JPH0423644A - Star optical network - Google Patents

Abstract

PURPOSE:To eliminate an overhead due to a preamble by operating all stations synchronously with a distributed clock at all times so as to make a time required for clock recovery actually zero. CONSTITUTION:A phase locked loop oscillator 10 is operated by a master clock supplied from a clock photodetector 9 and uses its output and a pseudo data in a wavelength lambdaD is sent. The signal is made incident on its own data photodetector 11 via a star coupler 21 and an optical multiplexer and demultiplexer 8. A phase comparator 7 outputs an error signal to a phase shifter 6 to adjust the phase shifter so that a phase shift in an output of the phase locked loop oscillator 10 is within a prescribed value in terms of the error signal. Thus, the phase of a transmission data is synchronized with the master clock, the station exits from the startup mode, the phase shift of the phase shifter 6 is fixed and the monopoly right of a bus is left. The procedure above is repeated to each slave station (node) to take synchronization of the entire system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a technology for configuring a star optical network.

BACKGROUND TECHNIQUES AND THEIR PROBLEMS In general, bus-type networks have various features compared to ring-type networks, but on the other hand, they also have disadvantages due to the fact that the transmitting station and receiving station are constantly changing. The most basic of these is the need for a preamble for each /"7t, which results in an overhead on data transmission. Particularly in applications where the (kerato) is short, this becomes a non-negligible problem. The lower limit of the preamble length is usually given by the sum of (1) the transmitter enable time, (2) the receiver setup time, and [3) the time required for clock recovery. , (2) is a particular problem when using light as a medium.In other words, the response of radar APC, DC regeneration of photodiode, etc. are problems.However, these problems are being overcome by devising drive circuits, etc. Regarding the remaining time required for clock regeneration (3) above, in the case of a normal method (for example, using a phase-locked loop circuit), if you try to shorten the response time (pull-in time), the stability of the regenerated clock will increase. There are fundamental problems such as deterioration of performance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a star optical network that can overcome the problems of the prior art as described above.

Means for Solving the Problems The present invention provides a star type optical network in which a star coupler and a plurality of stations are connected in a star type via optical fiber cables, each station has an optical transmitter for clock and an optical transmitter for data. a clock optical receiver, a data optical receiver, a phase-locked loop oscillator, a phase shifter for shifting the phase of the eight phase-locked loop oscillators, and a phase comparator. In some cases, one master station transmits the master clock using an optical clock transmitter to another slave station via a star coupler, and the slave station which has exclusive control of the bus transmits the master clock using an optical clock transmitter. When the clock optical receiver receives the master clock, the station operates a phase-locked loop oscillator with this master clock, and transmits pseudo or real data via the data optical transmitter at the output of the phase-locked loop oscillator. This pseudo or real data is received by its own data optical receiver via a star coupler, and its phase comparator compares the received signal with the master clock. After adjusting the phase shifter using the error signal from the slave station so that the phase of the transmitted pseudo or real data is synchronized with the master clock, the slave station relinquishes the exclusive right to the bus to another slave station and gains exclusive right to the bus. The other slave stations are characterized in that they are synchronized with the master clock in the same way, and in this way, all the stations are synchronized with the master clock.

According to the present invention, by operating all stations in synchronization with a constantly distributed clock, the time required for clock regeneration is virtually zero, and the preamplifier can be used in a bus type network using star couplers. It is possible to eliminate the overhead caused by files.

According to the present invention, when each station obtains exclusive rights to the bus, that is, access rights to the bus, and performs transmission, the transmission bit string is
By synchronizing with the master clock that is always distributed by the parent station, each receiving station uses the master clock to reproduce the bit string. For this purpose, it is essential that the transmission clock of each station is always synchronized with the master clock, and that the phases of the two clocks of each receiving station match. This is, in principle, the same as matching the phases of both on a star coupler, and is achieved as follows. Each station establishes exclusive rights to the bus by some means, and then transmits a bit pattern using a transmission clock synchronized with the mask clock (the phases are not yet aligned at this time).

Then, it compares its own signal with the master clock and adjusts the phase of the transmission clock with respect to the master clock so that the two match.

Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying drawings.

FIG. 1 is a block diagram showing an example of the configuration of an optical transceiver at each station in a star optical network as an embodiment of the present invention using optical wavelength multiplexing, and FIG.
FIG. 2 is a conceptual diagram of a star optical network configured of a plurality of stations having optical transceivers as shown in the figure and a star coupler.

As shown in Figure 2, this star-shaped optical network is
It includes a plurality of stations 22 respectively located at nodes 1 to N connected to a star coupler 21 via an optical fiber cable 23. The optical transceiver included in each station 22 is a stabilized crystal oscillator 1, as shown in FIG.
, a clock optical transmitter 2, an optical multiplexer/demultiplexer 3, a data buffer 4, a data optical transmitter 5, a phase shifter 6,
It includes a phase comparator 7, an optical multiplexer/demultiplexer 8, a clock optical receiver 9, a phase-locked loop oscillator 10, a data optical receiver 11, and a regenerator 12.

Next, the operation of a star optical network including such a plurality of stations 22 will be explained. First, only one station in the entire system becomes a master station and supplies a master clock to other stations (slave stations). A slave station has two operation modes (startup operation and normal operation), and the startup operation is performed for a certain period according to the present invention only when the system is started up or when the node (station) is added to an operating system. It is something that is done.

During startup operation, the station that has become the master station is
The stabilized output of the oscillator 1 is supplied as a master clock for the entire system from a clock transmitter 2 via an optical multiplexer/demultiplexer 3. The wavelength of this signal is λ. and
This signal is sent via the star coupler 21 to the clock optical receiver 9 through the optical multiplexer/demultiplexer 8 of each slave station. When the slave station is in its startup mode, it acquires exclusive rights to the bus by some method and then performs the following operations. That is, the phase-locked loop oscillator 1 is activated by the master clock supplied from the clock optical receiver 9.
0 is operated and its output is used to transmit pseudo data at wavelength λD. The signal enters its own data optical receiver 11 via the star coupler 21 and the optical multiplexer/demultiplexer 8. The electrical signal is sent to the phase comparator 7 through line 13 and compared with the master clock electrical signal sent from clock optical receiver 9 through line 14. As a result of such a comparison, the phase comparator 7 applies an error signal to the phase shifter 6 and adjusts the phase shifter so that the amount of phase shift of the 8 forces of the phase-locked loop oscillator 1o is determined by the error signal. Ensure that the value is below a predetermined value. If the above-mentioned error signal can be reduced to a predetermined value or less by such a feedback loop,
Since the phase of the transmitted data has been synchronized with the master clock, the station exits the startup mode, fixes the phase shift amount of the phase shifter 6, and relinquishes exclusive rights to the bus. This procedure is repeated for each slave station (node) to synchronize the entire system.

In the subsequent normal operation, data from any station is synchronized with the master clock at the input of all stations, and the output of the phase-locked loop oscillator 1o is transferred from the data optical receiver 11 to the output of the phase-locked loop oscillator 1o. If you demodulate using
It becomes possible to use the first bit of an incoming packet as valid data. Furthermore, if necessary, when the device itself acquires exclusive rights to the bus, it may perform fine adjustments similar to those described above using actual data packets.

In the above-mentioned embodiment, light is used as a medium and data transmission and clock distribution are performed on one transmission path by wavelength multiplexing. However, the present invention is not limited to this, and for example, The same effect can be achieved by using Further, in the transruber dedicated to the slave station, the clock optical transmitter can be omitted.

Effects of the Invention According to the configuration of the present invention as described above, in a star optical network using a star coupler, all stations can be operated in synchronization with the clock that is always distributed, so that the time required for clock regeneration is reduced. The time can be reduced to zero, and the overhead caused by preamplification can be eliminated, and therefore the efficiency of use of the transmission path can be increased.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an optical transceiver at each station in a star optical network as an embodiment of the present invention using optical wavelength division multiplexing. FIG. 2 is a conceptual diagram of a star optical network configured with four optical transceivers, a plurality of stations, and a star coupler. 1...Crystal oscillator, 2...Clock optical transmitter, 3...Optical multiplexer/demultiplexer, 4...
・Data buffer, 5... Data optical transmitter,
6... Phase shifter, 7... Phase comparator, 9... Optical multiplexer/demultiplexer, 9... Optical receiver for clock, 10... ...Phase-locked loop oscillator, 11...
... Data optical receiver, 12 ... Regenerator, 1
3... Data signal line, 14... Clock signal line, 21...
・Star coupler, 22...station, 23...
・Optical fiber cable.

Claims (2)

[Claims] (1) In a star optical network in which a star coupler and multiple stations are connected in a star configuration via optical fiber cables, each station has an optical transmitter for clock, an optical transmitter for data, and an optical receiver for clock. , a data optical receiver, a phase-locked loop oscillator, a phase shifter for shifting the output of the phase-locked loop oscillator, and a phase comparator. One station uses a clock optical transmitter to transmit the master clock to another slave station via a star coupler, and the slave station that has obtained bus exclusive rights transmits the master clock to its optical clock receiver. When receives the master clock, it operates a phase-locked loop oscillator with this master clock, and transmits pseudo or real data through an optical transmitter for data at the output of the phase-locked loop oscillator, and transmits this pseudo or real data. is received by its own data optical receiver via a star coupler, the received signal and the master clock are compared by its phase comparator, and the error signal from the phase comparator is used to convert the phase shifter. After adjusting the phase of the transmitted pseudo or real data so that it is synchronized with the master clock, the bus exclusive right is relinquished to another slave station, and the other slave stations that have obtained the bus exclusive right do the same. Obtain synchronization with master clock,
In this way, a star type optical network is characterized in that all stations can be synchronized with the master clock. (2) The star optical network according to claim 1, wherein the clock distribution and data exchange are performed via the same optical fiber cable by wavelength multiplexing, subcarrier transmission, or the like.