JPH01270427A - Transmission line switching system - Google Patents

Abstract

PURPOSE:To switch a current transmission line to a standby transmission line without a momentary break by substituting overlapping cells with idle cells in case of the occurrence of cell overlap and delaying and using reception information in case of the occurrence of drop-out at the time of switching to the stand-by transmission line. CONSTITUTION:A pair of an idle cell discriminating circuit 39 and a variable delay memory 42 are provided for current transmission lines 16a-16b and a stand-by transmission line 17. For example, at the time of switching from the current transmission line 16d to the stand-by transmission line 17, a control circuit 35 discriminates lead/ delay between the information string on the current transmission line 16d and that on the stand-by transmission line 17. When it is discriminated that the information string of the current transmission line 16d leads, an idle cell clock generating circuit 43 is connected to send idle cells corresponding to cell overlap, and the current transmission line is disconnected by a transmission line changeover switch 13 thereafter. When the information string of the current transmission line is delayed, information is delayed for the time corresponding to this delay by the variable delay memory 42 to prevent drop-out of the signal, and the current transmission line is disconnected by the switch 13 thereafter.

Description

[Detailed description of the invention] [Industrial application field] The present invention is utilized for time division multiplexed digital transmission.

In particular, the present invention relates to a transmission line switching method for switching a working transmission line, which transmits an information string in units of cells, to a protection transmission line. The present invention is suitable for use in optical fiber communication devices.

[Conventional technology]

FIG. 7 is a block diagram of a conventional digital transmission device.

In the sending device 10, the multiplexing converter 70 multiplexes the digital information string and sends it to the current transmission path 16 via the transmission path changeover switch 13 and ink face circuit 14.

In the receiving side device 19, the signal on the current transmission line 16 is received by the interface circuit 20, and is supplied to the demultiplexer 71 via the transmission line changeover switch 44. Demultiplexer 71
separates multiplexed information sequences.

If a line or transmission device in the current transmission line 16 breaks down, if it is necessary to stop operation for maintenance, or if you want to switch it back after repairing the faulty part, the transmission line changeover switches 13 and 44 The transmission line 16 is switched to the backup transmission line 17.

[Problem that the invention seeks to solve]

However, in the conventional transmission line switching system, switching from the working transmission line 16 to the backup transmission line 17 was performed regardless of the main signal. For this reason, the working transmission line 16 and the protection transmission line 17
This has the disadvantage that it is not possible to absorb the delay difference between the two, causing instantaneous interruptions during switching, and loss of synchronization due to missing or duplicating main signals, making it impossible to maintain normal transmission conditions. In particular, in high-speed optical fiber communication equipment, there is a propagation time difference that is greater than the frame length or cell length between the working transmission line and the protection transmission line, and frames or cells may be dropped or duplicated when switching between the working and protection transmission lines. There is sex. This essentially results in a momentary interruption of the transmission path. For example, hundreds! The backbone transmission line of Jb/s or higher has the disadvantage that even a very short momentary interruption when switching the transmission line will greatly affect all equipment and terminals in the Shimofuki group, degrading the transmission quality. Ta.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transmission line switching method that solves the above problems, eliminates instantaneous interruptions when switching transmission lines, and can always maintain a normal transmission state.

[Means for solving problems]

In the transmission line switching system of the present invention, the transmitting side device is provided with means for branching the information string of the working transmission path and transmitting it in parallel to the protection transmission path, and the receiving side device is provided with a means for branching the information string of the working transmission path and transmitting it in parallel to the protection transmission path. cell phase synchronization means including an elastic store memory that matches the cell phase of the information string received from the current transmission line with the contents of the two information strings output from this cell phase synchronization means; A means for measuring the delay difference between two information streams on a cell-by-cell basis; On the other hand,
When the output of the means for replacing the number of cells corresponding to the delay difference with empty cells and the means for measuring indicates that the delay amount of the protection transmission path is smaller than the delay amount of the working transmission path,
means for delaying the information string received from the backup transmission path in cell units;
The present invention is characterized by comprising means for disconnecting the working transmission line after detecting a state in which the contents of the part of the information string of the working transmission line excluding the empty cells are neither lost nor duplicated when switching to the backup transmission line. .

The measuring means may compare all bits of the two information strings, but it may also compare any side of - or more.

[For production]

The same information is transmitted on the working transmission line and the backup transmission line,
The receiving side synchronizes the cell phase. After that, when switching from the working transmission line to the protection transmission line, if duplication of cells occurs, that cell is replaced with an empty cell, and if a dropout occurs, the information received from the protection transmission line is replaced. Delay to avoid omissions. This makes it possible to eliminate instantaneous interruptions when switching transmission paths. When received information is delayed, the amount of delay can be gradually reduced to the minimum value by switching the transmission path and then discarding an empty cell when that cell arrives.

〔Example〕

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

This device switches between the working transmission paths 16a to 16d and the protection transmission path 17, which respectively transmit information strings in units of cells, each of which is a fixed length of digital information with a bit indicating its destination added. 10, one of the working transmission lines 16a-166, for example, the working transmission line 16.
The receiving device 19 is equipped with a transmission path changeover switch 13 that branches the information string of d and transmits it in parallel to the backup transmission path 17.
Cell phase synchronization means for matching the cell phase of the information sequence received from the protection transmission line 17 with the cell phase of the information sequence received from the working transmission line, that is, the interface circuit 20, the cell synchronization circuit 23, the elastic store memory 26, and the station Clock source 29 and elastic store memory 26
Means for comparing the contents of two information strings output by and measuring the delay difference between these information strings on a cell-by-cell basis, that is, a changeover switch 30, a variable delay circuit 32, and an exclusive OR circuit 33
and the control circuit 35, when the output of this measuring means indicates that the delay amount of the protection transmission line 17 is larger than the delay amount of the working transmission line, the delay difference of one of the two information strings is determined. The means for replacing the corresponding number of cells with empty cells, that is, the empty cell generation circuit 43 and the transmission line changeover switch 44, and the output of the measuring means are connected to the backup transmission line 17.
is provided with a variable delay memory 42 that delays the information string received from the protection transmission line 17 in units of cells when the delay amount of the transmission line is smaller than the delay amount of the working transmission line, The working transmission line is disconnected after detecting that the content of the part of the information string of the working transmission line excluding the empty cells is neither missing nor duplicated when switching to the protection transmission line 17 on both the side device 19 and the side device 19. means, that is, a transmission path changeover switch 13 and a control circuit 15 arranged in the sending device 10, and a control circuit 35 arranged in the receiving device 19.
．． 36, transmission path selector switch 44, and control circuit 15
and a data link 18 connecting the control circuit 36 and the control circuit 36 .

The transmitting device 10 further includes a cross-connect switch 1.
1, a cell synchronization button insertion circuit 12 and an interface circuit 14 are provided. The receiving device 19 further includes a cross-connect switch 11 .

In this embodiment, any of the working transmission lines 16a to 16d are connected to the backup transmission line 17, and if there is an unused working transmission line, that transmission line is used as a backup transmission line and is disconnected from other transmission lines. You can switch at a moment's notice. This selection is performed by operating the changeover switch 30 in response to the control signal 31 from the control circuit 35. Here, switching from the working transmission line 16d to the protection transmission line 17 will be explained as an example.

The cell synchronization button insertion circuit 12 inserts a cell synchronization button into the empty cell output from the cross-connect switch 11. At this time, if an empty cell does not arrive even after exceeding a certain number of cells, a cell synchronization button is forcibly inserted. The transmission line changeover switch 13 branches the information string of the working transmission line 16d to the backup transmission line 17 under the control of the control circuit 15.
The same information is transmitted in parallel through these transmission lines. The interface circuit 14 converts the information string from the transmission path changeover switch 13 into electro-optic converter and sends it to the corresponding transmission path.

The interface circuit 20 converts the optical signal into an electrical signal for each transmission path, synchronizes the bits, and outputs a clock 21d,
Play 22. The cell synchronization circuit 23 uses the received information sequence of the interface 20 and the clock 21d122 to reproduce cell phase pulses 24d and 25, respectively.

The elastic store memory 26 stores the cell phase pulse 2
Based on the phase of clocks 21d and 25, clocks 21d and 2
2, each received information string is stored. The information stored in the elastic store memory 26 is read out by the local clock 27 also supplied from the local clock source 29, with the phase of the local pulse 28 supplied from the local clock source 29 as a reference.

As a result, the cell phases of the received information sequences between the working transmission line 16d and the protection transmission line 17 match.

The changeover switch 30 receives a control signal 31 from a control circuit 35.
Thus, only the received information sequences of the working transmission line 16d and the protection transmission line 17 are connected to the variable delay circuit 32. The output of this variable delay circuit 32 is the exclusive OR circuit 3
3. The control circuit 35 includes the exclusive OR circuit 3
3, the delay amount of the variable delay circuit 32 is changed using control signals 37 and 38, and the output of the exclusive OR circuit 33 is controlled to be always "0".

That is, the delay amount of one variable delay circuit 32 is set to the minimum, and the delay amount of the other variable delay circuit 32 is increased in cell units so that the input of the exclusive OR circuit 33 always has the same bit sign. That is, the output of the exclusive OR circuit 33 is controlled to always be "0". If the output of the exclusive OR circuit 33 does not always become "0" even if the delay amount of the other variable delay circuit 32 is maximized, the delay amount of the other variable delay circuit 32 is minimized, and the The delay amount of one variable delay circuit 32 is similarly increased.

In this way, the control circuit 35 controls the exclusive OR circuit 33
When the output of is always "0", it is determined by how many cells the information string of either transmission path is delayed from the other transmission path based on the difference in the amount of delay (in cell units) of both variable delay circuits 32. can.

The empty cell determination circuit 39 is an elastic store memory 2
An empty cell is detected from the received information string from 6, and empty cell detection signals 40d and 41 are sent to the variable delay memory 42.

In this empty cell determination circuit 39, for each received information string,
A certain delay necessary for empty cell determination occurs.

The variable delay memory 42 is normally set so that the amount of delay is the minimum, and the amount of delay can be changed for each cell by control signals 45d and 46. Furthermore, an empty cell detection signal 40d is generated by the control signals 45d and 46.

If 41 is input, empty cells may not be stored.

The empty cell generation circuit 43 always outputs empty cells so that the cell phase matches the output of the variable delay memory 42.

The transmission path selector switch 44 switches between the output of the variable delay memory 42 on the active side and
The output of the spare side variable delay memory 42 and the output of the empty cell generation circuit 43 are selected and the cross-connect switch 11
supply to.

That is, if the information string on the protection transmission line 17 lags behind the information string on the working transmission line 16d, the control circuit 35
At a change point of an arbitrary cell, the output signal path (a) of the current variable delay memory 42 to the output signal path (a) of the empty cell generation circuit 43 is changed.
Switch quickly to C). Furthermore, after sending the empty cell corresponding to the delay difference between the information strings between the transmission paths to the cross-connect switch 11, the output signal path (C) is quickly switched to the output signal path (C) of the spare variable delay memory 42, etc.

Furthermore, if the information string on the working transmission line 16d lags behind the protection transmission line 17, the control signal 46 adds a delay to the protection variable delay memory 42 by the delay difference, and the control signal 47 switches the transmission line. The switch 44 is controlled to quickly switch from the output signal path (a) of the current variable delay memory 42 to the output signal path (a) of the spare variable delay memory 42 at an arbitrary bit position.

If there is no transmission delay difference between the working transmission line 16d and the backup transmission line 17, the signal line (a) is directly connected to the signal line (a) at any pit position.
(from signal path et al.) at high speed.

After performing this switching, the control circuit 35 switches the control circuit 36 to
A transmission path switching completion signal is sent to The control circuit 36 transmits the transmission line switching signal to the control circuit 15 via the data link 42. Based on this signal, the control circuit 15 controls the transmission path changeover switch 13 to disconnect the current transmission path 16d.

This completes transmission path switching.

When the delay amount of the reserve side variable delay memory 42 is increased, the variable delay memory 42 is controlled by the control signal 46 from the control circuit 35, and the empty cell detection signal 41 is maintained until the delay amount becomes the minimum. Writing to the variable delay memory 42 is prohibited at certain times. Since the read side of the variable delay memory 42 is always reading, the information delay gradually becomes smaller.

FIG. 2 shows the format of the information string.

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

Empty cells are replaced by synchronous cells on the transmitting side, so they do not exist in the information string on the transmission path. However, the empty cell identification bit string in the empty cell and the synchronous bit string F of the synchronous cell are the same button, and the empty cell determination circuit 39 detects the synchronous cell as an empty cell.

The variable delay circuit 32 takes in one or more arbitrary bits)D included in the main information (2) of the main information cell and the bits)D in the synchronization cell at the same bit position.

However, the position of the bit D to be captured needs to be the same bit position in each cell. It is also possible to capture all the bits in the main information I.

In this embodiment, an empty cell determination circuit 39 is arranged before the variable delay memory 42, and an empty cell detection signal is used to inhibit writing of empty cells into the variable delay memory 42 to reduce the delay. On the other hand, by skipping empty cells when reading from the variable delay memory 42, the delay can be reduced.

FIGS. 3 to 5 are diagrams showing the above operating principle.

3 and 4 show switching from the working side to the protection side when the transmission delay of the protection transmission line 17 is larger than that of the working transmission line 16d, and FIG. This figure shows switching from the working side to the backup side when the transmission delay is small.

In these figures, A to I are fixed length cells of equal length. In FIGS. 3 and 4, (a) shows the positional relationship of the information string of the working transmission line 16d and (b) of the information string of the protection transmission line 17 after the cell phases are matched. Moreover, (C) shows the output of the transmission path changeover switch 44. In addition, in FIG. 5, (a) and 3) show the same information string as in FIGS. 3 and 4, (C) shows the delayed information string on the standby side, and (d) shows the transmission line switching switch. 44 output is shown.

In FIG. 3, if the working transmission line 16d is switched to the protection transmission line 17 at a change point of an arbitrary cell, for example, at the point between cell E and cell F of the working transmission line 16d, the connection between these transmission lines will be changed. Cell duplication occurs by a transmission delay difference of . Therefore, the duplicate cells immediately after switching, for example, cell D and cell E, are replaced with empty cells. Since empty cells do not contain main information and are removed by the cross-connect switch 11, there is no problem no matter how many empty cells are added to the cell multiplex transmission device.

In FIG. 4, in order to prevent duplication of cells due to transmission path switching, cells received from the working transmission path 16d, for example, cells D and E, are replaced with empty cells by the transmission path delay difference, and then Switch the transmission path.

In both the case of FIG. 3 and the case of FIG. 4, an empty cell corresponding to the transmission delay difference is sent out as an output before switching from the working side to the protection side.

FIG. 5 shows that the information string of the protection transmission line 17 is the same as that of the working transmission line 17.
Since it is ahead of the information string d, the transmission delay difference between these transmission lines, for example, information for two cells, is delayed, and then the working transmission line 16d is switched to the protection transmission line 17. In this case, since the information strings of both transmission paths are completely the same, there is no need to switch at the change point of the cell, and it is possible to switch at any bit position.

FIG. 6 is a block diagram of a digital transmission device according to a second embodiment of the present invention.

In this embodiment, only one set of an empty cell determination circuit 39 and a variable delay memory 42 are provided for the working transmission lines 16a to 16d and the protection transmission line 17, a changeover switch 48 is provided for selecting these, and a delay This embodiment differs from the first embodiment in that an adjustment fixed delay circuit 50 is provided. Here, description of circuits other than these will be omitted.

The amount of delay of the fixed delay circuit 50 for delay adjustment is set to the sum of the delay in the empty cell determination circuit 39 and the minimum delay of the variable delay memory 42. The empty cell generation circuit 43 always outputs empty cells so that the cell phase matches the output of the fixed delay circuit 50 for delay adjustment.

Here, the case of switching from the working transmission line 16d to the backup transmission line 17 will be described as an example.

When the control circuit 35 determines that the information string on the working transmission line 16d is ahead of the information string on the protection transmission line 17,
First, the changeover switch 48 is controlled by the control signal 49,
Regarding the signal path on the backup side, the signal path (a) from the elastic store memory 26 to the fixed delay circuit 50 for delay adjustment is
).

After that, the control circuit 35 controls the transmission path changeover switch 44 using the control signal 47, and at the change point of any cell, the signal path (C) is changed from the fixed delay circuit 50 for delay adjustment on the working side to the cross-connect switch 11. , the signal path (f
). With this connection, the control circuit 35
Empty cells are sent to the cross-connect switch 11 by the difference in delay between the information strings of the two transmission paths detected in .

Furthermore, after sending out the empty cells corresponding to this delay difference, the signal path (f) is quickly switched to the signal path (d) from the reserve side delay adjustment fixed delay circuit 50 to the cross-connect switch 11.

After this, in the same manner as in the first embodiment, by disconnecting the working transmission line 16d using the transmission line changeover switch 13,
Transmission path switching is completed.

In addition, if the information string on the working transmission path 16d lags behind the backup transmission path 17, the changeover switch 48 is controlled by the control signal 49, and the signal path from the elastic store memory 26 to the empty cell determination circuit 39 ( Set b). Then, the control signal 46 causes the variable delay memory 42 to delay the information strings by the delay difference between the two transmission lines detected by the control circuit 35 . Thereafter, the control signal 47 switches the transmission path changeover switch 44 from the signal path (C) to the signal path (e) at an arbitrary bit position.

After this, the current transmission line 1 is switched by the transmission line changeover switch 13.
6d is separated, and the amount of delay of the variable delay memory 42 is minimized in the same manner as in the first embodiment. As a result, the delay amount of the fixed delay circuit 50 for delay adjustment becomes equal to the sum of the delay amounts of the empty cell determination circuit 39 and the variable delay memory 42.

Next, at the selector switch 48, the signal path (a) is connected while the signal path (5) is connected, and after the first information string passes through the fixed delay circuit 50 for delay adjustment, transmission is performed at an arbitrary bit position. The signal path (e) of the path changeover switch 44 is quickly switched to the signal path (d). After this switching, the signal paths etc. are opened at the changeover switch 48. therefore,
Even when switching to another transmission path, the common empty cell determination circuit 39 and variable delay memory 42 can be used.

Transmission path switching is completed by the above operations.

If there is no delay difference between the working transmission line 16d and the backup transmission line 17, after connecting the signal line (a) with the changeover switch 48, the transmission line changeover switch 4 is turned on at an arbitrary bit position.
4 directly from the signal path (C) to the signal path (d).

〔Effect of the invention〕

As explained above, in the transmission line switching method of the present invention, if switching from a working transmission line to a protection transmission line causes duplication of cells, the corresponding cell is replaced with an empty cell,
If a dropout occurs, the information received from the backup transmission path is delayed to prevent the dropout from occurring. Due to this,
The transmission line can be switched from the working transmission line to the backup transmission line without momentary interruption. Therefore, it is possible to prevent deterioration of transmission quality due to instantaneous interruptions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital transmission device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the format of an information string. FIG. 3 is a diagram showing the principle of operation. FIG. 4 is a diagram showing the principle of operation. FIG. 5 is a diagram showing the principle of operation. FIG. 6 is a block diagram of a digital transmission device according to a second embodiment of the present invention. FIG. 7 is a block diagram of a conventional digital transmission device. DESCRIPTION OF SYMBOLS 10... Transmission side device, 11... Cross-connect switch, 12... Cell synchronization button insertion circuit, 13...
Transmission path changeover switch, 14.20... Interface circuit, 15.35.36... Control circuit, 18... Data link, 19... Receiving side device, 23... Cell synchronization circuit, 26... ...Elastic store memory, 29
... Station clock source, 30... Changeover switch, 32.
...Variable delay circuit, 33...Exclusive OR circuit, 39
...Empty cell determination circuit, 42...Variable delay memory, 4
3... Empty cell generation circuit, 44... Transmission path changeover switch, 48... Changeover switch, 50... Fixed delay circuit for delay adjustment, 70... Multiplexing conversion device, 71... Multiplexing Separation device. Patent applicant: Nippon Telegraph and Telephone Corporation. Agent: Naotaka Ide, patent attorney.

Claims (1)

[Scope of Claims] 1. Transmission equipped with means for switching between a working transmission line and a backup transmission line, each of which transmits an information string in units of cells, each of which is a fixed length of digital information with a bit indicating its destination added. In the path switching method, the transmitting side device is provided with means for branching the information string of the working transmission path and transmitting it in parallel to the protection transmission path, and the receiving side device is provided with means for branching the information string of the working transmission path and transmitting it in parallel to the protection transmission path, Cell phase synchronization means including an elastic store memory that matches the cell phase with the cell phase of the information string received from the working transmission line is compared with the contents of the two information strings output from this cell phase synchronization means, and these two information strings are compared. means for measuring the delay difference of information strings in units of cells; means for replacing one of the information strings with a number of cells corresponding to the delay difference with empty cells, and the output of the means for measuring that the delay amount of the protection transmission path is smaller than the delay amount of the working transmission path. means for delaying the information string received from the protection transmission path in cell units when the information string is transmitted from the working transmission path to both the sending device and the receiving device. A transmission line switching system characterized by comprising means for disconnecting the working transmission line after detecting a state in which the contents of the portion excluding the empty cells are neither lost nor duplicated when switched to the protection transmission line.