JPH10145366A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system having a clock synchronous system that can perform the communication by an AAL1 system, despite the absence of a carrier network clock. SOLUTION: Plural switch component parts 2, which are connected to a center switch component part 1 via a transmission line 3 send the signals received from the upstream side via the line 3 to the downstream side and also perform the transfer of information to a local communication terminal via input/output ports 4. The part 1 and every part 2 include the clock synchronous control means 10a and 10b respectively. The means 10a and 10b have the PLL (phase-locked loop) circuits to perform the clock synchronous control, where a clock is extracted and reproduced from the signal received from the upstream side by the PLL circuit and used as the transmission timing for the data, which are turned into a cell and sent to the downstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a data processing center, a data generation source, a data reception device, and a communication network connecting them when data generation sources or data reception devices are linearly arranged. The present invention relates to a communication system, and more particularly, to a clock synchronization control for surely acquiring an operation clock in each of the above-described devices and a clock return control in the event of a transmission line failure.

[0002]

2. Description of the Related Art When a data generation source or a data receiving device is arranged in a straight line, a typical communication system including a data processing center, a data generating source, a data receiving device, and a communication network connecting them. Examples include a road management system, a railway management system, a sewer management system, an airfield management system, a river management system, a subway management system, and the like.

FIG. 7 is a schematic configuration diagram of these management systems. In particular, as a communication device such as the data receiving device or the data processing center, an ATM (Asynchronous Transfer Mobility) is used.
de: Asynchronous transfer mode) This is an example of realizing the system when a communication device that performs cell transfer using an exchange switch is applied. In the figure, a center switch component 1 corresponds to the data processing center, and a switch component 2 corresponds to the data receiving device. The switch component 1 and the switch component 2 are connected by a transmission line 3, and each switch component 2 is connected via an input / output port 4 to a local communication terminal corresponding to, for example, the data source. I have.

In a system having such a configuration, as a configuration for the center switch component 1 and the switch component 2 to acquire an operation clock, for example, as shown in FIG. 2, a local area network (LA) is used.
N), a configuration in which each device operates by a self-running clock unique to each device, or a method in which a carrier clock is used as a clock master and synchronized with this clock master as shown in FIG. 3 is adopted. General.

[0005] However, for example, when synchronization in data transfer is required between a data source and a data processing center in the ATM cell system, the AAL1 system is adopted.
When clock recovery is performed, a unified network clock is required, so that clock synchronization cannot be realized depending on the configuration such as the local area network.

[0006] In each of the above management systems, in most cases, each node of the network uses a private communication path in which no carrier exists. Therefore, similarly to the case of the local area network, a clock is externally required in the AAL1 system. It could not be extracted from the carrier and used.

Further, the clock system of a conventional communication device having an ATM exchange switch is not suitable for each of the above management systems because the clock is synchronized only between opposing communication devices.

[0008] As a part of measures against a failure in this type of management system, when a failure occurs in a transmission line, the transmission line in which the failure has occurred is cut off by turning back the transmission line.
A method of securing communication is known, but if such control is performed, the fault is recovered and the temporary clock disappears when returning to the normal operation mode, which has a significant effect on clock acquisition is what happened.

[0009]

As described above, in the above-mentioned conventional system, when a system is constructed with a communication device using an ATM switch, and when the AAL1 system is adopted, each node must be provided with a carrier. It is necessary to pull in the network clock, and there has been a problem that communication stabilization depends on the network clock.

[0010] Further, in the case where the transmission path in which the failure has occurred due to the return of the transmission path is disconnected to secure communication, the failure is recovered and a temporary clock disappears when returning to the normal operation mode, so that stable operation cannot be performed. There was a problem.

An object of the present invention is to provide a communication system having a clock synchronization system capable of realizing communication by the AAL1 system without a network clock of a carrier, eliminating the above problems.

Another object of the present invention is to provide a communication system provided with a clock synchronization system capable of maintaining stable communication even after switching back after a communication path has partially failed.

[0013]

The invention according to claim 1 comprises a plurality of node devices distributed and installed at a plurality of locations, one or more local communication terminals connected to each of the node devices, and In a communication system for transmitting and receiving cellularized data, a communication unit for connecting node devices in series is provided, and a clock is extracted from a signal received from upstream and reproduced, and downstream of cellularized data of the cellularized data. It is characterized by comprising clock synchronization control means for relaying a clock by using it as a transmission timing.

According to a second aspect of the present invention, in the first aspect of the present invention, the communication means is duplexed by using first and second communication means, and the first communication means is provided from the upstream to the downstream. The second communication means relays the clock from the downstream to the upstream, thereby performing clock relay in which the clock relay directions of the two communication means are opposite to each other.

According to a third aspect of the present invention, in the first and second aspects of the present invention, a clock extracted from a network accommodated in the local communication terminal is used as a clock source for a transmission path between the node devices. .

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, one of the plurality of node devices is provided with a free-running clock generating means, and the free-running clock of the node device is supplied to a network clock. As another source, the other node device reproduces a clock from data received from the node device having the free-running clock, and transmits the data to a downstream node device.

According to a fifth aspect of the present invention, in the second aspect of the invention, when a failure occurs in a part of the communication means, the failed communication means is disconnected, and the other communication means having no failure is disabled. By returning to the communication means where the
It is characterized in that clock relay can be maintained even when a failure occurs.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, a plurality of clock return points are provided so that the return can be performed at a plurality of locations on the user network interface or the node device. And

A seventh aspect of the present invention is characterized in that, in the first aspect of the invention, the node device is constituted by ATM switch means adaptable to an ATM (Asynchronous Transfer Mode) communication system.

According to a first aspect of the present invention, there are provided a plurality of node devices distributed and installed at a plurality of locations, one or a plurality of local communication terminals connected to each of the node devices, and the plurality of serially connected communication devices. And a center device connected to a start point and an end of the communication path means. The center apparatus transmits cellized data for the local communication terminal to the communication path means, and The device outputs the data for the local communication terminal connected to the node device from the cellized data from the communication path means to the local communication terminal, and outputs the data to the local communication terminal. Multiplexed transmission for multiplexing data from the local communication terminal connected to the device and data from the downstream of the communication path means and sending the multiplexed data to the communication path means The method is applicable to a management communication system that collects data from each of the local communication terminals by receiving data sent from the multiplexing transmission means to the communication path. For example, a clock can be extracted and reproduced from a signal received from a PLL by a PLL (Phase Lock Loop) circuit, and can be used as transmission timing of cellized data downstream.

According to the second aspect of the present invention, the communication means is independently 2.
A circuit is provided, and a clock is extracted and reproduced by the PL circuit L from the received signal independently of each communication means, and then the transmission timing of the cellized data to the communication means is used. Clock relays with opposite directions can be implemented.

According to the third aspect of the present invention, a carrier network is accommodated in a portion located at the local communication terminal, and a clock extracted from the network is used as a clock source of the communication means provided independently with two circuits between communication devices. be able to.

According to the fourth aspect of the present invention, in a network where there is no clock source such as a carrier network in a portion located at a local communication terminal, one node device in the network is operated by a free-running clock. A clock source for the communication means provided with two circuits, and the remaining node devices can extract and reproduce the clock by the PLL.

According to the fifth aspect of the present invention, if a failure occurs in a part of the communication means, the clock cannot be extracted and reproduced from the communication means in which the failure has occurred. By inputting the extracted and reproduced clock to the extraction and reproduction portion of the clock connected to the communication means in which the failure has occurred, it is possible to return to the position before the failure occurrence portion and continue to secure communication.

According to the sixth aspect of the present invention, by providing a plurality of return points, it is possible to speed up the return when a failure occurs, and to minimize the occurrence of a failure when the clock of the clock extraction part is switched at the time of recovery from the failure. be able to.

According to the seventh aspect of the present invention, a data generation source and a data processing center are connected by a distributed arrangement switch, and the present invention is applied to a communication system in which switch components are connected by a communication path using ATM technology, and a clock is supplied from upstream. By relaying downstream, a single clock in the system can be used as a clock source, and the entire system can be operated with the same clock, so that the AAL1 system of ATM can be synchronized.

[0027]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a communication system according to an embodiment of the present invention. A center switch component 1 that manages the entire switch is distributed and installed via a transmission line 3. And a local communication terminal (not shown) via input / output port 4
And a plurality of switch components 2 for transmitting and receiving information to and from the switch. In this system of the present invention, a center switch component 1 (hereinafter abbreviated as a center device) and a switch component 2 (abbreviated as a node device) are provided with clock synchronization control means 10a and 10b, respectively. These clock synchronization control means 10a, 10b
Has a PLL (Phase Lock Loop) circuit as described later, extracts and reproduces a clock from a signal received from an upstream by a PLL circuit, and uses the clock as a transmission timing of cellized data to a downstream. Performs clock synchronization control.

FIG. 2 shows the PLL in the node device 2.
FIG. 2 shows a clock system diagram of a portion including a circuit.
FIG. 3 is a diagram showing a functional configuration of a portion related to clock synchronization control by the PLL circuit in the node device 2. Similarly, FIG.
FIG. 3 is a diagram illustrating a functional configuration of a portion related to clock synchronization control by an LL circuit.

As can be seen from FIGS. 2 to 4, the PLL configuration according to the present invention is applied to the center device 1 and the node device 2, respectively.
The circuit includes at least three PLL circuits including a circuit 11 and a PLL circuit 12, and a PLL circuit 15 in the center device 1. The PLL circuit 15 in the center device 1 exists for each input / output port 4. Further, the node device 2 includes a clock selection unit 13, and is configured so that the clock source of the input / output port 4 can be selected from any of the PLL circuit 11 and the PLL circuit 12. Thus, in the present system, the clock source of the local communication terminal accommodated in the node device 2 via the input / output port 4 is the PLL circuit 11, the PLL circuit 12, the PLL circuit 15, and the free-running oscillator 14 (see FIG. 2) can be used as a clock master.

In the node device 2 (or the center device 1) in FIG. 3, two PLL circuits 11 and 12 for clock synchronization are provided for each device.
PLL circuits 11 and 12 extract clocks from signals received from downstream or upstream, respectively. The extracted clock is a transmission clock of the transmission path 3 opposite to the transmission path 3 that has been received. Thus, the clock can be relayed from upstream to downstream and from downstream to upstream.

Further, the node device 2 transmits the
By using the clock selection means 13 for selecting the clock extracted by the L circuit 11 or the PLL circuit 12, one of the above clocks can be input / output port 4
Can be supplied to the local communication terminal. For this reason, it is possible to supply the clock in the network to the local communication terminal, and to operate the local communication device by the clock of the same clock source.

Next, the case where the clock source is a network of carriers accommodated in the local communication terminal will be described. FIG. 4 shows a carrier network 17 in the center device 1.
Is used as a clock master and a master clock in a network is used. In this case, all devices in the network operate in synchronization with the master clock.

In FIG. 4, the center device 1 extracts a clock from the signal received from the network 17 by the PLL circuit 15. The extracted clock is input to the PLL circuit 11 and the PLL circuit 12. Here, the PLL circuit 11
And the PLL circuit 12 is configured to output the input clock as the transmission clock of each transmission path 3. Therefore, the clock extracted from the carrier network 17 may be used as the master clock of the transmission path 3. it can.

Further, in the other node devices 2, by setting the operation mode to extract the clock from the transmission line 3, the clock from the network 17 of the carrier supplied via the transmission line 3 is extracted. It becomes possible to operate. Further, one of the plurality of node devices 2 in the system is set to a mode in which the self-running oscillator 14 operates,
By setting the other node devices 2 to an operation mode for extracting a clock from the transmission line 3, the node devices 2 set to a mode in which the self-running oscillator 14 supplied via the transmission line 3 operates can be used. It becomes possible to extract and operate the running oscillator clock.

Next, with reference to FIG. 5, a description will be given of a method of ensuring communication by turning back the clock when the transmission path 3 becomes faulty. As shown in FIG. 5, when a failure (location indicated by a cross) 20 occurs on the transmission line 3, the failure 20
In the node device 2 that operates by extracting a clock from the transmission line 3 in which the error has occurred, the fault (clock interruption) occurs in one of the PLL circuits 11 and 12 under the influence of the fault 20. At this time, transmission from the node device 2 affected by the failure 20 to the center device 1 cannot be performed. In this case, in the adjacent node device 2, the transmission path 3 is controlled to the return state 30a, 30b as the failure avoiding means, and the communication is secured by disconnecting the transmission path 3 where the failure 20 has occurred.

Thereafter, when the return is canceled by restoration from a failure, it is conceivable that the clock source is lost as soon as the return of the transmission paths 30a and 30b is completed, causing a failure in communication. FIG. 6 shows a configuration example of the node device 2 (or the center device 1) for avoiding such a failure. In this example, a failure-time clock selecting means 16-1 to 16-4 is provided in the node device 2, and a switching operation of the clock is switched as necessary, thereby realizing a functional operation that does not cause a failure.

For example, in FIG. 6, when the fault 20 has occurred and the transmission line 30 indicated by the broken line has been turned back to perform communication, and the fault 20 is recovered, the return transmission line 30
Must be returned to the normal transmission path 3. The clock at the time of occurrence of the failure is supplied through the loopback transmission line 30 in the same way as the loopback of the transmission line. Therefore, at the time of restoration from a failure, if the return transmission line 30 is switched to the normal transmission line 3, a communication failure will occur. In order to switch so as not to cause a failure in the communication, in the node device 2 shown in FIG. 6, the failure-time clock selection means 16-1 to 16-4 are activated, and first,
The clock input to the fault-time clock selecting means 16-1 is selected by the fault-time clock selecting means 16-3 while keeping the return of the transmission line 30 unchanged. Thereafter, the return of the transmission path 30 is released, and the communication path is returned to the normal communication path. If the above-mentioned transmission path failure has occurred at the opposite position of the failure shown in FIG.
After selecting a clock to be input to the transmission line 3, a procedure for returning to the normal transmission path 3 is taken.

Further, there is another method for selecting a clock. This method is a method in which a signal output from the PLL circuit 11 is selected by the failure time clock selection means 16-4.
In the application of this method, when the fault position is reversed, the output of the other PLL circuit 12 is selected by the fault-time clock selecting means 16-2. In the former case, there is an advantage that the stability of the clock for switching the clock to pass through the PLL circuit is good. In the latter case, after switching the clock, the P connected to the failed transmission line
Since the LL circuit is not used for actual communication, there is an advantage that the PLL circuit can verify that the clock of the normal transmission line 3 has recovered normally after releasing the return of the transmission line 30. On the other hand, there is a problem that a clock abnormality occurs in one cycle at the moment when the clock is switched. However, this problem is caused by the L
The problem can be solved by using a PLL (synthesizer) built in an SI (Large Scale Integrated Circuit) that inputs 19.44 MHz and outputs 155 MHz. These clock selections are actually realized by a microprocessor for controlling the device.

The clock synchronization control method of the present invention is suitable for a communication system in which a data generation source and a data processing center are connected by a distributed arrangement switch, and the switch components are connected by a communication path using ATM technology. In this communication system, a PLL for clock synchronization extraction and reproduction is arranged in each of the first and second independent communication means, and the clock extracted by the first communication means is usually transmitted by the first communication means. The trusted clock is used as the transmission clock of the second communication unit, and the clock extracted by the second communication unit is used as the transmission clock of the first communication unit. Also,
If a failure occurs, the output of the PLL circuit is
Input to the L circuit. Therefore, the clock can be transferred from the first communication means to the second communication means and from the second communication means to the first communication means, and when a failure occurs, the clock can be turned back inside the apparatus. The communication can be maintained continuously even when the communication means section where the failure has occurred is disconnected.

[0040]

As described above, according to the present invention,
Since the clock is relayed from upstream to downstream, a single clock in the network can be used as a clock source, and the entire network can be operated with the same clock.
AAL1 method can be synchronized.

Further, it is possible to have a plurality of clock switching points, and to minimize the influence on the communication after the recovery of the clock return at the time of failure recovery.

Further, since the clock can be pulled from the network of the carrier accommodated at the location of the local communication terminal,
The network can be operated by the network clock of the carrier, and the network clock of the carrier can be supplied to the local communication terminal of the communication partner.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention.

FIG. 2 is a clock system diagram of the node device in FIG. 1;

FIG. 3 is a diagram showing a functional configuration of a node device in FIG. 1;

FIG. 4 is a diagram showing a functional configuration of a center device in FIG. 1;

FIG. 5 is a diagram showing an example of a transmission path return state when a failure occurs in the communication system in FIG. 1;

FIG. 6 is a diagram showing a configuration example of a node device useful for preventing clock interruption at the time of failure recovery.

FIG. 7 is a schematic configuration diagram of a communication system configured by a distributed installation type ATM switch.

8 is a system configuration diagram when each device of the communication system in FIG. 7 operates with a free-running clock.

FIG. 9 is a system configuration diagram when each device of the communication system in FIG. 7 operates in synchronization with a carrier network;

[Explanation of symbols]

Reference Signs List 1 center switch component (center device) 2 switch component (node device) 3 transmission line 4 input / output port 10a, 10b clock synchronization control means 11, 12, 15 PLL circuit 13, 13-1,..., 13-5 clock Selection means 14 Free-running oscillator 16-1, 16-2, 16-3, 16-4 Clock selection means at the time of failure 17 Carrier network 20 Failure location 30 Return transmission path at the time of failure

Claims (7)

[Claims] 1. A system comprising: a plurality of node devices distributed in a plurality of locations; one or a plurality of local communication terminals connected to each of the node devices; and communication means for connecting the plurality of node devices in series. In a communication system that transmits and receives cellized data, a clock is extracted from a signal received from the upstream, reproduced, and used as a timing for transmitting the cellized data to the downstream, thereby relaying the clock. A communication system, comprising: a clock synchronization control unit that performs the operation. 2. The communication means is duplexed using first and second communication means. The first communication means relays the clock from upstream to downstream, and the second communication means 2. The communication system according to claim 1, wherein the relay of the clock is performed from the downstream to the upstream so that the clock relay directions of the two communication units are opposite to each other. 3. The communication system according to claim 1, wherein a clock extracted from a network accommodated in the local communication terminal or the like is used as a clock source of a transmission path between the node devices. 4. A free-running clock generating means is provided in one of a plurality of node devices, and the free-running clock of the node device is used as a clock source of a network, and the other node devices have the free-running clock. 3. The communication system according to claim 1, wherein a clock is recovered from data received from the node device, and the data is transmitted to a downstream node device. 5. When a failure occurs in a part of the communication means,
By separating the failed communication means and turning back the other communication means having no failure to the failed communication means, the clock relay can be maintained even if a failure occurs. The communication system according to claim 2. 6. The communication system according to claim 5, wherein a plurality of clock return points are provided so that the return can be performed at any one of a user network interface and the node device. 7. The communication system according to claim 1, wherein the node device is constituted by ATM switch means adaptable to an ATM (Asynchronous Transfer Mode) communication system.