JPH07193560A - Transmission line signal switching system - Google Patents

Abstract

PURPOSE:To precisely detect a phase and to realize complete no-hit switch by measuring the absolute delay time difference and a frame phase difference of two transmission lines. CONSTITUTION:In an absolute delay difference detection circuit 14, a transmission-side marker 105 from a marker generation circuit 13 and markers 107a and 107b turned back from opposite stations are respectively timing- compared so as to measure absolute delay time. Then, the absolute delay differences are detected. A delay control circuit 17 calculates a final correction delay difference from absolute delay difference information 109 and frame phase difference information 110. Then, delay circuits 16 and 18 are controlled and the phases of two reception signals are matched. A selector 19 switches the reception signals whose phases are matched without bit. In the calculation of the correction delay difference in the delay control circuit 17, whether or not the delay difference is equal to or more than a frame period is judged from the absolute delay difference, and the correction delay difference is calculated from the known frame period and the frame phase difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission path signal switching system, and in particular, SDH (Synchronous Digi) recommended in CCITT G707, 708, 709.
TNI Hierareky) synchronous transmission apparatus, the NNI input from the transmission apparatus via different transmission paths.
(Network Node Interface) The present invention relates to a transmission path signal switching method for switching a reception transmission path signal having a frame structure without interruption.

[0002]

2. Description of the Related Art Conventionally, FIG. 3 shows an example of a system configuration using this type of transmission path signal switching system. FIG. 3 is a block diagram showing the system configuration of an SDH system synchronous transmission device.

The frame structure of this synchronous transmission apparatus is STM.
-1 (Synchronous Transport)
The transmission method is ATM (Asynchon) in Mode-1).
It is of a House Transfer Mode system. At station A in Figure 3, VC (Virtual Container)
SOH (Section Over Hea) with VC-3, 4 paths generated by the path generation termination device 3 as input
d) In the generation / termination device 1, the transmission path signal having the NNI frame structure to be transmitted is branched into two, and the same signal is transmitted to the transmission sides of the transmission path 5a and the transmission path 5b, respectively. Transmission line 5a,
5b is a 4-wire type transmission line for which transmission and reception are separate, and has a redundant relationship.

In the B station, each transmission path signal input to the SOH generating and terminating device 2 from the transmission paths 5a and 5b is sent to the VC path generating and terminating device 4 after one of them is selected by the switching unit. It The same applies to the direction from station B to station A. The switching units in the SOH generation termination devices 1 and 2 first match the phases of the reception transmission path signals from the transmission paths 1 and 2 and then perform the switching in order to perform the hitless switching. It is necessary to detect the phase difference. This phase difference detection generally detects the phase difference of the frame synchronization signal.

[0005]

As described above, according to the conventional transmission line signal switching system, the frame synchronization signal is used to detect the delay difference between the reception transmission line signals input via two different routes. Although the phase difference is detected, there is no problem if this frame phase difference is within the frame period, but if the delay is more than the frame period, it cannot be detected.
For this reason, for example, a frame synchronization signal or a marker is inserted in multiple frames to detect a delay difference of a frame period or more. However, in this case, since multiple frames are used, the detection accuracy may decrease, or the detection range may be exceeded. There is a problem that there is uncertainty.

[0006]

The transmission path signal switching system of the present invention is based on CCITT G70 of the basic recommendation concerning SDH.
No. 7, 708, and 709, the transmission line signals of the NNI frame structure are transmitted and received via the two 4-wire transmission lines in the redundant relationship, and two stations are provided on the receiving side of each of the A station and the B station opposite thereto. In a transmission path signal switching system in which a reception transmission path signal from the transmission path is received and the phases are matched, and the phases are alternately switched without interruption, the station A or the station B is for delay measurement in the SOH portion of the transmission path signal. The transmission transmission line signal in which the marker is inserted is transmitted to the two transmission lines at the same time.
The marker is extracted from each of the two reception transmission path signals, converted into a folding marker, inserted into the SOH portion of the transmission transmission path signal forming a pair, and folded, and the folding markers are respectively returned from the two reception transmission path signals. And measuring the time difference with the transmitted marker, and taking 1/2 of this measured value as the absolute delay time of each transmission / reception side, from the time difference of this absolute delay time, the absolute delay difference between the two reception transmission lines. A means for calculating a frame phase difference between the two frame synchronization signals of the reception transmission path signals, and a means for calculating an accurate corrected delay difference from the absolute delay difference and the frame phase difference. A means for controlling the delay amount of the reception transmission path signal from the corrected delay difference to adjust the phase, and the reception transmission path signal having the same phase as an external switching signal. Ri and means for switching to select one.

In particular, the means for calculating the correction delay difference is
The absolute delay difference is A, the phase difference is B, the frame period of the transmission path signal is C, the predicted measurement error of the absolute delay difference is α (absolute value), and the decimal point of the calculated value of A / C. When the integer including 0 above is n, the correction delay difference is C
When (1 + n) -A <α and B <α, C (1 + n)
+ B, and C (1 + n) -A <α and B>
When α and C (1 + n) -A> α, nC + B
The method of calculating may be used.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the switching unit of this embodiment. FIG. 2 is a timing chart for explaining the method of calculating the correction delay difference in FIG. FIG. 3 is a block diagram showing the configuration of a system including the application of FIG.

In FIG. 1, FIG. 1 shows the transmission line signal switching unit of the SOH generation termination device 1 of the station A shown in FIG. 3, but the SOH generation termination device 2 of the station B also has the same configuration. . Therefore, the following description of the operation of each section is for the A station, but is common to the B station. The transmission signal 103 from the SOH generation termination unit 1 is input to the transmission interfaces 11a and 11b, and the marker 10 from the marker generation circuit 13 is supplied to each.
5 is inserted into the Z1 byte which is the spare position of the SOH, and the transmission path 5 is used as the transmission transmission path signals 101a and 101b.
It is sent to the transmission paths a and 5b.

On the other hand, the reception transmission path signals 102a and 102b from the reception paths of the transmission paths 5a and 5b are input to the reception interfaces 12a and 12b, respectively, where the SOH of the NNI frame is terminated.

Generally, when a transmission line signal is input via two different transmission lines, if there is a difference in line length, the amount of delay will be different, and therefore the frame phase will be different. That is, the reception transmission path signal 1
Normally, 02a and 102b do not have the same phase. In the receiving interfaces 102a and 102b, first B
Z1 byte markers 106a and 106 inserted on the station side
b is extracted and input to the transmission interfaces 11a and 11b for returning to the B station side, respectively. The transmission interfaces 11a and 11b insert this Z1 byte marker signal into the Z2 byte and transmit it.

Further, the reception interfaces 11a and 11b
Is the Z2 byte marker 10 of its own station returned from the B station.
7a and 107b are extracted and input to the absolute delay difference detection circuit 14, respectively. In the absolute delay difference detection circuit 14, the timings of the markers 105a and 105b of the own station transmission and the markers 107a and 107b of the B station return are compared, and the time differences are measured, respectively, and one half of each result is unidirectional. The delay time is set, and the difference between the two is set as the absolute delay difference on the receiving side of one of the transmission lines 5a and 5b.

Since this value includes an error and the like due to the transfer from Z1 to Z2, the frame phase difference detection circuit 15 also detects the frame phase difference of the transmission lines 5a and 5b in order to correct this error. This is the frame synchronization signal 108 terminated at the reception interfaces 12a and 12b.
a, 108b.

The delay control circuit 17, which receives the absolute delay difference information 109 output from the absolute delay difference detection circuit 14 and the frame phase difference information 110 output from the frame phase difference detection circuit 15, transmits the information from both. The correction delay difference between the paths 5a and 5b is obtained, and the delay circuit 16
8 delay amount is controlled. That is, when the received data written in the delay circuits 16 and 18 is read from the delay circuits 16 and 18, if the phase of the switching destination is advanced, the delay amount of the switching destination is increased and the phase of the switching destination is delayed. If so, the delay at the switching destination is reduced so that the read phases of the two signals are the same, and the phases of the received signals coming from the two transmission lines are matched. One of the received signals having the same phase is selected by the control signal from the outside in the selector 12, but there is no discontinuity or duplication of data at the time of this switching, and switching can be performed without interruption. it can.

Next, a method of obtaining the corrected delay difference in the delay control circuit 17 will be described. The measured absolute delay difference has a slight error as described above, while the frame phase difference can be accurately detected. The absolute delay difference is for determining whether or not the frame phase difference exceeds the frame period, and the final delay difference is calculated by the known frame period and the frame phase difference that can be accurately detected.

That is, as shown in FIG. 2 (FIG. 2 shows an example in which the absolute delay difference is one frame period or more), the absolute delay difference of the absolute delay difference information 109 is A, and the frame phase difference information 11
When the frame phase difference of 0 is B, the frame period of the transmission path signal is C, and the predicted measurement error of the absolute delay difference is α (absolute value), the corrected delay difference is C (1 + n) -A <α
And when B <α, C (1 + n) + B is calculated, and when C (1 + n) −A <α and B> α and C (1 + n) −A> α , NC + B.

However, n is calculated as an integer part including 0 above the decimal point of the calculated value of A / C.

[0018]

As described above, according to the present invention, the detection of the phase difference caused by the difference in the delay amount of the received signal passing through two different transmission lines is transmitted by returning the marker sent from the transmitting side to the opposite station. Since the absolute delay time of the path is measured, and at the same time, the frame phase difference is measured by the frame synchronization signal and the corrected delay difference is obtained from the both, accurate and stable phase difference detection can be performed. Therefore, there is an effect that complete non-instantaneous switching can be performed.

[Brief description of drawings]

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

FIG. 2 is a timing chart diagram for obtaining a correction delay difference in FIG.

FIG. 3 is a block diagram showing a system using FIG.

[Explanation of symbols]

 1, 2 SOH generation termination device 3, 4 VC path generation termination device 5a, 5b Transmission line 11a, 11b Transmission interface 12a, 12b Reception interface 13 Transmission marker generation part 14 Absolute delay difference detection circuit 15 Frame phase difference detection circuit 16, 18 Delay circuit 17 Delay control circuit 19 Selector

Claims (2)

[Claims] 1. CCITT of basic recommendation on SDH
Two stations are respectively provided on the receiving side of the station A and the station B opposite to the station A, which transmits and receives the transmission path signals having the NNI frame structure defined in G707, 708, and 709 via the two 4-wire transmission paths in the redundant relationship. In a transmission path signal switching system in which a reception transmission path signal from the transmission path is received and the phases are matched, and the phases are alternately switched without interruption, the station A or the station B is for delay measurement in the SOH portion of the transmission path signal. The transmission transmission line signal in which the marker is inserted is simultaneously transmitted to the two transmission lines, and the markers are extracted from each of the two reception transmission line signals, and the SOH portion of the transmission transmission line signal that forms a pair is used as a folding marker. And the return marker is extracted from each of the two reception transmission path signals and the time difference from the transmitted marker is measured. A series of means for calculating an absolute delay time between the two reception transmission paths from the absolute delay time of the transmission path receiving side, and the frame position of the frame synchronization signal of the two reception transmission path signals. Means for detecting a phase difference, means for accurately calculating a corrected delay difference from the absolute delay difference and the frame phase difference, and means for controlling the delay amount of the reception transmission path signal from the corrected delay difference to match the phase And a means for selecting and switching one of the reception transmission path signals having the same phase by an external switching signal, and a switching means for switching the transmission path signal. 2. The means for calculating the corrected delay difference comprises: the absolute delay difference A, the frame phase difference B, the frame period of the transmission path signal C, and a predicted measurement error of the absolute delay difference. When α (absolute value) or an integer including 0 of the decimal point of the A / C value is n, the correction delay difference is C (1 + n) -A <α, and when B <α, C (1+
n) + B, and when C (1 + n) -A <α and B> α, and when C (1 + n) -A> α, nC + B is calculated. Transmission line signal switching method described.