JP2013150339A - Digital transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve error correction processing with a high error correction rate by flexibly adapting to a communication state such as a transmission path characteristic, a type of accommodated client, and a transmission system.SOLUTION: In a receiving side transmission device 30, when signal quality monitoring means 311 detects a change in signal quality, notification means 34 transmits a signal quality change notification signal to a transmitting side transmission device 20. In the transmission device 20, when notification means 23 receives the signal quality change notification signal, the transmission device 20 transmits a switch timing notification signal to instruct switch timing to the transmission device 30. The transmission device 30 switches an error correction circuit at the switch timing by an error correction circuit switch circuit 321. The transmission device 20 switches error correction circuits 214-1 to 214-N at the timing when the transmission device 20 has instructed the switch timing, by an error correction circuit switch circuit 211.

Description

  The present invention relates to a digital transmission system using an error correction code, and more particularly to a frame transmission system, and more particularly to a digital transmission system that switches adaptively to an optimum error correction code circuit according to signal quality or client signal type.

  Conventionally, in the field of optical communication, the influence of noise on a communication path is small compared to wireless communication and the like, so there is little need to introduce forward error correction (hereinafter referred to as FEC). However, since 1990, the necessity has increased with the increase in transmission capacity. The merit of applying FEC to optical communication is that even a low OSNR (Optical Signal to Noise Ratio) signal can be received with high sensitivity, so that the transmission distance can be easily extended.

  At present, a large-capacity digital transmission system using a 40 Gbit / s class OTN (Optical Transport Network) has already been commercialized, and FEC is mounted as a standard function. The application method of FEC in OTN is recommended by ITU-T (International Telecommunication Union Telecommunication Standardization Sector). 709 (see Non-Patent Document 1, for example) as standard FEC (GFEC: Generalized Forward Error Correction, OTN uses Reed-Solomon code).

  However, in high-speed digital transmission, the influence of deterioration factors such as nonlinear optical effects and polarization mode dispersion appears more conspicuously than before, so the flow of applying error correction codes with performance superior to GFEC Is progressing globally. For this reason, many researches and developments have been made on enhanced FEC (EFEC: Enhanced Forward Error Correction) schemes with improved error correction capability. In current digital transmission systems, multiple error correction codes such as EFEC have been added to GFEC. Most cases are equipped.

  As the transmission capacity increases, the form of the optical network is also changing. Previously, it was point-to-point communication, but now it has evolved into a ring type and mesh type. Along with the evolution of the network form, there is an increasing demand for dynamically changing the optical path, which has been fixed so far, according to the service demand. As a technique for changing the optical path autonomously and dynamically, there is a control protocol called GMPLS (Generalized Multi Protocol Label Switch) standardized by the IETF (The Internet Engineering Task Force) (for example, see Non-Patent Document 2). .

  GMPLS has conventionally used MPLS (Multi Protocol Label Switch) technology, which has been used for IP (Internet Protocol) networks and ATM (Asynchronous Transfer Mode) networks, as WDM (Wavelength Division Multiplexing). ) Is extended to an optical network. It handles light wavelengths as labels and has functions such as dynamic path switching, failure recovery, and traffic control.

  With the introduction of GMPLS, it has become possible to configure a more flexible optical network, but a change in transmission path characteristics that occurs at the time of path switching has become a problem. The transmission path characteristics greatly depend on the dispersion amount of the optical fiber, the transmission loss characteristics, and the installation situation. Currently, many optical fibers are laid, but the influences of the transmission paths are different. In the field of optical communications, adaptive compensation technology is not sufficiently mature, so when a new digital transmission system is introduced, the entire system is designed assuming the worst conditions.

  On the other hand, in the field of wireless communication, since the influence of noise, interference, etc. changes from moment to moment, an error correction method for adaptively switching the error correction capability against communication quality degradation has been proposed (for example, Non-patent document 3, Patent document 1, Patent document 2).

  FIG. 11 is a block diagram illustrating a configuration of the transmission device described in Patent Document 1. In the figure, the transmission apparatus 1 performs buffering of the input signal by the input buffer 2, and performs error correction encoding and interleaving processing by the cross encoder 3. The transmission unit 4 transmits packet data to the reception device.

  On the other hand, the receiving unit 5 receives packet data sent from the receiving device. The retransmission control unit 7 performs control to read again the lost packet when receiving the NACK signal from the input buffer. The round trip time determination unit 8 estimates an elapsed time (round trip time) from transmission to reception based on data from the receiving device. The round trip time storage unit 9 holds the round trip time for a certain period.

  The ACK reception timer 11 determines whether or not the transmission unit 4 has transmitted a packet and received an ACK signal within the round trip time. Further, the switching determination unit 10 obtains the packet loss rate of the communication channel and switches the error correction code system under a certain condition. The packet counter 12 counts the number of packets transmitted from the transmission unit 4, and the error counter 13 counts the number of NACK signals transmitted from the receiving device or the ACK reception timer 11.

  The encoder configuration information storage unit 15 holds circuit configuration information of the encoding circuit. The encoder reconfiguration unit 14 receives the signal from the switching determination unit 10 and changes the circuit configuration of the cross encoder 3.

  The transmission device described in Patent Document 1 reduces the device scale by including reconfigurable hardware, and further, according to the error rate of the communication channel within a given amount of hardware, The error correction code is adaptively switched so as to maximize the packet transmission throughput.

JP 2005-252622 A JP 2004-32283 A

ITU-T G.709, “Interfaces for the Optical Transport Network (OTN)”, p. 28, 94-95 IETF RFC3945, “Generalized Multi-Protocol Label Switching (GMPLS) Architecture”, p. 7-10 Jong-Suk Ahn, and John Heidmann, “An adaptive FEC algorithm for Mobile Wireless Networks”, Technical Report ISI-TR-555, USC / InformationSciences Institute, March, 2002

  However, since the above-described conventional technology uses reconfigurable hardware, in an optical communication transmission system that is much faster than wireless communication, the configuration of the error correction circuit with reconfigurable hardware is realized. The processing speed that can be performed and the circuit scale are limited, and it is difficult to realize a high error correction processing function.

  Furthermore, the above-described prior art is a method specialized for packet transmission systems in wireless communication, and in frame-based transmission systems mainly used in optical communication or the like, data synchronization is not performed on a packet-by-packet basis. Synchronizing between devices. For this reason, when the above-described conventional technique based on packet transmission is applied to an optical communication system as it is, there is a problem that data is lost for a certain period of time due to a difference in processing time of each error correction code when the error correction code is switched. .

  The present invention has been made in consideration of such circumstances, and its purpose is to flexibly adapt to communication conditions such as transmission path characteristics, types of accommodated clients, transmission systems, etc., and high error correction. An object is to provide a digital transmission system capable of realizing processing.

  In order to solve the above-described problem, the present invention provides a digital transmission system including a transmission device on a transmission side and a transmission device on a reception side, wherein the transmission device on the transmission side is configured to input the input signal based on a type of an input signal. Signal type information insertion means for adding signal type information to the signal, each having a different error correction method, and an error correction code by an error correction method based on the signal type information added by the signal type information insertion means A transmission-side error correction processing unit having a plurality of transmission-side error correction circuits for performing transmission, and the reception-side transmission device includes signal type information added to the signal transmitted from the transmission-side transmission device Based on the signal type identification means for identifying the type of the received signal, and a plurality of receiving side error corrections each having a different error correction method and performing error correction on the received signal A receiving side error correction processing unit having a path, an error correction circuit selection unit for determining an error correction method based on the signal type identified by the signal type identification unit, and the error correction circuit selection unit A digital transmission system comprising receiving-side error correction circuit switching means for switching to a receiving-side error correction circuit corresponding to an error correction method.

  The present invention is characterized in that, in the above-described invention, the transmission device on the receiving side further includes a buffer circuit that temporarily buffers a signal until the switching of the plurality of error correction circuits is completed.

  According to the present invention, it is possible to obtain an advantage that high error correction processing can be realized by flexibly adapting to communication conditions such as transmission path characteristics, types of accommodated clients, and transmission systems.

It is a block diagram which shows the structure of the transmission apparatus by 1st Embodiment of this invention. It is a block diagram which shows the structure of the transmission apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structure of the transmission apparatus by 3rd Embodiment of this invention. It is a conceptual diagram for demonstrating the switching timing in the 3rd Embodiment. In this 3rd Embodiment, it is a conceptual diagram which shows the control flow until error correction circuit switching. It is a figure which shows the flame | frame structure of OTN. It is a figure which shows the frame structure of SDH. It is a conceptual diagram which shows the communication procedure when GMPLS (Generalized Multi Protocol Label Switch) is used. It is a conceptual diagram which shows an error correction circuit switching flow in the case where switching of an optical path is accompanied. It is a conceptual diagram which shows the communication procedure in the case of switching an optical path and an error correction circuit simultaneously. 10 is a block diagram illustrating a configuration of a transmission device described in Patent Literature 1. FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the digital transmission system, the transmission side and the reception side both include a plurality of error correction circuits, the reception side monitors the received signal quality, selects an error correction method according to the signal quality, and the selected The error correction method is notified to the transmission side, the transmission side notifies the timing of switching the error correction circuit to the reception side, the error correction circuit is switched according to the error correction method notified at the notified timing, and the reception side is notified. The error correction circuit is switched at the switching timing.

A. First Embodiment First, a first embodiment of the present invention will be described.
FIG. 1 is a block diagram showing a configuration of a transmission apparatus according to the first embodiment of the present invention. In the figure, a transmission device (transmission unit) 20 includes an error correction processing unit 21 that adds redundant information for error correction to an input signal, a signal transmission unit 22 that transmits encoded data to a reception side, And notification means 23. The error correction processing unit 21 includes an error correction circuit switching unit 211 that switches an error correction circuit.

  The transmission device (reception unit) 30 includes a signal reception unit 31 that receives a transmitted signal, an error correction processing unit 32 that corrects an error using redundant information added on the transmission side, and a signal quality monitor of the error correction processing unit 32 An error correction circuit selection unit 33 that determines an error correction method based on the signal quality data output from the unit 322, and an error notification unit 34 that notifies a transmission side device of an instruction to switch the error correction method. The signal receiving unit 31 includes signal quality monitoring means 311 for monitoring signal quality. The error correction processing unit 32 includes an error correction circuit switching unit 321 that switches an error correction circuit, and a signal quality monitor unit 322 that monitors signal quality.

  A plurality of error correction circuits 214-1 to 214 -N are arranged in the error correction processing unit 21 of the transmission device (transmission unit) 20, and a clock to be supplied to each error correction circuit 21 in the preceding stage of the error correction circuit 21. And a power supply unit 212 and a selector circuit 213 for switching them. The selector circuit 213 in the previous stage of the error correction circuit 21 plays a role of selecting a power supply and a clock to be supplied to the error correction circuit 21. Therefore, power consumption can be reduced by stopping operations other than the selected error correction circuit among the plurality of error correction circuits 214-1 to 214-N by the selector circuit 213 in the previous stage.

  Each of the plurality of error correction circuits 214-1 to 214-N has different error correction capabilities, different power consumption, different algorithms, or a combination of these.

  When the selector circuit 213 receives an instruction to switch the error correction circuit, the selector circuit 213 supplies the power and clock from the power supply unit 212 to the switching destination error correction circuit in addition to the operating error correction circuit. . By supplying power and a clock to the error correction circuit at the switching destination in advance, stable operation is possible even at the time of switching. After switching, supply of power and clock to the error correction circuit that was operating before switching is stopped to reduce power consumption.

Next, the operation of the first embodiment will be described.
In the signal quality monitoring means 311 in the signal receiving section 31 of the transmission apparatus (receiving section) 30 or the signal quality monitoring means 322 in the error correction processing section 32, the transmission apparatus (transmitting section) 20 and the transmission apparatus (receiving section) 30 The quality of the signal transmitted between them is monitored, and the signal quality data is sent to the error correction circuit selection means 33. Examples of signal quality data include a code error rate before and after error correction, the number of error corrections, a Q value (Quality Factor), OSNR, and received power. In a transmission system using SDH or OTN, BIP-8 (bit-interleaved parity 8, for example, Non-Patent Document 1, Reference 1 “ITU-T G.707,“ Network node interface for the Synchronous Digital Hierarchy (SDH ) ”, P. 66”), it is possible to measure the bit error rate on the transmission line.

  The error correction circuit selection means 33 determines an error correction code to be used based on the received signal quality data. As a specific determination method, for example, when a code error rate after error correction is received as signal quality data and the code error rate deteriorates beyond a predetermined threshold value, an error correction circuit with higher error correction capability is provided. On the contrary, when the code error rate is improved beyond a predetermined threshold, a method of switching to an error correction circuit with low error correction capability but lower power consumption is conceivable. When the code error rate is sufficiently low (that is, the signal quality is high) and error correction is not required, the error correction circuit may not be used at all (no error correction is selected).

  In addition, various algorithms are used for the error correction code, and different algorithms have different tolerances for different types of errors. Therefore, in the signal quality monitoring means 311 (or 322), for example, the randomness or burstiness of the error can be identified based on the position information of the bit (or block) subjected to error correction. An application method of switching to an error correction circuit having a high effect on the error characteristics is also conceivable.

  For example, BCH codes are generally resistant to random errors, and Reed-Solomon codes are resistant to burst errors. By selecting an appropriate error correction circuit, processing suitable for the degradation factor can be performed. . Further, by performing the interleaving process in the error correction processing unit 21, it becomes possible to randomize the burst error, and it is possible to switch the presence / absence of the interleaving process and the parameters of the interleaving process according to the nature of the error.

B. Second Embodiment Next, a second embodiment of the present invention will be described.
Currently, various types of data (applications) are transmitted in an optical communication system. Examples of applications include voice, still images, moving images, and e-mail. When these data are transmitted, the requirements vary depending on the application. For example, in the case of speech, a low delay is required even if the code error rate is somewhat bad, and in the case of electronic mail, a low code error rate is required even if there is a delay.
Therefore, transmission suitable for each application can be performed by switching the error correction code according to the type of the client signal accommodated.

  FIG. 2 is a block diagram showing the configuration of the transmission apparatus according to the second embodiment. In the figure, a transmission device (transmission unit) 20 performs signal type information insertion means 24 for adding signal type information according to the type of the input client signal, and performs error correction encoding according to the type of the client signal. It comprises an error correction processing unit 21 that performs and a signal transmission unit 22 that transmits the encoded data to the receiving side. The error correction processing unit 21 includes error correction circuit switching means 21 that switches the error correction circuit, as in the first embodiment described above. Since the configuration of the error correction processing unit 21 is the same as that of the first embodiment described above, the same reference numerals as those in FIG.

  A transmission device (reception unit) 30 includes a signal reception unit 31 that receives a transmitted signal, an error correction circuit selection unit 33 that determines an error correction method according to the identified signal type, and a transmission side. It comprises an error correction processing unit 32 that corrects errors using redundant information. The signal receiving unit 31 includes a signal type identifying unit 312 that identifies the type of the signal based on the information of the signal type added to the received signal. In addition, the error correction processing unit 32 includes an error correction circuit switching unit 321 that switches an error correction circuit.

  In addition, the error correction processing unit 32 of the transmission device (reception unit) 30 is provided with a buffer circuit 323 in the preceding stage of the selector circuit 324, and signals are transmitted until the switching of the error correction circuits 325-1 to 325-N is completed. Buffer temporarily. Switching according to the signal type of the error correction circuits 325-1 to 325-N is performed in advance by switching the error correction circuits 214-1 to 214-N according to the type of the client signal in the transmission device (transmission unit) 20. Therefore, the error correction circuits 325-1 to 325-N can be switched on the reception side without using the notification means 23 and 34 in the first embodiment described above.

  To identify the type of client signal, for example, when OTN is used as a transmission method, the value of PT (Payload Type) in PSI (Payload Structure Identifier) or information from the network operation system is selected as an error correction circuit. It becomes possible to identify by transmitting to the means 33. For applications that require low delay, it is possible to operate the application optimally by using an error correction circuit with the shortest processing time within a range where the code error rate satisfies the allowable value of the application. .

C. Third Embodiment Next, a third embodiment of the present invention will be described.
FIG. 3 is a block diagram showing the configuration of the transmission apparatus according to the third embodiment. It should be noted that portions corresponding to those in FIG. In the figure, the transmission apparatus (transmission unit) 20 further includes a transmission frame counter unit 25 that counts the number of transmission frames, and a switching timing control unit 26 that determines the switching timing and determines the switching timing from the frame count number. . Similarly, the transmission apparatus (reception unit) 30 further includes a reception frame counter unit 35 that counts the number of received frames, and a switching timing control unit 36 that determines a switching timing and determines a switching timing from the frame count number. .

  The error correction processing unit 21 on the transmission side is provided with delay difference adjusting means 216 for adjusting the delay time difference between the data output from the error correction circuits 214-1 to 214-N. The error correction processing unit 32 on the receiving side is provided with delay time difference adjusting means 327 for adjusting a delay time difference during transmission or a temporal phase shift.

The switching timing control means 26 and 36 determine the position of the frame serving as a reference for starting the counter and the position of the frame to be switched (see FIG. 4). On the transmission side and the reception side, the counter is operated from the reference frame, and the error correction circuits 214-1 to 214 -N and 325-1 to 325 -N are switched from the frame after N frames based on the switching timing notification signal. Do.
In view of application to OTN, it is also possible to perform switching based on MFAS (Multi Frame Alignment Signal). The MFAS is a multi-frame identification number, and a number is assigned to each frame in a cycle of 256 frames. Therefore, it is possible to instruct the positions of the reference frame and the switching start frame by the switching timing control means 26 and 36 without using the counter.

  The transmission-side delay difference adjusting means 216 is a means for compensating for the delay difference of the data output from each of the error correction circuits 214-1 to 214-N, and matches the delay time of the error correction circuit with the largest processing delay. A delay is given at the front stage, the rear stage, or both of the error correction circuits 214-1 to 214-N (in FIG. 3, the delay difference adjusting means 216 is provided at the rear stage). By adjusting the processing delay time, the error correction circuits 214-1 to 214-N can be switched without signal interruption.

  FIGS. 5A and 5B are conceptual diagrams illustrating a control flow until switching of the error correction circuit in the third embodiment. When the signal quality is monitored between the transmission apparatuses 20 (A) and 30 (B) and a change in the signal quality is detected by the transmission apparatus 30 (B) (Sa1), the transmission apparatus 30 (B) to the transmission apparatus 20 are detected. A signal quality change notification signal is transmitted to (A) (Sa2). The transmission apparatus 20 (A) receives the signal quality change notification signal, and transmits a switching timing notification signal for instructing the switching timing of the error correction circuits 325-1 to 325-N to the transmission apparatus 30 (B) (Sa3). When the transmission device 30 (B) can switch at the instructed timing, the transmission device 30 (B) transmits an ACK signal to the transmission device 20 (A) (Sa4), and the error correction circuits 325-1 to 325-N at the instructed timing. Switch. The transmission device 20 (A) that has received the ACK signal recognizes that the transmission device 30 (B) has accepted the switching timing, and switches the error correction circuits 214-1 to 214-N at the instructed timing (Sa5). ).

D. Fourth Embodiment Next, a fourth embodiment of the present invention will be described.
The fourth embodiment relates to a frame configuration used in communication means used between the transmission apparatuses according to the first embodiment or the third embodiment described above.

  FIG. 6 is a diagram illustrating a frame configuration of OTN. In the first to third embodiments described above, when OTN is used as the notification means 23 and 24, the channel GCC (General Communication Channel) byte for general communication in the OTU (Optical Channel Transport Unit) overhead shown in FIG. Alternatively, the notification signal can be transmitted using bytes in the unused area.

  FIG. 7 is a diagram illustrating an overhead configuration of an SDH frame. In the first embodiment or the third embodiment described above, when SDH is used as the notification means 23, 24, the general communication channel DCC (Data in the SOH (Section Overhead) shown in FIG. The notification signal can be transmitted using a communication channel) byte or a byte in an unused area. Further, notification may be made using an OSC (Optical Supervisory Channel) transmitted at a wavelength different from that of the main signal.

E. Fifth Embodiment Next, a fifth embodiment of the present invention will be described.
8A and 8B are conceptual diagrams showing communication procedures when GMPLS (Generalized Multi Protocol Label Switch) is used as the notification means 23 and 24 in the first embodiment or the third embodiment described above. It is. The transmission apparatuses 20 (A) and 30 (B) are connected to an optical network, and an OXC (Optical Cross Connect) for switching an optical path is provided in the optical network. As shown in FIG. 8A, when the transmission path is not switched before and after the error correction circuit switching (when the paths of the dotted line and the broken line are the same), the first to third embodiments described above are applied. The error correction circuits 214-1 to 214-N and 325-1 to 325-N can be switched according to the switching flow described in the embodiment.

  That is, the signal quality is monitored between the transmission apparatuses 20 (A) and 30 (B), and when a change in the signal quality is detected, a BER deterioration notification signal is transmitted from the transmission apparatus 30 (B) to the transmission apparatus 20 (A). (Sb1), and the transmission apparatus 20 (A) receives the BER deterioration notification signal and sends a switching timing notification signal to the transmission apparatus 30 (B) instructing the switching timing of the error correction circuits 325-1 to 325-N. If transmission is possible at the instructed timing, the transmission device 30 (B) transmits an ACK signal to the transmission device 20 (A) (Sb3), and the error correction circuit is switched at the instructed timing. I do. Receiving the ACK signal, the transmission apparatus 20 (A) recognizes that the transmission apparatus 30 (B) has accepted the switching timing, and switches the error correction circuit at the instructed timing (Sb4).

  In the notification means 23 and 24, the signal quality change notification signal, the switching timing instruction signal, and the like are notified via the GMPLS control plane (for example, Reference 2 “Adrian Farrel and Igor Bryskin,“ GMPLS Architecture and Applications ”, Morgan Kaufmann Publishers, December 2005, p. 47-48”).

  FIGS. 9A and 9B are conceptual diagrams showing an error correction circuit switching flow when switching of optical paths is involved. In response to an optical path switching event (optical path switching due to failure recovery, service change, trouble transfer, etc.), each OXC (1) to OXC (4) control unit (not shown) confirms that the path is free. A new optical path is set using the Path signal to be used and the Resv signal for reserving the path (Sc1). The error correction circuit is switched when the optical path switching is completed.

  That is, similarly to the switching flow in FIGS. 8A and 8B, after the switching of the optical path is completed, the signal quality is monitored, and when a change in the signal quality is detected, the transmission apparatus 30 (B) receives a BER. The deterioration notification signal is notified to the transmission device 20 (A) (Sc2), and the transmission device 20 (A) receives the BER deterioration notification signal and instructs the switching timing of the error correction circuits 325-1 to 325-N. A notification signal is transmitted to the transmission device 30 (B) (Sc3). When the transmission device 30 (B) can be switched at the instructed timing, an ACK signal is transmitted to the transmission device 20 (A) (Sc4). The error correction circuit is switched at the instructed timing. The transmission device 20 (A) that has received the ACK signal recognizes that the switching timing has been accepted by the transmission device 30 (B), and switches the error correction circuits 214-1 to 214-N at the instructed timing (Sc5). ).

  FIGS. 10A and 10B are conceptual diagrams showing a communication procedure when the optical path and the error correction circuit are simultaneously switched. Switching between the error correction circuits 214-1 to 214 -N and 325-1 to 325 -N has two stages of temporary switching and main switching. First, in the temporary switching, when the transmission apparatus 20 (A) receives a path switching notification, the transmission apparatus 20 (A) stores the switching timing instruction signal in an unused area byte in the Path signal, and the transmission apparatus 30 (B) is notified (Sd1). At this time, each control unit (not shown) of OXC (1) → OXC (2) → OXC (3) → OXC (4) performs path empty confirmation based on the message of the Path signal.

  When the transmission device 30 (B) receives an instruction of switching timing and can switch the error correction circuit at a desired timing, the transmission device 30 (B) stores the ACK signal in an unused area byte in the Resv signal, and transmits the transmission device 20 (A ) (Sd2). At that time, each control unit (not shown) of OXC (4) → OXC (3) → OXC (2) → OXC (1) reserves a path based on the message of the Resv signal.

  In the transmission apparatus 20 (A), after receiving the ACK signal, the error correction circuits 214-1 to 214-N are switched at a desired timing (Sd3). Up to this point is provisional switching, and here, switching to an error correction circuit having the highest error correction capability is performed. In this switching, the signal quality is monitored in the same manner as the switching flow in FIGS. 8A and 8B, and switching to an error correction circuit suitable for the transmission path characteristics is performed.

  That is, the signal quality is monitored between the transmission apparatuses 20 (A) and 30 (B), and when a change in the signal quality is detected, a BER deterioration notification signal is transmitted from the transmission apparatus 30 (B). (Sd4), and the transmission apparatus 20 (A) receives the BER deterioration notification signal and sends a switching timing notification signal to the transmission apparatus 30 (B) to instruct the switching timing of the error correction circuits 325-1 to 325-N. When the transmission device 30 (B) can switch at the instructed timing, the transmission device 30 (B) transmits an ACK signal to the transmission device 20 (A) (Sd6), and the error correction circuit 325-at the instructed timing. 1 to 325-N is switched. The transmission device 20 (A) that has received the ACK signal recognizes that the transmission device 30 (B) has accepted the switching timing, and switches the error correction circuits 214-1 to 214-N at the instructed timing (Sd7). ).

  In the switching method shown in FIG. 9 described above, when the transmission path characteristics deteriorate when the optical path is switched, the signal quality is degraded until the error correction circuits 214-1 to 214-N and 325-1 to 325-N are switched. In addition, data may be lost. Therefore, in the method shown in FIG. 10, first, at the same time as switching the path at the initial stage, switching to an error correction circuit having high error correction capability (in the example shown, error correction circuit (2)), the signal quality is improved. Deterioration can be suppressed.

  According to the first to fifth embodiments described above, even in a high-speed frame transmission system using optical communication, an error correction circuit is adaptively optimized according to transmission path characteristics, the type of client accommodated, and the like. You can switch to anything.

  In addition, adaptive error correction applicable to a frame transmission system normally used in optical communication can be realized instead of the packet transmission system shown in the prior art. More specifically, it is possible to adaptively switch the error correction circuit without causing a loss of synchronization between devices by compensating for the delay time difference of data transmission that occurs when the error correction circuit is switched.

20 Transmission device (transmitter)
21, 32 Error correction processing unit 211, 321 Error correction circuit switching unit 22 Signal transmission unit 23, 34 Notification unit 30 Transmission device (reception unit)
31 Signal receiving unit 311, 322 Signal quality monitoring means 212, 322 Clock and power supply unit 213, 215, 324, 326 Selector circuit 214-1 to 214 -N, 325-1 to 325 -N Error correction circuit 24 Signal type insertion Means 33 Error correction circuit selection means 312 Signal type identification means 323 Buffer circuit 25 Transmission frame counter section 26, 36 Switching timing control means 35 Reception frame counter section 216, 327 Delay difference adjustment means

Claims (2)

In a digital transmission system comprising a transmission device on the transmission side and a transmission device on the reception side,
The transmission device on the transmission side is:
Based on the type of the input signal, signal type information insertion means for adding signal type information to the input signal;
Transmission side error correction having a plurality of transmission side error correction circuits each having a different error correction method and performing error correction coding by an error correction method based on signal type information added by the signal type information insertion means A processing unit and
The transmission device on the receiving side is
A signal type identifying means for identifying the type of the received signal based on signal type information added to the signal transmitted from the transmission device on the transmission side;
Receiving side error correction processing unit having a plurality of receiving side error correction circuits each having a different error correction method and performing error correction on the received signal;
An error correction circuit selection means for determining an error correction method based on the signal type identified by the signal type identification means;
A digital transmission system comprising: a reception-side error correction circuit switching unit that switches to a reception-side error correction circuit corresponding to the error correction method determined by the error correction circuit selection unit. The transmission device on the receiving side is
The digital transmission system according to claim 1, further comprising a buffer circuit that temporarily buffers a signal until switching of the plurality of error correction circuits is completed.

Images