JP2640909B2 - Digital information transmission path abnormality detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting an abnormality in a digital information transmission line, and more particularly to a method for detecting an abnormality such as disconnection or cross-connection of a digital information transmission line such as a local area network.

[0002]

2. Description of the Related Art An abnormality detection method for a digital information transmission line such as a local area network can be roughly classified into a method for specifying a place where an abnormality such as a disconnection has occurred, and a method for specifying which transmission path has a disconnection. .

As one of the conventional systems, as shown in Japanese Patent Application Laid-Open No. 63-246947, a device for inspection is not used, and a signal is transmitted at regular time intervals while a transmission path is kept alive. There is a connection check pulse detection method in which an error occurs when a signal is not received for a set time or longer.

As another method, there is a carrier detection method in which a carrier is constantly transmitted to a transmission line by FSK modulation, and abnormal detection is performed when the carrier cannot be received for a certain period of time.

[0005]

However, the connection check pulse detection method described above has a problem that it takes some time from occurrence of an abnormality to detection of the abnormality.
On the other hand, the carrier detection method does not have the problem that the detection time takes a long time, but it cannot be used with baseband modulation that can make the best use of the frequency characteristics of the transmission path, that is, the problem that the data transfer rate decreases. is there.

An object of the present invention is to solve the above-mentioned problem and provide an abnormality detection method for detecting an abnormality such as disconnection or cross-connection of a digital information transmission line without reducing a data transfer rate using a baseband FM modulation code. It is intended to provide.

[0007]

Means of the present invention taken to solve the above problems are as follows. That is, the present invention is a system for detecting an abnormality in a digital information transmission path using a baseband FM modulation code.
If there is valid data that has been subjected to baseband FM modulation, the valid data is transmitted. If there is no valid data, a transmitting means for transmitting a connection carrier having a frequency different from that of the valid data, and a clock is extracted from the received data. Includes a clock recovery circuit, receiving means on the receiving side for recognizing and extracting valid data and connection carrier based on the frequency of received data, and detecting both valid data and connection carrier.
If the error is not detected, the receiver's
And a step for detecting an abnormality of the digital information transmission path.

Operation The present invention uses a baseband FM modulation code and is composed of a transmitting means on the transmitting side and a receiving means on the receiving side. The transmitting means transmits, if there is valid data which has been baseband FM-modulated, such as an FM modulation code, a CMI modulation code, or a Manchester modulation code, if any. If there is no valid data, a connection carrier having a frequency different from that of the valid data is transmitted.

The receiving means reproduces a clock from the received data, recognizes the connection carrier and the valid data using the clock, and detects the presence of the valid data and the connection carrier. If neither valid data nor a connection carrier is detected, it is recognized that an abnormality such as disconnection or cross-talk has occurred in the digital information transmission path.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing an embodiment of a method for detecting an abnormality. The transmitting means A includes a switch 101 for switching between valid data and a connection carrier, and an oscillator 102 for generating a connection carrier. Oscillator 10
2 transmits 1/2 of the modulation frequency of the valid data. The receiving means B includes a detector 103 for recognizing valid data and a connected carrier, and a clock regenerator 104 for regenerating a modulated clock from the received data.

FIG. 2 is a block diagram showing one embodiment of the oscillator circuit shown in the transmitting means A of FIG. Transmission means A
Is provided with a switch 101. The switch 101 has NO
The circuit includes a T circuit 201, an AND circuit 203, an AND circuit 204, and an OR circuit 205. When there is no valid data, the output from the oscillator 102 is used as transmission data and FM-modulated. If there is valid data, switching is performed so that the valid data is used as transmission data.

Table 1 shows the FM modulation effective data and the transmission code of the connection carrier when the frequency of the connection carrier is １ ／ times the modulation frequency of the effective data.

[0013]

[Table 1]

In Table 1, the signal of the "0" level in the effective data is represented by the transmission code "01" or "10", and the sign is inverted at the start and the center of the bit. In the valid data, the signal of "1" level is represented by the transmission code "00" or "11", and the sign is inverted only at the start of the bit.

Further, the transmission code of the connection carrier is “000”.
The connection carrier has the same sign for two bits of valid data and the sign is inverted by two bits of valid data.The valid data "0" and "1" A reverse modulation scheme is also possible.

FIG. 3 shows an embodiment of the apparatus shown in the receiving means B of FIG. 1, and is an explanatory diagram showing a circuit of the receiving means in which the state transitions shown in Table 2 are realized by hardware. The receiving means B uses a programmable logic element with a register and implements a state machine for performing a state transition as shown in Table 2 by hardware. However, other configurations can be adopted.

That is, the receiving means B comprises a clock regenerator 104 for regenerating a modulated clock from the received data, an AND circuit 302 for extracting valid data from the received data, an abnormality detection register 303, a validity determination register 304, and a state holding register. I have. The state holding register 1
305, the status holding register 2 is denoted by 306, and the status holding register 3 is denoted by 307.

A modulated clock of valid data is extracted from the received data by the clock regenerator 104. This modulated clock is used for the transition timing in Table 2. The output of the received data and the output with / without valid data is performed by
D outputs only valid data from the received data.

(Operation) According to the above configuration, the signal on the transmission line repeats the inversion of the signal of "1" level and the signal of "0" level without interruption.

The receiving means B includes a clock regenerator 104, and when the period of the level inversion of the signal being received becomes longer than the period of the level inversion of the valid data or the period of the level inversion of the connection carrier, the transmission path is changed. It can be determined that an abnormality has occurred. Note that the effective data and the connection carrier have different frequencies, so that the hardware configuration for separation is simplified.

[0021]

[Table 2]

Table 2 summarizes the state transition when the frequency of the connection carrier is 倍 times the modulation frequency of the effective data. The transition is made at the timing of the clock reproduced by the clock regenerator 104. Since this embodiment has such a configuration, each communication station connected to the transmission path can transmit valid data at an arbitrary timing, and can perform abnormality detection without burdening software. It becomes possible. The present invention is not limited to the illustrated embodiment, and various modifications can be made within the scope of the claims.

[0023]

As is clear from the above description, according to the present invention, it is possible not only to detect an abnormality in a transmission line in real time with a hardware configuration without using software, but also to detect valid data and a connection carrier. Can be separated. Accordingly, since each communication station connected to the transmission path can transmit valid data at an arbitrary timing, it is effective to use the communication station in a network backup system that switches the transmission path when an abnormality occurs.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a method for detecting an abnormality.

FIG. 2 is a block diagram showing one embodiment of a circuit of a transmitter shown in a transmitting means A of FIG. 1;

FIG. 3 is an explanatory diagram showing an embodiment of the device shown in the receiving means B of FIG. 1 and showing a circuit of the receiving means in which the state transitions shown in Table 2 are realized by hardware.

[Explanation of symbols]

 A transmitting means B receiving means

Claims (1)

(57) [Claims] 1. A method for detecting an abnormality in a digital information transmission path using a baseband FM modulation code. In this method, if there is baseband FM-modulated valid data, the data is transmitted. When there is no valid data, the transmitting means includes a transmitting means for transmitting a connection carrier having a different frequency from the valid data, and a clock recovery circuit for extracting a clock from the received data. Neither valid data nor connected carrier is detected on the receiving side that recognizes and extracts
In the case, an abnormality detection method of the digital information transmission path , comprising: an abnormality detection unit on the receiving side that recognizes occurrence of an abnormality.