JPS60260246A - Optical data transmitter - Google Patents

Abstract

PURPOSE:To avoid collision between communication stations by retarding the time of sum of a specific constant time and a random time before starting the transmission of the own station after the end of the signal of other station received via a star coupler is detected. CONSTITUTION:Transmission data is stored once in a transmission buffer 31, and when no detection signal from a reception detecting circuit 27 exists, a communication control circuit 30 transmits data from the buffer 31 to the star coupler 4 via a transmitter in addition to a redundancy bit from a generator immediately. While an output signal 26 of a timer circuit 25 is at level 1, when the circuit 27 receives a signal from the other station via the coupler 4, the circuit 30 stops the transmission of the data from the buffer 31 immediately. When the end of the signal from the other station is detected by the circuit 27, a delay circuit 29 adds a random time different depending on each detection of the end of reception signal from a random number generator and retards the result at a delay control circuit 40 to a prescribed delay time decided at each station by the delay circuit 29, and the transmission data in stand-by to the buffer 31 via the circuit 30 is added to the redundancy bit and the result is transmitted.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] 20 The invention relates to optical communications, particularly '-'b' [) (sta
The present invention relates to optical communication having a transmission line equipped with a r coupler.

Multiple optical fibers for optical signal input and multiple optical fibers for optical signal output are connected to the star coupler, and the optical signal input from each optical fiber for optical signal input to the star coupler is optically transmitted within the star coupler. It is distributed to all optical fibers for signal output to form a signal transmission path. Therefore, in order to use such an optical signal transmission line among a plurality of communication stations, it is necessary to avoid signal collisions on the transmission line and use the transmission line in a time-division manner.

This invention relates to prevention of signal collision on a transmission path.

[Prior art]

FIG. 1 is a block diagram showing a conventional device of this type, in which (1) is a transmission signal line, (2) is a transmitter, (
3) is a light emitting element, (4) is a star coupler, and (5a).

(5b), (5c) are fibers for each party for optical signal input (viewed from the star coupler side), (6a), (6b), (&c
) is each party fiber for optical signal output (as seen from the star coupler side), (7) is the light receiving element, (8) is the amplifier (amplification circuit), (9) is the waveform shaping circuit, 1 [ is the receiving signal line, tt
U is an integrating circuit, (2) is a threshold setting terminal, (1 is a comparator, (14a)).

(14b) is an AND gate, (15a), (1
5b) are SR type rough flip-flop α timers, and (15a), (15b), and (16') constitute a transition detection circuit, (In is a transmission control circuit, and (
181 is a redundant bit generator, u! J is a collision detection signal line,
(20) is a transmission start signal line, (21) is an output signal line of the flip 70 tube (15b), and (22) is an output signal line of the integrating circuit συ.

FIG. 2 is a waveform diagram showing the signal waveforms of each part of the circuit in FIG.
b)).

(12a), (19a), (21a), ((22a)
, (22b)) Signal lines +11 and 1lUl, respectively
, (2), (21), and (22), and (23) and (24) respectively indicate the time point at which the output of the comparator t131 becomes logic "1".

Next, the operation will be explained. The transmission data input to the transmission control circuit r1η has redundant bits of a predetermined length added to the beginning by a redundant bit generator (181), and then becomes a signal in the form shown in FIG. 2 (1a) and is sent to the transmitter (181). The transmitter (2) fully drives the light emitting element (3) in response to the transmission signal (1a). The optical signal output from the light emitting element (3) is input to the optical fiber (5a) and is transmitted to the optical fiber (5a). Propagate through the optical fiber, input to the star coupler (41), and connect to the optical fiber (6a).
, (6b), (6c). The optical signal input to the optical fiber (6a) is converted into an electrical signal by the light receiving element (7), and then sent to the amplifier (8) and the waveform shaping circuit (
9), the signal becomes the signal shown in FIG. 2 (10a) and is output onto the signal line III.

On the other hand, the transmission control circuit (17) controls the signal line (
20) Outputs a logic "1" signal on the top to set the flip-flop (15a), so the signal a (the signal on 11 is an ant game) passes through to (14a)' and sets the flip-flop (15b). At the same time, set the timer limit. The signal (21a) on the signal line (21) becomes logic "1" when the flip-flop (15b) is set, and after a predetermined time from that point, the timer (16) outputs a pulse and the flip-flop (15b) is set. 15b) and thus the flip-flop (15a).

The predetermined time set in this timer (16) (that is, the time when the signal (21a) in FIG. 2 is logic "1") is transmitted from the transmitter (2) via the star coupler (41) to the waveform shaping circuit (5 ).Thus, the signal (10a) in FIG. 2 starts from the point where the signal (21a) was reset.

In the example shown in FIG.
5b) and is input to the star coupler (41) and the optical fiber (6
a) is outputted to the signal line (10) as shown in Fig. 2 (10b) through +71, 181, and +91, and is integrated as signal (z2b) by the integrating circuit (11) and fC , is the case. At the time indicated by (24), the output of the comparator (13i) becomes logic "1", and at that time the signal (21a) is logic "1", so the AND gate (1
The signal (19a) which is the output of the circuit 4b) becomes logic "1" and completely prohibits the transmission of the signal (1a) from the transmission control circuit (17). This causes the signal (10b) to change from the signal (1a
) will not be interfered with.

However, the part of the signal (1a) that was sent before the signal (19a) becomes logic "1" will interfere with the signal (10b), but also the beginning of the signal (10b) that is farthest from the station. Since redundant bits are added that are slightly longer than the propagation delay time to the station,
Since the portion of the signal (10b) that is lost due to interference by the signal (1a) before the signal (1a) is detected does not contain true information, the necessary information can be transmitted by continuing the transmission.

If no signal from another station arrives while the signal (21a) is at logic "1", the first signal that appears on the signal line (10) is the signal (10a), and in that case, the output of the integrating circuit (11) is The output of the comparator (13) becomes logic "1" at the time point shown in (23), but at this time the signal (21a) is logic "0", so the signal (19a) becomes as shown in the signal (22a).
) is not output, and it is assumed that no signal collision will occur even if the signal (1a) continues to be transmitted.

However, after receiving the signal (10a), a signal from another station may be received. In this case, the signal (19a) is not output and the transmission of the signal (1a) continues, but the other station that has transmitted such a signal generates a collision detection signal, and the transmission of the other station is stopped. Since the portions that are interfered with by transmissions from other stations are redundant bits, the information to be transmitted will not be lost.

FIG. 3 is an explanatory diagram showing a case where a plurality of communication stations are connected to a star coupler, and the same reference numerals as in FIG. 1 indicate the same or corresponding parts (30), (31).

(32), (33), and (34) are the respective communication stations, and the communication station (31) is the most star coupler (4).
) and the communication station (32) is farthest from the star coupler (41). Therefore, the length of the optical fiber is (5b
).

(6b) is the shortest, and (5c) and ('6c) are the longest.

If the apparatus shown in FIG. 1 is used under the circumstances shown in FIG. 3, the following problems will occur.

In other words, since the communication station (31) can detect the end of signal transmission from other stations the earliest (optical fiber (6b) is the shortest), it is possible to start signal transmission from the own station earlier than other stations. At the same time, the time required to reach the star coupler (41) is also the shortest (optical fiber (5b) is the shortest), so the probability of winning the competition with other stations at the start of transmission increases.For this reason, the communication station (32 ) will reduce the probability of successful transmission.

These drawbacks are common regardless of the location of the station, and optical fiber (
This can be prevented by making the lengths of 5a), (5b), (5c)... and the optical fibers (6a), (6b), (6c)... the same. Star coupler (needs to match the length of the optical fiber from 41 to the farthest station, requiring an extra optical fiber and requiring accurate design of the length of each party fiber,
This has the disadvantage that flexibility in adapting to changes in the location of the communication station is reduced.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.In this invention, the time from the time when the end of the signal transmission of another station is detected to the time when the transmission of the own station's signal is started is constant. By giving a waiting time of This prevents a situation where a plurality of stations in the transmission standby state start transmitting at the same time, resulting in signal collision. For this reason, in the first invention of this application, in addition to the above-mentioned fixed waiting time, a random waiting time is given to each station, and in the second invention, which is filed concurrently with the above-mentioned first invention, in addition to the above-mentioned fixed waiting time, A waiting time is given in proportion to the difference between the communication station number of the source of the signal currently being received and the communication station number of the own station.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram showing an embodiment of the first invention of this application, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts,
α→ is an AND gate, (25) is a timer circuit, (26)
is the output signal line of the timer circuit (25), (27) is the reception detection circuit, (28) is the OR gate, (29) is the delay circuit,
(30) is a transmission control circuit, (31) is a transmission buffer, (
32) is a reception buffer, (33) is a transmission data input signal line, (34) is an output signal line of the reception detection circuit (27), (
35) is the received data output signal line, (36) is the delay circuit (
25) output signal line, (37) issue is or game) (28) output signal line, (38) is the transmission start activation signal line, (39) is the transmission request signal line, (
40) is a delay control circuit, and (41) is a delay control circuit (40).
) is the output line of

FIG. 5 is a waveform diagram showing signal waveforms of each part of the circuit of FIG. 4, and in the figure, ((la), (lb)), ((10
a).

(10b)), (19a), ((20a), (20
c)), (26a), (34a).

(36a), (37a), ((38a), (38b)
, (38c)) are the signal lines fil, (10),
(19), (20), (26), (34), (36).

(37), (3B) shows the above signal.

Next, the operation will be explained. Transmission data input signal line (3
The transmission data from 3) is temporarily stored in the transmission buffer (31), and a transmission request signal is sent to the transmission control circuit (30) via the signal line (34). When the transmission control circuit (30) receives the transmission request signal, it transmits the signal (19a) and the signal (37a).
) (referred to as the transmission standby control signal) is a logical “
0”, data transmission starts immediately. To start data transmission, a transmission start signal is first output onto the signal line (20). In the example shown in FIG. 5, the signals (20b), (20c
) was output under the above conditions.

Indicate the case. Under the control of the signals (20b) and (20c), a constant length of redundant bits is transmitted from the redundant bit generator (18) in advance of the data. Following this redundancy bit, the transmission buffer (31) sends a transmission start activation signal (38c).
It is activated by K, data is transmitted, and the transmitter (2)
sent to. However, in the example shown in FIG. 5, the signal (38c)
This is the only example that actually occurred.

The timer circuit (25) and reception detection circuit (2) in Fig. 4
4) The operation of the AND gate (14) is as shown in FIG.
15a), (15b), Thailand? (16), integration circuit (corresponds to 111, comparator (131), timer circuit (2)
If there is an output to the reception detection circuit (27) within the time set in 5) (that is, while the signal (26a) is logic "1"), the signal (19a) is output and the transmission control circuit (30
) immediately stops the transmission of signal (1a). In the example shown in Figure 5, a transmission from another station is received, and the reception detection circuit (2
7) output (signal (34a)) becomes logical at time tl.
1”, the signal (19a) is emitted, and the signal (1a)
is stopped in the middle of redundant bits. The redundant bits sent as signal (1a) before this stop are signal (10a)
It is output as a redundant bit of the signal (io
The data in the signal (10b) is not lost because it only overlaps with the redundant bit in b), and the data in the transmission buffer (31) is not transmitted.

If the delay time t due to the delay circuit (29) is TD + Tn, then the other station finishes transmitting and the signal (34a) pi logic "0".
'', the signal (36a) becomes logic "o" after a delay of TD+Tn, and while the signal (37a) is logic "1", the transmission control circuit (30) causes the own station to wait for transmission.

When detecting the point where the logic of the signal (37a) changes to "0", the transmission control circuit (3o) sends out the signal (20c) to 1, and sends out a redundant bit from the redundant bit generator (18).
Since the signal (19a) is not sent out this time, the transmission start activation signal (38c) is outputted, and the transmission buffer (3
The transmission data is read from 1) and sent as a signal (1a). This sent signal (1a) is received as a signal (10a), but even if a signal from another station is received before that, the signal (19a) is not emitted, and the collision detection signal is not emitted by the other station. signal transmission of other stations is stopped.

When the own station's transmission signal is received, the signal (37a) does not affect the transmission control of the own station data currently being transmitted.

However, the signal (
37a) functions effectively, and while the signal (37a) is significant, the next transmission start signal and data transmission start signal are not output.

The roles played by the delay circuit (2g) and the delay control circuit (40) in the above operation will be explained in more detail. The delay circuit (29) generates a signal (
37a). In other words, even if reception from another station is finished, transmission does not start immediately; the delay time (T
After waiting for D+Tn), a transmission start signal is output.

The delay time (TD+Tn) is a fixed delay time TD that is unique to each station, and a delay time T that is set to a different value when the delay control circuit (40) detects the rising edge of the reception detection signal.
is given by the sum of In the example shown in Figure 3, the length of the optical fiber is (5c) = (6c) = (5a)
−(6a) is the longest, and this value is Lrr+ax
Then, TD at communication stations (30) and (32) is 0.
and (5b) = (6b) = L, Lmax
If −L=ΔL, then if the delay time TD at the communication station (31) is the transmitting station (30), (31), (32)
The transmission success probabilities of the two can be made equal.

However, in the formula +I+, Cg is the speed of light within the optical fiber.

On the other hand, the delay time Tn has the following role.

If Tn is set to O and TD is set for each station according to the relationship in equation (1), the transmission success probability of all stations can be configured to be equal. When the currently transmitting station finishes transmitting, multiple stations will start transmitting in equal competition, and the transmitted signals from multiple stations will be received at the same time, resulting in a collision detection signal being output from each station. This may result in a situation where a collision cannot be avoided. This is because the falling point of the signal (26a) is set slightly before the reception detection signal is output by the own station's transmit signal so that the collision detection signal is not output by the own station's transmit signal. The time difference leads to a state in which a collision cannot be detected. Therefore, by configuring the delay time Tn to be set to a random value within a predetermined range by detecting the rising edge of the signal (34a) every time the signal (34a) is output, the delay time Tn is set to a random value within a predetermined range. By making a difference in the delay time Tn of multiple stations that have entered the state, the rate at which transmitted signals from multiple stations are simultaneously received by all stations is reduced, and the probability of occurrence of a state in which collision cannot be detected is reduced. It is something. As a method of generating the set value of the delay time Tn, for example, a random number generator is built in,
The delay time T□ may be set according to the generated random number.

FIG. 6 is a block diagram showing an embodiment of the second invention of this application, and the same reference numerals as in FIG. 4 indicate the same or corresponding parts and operate in the same manner, so a redundant explanation will be omitted. (42
) is the source address detection circuit, (43) is the transmission standby control circuit, (44) is the output signal line of the source address detection circuit (42), and (45) is the connection from the transmission control circuit (30) to the transmission standby control circuit ( signal line for control signals sent to (43), (46)
is a signal line for a transmission standby signal.

In addition, the OFF diagram is a waveform diagram showing the signal waveforms of each part of the circuit in FIG. 6, where the same reference numerals as in FIG. 5 indicate the same or equivalent signals, and (46a) is from the transmission standby control circuit (43). Represents a transmission standby signal sent out on the signal line (46).

In the circuit shown in FIG. 4, the signal (34a) and the signal (34a) in FIG.
36a) Let the delay time between 'I'D+Tn and T
D is a fixed value determined for each communication station, and T
n was set to a random value that changes each time, but in the circuit shown in Figure 6, the off-diagram signals (34a) and (3
6a) is a fixed value determined for each communication station, and a signal (46a) having a time width of Tm is generated from the falling point of the signal (37a), and the time width T is The value is different for each communication station, and the signal (46a
) is detected by the transmission control circuit (30), the signal (20c) is sent out, and the signal (37a) becomes logic "1".
Otherwise, a signal (38c) is sent out to perform data transmission. However, the transmission standby control signal (46a) functions only for transmission data that is in a transmission waiting state, and does not function for transmission data that arrives after the signal (37a) becomes logic "0". controlled.

Next, a method of setting the value of Tm for each communication station will be explained. A station address is determined for each communication station, and the transmission data of the off-line signal (1a) is transmitted with the destination address in the first field and the source address in the following field. This station address is expressed by a numerical value indicating the station number, and if there are N stations in total, then i
d'l, 2, 3°...k,...N are each station address.

Assuming that the station address of the station currently transmitting is fx, if the station address is k and Fik>x, then T=△'l'm(k-
x) and when x>k, Tm=ΔTm(k-x+N)
Set to . Here, 61 m is a value slightly larger than the time interval at which collision detection becomes impossible, and is the minimum identification time difference for collision detection. By setting Tm in this manner, it is possible to prevent the occurrence of a state in which a collision cannot be detected. □Also, while the station at the address is waiting for transmission, the value of the address X of the station currently transmitting changes randomly to some extent, so
A situation in which only a specific station has a large value of Tm and suffers a disadvantage does not occur.

Regarding the circuit in Figure 76, the source address detection circuit (42
) detects the value X of the source address and sends it to the transmission standby control circuit (43) via a signal line (44).

The transmission standby control circuit (43) stores the value of its own station address υ, Tm = ΔTm (k-x) or Tm-
Determine Tm by calculating △Trn(k-x+N),
Off diagram signal (37a) input by signal *45)
A signal (46a) is generated starting from the falling point of and sent to the transmission control recovery 30).

Figure 8 shows that the optical fiber length in Figure 3 is (5a) - (
Assuming that 6a) = (5c) = (6c) -Lmax and #) (5b) - (6b) = L, the following shows the signal flow when TD according to equation (1) is set at the communication station (31). , the horizontal axis is time t1, and the vertical axis is the star coupler (41) and communication stations (30), (31).

(32) shows the relative distance. Communication station (32) at time t1
ends data transmission. Signal indicating end of transmission (60)
reaches the star coupler (4) at time t2, reaches the communication station (31) at time t3, and reaches the communication station (3o) at time t4.

At the communication station (3o), TD is set to 0, but the 4th
In the case of the figure, transmission becomes possible at time t6 after Tnl (1d Tm in the case of Fig. 6, but to simplify the explanation, 'rnm = Tml), and the communication station (32)
Transmission becomes possible at time t5, which is delayed by TD + Tn2 (or TD + Tm2, where Tnz=Tm2) from time 3.

If Tnl = TD2 = O and the communication station (
30) at time t4, and the communication station (31) transmits at time t5, the delay time is determined so that the signals from both communication stations arrive at the star coupler (41) at the same time.

In the example shown in FIG. 8, the communication station (31) starts sending out the signal (61) at time t5, the communication station (30) starts sending out the signal (62) at time t6, and Tnl>TD2. Then, the signal (61) becomes the signal (
26a) is at logic "1";
The signal (19a) is output and the signal transmission of the communication station (30) is immediately stopped. The signal (62) reaches the communication station (31) at time t8, but at this time, the signal (26a) is at logic "0" at the communication station (31), so the signal (1
9a) is not output. However, during the period from t8 to t, the signal sent from the communication station (30) collides with the signal sent from the communication station (31), but this is a redundant bit and does not impede information transmission.

In the embodiment shown in FIG. 5, the transmission standby control signal (3
7a) is generated using a delay circuit (29) and an OR gate (28), but it can also be generated by other means such as a combination of a 7 lip-flop and a delay circuit.

In addition, in the above embodiment, a method was explained in which the delay time TD is set so that the transmission success probability of each station is equal, but by setting the delay time appropriately large or small, the transmission success probability differs. It is also possible to give probabilistic priority to each communication station.

It is also possible to set the delay time TD to 0 in each communication station, make the optical fiber lengths the same, and operate with only the delay time Tn (or Tm).

Furthermore, in the embodiment shown in FIG.
1) The signal (
46a), the design is such that the signal (46a) is always sent at the falling point of the signal (37a) when the source address is detected by the source address detection circuit (42). You may.

Further, in the embodiment shown in FIG. 6, the station address of each station is a numerical value representing the station number of the station concerned, but the station address may be represented by another code and the numerical value representing the station number of the concerned station may be determined from that code. can. According to this method of assigning addresses, it is possible to respond more flexibly to expansion of the system.

〔Effect of the invention〕

As described above, according to the present invention, after detecting the end of a received signal from another station, permission to start transmitting a signal from one's own station is granted using a fixed delay time unique to that station and a random difference every time a received signal is detected. The length of the fiber from the star coupler to the station can be made equal by delaying the received signal r by a time corresponding to the sum of the received signal r and the variable delay time set to the value determined according to the station that is transmitting it. The same effect can be obtained and the occurrence of a situation in which collision cannot be detected can be prevented.In an optical data transmission system that communicates between multiple communication stations via a star coupler while avoiding signal collision, system design is possible. It is possible to improve the flexibility and practicality of system construction.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional device, Fig. 2 is a waveform diagram showing signal waveforms of each part of the circuit in Fig. 1, Fig. 3 is a diagram showing the relative positions of each communication station and star coupler, Fig. 4 The figure is a block diagram showing an embodiment of the first invention of this application, Fig. 5 is a waveform diagram showing signal waveforms of each part of Fig. 4, and Fig. 6 is an embodiment of the second invention of this application. The block diagram and OFF diagram are waveform diagrams showing signal waveforms of each part in FIG. 6, and FIG. 8 is a diagram showing the signal flow in FIG. 3. (2)...Transmitter, (31...Light emitting element, (41...
・Star Cabra, (5a), (sb), (sc) ・
- Optical 7 fiber for optical signal use, (6a). (6b), (6c)... Optical fiber for optical signal output, (
7)...Receiving g-son, (81...Amplifier, (9)...
・Waveform shaping circuit, (14... Ant game 1・, αto・
Redundant bit generator, (25)...Timer circuit, (27
)...Reception detection circuit, (28)...OR gate, (
29)...delay circuit, (30)...transmission control circuit,
(31)...Transmission buffer, (32)...Reception buffer, (40)...Delay control circuit, (42) Source address detection circuit, (0)...Transmission standby control circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa Figure 2 10 [----------- 3rd v! J

Claims (1)

[Claims] il+ Each input optical fiber for inputting an optical signal from each communication station to the star coupler between the plurality of communication stations and the star coupler, and each input optical fiber for inputting an optical signal from the star coupler to each communication station. Each output optical fiber that outputs an optical signal is connected, and the star coupler distributes the optical signal from each input optical fiber to all output optical fibers, thereby providing mutual communication between the plurality of communication stations. In an optical data transmission device that performs data transmission, each of the communication stations includes means for adding redundant bits of a predetermined length to the beginning of transmission data and transmitting the data, and a point at which each of the communication stations starts transmitting the redundant bits. If a transmission signal from another communication station is received between the time when the signal at the start of transmission is received by the communication station concerned, a means for immediately stopping the transmission of the own station; A transmission signal from a communication station is received, and the existence time of this received signal, the fixed delay time determined for each communication station from the end point of the received signal, and the fixed delay time that changes randomly each time within a predetermined range. Means for controlling so that no signal is transmitted from the own station during the time including the delay time of the communication; A transmitting buffer for temporarily storing transmitted data and a transmitting buffer for temporarily storing received data, provided in each of the above communication stations; An optical data transmission device comprising a reception buffer. )2) The fixed delay time at each communication station is set to a value that compensates for the difference in the length of the optical fiber from each communication station to the star coupler so that the transmission success probability of each communication station is the same. An optical data transmission device according to claim 1, characterized in that: (3) The fixed delay time at each communication station is determined according to the priority order based on the transmission success probability to be given to each communication station, as claimed in claim 1. The optical data transmission device described. (41 Each input optical fiber between the plurality of communication stations and the star coupler inputs an optical signal from each communication station to the star coupler, and outputs an optical signal from the star coupler to each communication station. Each output optical fiber is connected, and the star coupler distributes the optical signal from each input optical fiber to all output optical fibers, thereby mutually transmitting data between the plurality of communication stations. In the optical data transmission device, means for adding redundant bits of a predetermined length to the beginning of transmission data at each of the communication stations and transmitting the data; If a transmission signal from another communication station is received before the signal is received by the communication station concerned, means for immediately stopping the transmission of the own station; A signal is received, and the existence time of the received signal, the fixed delay time determined for each communication station from the end point of the received signal, and the station number of the communication station from which the received signal is sent. A means for controlling the transmission of signals from the own station during a period of time including a delay time that varies depending on the relationship with the station number of the said communication station; An optical data transmission device characterized by comprising a transmission buffer for storing and a reception buffer for temporarily storing received data. (5) The fixed delay time at each communication station is such that the transmission success probability of each communication station is equal to each other. The optical data transmission device according to claim 4, wherein the value is set to correct a difference in the length of the optical fiber from each communication station to the star coupler so that The optical data transmission apparatus according to claim 4, wherein the fixed delay time at each communication station is determined according to a priority order based on the transmission success probability to be given to each communication station. .