JPS63184428A - Signal transmission system in collision detection type packet exchange system - Google Patents

Abstract

PURPOSE:To allow a medium access unit to easily detect collision with high performance by providing a signal generating means of Manchester code rule violation, a pseudo random code generating means and a Manchester coding means. CONSTITUTION:A basic Manchester (MC) coding signal Dob from a data terminal equipment DTE is inputted to a signal line 21 under the control of a control section 6 till n1/f0 sec after a transmission data signal detection signal CSTX is set. A control signal to select the output signal SCRJ of a signal generating section 7 is outputted to a selection section 10 till the 4n1-bit is counted by using a 4f0 clock from the signal CSTX to be set. Thus, a signal representing the MC code violation of the signal speed 2f0[bit/sec]from the signal generating section 7 is inputted to a waveform shaping section 11. On the other hand, the signal Dob is outputted from the signal selection section 8 and the MC coding signal of the signal speed 2f0 is inputted to the shaping section 11 via the coding section 9 and the selection section 10. The input signal is waveform-shaped and outputted to the optical transmission line via the converter 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal transmission method in a collision detection type packet switching system.

A system called C3MA/'CD is known as one of the transmission medium access systems in local area networks. This will be briefly explained below.

Among the stations (terminal stations) connected to the network,
A station that has issued a transmission request first monitors the common transmission path to check whether other stations are transmitting (car
If the common transmission path is in use, transmission is awaited, but if it is free, the signal is sent in a frame format (hereinafter simply referred to as a frame).
Send out. In this way, multiple stations send out frames using a common transmission path (multipi
access), there is a frame propagation delay, so if multiple stations send frames at the same time, collisions may occur and normal frames may not be delivered to the destination, if only by detecting the availability of a common transmission path. Sometimes.

In order to shorten the time during which a frame in which a collision occurs continues to occupy the common transmission channel, each station should monitor the presence or absence of a collision during transmission (collision detection).
When a collision is detected, transmission is stopped, and after waiting for a certain period of time,
Repeat the same procedure again for retransmission. This method is C3
MA/CD (carrier 5ense mul
tip access/collision d
efection).

The present invention relates to a signal transmission method for a system that performs packet communication using Manchester codes in such a C3MA/CD local area network, and in particular to an optical star network using an optical passive star coupler (OS C). The present invention relates to a signal transmission method suitable for use in.

[Conventional technology]

As a C3MA/CD local area network using optical fiber as a transmission medium, N
A bus transmission line is logically configured using an optical passive star coupler OSC with N inputs and outputs (N is an arbitrary integer), and optical fiber cables FK with one core each for transmission and reception.
As recommended in Dis 8802/3 (C3MA/CD access method), MAU (Media Access Uni-no)
Unit) and 8 media access unit MAU
and data terminal DTE (Data Terminal
Acquisition unit interface AUI (Attachmen)
Research and development is being conducted on an optical star network that organically connects a plurality of data terminals DTE via cables.

Note that the functions of the media access unit MAU and the data terminal DTB mentioned here together constitute the station (terminal station) described above. Further, the optical passive star coupler O8C is an optical passive element for almost equally distributing optical signals input from any input port to all output ports.

An example of the operation of the optical star network shown in FIG. 4 will be described below. Note that FIG. 4A is an explanatory diagram showing an example of the formant of a packet transmitted by each data terminal DTE.

First, normal packet communication operations in an optical star network will be explained.

The data terminal DTE that has generated the transmission request sends a preamble and 5FD (Start Frame) to establish synchronization with the receiving data terminal DTE prior to transmitting data.
Delimiter), the destination address, source address, and data length are added.Furthermore, following the data to be transmitted, Fe2 (Frame Check 5equen) is used to detect transmission errors at the receiving data terminal DTE.
After adding ce) bits, Manchester encoding is performed and the media access unit) M
Output to AU side. The MAU converts the input electrical signal into an optical signal and outputs it to the optical transmission line.

The optical signal output by the media access unit MAU is input to the optical passive star coupler O8C through the uplink fiber of the optical fiber cable FK, and is distributed and outputted to all output ports almost equally. The optical signal distributed and output by the optical passive star coupler O8C is input to all media access units MAU through the downlink fiber of the optical fiber cable FK.

All media access units MAU convert the received optical signals into electrical signals and send them to their own data terminal D via the AUI cable.
Output to TE. The data terminal DTE decodes the input Manchester encoded signal and sends it to its own data terminal DT.
If the E address and the destination address of the packet match,
The packet is taken in, and if it does not match, it is discarded.

Next, an explanation will be given of the operation when a collision situation occurs in which a plurality of data terminals DTE transmit packets at approximately the same time in the optical star network.

Currently, there are multiple data terminals DT'E, such as D'rE+ and D.
T E z is almost the same time, that is, the data terminal DTE
, before starting to receive packets from D T E z, and before DTE starts receiving packets from DTEI, both data terminals DTE+ and DTEZ turn off the carrier indicating that the transmission path is in use. After confirming that this is the case and transmitting the packet by performing the same transmission process as in the case of normal bucket communication, the optical signal output from the media access unit MAU connected to the data terminal D'r"El and the data terminal A collision state occurs in which the optical signals output from the media access unit M A U z connected to D T E 2 are mixed by the optical passive star coupler O8C.The optical passive star coupler O8C superimposes the two optical signals. The optical signal is distributed and outputted to all the output ports in a form, and the optical signal is received by the media access unit MAU through the downlink fiber of the optical fiber cable FK, and all the media access units MAU detect the collision state from the received optical signal. , and notifies its own data terminal DTE of the collision through the AU1 cable.

The data terminal DTE+ that received the notification of the collision and was involved in the transmission
1DTE2 attempts to retransmit the packet after waiting a certain period of time according to a predetermined backoff algorithm.

[Problem that the invention seeks to solve]

Therefore, in the optical star network mentioned above,
The media access unit MAU directly optically intensity modulates the Manchester-encoded electrical signal from the data terminal DTE and outputs it to the optical transmission path. The problem was that I couldn't do it.

The collision detection method of the media access unit MAU and its problems will be described below.

Conventionally, the following two methods have been mainly used as collision detection methods for media access units MAUs for optical star networks, but each method has its own problems.

(Received light level judgment method) The threshold is set to a level slightly higher than the maximum medium access unit MAU light received level when a single data terminal DTE is transmitting data, and the light actually received is determined to be higher than the threshold. This method determines a collision when the received signal level is high, but the problems are as follows.

(Problems with the received light level determination method) A single media access unit MAU outputs an optical signal in order to determine a collision when the received light level of the actually received optical signal is higher than the threshold value. In this case, it is necessary that twice the light receiving level of the minimum media access unit MAU is greater than the maximum light receiving level of the medium access unit MAU, and it is necessary to keep the light receiving level within a 3 dB range for all media access unit MAU transmissions.

However, in actual systems, distribution variations in optical passive star couplers, connection loss variations in fiber connectors/splices, etc., media access unit M
Transmission loss variations due to differences in fiber length between AU and optical path coupler and variations in individual optical fibers,
Furthermore, when considering temperature changes in the output power of the light emitting element inside the media access unit MAU, deterioration over time, etc., the dispersion in the light reception level of the media access unit MAU becomes quite large. The light reception level is 3dB.
It never falls within the range.

Therefore, in order to make the received light level almost constant for all media access unit MAU transmissions by considering these dispersion factors, the transmission path loss, which is the sum of the optical fiber transmission loss and the connection loss, and the optical passive star coupler must be adjusted in advance. The distribution loss between all input and output ports of the optical passive star coupler and the emission level of each media access unit MAU are measured independently, and the optical It is necessary to find a combination of a fiber cable and an optical passive star coupler, and to adjust the light emission level of the media access unit MAU.

As mentioned above, a great deal of effort is required to construct and change the network, and even if the light emission level of the media access unit (MAU) is adjusted, the light reception level is generally 3 dB.
There is generally a combination of optical fiber cable and optical passive star coupler that does not fit within the range, resulting in wasted network resources.

(CRV collision detection method) When multiple media access units MAU simultaneously output Manchester-encoded intensity modulated optical signals, these signals are mixed by an optical passive star coupler, and multiple optical signals are output from an optical passive star coupler. Although the optical signal is distributed almost equally in a superimposed form, generally when the optical signal is received and binary identified, it violates the Manchester coding rule (CRV: C
This method determines that a collision occurs when a collision occurs.

In other words, the Manchester code has a bit interval of 2 in time.
It is a transmission code in which the second half of the bit interval has a complementary level to the first half of the bit interval, and the rule is that a level transition from 0 to 1 or from 1 to 0 always occurs at the center of each bit interval. Therefore, if the interval 1 continues between the first and second half of the bit interval, it will be detected as a code rule violation CRV,
This allows it to be determined that there is a collision.

(Problems with the CRV collision detection method) The CRV collision detection method uses a single media access unit)
If the intensity modulated optical signal received at the minimum reception level when the MAU is outputting an optical signal can be correctly identified in binary terms, collisions between optical signals within a specified level range can be easily identified from the received optical signal. CRV (coding rule violation) can be detected and determined to be a collision.

Therefore, unlike the received light level determination method, this method does not require level measurement or level adjustment for collision detection, and has the advantage that actual network construction and modification can be easily performed. However, there is a problem in that if a plurality of colliding signal patterns are exactly the same, CRV will not occur in principle.

According to ISODIS 8802/3 (C3MA/CD access method), the transmitting data terminal DTE transmits a fixed pattern preamble (56 bits: 1010
1010 pattern repeated 7 times) and SFD (8 bits: 10101011) are Manchester encoded and output.

Here, FIG. 5a shows that when the media access unit MAU directly modulates the optical intensity of the signals transmitted by the two data terminals DTE and outputs them, if the signals arrive at the optical pensive star coupler at the same time and in the same phase, they will be equally distributed. Figure 5b is an explanatory diagram showing that CRV occurs only after the address part in the distributed optical signal, and the media access unit MAU directly modulates the optical intensity of the signals transmitted by the two data terminals DTE. FIG. 12 is an explanatory diagram showing that when outputted, CRV occurs only after the address part in an optical signal that is evenly distributed when it arrives at the optical pensive star coupler with the same phase and a delay of an even number of bits.

Now, for example, as shown in Figure 5a, two data terminals DTE
(DTEi and DTEj) send packets to two media access units MAU (MAU, and MAU).
, ), and are input into the optical passive star coupler at the same time and in the same phase.As can be seen from Figure 5a, at least when the preamble section and the SFD section collide, the optical passive star The optical signals superimposed and distributed by the coupler do not contain CRV, so collisions cannot be detected. Under this collision condition, the worst case is that the destination address also matches, and the source address also matches except for the final focus. In this case, the optical signal distributed by the optical passive star coupler has the same final bit of the source address CRV does not occur until a collision occurs, and the media access unit MAU cannot detect the collision even though the collision has occurred.

In addition, in the waveform diagram of the distributed optical signal of the optical passive star coupler in FIG. 5a, in the bit section indicated as CRV, the signal level is between the level 1 and the level O (
The intermediate level that takes the average) is shown, but this intermediate level is also determined by adopting a threshold level that is determined to be logical 1, so that a violation of the Manchester coding rule occurs in this bit interval indicated as CRV. This means that

Next, as shown in Figure 5b, the two data terminals DTE
Packets sent by (DTEi and DTEJ) are sent by two media access units MAU (MAU, and MAU).
If a collision occurs in which the output is emphasized modulated by , ) and is input to the optical passive star coupler with the same phase but shifted by an even number of bits, as can be seen from Figure 5b, the preamble section and the SFD section or the SFD section will collide with each other. CRV does not occur until , and even though a collision has occurred, the media access unit MAU cannot detect the collision.

As described above, the Manchester encoded electrical signal output from the data terminal DTE is transmitted to the media access unit).
When the MAU directly modulates the optical intensity and outputs it to the optical transmission line,
When signals of the same pattern collide with each other in the same phase, CRV does not occur even though a collision actually occurs, so collision detection is delayed until CRV occurs due to a collision of different signal patterns. Therefore, due to the delay in collision detection described above, C3M is set under conditions where collision detection is possible.
A problem arises in that the network length of the A/CD system is limited.

This problem can be avoided by randomizing the signal pattern using a certain scrambling rule in the transmitting media access unit MAU for each bit of a packet to be transmitted, but in order to perform effective signal randomization, it is necessary to The configuration of the side media access unit MAD became complicated, which led to the following new problems.

In other words, even if the signal is randomized by a fixed scrambling operation from a fixed bit position for the transmitted packet, the packets transmitted by the two data terminals DTE will not be input to the optical passive star coupler at the same time and in the same phase. If a collision occurs, the randomized signal will still be converted into a signal with the same signal pattern, and no CRV will occur from the signal received by the media access unit MAU. It is necessary to change.

Furthermore, since it is necessary to guarantee normal communication between data terminals DTE in the case of non-collision, scrambling rule information is inserted into the packet transmitted from the transmitting media access unit MAU, and a scrambling operation is performed to randomize the signal. It is necessary.

Conventionally, this bit string for scrambling rule information is
As shown in the figure, the sending media access unit M
In the AU, the scrambling rule information is continuously inserted into the bit string start delimiter during the preamble input period from the transmitting data terminal DTE, and then the transmitting data terminal DT
A scrambling operation was performed on the second half of the preamble input from E, SFD, destination address, source address, data, and Fe2 to randomize the signal. Therefore, the receiving media access unit (MAU)
Then, the scrambling rule information bit string start delimiter is detected from the received signal, and the scrambling rule information bit string is sequentially stored. Meanwhile, a preamble of a known pattern is internally reproduced and output to the receiving data terminal DTE, and all scrambling rules are stored. After accumulating information bits, a descrambling operation is performed on the received signal and output to the receiving data terminal DTE.

As described above, there is a drawback in that a complicated descramble operation is required in the receiving media access unit MAU in addition to the scramble operation in the transmitting media access unit MAU.

It is an object of the present invention to eliminate the need for special level adjustment when constructing or changing a system, and without depending on the phase between colliding signals or the code pattern of colliding signals, and furthermore, it is possible to generate normal signals when there is no collision. The present invention provides a signal transmission method in a collision detection type packet switching system in which the media access unit MAU can perform high-performance collision detection without requiring a complicated descrambling operation in the receiving media access unit MAU to guarantee reception. It is about providing.

[Means for solving problems]

In order to achieve the above object, in the present invention, each terminal station transmits a signal in packet format to a transmission path resource shared by a plurality of terminal stations, and if a signal collision is detected, the signal is retransmitted to the terminal. In a collision detection type packet switching system for communicating between stations, terminal stations are provided with means for generating a signal that violates the Manchester code rule, means for generating a pseudo-I random code, means for Manchester encoding, and the like.

[Effect]

When a transmitting terminal station that transmits a signal (hereinafter simply referred to as a packet) transmits a packet at a signal speed of f0 (bits/second), a certain number of bits are transmitted from the beginning of the preamble section of the packet. In the section, the signal speed (N
A signal that violates the Manchester coding rule is transmitted at The bit interval (1/f0 [seconds]) is divided into N in terms of time, and for each of the N divided small bit intervals, the value of the transmission code of the 1 bit interval as a preamble part or its complement value is set. Based on the signal speed (N x f0 [bits/second]), it is transmitted in a code format that is Manchester encoded at a signal rate of The signal speed is divided into N in time, and for at least one of the N divided small bit sections, the signal speed is determined based on the value of the transmission code of the 1 bit section as a packet component, or its complement value. (N×f0 [bits/second]) Manchester encoding is performed, and at least one of the remaining small bit sections is determined based on a separately given random code value at a signal speed of (N×f0 [bits/second]). [bits/second]) is transmitted as a Manchester encoded code format.

〔Example〕

An embodiment of the present invention will be described below with reference to the communication speed f in which a data terminal DTE is connected to an optical star type transmission path using an optical passive star coupler via an AUI cable and a media access unit MAU.

An example of the simplest signal transmission method in a C3MA/CD type optical star network of [bits/second] will be explained.

FIG. 1 is a block diagram showing the configuration of a media access unit MAU as a main part of an embodiment of the present invention.
2 and 3 are timing charts of the main signals in FIG. 1. Note that FIG. 3 is the same chart shown in FIG. 2 with a longer time scale.

As shown in Figure 1, the media access unit (MAU)
consists of a transmitter TX for processing the Manchester encoded signal from the data terminal DTE and outputting it to the transmission line side, and a receiving unit RX for processing the signal received from the transmission line side and outputting it to the data terminal DTE side. Ru.

The transmitter TX receives a Manchester encoded signal D0. A transmitting 4fO clock extraction unit 1 extracts a 4f0 [Hz] clock from a 4f0 [Hz] clock (hereinafter referred to as the basic Manchester code), and uses the transmitting 4fO clock to form a phase relationship between the Manchester encoded signal D05 and the phase relationship (basic Manchester code) shown in FIG. 2C. Transmission 2f with a high state immediately after the start of the bit period of the encoded signal nob
The transmitting 2fO clock synchronizer 2 outputs the O synchronization signal, and uses the transmitting 2fO clock to generate the Manchester encoded signal Da.
Transmission fO clock synchronization unit 3 that outputs a transmission fo synchronization signal having the phase relationship shown in the second diagram with b (basic Manchester encoded signal; becomes Low state immediately after the start of the bit period of b), Manchester encoding a transmission data signal detection unit 4 that outputs a transmission data signal detection signal C3TX indicating that the signal DOb is input to the transmission data signal line 21 and that the transmission 2fO clock synchronization unit 2 and the transmission fo clock synchronization unit 3 have established synchronization; A pseudo-random code generator 5 that outputs a pseudo-random code PSN using a transmission fO clock synchronization signal, a signal selection section switching control section 6 that generates a signal to control signal selection sections 8 and 10 (to be described later), and a signal selection section switching control section 6 that outputs a pseudo-random code PSN using a transmission fO clock synchronization signal; A coding rule violation signal generation unit 7 that generates a signal S CRU that violates the Manchester coding rules to be inserted.
, a signal selection unit 8 that replaces the second half of the bit interval of the basic Manchester code with a pseudorandom code generated by the pseudorandom generation unit 5 according to a control signal from the signal selection unit switching control unit 6;
, a 2fO Manchester coder 9 which outputs a Manchester code Do4 having a signal speed twice that of the basic Manchester code from the input signal from the signal selection unit 8, and a basic Manchester code according to the control signal from the signal selection unit switching control unit 6. Manchester code with twice the signal speed of the code. A signal selection unit 10.2fO selects and outputs the signal sciu that violates the Manchester encoding rule and the Manchester coding rule.The signal selection unit 10.2fO removes the spike noise generated in the Manchester encoding unit 9 or the signal selection unit 10 and outputs the signal sciu that violates the Manchester encoding rule. It includes a waveform shaping section 11 made of a flip-flop for generating a Munich-encoded signal, and an electric/light intensity conversion section 12 for converting the waveform-shaped signal into an intensity-modulated optical signal.

On the other hand, the receiving section RX includes an optical/electrical converter 13 that converts a received signal subjected to optical intensity modulation into an electrical signal;
a reception 4fO clock extraction unit 15 that extracts a 4f0 [Hz] clock from the received Manchester code D1d having a signal speed twice that of the basic Manchester code output from the identification unit 14; , received Manchester code using the received 4fO clock, ll
and the phase relationship as shown in FIG.
The reception 2fO clock synchronization section 16 outputs a reception 2fO synchronization signal with a reception 2fO synchronization signal which has a reception 2fO synchronization signal which has a reception 2fO synchronization signal which has a reception 2fO synchronization signal which has a reception 2fO synchronization signal which has a reception 2fO clock. A received Manchester encoded signal having a speed of 0.00000000000000000000000000000' is received a Manchester coded signal with a speed of
A reception fO clock synchronizer 17 outputs a synchronization signal, and a reception 2fO indicates that an optical signal is being received from the transmission path.
Clock synchronization section 16 and reception fo clock synchronization section 17
Optical signal reception detection signal C3RX indicating that synchronization has been established.
an fQ Manchester code decoding unit 19 that decodes the basic Manchester code from the received Manchester code Dia, and a collision detection unit that detects violation of the Manchester code rule in the output signal of the identification unit 14 and determines it as a collision. 20.

Also, in Figures 2 and 3, A is the basic Manchester code from the data terminal DTE.

b, B is the transmission 4f which is the output of the transmission 4fO clock extractor 1
0 [Hz) clock, C is the transmission 2f which is the output of the transmission 2fO clock synchronization section 2
0 [Hz] synchronization signal, D is the transmission f0 [which is the output of the transmission fo clock synchronization section 3]
Hz) synchronization signal, E is the transmission data signal detection signal C3TX which is the output of the transmission data signal detection section 4, and 2nd F is the transmission Manchester code Dod( Note that the receiving Manchester code Di, which is the output of the optical/electrical converter 13 on the receiving side, also shows the same waveform), G is the receiving 4f0 [Hz] clock, which is the output of the receiving 4fO clock extracting unit 15, and H is the transmitting 2fO clock. Reception 2 which is the output of the synchronization section 16
f0 [Hz] synchronization signal, ■ is the reception f0 which is the output of the reception fO clock synchronization section 17
[Hz] synchronization signal; J is the optical signal reception detection signal C3RX which is the output of the optical signal reception detection section 18;

K is the received Manchester code D1 of the signal speed f0 [bits/second] which is the output of the fo Manchester code decoding unit 19
It is b.

Next, the operation of the transmitting section TX will be explained by focusing on the input points of the waveform shaping section 11 by time.

(1) After the transmission data signal detection signal C3TX is turned on, the signal selection unit switching control unit 6 inputs the basic Manchester encoded signal D6b to the transmission data signal line 21 from the data terminal DTE until the time nl /fo (seconds). After the output signal C3TX (Fig. 2E) of the transmission data signal detection unit 4 turns on, indicating that the transmission 2fO clock synchronization unit 2 and the transmission fO clock synchronization unit 3 have established synchronization, the 4fO clock 4Xn, and until the bits are counted (time from tl to t2 in FIG. Therefore, the output signal S CIIIU of the coding rule violation signal generation section 7 is input to the waveform shaping section 11 .

Here, the code rule violation signal generation unit 7 generates 1/4 fo (seconds)
A signal that violates the Manchester sign rule in units of time,
For example, a signal such as 0110 0110 is output.

In other words, this signal is H at the part with the unlined line.
This is a code that does not have a high to Lotms or low to high transition, and is a signal from a code that violates the Manchester code rule with a signal rate of 2 fo (bits/second).

(2) After the transmission data signal detection signal C3TX turns on, nz/f0 [seconds] elapses.
seconds] until the time elapses (however, n.

<n2) The signal selection unit switching control unit 6 transmits the basic Manchester encoded signal 1) o from the data terminal DTE to the transmission data signal line 21.
After the output signal C3TX (Fig. 2E) of the transmission data signal detection unit 4 indicating that the signal b is being received is turned on,
After counting 4×n1 bits with the fO clock (that is, after the time from t to t2 in Figure 2 F),
A control signal is output to the signal selection section 10 so as to select the output signal of the 2fO Munich encoder 9. Also 4×n
.

After counting bits, until counting 4×n2 bits (that is, from time t2 to t3 in Figure 3 F),
The signal switching unit 8 sends a control signal to invalidate the pseudorandom code PSN input from the pseudorandom code generator 5 and the transmission fO synchronization signal input from the transmission fo clock synchronization unit 3.
Output to. Therefore, n, < f0 [seconds] time to nz
/f0 [seconds] (from time t2 to t3 in FIG. 3F), the signal selection unit 8 receives the basic Manchester encoded signal input from the data terminal DTE. b is output.

This signal is transmitted to the transmission 2 by the 2fO manti star encoder 9.
Encoded into Manchester code at a signal rate of 2fO [bits/second] using the f synchronization signal (Fig. 3C) and the transmitted 4fO clock signal (Fig. 3B) (the part from time t2 to t3 in Fig. 3F) (the same signal waveform) and is input to the waveform shaping section 11 via the signal selection section 10.

(3) After the transmission data signal detection signal C3TX turns on, the detection signal C3 is detected from the time nz/fo (seconds).
The signal selection unit switching control unit 6 sends the basic Manchester encoded signal 06b from the data terminal DTE to the transmission data signal line 21 until the TX is turned off.
After the output signal C3TX (Fig. 3E) of the transmission data signal detection unit 4, which indicates that the transmission data signal is being received, turns on,
After counting 4×n2 bits with the fO clock (that is, after the time from time t to t3 in FIG. A control signal for validating the input transmission fo synchronization signal is output to the signal selection section 8. By inputting these signals, the signal selection unit 8 selects the basic Manchester code from the data terminal DTE, which is the signal on the transmission data signal line 21, in the first half of the bit period of the basic Manchester code. b is selectively output, and in the second half of the bit period of the basic Manchester code, the pseudorandom code PSN is selectively output. This time-division signal is processed by the 2fO multicast encoder 9 at a signal rate of 2
The signal is encoded into a Manchester code of fO (bits/second) (the same signal waveform as the broken line arrow in FIG. 3F), and is input to the waveform shaping section 11 via the signal selection section 10.

In addition, in FIG. 3F, after time t3, the first half of each bit section (
b) is a signal of the transmission data signal line 21 in basic Manchester code. 5 is selected, and in the second half (b), it will be recognized that the pseudorandom code PSN (as it is random, the level is not determined whether it is High or Low, so it is shown by a broken line) is selected.

As described above, the signal input to the waveform shaping unit 11 through the times (1), (2), and (3) above is waveform-shaped using the transmission 4fO clock signal (FIG. 3B), and is converted into an optical signal by the electrical/optical converter 12. It is intensity modulated and output to the optical transmission line (Fig. 3F)
. The signals output to the optical transmission line are equally distributed by the optical star coupler and input to the receiving sections of all media access units MAU.

The operation of the receiving section RX will be explained below.

The received optical signal is converted into an electrical signal by the optical/electrical converter 13, and then becomes a binary-identified signal by the identifier 14. This binary identification signal is input to the reception 4fO clock extraction section 15, the reception 2fO clock synchronization section 16, the reception fO clock synchronization section 17, the optical signal reception detection section 18, the fo Manchester code decoding section 19, and the collision section 20. .

The reception 2fO clock synchronization unit 16 and the reception fO clock synchronization unit 17 output nt/f0 after the output C3ix (J in FIG. 2) of the optical signal reception unit 18, which indicates that an optical signal is being received, is turned on. By the time [seconds], the received 2fO synchronization signal and the reception fO synchronization signal, which are the output signals, are shown in Fig. 2H.
Then, synchronization is established through an indefinite interval so that a phase relationship as shown in FIG. 1 is obtained. This means that when the signal from the identification unit 14 is started to be input to the reception 2fO clock synchronization unit 16 and the reception fO clock synchronization unit 17, the nz
/f0 (seconds) (at time t2 in Figure 3 F)
The signal corresponding to the period from t3 to t3) corresponds to a signal in which the preamble, whose original code is a repetition of 1.0, is Manchester-encoded at a signal speed of 2fO [bits/second] without randomization on the transmitting side. , 1001 on 4fO clock
Since this is a repeating pattern of 0110, this can be detected and synchronization can be easily achieved.

Note that on the transmitting side, the beginning of the packet (t in FIG. 3F).

The Manchester coding rule violation signal inserted in the period from
If n is set to be about the time required to stabilize the clock synchronizer 16 and the fO clock synchronizer 17, then
This has no effect on synchronization establishment on the receiving side.

The fO Manchester code decoder 1 uses these received 4fO clock, received 2fO synchronization signal, received fO synchronization signal, optical signal reception detection signal C3'RX, and binary identification signal.
9 can decode the basic Manchester code. In other words, the binary identification signal (see (a) in Figure 3 F) in the section where the received 2fO synchronization signal (H in Figure 3) is 1 and the received fo synchronization signal (I in Figure 3) is 0 is the transmission information value. Therefore, based on that value, a flip-flop using the received fo synchronization signal as a clock holds it for 1/f0 [seconds], and by taking the exclusive OR of this signal and the delayed received fo synchronization signal, Basic Manchester codes can be easily decoded. The decoded basic Manchester code D i b is waveform-shaped by the received 2fO synchronization signal (K in FIG. 2, K in FIG. 3), and is transmitted to the data terminal DTE via the received data signal line 22.

On the other hand, a violation of the Manchester code rule of the binary identification signal can be detected using the received 4fO clock, the received 2fO synchronization signal, the reception fo synchronization signal, and the optical signal reception detection signal C3+tX. In other words, the transition (from 1 to O) of the binary identification signal (F in Fig. 3) is performed using the received 4fO clock signal (G in Fig. 3) every 1 section and 0 section of the received fo synchronization signal (■ in Fig. 3). , or a transition from 0 to 1), and if there is no transition (1-1, or 0 → 0), it is a violation of the Manchester sign rule with a signal speed of 2fO [bits/second]. If this is determined to have occurred due to a collision, the collision can be easily detected, and the data terminal D
The TE side will be notified.

In the above embodiment, the media access unit MAU connected to the transmitting data terminal DTE is n+/f0 seconds (n
, is a positive integer), transmits a signal that violates the Manchester coding rule at a signal rate of 2f0 (bits/second), and then transmits a signal that violates the Manchester coding rule at a signal rate of 2f0 (bits/second), and then transmits a signal that violates the Manchester coding rule at a signal rate of nz/f0 after starting reception of the signal from the transmitting data terminal DTE.
[seconds] (nz is a positive integer, where nl<nz), the first half of the bit period from the Manchester code of the signal rate f0 [bits/second] transmitted from the transmitting data terminal DTE is transmitted. Signal speed 2 corresponding to complement value
A Manchester code of f0 [bits/second] is transmitted, and in the second half of the bit period, a signal converted to a Manchester code of signal speed 2f0 [bits/second] corresponding to the transmission information value is transmitted, and after the signal reception from the transmitting data terminal DTE starts. After the time n2/f0 [seconds] (nz is a positive integer, nl<n2) has elapsed, the first half of the bit period starts from the Manchester code of the signal rate f0 [bits/second] transmitted from the transmitting data terminal DTE. Signal speed 2f0 corresponding to complement value of transmission information
[bits/second] Manchester code, the second half of the bit period is a signal rate of 2f0 [bits/second] corresponding to the pseudo-random code value generated inside the media access unit MAU.
The case where a signal converted to Manchester code is sent out is explained, but generally speaking, the signal speed that violates the Manchester code rule at the beginning of a packet is expressed as N×f0 [bits/
seconds], and each bit interval is divided into N, and the signal speed is N×f
A similar method and effect can be obtained in the case of Manchester encoding at 0 [bits/second]. However, N is an arbitrary integer.

〔Effect of the invention〕

As explained above, according to the present invention, the media access unit (M) connected to the transmitting data terminal DTE
For a certain period of time after the AU starts receiving signals from the transmitting data terminal DTP, it sends a signal that violates the Manchester code rule at a signal rate of 2fO [bits/second], so it sends out a signal that violates the Manchester code rule to the optical passive star coupler in the same phase. Even if a collision occurs in which the optical signal arrives late, CRV can easily occur.
This has the advantage that collisions can be detected early.

Similarly, after a certain period of time after the media access unit MAU connected to the transmitting data terminal DTE starts receiving a signal from the transmitting data terminal DTE, bits are received from the Manchester code at a signal rate f0 [bits/second] from the data terminal DTE. The first half of the section is a Manchester code with a signal rate of 2fO [bits/second] corresponding to the complement value of the transmission information, and the second half of the bit section is a signal rate of 2f0 [bits/second] corresponding to the pseudorandom code value generated inside the media access unit MAU. By sending a signal converted to Manchester code, even if a collision occurs that arrives at the optical passive star coupler at the same time and in the same phase, CRV can easily occur and the collision can be detected early. be.

Furthermore, since the scrambling (randomization) operation is performed only by the transmitting media access unit MAU, and the descrambling operation by the receiving media access unit MAU is not required, the transmitting and receiving media access unit M
This has the advantage that synchronization between AUs is easy and the receiving section is simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a media access unit MAU as a main part of an embodiment of the present invention, FIGS. 2 and 3 are timing charts of main signals in FIG. 1, and FIG. 4 4A is a system configuration diagram of a general C3MA/CD type local area network, FIG. 4A is an explanatory diagram of the formant of a packet transmitted from a data terminal station, and FIG. 4B is an explanatory diagram of the formant of a packet containing scrambling rule information bits. , FIG. 5a, and FIG. 5b show Manchester coding rule violations (
FIG. 2 is an explanatory diagram showing that CRV) occurs. Explanation of symbols 1... Transmission 4fO clock extractor, 2... Transmission 2f
O clock synchronization unit, 3... transmission fO clock synchronization unit,
4... Transmission data signal detection unit, 5... Pseudo-random code generation unit, 6... Signal selection unit switching control unit, 7...
Sign rule violation signal generation section, 8... Signal selection section, 9...
2fO manti star encoding unit, 10... signal selection unit,
11...Waveform shaping section, 12...Electrical/optical conversion section, 1
3... Optical/electric conversion section, 14... Identification section, 15...
- Reception 4fO clock extraction unit, 16... Reception 2fO clock synchronization unit, 17... Reception fO clock synchronization unit, 1
8... Optical signal reception detection section, 19... fO Manchester code decoding section, 20... Collision detection section, 21... Transmission data signal line, 22... Reception data signal line, 23.
・Collision display line

Claims (1)

[Claims] 1) Each terminal station transmits a signal in packet format to a transmission path resource shared by a plurality of terminal stations, and if a signal collision is detected, the signal is retransmitted and the terminal stations communicate with each other. In a collision detection type packet switching system that communicates between In the preamble part of the preamble part, in a certain number of bit sections from the beginning of the preamble part, the signal speed (N
×f0 [bits/second]) (where N is an arbitrary integer), a signal that violates the Manchester coding rule is sent, and after that, in a certain number of bit sections in the preamble part, each 1 bit section (1/f0 [seconds]) is temporally divided into N, and for each of the N divided small bit sections, the value of the transmission code of the 1 bit section as a preamble part or its complement value is calculated. It is transmitted in a code format that performs Manchiesta encoding at a signal speed (N x f0 [bits/second]), and in the subsequent packet components, each 1-bit section (1/f0 [seconds]) is For at least one of the N-divided small bit sections, the signal speed (N x f0 [bits/second]), and for at least one of the remaining small bit sections, the signal speed (N x f0 [bits/second]) is determined based on a separately given random code value. A signal transmission method in a collision detection type packet switching system, characterized in that the signal is transmitted in a code format that is Manchiesta-encoded (1/sec).