Communication system, master communication device, and slave communication device

• US 20070086487A1
• Filed: 08/29/2006
• Published: 04/19/2007
• Est. Priority Date: 09/28/2005
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Ashi, Yoshihiro, Yasuda, Takeshi, Mutou, Ken
• Granted Patent: US 7,620,074 B2
• Time in Patent Office: Days
• US Class Current: 370/503
• CPC Class Codes: H04J 2203/0085 Support of Ethernet
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04L 12/403 with centralised control, e.g. polling

Abstract

A communication system is provided which allows synchronous devices in different synchronous communication networks to have synchronous communications with one another via an asynchronous communication network. In the communication system of the present invention, a master communication device generates a master clock based on a reference clock which is provided by a clock supplier. The master communication device sends a synchronization information frame, which contains information about the generated master clock, to plural slave communication devices via the asynchronous communication network. The slave communication devices each reproduce the master clock from the received synchronization information frame.

Claims

1. A communication system using an asynchronous communication network for synchronous communication, comprising:

a clock supplier which generates a reference clock;

a master communication device interposed between the clock supplier and the asynchronous communication network; and

plural slave communication devices one of which is provided for each of plural synchronous communication networks and is interposed between a corresponding synchronous communication network and the asynchronous communication network,

wherein the master communication device includes;

a reference clock receiving means which receives the reference clock generated by the clock supplier;

a master clock generating means which generates a master clock which is synchronized with the reference clock received by the reference clock receiving means;

a synchronization information generating means which generates synchronization information which contains information about the master clock; and

a synchronization information frame transmitting means which generates a synchronization information frame which stores the synchronization information, and which sends the generated synchronization information frame to each of the plural slave communication devices through the asynchronous communication network, and

wherein each of the slave communication devices includes;

an asynchronous frame transmitting and receiving means which receives, through the asynchronous communication network, a synchronization information frame sent from the master communication device and an asynchronous frame sent from another slave communication device, and which sends an asynchronous frame to another slave communication device through the asynchronous communication network;

a synchronous frame transmitting and receiving means which communicates a synchronous frame with a communication machine in the synchronous communication network;

a frame converting means which converts a synchronous frame which is received by the synchronous frame transmitting and receiving means into an asynchronous frame format, to have the asynchronous frame transmitting and receiving means send an asynchronous frame obtained through the conversion, and which converts an asynchronous frame which is received by the asynchronous frame transmitting and receiving means into a synchronous frame format, to have the synchronous frame transmitting and receiving means send a synchronous frame obtained through the conversion;

a synchronous frame extracting means which extracts the synchronization information frame from a frame which is received by the asynchronous frame transmitting and receiving means; and

a clock reproducing means which reproduces the master clock from the synchronization information frame extracted by the synchronous frame extracting means, and which supplies the reproduced master clock to the asynchronous frame transmitting and receiving means, the synchronous frame transmitting and receiving means, the frame converting means, and the synchronous frame extracting means, respectively.

2. A communication system according to claim 1,

wherein the synchronization information frame transmitting means sends the synchronization information frame to each of the plural slave communication devices via the asynchronous communication network at each preset clock count, based on a master clock generated by the master clock generating means, and

wherein the clock reproducing means reproduces the master clock by performing statistical processing of reception intervals of the synchronization information frame.

3. A communication system according to claim 1,

wherein the synchronization information generating means generates, at given timing, synchronization information containing a time stamp value of a counter which operates in sync with the master clock generated by the master clock generating means, and

wherein the clock reproducing means reproduces the master clock from time stamp values contained in synchronization information of the plural synchronization information frames.

4. A communication system according to claim 1,

wherein the synchronization information generating means also generates clock information which is information indicating whether or not the reference clock is received normally by the reference clock receiving means,

wherein the synchronization information frame transmitting means stores the clock information in the synchronization information frame, and

wherein, when there is an indication stored in the clock information in the synchronization information frame that the reference clock receiving means has failed to receive the reference clock normally, the clock reproducing means continues by supplying the master clock, which has been reproduced immediately beforehand, to the asynchronous frame transmitting and receiving means, the synchronous frame transmitting and receiving means, and the frame converting means, respectively.

5. A communication system according to claim 1, wherein each of the slave communication devices further includes:

means which receives synchronization information frames which are sent from the master communication device via plural routes;

means which monitors failure; and

means which switches selected synchronization information frame when a failure is detected.

6. A communication system according to claim 1, wherein the master communication device and the plural slave communication devices respectively form virtual mutual communication paths through the asynchronous communication network.

7. A communication system according to claim 6, wherein the virtual communication paths are formed using VLAN technology conforming to IEEE 802.1Q.

8. A communication system according to claim 7, wherein a value of a user priority field in a VLAN header which is attached to the synchronization information frame is set at a higher priority than a value of a user priority field in a VLAN header which is attached to an asynchronous frame communicated among the plural slave communication devices.

9. A master communication device used in a communication system which uses an asynchronous communication network for synchronous communication and interposed between a clock supplier which generates a reference clock and the asynchronous communication network, comprising:

a reference clock receiving means which receives the reference clock generated by the clock supplier;

a master clock generating means which generates a master clock which is synchronized with the reference clock received by the reference clock receiving means;

a synchronization information generating means which generates synchronization information which contains information about the master clock; and

a synchronization information frame transmitting means which generates a synchronization information frame that stores the synchronization information, and which sends the generated synchronization information frame, through the asynchronous communication network, to slave communication devices that are respectively connected to plural synchronous communication networks.

10. A slave communication device used in a communication system which uses an asynchronous communication network for synchronous communication, and interposed between asynchronous communication network and the asynchronous communication network, comprising:

an asynchronous frame transmitting and receiving means which receives, through the asynchronous communication network, a synchronization information frame, which stores synchronization information containing information about a reference clock, sent from a master communication device, and an asynchronous frame sent from another slave communication device, and which sends an asynchronous frame to another slave communication device through the asynchronous communication network;

a synchronous frame transmitting and receiving means connected to the synchronous communication network to communicate a synchronous frame with communication machines in the synchronous communication network;

a frame converting means which converts a synchronous frame, which is received by the synchronous frame transmitting and receiving means, into an asynchronous frame format, to have the asynchronous frame transmitting and receiving means send an asynchronous frame obtained through the conversion, and which converts an asynchronous frame, which is received by the asynchronous frame transmitting and receiving means, into a synchronous frame format, to have the synchronous frame transmitting and receiving means send a synchronous frame obtained through the conversion;

a synchronous frame extracting means which extracts the synchronization information frame from a frame which is received by the asynchronous frame transmitting and receiving means; and

a clock reproducing means which reproduces a master clock from the synchronization information frame extracted by the synchronous frame extracting means, and which supplies the reproduced master clock to the asynchronous frame transmitting and receiving means, the synchronous frame transmitting and receiving means, the frame converting means, and the synchronous frame extracting means, respectively.