JPS6130836A - Digital signal transmission system - Google Patents

Abstract

PURPOSE:To prevent collision from taking place after a collision window by transmitting a dummy signal having a determined length at a position of an area in the order of a station at a frame next to the transmission of a last digital signal. CONSTITUTION:A carrier sense is supervised for one frame and when no carrier sense output exists, a packet is transmitted at a period according to a frame clock of the own station. If the first packet is transmitted and the collision with a packet of other station does not exist at the outside of a priority window, a dummy preamble is transmitted according to the frame clock and then the master packet is transmitted. When the first packet collides at the outside of the priority window, back-off takes place, the carrier sence in one frame just before transmission is supervised and the packet is retransmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital signal transmission system for transmitting data by time division multiplexing using communication cables.

BACKGROUND OF THE INVENTION With the spread of electronic computers and the development of digital signal processing technology, data communication, which combines communication systems and data processing systems to process information online, has been in the spotlight. In particular, for small-scale communication systems such as in-house communication conducted within the premises of government offices and companies, packet-based communication methods using communication cables such as coaxial cables are preferred due to their economic efficiency, reliability, and high transmission efficiency. is attracting particular attention.

In this packet-based communication system, a communication cable for bidirectional transmission is laid in a research institute, etc., and a large number of stations (-sonal stations) are connected to it. Then, from each station, for example, 10θ0~. A message divided into too-pit data blocks is transmitted. Messages have destination, communication, and other headers attached to them. In this communication system, the network itself is a passive transmission medium with no control functions, and control is completely distributed to each station. Therefore, each station starts transmitting a message after confirming that the transmission path is free, and if a collision with another packet occurs during transmission, both stations stop transmitting. A station that has stopped transmitting will attempt to retransmit the message after a random waiting period. This is c S M A / C
This is called a D-type packet-switched communication system.

With this communication method, users at each location can of course access seven computers.
It is possible to mutually utilize hardware such as storage devices and software such as programs that are distributed in various locations.

In other words, with this communication method, devices such as high-speed or high-precision printers and large-capacity files, which were concentrated on a large central computer in a TSS (time sharing system), can now be used in a distributed manner at various locations. can. Therefore, in addition to saving resources and improving usage efficiency, it is also possible to develop large software systems by accommodating programs and data. In addition, in this communication method, each user (personal station)
There is no priority in using the transmission path between them, and they are equal. Therefore, there is no master-slave hierarchy between stations, which is often seen in other communication systems, and communication is possible between any connected stations. Furthermore, since the transmission line such as a coaxial cable is completely composed of passive circuits, a highly reliable system can be easily created.

On the other hand, a line-switched communication system called Faxnet has been proposed. In this system, each station sends /4' packets in order starting from its master /4' packet based on packets transmitted by a station that has the initiative in frame synchronization, called a master station. The master station transmits masterno and kerato at every frame period. By the above, time division multiplex line switching is realized. This circuit-switched communication system is advantageous for real-time transmission.

The CSMA/CD system described above is currently an international standard for packet-switched communication systems in local area networks. Therefore, communication systems employing the CSMA/CD method are widely used. Just C'3M^7
The co system has difficulty in real-time transmission (real-time transmission) and is considered disadvantageous for voice data transmission. Therefore, it becomes necessary to use both the packet-switched communication system and the circuit-switched communication system within the same area.

However, in the past, two cables were required to use both methods together. Even if both systems are mixed on a single cable, collisions will occur because the transmission methods are different, and real-time transmission cannot be achieved with conventional Faxnet. Therefore, the present applicant has previously proposed Faxnet, a line-switched communication system that can construct both types of communication systems using a single cable.

In this proposed Faxnet, the preamble length at the beginning of the packet is increased. Suppose CSM A,/
The original proposed Faxn collided with the CD-type Nokket.
The transmitting station of et does not stop sending packets.

In addition, the transmission-in station always transmits kerat every frame until the transmission is finished. This allows this =
1'Faxnet's No Kerato is C9MA/
It can be transmitted with priority over CO type packets, and real-time transmission is possible.

A specific example of this 4LF' Faxnet will be shown below. - Faxne on a wooden cable
The following two priority functions are added to Faxnet in order to transmit T/ and Kerato with priority over CSMA/CD type Kerato.

■ During packet transmission, within a predetermined time (priority window), transmission will not be stopped even if CDoN (US 1) is detected.

■ After sending a packet/After a frame has elapsed - Even if there is no local sending order in the packet order, or even if C3oN (US 2) is detected, the packet is sent.

If a collision occurs, a CSMA/CD type station will stop transmitting Kerat after τ1+T time. Because this collision will prevent fields after the Faxnet/#ket preamble from being sent, the length of the preamble will be reduced to 2a.
+τ, +τ2+τ6. (Figure 19) (Figure 20) Here, 8 is the fastest inter-station propagation delay time τ is the time required for a C5MA/CDm station to detect a collision τ2 is the time required for a C3M^/CD type station to transmit after a collision The jam signal time τ3 is the minimum necessary Noriamp length for the receiving circuit to stabilize and establish bit synchronization, and is the predetermined period (priority window) shown in ■ above.
From the above, it is 280τ, 10τ20Note*1)
What is CDON?
This means that a collision detection signal is output from the collision detection circuit.

Orai 2) What is CS ON? Carrier 5ens
This means eON (signal on cable).

Faxnet/f proposed in Figures 21 to 23
Figure 1: This shows how it is transmitted with priority over the C3M^/CD type i+ packet. The stations that send out Noquettes of Faxnet fJ) are MST station, A station, 8 stations, CSMA/
Assume that the station that sends out CD-type notebooks is station 0.

In the F(n) frame in Figure 21, 0 stations are in the free area.
and Kerato have been successfully sent out. In the F(n+4) frame, station 0 sends a packet next to the packet of station MST and collides with the mother packet of station A. Station A continues to transmit and is successful. Station 0 stops transmission and retransmits again.

In the F(n) frame of FIG. 22, station c transmits the mother packet immediately before the MST station and the kerat are transmitted.

Since the MST station transmits each frame regardless of the C3ON10FF VC, a collision occurs in the middle of the packet sent by the C station. The MST station continues to transmit and is successful.

Station 0 stops transmission and retransmits.

Suppose that in the F (n+1) frame of FIG. 23, when station A finishes transmitting and the area occupied by station A becomes vacant, station C sends a packet there. There is no problem if the 0 station packet is smoky, but if it is long, the 8 station sends out every frame regardless of the /f ticket number and C3OIOFF, so a collision occurs in the middle of the 0 station sending packet. 8
The station continues to transmit and is successful. Station 0 stops transmission and retransmits.

[Problem that the invention seeks to solve]

In conventional Faxnet, the station that has completed the transmission of the call stops transmitting packets, and other stations detect the resulting free time on the time axis and recognize that the transmission of the call has ended. (Operation of the 1° timer circuit) Faxn using this empty detection transmission end notification method
In the case of the above-mentioned Faxnet proposed in which the ET and C9M^/co systems are mixed on one cable, there is a possibility that KC'3MA/CD type 1,000 kets will be inserted into the vacant space. And that packet is
xnet Transmission Timeout Detection Circuit
There was a possibility of causing Co11lslon. )
1ate Co11lslon is C5MA/C
This is a phenomenon that would never occur in the D method. 1ate here
Co11lsfan is the collision window for CSMA/CD type packets (when only CSMA/CD type packets are transmitted on the cable, a period during which a collision may occur; generally, it is one time the fastest inter-station propagation delay time)
This means that a collision occurs when the distance is exceeded.

Therefore, the purpose of the present invention is to improve the conventional Faxnet transmission system so that when it is mixed with CSMA/CD type 74' Kent switched communication system on one cable, C'3M
A/CD type/4-ket VClate o3111s
The purpose of the present invention is to realize a circuit-switched communication system in which ton is not generated.

〔Example〕

An embodiment for implementing digital transmission of the present invention will be described below.

In the communication system shown in FIG. 4, a coaxial cable 1 installed as a transmission line has both ends connected to an impedance matching terminator 2 having a resistance value equal to the characteristic impedance.

Each station is connected by coaxial cable IK through T connectors (taps) 31 to 3N. Since all of these stations have basically the same configuration, only the main part of station A connected to connector 3□ is shown in the figure.

Each station is equipped with a user device 4 including a computer and a telephone. The user device 4 includes: a transmitter (encoder) 41 for transmitting a digital signal in ticket units to other stations;
A receiver (decoder) 42 for receiving the same packet-based digital signal sent from another station, a terminal controller 43 for controlling the terminal, and the like are provided. Of these, the signal output from the transmitter 41 is temporarily stored in the transmission buffer 7 and 51. The information is then read out at a predetermined time using a clock signal equal to the transmission speed on the coaxial cable l, which is the transmission medium. This extracted signal is sent to a predetermined bucket)K by the transmission logic circuit 52.
converted. After passing through the transmission buffer amplifier 53,
It is sent out to the coaxial cable L-H through the T connector 31.

On the other hand, all packet signals transmitted on the coaxial cable 1 are received by the reception buffer amplifier 54 through the connector 31. The reception logic circuit 55 selects only the /4' packet addressed to its own station from the received packets, and temporarily stores 11 in the reception panzer memory 56. This stored signal is continuously read out in the receiver 42 using a predetermined clock. A received output signal is obtained from this K.

As described above, signals are sent and received using the transmission lock transmitter 57.
◇Transmission control circuit 61 is generated from reception logic circuit 6
The terminal controller 43 receives the received signal addressed to its own station obtained from 5.
It also controls the transmission logic circuit 52 according to instructions from the terminal controller 43. Further, the collision detection circuit 62
When transmitting a nokket signal, it is detected whether or not there is a collision with another station's queket signal.

Each station is also provided with a frame control circuit 801t, a timer circuit B1, and a packet management circuit 82.

The frame control circuit 80 is flc s t
Transmission lock oscillator 57 as shown in Figure l86.
The bit clock a (which has a frequency almost equal to the transmission lock of the mother packet on the transmission path) is supplied from the reception logic circuit 55, and the master detection signal and the master reset signal g are supplied from the reception logic circuit 55. In this circuit, when the master detection signal f is on, the frame clock h and master window signal 1 are generated by the master reset signal g, and the master When the detection signal f is off, a trigger generated inside the circuit generates a frame clock h and a master window 1 with - pulses.

The timer circuit 81 is a timer circuit for detecting that there is a station that has stopped sending out 4 packets without being able to send out an end notification dummy packet due to a failure, and uses the received signal 1 and frame clock h as input signals. As, the frame
The timer is started at clock h or when the received signal is turned off, and reset when the received signal is turned on. If the reception signal does not turn on even after time t1 has elapsed since the timer was started, a timeout signal k is output. Note that when the timeout signal k is output, the timer automatically restarts and checks for the existence of the next parent packet.

The kerat management circuit 82 receives the frame clock h, received signal 1 and tl as shown in FIGS.
It is supplied with a time-out signal from a timer circuit 81. From these input signals, it detects the order in which its own station sends out packets and outputs a transmission control signal l. This output signal is supplied to the transmission control circuit 61.
1, a transmission request signal to the transmission logic circuit 52 is generated under control together with a transmission signal from the controller of the terminal device.

It also checks and stores the transmission order of its own station for each frame to be transmitted in the next frame.

FIG. 15 shows details of the frame control circuit M80. Referring to this figure, the frame control circuit 6o is composed of a bit counter 90, a flip-flop 91, and several dart elements. The bit counter 90 is a counter that counts pit clocks, and generates a frame clock signal according to the states of the master detection signal f and the master reset signal g, as described above. This frame clock signal is input to the flip-flop 910 set input SK, and the master fnd I is output from the Q output of this flip-flop 9X.

The operation of this frame control circuit is clearly shown in the timing chart of FIG. 6. Further, FIG. 7 shows the relationship between the frame clock output from this circuit and the packet signal on the transmission path.

FIG. 8 shows the details of the packet management circuit 82, and referring to this figure, the packet management circuit 82 is as follows:
Packet order memory 100% 1st log counter 1
07th, l/f packet counter 10B.

It consists of a packet length timeout detector 109, t, a timer timeout output counter 102, a comparator 103, and an adder 104, and further includes seven flip-flops 1.
05 and seven AND gates 106 are provided.

Bucket) I11 memory ioo should be sent by your own station.
The first packet counter 107 is a counter that counts the number of packets in a frame, and the first packet counter 107 counts the output of the packet length timeout detector 109. The timer timeout output counter 102 is a counter that counts the timeout output from the tie V-. The length timeout detector 109 generates a timeout output when a packet longer than a certain predetermined length is received. The adder adds the counter value of the first socket counter and the number of timeout outputs of the tl timer, and the comparator compares the added value with the own station's sending/receiving number and calculates the addition. When the value reaches the value seven times before the packet number, that is, when it matches the value in the packet order memory, an output signal is generated in response to the frame clock h. The packet order memory 100 stores the value of the second bucket counter at that time according to the frame clock h.

The transmission control method according to the present invention will be described in detail below.

Note that the packet format used is the previously proposed packet format with a long Fourier pull length.

(2) FIG. 10 shows the transmission packet of a station that starts transmission first when the transmission path is silent.

In this case, follow the steps below to send out 7 kesoto.

■ The carrier sense is checked for every frame, and if there is no carrier sense output, packets are sent out at a frequency according to the frame clock of the local station. At this time, a flag indicating that the packet is a master packet can be kept in the control field of the packet to be sent. Or, by setting an axial force υ indicating the packet order in the control field,
#/ may be displayed there to indicate that it is a packet.

■ Sends the first /P packet, and if there is no collision with another station's packet outside the priority window, sends out a dummy preamble according to the frame clock (described later), then sends out the master packet.

■ When the first packet collides outside the priority window,
Perform back-off and monitor the carrier sense between frames immediately before sending out the packet, and if there is a carrier,
If not, resend the 7 packets according to each procedure.

L If there is a signal on the transmission path, follow the steps below. (Refer to Figure 11) When R-1, master packet is detected ■ Master packet
A packet is detected, and the number of packets of a certain length or more after the master packet including the master 74' packet is counted by the first column or kerato counter, and the master window in the next frame is detected. The packet count is stored in the memory at the point in time. (The master window will be explained later) ■ Detect an empty area and determine whether the following conditions are satisfied.

Empty area ≧ () or kerato size + 2a + α) (details on empty area detection will be described later) ■ If the judgment is OK, then the kerato from the master packet in the next frame is set to the first packet counter. When the number of packets stored in the previous frame is counted, the carrier sense off of the packet is detected, and the packet is sent out after α time from that point.

■ If a packet is sent and there is a collision outside the priority window, back off and try again.

■ If the packet is sent successfully, C in the next frame.
Immediately perform the SMA/CD type Pket adjustment process,
Thereafter, a node is sent every frame until there are no more e-keratos to be sent.

(C3M^/CO type) and packet execution processing will be described later) ■ When the own station sends a packet, if there is a station that has finished transmitting, follow the procedure in ■.

I-2, if the master packet is not detected■Furthermore, if there is no carrier sense output for 5/frame-to-frame monitoring, follow the procedure of I, and if the master packet is detected, follow the procedure of I-1.
■If the master/4' butt is not detected according to the procedure in , follow the procedure below. The reason for additionally/interframe monitoring is that if the master station monitors only when a transition occurs/between frames, the master/4' frame may not be detected.

■ At the frequency according to the own station's frame clock! send a packet. At this time, a flag is set to indicate that this is the control field master packet of the mother packet to be sent.

Alternatively, an area may be provided in the control field to indicate the order of #/kerat, and the fact that it is #/'s booklet may be displayed there.

■ If the first packet is sent and there is no collision with another station's packet outside the priority window, a dummy preamble is sent out according to the frame clock, and then the master/mother packet is sent out.

■ When the first packet collides outside the priority window,
Performs back-off and monitors the carrier sense between frames immediately before packet transmission, and if there is a carrier,
If there is none, send the packet according to each procedure.

(2) When there is a station that has finished sending out a packet (2) A station that wants to end sending out a packet sends out a mother packet of a predetermined length (Ja+γ) at the end and ends the sending. This packet does not stop sending even if it collides. (r is optional)■
Each station has a motherboard length timeout detector (timer for t2 time) that starts with each 7 or kerato carrier sense on. This timer is reset when the carrier sense is turned off, and if it is not reset until time t2, a packet length timeout output is generated.

t2=da+r ■ Each station determines that the number of packets received from the master packet (the sum of the value of the first bucket counter, t, and the number of times the timer times out) is the value immediately before the socket number that should be sent by the station itself. If a Kzi packet is detected, that is, if it matches the value in the packet order memory, then if there is a Kzi packet, the carrier sense-off is detected and a packet is sent out a time after α time. (The relationship between the packet number and the value in bucket hIIF jth memory is packet number = (value in packet order memory) +/) ■ The copacket counter of each transmitting station is calculated from the master packet to the own station every frame. The number of R packets having a length of t2 up to the turn to send out the packet is counted, including the master packet. For example, in the F(n-T) frame of FIG. 12, the counter candy of the second packet counter of Bq is 2.0 and the counter value of the second packet counter is 3.

If a station finishes transmitting between the master packet and its own station's turn to send out /4' packets, the value of its own station's counter or kerato counter will be moved forward by that amount. It will be less than the value in the frame. (B station → 1, C station → 2) Therefore, in the next frame, this updated /? Packets are sent according to the packet sending application number.

Note that the second and second packet counters of stations that are not transmitting count the number of kerats (including the master . . . and keratos) having a length of t2 or more between master packets.

■In case there is a station that fails during transmission and stops transmitting without being able to send out a completion notification packet (operation in ■), each station starts with the frame clock and carrier sense off for each node and kerato. I have a timer for 4 hours.

This timer is for carrier sense on and frame
It is reset by the clock, and if there is no reset until t1 time, it will automatically restart after tl timeout.

t 1 =-2a+β This t and timeout output of the timer are also used when detecting free space. (Described later) ■ When the master station finishes transmission, it continues to send out a dummy preamble to notify the end of the transmission.
Send out Gukerat.

■When the master packet disappears (see Figure 13) ■Each station monitors the master packet, and if the master packet cannot be detected at the position where it should appear in that frame, it will automatically The presence of a master /4' packet is monitored until the timing of transmitting the station packet /4' packet, and if there is no master /4' packet, the master flag of the own station's sending packet is set and sent.

(2) In the next frame, the station that has become the master sends out a dummy packet 777/le according to its own frame clock, and sends out a master packet at the parent packet position of #/.

■Detecting and checking the master and packet (see Figure 14) ■When the master and the 74 bits are detected, the master and the window are ,
Start the timer.

■ Generates a master window at the position where the master packet should appear in the next frame. This master window is the master window.

When the Nogukerato transitions, the master and Nogukerato positions change, and the changes are determined so that the master and flag can be detected even in the worst case.

■Each station is this master, the master within the window.

Check the presence or absence of the flag.

■ When a master flag is detected in a master or window, it is treated as a master or packet, and the master, window, or timer is reset and restarted at a certain reference point determined by ■ of the /4' packet of that master. . (A in the figure) ■ When the master flag is not detected within the master or window, or when the carrier sense is turned off, it is determined that there is no master or 9-ket; in that case, from the end of the master or window. Restart the periodic timer. (Exit in the figure) Also, the end of the master and window must be aligned with a certain reference point defined by ■.

■, Detection of empty area (see Figure 15) ■ Each station detects the master, Noyakeet, and this master,
When the carrier, sense, and sense of the 9th packet are turned off, the empty area detection counter is started (a in the figure). , the counter is stopped when the sense is turned on (b in the figure), and the counter is reset and restarted when the carrier and the sense are turned off.

■ When the master or window is detected, stop the counter and read the counter value at that time (C in the figure).

This value becomes the empty area.

However, this empty area detection counter is not reset until the master window is detected when the tl timer timeout output is output. (d in the figure) This is tl
Packets after the timer times out are CS
This is because it is regarded as an MA/CD type packet and is counted as a free area. This is because the C9MA/CD motherboard does not dedicate any area in the next frame.

The deisotal signal transmission system of the present invention has been described above.

Explanations and supplementary information about the signals used here are provided below.

The value a is the fastest inter-station propagation delay time.

Further, the value of α time is a value determined from the performance of the hardware in order to maintain an appropriate kerato interval.

That is, the time required for the channel to recover to Xyrent's 14tlE level after the 9 bits after EL on the channel have passed, and the time required for the receiving logic circuit of the other station to process and receive the packet just received. This value is determined from the time required to recover to a possible state, such as 11u.

The dummy preamble of ■■ is a CS at the end of the frame.
It is sent so that MA/'CD type packets are not sent. Normally, the master station sends out this grid angle. The sending timing is the timing at which C3 is turned OFF between the frame timing (rough frame length - (C5MA/GO type general Nouket length) of the following formula) and the end of the frame. This dummy preamble is sent to the end of the frame.

Therefore, CSMA/CD type packets will not be sent during this period.

1-1 (■) is designed to prevent the packet from overlapping with the master packet at the beginning of the next frame when attempting to access the channel at the rear of the frame.

In other words, when considering the fastest speed between stations, the remaining frame time must be the packet size + 2a+α time as shown in FIG. Equation 0 in 11-1 is the limiting condition determined by this.

1-10 CS M A/CD type armpit displacement processing is a C! 9 M A / CD @ This is a process to exclude packets from being sent.

A station that starts a new transmission must Fa
I don't know if it's an xnet packet or not.

Therefore, this process is performed at the time of starting transmission, and Fa
Ensure that only Xnet packets are continuous.

If the CSM is in the middle of Faxnet backup group,
If there is an A/CD type or ketsu, there is a possibility that it will be sent there in the next frame with a long clasp, and at that time F
This is because there is a possibility that the axnet or kerato may protrude from the frame.

Specifically, the processing is performed as follows.

An escape signal is sent every time C5off from the master 79 bit to the own station's sending turn.

The timing of sending is C3o as well as No9ket in the first part.
One hour after ff. The length of the exit signal is (τj - T2). When a collision is detected, whether the transmission is stopped or not, this reset processing (, 1 is Roe 1'1hi).The C5MA/CD type packets sent before the own station's sending turn are as follows. It collides with the inoexion signal and stops transmitting.

Faxnet/Gukerat has no trace whatsoever. In the frame where this error processing is performed, there will be no C5MA/CD type packet between the master packet and the packet sent from the local station, so if you send the packet to the subsequent frames in the sending order of this frame, Faxnet
Only /4' kets can be transmitted consecutively.

1) is to send out a short knocket that does not get caught by the ) or kerat length timeout detector of each station, and to notify all stations of the Faxnet that the transmission has ended at 9 bits.

Cao's 27t2 has the above termination notice and CSMA/
'Determined from the longest O3on time of a collision with a CD type packet. (FIG. 17) Furthermore, due to the above, the i4 packet size in this method must be longer than t2.

Packet size > t2 = 411 +1 This is the main packet length timeout detector (timer for t2 time)
This is determined by the fact that the only valid Nogukerato is the one that times out.

The 2a+β time of tl in ■■ is a value obtained from the following.

As shown in FIG. 18, consider the case where the end station of the cable is transmitting the m-th nof packet, and the end station on the opposite side is transmitting the m+/th 29-f packet. The leading pit of the m+/th i4 packet should be detected at all stations within 2a+α time after detecting the mth or kerato packet.

If it is not detected, that is, if it remains silent even after 2a+α time, all stations may recognize that the m + /th packet has ended. As a result, the m+2nd mother ket becomes m+/th earlier in order. Similarly, the order of subsequent packets is advanced one by one.

Also, β>α and 2a+β)2a+α, which is 2a+
This indicates that if it is silent during β time, it is also silent during 2a+α time.

Although the embodiments of the present invention have been described above, Faxne
It is also possible to set the area in which ``t'' and kerato can be sent within a predetermined period from the beginning of the frame, and the remaining area until the end of the frame to be an area in which only CSMA/CD ill packets can be sent. This is the transmission lock a output from the transmission lock oscillator 57.
Further, a frame counter is added which counts the number of frames and is reset to 0 (zero) by the master detection signal from the reception logic circuit. The above function is accomplished by sending a transmission request prohibition signal to the transmission control circuit at a predetermined frame count value and canceling the signal each time the frame count is reset to 0 (-V port).

By doing this, when Nogukerato becomes crowded, CS
The probability that M^/CD type packets will be successfully transmitted increases,
It becomes possible to shorten the time (transmission delay time) until a C5MA/CD type packet is successfully transmitted.

Furthermore, by setting the maximum four-ket length of the Faxnet according to the present invention to the maximum four-ket length defined by the CSMA/CD system, it is possible to eliminate the need for a free space detection function. This is the F that is trying to start a new transmission.
This is because even if the aXnelt station sends out a packet at the rear end of the frame, the dummy preamble sent by the master station causes a collision and automatically makes transmission impossible.

Consider coexistence with the CSMA/CD method, which requires a long interval between detecting C3off at the rear end of the e-ket and sending out the own e-ket. For example, if the interval is made longer than 2a-)-β, there will be no collision between the Faxnet node immediately after E OC (End of Carrler) and the CSMA/CD system motherboard. Because FaXne
This is because the CSMA/CD system station detects the carrier and gives up on sending out the t packet because it is sent out earlier. Therefore, when the above-mentioned CSMA/CD method is mixed, the Faxnet/f ticket no longer length τ3 is sufficient. Also, there is no longer a need for a function that does not stop sending out gas even if there is a collision.

It is also possible to notify each station of the end of transmission by attaching an end flag to the control field of the packet and sending it. In this case, there is no need for a termination notification function by sending a dummy signal of a certain predetermined length.

In addition, the previously proposed transmission timeout detection circuit that generates a transmission request signal that requests unconditional transmission after sending a digital signal/interframe signal if the interframe signal cannot be sent, and the own station It is also possible to improve reliability by providing a reception timeout detection circuit that generates a reception request signal that requests to start reception unconditionally if the destination signal cannot be received. By doing this, if another station's failure occurs, your own station's 1tf
It can be avoided to a large extent that it has a negative impact on the FL communication.

[Effect of invention]

In a communication system in which CSMA/CD type No. 1 and Faxnet type No. 9 packets are mixed on a single cable, this prevents the CSMA/CD method from entering into the vacant area after transmission of Faxnet type/Archive is stopped. In order to prevent this, a dummy digital signal was generated, so the 1ate Co111s that occurred in the conventional method
lon no longer occurs.

[Brief explanation of drawings]

Figures 1 to 3 are detailed explanatory diagrams of the present invention, Figure 4 is a block diagram schematically showing the communication system of the present invention, Figure 5 is a detailed circuit diagram of the frame and control circuit, and Figure 6. is frame, control circuit timing,
The chart, Figure 7 shows the packet signal on the transmission path, the frame of each station,
A diagram showing the relationship on the time axis with the clock, Figure 8 is a detailed block diagram of the Nogukerato management circuit, Figure 9 is the packet management circuit timing, -i-yard, Figures 10 to 18 are , an explanatory diagram for explaining the present invention in detail, and FIG. 19 is an explanatory diagram for explaining the present invention in detail. An explanatory diagram showing what happens when a packet collides with a /4' packet based on the CSMA/CD system, and a comparison diagram of the packet formats of the 20th or previously proposed Faxnet and the conventional Faxnet. From Figure 2113 to Figure 23, FllX was proposed earlier.
FIG. 3 is an explanatory diagram showing how n19t packets are given priority over CSMA/CO type packets. 1-----One coaxial cable, 2-----One terminator, 3-----T connector, 4-
-----One user device. 41,,-----one transmitter, 42----
1 Receiver, 43 ----> End controller, 51
−−−−−1 transmission buffer memory,
52-----One transmitting logic circuit, 53----One transmitting puffer amplifier, 54----One receiving puffer amplifier. 55 --- Transmission logic circuit, 56 --- Receive buffer unit, 61 ---
1 transmission control circuit, 62 ---- 1 collision detection circuit,
72------Transmission logic circuit, 80---Frame control circuit, 81---tl timer circuit. 81---Packet management circuit. 90---Bit counter, 91.105---7 lip counter, 100-
−−−−−ΔKerato order memory. 101---t1 timer timeout output counter. 103---One comparator, 104---One adder. 106------and dirt. 107-----First Noya Kerato Counter. 108-----First Kono 9-ket counter, 109-
----p4 ket length timeout detector.

Claims (7)

[Claims] (1) Digital signals transmitted on a communication cable are fixedly positioned within a frame that is periodically repeated on the time axis, and each station connected to this communication cable via a tap A multi-station communication network in which a plurality of stations actually transmit signals and/or a plurality of stations occupy areas on the time axis that are further divided within the frame, and transmit time-division multiplexed digital signals. A digital system in which the order of the areas occupied by each station is determined for each frame so that the area in use is continuous with one group within one frame, and signals are transmitted in the order of each area. In a signal transmission system, a station that wants to finish transmitting a signal transmits a dummy signal of a predetermined length at the position of the station's sequential area in the frame following the transmission of the last digital signal. ,
A digital signal transmission system characterized by comprising means for notifying each station of the end of use of its own exclusive area. (2) Between the timing determined by the maximum digital signal length allowed by the CSMA/CD system and the end of the frame, the master station designated as the reference station for frame synchronization turns off CS (carrier sense).
By sending a dummy digital signal from the time when the frame is detected to the end of the frame, the CSMA/CD
2. The digital signal transmission method according to claim 1, further comprising means for preventing transmission of a digital signal transmitted in accordance with the method. (3) The transmission logic circuit is equipped with a function in the station that does not stop the transmission of the digital signal even if it collides with the digital signal transmitted according to the CSMA/CD method. 2. The digital signal transmission system according to claim 1, further comprising a reception logic circuit having a function of not stopping reception of the digital signal even if a collision is detected. (4) A first counter that counts received signals within the station, stops the counting operation when the timing for transmitting it to the local station, and resets it every frame; It is equipped with a second counter that stops counting operation and resets every frame when the sending timing comes, and a memory that stores the value of the second counter every frame, and the value of the memory matches the value of the first counter. 2. The digital signal transmission method according to claim 1, wherein the digital signal transmission method enters a signal sending operation when the signal is transmitted. (5) When a station tries to start a new signal transmission and successfully sends out the first signal, it transmits a short-length error signal called an ejection signal in the next frame from the signal sent by the master station to its own sending order. CS (carrier sense) signal
4. The digital signal transmission method according to claim 3, wherein the digital signal transmission method is transmitted every time the signal is transmitted in the CSMA/CD method. (6) When EOC (End of Carrier) is detected, CS (Ca
2. The digital signal transmission system according to claim 1, wherein the digital signal transmission system coexists on the same cable with a CSMA/CD system in which the digital signal is not sent out if the digital signal is detected up to that point. (7) By prohibiting transmission requests from stations other than the master station from a predetermined timing to the end of the frame, digital signals are only allowed to be sent to the area from the beginning of the frame to the predetermined timing mentioned above. 2. The digital signal transmission method according to claim 1, characterized in that: