JP2829074B2 - Communications system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a communication system in which an exchange is connected to a station of a network connected by a transmission line.

(Prior Art) Conventionally, exchanges often adopt a duplex structure to ensure reliability. Similarly, a method of duplexing a network connected to an exchange can be considered. However, it is necessary to duplicate a station along with a transmission line, which greatly increases the cost. Therefore, a method is conceivable in which one exchange is connected to two offices and one of the exchanges is selected.

However, since the exchange and the network perform communication in synchronization with each other, if a clock is exchanged from the exchange to the network, there is a possibility that the clock delivered at the time of switching between stations is temporarily disturbed. For example, when voice data of a telephone is exchanged between the exchange and the network, the noise is left because the synchronization is disturbed when the station is switched.

(Problems to be Solved by the Invention) As described above, in a communication system in which a conventional switch is connected to two stations in a network and synchronous communication is possible, the switch and the network perform communication in synchronization with each other.
When a clock is delivered from the exchange to the network, there is a problem that the clock delivered when the station is switched may be temporarily disturbed.

Therefore, the present invention provides a communication system in which an exchange is connected to two stations of a network and synchronous communication is possible.
An object of the present invention is to eliminate a temporary disturbance of synchronization that occurs when a station is switched.

[Means for Solving the Problems] According to the present invention for achieving the above object, at least two stations in a network having a plurality of stations connected by a transmission line are connected to an exchange, and the exchange has In a communication system in which one of the connected stations performs data communication by selecting one of the connected stations and one of the stations connected to the exchange performs data communication synchronized with the exchange by a clock received from the exchange, the exchange comprises Are respectively connected to a first switch means for opening and closing a data communication path with the exchange, a second switch means for opening and closing a clock input path from the exchange, and a clock input from the exchange. And a determination unit for determining whether the communication is normal or abnormal. When a station communicating with the exchange is changed, the data communication path of the change source station is opened and the change destination is changed. The first switch means of each of the change-source station and the change-destination station is respectively switched so as to close the data communication path of the station. If an abnormality is determined, the second switch means is switched so as to simultaneously change the stations which transfer clocks to and from the exchange, and the determination means of the station receiving the clock from the exchange uses the determination means. When it is determined that the clock input is normal, the switching of the second switch is canceled.

(Operation) As described above, even if the station that performs data communication is switched, the station that performs clock transfer is not changed as long as the clock input of the station that performs clock transfer is not disturbed. There is no.

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

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

In the figure, 1 is a transmission line, 2 and 3 are stations, 4 is an exchange,
5 is a wide area network. As shown in FIG.
2 and 3 of the network connected in a loop by
Connected to each other.

The exchange 4 extracts a synchronous clock from the wide area network 5 and outputs the same clock to the stations 2 and 3 to perform synchronous communication with the transmission line 1. Here, the transmission line 1 is the station 2
It is assumed that synchronous communication in the network is being executed based on the clock received in step (1). In this communication system, a clock is output to both the stations 2 and 3 to which the exchange 4 is connected, and the clocks input to the stations 2 and 3 that have passed the clock when the stations 2 and 3 are switched are disturbed. As long as there is no change, the clock delivery station is not changed.

 FIG. 2 is a diagram specifically showing such a configuration.

As shown in the figure, data from the exchange 4 is input to the transmission line 1 by data input / output units 6 and 7, and data of the transmission line 1 is similarly input via the data input / output units 6 and 7. The information is transmitted to the exchange 4.

The network clock from the exchange 4 is output to both the stations 2 and 3 to which the exchanges belong, and the clock detection circuits 8 and 9 of the stations 2 and 3 monitor the clocks input to the respective stations.
When the clock detection circuits 8 and 9 detect an input abnormality, the clock detection circuits 8 and 9 notify the monitoring station 10 and switch the switches according to a command from the monitoring station 10.
Switch between 11,12. The switching of the clock by the switches 11 and 12 is independent of the switching of the data transmission path by the switches 13 and 14. Even if the data communication with the exchange 4 becomes abnormal, the clock detection circuits 8 and 9 detect the abnormality. If not, there is no change in the location where the clock is detected.

In FIG. 2, reference numerals 15 and 16 denote data switch switching control circuits, and reference numerals 17 and 18 denote station control units.

FIG. 3 is a diagram showing a state in which the station 2 is changed to the station 3 which performs communication due to the abnormality of the station 2.

For example, even if the exchange 4 changes the station that exchanges data from the station 2 to the station 3, if there is no abnormality in the clocks passed from the exchange 4 to the station 2 and the transmission line 1, the station that exchanges the clock is switched from the station 2. Do not change to station 3. Therefore, exchange 4
There is no disruption to synchronization between the network and the network.

[Effects of the Invention] As described above, according to the communication system of the present invention,
Even at the time of switching between stations, unless the clock input to the station that has passed the clock is disturbed, the clock passing station is not changed, so that the synchronization between the exchange and the network is not disturbed.

[Brief description of the drawings]

FIG. 1 is a system diagram of a communication system according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration of a station, and FIG. 3 is an explanatory diagram of station switching. 1 ... transmission line, 2,3 ... station, 4 ... switch, 5 ... wide area network.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-288134 (JP, A) JP-A-1-311646 (JP, A) JP-A-56-147587 (JP, A) JP-A-62-1987 102643 (JP, A)

Claims (1)

(57) [Claims] At least two stations in a network having a plurality of stations connected by a transmission line are connected to an exchange, and one of the stations connected to the exchange is selected to perform data communication, In a communication system in which one of the stations connected to the exchange performs data communication synchronized with the exchange by a clock received from the exchange, each of the stations connected to the exchange establishes a data communication path with the exchange. A first switch for opening and closing, a second switch for opening and closing a clock input path from the exchange, and a determination unit for determining whether a clock input from the exchange is normal or abnormal; When changing the communication station, the change source and the change destination are set so that the data communication path of the change source station is opened and the data communication path of the change destination station is closed. A station that switches the first switch means of the station and transfers the clock to and from the exchange when the determination means of the station receiving the clock from the exchange determines that the clock input is abnormal. Are switched simultaneously so that the clock input is changed, and when the clock input is determined to be normal by the determination means of the station receiving the clock from the exchange, switching of the second switch means is performed. A communication system characterized by canceling.