JPH08223130A - Switching system without short break - Google Patents

Abstract

PURPOSE: To absorb the variance or the relative phase to prevent the momentary line disconnection by controlling the reception part of the standby system to perform switching so that pointer values of the standby system and the current system coincide with each other. CONSTITUTION: 'm' is stored in the pointer area of the frame of a reception signal, and the information signal corresponding to the position of address (m) after it is mounted. A line signal is stored in a buffer memory 11 of a write address counter 14, and the pointer value of the line signal is supplied to a comparator 16. With respect to the line signal stored in the memory 11, pointer values of storage means of reception parts 10 and 10' operated as the standby system and the current system respectively are read off by a control part 23 of the communication system. These pointer values are compared with each other by the comparator 16. The switching control is performed after the coincidence between read pointer values is confirmed. If pointer values are different from each other, the phase difference between the standby system and the current system is obtained, and the stuffing processing is performed in the reception part 10' of the standby system to absorb the phase difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hitless switching system for a communication system. In recent years, standardized SDH (Sy) has been used for synchronously multiplexing and transmitting digital signals of various speeds.
nchronous Digital Hierarchy) has been adopted. In this SDH transmission method, signals of different speeds have pointers (frame phase information) in each layer.
Can be used for synchronously multiplexing. On the other hand, in the case of a digital line, it is often duplicated in preparation for a failure, and when it detects that the working line has failed,
It is designed to switch to the backup line instantaneously, and in that case a momentary interruption occurs, so improvement is desired.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of an SDH frame structure,
FIG. 5 is an explanatory diagram of the transmission system and the duplication operation.

In SDH, a synchronous transfer module (STM:
Multiple levels are provided as a Synchronous Transfer Module), and STM-1 (STM level 1) shown in FIG. 4 is a basic multiplexing unit and has a bit rate of 155.52 Mbps (2016 channels for 64 Kbps conversion). As shown in the figure, this frame is represented by a two-dimensional byte array of 9 rows and 270 columns, and the top 9 rows × 9 columns are section overhead (displayed in SOH) and AU pointer (AUPTR).
Displayed by: Administrative Unit Pointer), and the subsequent 9 rows by 261 columns is a payload for accommodating multiplexed information. In this payload, VC-3 (Virtual Container3: 64 Kbps equivalent 67
2 channels) or 3 VC-4s are multiplexed, and the figure shows an example in which 3 VC-3s are multiplexed.
As shown in the figure, C-3 is composed of 9 rows and 85 columns, and is represented by a path overhead (POH) and a payload.
When three VC-3s are multiplexed, a pointer (corresponding to an address or time) to the head position of each frame of each VC-3 is sequentially stored in the AU pointer.
Thus, the frame time phase of the STM-1 and each frame time phase of the multiplexed VC-3 can be dynamically changed according to the value of the pointer, and this pointer can transmit various information from low speed to high speed. And can identify low-speed information directly from the high-speed pulse train,
This structure is realized in each layer of SDH.

The pointer is an offset value (address value) indicating a shift between the transmission frame and the multiplexed information frame, and when a high-order VC (VC-3, 4 etc.) is accommodated in the management unit, its management is performed. STM in which the unit is housed
The time difference between the frame phase of the high-order VC and the frame phase of the high-order VC is indicated by an address. Low-order VC (VC-11, 12 etc.)
When accommodating in a U (Tributary Unit Pointer) unit, a pointer (TU pointer) indicating the time difference between the frame phase of the high-order VC and the frame phase of the low-order VC in which the TU unit is accommodated is added. In the following explanation,
These pointers are simply called pointers.

FIG. 5A. A transmission system is shown in FIG. 2, a line having an existing interface from the exchange 50 is converted into an SDH interface in the interface conversion device 51, and each SDH is converted in the next cross connect 52.
Cross connect information signals. Next, in the terminal repeater 53 provided corresponding to the optical transmission line 54, S
DH multiplexing and long-distance optical repeater transmission are performed. The next-stage system provided on the opposite side of the optical transmission line 54 is also provided with a terminal repeater 55, a cross connect 56, an interface converter 57, and a switch 58.

The line signal is transferred to the interface converter 51.
Framed at, cross-connect 52 converges paths,
Cross-connect editing such as separation and refilling is performed, the terminal multiplex repeater 53 multiplexes to a higher-order STM to process pointers, and also processes each byte defined in the SOH, Error monitoring, alarm transfer,
Separation and insertion of switching control information, conversion of a transmission path clock to a station clock by a pointer, etc. are performed. If there is a repeater on the transmission line, frame synchronization, error monitoring, etc. are performed for the relay section in the SOH.

The terminal repeater 55 of the next-stage system that receives a signal from the optical transmission line 54 is provided with a pointer processing unit (not shown), and is provided between the phase of the received frame and the reference frame provided in the receiving station system. If there is a gap in
In SDH, frame synchronization is achieved by replacing the pointer value of the received frame with a value obtained by adding (or subtracting) a value corresponding to the time difference.

Further, when there is a slight difference between the clock frequency of the transmission frame and the clock frequency of the multiplexed information at the time of multiplexing, stuffing is performed to prevent loss of information transfer information, and destuffing is performed on the receiving side. To do. On the receiving side, if there is a difference between the clock frequency of the received frame and the clock frequency of the receiving station, a stuffing operation is performed to correct the pointer value and replace it. That is, when the frequency of the received STM clock <the clock frequency of the receiving station,
When reading with the clock of the receiving station, one byte is insufficient, so positive stuffing is performed, the pointer value is incremented by 1, and if the frequency of the received STM clock> clock frequency of the receiving station, negative stuffing is performed, and the pointer value is −. The process of 1 is performed.

The above optical transmission line 54 and the devices in the terminal multiplex repeaters 53 and 55 for transmitting and receiving signals from the optical transmission line 54 are normally duplicated for fail-safe operation, so that the next stage system is used. Then, either system is selected. However, the relative phase fluctuation of the optical transmission line 54 with respect to the frame in the system is absorbed by performing the stuffing process on the line signal as described above, but the duplicated optical transmission lines are independent of each other. Therefore,
Since the same relative phase fluctuation does not necessarily occur in the two transmission lines, the stuffing process may occur in only one system.

FIG. 5B. Indicates the pointer value of each frame of the working system and the non-working system in the duplicated transmission line, and the pointer of each of the 0 system (working system) and the 1 system (working system) in that state. That is, before switching the active system from the 0 system to the 1 system, when the pointer value of the 0 system is “n + 1” and the pointer value of the 1 system is “n”, the control of switching the active system is performed according to the instruction from the higher-level device. As a result, the phases of the 0-system and the 1-system are different. At the moment of switching,
The signal corresponding to the difference between the pointers is momentarily cut off.

[0011]

As described above, SD
It is equipped with a duplexed transmission line by the H transmission method, and when one of them is used as the active system for transmission, when switching to the non-active system, the relative phase fluctuations of each transmission line differ If there is a phase difference between both transmission lines, such as when stuff processing is performed, there is a problem that the line signal will be momentarily cut off when switching from the active system to the non-active system. It was When switching the system, the system may be switched to the non-operating system for maintenance when it is desired to reset the active transmission line, or the device that has detected a failure may switch autonomously. When an interruption occurs, the line service is degraded.

According to the present invention, since the relative phase fluctuation generated in one or both of the duplicated optical transmission lines is absorbed, even if there is a difference between the pointers of the active system frame and the non-operation system frame, the line interruption is prevented. It is an object of the present invention to provide a hitless switching system for a communication system capable of performing the same.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, 1 to 5 are the 0-system, 1'to 5'are the 1-system parts, 1 and 1'are the 0-system and 1-system transmission lines,
2, 2'are receivers of 0 system and 1 system, 3, 3'is a synchronization control unit in each receiver, 4, 4'is a staff control unit for performing corresponding staff control when an instruction is given from the control unit. , 5,
Reference numeral 5'denotes a pointer storage means for storing a pointer generated internally or a pointer supplied from the control portion, 6 a system switching means, and 7 a control portion of the system.

In the present invention, when switching the active system (selection system), the pointer value of the active system and the pointer value of the non-operation system (non-selection system) are extracted and the pointer value of the non-operation system is set to the pointer of the active system before switching. In addition to correcting the value, the number of staff (including positive and negative) for performing the correction is calculated, and the staff processing and the pointer value are supplied to the non-operation system to perform the staff processing to make the pointer value the same value. .

[0015]

In FIG. 1, assuming that the 0-system is the active system and the 1-system is the non-operation system, the frame phase of the received signal from the transmission line 1 of the 0-system and the phase of the in-system frame in the synchronization control unit 3 will be described. A pointer corresponding to the phase difference is generated in comparison with the above, and the frame signal to which the pointer is added is input to the system switching means 6 and output to the next stage of the system. At this time, the generated pointer is stored in the pointer storage means 5. When the relative phase of the two frames fluctuates, the synchronization control unit 3 detects it and executes the stuff (positive or negative) operation corresponding to the phase difference, and also corrects the pointer value (+1 or -1).

On the other hand, at this time, even in the 1-system, which is the non-operation system, the reception unit 2 ′ performs the same processing as that of the reception unit 2 on the reception signal from the transmission line 1 ′. In this case, the transmission lines 1 and 1'are not the same transmission medium, and the circuits that perform processing such as mutual conversion of light and electricity are not completely the same. Therefore, even if the relative phase fluctuates in the 0-system, it may not occur in the 1-system, and vice versa. Therefore, in the present invention, when the line is switched for maintenance, the pointer values are read from the pointer storage means 5 of the active system and the pointer storage means 5'of the non-operation system before the instruction from the control unit 7. Be taken.

The control unit 7 compares the read pointer values, and when they match, the system is switched as it is, but when there is a difference, the difference value and the polarity (positive, negative) are
The control unit 7 indicates the number of times of positive or negative stuff processing necessary to match the protection system with the pointer value of the production system.
Control the non-operation staff control unit 4'to execute necessary staff. In the non-operating system synchronization control unit 3 ', the generated pointer value is corrected corresponding to this stuffing process, and becomes the same value as the operating system pointer value. After this,
When the control unit 7 causes the non-operating system to execute the stuffing process and then supplies control for switching the active system from the 0 system to the 1 system to the system switching means 6, the system switching is performed without interruption.

After the stuffing process, if the pointer storage means 5, 5'of both systems are read from the control unit 7 and it is confirmed that the read pointer values match, switching control is performed. The switching can be made more reliable.

[0019]

FIG. 2 is a block diagram of an embodiment. In FIG. 2, 1 is an O / E (optical / electrical) converted 0-system line signal input received from the 0-system optical transmission line, and constitutes a framed signal of the line to which a pointer is added. 1'is a 0-system line signal input from the 1-system optical transmission line. 10 is 11
-19 is a 0-system receiving section, 10 'is a 1-system receiving section having the same configuration as the 0-system, and 20 is an operating system of the line signal in which the in-system pointer of the receiving system is inserted. A selector for selecting 21 is an output terminal for supplying the operation system signal selected by the selector 20 to the next stage, 2
Reference numeral 2 is a control circuit for selecting and instructing the selector 20 according to an instruction from the system control unit, 23 is a system control unit, and 24 is a bus for transferring control signals and data between the control unit 23 and the receiving units 10 and 10 '. Is. Further, S is a terminal to which a signal indicating the frame phase in the system is input.

In the receiving unit 10, 11 is a buffer memory (or elastic store) for stuffing processing, 12 is a selector for incorporating the in-system pointer on the receiving side into the line signal, and 13 is a memory for detecting the pointer and storing it. A synchronous circuit for offsetting the write address counter, 14 a write address counter for generating a write address to the buffer memory 11, 15 a read address counter for generating a read address of the buffer memory 11, 16 a frame phase in the system (from the terminal S) The phase comparator that detects the relative phase fluctuation of the transmission line with respect to the input) and generates the trigger for the stuff processing, 17 calculates the difference between the frame phase in the system and the head phase of the line signal, and the difference (time difference) To a pointer to convert the frame to a pointer Pointer generation circuit for generating a, 18
Is a stuffing control circuit (corresponding to the stuffing control unit 4 in FIG. 1) for instructing positive and negative stuffing processing according to an instruction from the control unit 23 in the system, and 19 is a pointer register (5 in FIG. 1) for reading and storing the in-system pointer. 2), 2
A stuff detection circuit 5 detects the magnitude relationship between the frequency of the extracted clock from the line input signal and the frequency of the system clock and generates a stuff operation trigger.

Reference numeral 10 'denotes a 1-system receiver having the same structure as that of the 0-system receiver 10, and although not shown, it corresponds to each of the above-mentioned 11 to 19 and 25.
Each of 1'to 19 'and 25' is provided.

FIG. 3 shows an example of the operation according to the present invention. The symbols A to A represent signals of the 0-system receiving section, and symbols B are shown in FIG.
Represents the signal of the receiving unit of the 1-system, and it is assumed that the 0-system signal is initially selected as the operating system and the 1-system signal is the non-operating system.

The operation of the embodiment shown in FIG. 2 will be described with reference to FIG. In the receiving unit 10 of the 0 system in the active system, the received signal as shown in FIG. 3 is inputted from the 0 system line (transmission path) signal input 1. In this case, "m" is contained in the pointer area of the frame of the received signal, and the information signal corresponding to the position of the address m after the pointer area is mounted. The line signal is stored in the buffer memory 11 under the control of the write address counter 14, and the pointer value of the line signal is supplied to the phase comparator 16. The read address counter 15 performs reading according to the frame phase (input from the terminal S) in the system. As a result, the frame configuration of the line signal is changed to the frame phase in the system, output, and supplied to the selector 12.

On the other hand, the phase comparator 16 compares the frame phase in the system with the frame phase of the received signal and finds the difference. In the example of FIG. 3, the difference between the tip of the area in which the pointer m is stored and the tip of the storage area of the pointer is calculated. This phase difference is supplied to the pointer generation circuit 17, the difference value is converted into a pointer value, and the pointer value is supplied to the selector 12 and inserted into the pointer area in the frame in the system. At this time, the pointer generated by the pointer generation circuit 17 is the pointer register 1
9 and is stored.

The operation of the pointer generation will be described with reference to FIG. 3. The difference between the frame phase in the system and the line signal of is found by the phase comparator 16, and the difference is designated as "a". The difference "a" is converted into a pointer value by the pointer generation circuit 17, but at this time, the time excluding the length of the pointer value storage area (from the byte next to the last byte of the pointer area to the information signal (The period up to the end of) is obtained as a pointer and stored in the pointer area of the frame in the system. In this case, the value of the pointer is "n", and "n" is set in the pointer area of the in-system frame phase.

However, when the clock of the line input signal of the 0 system and the clock in the system are different due to the phase fluctuation, the stuff detection circuit 25 detects this, and when the difference is a value that requires correction of the pointer value, Perform staff operations. The stuffing operation controls the write address counter 14 and the read address counter 15 through the phase comparator 16 according to the trigger generated from the stuff detection circuit 25 in accordance with the magnitude relationship between the clock frequency of the line input signal and the clock frequency in the system. Then executed,
At the same time, the pointer value is incremented by 1 to the pointer generation circuit 17.
(Positive staff) or -1 (Negative staff). This stuffing process may be performed multiple times depending on the magnitude of the phase fluctuation.

FIG. 3 shows an example in which the positive stuff process is executed once due to the occurrence of relative phase fluctuation in the 0 system, and the pointer value becomes "n + 1" correspondingly. In this case, “n + 1” is stored in the pointer register 19.

On the other hand, also in the receiver 1'of the non-operation system 1, the signal shown in FIG. 3 is similarly inputted from the line signal input 1'of the system 1 and the same operation is performed to correspond to the frame phase in the system. As shown in (1), the pointer of "n" is set and output from the selector 12 '(not shown), and "n" is stored in the 1-system pointer register 19'.

When the frame signal shown in FIG. 3 is generated from the selector 12 of the operating system (0 system) and is selected by the selector 20 and is output to the latter stage of the system, the transmission line of the transmission line is related to the maintenance work. When a switching request occurs, the control unit 23
The content of the pointer register 19 of the active system (0 system) is read via the bus 24, and then the content of the pointer register 19 'of the non-active system (1 system) is read. Next, the difference (including polarity) in the pointer values for matching the read pointer of the non-operation system with the pointer of the operation system is obtained. Based on the obtained difference in pointer value, the control unit 23 determines that the bus 2
The stuff processing circuit 18 is instructed to the non-operation system (1 system) stuff control circuit 18 via 4.

In the case of the operation example of FIG. 3, the pointer of the active system (0 system) is "n + 1" as shown in
Since the pointer of the (system) is “n” as shown by, the staff processing of “+1” is instructed to the non-operation system (system 1).

In the receiving section 10 'of the non-operation system (1 system), the number of times the stuff control circuit 18' instructed to perform stuff processing has instructed the phase comparator 16 'to perform stuff processing of the instructed polarity ( Execute only stuffing (+1 or -1 at a time). At this time, the pointer generation circuit 17 'receives a signal from the phase comparator 16' for each stuffing process, and performs an operation to increase the pointer value by +1 (when positive stuffing) or -1 (when negative stuffing). Is stored in the pointer register 19 '. If the pointer value of the active system (0 system) is “0”, the non-active system (1 system)
If the pointer value is "-2", the normal stuffing process (the process of incrementing the pointer value by 1) is executed twice.

The control unit 23 reads the pointer registers 19 and 19 'of the receiving units 10 and 10' after the stuffing process is finished or after the stuffing process is instructed, and confirms that the two pointer values match. A switching instruction is issued to the control circuit 22 to select the output signal of the 1st system as the operating system. When the selector 20 switches in response to this, its output is switched from the 0-system signal to the 1-system signal without interruption.

In the case of the operation example of FIG. 3, the positive stuffing control instruction of "+1" is given to the state of the frame signal in the system of the first system, and the stuffing process is executed. Becomes "n + 1". When switching is performed after reading each pointer value of the two receiving units to confirm that this state has been reached, the signal of is switched to the signal of, so that the signal is non-interrupted.
In addition, for reference, in the past, the signal was switched from the signal of to, so a momentary interruption occurred.

[0034]

According to the present invention, the phase difference between the pointer phase difference of the duplicated line signal and the operation system in the non-operation system can be absorbed by the stuffing process without providing a new processing circuit. It is possible to prevent instantaneous interruption of the line signal due to maintenance switching of the optical transmission line, and improve the reliability of the line service.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment.

FIG. 3 is a diagram showing an operation example according to the present invention.

FIG. 4 is an explanatory diagram of a frame structure of SDH.

FIG. 5 is an explanatory diagram of a transmission system and a duplication operation.

[Explanation of symbols]

 1 0 transmission line 2 0 reception unit 3 synchronization control unit 4 stuff control unit 5 pointer storage means 1'1 transmission line 2 '1 reception unit 3' synchronization control unit 4'stuff control unit 5 ' Pointer storage means 6 system switching means 7 System control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazunori Hanae, inventor Kazunori Kamitadan, Nakahara-ku, Kawasaki, Kanagawa 1015, Fujitsu Limited (72) Kosuke Nishine, 1015, Uedaka, Nakahara, Kawasaki, Kanagawa Prefecture, Fujitsu Limited

Claims (3)

[Claims] 1. A duplexed receiving unit that receives a signal from a duplexed transmission line that transmits a framed signal by adding a pointer indicating a frame phase, and that independently synchronizes the signal, and the duplexed receiving unit. In the hitless switching system in the communication system including the system switching means for selecting one signal output of the receiving unit as the active system, each receiving unit synchronizes the frame of the input line with the frame of the receiving side system. A synchronization control unit having a pointer processing function for storing the generated pointer, and a pointer storage unit for storing the generated pointer. And the pointer value of each pointer storage means of the receiving unit that operates as the protection system is read, and the pointer value of the protection system is checked so that it matches the pointer value of the protection system. A non-instantaneous switching system in a communication system, characterized in that a receiving unit of an active system is controlled to perform switching by the system switching means. 2. The stuff control unit according to claim 1, further comprising a stuff control unit for performing stuff control in accordance with an instruction from the outside, wherein the control unit of the communication system does not match the read pointer values of the respective receiving units. Until the pointer value of the protection system matches the pointer value of the protection system, the stuff control unit of the reception unit of the protection system is instructed to perform positive or negative stuff processing, and after the staff operation of the protection system ends. A non-instantaneous switching system in a communication system, characterized in that switching is performed by the system switching means. 3. The system switching unit according to claim 2, wherein the control unit of the reception side system reads the pointer value from the pointer storage means of each of the reception units after instructing the staff, and confirms that the pointer values match. A non-instantaneous switching system in a communication system characterized by performing switching by means.