JPH0514300A - Subsidiary synchronizing system - Google Patents

Abstract

PURPOSE:To abolish the limitation that the frequency accuracy at the time of the self-travelling of a higher order station must be more excellent than the frequency accuracy of a lower order station when a synchronous digital transmitting network is constructed. CONSTITUTION:In a subsidiary synchronizing system to extract a clock component from a multiplexing signal to multiplex plural digital signals sent from one side station, and keep the clock frequencies of both stations equal by synchronizing the clock of other side station to the clock component, a digital signal used for the communication between a station A and a self-station C stipulated beforehand out of the multiplexed digital signals is monitored, and when the abnormality is detected at the digital signal, the clock extraction from a transmitting signal at the self-station is stopped and switching is performed to the self-travelling clock.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a network synchronization system which is a prerequisite for a synchronous digital transmission network. In particular, transmission between a plurality of stations passing on a path by including monitoring information of a path connecting two specific stations in a multiplexed signal of a hierarchical frame format such as an SDH multiplexed signal The present invention relates to a transmission network capable of detecting a path failure between two stations at both ends of a path and capable of absorbing a clock frequency difference between the two stations to some extent by stuff / destuff control.

[0002]

2. Description of the Related Art In FIG. 2, a station B is subordinately synchronized with a station A by extracting a transmission clock component from a multiplexed signal obtained by multiplexing a plurality of digital signals received from the station A and generating a clock synchronized therewith. is doing. The station C is slave-synchronized with the station B by extracting a transmission clock component from a multiplexed signal obtained by multiplexing a plurality of digital signals received from the station B and generating a clock synchronized therewith. In this way, the slave synchronization of the stations A, B and C is established. Now, if a failure occurs in the transmission path of the multiplexed signal sent from the station A to the station B, the station B cannot obtain the extraction clock to be subordinated, but since the transmission path from the station B to the station C is normal, Station C
Remains slaved to station B. In this state, the frequency accuracy of station C is determined by the free running accuracy of station B.

[0003]

In such a conventional example, when a certain station becomes free-running, the frequency accuracy of the subordinate stations subordinate to that station is determined by the frequency accuracy of the free-running station. When constructing the network, it was necessary to realize high frequency accuracy in the higher station regardless of the scale of the station.

The present invention eliminates such drawbacks, and provides a slave synchronization system which can construct a synchronous network at a relatively low cost without having to improve the frequency accuracy of the upper station in consideration of the influence on the lower station. The purpose is to

[0005]

The present invention comprises a plurality of stations connected in cascade, each of the plurality of stations including a free-running clock signal generator for generating a free-running clock. Each of the stations extracts a free-running clock signal of the uppermost station of the upper side station from the multiplexed signal obtained by multiplexing the digital signals transmitted from the upper side stations. A selection unit for selecting either one of the clock signal extracted by the extraction unit or the free-running clock signal, a control unit for giving a selection command to this selection unit, and an automatic unit according to the clock signal selected by this selection means. In a subordinate synchronization system provided with a synchronous clock generating unit for generating a synchronous clock of a station, the control unit includes a digital signal included in a multiplexed signal transmitted from the plurality of upper stations. Extracting a digital signal that is used for communication between a given host station and the own station among the signals,
It is characterized in that it is provided with means for giving a selection command for selecting the free-running clock signal to the selection section of the own station when an abnormality is detected in the extracted digital signal.

[0006]

When the abnormality is detected in the digital signal used for the communication between the predetermined station and the own station among the multiplexed digital signals, the clock extraction in the own station is stopped and the self-running is performed. The clock signal is supplied to the synchronizing section. This removes the restriction that the frequency accuracy of the higher station when it is running must be higher than the frequency accuracy of the lower station.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a case where a synchronous network is composed of three stations A, B and C as an example of the case where the subordinate synchronization method of the present invention is used. This embodiment, as shown in FIG.
It is composed of a plurality of stations A, B and C connected in cascade,
Each of the plurality of stations A, B and C is provided with a free-running clock signal generator 1 for generating a free-running clock, and each of the lower stations B and C is transmitted from each of the upper stations. A clock extraction unit 2 for extracting the free-running clock signal of the uppermost station of this upper-side station from the multiplexed signal obtained by multiplexing digital signals, either the clock signal extracted by this clock extraction unit 2 or the free-running clock signal. Selector 3 for selecting one of the clock signals, and this selector 3
And a synchronization clock generator 5 for generating a synchronization clock of its own station in accordance with the clock signal selected by the selection means 4, and further, as means characterized by the present invention, The control unit 4 selects a digital signal used for communication between a predetermined upper station and its own station among the digital signals included in the multiplexed signal transmitted from the plurality of upper stations A, B and C. It is provided with means for extracting, and giving a selection command for selecting the free-running clock signal to the selecting unit 3 of the own station when an abnormality is detected in the extracted digital signal.

Next, the operation of this embodiment will be described. Station B
Establishes slave synchronization based on the transmission clock component extracted from the multiplexed signal received from station A, and station C extracts the transmission clock component from the multiplexed signal received from station B at the clock extraction unit. , Have respectively established subordinate synchronization.
In the station C, a means for monitoring a digital signal used for communication between the stations A and C from among multiplexed signals obtained by multiplexing a plurality of digital signals received from the station B by the digital signal monitoring unit is provided. Have. If a failure occurs in the transmission line between the station A and the station B, the digital signal monitoring section of the station C monitors the digital signal used for communication from the station A. By knowing that a failure has occurred in the transmission line, it is possible to stop the extraction of the clock component with the frequency accuracy of the free-running station B. Therefore, the frequency accuracy when the station B is free running can be lower than the frequency accuracy required for the station C. That is, since the frequency accuracy of the stations B and C can be determined without limitation, the cost of the network synchronizer in the station B can be reduced.

[0009]

As described above, according to the present invention, even if a certain station becomes free-running, the frequency accuracy of subordinate stations subordinate to that station is limited by the frequency accuracy of the free-running station. Since it is not affected, there is an effect that there is no need to increase the frequency accuracy in order to prevent the influence of a failure in a certain transmission line from affecting a station lower than the station unlike the conventional method.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block configuration diagram showing a configuration of a conventional example.

[Explanation of symbols]

 1 Free-running clock signal generator 2 Clock extractor 3 Selector 4 Controller 5 Synchronous clock generator

Claims (1)

Claims: 1. A plurality of stations connected in cascade,
Each of the plurality of stations includes a free-running clock signal generator that generates a free-running clock.
A clock extraction unit that extracts the free-running clock signal of the uppermost station of this upper station from the multiplexed signal obtained by multiplexing the digital signals sent from each of the upper stations, and this clock extraction unit extracts it. A selection unit that selects one of the clock signal and the free-running clock signal, a control unit that gives a selection command to this selection unit, and a synchronization timing of the own station according to the clock signal selected by this selection unit. In the subordinate synchronization method including a determining synchronization unit, the control unit controls communication between a predetermined upper station and its own station among digital signals included in the multiplexed signal transmitted from the plurality of higher stations. A selection command of the own station is used to extract the digital signal being used and to select the free-running clock signal when an abnormality is detected in the extracted digital signal. A subordinate synchronization method, characterized in that it is provided with a means for giving.