JP2627128B2 - Clock phase telemetry device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used in digital communication networks. The present invention provides an STM (Synchronous Transfer Mod)
e) Suitable for use in methods. According to the present invention, another station belonging to one digital communication network is set as a station to be measured, and the phase of the synchronization clock signal of the station to be measured is remotely measured at the measuring station from information transmitted through the digital communication network. Related to the device.

[0002]

2. Description of the Related Art In recent years, the precision and accuracy of clock signal generators have been improved.
Instead of employing a system in which all the stations belonging to the communication network are subordinately synchronized with a standard clock signal, a system in which each station independently generates a clock signal has been used. In such a synchronous system, a phase shift occurs between clock signals with the passage of time, and the phase shift fluctuates.

Conventionally, no suitable method for measuring this phase shift has been established. In other words, the phase shift is treated as being within a certain allowable range by arranging a clock signal generator capable of maintaining a certain deviation in a test at a manufacturing stage in each station. When measurement is absolutely necessary, such as when an error occurs, an extremely high-precision standard oscillator is physically moved to the station to measure the phase difference from this standard oscillator, or temporarily a clock signal is used. The generator is switched to the standby device, and the clock signal generator is moved to a position of the reference clock signal generator, and the variation is compared and observed. Alternatively, as still another method, each station is provided with an extremely accurate clock signal generator serving as a reference, and the phase of a clock signal for synchronization with this reference is measured.

[0004]

In order to maintain the quality of a communication network high, it is necessary to observe or measure the phase difference between clock signals generated independently of each other and the fluctuation value thereof in some way as described above. Is desirable. Even if the scale is not very accurate, knowing the direction and extent of the fluctuations accordingly would be excellent information for performing advanced maintenance. As described above, it is not practical to physically move the hardware for measurement, and it is not appropriate to equip each station with extremely expensive equipment. It is desirable to observe or measure with equipment of reasonable price.

SUMMARY OF THE INVENTION The present invention has been made in such a background, and a phase difference of a clock signal and a temporal variation thereof in a state where a clock signal generator is used in each station in a communication network. The aim is to telemeter the approximate value of.

[0006]

According to the present invention, there is provided a station to be measured included in one synchronous transmission system, which is created by using a clock signal of the station to be measured, and a digital communication network is provided from the station to be measured. Detecting means for detecting a specific unit including information dependent on the phase of the clock signal from the signal transmitted to the unit, and detecting the specific unit detected by the detecting means from the information included in the unit in a predetermined form. A converting means for reproducing the clock signal phase information of the measured station, the clock signal phase information of the measured station obtained by the converting means, and the standard clock signal as a comparison reference, which has been converted into the predetermined form. And comparing means for comparing the phase information with the clock signal phase information.

[0007] The predetermined form may be a clock signal itself or a convenient form of signal representing the phase of the clock signal. This convenient form of signal may be an analog signal or a digital signal.

[0008]

In the management frame of the STM system, a pointer value that fluctuates with the fluctuation of the phase of the clock signal of the station is set when the management frame is created in each station. This means that the information on the phase change of the clock signal of the station is included.
Even if this management frame is transmitted in the communication network via a synchronization system with stuff synchronization, its pointer value is maintained without being substantially changed. The present invention pays attention to this state, and attempts to use the information on the phase fluctuation of the clock signal in another station (measurement station) in order to know the approximate value of the fluctuation of the clock signal of the station (measured station). It was invented.

The measuring station has a standard clock signal as a reference for comparison. This is not necessarily an absolute high standard,
A clock signal generated from a normal clock signal generator of the measuring station may be used. That is, in such a case, the relative phase deviation is measured, and accordingly, the corresponding information necessary for maintenance is obtained. In order to compare the phase of the clock signal of the measured station with the standard clock signal, a predetermined form of clock signal phase information is reproduced from the information on the phase fluctuation of the clock signal of the measured station transmitted from the measured station. I do. On the other hand, with respect to the standard clock signal, clock signal phase information of this predetermined form is obtained in the same manner. By comparing the two pieces of clock signal phase information, an approximate phase difference and its fluctuation can be observed.

The simplest form of the clock signal phase information is the clock signal itself. That is, a copy of the clock signal of the measured station is reproduced at the measuring station, and the reproduced clock signal is compared with the clock signal of the measuring station. The clock signal phase information may be an analog signal or a digital signal in any other convenient form, not necessarily the clock signal itself.

[0011]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. This apparatus is included in one synchronous transmission system, and includes a station under test 1, a digital communication network 2, and a measuring station 3. The measured station 1 is an arbitrary station belonging to the synchronous network and is a station to be measured. The clock signal generator 11 in the station under test 1 is the device under test. The measuring station 2 is a station belonging to the same synchronous network and has equipment for measurement.
A clock signal generator 33 for generating a standard clock signal serving as a reference for comparison is included. The measured station 1 generates a transmission signal using the clock signal, and transmits the transmission signal to the digital communication network 2 from the measured station 1.

The measuring station 3 has a demultiplexer 31 as a detecting means for detecting a specific unit including information dependent on the phase of the clock signal from the signal, and a demultiplexer 31 for detecting the specific unit detected by the detecting means. A clock signal regenerating device 32 as conversion means for reproducing clock signal phase information of the measured station in a predetermined form from the information contained in the unit. Further, the measuring station 3 compares the clock signal phase information of the measured station 1 obtained by the conversion means with the clock signal phase information converted into the above-mentioned predetermined form with respect to the standard clock signal as a comparison reference. It includes a comparing means 35. The standard clock signal is generated by the clock signal generator 33.
A display device 36 is connected to the output of the comparing means 35. The multiplexer 34 is for transmitting the transmission signal of this measuring station to the station at the subsequent stage.

In this example, the synchronous transmission system is the STM system, the specific unit is a management unit (AU), and the information depending on the phase is a pointer value.

FIG. 2 is a diagram for explaining the phase comparison of the comparing means 35, where fm is the clock signal generator 1 of the station 1 to be measured.
The clock signal fmc generated by 1 is a copy of the clock signal reproduced by the clock signal reproducing device 32, that is, the clock signal fm. fs is a standard clock signal generated by the clock signal generator 33. The phase of the clock signal of the measured station 1 has a slight error δ ′.
(= T2-t1) shows a state reproduced by the measuring station 3. Thus, the phase difference δ (= t) between the clock signal fm of the measured station 1 and the standard clock signal fs of the measuring station 3
1-t2) can be measured. This is approximately equal to (t2-t0).

FIG. 3 is a diagram showing an STM-1 (AU-3 × 3) frame format embodying the present invention. AU is an administrative unit (Administrat
iveUnit). The unit of the number in parentheses indicating the horizontal size in FIG. 3 is a byte. This frame format is composed of a set of 261-byte virtual containers (VC, Virtual Container) following a 9-byte header, which are repeatedly transmitted nine times. Six bytes of the STM-1 frame synchronization signal are transmitted, and the management unit pointer (AU-3 pointer) is transmitted in the fourth header.

FIG. 4 is a diagram showing the contents of the STM-1 frame synchronization. That is, the signal A1 as shown in FIG.
And the signal A2 is repeated three times.

FIG. 5 shows the structure of the AU-3 pointer. The figure shows the structure of the 9 bytes and the contents of the structure.

FIG. 6 is a diagram for explaining the code content of the AU-3 pointer more specifically for each bit. That is, the AU-3 pointer has an area indicating a 10-bit pointer value from the area H1i to the area H2i.
A pointer value from 0 to 782 can be indicated by 0 bits. This pointer value is for transmitting position information indicating the first byte position of the virtual container VC in the transmission frame, and this pointer value fluctuates under the influence of the phase of the clock signal of the station that creates it. . That is, this pointer value includes the phase information of the clock signal of the station that created this management unit.

[0019]

[Table 1] This will be described in more detail with reference to Table 1. Assuming now that the average pointer value is 300 (no unit), the measured station 1
The pointer value fluctuates back and forth from 300 due to the influence of the phase fluctuation of the clock signal of FIG. This situation is shown in Table 1. X, Y, and Z in Table 1 are pointer values at positions X, Y, and Z indicated by arrows in FIG.
Indicates a state after a lapse of time. When the transmitted signal passes through the positions X, Y, and Z, the pointer value slightly fluctuates under the influence of the stuffing. However, the pointer value is transmitted from the position X to the position Z. The numbers in parentheses in Table 1 indicate this variation in time (μ
s).

FIG. 7 is a diagram showing an example of the phase characteristic of the clock signal to be measured. Although the phase of the clock signal changes continuously with the passage of time, the apparatus according to the embodiment of the present invention is measured so as to change in a sawtooth shape as shown in the drawing under the influence of the stuff byte.

To explain the effect of the stuff byte,
In this STM-1 system, the bit rate is 155.2M.
b / s, and a possible phase shift in the clock signal generator is about 10 ns. The number of stuff bytes added or deleted in the communication network is about 1-2, and the time of one stuff byte is 154 ns. Therefore, the created management unit is transmitted through the stuff synchronous relay several times. Even in this case, it can be considered that the phase information is roughly maintained.

Although the above example describes the virtual container VC-3, the present invention can be similarly applied to the virtual container VC-4. In addition, the same method can be applied to a method in which the other management units include the phase information of the clock signal of the measured station.

In the measurement by the apparatus of the present invention, a remote station can be a measurement station even if synchronous relay is repeated, unless the fluctuation information of the clock signal in the management unit is terminated. When the fluctuation information of the clock signal is terminated and a new management unit is created, subsequent remote stations cannot know the phase information of the station before the termination, and the remote measurement according to the present invention becomes impossible. Become.

[0024]

As described above, according to the present invention,
By utilizing the fact that the management unit contains the phase information of the clock signal of the station that created the management unit, this phase information is detected at a remote station and compared with a standard clock signal. A phase measurement of the clock signal can be performed at a remote station. Although the measurement accuracy is not always high, the phase fluctuation of the clock signal can be remotely measured to a practically sufficient degree. By using the device of the present invention, it is not necessary to provide expensive equipment at each station or physically move a precise device, and maintenance of a communication network can be performed at a high level. Become like

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a view for explaining clock signal phase measurement of the device according to the embodiment of the present invention.

FIG. 3 is an STM-1 frame format diagram for implementing the present invention.

FIG. 4 is a configuration diagram of an STM-1 frame synchronization signal that embodies the present invention.

FIG. 5 is a view for explaining the configuration of an STM-1 management unit (AU-3) pointer for implementing the present invention;

FIG. 6 is a diagram illustrating coding of an STM-1 management unit (AU-3) pointer that implements the present invention.

FIG. 7 is a diagram showing an example of a clock signal phase change with time.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 station to be measured 2 digital communication network 3 measuring station 11 clock signal generator to be measured 12 demultiplexer 13 multiplexer 21 demultiplexer 22 multiplexer 31 demultiplexer (detection means for detecting a specific unit) 32 clock signal reproducing apparatus ( Means for reproducing phase information) 33 Clock signal generator for generating standard clock signal 34 Demultiplexer 35 Comparison means 36 Display device

Claims (1)

(57) [Claims] 1. A measured station included in one STM transmission system, which is created by using a clock signal of the measured station, and receives a pointer value from a signal transmitted from the measured station to a digital communication network. means for detecting a management unit including a POI of the management unit which is detected by the detection means
Converting means for <br/> reproduce a clock signal of the measured station in a predetermined form from pointer value, and the clock signal of the measured station obtained by the conversion means, and the standard clock signal to the comparison reference And a comparing means for comparing the clock phase.