JPS61121626A - Optical fiber-local area-network with signal collision detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fiber optic local area network with a signal collision detection device.

[Conventional technology]

Typical CSMA/CD (Carrier Sens
eMultiple Access/Co11isio
A fiber optic local area network of the nDetection) type includes a plurality of computers or stations connected together such that one station communicates with another station through a common bus. In particular, such networks consist of a plurality of stations, each station equipped with a transmitting and receiving device, and connected to a common bus, for example a 5-tar coupler, via transmitting and receiving optical fibers. . In such a network, only one station can access the system's nested channels at any time. A transmission made from one station becomes a transmission to all stations through the star coupler. The problem faced by conventional networks of this type is signal collision, which occurs when two or more stations transmit at the same time.
It is J. When this signal collision occurs, the data group is lost, ie, the data group is destroyed beyond recognition. Therefore, conventionally, a signal collision detection means has been provided in a transmitter/receiver (transceiver) unit.

The signal that reaches the signal collision detection means during such a signal collision is not a nest signal, but a mixture of signals of 2t or more. Conventional signal collision detection circuits rely on the assumption that the colliding signals generate a detectable amount of distortion or abnormal signal and that such distortion or abnormal signal is detectable because it is different from the normal signal. ing.

In local area networks (LANs) using fiber optic cables, the above assumption is not necessarily true, for example, if one station is located physically closer to a star coupler than another station. Station 22 in Figure 1
Or compare station 21 to station 4. The amplitude of an optical signal attenuates as it propagates through an optical fiber, so that the signal transmitted from the station closest to the star coupler to all other stations during a collision will be as weak as the signal not transmitted from a station further away. Also, the amplitude is strong. In such a case,
The transmitted mixed signal is very similar to the signal originating from the station closest to the star coupler. In other words, the signal from the farthest station will be much weaker compared to the signal from the closest station, and signal collisions will not cause any detectable amount of distortion. Signal collision detection circuitry in the far station's transceiver may detect collisions, a problem known in the art as the "dynamic Tsukulenz problem."

[Summary of the invention]

C3MA/CD type local area network (L
AN), especially when this C3MA/CD type network is configured using optical fiber, the signal transmitted from one station and reaching the star coupler via the optical fiber is split equally and sent to all stations in the network. distributed to. In such a network, the two signals will only have a signal collision after they reach the star coupler. The present invention takes advantage of this fact.

According to the present invention, an optical tap
is placed in the optical fiber near or far from the star 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 off to a signal collision detection device located physically very close to the star coupler. Each transmit fiber (but not the receive fiber) is individually tapped. The amount of light extracted from the tap is a small fraction (eg, 10%) of the amount of originally transmitted light, and most of the light is transmitted through this tag to the star coupler.

The signal collision detection device of the present invention comprises an individual optical receiver for each tap, each connected to each tap by an optical fiber. The functions of this optical receiver are 10
It receives an optical signal of megabits per second and converts it into an electrical signal, and then processes this electrical signal of 10 megabits per second with a signal collision detection device and converts it into a signal, that is, a DC voltage. . Regardless of the strength of the optical signal received by an optical receiver, each optical receiver receives this electrical signal as long as the strength of this electrical signal is within a predetermined range determined by the limits of this system and its components. Amplify to a predetermined standard amplitude. After amplification, the AC signal is rectified and P-waved and transmitted to the logic device. For example, a signal may be P-waved and rectified to generate a DC signal that is used to trip a comparator, and the output of this circuit circuit will trip a logic device responsive to this output. The tap is placed just before the star coupler in the signal collision detection device, so that if any optical receiver receives the signal, it receives the signal faithfully, i.e. without signal collisions. I will do it. The output of each optical receiver is electrically communicated to a logic device that continuously monitors the output of the optical receiver and detects the simultaneous presence of two or more signals at any time. is being done.

The signal collision detection device includes a jam signal generator connected to the logic device and the star coupler. Upon detecting the presence of one or more coexisting optical signals, the logic device actively responds to a predetermined signal sent from the logic device. The jam signal (1 MHz) is chosen to be easily distinguishable from the normally transmitted signal (10 MHz). When the jam signal reaches the transceiver, several processing steps occur. For example, (a) a jam signal activates a portion of the transmitting/receiving circuit so as to completely stop transmission for a predetermined period of time; or (b) activating the circuit with a jam signal so that the station transmits an arbitrary sequence of ``1''s and ``0'' for a predetermined length of time instead of transmitting the remainder of the data to be transmitted. or (c) a circuit for recording appropriate data of signal collisions and signal collisions compared with previous signal collisions, such as the length of signal collisions, the time between signal collisions and the number of signal collisions within a unit time. Uses jam signal to activate. Alternatively, a combination of the above (a), (b) and (c) is performed, but the process 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. connected to coupler 10 by optical fibers 14 and 15 so that one station can communicate with all other stations.
C S MA/C with 6.21.22 and 23
A D-type fiber optic local area network 1 is shown. Coupler 10 is commonly known in the art as a "star coupler" and is, for example, an rTSC8X8- 1
This is a 00J type star connection optical coupler capable of transmitting data. Optical fiber 15 is a signal transmission optical fiber, and 14 is a star fiber.
Coupler] This is an optical fiber for receiving signals from 0.

Only one station is connected to optical fiber 14 at any time.
and 15 and a star coupler 10. Transmissions from one station are distributed to all stations through star coupler IO. If more than one station transmits at the same time, collisions will occur between the signals.

In the embodiment of the local area network signal collision detection apparatus shown in FIG.
Cod 7'13, optical fiber 12, logic device 18, optical fiber 9, jam signal generator 8 and optical fiber 11 are arranged in the vicinity of star coupler IO. However, the signal collision detection device 7 may be located at a position slightly distant from the star coupler, and will function properly even if it is somewhat far away, especially when a jam signal stronger than the transmitted signal is used.

As long as the station receives jam signals that are stronger than other signals, the device works well.

If a signal collision occurs, it is detected and processed by the signal collision detection device 7. In conventional systems in which a signal collision detection device is installed in the station, in such a case, the signal that reaches one station after a signal collision is not a single signal but a mixture of two or more signals. be. Conventional in-station signal collision detection equipment relies on the assumption that this mixed signal generates a detectable amount of distortion, and that such distortion is easily recognized because it is different from a normal signal. However, such an assumption is particularly true for stations 2.21 and 23 compared to stations 3.4.5.6 and 22.
This is not necessarily true if it is located close to. Since the amplitude of the optical signal is attenuated as it propagates through the optical fibers 14 and 15, the signal from station 21 is transmitted to station 4.
For example, if the signals from stations 21.4 and 22 collide, the distributed mixed signal will be distributed to all stations with a larger amplitude than the signal from station 21. Also, since the signals from stations 4 and 22 are very weak compared to the signal from station 21, the amount of distortion in the signal from station 21 is undetectable. This is the "dynamic range problem" mentioned above.

Network 1 in FIG. 1 solves this problem. The signal from any station reaching star coupler 10 is split equally and distributed to all stations in network l. Star coupler] A signal cannot collide with another signal until after reaching 0.

Fiber cables (optical fibers 14 and 15) are connected to star coupler 10 and the various stations to form transmit and receive paths. The tap 13 is inserted into the transmission optical fiber 5, that is, the transmission optical fiber 1
Tap 5 is a passive optical element used for the transmission signal of each station. Tap 3 separates the transmission optical signal into two outputs. One of these outputs is connected to star coupler 1 as shown.
0, 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 detection device 7 may or may not be physically very close to the star coupler 10.

The amount of light extracted from the original signal by tap 13 is a small portion (say 10%), and most of the light output is from the star signal.
It is not distributed to other stations through coupler 10.

A portion (10 or less) of the light transmitted by either station enters the optical fiber 12 through the beam 77° 13 and then enters the signal collision detection device 7. As will be clearer from FIG. 2, the signal collision detection device 7 includes a plurality of taps 13 and one optical receiver 16 for each tap connected to one tap by an optical fiber 12. , logic circuit 18 and Soyam signal circuit 8
It becomes more. Note that some optical receivers are omitted in FIG. 1. The signal received by any one of optical receivers 16 may be weak or strong depending on the physical distance from star coupler 10 to the corresponding station. The function of these optical receivers 16 is 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. be. This output voltage is programmed to respond to two or more leads 1
adapted to detect the simultaneous presence of signals at 7;
That is, it is input via lead 17 to a logic device 18 adapted to respond if two or more stations transmit simultaneously (signal collisions occurring). When logic device 18 detects the presence of two or more signals on lead wire 17, it sends a predetermined signal to jam signal generating device 8 through lead wire 9 in response. The jam signal generator 8 is adapted to respond to this predetermined signal issued from the logic device 18, and in response to this signal transmits the jam signal to all stations through the optical fiber 1. Within each station, there is logic means (not shown) that responds to the jam signal issued from the jam signal generator 8.
are provided which, when actuated, perform one or more pre-associated functions.

〔Effect of the invention〕

One advantage of the local area network according to the invention
One is that the signal collision detection device completely avoids and solves the dynamic lens problem. Even when very strong and weak signals are colliding, each signal accessing a channel of the local area network is detected by a tap 13 and an optical receiver 16 connected to the tap. The signal collisions may not be successfully detected because they are detected individually by the signals.

Identification of signal collisions by logic bag #18 is based on the number of signals present in the channel at any given time, and not on the amplitude of the individual signals. In other words,
Logic device 18 is programmed to detect the simultaneous presence of two or more signals on lead 17 and when this detection is made, logic device 18 sends a predetermined signal through lead 9 to jam signal generating device 8. This jam signal generating device 8 outputs the jam signal to the optical fiber ]l, the star coupler ]0, and the receiving optical fiber 1.
4 to the station.

Another local area network according to the present invention
One advantage is that the signal collision detection device is provided independently of the actual functioning of the network. For example, different bit rates or different signal codes are used to detect signal collisions within a network.

When activated, the jam signal generator 8 excites a light emitting diode, which outputs an optical signal, which is transmitted to all stations through an optical fiber 11, a star coupler 10, and a receiving optical fiber 14. Send. This optical signal need not be of any special form. This signal can be selected for best results and can be made to best suit the system conditions.

The optical fiber 11 attached to the jam signal generating device 8 is connected to one input port (not tapped) of the star coupler 10, and the light from the jam signal generating device 8 passes through this optical fiber 11fr to star.・Coupler 10
The signal is then branched and distributed to all stations on the network. As previously mentioned, all stations are equipped with a simple circuit that recognizes all jam signals and, in response, performs one or all of the functions described above. Execute.

This signal collision detection device [7 is station 2.3.4.5.6.21
．． By virtue of being closer to star coupler IO than either 22 or 23, each station will receive the jam signal at a higher level than any other signal. All other signals emitted from each station are transmitted by the jam signal generator 8.
Longer distance, compared to the jam signal emitted from
That is, the jam signal must propagate the distance from this station to the star coupler 10''1 plus the distance from the star coupler 10 to the other station. This ensures the detection of a jam signal and the recognition that it is a jam signal rather than a data signal.Also, a jam signal has all the characteristics different from signals emitted from individual stations. Another implementation using a jam signal that is different from the data signal emitted by each station makes it much easier to detect the jam signal at each station. For example, if a higher power light source (as compared to any other light source in the system) is used, the signal collision detection device does not need to be placed in close proximity to the star coupler. .

[Brief explanation of the drawing]

FIG. 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 device of FIG. In the drawing, 1 is a local area network; 2 is a local area network;
．． 3.4.5.6.21.22 and 23 are stations, 7 is a signal collision detection device, 8 is a jam signal generator, 9 and 1
7 is lead wire, 10 is star coupler, 11.12.1
4 and 15 are optical fibers, 13 is a tap, 16 is an optical receiver, and 18 is a logic device, respectively.

Claims (1)

[Claims] 1. Two or more transmitting/receiving devices capable of transmitting and receiving optical energy, coupler means, and a signal for detecting when two or more transmitting devices are transmitting simultaneously. The signal collision detection device comprises: a collision detection device; and a plurality of optical fibers for transmitting and receiving optical signals connecting the coupler means and the transmitting/receiving device to form an optical transmission path therebetween; (b) tap means connected to each transmitting optical fiber for extracting a portion of the optical energy transmitted by said optical fiber; (c) an optical transmission line provided between each of the tap means and the optical reception means; (d) connected to the optical reception means; a logic device adapted to detect the simultaneous presence of one or more optical signals received by two or more of said optical receiving means and to transmit a predetermined signal in response to said detection; A fiber optic local area network having a signal collision detection device characterized in that: 2. The network according to claim 1, wherein said coupler means comprises a star coupler. 3. A jam signal generating device connected to the logic device and the coupler means and configured to send a jam signal to the transmitting/receiving device in response to the predetermined signal from the logic device. A network according to claim 1. 4. The network of claim 3, wherein each said transmitting/receiving device comprises logic means connected to said transmitting/receiving device and said jam signal generating device and adapted to respond to said jam signal. 5. The network according to claim 1, wherein the optical receiving means converts optical energy into an electrical signal. 6. The network according to claim 5, wherein said optical receiving means includes means for amplifying said electrical signal to a predetermined level. 7. The network of claim 6, wherein said logic device is adapted to respond to simultaneous detection of electrical signals from two or more of said optical receiving means. 8. The network according to claim 1, wherein said signal collision detection device is located closer to said coupler means than any of said transmitting/receiving devices.