JPH0640635B2 - Fiber Optic Local Area Network with Signal Collision Detector - Google Patents

Description

The present invention relates to an optical fiber local area network provided with a signal collision detection device.

[Conventional technology]

Typical CSMA / CD (Carrier Sense Multiple Access / C
An ollision detection type fiber optic local area network comprises a plurality of computers or stations connected to each other so that one station can communicate with another station over a common bus. In particular, such a network is one in which each station is equipped with a transmitter / receiver and, for example, via a transmitting optical fiber and a receiving optical fiber, for example a star coupler.
It is composed of a plurality of stations connected to a common bus such as. In such a network, only one station can access a single channel of the system at any given time. The transmissions made by one station will be for all stations through the star coupler. The problem faced by this type of conventional network is the "signal collision" that occurs when two or more stations transmit at the same time.
llision) ”. When this signal collision occurs, the data group is lost, that is, the data group is unknowingly destroyed. Therefore, conventionally, a signal collision detecting means is provided in a transceiver (transceiver) unit. The signal arriving at the signal collision detection means during such a signal collision is not a single signal but a mixture of two or more signals. Conventional signal collision detection circuits rely on the assumption that this colliding signal is producing a detectable amount of distortion or anomalous signal and is detectable because such distortion or anomalous signal is different from the normal signal. ing.

In a local area network (LAN) using fiber optic cables, the above assumption is not always true, for example, when one station is physically closer to the star coupler than another station. Compare station 21 to station 22 or station 4 in FIG. The amplitude of the optical signal is attenuated as it propagates through the optical fiber, so the signal transmitted from the station closest to the star coupler to all other stations during a collision is less than the signal transmitted from stations further away. The amplitude is strong. In such a case, the transmitted mixed signal is
Very similar to the signal emanating from the station closest to the star coupler. In other words, the signal from the furthest station is much weaker than the signal from the closest station, and signal collisions do not produce any detectable amount of distortion. The signal collision detection circuit provided in the transceiver of the distant station cannot detect collisions, and this problem is known to those skilled in the art as the "dynamic range problem".

Further, Japanese Patent Application Laid-Open No. 58-96436 discloses an optical data communication system in which an optical star repeater is provided with a collision detection device for detecting that a plurality of terminal devices simultaneously perform transmission operations. That is, an optical signal from each terminal device is converted into an electric signal and amplified, and then converted into an optical signal again, and then transmitted to all the terminal devices via the receiving optical fibers. An electric collision detection device is provided in the optical star repeater. This collision detection device detects a signal collision by comparing a change in input signal amplitude with a comparator or by simultaneously generating a plurality of signals in a logic circuit. When a signal collision is detected, the collision signal is transmitted to each terminal device or the signal transmission to each terminal device is interrupted.

However, in this conventional optical data communication system,
It is necessary for the optical star repeater to have a complicated collision detection device in addition to its original function of receiving the optical signal transmitted from the terminal device and transmitting it to all the terminal devices via the transmission optical fiber. Therefore, it is necessary to change the entire optical star repeater in order to apply it to the existing optical data communication system. Further, there is no freedom to install the collision detection device at any place.

Therefore, an object of the present invention is to provide a basic part of an optical fiber local area network, that is, a plurality of station couplers and optical fibers for transmitting and receiving signals connecting them, without substantially affecting these bypasses (sides). To provide a fiber optic local area network with a new signal collision detection device that is coupled to these via optical fibers. Another object of the present invention is to provide an optical fiber local area network including a signal collision detection device that can be easily applied to an existing system and has a large degree of freedom of installation location.

[Means and Actions for Solving Problems]

In order to solve the above-mentioned problems of the prior art, the optical fiber local area network of the present invention is configured so that the signal collision detection device is bypassed from the backbone. That is, the plurality of stations, the coupler, and the signal transmitting and receiving optical fibers interconnecting them form a network for transmitting and receiving data between the stations via the coupler by an optical signal. The signal collision detection device is provided with a tap for extracting the optical signal of each signal transmission optical fiber by the detection optical fiber. The output of the detection optical fiber is converted into an electric signal by the optical receiver and amplified, and the signal collision is detected by the logic device. The jam signal generator is driven by this detection output, and the optical jam signal is transmitted through the optical fiber.

According to the present invention, an optical tap is a star
Installed in an optical fiber near or far from the coupler. A tap is a passive optical element that separates the transmitted light into two parts. One part of the light is transmitted to the star coupler and the other part is branched to the signal collision detector, which is physically very close to the star coupler. Each transmitting fiber (not the receiving fiber) is tapped. The amount of light extracted from the tap is a small fraction (eg, 10%) of the original amount of transmitted light, and most of the light is transmitted through this tap to the star coupler.

The signal collision detection device in the present invention comprises an individual optical receiver for each tap, which is connected to each tap by an optical fiber. The function of this optical receiver is 10
Receiving a megabit / second optical signal, converting it to an electrical signal, and then converting this 10 megabit / second electrical signal to a signal that can be processed by a signal collision detector, ie a DC voltage. Regardless of the intensity of the optical signal received by the optical receiver, each optical receiver will output this electrical signal as long as it is within a predetermined range determined by the limits of the system and its components. Amplify to the desired standard amplitude. After amplification, the AC signal is rectified and waved and transmitted to the logic device. For example, the signal is waved and rectified to produce a DC signal which is used to trip a comparator whose output triggers a logic device responsive to this output. The tap is placed immediately before the star coupler in the signal collision detection device, so that when any optical receiver receives the signal, that optical receiver receives the signal faithfully, that is, in the form of no signal collision. Will be done. The output of each optical receiver is electrically transmitted to a logic device which continuously monitors the output of the optical receiver and detects the simultaneous presence of two or more signals at any time. Has been done.

A jam signal generator connected to the logic device and the star coupler is provided in the signal collision detection device, and the jam signal generator is provided in an optical receiver having two or more logic devices. If it detects the presence of one or more coexisting optical signals, it will positively respond to a given signal sent from this logic device. The jam signal (1 megahertz) is chosen to be easily distinguishable from the normally transmitted signal (10 megahertz). When the jam signal reaches the transceiver, some processing can be done. For example, (a) a part of the transmission / reception circuit is operated by a jam signal so as to completely stop the transmission for a predetermined period. Or (b) actuating the circuit with a jam signal such that the station sends an arbitrary sequence of "1" s and "0" s for a predetermined length of time instead of sending the rest of the data to be sent. Or (c) a circuit that records appropriate data for signal collisions compared to signal collisions and previous signal collisions, that is, the length of signal collisions, the time between signal collisions, the number of signal collisions per unit time, etc. Uses jam signal to activate. Alternatively, a treatment combining the above (a), (b) and (c) is performed,
It is not limited to these.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a plurality of computers or stations 2, 3, 4, 5, 6, 21, connected to coupler 10 by optical fibers 14 and 15 so that one station can communicate with all other stations. A CSMA / CD type fiber optic local area network with 22 and 23 is shown. Coupler 10 is commonly known to those of ordinary skill in the art as "Star Coupler," for example, "TSC8," manufactured by "Canstar Communications Division" of "Canada Wire and Cable Limited" of Ontario, Canada. It is a star-connectable optical coupler of the type x8-100 "that can be transmitted. The optical fiber 15 is an optical fiber for signal transmission, and 14 is an optical fiber for signal reception from the star coupler 10.

Only one station can access the transmission channel constituted by the optical fibers 14 and 15 and the star coupler 10 at any one time. The transmissions from one station are distributed to all stations through the star coupler 10. Collisions between signals occur when more than one station transmits at the same time. In the embodiment of the signal collision detection device of the local area network shown in FIG. 1, tap 13, optical fiber 12, logic device 18, lead wire 9, jam signal generator 8 and An optical fiber 11 is arranged near the star coupler 10. However, the signal collision detection device 7 may be provided at a position slightly distant from the star coupler, and even if the jam signal stronger than the transmission signal is used, the signal collision detection device 7 functions properly even if it is a little far.
As long as the station receives a stronger jam signal than the other signals, the device works well.

When a signal collision occurs, it is detected and processed by the signal collision detection device 7. In the conventional system in which the signal collision detection device is provided in the station, in such a case, the signal reaching one station after the signal collision is not a single signal but a mixed signal of two or more signals. Is. Conventional signal collision detectors installed in stations rely on the assumption that this mixed signal causes a detectable amount of distortion, and that such distortion is different from the normal signal and is easily recognizable. However, such an assumption is based on the fact that the stations 2, 21 and 23 are particularly suitable for the coupler
Not always correct when placed close to. Because the amplitude of the optical signal is attenuated as it propagates through the optical fibers 14 and 15, the signal from station 21 is distributed to all stations with a greater amplitude than the signal from station 4 or 22. If, for example, the signals from stations 21, 4 and 22 cause a collision, the distributed mixed signal will be very similar to the signal from station 21. Also, since the signals from stations 4 and 22 are much weaker than the signal from station 21,
The amount of distortion in the signal from station 21 will be undetectable. This is the "dynamic range problem" described above.

The network 1 of FIG. 1 solves this problem. The signal from any station that reaches the star coupler 10 is split into equal parts and distributed to all stations in the network 1. Only after reaching the star coupler 10 can a signal collide with another signal. Fiber cables (optical fibers 14 and 15) are star coupler 1
0 and various stations are connected to form a transmission path and a reception path. The tap 13 is inserted into the transmitting optical fiber 15, that is, the transmitting optical fiber 15
The tap 13, which is a passive optical element used for the transmitted signal of each station, separates the transmitted optical signal into two outputs. One of these outputs is a star
It is connected to the coupler 10 and the other output is connected to the signal collision detection device 7 through the tap 13 and the optical fiber 12. The signal collision detector 7 may or may not be physically very close to the star coupler 10. Tap 13
The amount of light that is extracted from the original signal by the
And distributed to other stations.

Some of the light transmitted by either station (1
0% or less) flows into the optical fiber 12 through the tap 13 and is then input to the signal collision detection device 7.
The signal collision detection device 7 has a plurality of taps 13 and one optical receiver 16 for each tap connected to one tap by the optical fiber 12, as will be more apparent with reference to FIG. , A logic circuit 18 and a jam signal circuit 8. The optical receiver 16 is also provided between the taps 13 of the stations 3 to 6 and the logic device 18, but the illustration is omitted in FIG. 1 for convenience.
The signal received by any one of the optical receivers 16 may be weak or strong, depending on the physical distance from the star coupler 10 to the corresponding station. The function of these optical receivers 16 is then to detect the presence of an optical signal, convert this optical signal into an electrical signal, and then convert this electrical signal into a DC output voltage for processing as described above. is there. This output voltage is programmed to respond to it and has two or more leads 1.
Made to detect the simultaneous presence of signals in 7.
That is, it is input via a lead 17 to a logic device 18 adapted to respond when two or more stations are transmitting at the same time (signal collision has occurred). When the logic device 18 detects that two or more signals are present on the lead wire 17, it responds by sending a predetermined signal through the lead wire 9 to the jam signal generator 8.
Send to. The jam signal generator 8 is adapted to respond to this predetermined signal emitted from the logic device 18, and responds to this signal by sending a jam signal to the optical fiber 11
To all stations via. Within each station there is provided logic means (not shown) responsive to the jam signal emitted by the jam signal generator 8 which, when activated, has one or more pre-associated Perform a function.

〔The invention's effect〕

According to the optical fiber local area network provided with the signal collision detection device of the present invention, the signal collision detection device does not change the backbone of the network including a plurality of station signal transmission / reception optical fiber pairs and couplers,
By bypassing this, the signal collision detection device is coupled via an optical fiber. Therefore, the installation location of the signal collision detection device can be freely selected with respect to the network backbone or the coupler, and the signal collision detection device can be easily added to the existing network. Further, the coupler has a remarkable effect such that it is sufficient to simply perform the original function of simply transmitting the optical signal received from each station and the jam signal generator to all the stations via the signal transmitting optical fiber.

[Brief description of drawings]

1 is a schematic diagram of a local area network according to the present invention, and FIG. 2 is a block diagram of the signal collision detection apparatus of FIG. In the drawing, 1 is a local area network,
2, 3, 4, 5, 6, 21, 22 and 23 are stations, 7 is a signal collision detector, 8 is a jam signal generator, 9 and 17 are leads, 10 is a star coupler, 11, 12,
Reference numerals 14 and 15 are optical fibers, 13 is a tap, 16 is an optical receiver, and 18 is a logic device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Geely Richardson John Jones, Tory Burk Court, Raleigh, North Carolina 10516 (72) Inventor Richard Peekery, Howard Road 2616 (56), Raleigh, North Carolina, United States References 58-96436 (JP, A)

Claims (1)

[Claims] 1. A plurality of stations, a coupler, a pair of optical fibers for signal transmission and reception for interconnecting the stations via the coupler, and an optical fiber for signal transmission from the station. In the optical fiber local area network comprising a signal collision detection device for detecting the collision of signals sent to the coupler, the signal collision detection device is connected to the signal transmission optical fiber of each station, A tap for extracting a part of the optical signal transmitted through the signal transmitting optical fiber to the detecting optical fiber, and a plurality of optical receivers for amplifying the optical signal extracted to the detecting optical fiber by the tap to obtain an electric signal A logic device for detecting collisions of two or more signals of the plurality of optical receivers, and an output of the logic device. A jam signal generator that is driven to generate a jam signal, and an optical fiber that inputs an optical signal of the jam signal generator to the coupler, and the signal collision detection device is configured to be bypassed by the optical fiber. An optical fiber local area network equipped with a signal collision detection device characterized in that