JPS59236A - Signal collision detecting system - Google Patents

Abstract

PURPOSE:To detect a collision at a low cost and with high reliability, by monitoring a receiving optical level by a collision detecting device installed adjacently to a star coupler. CONSTITUTION:When a transmitting signal is sent out from a transmitter 2, the signal is sent to all connected stations through a star coupler 4, also is received by an amplifier 20 of a collision detecting device 25 connected to a pair of short ports of the star coupler 4, and an output of the amplifier 20 is inputted to an integration circuit 21. In case when the transmitting signal is sent out from only one station, an output of the integration circuit 21 is smaller than a decided threshold level 24 of a discriminator 22, and no alarm signal is sent out from an alarm signal transmitter 23. On the other hand, in case when optical signals are sent simultaneously to the star coupler 4 from two or more stations, and a collision of the opticals occurs, the output of the amplifier 20 increases, the output of the circuit 21 also exceeds the threshold level 24, and an alarm signal is sent out from the transmitter 23. When the station which transmits the optical signal detects this alarm signal, it detects a collision with the optical signal of other station.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a passive star-like optical branch circuit to connect signals transmitted by two or more different stations in a star-like optical fiber communication network in which a large number of stations are connected. This invention relates to a signal collision detection method for detecting a collision.

A conventional system of this type is shown in FIG.

In the figure, (1) is the transmission signal line, (2) is the transmitter, (
31 is a light emitting element, (4) is a star coupler, (5a),
(5b), (5c), (6a), (6b
), (6c) are the optical fibers connected to the star coupler, (71 is the light receiving element, (8) is the amplifier, (9
) is a waveform shaping circuit, (11 is a receiving signal line, (Ill
is an integrator circuit, (I3 is a discriminator, (IJ is a threshold setting terminal, and (I4 is a collision signal line.) Figure 2 is a waveform diagram showing time changes of signals in each part of the transmission system. (1a) is a transmitted signal, (15a) is a received signal in which the transmitted signal in (1) above is received by the amplifier (8) via a star coupler,
(16a) is the output signal of the integrating circuit when receiving (15a), (15b) is the received signal when a collision occurs, (16b) is the output of the integrating circuit when receiving (15b), (lη is the collision This is the detection time.

Next, the operation will be explained. When there is no collision between the local station signal light and the other station signal light on the transmission path, the output signal (15a) of the amplifier (8) for the local station transmission signal (1) is input to the integrating circuit I. In response to this input, the integrating circuit I outputs an integral value output (16a) to the comparator. The determination threshold value is set to a value larger than the integral value output for the signal light of the own station (<16a), and no significant signal is output from the comparator (13), indicating that normal transmission is being performed.

When a collision occurs between the local station signal light and the other station signal light on the transmission path,
The output signal (16b) of the amplifier (8) has a large amplitude from the point where the collision occurs. Integrating circuit I for this signal
The integral value output (16b) output from the comparator exceeds the determination threshold value a at time 0η, and a significant signal is output from the comparator a. The determination threshold value 0 is calculated from the integral value output (16a) for the own station signal to the integral value output (16a) for the own station signal.
By setting the value between 6a) and the sum of the integral value output of the signal with the lowest level among the signals of other stations, even if the own station collides with the signal of any other station during transmission, This means that it can be detected.

Since the conventional system is configured as described above, if the transmission path length differs from station to station or if the branching characteristics of the star coupler (4) vary.

Since the light level received by one station has a different value for each transmitting station, it becomes difficult to set the judgment threshold for the above discriminator ← 2, and the 1 judgment tolerance becomes small, making it difficult to detect collisions. There were drawbacks such as reduced reliability.

In order to eliminate these drawbacks, this invention utilizes a pair of boats in a star coupler to monitor collisions of two or more signal lights within the star coupler, and if a collision occurs, connects A warning signal is sent to all stations that are connected to the station to notify them that a collision has occurred, and each station detects a collision by receiving this warning signal.

The drawings will be explained in detail below.

FIG. 8 is an embodiment of the present invention, and shows a block diagram of a collision detection circuit.

In FIG. 8, (1) to I are the same or equivalent parts as in FIG. 19a) (19b) is a star coupler (4
) A pair of short boats, (A) is an amplifier, C19 is an integrating circuit, (To) is a discriminator, (2) is an alarm signal transmitter that sends out in the event of a collision, (C) is a terminal for setting a threshold value. ,
@ is the entire collision detection device placed adjacent to the star coupler.

Now, when a transmission signal is sent out from the transmitter (2).

The signal is sent to all connected stations via the star coupler (4), and is also received by the amplifier of the collision detection device [@] connected to the star coupler's short pair of boats. The output of is input to the integrating circuit QB. If the transmission signal is sent out from only one station, the output of the integrating circuit 01) is smaller than the determination threshold @ of the discriminator 1, and no alarm signal is sent out from the alarm signal transmitter (c).

On the other hand, when optical signals are simultaneously sent from two or more stations into the star coupler and a collision of optical signals occurs, the output of the amplifier (2) of the collision detection device (to) increases 1-7. Integral circuit c
The output of lp also increases and exceeds the judgment threshold Q4 of the discriminator @,
An alarm signal is sent from the alarm signal transmitter (c) for a certain period of time. By detecting this alarm signal, the station that was transmitting the optical signal can detect that it has collided with the optical signal of another station.

With this method, the light level reaching the amplifier ■ of the collision detection device (to) can be designed to be almost the same regardless of the source station, making it easy to set the judgment threshold of the discriminator (2) and making a 1 judgment. The reliability of collision detection is significantly increased due to the large tolerance.

As a way to equalize the light level received by the amplifier of the collision detection device (toward), an attenuator was inserted to compensate for the difference in transmission loss due to variations in the coupling rate of the optical power between the optical fiber length and the star coupler. Possible methods include adjusting the transmitting light level or adjusting the level of the transmitted light.

Further, the warning signal may be of any type as long as it can convey the occurrence of a collision; for example, a periodic signal with little overlap with the spectrum of the transmitted signal can be used. - For example, if the transmitted signal is a 10 Mb/s bi-phase encoded signal, if it is a sine wave signal with a frequency lower than about 2.5 MHz, the filter will not pass even if it is sent superimposed with the transmitted signal. can be easily separated by

Note that above 9 describes the case where the input side optical fiber and the output side optical fiber are applied to a so-called transmission type star coupler where the input side optical fiber and the output side optical fiber are independent. If there is a position where the optical signals sent out by the station can also be tracked in common, place the above-mentioned collision detection device at that position.

By providing each station with a device for receiving the alarm signal from this collision detection device, an optical signal collision detection system can be constructed. Further, similar effects can be obtained even if this method is applied to an electrical transmission line.

As described above, in the collision detection method according to the present invention, the level of received light is monitored by a device dedicated to collision detection installed adjacent to the star coupler, and when a collision occurs, all connected stations are By sending out a warning signal to notify the occurrence of a collision, an inexpensive and highly reliable collision detection device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a ninth block diagram for explaining a conventional collision detection method, FIG. 2 is a waveform diagram of each part in a conventional collision detection device, and FIG. 8 is a block diagram for explaining a collision detection method according to the present invention. It is a diagram. In the figure, +71. (to) is the light receiving element, (81, ■ is the amplifier. (Yang is the alarm signal identification circuit, (19a) is the short star coupler input terminal, (19b) is the short star coupler output terminal, Qυ is the integrating circuit, ( 23 is a discriminator, (to)
is the alarm signal transmitter, 6!4 is the judgment threshold setting terminal, (to)
is a collision detection device, and @ is a light emitting element. In FIG. 1, the same or corresponding parts are designated by the same reference numerals. Agent Shin Kuzuno - Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A star coupler that is a passive star-shaped optical branching/coupling circuit, a plurality of optical transmitting/receiving stations connected to each input/output terminal of the star coupler by a long optical fiber, and a star coupler of the star coupler. In a star-shaped optical fiber communication network consisting of a signal collision detection device connected to a pair of input/output terminals by a short optical fiber, the signal collision detection device does not generate a significant signal while only one station is transmitting an optical signal. Did not occur. If two or more stations send out optical signals at the same time, the signal collision detection device detects this. An alarm signal is sent to all connected stations via the star coupler, and the station that is sending out the optical signal is automatically triggered by a trap when it receives this alarm signal.