', C 'or D' remote Le'modem 24 detects the transmission

  of this coded signal in the data he manages by multi-

  plexing to one, corresponding, collectors of

  data A ', B', C 'and DI, and transmits a signal to the

  appropriate data reader A ', B', C 'or D' in order to make it abandon its carrier detection signal

of data.

  The coded signal that has been chosen in accordance with the present invention is a relatively long 1-bit queue, for example at least 128, 64, 32 or 24, followed by an additional code word, for example 8-bit

  of length that is repeated, for example three times.

  The remote modem 24 comprises a logic circuit which detects the presence, in the data received from an appropriate terminal data processing equipment A ', B', C 'or D', of a sequence of "1" in a light number. less than that of the transmitted sequence, for example 120, 60, 24 or 18, in any data block received with a length of 128, 64, 32 or 24 respectively.

  tenif account for some possible transmission errors.

  This detection performed on the input data triggers

  an additional logic circuit forming part of the remote modem 24 to maintain and sample the following data in groups, for example 6 bits, to detect the presence of a code, for example 01, 1001, that is, say -19 in hexadecimal, in any one of the following three groups, for example 6 bits This redundancy is also provided to take account of possible transmission errors in one or both of the groups

of 6 bits.

  If the code is found, the remote modem 24 transmits

  sends a signal to the appropriate terminal equipment for processing

  data A ', B', C 'or D' so that he abandons his

  DCD signal If the code is not found, the data

  stored and tested for code are useful data rather than code data, and are assigned to the appropriate terminal equipment A ', B', C 'or D',

as such.

  This code arrangement has the advantage, over prior art coded signals, of simulating data carrier detection in multi-access operation, in the prior use of long, repetitive sequences of data bits. for example 0s, 1s or 01s that can appear at times

  in useful data and be mistaken for a code of aban-

  data carrier detection, which results in accidentally completing the reception of data by the corresponding data processing terminal equipment A ', B', C 'or D' The fact that it is necessary to to find two codes simultaneously, that is to say a sequence

  bits of repetitive data of a certain length-

  minimum and a code word that follows, for example 8 bits, significantly reduces the risk of occurrence of the code in the actual payload Plus the repetitive data queue is long, as the first part of the coded signal, plus the risk of presence of the coded signal

  in the payload is low.

  The detection of the coded signal in the remote modem 24 can be carried out by means of a microprocessor It should be noted that it is also possible to use

  other large-scale integrated circuits designed specifically

  to fulfill the logical functions required.

  The remote modem 24 contains at least one microprocessor which may, for example, be an 8-bit byte microprocessor or bytes When the data that has been demodulated by the remote modem 24 and assigned to the access connected to the terminal equipment A ', for example, data processing, are applied to this equipment A', they are recorded by the microprocessor, in the form of bytes, in selected memory positions in the memory of the microprocessor These memory positions represent , at any given instant, the last 128 bits, for example, (16 bytes) of data assigned to the equipment A 'Some other positions of a memory,

  for example a ROM, contained in the micro-

  processor, contain the chosen code which is registered for the selected lower number of bytes, for example 15, i.e. 120 bits The processor is programmed to compare the previous -16 bytes, i.e. 128-bit in order to determine if any combination of 15 of these bytes contains the repetitive code chosen, for example 0s, 1s or 01s. If a transmission error occurred in any of the previous 16 octets, the fact that fault find the repetitive code only in these 15

  bytes indicates a possibility of transmission error.

  When the repetitive code is detected in the requested number of bytes from the previous 16 bytes, the microprocessor is programmed to record in its random access memory the following predetermined number, for example 3, of received bytes and to compare each with another stored code in the memory, alive or dead, as desired This other code is, for example, 011001 If any one of the predetermined numbers of bytes contains the other selected code, the microprocessor is programmed to transmit an output signal to the appropriate data collector, for example the data processing terminal equipment A ', to cause the abandonment of the data carrier detection.

  It goes without saying that many modifications can

  It should be made to the device described and shown without departing from the scope of the invention. For example, the particular separated code chosen, that is to say 011001, is chosen because of its low risk of occurrence in the useful data, but the code can be composed of any other combination, chosen at random, of eight "1" and "0" binaries Furthermore, the separate code can be

  based, for example, on one or two bytes.

  particulars described above to indicate possible transmission errors in the repetitive sequence or the separate code can also be easily modified as is well known to those skilled in the art, for example by determining that a smaller number, for example 14 bytes out of 16 (in the example where the repetitive sequence is 128 bits), each contain the appropriate repetitive sequence, or by determining whether two of the following three bytes contain the appropriate selected separate code In addition, the following number of bytes may be greater than or equal to 3 provided that a number, less than the total of these bytes, are found to have the selected separate code indicating

  thus a possible error of transmission in one or more

of these bytes.

Claims (1)

CLAIM   A data transmission system comprising a multi-access data receiver / transmitter having multiple transmission ports each connected by a remote data receiver / transmitter transmission line (22) and connected to a corresponding one of plurality of first data terminals (12-18) so that data is transmitted from said first terminal to a corresponding one of a plurality of second data terminals (26, 32) each connected to one of a plurality of transmission ports of the remote data receiver / transmitter, each data receiver / transmitter transmitting or receiving data in time-sharing mode, the system characterized by comprising means for maintaining the second data terminal in demand simulation for transmit (RTS) / Data Carrier Detection (DCD) unless there is an effective end of data to the corresponding first data terminal, which means includes a device for detecting the presence, in the transmitted data to be assigned to the corresponding second data terminal, of a repetitive sequence of "1" or "1 binary integers" or repetitive sequences of these "1" or "O" , and then detecting the presence of a predetermined coded sequence of bits in a predetermined number of bits received successively.