JPH01264426A - System for switching transmission line - Google Patents

Abstract

PURPOSE:To obtain completely synchronized information strings so as to prevent deterioration of the transmission quality by utilizing a long frame constituted of plural frames or plural cells and switching the currently used transmission line to a standby transmission line after completely synchronizing the information string of the currently used line to that of the standby line. CONSTITUTION:Currently used transmission lines 2a-2d which transmit transmission strings of digital information in the transmission unit of a fixed length and a standby transmission line 3 are provided between a transmitting side device 1 and receiving side device 4 of a transmission line switching system and switching between both lines is performed by means of a switching means. The long frame pattern inserting circuit 11 of the transmitting side device 1 forms a long frame composed of plural transmission units and switches the long frame from the transmission lines 2a-2d to the standby transmission line 3 by means of a transmission line switching means 12. The synchronizing means including an elastic store memory 23 of the receiving side device 4 which receives the signals synchronizes the phase of the long frame to the phases of the long frames received from the transmission lines 2a-2d.

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 to a protection transmission line. The present invention is suitable for use in optical fiber communication devices.

[Conventional technology]

FIG. 4 is a block diagram of a conventional digital transmission device.

At the transmitting side device l, the multiplexing conversion device 10 multiplexes the digital information string into frames, and the transmission path changeover switch 12
Then, it is sent to the current transmission line 2 via the interface circuit 14.

In the receiving side device 4, the signal on the current transmission line 2 is received by the interface circuit 16, and is supplied to the multiplexing/demultiplexing device 32 via the transmission line changeover switch 30. The demultiplexer 32 is
Separate multiplexed information strings.

If the line or transmission equipment breaks down in the current transmission line 2,
When it is necessary to stop the operation for maintenance or when switching back after repairing a faulty part, the transmission line changeover switches 12 and 30 are used to switch the working transmission line 2 to the backup transmission line 3.

[Problem that the invention seeks to solve]

However, in the conventional transmission line switching system, switching from the working transmission line 2 to the backup transmission line was performed regardless of the main signal.

As a result, it is not possible to absorb the delay difference between the working transmission line 2 and the protection transmission line 3, causing instantaneous interruptions during switching, and loss of synchronization due to missing or duplicating main signals, resulting in normal transmission status. There was a drawback that it could not be maintained. In particular, in high-speed optical fiber communication devices, there is a propagation time difference greater than the frame length between the working transmission line and the protection transmission line, and there is a possibility that frames may be dropped or duplicated when switching between the working and protection transmission lines. This essentially results in a momentary interruption of the transmission path.

For example, in a backbone transmission line of several hundred Mb/s or more, even a very short momentary interruption when switching the transmission line will greatly affect all the equipment and terminals in the Shimofuki group, degrading the transmission quality. There are drawbacks.

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 method of the present invention, the transmitting side device includes means for forming a long frame using a plurality of transmission units, and means for branching the long frame from the working transmission line to the backup transmission line and transmitting it in parallel. , the receiving side device is provided with a synchronization means including an elastic store memory for synchronizing the phase of the long frame received from the protection transmission path with the phase of the long frame received from the working transmission path, and the sending side device and the receiving side device are connected to each other. The present invention is characterized in that both of the transmitter and the transmitter are provided with means for disconnecting the working transmission line after detecting a state in which the phases are synchronized by the synchronizing means.

INDUSTRIAL APPLICATION This invention is utilized for a frame multiplex transmission apparatus and a cell multiplex transmission apparatus. A frame multiplex transmission device is a device that allocates information sequences from multiple terminals to predetermined bit positions within a frame and multiplex transmits them. To implement the present invention in such a device, a long frame is constructed using surplus bits within the frame. In addition, the cell multiplex transmission equipment is
In order to establish synchronization between cells, the information string is divided into a certain length and a bit indicating the destination is added to each cell (this cell is especially called the "main information cell"). This is a device that multiplex transmits a main information cell in which a synchronization bit is placed at a specific position and a cell of the same length (referred to as a "synchronization cell").

To implement the present invention in such a device, a long frame is constructed using surplus bits within a cell.

Preferably, the means for forming a long frame includes means for inserting a long frame pattern such that the frame length is twice or more the maximum transmission delay difference between the working transmission line and the protection transmission line. In this case, the synchronization means includes an elastic store memory that temporarily stores the information string received from the working transmission path and the information string received from the backup transmission path, and a long frame synchronized with the long frame pattern of the working transmission path. A means for generating a pulse, a delay means for delaying the long frame pulse by a time half the length of the long frame, and a clock regenerated from information received from the current transmission line using the delayed long frame pulse as a reference. It is preferable that the information string is read out from the elastic store memory.

[For production]

A long frame is formed in which a plurality of transmission units are further made into one transmission unit. The same information sequence is transmitted on the working transmission line and the protection transmission line, and their long frame phases are synchronized.

As a result, the information strings to be switched are completely synchronized on both transmission paths. Furthermore, the protection transmission line is switched from the working transmission line in a completely synchronized state. In this way,
It is possible to eliminate instantaneous interruptions when switching transmission paths.

〔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 frame multiplex transmission device using an optical fiber transmission line.

This digital transmission device consists of two working transmission lines, each of which transmits a string of information using a fixed length of digital information as a unit of transmission.
In order to switch between a to 2d and the protection transmission line 3, the transmitting side device 1 includes a long frame button insertion circuit 11 that forms a long frame by a plurality of transmission units, and a long frame insertion circuit 11 that forms a long frame from a working transmission line to the protection transmission line 3. and a transmission line changeover switch 12 that branches into three transmission lines and transmits them in parallel, and provides synchronization for the receiving side device 4 to synchronize the phase of the long frame received from the protection transmission line 3 with the phase of the long frame received from the working transmission line. means, that is, a long frame synchronization circuit 20, an elastic store memory 23, and a delay circuit 24, detects a state in which the phases are synchronized by the synchronization means in both the transmitting side device 1 and the receiving side device 4, and performs the current transmission. A means for disconnecting the transmission line, that is, a transmission line changeover switch 12 and a control circuit 13 arranged in the transmission side device 1, and a transmission line changeover switch 30, a control circuit 27, and the control circuit 1 arranged in the reception side device 4.
3 and a control circuit 27.

The transmitting device 1 further includes a multiplexing conversion device 10 and an interface circuit 14 connected to each of the working transmission lines 2a to 2d and the protection transmission line 3.

The receiving device 4 further includes an interface circuit 14 connected to each of the working transmission lines 2a to 2d and the protection transmission line 3, a changeover switch 19, 26 for setting the working transmission line to be switched, and a demultiplexer. A device 32 is provided.

This device can switch from any of the working transmission lines 2a to 2d to the backup transmission line 3 without momentary interruption. This selection is performed by controlling the changeover switches 19.26 using control signals 28.29 from the control circuit 27. here,
The operation of this device will be described by taking as an example the case where the working transmission line 2d is switched to the protection transmission line 3.

The multiplexing/converting device 10 allocates information sequences from a plurality of terminals to predetermined bit positions within a frame and multiplexes them. The long frame batten insertion circuit 11 inserts a blank bit position in the frame output from the multiplex conversion device 10 so that the maximum transmission delay difference between the working transmission line 2d and the protection transmission line 3 is twice or more. Insert a long frame pattern. Under the control of the control circuit 13, the transmission path selector switch 12 branches the information string on the working transmission path 2d to the protection transmission path 3, and causes the same information to be transmitted in parallel on these transmission paths. The interface circuit 14 converts the electrical signal into an optical signal and sends it to each transmission path.

The interface circuit 16 converts the optical signal into an electrical signal for each transmission path, synchronizes the bits, and outputs a clock 17d,
Play 18. The long frame synchronization circuit 20 receives the received information sequence of the interface circuit 16 and the clock 17d.
, 18, and the long frame pulse 21d, respectively.
, 22 is played. Elastic store memory 23
has a storage capacity equal to the length of the long frame, and the long frame l
, 21d and 22, and store received information sequences using clocks 17d and 18, respectively.

The information string written to the elastic store memory 23 on the active side is based on a signal obtained by delaying the long frame pulse 25d and the long frame pulse 21d that have passed through the delay circuit 24 by half the length of the long frame pulse 25d. , the clock 17d. The information string written in the elastic store memory 23 on the spare side is the same long frame pulse 25d as on the active side via the changeover switch 26.
is read out using the same clock 17d as that on the current side via the changeover switch 19. by this,
The long frame phases of the received information sequences between the working transmission line 2d and the protection transmission line 3 match, and the received information sequences are completely synchronized between both transmission lines. The changeover switches 19 and 26 are controlled by control signals 28 and 29 from the control circuit 27, respectively, and determine which of the working transmission lines 2a to 2d is to be switched to the backup transmission line 3.

When the synchronization of the information example is ensured between the working transmission line 2d and the protection transmission line 3, the control circuit 27 controls the transmission line changeover switch 30 using the control signal 31, and the elastic store memory 23 on the working side The output of the elastic store memory 23 on the spare side is connected to the demultiplexer circuit 32. After this, the control circuit 27 notifies the control circuit 13 of the transmission path switching via the data link 15. The control circuit 13 controls the transmission line changeover switch 12 to disconnect the working transmission line 2d.

FIG. 2 shows the format of the information string, where (a) shows the information string on the working transmission path, and (b) shows the information string on the protection transmission path.

This information string is composed of frames, and each frame is composed of a frame synchronization bit F and main information (2). The long frame punch insertion circuit 11 forms a long frame by inserting a frame synchronization bit SF.

On the receiving side, the difference in transmission delay between the working transmission path and the backup transmission path is less than half that of a long frame.

FIG. 3 shows a time chart of input and output of the elastic store memory 23. (a) is the information string on the active side before writing, et al.) is the information string on the backup side before writing, (C) is the information string on the active side after reading, and (d) is the information string on the backup side after reading. Indicates an information string. In addition, ■ is a long frame pulse 21d for writing to the elastic store memory 23 on the active side.
■ is the time position of the long frame pulse 22 for writing to the elastic store memory 23 on the backup side, ■ is the time position of the long frame pulse 22 for reading the elastic store memory 23 on both the active side and the backup side 2
The time position of 5d is shown.

The time position of the long frame pulse 25d lags the time position of the long frame pulse 21d by half its length. Since the transmission delay difference between both transmission paths is less than half of the long frame, the time position of the long frame pulse 22 is included in the range indicated by A in FIG. 3. Therefore, elastic store memory 2 on both the active side and the backup side
The information strings read from No. 3 always match perfectly. Therefore, after this, it is possible to switch from the working transmission line to the backup transmission line without momentary interruption.

Although the above description has been made using a frame multiplex transmission device as an example, the present invention can be similarly implemented in a cell multiplex transmission device by using a cross-connect switch in place of the multiplex converter 10 and the demultiplexer 32.

〔Effect of the invention〕

As explained above, the transmission line switching method of the present invention utilizes long frames made up of multiple frames or multiple cells to completely switch the information string of the working transmission path and the information string of the backup transmission path. , and then quickly switches the working transmission line to the protection transmission line. As a result, a completely synchronized information sequence can be obtained before and after transmission path switching, and instantaneous interruptions caused by switching can be eliminated. Therefore, there is an effect that deterioration in transmission quality can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital transmission device according to an embodiment of the present invention. FIG. 2 is a diagram showing the format of an information string. Figure 3 is an input/output time chart of elastic store memory. FIG. 4 is a block diagram of a conventional digital transmission device. DESCRIPTION OF SYMBOLS 1... Sending side device, 2.2a-2d... Working transmission line, 3... Backup transmission line, 4... Receiving side device, 10.
...Multiplex conversion device, 11...Long frame button insertion circuit, 12...Transmission path changeover switch, 13.27...
・Control circuit, 14.16...Interface circuit, 1
5... Data link, 19.26... Changeover switch, 20... Long frame synchronization circuit, 23... Elastic store memory, 24... Delay circuit, 30...
Transmission line changeover switch, 32... demultiplexing device. Patent applicant: Nippon Telegraph and Telephone Corporation Representative Patent attorney: Naotaka Ide

Claims (1)

[Scope of Claims] 1. In a transmission line switching system that includes switching means for a working transmission line and a protection transmission line, each of which transmits an information string using a fixed length of digital information as a transmission unit, the transmitting side device has a plurality of means for forming long frames in units of transmission; and means for branching the long frames from the working transmission line to the protection transmission line and transmitting them in parallel; A synchronization means including an elastic store memory for synchronizing the phase of the long frame with the phase of the long frame received from the working transmission path is provided, and the synchronization means synchronizes the phase of both the transmitting side device and the receiving side device. A transmission line switching system characterized by comprising means for disconnecting the working transmission line after detecting a synchronized state.