JP2611805B2 - Transmission line switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for time division multiplex digital transmission. In particular, the present invention relates to a transmission line switching method for switching an active transmission line for transmitting an information sequence in units of cells to a protection transmission line. The present invention is suitable for use in an optical fiber communication device.

[Conventional technology]

FIG. 6 is a block diagram of a conventional digital transmission apparatus.

In the transmitting device 1, the digital information sequence is multiplexed by the multiplexing conversion device 2 and transmitted to the working transmission line 5 via the transmission line switch 12 and the interface circuit 14.

In the receiving side device 7, the signal of the working transmission line 5 is received by the interface circuit 16 and supplied to the demultiplexing device 9 via the transmission line switch 38. The demultiplexing device 9 separates the multiplexed information sequence.

When the line or the transmission device fails in the working transmission line 5, when the operation needs to be stopped for maintenance, or when the faulty part is repaired and then switched back, the transmission line switching switches 13 and 38 are used. The transmission line 5 is switched to the backup transmission line 6.

[Problems to be solved by the invention]

However, in the conventional transmission line switching method, switching from the working transmission line 5 to the protection transmission line 6 is performed independently of the main signal. For this reason, the delay difference between the working transmission line 5 and the protection transmission line 6 cannot be absorbed, an instantaneous interruption occurs at the time of switching, and the main signal is lost or duplicated, the synchronization is lost, and the normal transmission state is lost. There was a disadvantage that it was not possible to maintain. Especially,
In a high-speed optical fiber communication device, there is a propagation time difference between the working transmission line and the protection transmission line that is longer than the frame length or the cell length. is there. This results in an instantaneous interruption of the transmission path. For example, on a backbone transmission line of several hundred Mb / s or more,
Even if there is a very short interruption during transmission line switching,
There is a drawback that transmission quality is greatly affected by greatly affecting all devices and terminals in the lower group.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a transmission line switching method capable of eliminating instantaneous interruption during transmission line switching and always maintaining a normal transmission state.

[Means for solving the problem]

The transmission line switching method according to the present invention is characterized in that the transmission side device includes means for branching the information sequence of the active transmission line and transmitting the information sequence in parallel to the protection transmission line, and the reception side device includes an information sequence received from the protection transmission line. The cell phase synchronization means including an elastic store memory for matching the cell phase of the information sequence received from the working transmission line with the cell phase of the information sequence is compared with the contents of the two information sequences output from the cell phase synchronization means. Means for measuring the delay difference of the information sequence in units of cells, and when the output of the measuring means indicates that the delay amount of the protection transmission line is larger than the delay amount of the working transmission line, For a column, when the output of the means for detecting the number of continuous empty cells corresponding to the delay difference and the measurement means indicates that the delay amount of the protection transmission line is smaller than the delay amount of the working transmission line. Of the backup transmission line Means for detecting consecutive empty cells of the number of delay differences with respect to the broadcast sequence, and the contents of the portion excluding the empty cells from the information sequence of the working transmission line are provided to both the transmitting device and the receiving device. The present invention is characterized in that a means is provided for disconnecting the working transmission line after detecting a state in which there is no loss or overlap when switching to the protection transmission line.

The transmitting device includes a buffer memory having a fixed capacity, an empty cell generating means for continuously outputting empty cells, an output of the buffer memory and the empty cell generating means, between the cross connect switch and the transmission path switch. And a selector for selecting the output of the cross-connect switch, wherein the buffer memory is configured to write a main information cell excluding an empty cell in the output signal of the cross-connect switch at the time of writing the information sequence, and the buffer memory is a main information cell. It is preferable to provide a means for continuously reading when the cell of the buffer memory is filled, until the cell of the buffer memory becomes empty.

The measuring means may compare all the bits of the two information strings, but may also compare one or more arbitrary pieces.

(Operation)

The same information is transmitted to the working transmission line and the protection transmission line, and the cell phase is synchronized on the receiving side. After that, if cells are duplicated when switching from the working transmission line to the protection transmission line as it is, an empty cell that is continuously included in the information sequence and sent is used, and the working transmission line is used for the protection transmission line. If the delay amount is smaller than the working line, the empty cell of the working transmission line is counted and detected by the difference of the delay amount. The empty cell is counted and detected by the difference of the delay amount, and the transmission path is switched in such a state that the content of the portion from which the empty cell is removed is not lost. As a result, instantaneous interruption during transmission line switching can be eliminated. An empty cell can transmit a continuous information sequence by discarding it later.

〔Example〕

FIG. 1 is a block diagram of a digital transmission apparatus according to an embodiment of the present invention. In this embodiment, the present invention is applied to a cell multiplex transmission device using an optical fiber transmission line.

This device includes an active transmission line 5a-5d and a protection transmission line 6 for transmitting an information sequence in units of cells in which a bit indicating a destination is added to digital information of a fixed length.
In order to switch between the transmission paths, the transmitting apparatus 1 is provided with the working transmission paths 5a to 5d.
For example, a transmission line switch 12 for branching the information sequence of the working transmission line 5d and transmitting the information sequence in parallel to the protection transmission line 6; Cell phase synchronization means for matching the cell phase to the cell phase of the information sequence received from the working transmission line, that is, the interface circuit 16, the cell synchronization circuit 19, the elastic store memory 22, the station clock source 25, and the Means for comparing the contents of the two information strings to be output and measuring the delay difference between these information strings in units of cells, namely, a changeover switch 26, a variable delay circuit 28, an exclusive OR circuit 31, and a control circuit 32; According to the output of the measuring means, when the delay amount of either the working transmission line 5 or the protection transmission line 6 is large, for one of the two information sequences, the number of consecutive A cell detection circuit 34 for detecting the number of empty cells, and when the cell detection circuit 34 detects an empty cell corresponding to the delay amount, the current transmission line 5 and the protection transmission line 6, a transmission information changeover switch 38, and a reception information sequence corresponding to the time required for one empty cell of the cell detection circuit 34 and the time required for detecting a continuous cell from the detection of a continuous cell to the transmission path changeover at the transmission path changeover switch 38. And a fixed delay circuit 37 for delaying the delay. Then, in both the transmitting side apparatus 1 and the receiving side apparatus 7, a state in which the content of the information sequence of the working transmission line 5 excluding the empty cell is neither lost nor duplicated when switching to the protection transmission line 6. Means for disconnecting the working transmission line 5 after detection, that is, the transmission line changeover switch 12 and the control circuit 13 disposed in the transmitting device 1 and the control circuits 32 and 33 disposed in the receiving device 7
And transmission line switch 38, control circuit 13 and control circuit
33 and a data link 15 for connecting to

The transmitting device 1 further includes a cross connect switch 1
0, a cell synchronization pattern insertion circuit 11 and an interface circuit 14. The receiving device 7 further includes a cross connect switch 40.

In this embodiment, if there is an unused working transmission line from any of the working transmission lines 5a to 5d to the protection transmission line 6, and if there is an unused working transmission line, that transmission line is used as a protection transmission line, and It is possible to switch from the transmission line without interruption. This selection is performed by operating the changeover switch 26 according to the control signal 27 from the control circuit 32. Here, switching from the working transmission path 5d to the protection transmission path 6 will be described as an example.

The cell synchronization pattern insertion circuit 11 inserts a cell synchronization pattern, monitoring information, and the like into an empty cell output from the cross connect switch 10. At this time, if an empty cell does not arrive even after exceeding a certain number of cells, a cell synchronization pattern and monitoring information can be forcibly inserted. Transmission line switch 12
Under the control of the control circuit 13, the information sequence of the working transmission path 5d is branched to the protection transmission path 6, and the same information is transmitted in parallel to these transmission paths. The interface circuit 14 performs an electro-optical conversion of the information sequence from the transmission line switch 12 and sends out the information sequence to the corresponding transmission line.

The interface circuit 16 converts an optical signal into an electric signal for each transmission path, and reproduces clocks 17d and 18 with bit synchronization. The cell synchronization circuit 19 regenerates the cell phase pulses 20d and 21 using the received information sequence of the interface 16 and the clocks 17d and 18 respectively. The elastic store memory 22 stores the received information sequence by the clocks 17d and 18 based on the phases of the cell phase pulses 20d and 21. The information stored in the elastic store memory 22 is read by the station clock 23 also supplied from the station clock source 25 with reference to the phase of the station cell phase pulse 24 supplied from the station clock source 25. As a result, the cell phases of the received information sequence between the working transmission line 5d and the protection transmission line 6 match.

The changeover switch 26 is connected so that only the received information sequence of the working transmission line 5d and the protection transmission line 6 is pulled into the variable delay circuit 28 by the control signal 27 from the control circuit 32. The output of the variable delay circuit 28 is supplied to an exclusive OR circuit 31.
The control circuit 32 changes the delay amount of the variable delay circuit 28 by the control signals 29 and 30 while referring to the output of the exclusive OR circuit 31, and the output of the exclusive OR circuit 31 is always “0”. Control.

That is, the delay amount of one variable delay circuit 28 is minimized, and the delay amount of the other variable delay circuit 28 is increased in cell units so that the input of the exclusive OR circuit 31 always has the same bit code. That is, control is performed such that the output of the exclusive OR circuit 31 is always “0”. If the output of the exclusive OR circuit 31 does not always become “0” even if the delay amount of the other variable delay circuit 28 is maximized, the delay amount of the other variable delay circuit 28 is minimized, and One variable delay circuit
Similarly, the delay amount of 28 is increased.

In this way, when the output of the exclusive OR circuit 28 is always "0", the control circuit 32
, It is possible to determine which information line of which transmission path is delayed by how many cells from the other transmission path.

The empty cell detection circuit 34 is provided in the elastic store memory 22.
Empty cell is detected from the received information sequence from
35d and 36 are sent to the control circuit 32. This empty cell detection circuit 3
In 4, for each received information sequence, a cell unit for detecting an empty cell is set by control signals 35d and 36 from the control circuit 32, and a continuous number of empty cells set by the control circuit 32 is detected. Sometimes, an empty cell detection signal is output.

The transmission line changeover switch 38 controls the control signal from the control circuit 32.
39, the output of the fixed delay circuit 37 on the working side and the output of the fixed delay circuit 37 on the protection side are selected and supplied to the cross-connect switch 40.

That is, when the information sequence of the protection transmission line 6 is delayed from the information sequence of the active transmission line 5d, the control circuit 32 outputs a detection output 35d obtained by counting the empty cells corresponding to the delay amount by the empty cell detection circuit 34. Accordingly, the output signal path (b) of the working fixed delay circuit 37 is switched to the output signal path (c) of the fixed delay circuit 37 of the protection transmission line 6 at high speed.

If the information sequence of the working transmission line 5d is behind the protection transmission line 6, the empty cell detection circuit 34 of the protection transmission line 6
Then, count the consecutive empty cells only for the delay difference,
The transmission output changeover switch 38 is controlled by the detection output 36 and the control output 39 of the control circuit 32 so that the output signal circuit (b) of the working fixed delay circuit 37 is used as a spare variable delay circuit.
High-speed switching to 37 output signal paths (c).

If there is no transmission delay difference between the working transmission line 5d and the protection transmission line 6, the signal path (b) is directly switched to the signal path (c) at an arbitrary bit position at high speed.

After performing this switching, the control circuit 32 sends a transmission path switching completion signal to the control circuit 33. The control circuit 33 transmits a transmission line switching signal to the control circuit 13 via the data link 15.
The control circuit 13 uses the signal to
To disconnect the working transmission line 5d. Thereby, the transmission path switching is completed.

 FIG. 2 shows the format of the information sequence.

This information sequence is composed of a main information cell and a synchronization cell. The main information cell is a logical channel number LCN indicating the destination
, An area V including a route identifier for selecting an outgoing route in the cross-connect switch, and main information I. The logical channel number LCN and the area V constitute a header H. The synchronization cell includes a synchronization pit string F and an area S including monitoring information and the like. Each cell has the same bit length.

An empty cell is replaced by a synchronization cell on the transmission side, and therefore does not exist in the information sequence on the transmission path. However, the empty cell identification bit string in the empty cell and the synchronization bit string F of the synchronization cell have the same pattern, and the empty cell detection circuit 34 detects the synchronization cell as an empty cell.

The variable delay circuit 28 takes in one or more arbitrary bits D included in the main information I of the main information cell and the bit D in the synchronous cell at the same bit position as the bit D. However, the position of the bit D to be captured needs to be the same bit position in each cell. All bits in the main information I can be captured.

FIG. 3 and FIG. 4 are diagrams showing the above operation principle. 3 and 4 show switching from the working side to the protection side when the transmission delay of the protection transmission line 6 is larger than that of the working transmission line 5d. FIG. 4 shows the switching from the protection transmission line 6 to the protection transmission line 6d. FIG. 6 shows switching from the working side to the protection side when the transmission delay is small.

In these figures, A to L are fixed-length cells having the same length, and hatched cells E to G are empty cells.
3 and 4, (a) shows the information sequence of the working transmission line 5d, and (b) shows the positional relationship of the information sequence of the protection transmission line 6 after the cell phases are matched.

In FIG. 3 (a), the transmission delay difference between the working and protection transmission lines on the working transmission line side is 3 cells in the figure, and continuous empty cells of the 3 cells were detected. At this time, immediately after the detection, the active transmission line 5d is switched to the protection transmission line 6 at the cell break. In this case, empty cells will be transmitted redundantly, but empty cells are cells without main information and are excluded by the cross-connect switch 40 following the transmission path switch 38. Does not occur.

Further, FIG. 4 shows a case where the transmission delay difference on the protection transmission line is small. At this time, the transmission delay difference between the two transmission lines on the protection transmission line 6, ie, the continuous When an empty cell to be detected is detected, immediately after the detection, control is performed so that the active transmission line 5d is switched to the protection transmission line 6 at a cell break. In this case, unlike FIG. 3, there is no empty cell, but no problem occurs in the transmission information as in FIG.

In the above embodiment, continuous empty cells need to exist in the information sequence of the transmission path. Therefore, the table shows the time intervals at which continuous empty cells occur when the probability of occurrence of the main information cell including the main information follows the Poisson distribution. This table shows that the average main information cell occupancy of the transmission line is 0 when the transmission speed of the transmission line is 150 Mb / s and the cell code length is 500 bits.
It shows the average continuous empty cell generation interval in the case of 2, 0.5, and 0.8. This table also shows the difference between the active and standby transmission path lengths that enables the transmission path switching corresponding to the number n of consecutive empty cells. The transmission path delay time is 5 ns / m. As shown in this table, it can be understood that the transmission line switching method of the present invention can be applied when the average main information cell occupancy of the transmission lines is small and the transmission line difference between the two transmission lines is relatively small.

FIG. 5 is a block diagram of a digital transmission apparatus according to a second embodiment of the present invention.

This embodiment shows a configuration for continuously generating and transmitting empty cells in the transmitting apparatus 1 when continuously long empty cells are required, such as when the transmission delay difference is large.

In the second embodiment, a cross-connect switch 10,
Between the cell synchronization pattern insertion circuit 11, a buffer memory 41 having a fixed capacity, an empty cell generation circuit 42, and a selector 43 which receives the outputs of the buffer memory 41 and the empty cell generation circuit 42 and selects both are provided. The other circuits are the same as those in FIG. 1, and the configuration of the receiving device 7 is the same as that in FIG.

 Next, the operation of the second embodiment will be described.

Only the main information cells excluding the empty cells of the output of the cross connect switch 10 are written in the buffer memory 41.
When the buffer memory 41 is full of main information cells, the main information cells are continuously read until the buffer memory 41 becomes empty. The empty cell generation circuit 42 always outputs empty cells, and the output cell phase matches the cell phase read from the buffer memory 41. The selector 43 passes the main information cell from the buffer memory 41 while the main information cell from the buffer memory 41 is being read by the control signal 44 from the buffer memory 41, and generates an empty cell at other times. The empty cells from circuit 42 are passed. Then, a cell synchronization pattern insertion circuit is inserted into this empty cell.
The cell is replaced by a synchronization cell by 11 and transmitted to the receiving device 7.

As a result, the receiving side device 7 continuously receives empty cells for a long time. In particular, when the average main information occupation rate of the transmission path shown in the above table is small, the tendency that a continuous section of empty cells is long is remarkable. For this reason, transmission line switching between the working transmission line and the protection transmission line having a longer transmission line length difference than in the first embodiment becomes possible. As described above, the continuous empty cells generated by the empty cell generating circuit 42 of the transmitting apparatus 1 and selected by the selector 43 are replaced by the synchronous cells by the cell synchronization pattern inserting circuit 11, but Since the continuous empty cell detection circuit 34 of the device 7 determines that the synchronization cell is also an empty cell, even if a synchronization cell is transmitted, the continuous empty cell detection circuit 34 determines the switching time point between the working transmission line 5 and the protection transmission line 6. No problem.

〔The invention's effect〕

As described above, the transmission line switching method of the present invention utilizes empty cells that continuously appear on the transmission line, and when switching from the current transmission line to the protection transmission line as it is, when cell overlap occurs, Is switched from the working transmission line to the protection transmission line at the break of the continuous empty cell to prevent the loss of information. Thus, the transmission path can be switched from the working transmission path to the protection transmission path without any instantaneous interruption. Therefore, there is an effect that transmission quality can be prevented from deteriorating due to an instantaneous interruption.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital transmission apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing a format of an information sequence. FIG. 3 is a diagram showing an operation principle. FIG. 4 is a diagram showing the principle of operation. FIG. 5 is a block diagram of a digital transmission apparatus according to a second embodiment of the present invention. FIG. 6 is a block diagram of a conventional digital transmission apparatus. 1 ... transmitting side device, 7 ... receiving side device, 10, 40 ... cross connect switch, 11 ... cell synchronization pattern insertion circuit,
12, 38 ... transmission line switch, 14, 16 ... interface circuit, 13, 32, 33 ... control circuit, 15 ... data link, 19 ... cell synchronous circuit, 22 ... elastic store memory, 25 …… Station clock source, 26 …… Changeover switch, 28
... Variable delay circuit, 31 exclusive OR circuit, 34 empty cell determination circuit, 37 fixed delay circuit, 41 buffer memory, 42 empty cell generation circuit, 43 selector, 2 ......
Multiplexing conversion device, 9: Multiplexing / demultiplexing device.

Claims (1)

(57) [Claims] 1. A transmission line switching method comprising: means for switching between an active transmission line and a protection transmission line for transmitting an information sequence in units of cells in which bits indicating a destination are added to digital information of a fixed length. In the transmitting device, there is provided means for branching the information sequence of the working transmission line and transmitting the information sequence in parallel to the protection transmission line, and the receiving device detects the cell phase of the information sequence received from the protection transmission line. A cell phase synchronizing means including an elastic store memory for matching the cell phase of the information sequence received from the working transmission line with the cell phase synchronizing means, and comparing the contents of the two information sequences output by the cell phase synchronizing means, Means for measuring the delay difference in cell units; and when the output of the measuring means indicates that the delay amount of the protection transmission line is larger than the delay amount of the working transmission line, Means for counting the number of consecutive empty cells corresponding to the delay difference of the information sequence received from the path, and that the output of the measuring means is such that the delay amount of the protection transmission path is smaller than the delay amount of the working transmission path. Means for counting the number of consecutive empty cells corresponding to the delay difference in the information sequence received from the protection transmission line in units of cells when the transmission side device and the reception side device Means for disconnecting the working transmission line after detecting a state in which the content of the part excluding the empty cell from the information sequence of the working transmission line excluding the empty cell does not drop or overlap when switching to the protection transmission line. A transmission line switching method characterized by comprising: