JP4425258B2 - Optical transmitter frame generation circuit and optical transmission method - Google Patents

Description

The present invention is used for OTN (Optical Transport Network). In particular, the frequency synchronization of a client signal having a large clock frequency deviation is performed, and the client signal is transmitted by OTU (Optical in OTN).
The present invention relates to an optical transmission system in which data is accommodated or multiplexed in a transfer unit) frame.

In an optical transmission system, SDH (Synchronous Digital Hierarchy) is internationally standardized as a digital hierarchy for multiplexing existing service signals. In the US, SONET (Synchronous
Optical Network) is the de facto standard. As the current optical transmission system, an optical transmission system compliant with the SONET / SDH specification has become the mainstream, and has been introduced in large quantities all over the world.

  As a platform for transparently transmitting various client signals such as ATM and Ethernet (registered trademark) as well as SDH / SONET, based on the assumption that the wavelength division multiplexing (WDM) system that can cope with the explosive increase of Internet traffic in recent years. Optical Transport Network (OTN) (see Non-Patent Document 1) has been standardized and is expected to become the mainstream of future optical transmission systems.

  Similar to SONET / SDH, the bit rate (clock frequency accuracy) in OTN is defined as ± 20 ppm, and the bit rate of the payload area (client signal area) that accommodates the client signal is also defined as ± 20 ppm. When the clock of the client signal and the clock of the OTN signal (transmission path side) are asynchronous, the phase of the client clock and the OTN clock shifts due to the difference in bit rate, and a bit slip occurs. In order to prevent bit slip, stuff processing is performed in OTN.

  FIG. 1 shows the OTU frame structure of OTN. In the overhead of the Optical Channel Payload Unit (OPU) in the OTU frame, the stuff processing control byte (hereinafter referred to as JC: Justification Control byte), the stuff byte insertion byte at the time of positive stuff (hereinafter referred to as PJO: Positive Justification Opportunity byte). (Referred to as a positive stuff byte) and a data storage byte during negative stuff (hereinafter referred to as NJO: Negative Justification Opportunity byte (negative stuff byte)). If the bit rate of the client signal and the bit rate of the payload area do not match, positive or negative stuffing processing is performed according to the difference to achieve frequency synchronization of the client signal and multiple clients The signal can be time-division multiplexed and the clock accuracy can be kept within the clock accuracy of the OTN standard.

  Note that PSI in FIG. 1 is a payload structure identifier byte, and is used for notification of what kind of signal is accommodated in the payload area or notification of mapping information. RES is a Reservation byte and is an undefined byte. Further, FS is a Fixed Stuff byte, which is a stuff byte fixedly defined in the payload area in order to synchronize the bit rate of the client signal and the bit rate of the payload area.

  The frequency range in which the frequency synchronization of the client signal is possible is determined by the ratio of the PJO byte and the NJO byte to the payload area byte in the frame. In the case of an OTU frame, one byte is defined for each PJO byte and NJO byte for an OPU payload area of 4 × 3808 bytes, and a frequency difference up to ± 65 ppm can be absorbed. However, considering the frequency accuracy of ± 20 ppm of the OPU payload, client signals up to frequency accuracy of ± 45 ppm can be accommodated without bit slip.

ITU-T G. 709

  With the explosive spread of the Internet, the Ethernet signal has been speeded up. Currently, 10 Gbit / s Ethernet (10 GbE) has been standardized and has been introduced. In the future, 10GbE is expected to become the mainstream as a client signal for communication carriers. Furthermore, there is an increasing demand for connecting LAN environments scattered in remote locations as they are with LAY-PHY.

  The bit rate of the 10 GbE LAY-PHY is 10.3123 Gbit / s, which is different from the SONET / SDH 9.95328 Gbit / s, and thus cannot be accommodated in the OTN as it is. By slightly increasing the OTN bit rate according to the difference between SONET / SDH and 10 GbE, it becomes possible to accommodate 10 GbE LAY-PHY directly in OTN. However, the frequency accuracy of the 10 GbE LAY-PHY is defined as ± 100 ppm, unlike SONET / SDH, and a problem arises when accommodated in the OTN of a communication carrier.

  When the OTN clock is kept within ± 20 ppm of the regulation, the positive / negative stuff processing using the OPU overhead can absorb only the frequency difference of the client signal up to ± 45 ppm, causing a problem of bit slip. Further, when the OTN clock frequency is adjusted so as not to cause bit slip or when it is synchronized with the client signal, there arises a problem that the frequency accuracy of the OTN clock does not fall within the prescribed value ± 20 ppm.

  The present invention provides a frame generation circuit and an optical transmission method for an optical transmitter that can perform frequency synchronization even for client signals with low frequency accuracy such as 10 GbE LAY-PHY, and can accommodate or multiplex them without bit slip. For the purpose.

  The present invention provides an optical transmitter including means for absorbing a frequency deviation of a client signal accommodated in the OTU frame by using a PJO or an NJO byte in the OTU frame when transmitting an OTU frame in the OTN. It is a frame generation circuit.

  Here, the feature of the present invention is that when absorbing a frequency deviation exceeding the frequency deviation amount that can be absorbed by the NJO byte, the FS (Fixed Stuff) byte defined in the OTU frame is Means for storing data corresponding to the frequency deviation corresponding to the amount exceeding the allowable absorption amount of the NJO byte is provided.

  Thereby, it is possible to cope with a client signal having a large frequency deviation by using the NJO byte and the FS byte together to increase the absorption tolerance of the frequency deviation.

  Further, when absorbing a frequency deviation that exceeds the frequency deviation amount that can be absorbed by the PJO byte, for example, the frequency that exceeds the allowable absorption amount of the PJO byte in the payload area defined in the OTU frame. This is dealt with by providing means for inserting stuff bytes corresponding to the deviation.

  Alternatively, there is provided means for using an FS byte defined in the OTU frame in place of the NJO byte. Furthermore, when absorbing a frequency deviation that exceeds the frequency deviation amount that can be absorbed by the PJO byte, a means for increasing and using the byte amount of the PJO byte in the payload area defined in the OTU frame is provided. it can.

  Thereby, an OTU frame with a large absorption tolerance of frequency deviation can be configured.

  Alternatively, when defining a JC byte, an NJO byte, and a PJO byte for each of the plurality of client signals in order to multiplex a plurality of the client signals, the FS byte defined in the OTU frame is changed to the NJO byte or the Means for allocating as a JC byte and the NJO byte is provided. Furthermore, when absorbing a frequency deviation exceeding a frequency deviation amount that can be absorbed by the PJO byte, a means for allocating a PJO byte to a payload area defined in the OTU frame can be provided.

  Here, as a form in which a plurality of client signals are multiplexed and mapped to the payload area of the OTU frame, in time division multiplexing, bit multiplexing, byte multiplexing, division of the payload area into a plurality of division units, or the like can be used. .

  As described above, when a plurality of client signals are multiplexed and transmitted, conventionally, there are cases where the number of multiplexed client signals is larger than the number of NJO bytes. In some cases, frequency synchronization cannot be performed. However, in the present invention, since FS bytes with a large number of bytes are used as NJO bytes, each client signal can be assigned an FS byte as an NJO byte. Even in the case of multiple multiplexing, frequency synchronization can be performed individually for each client signal. Thereby, the margin (degree of freedom) of staff processing can be improved. Further, the shortage of the JC byte can be compensated by the FS byte.

  The present invention can be viewed from the perspective of an optical transmitter. That is, the present invention is an optical transmitter including the frame generation circuit of the present invention, an optical transmission unit, and an optical reception unit.

  The present invention can be viewed from the viewpoint of an optical transmission apparatus. That is, according to the present invention, when transmitting an OTU frame in an OTN, an optical transmission provided with means for absorbing a frequency deviation of a client signal accommodated in the OTU frame using a PJO or an NJO byte in the OTU frame. This is an optical transmission method executed by the frame generation circuit of the optical device.

  Here, a feature of the present invention is that, when absorbing a frequency deviation exceeding the frequency deviation amount that can be absorbed by the NJO byte, the NFS byte of the NJO byte is defined in the FS byte defined in the OTU frame. The data corresponding to the frequency deviation exceeding the allowable absorption amount is stored.

  Further, when absorbing a frequency deviation that exceeds the frequency deviation amount that can be absorbed by the PJO byte, for example, the frequency that exceeds the allowable absorption amount of the PJO byte in the payload area defined in the OTU frame. This is dealt with by inserting stuff bytes corresponding to the deviation.

  Alternatively, the optical transmission method of the present invention is characterized in that the FS byte defined in the OTU frame is used instead of the NJO byte. Further, when absorbing a frequency deviation that exceeds the frequency deviation amount that can be absorbed by the PJO byte, the byte amount of the PJO byte in the payload area defined in the OTU frame can be increased.

  Alternatively, the optical transmission method of the present invention is defined in the OTU frame when defining a JC byte, an NJO byte, and a PJO byte for each of the plurality of client signals in order to multiplex a plurality of the client signals. An FS byte is allocated as the NJO byte or the JC byte and the NJO byte. Furthermore, when absorbing a frequency deviation exceeding the frequency deviation amount that can be absorbed by the PJO byte, the PJO byte can be assigned to the payload area defined in the OTU frame.

  According to the present invention, it is possible to realize an optical transmission system that can perform frequency synchronization even for client signals with low frequency accuracy such as 10 GbE LAY-PHY, and accommodate or multiplex them without bit slip.

(First Example)
The optical transmitter and optical transmission method of the first embodiment will be described with reference to FIGS. FIG. 1 is an overall configuration diagram of an optical transmission system including an optical transmitter 1 according to this embodiment. As shown in FIG. 1, the client signal input to the optical transmitter 1 is received by the optical receiver 10 and is accommodated in the OTU frame by the OTU frame generator 11. This OTU frame is sent to the optical transmission line 2 by the optical transmitter 12. The optical receiver 3 that receives the OTU frame from the optical transmission line 2 receives the OTU frame by the optical receiving unit 30, and extracts the client signal accommodated in the OTU frame by the client signal extracting unit 31. This client signal is transmitted to the client terminal or the like by the optical transmitter 32. The client signal is, for example, an SDH frame or an Ethernet frame.

  FIG. 2 is a diagram showing a JC processing configuration in the OTU frame generation unit 11 of the optical transmitter 1. In the OTU frame generation unit 11 of the optical transmitter 1, the client signal is accommodated in the OTU frame using the mapping FIFO 41. At this time, the client clock and the line clock are compared by the clock deviation detecting unit 40 to detect the clock deviation between the client clock and the line clock.

  In other words, if the client clock and the line clock completely match, the client signal can be transmitted simply by being accommodated in the payload area of the OTU frame, but if this does not match, the client signal Therefore, the JC processing unit 42 needs to perform positive or negative stuffing processing according to the difference.

  FIG. 3 shows the concept of staff processing. The predetermined data length in FIG. 3 is the data length that can be accommodated in the payload area of the OTU frame. When the actual client signal is excessive than the predetermined data length, the excessive client signal is stored in the NJO byte. Then transmit. If the actual client signal is less than the predetermined data length, the client signal is compensated for by inserting a PJO byte.

  FIG. 4 is a diagram for explaining the negative stuffing byte in the first embodiment. An NTU byte is defined in the OTU frame. In the present invention, in addition to the NJO byte defined from the beginning, an FS (Fixed Stuff) byte is used as the NJO byte.

  Next, the JC processing procedure of the first embodiment is shown as a flowchart in FIG. In the first embodiment, when the required JC processing amount is determined by the clock deviation detection unit 40 (S1), the JC processing unit 42 determines whether or not the JC processing amount can be handled only by NJO bytes. (S2) If JC processing is possible with only the NJO byte if it can be handled only by the NJO byte (S5), and it is determined that the frequency deviation amount that can be handled by the NJO byte is exceeded (S2), the NJO byte Then, the amount of data that cannot be stored is calculated (S3), and the data that cannot be stored in the NJO byte is stored in the FS byte (S4).

(Second embodiment)
The optical transmitter and optical transmission method of the second embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing the JC processing procedure of the second embodiment. In the first embodiment, the FS byte is used only for storing data corresponding to the frequency deviation amount that cannot be absorbed by the NJO byte based on the determined JC processing amount, but in the second embodiment, it is determined. Based on the JC processing amount (S11), it is determined in advance whether only the FS byte is used (S13) (S12) or only the NJO byte is used (S14) (S12).

  As described above, the second embodiment differs from the first embodiment in that the byte type used for the stuff process is determined in advance before the stuff process is executed. As a result, as in the first embodiment, the amount of data that cannot be stored in the NJO byte is calculated (S3), and the data that cannot be stored in the NJO byte is stored in the FS byte (S4). The processing procedure can be omitted.

  For example, in the second embodiment, instead of determining the JC processing amount in step S11 based on the JC processing amount detected in real time by the clock deviation detection unit 40, the JC processing is performed in advance according to the signal type to be transmitted in the future. By predicting the amount, it can be determined in advance whether only the FS byte is used (S13) or only the NJO byte is used (S14). According to this, the processing time after the arrival of the signal can be shortened as compared with the first embodiment.

  For example, if the client signal is an SDH signal, it can be handled with only the NJO byte as usual (S12), so only the NJO byte is used (S14). However, if the client signal is a client signal with low frequency accuracy such as 10 GbE LAY-PHY, it may not be possible to deal with only the NJO byte (S12), so only the FS byte is used from the beginning (S13).

  In this case, the determination of the client signal type is performed by providing a client signal type determination unit (not shown) in the preceding stage of the mapping FIFO 41 shown in FIG. 2 and notifies the JC processing unit 42 of the determination result. Alternatively, a client signal type determination function is provided in the mapping FIFO 41 and the determination result is notified to the JC processing unit 42.

  That is, the first embodiment is suitable when the JC processing form (NJO byte only or NJO byte + FS byte) is adaptively changed for each client signal according to the detection result of the clock deviation detecting unit 40. It becomes an embodiment. On the other hand, the second embodiment is an embodiment suitable for the case where the JC processing form (only the NJO byte or only the FS byte) is determined according to the type of client signal (SDH or Ethernet). . Thus, when the type of the client signal is not changed for a long time, the second embodiment is more suitable, and when the client signal type is changed frequently within a short time, the first embodiment is more suitable. Suitable.

(Third embodiment)
A third embodiment will be described with reference to FIG. FIG. 7 is a diagram conceptually showing multiplexed client signals and FS bytes. When client signals # 1 to # 4 are multiplexed, FS bytes defined in the OTU frame are assigned as NJO bytes for each of client signals # 1 to # 4. Conventionally, there may be a case where the number of multiplexed client signals is larger than the number of NJO bytes. In such a case, frequency synchronization cannot be performed individually for a plurality of client signals. Since an abundant number of FS bytes are used as NJO bytes, it is possible to assign FS bytes as NJO bytes to each client signal, and frequency synchronization is individually performed for each client signal even when multiple client signals are multiplexed. be able to. Thereby, the margin (degree of freedom) of staff processing can be improved. Further, when the JC byte is insufficient, the FS byte can be allocated as the JC byte.

(Fourth embodiment)
In the fourth embodiment, regular staff processing will be described. The regular stuff processing will be described very simply because it can be processed by simply inserting a PJO byte in the payload area, whether it is the above-mentioned 10 GbE LAY-PHY or SONET / SDH, for example. .

  When absorbing a frequency deviation that exceeds the frequency deviation amount that can be absorbed by the PJO byte, a stuff byte corresponding to the frequency deviation that exceeds the allowable absorption amount of the PJO byte is added to the payload area defined in the OTU frame. insert. Alternatively, it is used by increasing the amount of PJO bytes in the payload area defined in the OTU frame. Alternatively, PJO bytes are allocated to the payload area defined in the OTU frame.

  ADVANTAGE OF THE INVENTION According to this invention, the restriction | limiting of the client signal type accommodated in an OTU frame can be eased, and a user's convenience can be improved. Further, the network operator does not need to prepare different resources for each client signal type, and can perform efficient network operation.

1 is an overall configuration diagram of an optical transmission system to which an optical transmitter according to an embodiment of the present invention is applied. The figure which shows the JC process structure in the optical transmitter of this invention Example. Conceptual diagram of staff processing. The figure for demonstrating the negative stuff process of a 1st Example. The flowchart which shows the staff processing procedure of a 1st Example. The flowchart which shows the staff processing procedure of 2nd Example. The figure for demonstrating the staff process of a 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical transmitter 2 Optical transmission path 3 Optical receiver 10, 30 Optical receiving part 11 OTU frame generation part 12, 32 Optical transmission part 31 Client signal extraction part 40 Clock deviation detection part 41 Mapping FIFO
42 JC processing section

Claims (9)

When transmitting an OTU (Optical Transfer Unit) frame in an OTN (Optical Transport Network), a frequency deviation of a client signal accommodated in the OTU frame is absorbed using a positive or negative stuff byte in the OTU frame. In a frame generation circuit of an optical transmitter comprising means,
The means for absorbing is
Means for storing data corresponding to the frequency deviation in the negative stuff byte for the frequency deviation that can be accommodated by the negative stuff byte defined in the OTU frame;
For frequency deviation exceeding the absorbable frequency deviation by negative stuff bytes defined in the OTU frame, the on FS (Fixed Stuff) byte defined in the OTU frame, defined in the OTU frame Means for storing data corresponding to the frequency deviation in excess of the absorption allowance of the negative staff byte ;
Frame generating circuit, characterized in that it comprises a. Wherein when absorbing frequency deviation exceeding the absorbable frequency deviation by positive stuff bytes defined in the OTU frame, absorption unto the positive stuff byte in the payload area defined in the OTU frame 2. The frame generation circuit according to claim 1, further comprising means for inserting a stuff byte corresponding to a frequency deviation exceeding the capacity. Frame generation of an optical transmitter having means for absorbing a frequency deviation of a client signal accommodated in the OTU frame using a positive or negative stuff byte in the OTU frame when transmitting an OTU frame in the OTN In the circuit
Means for determining the type of the client signal;
When the determination result of the determining means is a signal type that can absorb the frequency deviation only by the negative stuff byte defined in the OTU frame, the negative stuff byte defined in the OTU frame is absorbed. Means for negative staff bytes in the means to
When the determination result of the determination means is a signal type that may not be supported only by the negative stuff byte defined in the OTU frame, the FS byte defined in the OTU frame is absorbed. frame generating circuit, characterized in that a means for negative stuff byte in means. When absorbing frequency deviation exceeding the absorbable frequency deviation by positive stuff bytes defined in the OTU frame, a byte of positive stuff byte payload area defined in the OTU frame 4. The frame generation circuit according to claim 3, further comprising means for use in an increased manner. Optical transmitter is constituted by a frame generation circuit according to any one of claims 1 to 4, the optical transmitter and the optical receiver. Frame generation of an optical transmitter having means for absorbing a frequency deviation of a client signal accommodated in the OTU frame using a positive or negative stuff byte in the OTU frame when transmitting an OTU frame in the OTN In an optical transmission method performed by a circuit,
For the frequency deviation that can be accommodated by the negative stuff byte defined in the OTU frame, data corresponding to the frequency deviation is stored in the negative stuff byte,
For the frequency deviation exceeding the frequency deviation amount that can be absorbed by the negative stuff byte defined in the OTU frame, the negative stuff byte defined in the OTU frame is added to the FS byte defined in the OTU frame. An optical transmission method characterized by storing data corresponding to a frequency deviation corresponding to a portion exceeding the allowable absorption amount. Wherein when absorbing frequency deviation exceeding the absorbable frequency deviation by positive stuff bytes defined in the OTU frame, absorption unto the positive stuff byte in the payload area defined in the OTU frame 7. The optical transmission method according to claim 6, wherein a stuff byte corresponding to a frequency deviation exceeding the capacity is inserted. When transmitting an OTU frame in the OTN, an optical transmitter having means for absorbing a frequency deviation of a client signal accommodated in the OTU frame using a positive or negative stuff byte in the OTU frame is executed. In the optical transmission method,
Determining the type of the client signal;
If the result of this determination is a signal type that can absorb the frequency deviation only by the negative stuff byte defined in the OTU frame, the means for absorbing the negative stuff byte defined in the OTU frame Bytes for negative staff in
The means for absorbing the FS byte defined in the OTU frame when the determination result is a signal type that may not be supported by only the negative stuff byte defined in the OTU frame. An optical transmission method characterized in that it is a negative stuffing byte . When absorbing frequency deviation exceeding the absorbable frequency deviation by positive stuff bytes defined in the OTU frame, a byte of positive stuff byte payload area defined in the OTU frame The optical transmission method according to claim 8 , wherein the optical transmission method is used in an increased manner.

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