JP2001237815A - Transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission system that stably selects a clock without the need for incorporating a clock source. SOLUTION: The transmission system where a clock generated by an optical transmission section 10 is used by the optical transmission section 10 and a clock generated by an optical reception section 20 is used by the optical reception section 20 in a normal state, is configured such that the interpolation transmission section 10 captures the clock generated by the optical reception section 20 via a clock selection section 16 when input interruption of a signal reaching the optical transmission section 10 or out of frame synchronism is detected, and the optical reception section 20 captures the clock generated by the optical transmission section 10 via a clock section section 26 when input interruption of a signal reaching the optical reception section 20 or out of frame synchronism is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to, for example, SDH (S
(ynchronous Digital Hierarchy) standard or SONET
(Synchronous Optical Network)
TU-T Recommendation G. The present invention relates to an improvement of a transmission device (relay device) having a relay function provided on a transmission line extending from a transmission device that autonomously switches a transmission line using an APS byte specified in 841.

[0002]

2. Description of the Related Art In recent years, there has been a demand for the development of a broadband ISDN based on a globally unified user network interface.
A standard for uniformly multiplexing various high-speed services and existing low-speed services, that is, SDH (in the United States, SON
Called ET. Although both are strictly different, 155.5
Since the same standard is used in stages after 2 Mb / s,
Interconnection is possible. In the following text, the description will be made as SDH, but it also includes SONET. ) Is standardized. In response to this, technical development on an international network in which SDH transmission devices installed in various countries are connected by a large-capacity optical submarine cable or the like is being actively performed.

In such an international SDH network, as shown in FIG. 3, a plurality of transmission devices (nodes: No.
de) a to f are replaced with the working system SL (solid line) and the protection system PL
(Dotted line), a form of connection in a ring shape by a duplicated transmission line is adopted. Each of the transmission lines of the working system and the protection system has clockwise (CW) and counterclockwise (Counter ClockWise) lines, respectively. When a failure occurs, these transmission lines are switched. To relieve the transmission signal.

[0004] A procedure for switching a transmission path when a failure occurs in an SDH transmission system is described in ITU-T Recommendation G. 841. When a failure occurs, each node follows the above-mentioned recommendation, and the APS (Automated Autonomous System) defined in the section overhead (SOH) of the SDH transmission frame.
By rewriting and exchanging (atic protection switching) bytes (K1, K2 bytes), transmission line switching is executed autonomously.

Here, between nodes a and b, between bc,
Segments A, B, C, D, E, and F are defined between cd, de, de, ef, and fa, respectively.
In FIG. 3, each of the nodes a to f extracts any information from the information transmitted through the working transmission line SL and the protection transmission line PL, and outputs the multiplexing device (or the exchange) via the low-speed line ML. ) Dropping each of the lower-level communication devices such as Sw, and adding the information sent from each multiplexer Sw to the working transmission line SL or the protection transmission line PL. Here, each multiplexing device Sw is connected to equipment (not denoted by reference numerals) such as a lower-level subscriber line switch.

Here, the working transmission line SL and the protection transmission line PL are, for example, ST standardized in SDH.
In a multiplex line such as M-16, signals transmitted through communication paths respectively set between the nodes a to f are time-division multiplexed. For example, the node a receives the high-speed time-division multiplexed signal transmitted from another node via the adjacent node f, and sets the channel addressed to the own node to the working transmission line SL (standby transmission line PL). From the low-speed line ML. Then, the time-division multiplexed signal of another channel not addressed to the own node is added to the low-speed line ML of the own node.
And multiplexes (adds) the signals transmitted from the first and second nodes, and outputs a high-speed time-division multiplexed signal to an adjacent node b. Similarly, the high-speed multiplexed time-division signal transmitted from the node b, which is a transmission signal in the reverse direction, is also multiplexed / separated (added / dropped) to the low-speed line ML of the own node and output to the node f. Has become.

FIG. 4 shows a main configuration of each of the nodes a to f. That is, each of the nodes a to f is configured by an add / drop multiplexer (ADM). Synchronous transmission data transmitted via the working transmission line SL (standby transmission line PL) is transmitted to the TSA unit (or the protection system interface unit (I / F) 3 via the working system interface unit (I / F) 3). (MSW unit) 1 and then dropped to the low-speed line ML via the low-speed interface unit (I / F) 4.
In the above description, the TSA section is a Time Slot Assignment section, and the MSW section is a Matrix Switch. Further, synchronous transmission data input from the low-speed line ML is introduced into the TSA 1 via the low-speed interface unit 4 and multiplexed on the working transmission line SL (standby transmission line PL).

The operation of the TSA 1 is controlled by the control unit 5 based on information provided from each of the interface units (I / F) 2 and 3. The control unit 5 stores programs and data related to various controls in the storage unit 6.

A clock supply unit 7 is provided, and the TSA 1 and each active / standby system interface unit (I /
A reference clock used for signal transmission and the like is supplied from the clock supply unit 7 to the F) 2, 3 and the low-speed interface unit (I / F) 4.

Further, each of the primary and secondary interface units (I / F) 2 and 3 and the active transmission line SL (the standby transmission line P
During L), LTE (Line Terminating Equipment)
A transmission device (relay device) called “relay device” is provided. Conventionally,
This LTE was configured as shown in FIG. In other words, the primary and standby system interface units (I / F) 2, 3
STM-N (N = 1, 4, 16, 64)
Etc.) and an STM-N + FEC optical transmission signal, and an STM-N (N = 1, 4, 16,...)
64) are transmitted to the primary and standby system interface units (I / Fs) 2 and 3 side.

[0011] The optical transmission unit 100 includes an STM-N receiving circuit 1
01, an FEC coder (FEC_COD) 103 including a coder (COD) buffer 102, an optical transmission circuit 104, a clock source 105, a clock selection circuit 106, a clock generation circuit 107, a LOS / LOF detection circuit 108, and a switching control unit 109. I have.

In the optical transmission unit 100, an STM-N transmission signal is received by an STM-N receiving circuit 101, and an FEC coder (FEC_COD) 103 receives an FEC (Forward Err) signal.
(rorCorrection) function, an error correction code is added, and the transmission speed is increased. The optical transmission circuit 104 performs electrical / optical conversion and transmits an STM-N + FEC optical transmission signal.

The switching control unit 109 controls the LOS / LOF detection circuit 108 to disconnect the STM-N transmission signal (Loss Of
Signal) or loss of frame (Loss Of Frame), an instruction is given to the clock selection circuit 106 which normally passes the clock output from the STM-N receiving circuit 101, and the output of the clock source 105 is output. Select a clock. The clock generation circuit 107 converts the output clock of the clock selection circuit 106 into a clock of a predetermined frequency and sends it to the optical transmission circuit 104.

The light receiving / transmitting unit 200 includes a light receiving circuit 201,
A FEC decoder (FEC_DECOD) 203 including a decoder (COD) buffer 202, an STM-N receiving circuit 204, a clock source 205, a clock selecting circuit 206,
Clock generation circuit 207, LOS / LOF detection circuit 20
8, a switching control unit 209 is provided.

The light receiving / transmitting section 200 includes a light receiving circuit 201
Receives an STM-N + FEC optical reception signal, performs optical / electrical conversion, and performs FEC decoder (FEC_DECOD) 2
03, an error correction using an error correction code is performed, the transmission rate is reduced, and the transmission rate is supplied to an STM-N receiving circuit 204 to transmit an STM-N reception signal.

The switching control unit 209 detects the loss of input (Loss Of Signal) or the loss of frame synchronization (Loss Of Frame) of the signal obtained by the LOS / LOF detecting circuit 208 converting the optical received signal of STM-N + FEC into an electric signal. sometimes,
Normally, an instruction is given to the clock selection circuit 106 that passes the clock output from the optical reception circuit 201 to select the output clock of the clock source 205. The clock generation circuit 207 converts the output clock of the clock selection circuit 206 into a clock of a predetermined frequency and sends the clock to the FEC decoder (FEC_DECOD) 203.

[0017]

In the above-mentioned LTE, the clock sources 105 and 205 for generating a clock for an emergency in the case of loss of signal input or loss of frame (Loss Of Frame) are described. Although it is preferable to have high accuracy, there is a problem that the cost is high. On the other hand, the clock sources 105 and 205
When a low-precision signal is used, the frequency error increases when an alarm is transmitted to notify the occurrence of an abnormality such as the input loss of the signal or the loss of frame synchronization. It is necessary to be able to receive a signal even when is larger.

In addition, when the frequency difference between the clock reproduced in the normal state and the clocks of the clock sources 105 and 205 becomes large, there is a problem that the signal generated at the time of switching is so disturbed that stable switching cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the conventional transmission apparatus as described above, and has as its object to eliminate the need to incorporate a clock source, to cut off signal input or to lose frame synchronization. It is an object of the present invention to provide a transmission device capable of performing stable clock switching when an abnormality occurs.

[0020]

A transmission apparatus according to the present invention comprises a first signal line for transmitting a signal at a first transmission speed and a second signal line for transmitting a signal at a second transmission speed. And a first relay unit for receiving a signal coming from the first signal line side and transmitting a signal to the second signal line side, and a first relay unit coming from the second signal line side. And a second relay unit for receiving a signal to be transmitted and transmitting the signal to the first signal line side, wherein the input of the signal received by the first relay unit is lost or frame synchronization is lost. Detecting means for detecting an input loss or loss of frame synchronization of a signal received by the second relay unit; and first clock recovery means for recovering a clock using a signal received by the first relay unit. Regenerating a clock using a signal received by the second relay unit And the first relay unit obtains the clock normally obtained from the first clock recovery unit from the second clock recovery unit in accordance with the detection result of the second clock recovery unit and the detection unit. Switching means or control means for switching the second relay unit so that the clock normally obtained from the second clock recovery means is obtained from the first clock recovery means. Thus, when the first relay unit loses signal input or loses frame synchronization, the clock recovered by using the signal received by the second relay unit or the second relay unit loses signal input or frame recovery When the synchronization is lost, the clocks recovered using the signals received by the first relay unit are used.

The transmission apparatus according to the present invention comprises: an optical transmission unit that receives a digital transmission signal, adds an error correction code to the transmission signal, increases the transmission speed, converts the transmission signal into an optical transmission signal of a predetermined wavelength, and outputs the optical transmission signal; A light receiving unit that receives an optical transmission signal of a predetermined wavelength, converts the received signal into an electric signal, performs error correction processing, and reproduces a digital transmission signal, and inputs the digital transmission signal received by the optical transmission unit. Detecting means for detecting disconnection or loss of frame synchronization, and input loss or loss of frame synchronization of an electrical signal received and received by the optical receiving unit, and regenerating a clock using a digital transmission signal received by the optical transmitting unit A first clock regenerating unit, a second clock regenerating unit that regenerates a clock using an electric signal received by the optical receiving unit, and a detection result of the detecting unit. The optical recording transmission unit switches so that the clock normally obtained from the first clock recovery unit is obtained from the second clock recovery unit, or the optical reception unit is normally switched from the second clock recovery unit. And control means for switching so as to obtain the obtained clock from the first clock reproducing means. As a result, the clock recovered by using the signal received by the optical receiver when the signal input is lost or the frame is out of synchronization in the optical transmitter, or the optical transmission is performed when the signal input is lost or the frame is out of synchronization in the optical receiver. The clock reproduced using the signal received by the unit will be used.

The transmission apparatus according to the present invention includes an alarm signal transmitting section for transmitting an alarm signal of a predetermined pattern in accordance with the detection result of the detecting means. Thus, when an input is lost or frame synchronization is lost, a loopback is performed and a warning signal of a predetermined pattern can be transmitted.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A transmission device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the respective drawings, the same components are denoted by the same reference numerals, and redundant description will be omitted. FIG. 1 shows a transmission apparatus (LTE) according to an embodiment of the present invention. The transmission device is provided between each of the primary and secondary interface units (I / F) 2 and 3 and the active transmission line SL (standby transmission line PL). I / F) STM-N coming from 2, 3 side (N = 1,4,16,64 etc.)
The optical transmission unit 1 receives the STM-N + FEC optical transmission signal and receives the STM-N + FEC optical transmission signal, and receives the STM-N + FEC optical transmission signal and receives the STM-N (N = 1, 4, 16, 64, etc.)
The primary / standby interface unit (I / F)
And an optical receiving unit 20 for transmitting to the second and third sides.

The optical transmitting unit 10 is an STM-N receiving circuit 1
1. An FEC coder (FEC_COD) 13 including a coder (COD) buffer 12, an optical transmission circuit 14, a clock selection circuit 16, a clock generation circuit 17, a LOS / LOF detection circuit 18, and a switching control unit 19 are provided.

The STM-N receiving circuit 11 receives an STM-N transmission signal and extracts a clock. F
The EC coder 13 adds an error correction code to the data received from the STM-N receiving circuit 11 to increase the transmission speed. The EC coder 13 uses the coder buffer 12 to absorb the difference in transmission speed. The optical transmission circuit 14 converts data output from the FEC coder 13 into an optical signal. The clock selection circuit 16 selects one of a clock transmitted from the STM-N reception circuit 11 and a clock transmitted from the clock generation circuit 27 of the optical reception unit 20.
The clock generation circuit 17 generates a clock of a predetermined frequency from the clock selected by the clock selection circuit 16 and sends the clock to the optical transmission circuit 14 and the clock selection circuit 26 of the optical reception unit 20. The LOS / LOF detection circuit 18
It detects an input loss (Loss Of Signal) or loss of frame synchronization (Loss Of Frame) based on an STM-N transmission signal passed by the STM-N receiving circuit 11. The switching control section 19 switches the clock selection circuit 16 based on the detection result of the LOS / LOF detection circuit 18.

The light receiving / transmitting unit 2 includes an FEC decoder (FE) including an optical receiving circuit 21 and a decoder (COD) buffer 22.
C_DECOD) 23, STM-N receiving circuit 24, clock selecting circuit 26, clock generating circuit 27, LOS / L
An OF detection circuit 28 and a switching control unit 29 are provided.

The optical receiving circuit 21 receives the incoming STM-N +
It receives the FEC optical reception signal and performs optical / electrical conversion. The FEC decoder 23 performs error correction using the error correction code included in the output signal of the optical receiving circuit 21 to reduce the transmission speed.
2 is used to absorb the difference in transmission speed. STM
The -N receiving circuit 24 sends out the data output from the FEC decoder 23 as an STM-N reception signal. The clock selection circuit 26 is configured to control the clock output from the optical reception circuit 21 and the clock generation circuit 1 of the optical transmission unit 10.
7 is selected. The clock generation circuit 27 generates a clock of a predetermined frequency from the clock selected by the clock selection circuit 26 and sends it to the FEC decoder 23 and the clock selection circuit 16 of the optical transmission unit 10. The LOS / LOF detection circuit 28 detects an input loss (Loss Of Signal) or loss of frame synchronization (Loss Of Frame) based on the signal optically / electrically converted by the optical receiving circuit 21. The switching control unit 29 switches the clock selection circuit 26 based on the detection result of the LOS / LOF detection circuit 28.

The operation of the transmission device configured as described above will be described. In the normal (normal) state, the clock output from the STM-N receiving circuit 11 is selected by the clock selecting circuit 16, and the clock generating circuit 17 generates a clock of a predetermined frequency based on the selected clock, and When the LOS / LOF detection circuit 18 detects that the input of the STM-N transmission signal is lost or the frame is out of synchronization, the switching control unit 19 controls the clock selection circuit 16 based on this. Then, the clock output from the clock generation circuit 27 of the optical receiver 20 is selected.

The FEC coder 13 adds an error correction code to the data using the clock received from the STM-N receiving circuit 11 to increase the transmission speed. The optical transmission circuit 14 uses the clock output from the clock generation circuit 17 to convert the data output from the FEC coder 13 into an optical signal.

In contrast to the above, the LOS / LOF detection circuit 18
Detects that the input of the STM-N transmission signal is lost or the frame is out of synchronization, the switching control section 19 controls the clock selection circuit 16 based on the detection to select the clock output from the clock generation circuit 27 of the optical reception section 20. . As a result, the clock output from the clock generation circuit 27 of the optical receiving unit 20 is supplied to the clock generation circuit 17, and the clock generation circuit 17 generates a clock of a predetermined frequency from the clock selected by the clock selection circuit 16 to generate an optical signal. The signal is transmitted to the transmission circuit 14 and the clock selection circuit 26 of the optical receiver 20.

As a result, if the STM-N + FEC optical reception signal arrives despite the interruption of the input of the STM-N transmission signal, the optical transmission circuit 14 uses the clock generated from the STM-N + FEC optical reception signal. An alarm signal can be sent.

Contrary to the above, also in the optical receiver 20,
In the normal state, a clock output from the optical receiving circuit 21 is selected by the clock selecting circuit 26, and the clock generating circuit 27 generates a clock of a predetermined frequency based on the selected clock, and uses this to use the FEC decoder 2
3 operates, but the LOS / LOF detection circuit 28
Detects that the input of the STM-N + FEC optical reception signal is lost or the frame is out of synchronization, the switching control unit 29
Controls the clock selection circuit 26 to select the clock output from the clock generation circuit 17 of the optical transmission unit 10.

As a result, if the STM-N transmission signal arrives despite the interruption of the input of the STM-N + FEC optical reception signal, the FEC decoder 23 uses the clock generated from the STM-N transmission signal to cause the FEC decoder 23 to issue the alarm signal. Can be sent. The two clocks input to the clock selection circuit 16 are of the same quality as the clocks used for transmission and reception of the STM-N signal, and the two clocks input to the clock selection circuit 26 are used for transmission and reception of the STM-N + FEC signal. Since the clock is of the same quality, it is possible to prevent a problem that a transient response at the time of switching becomes large.

In the above embodiment, when the input of the STM-N transmission signal is interrupted, there is no data input to the optical transmission circuit 14 and an all-zero signal is output from the optical transmission circuit 14 as data. When the input of the N + FEC optical reception signal is interrupted, there is no data output in the optical reception circuit 21, and
An all-zero signal is output from the FEC decoder 23 as data. In a system in which the signal of all 0s is not used as the alarm signal of the input disconnection, the above configuration is inconvenient. Thus, the transmission apparatus according to the second embodiment shown in FIG. 2 can be provided.

In the transmission apparatus according to the second embodiment shown in FIG.
AMS (Alarm Maintenance Signal) generating circuit 1 on the transmitting side that generates an alarm signal of a predetermined pattern to the optical transmitting unit 10A.
5 is provided on the optical receiving unit 20A with a receiving-side AMS generating circuit 25 for generating an alarm signal of a predetermined pattern, and the switching control units 19 and 29 are provided with LOS / LOF detecting circuits 18 and 28, respectively.
Is instructed to generate a pattern based on the detection result.

As described above, when the input of the STM-N transmission signal is cut off, the transmission side AMS generation circuit 1
The data input of the predetermined pattern output from 5 arrives,
The data of this pattern is output from the optical transmission circuit 14. When the input of the STM-N + FEC optical reception signal is interrupted, the data input of the predetermined pattern output from the receiving side AMS generation circuit 25 arrives at the STM-N transmission circuit 24, and the data of this pattern is transmitted to the STM-N transmission circuit. 24.

[0037]

As described above, according to the transmission apparatus of the present invention, when the input of the signal is interrupted or the frame is out of frame at the first relay section, the signal is reproduced by using the signal received by the second relay section. Since the clock or the clock recovered by using the signal received by the first relay unit when the input of the signal is interrupted or the frame is out of synchronization in the second relay unit is used, a clock source is incorporated. No need,
In addition, it is possible to perform stable clock switching when an abnormality such as a signal input loss or frame synchronization loss occurs.

Further, according to the transmission apparatus of the present invention, when a signal input or frame synchronization is lost in the optical transmission unit, a clock recovered by using a signal received by the optical reception unit, or a clock recovered by the optical reception unit. If signal input is lost or frame synchronization is lost, clocks recovered using signals received by the optical transmission unit will be used, respectively, so there is no need to incorporate a clock source, and signal input or frame synchronization is lost. It is possible to perform stable clock switching when an abnormality such as disconnection occurs.

Further, according to the transmission apparatus of the present invention, since there is provided an alarm signal transmitting section for transmitting an alarm signal of a predetermined pattern in accordance with the detection result of the detecting means, when an input is disconnected or frame synchronization is lost. And a warning signal of a predetermined pattern can be transmitted.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a transmission device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a transmission device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an international SDH network to which the present invention is applied.

FIG. 4 is a diagram showing a detailed configuration of each node in FIG. 4;

FIG. 5 is a configuration diagram of a transmission device according to a conventional example.

[Explanation of symbols]

Reference Signs List 10 optical transmission unit 20 optical reception unit 11 STM-N reception circuit 12 coder buffer 13 FEC coder 14 optical transmission circuit 15 transmission side AMS generation circuit 16 clock selection circuit 17 clock generation circuit 18 LOS
LOF detection circuit 19 switching control unit 21 optical reception circuit 22 decoder buffer 23 FEC decoder 24 STM-N reception circuit 25 reception side A
MS generation circuit 26 Clock selection circuit 27 Clock generation circuit 28 LOS / LOF detection circuit 29 Switching control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04L 7/08 H04L 7/02 Z F term (Reference) 5K028 AA01 BB08 CC02 DD04 NN01 NN32 PP03 PP12 QQ02 SS02 SS12 5K042 AA03 BA10 CA10 CA15 DA21 LA09 5K047 AA01 BB02 GG07 GG08 HH01 KK04 KK17 KK18 MM03 MM05 MM12 MM49

Claims (4)

[Claims] A first transmission line for transmitting a signal at a first transmission speed and a second transmission line for transmitting a signal at a second transmission speed; A first relay unit for receiving a signal arriving from the line side and transmitting a signal to the second signal line side, and receiving the signal arriving from the second signal line side and receiving the signal arriving from the second signal line side And a second relay unit for transmitting a signal to the side, wherein the input of the signal received by the first relay unit is lost or the frame is out of synchronization, and the signal received by the second relay unit is lost. Detection means for detecting an input loss or loss of frame synchronization; first clock recovery means for recovering a clock using a signal received by the first relay section; and a signal received by the second relay section. Second clock recovery means for recovering a clock by using the detection means , The first relay unit switches so that the clock normally obtained from the first clock recovery unit is obtained from the second clock recovery unit, or the second relay unit A transmission unit that normally switches a clock obtained from the second clock recovery unit so as to obtain the clock from the first clock recovery unit. 2. An alarm signal transmitting section for transmitting an alarm signal of a predetermined pattern to an output side of the first relay section or an output side of the second relay section according to a detection result of the detection means. The transmission device according to claim 1, wherein: 3. An optical transmission section for receiving a digital transmission signal, adding an error correction code to the transmission signal, increasing the transmission speed, converting the transmission signal into an optical transmission signal having a predetermined wavelength, and outputting the optical transmission signal. And an optical receiving unit for receiving and converting the digital transmission signal into an electric signal, performing error correction processing, and reproducing the digital transmission signal, when the input of the digital transmission signal received by the optical transmission unit is lost or frame synchronization is lost. Detecting means for detecting an input loss or loss of frame synchronization of an electrical signal received and received by the optical receiving unit; and a first clock recovery device for recovering a clock using a digital transmission signal received by the optical transmitting unit. Means, a second clock recovery means for recovering a clock using an electric signal received by the light receiving unit, and the optical transmission unit is normally provided in accordance with a detection result of the detection means. Switching the clock which is obtained from the serial first clock reproducing means to obtain from the second clock reproducing means,
Alternatively, the transmission apparatus includes a control unit that switches the optical reception unit so that the clock normally obtained from the second clock recovery unit is obtained from the first clock recovery unit. 4. An alarm signal transmitting section for transmitting an alarm signal of a predetermined pattern to an output side of the optical transmitting section or an output side of the optical receiving section according to a detection result of the detecting section. The transmission device according to claim 3, wherein: