JP5091489B2 - Digital transmission system and digital transmission method - Google Patents

Description

  The present invention relates to a digital transmission system and a digital transmission method for performing transmission by accommodating or multiplexing a plurality of types of client signals having different bit rates.

  In the optical transmission system, SDH (Synchronous Digital Hierarchy) is internationally standardized as a digital hierarchy for multiplexing existing service signals. In the US, SONET (Synchronous 0ptica1 NETwork) similar to SDH 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. In recent years, as a platform for transparently transmitting not only SONET / SDH but also various client signals such as ATM and Ethernet (registered trademark, hereinafter omitted), wavelength division multiplexing (WDM) that can cope with the explosive increase in Internet traffic. OTN (Optical Transport Network) (see Non-Patent Document 1) premised on the Wavelength Division Multiplexing method has been standardized and is expected to become the mainstream of future optical transmission systems.

  In recent years, due to the explosive spread of the Internet, the number of Ethernet interfaces has increased rapidly, and in 2007, the number of Ethernet interfaces shipped is predicted to exceed the SONET / SDH interface. As a Gigabit class Ethernet signal, a 1.25 Gbit / s 1 Gigabit Ethernet (1 GbE) signal and a 10.3125 Gbit / s 10 Gigabit Ethernet (10 GbE) LANPHY signal are standardized. In the future, 10 GbE is expected to become the mainstream as a client signal for communication carriers. Furthermore, there is an increasing demand for connecting LAN (Local Area Network) environments scattered in remote locations as they are with LAY-PHY (physical layer). In addition, in the Ethernet signal, there are users and device vendors that use a preamble and an inter frame gap (IFG: Inter Frame Gap) with a unique specification different from the IEEE standard (see Non-Patent Document 2). For this reason, the carrier network is required to transparently transfer the entire signal including the preamble and IFG other than the frame for several Ethernet signals whose bit rates are not integer multiples.

  However, OTN client signals are premised on SONET / SDH signals, and 2.48832 Gbit / s, 9.95328 Gbit / s, and 39.8112 Gbit / s are defined as OTN client signal bit rates. The bit rate is different from the signal and 10 GbE signal. As a method of accommodating a 10 GbE-LANPHY signal having a bit rate different from the currently standardized OTN client signal bit rate in a transparent and efficient manner, an OTN using an overclocking method is widely used. The application of the overclocking method means that only the bit rate is increased at a ratio of 10.3125 / 9.995328, and there is no change in the frame structure or function of the OTN, and 10GbE of 10.3125 Gbit / s. -This means that the LANPHY signal is stored as it is in the payload of the OTN as a client signal.

  FIG. 1 shows a conventional digital transmission system in which an STM-64 (9.995328 Gbit / s) signal and a 10 GbE-LANPHY signal are directly accommodated in a payload area of an OTU (Optical channel Transport Unit) frame and transmitted by wavelength multiplexing. FIG. 2 shows a configuration diagram of the OTU frame structure. When the 10GbE-LANPHY signal 102a is accommodated in the OTU frame shown in the lower part of FIG. 1, an overclocking method is applied in the OTN transmission apparatus 104 to add overhead, FS (Fixed Stuff) bytes, and FEC. The bit rate is increased, and the 10 GbE-LANPHY signal is directly accommodated in the 11.0957 Gbit / s OTU frame. OTN is premised on WDM and is widely used because a large capacity system can be realized by wavelength multiplexing even if the bit rate differs for each wavelength. In addition, when accommodating 10 GbE-LANPHY signals, additional signal processing is not required, and efficient accommodation is possible at low cost. Therefore, this method is also documented in ITU-T (non- (See Patent Document 3).

ITU-T G.709 H. Ichino et al., IJHSES, vol.15, no.3, pp.191-228, 2005 ITU-T G.Sup.43

  However, when a 10 GbE-LANPHY signal is accommodated in an OTU frame using the overclocking method, the bit rate is different from that when an STM-64 signal is accommodated, and a transmission signal having a plurality of bit rates is wavelength-multiplexed. Become. For this reason, in the transmission system, it is necessary to prepare a plurality of types of optical transmission / reception modules and frame processing circuits corresponding to each bit rate, leading to an increase in price. When client signals are multiplexed in a 40 Gbit / s OTN system, a 10 Gbit / s signal is time-division multiplexed up to a 40 Gbit / s signal, so that a difference in bit rate cannot be allowed. A normal 40 Gbit / s OTN system can multiplex-accommodate STM-64 signals, but cannot multiplex-accommodate 10 GbE-LANPHY signals with different bit rates. In addition, an overclocked 40 Gbit / s OTN system can multiplex-accommodate 10 GbE-LANPHY signals, but cannot multiplex-accommodate STM-64 signals. Therefore, with a single wavelength of 40 Gbit / s signal, STM-64 signal and 10 GbE-LANPHY signal cannot be mixed and multiplexed. Therefore, when transmitting one STM-64 signal and one 10GbE-LANPHY signal, the wavelength multiplexing of 40 Gbit / s obtained by multiplexing the STM-64 signal and 40 Gbit / s obtained by multiplexing the 10 GbE-LANPHY signal is performed. Two wavelengths of 40 Gbit / s signal are required, and the accommodation efficiency cannot be improved.

  Therefore, in view of the above points, the present invention is a digital transmission that transmits a plurality of types of client signals having different bit rates in a transparent manner that can be improved in accommodation efficiency at a low cost. It is an object to provide a system and a digital transmission method.

In order to achieve such an object, according to the first aspect of the present invention, a plurality of types of client signals having different bit rates are accommodated or multiplexed in a digital frame and transmitted from the received digital frame. A digital transmission system for separating multiplexed signals and outputting the client signal, wherein a specific fixed frame is applied to a client signal other than the client signal having the highest bit rate among the plurality of types of client signals. The bit rate of the plurality of types of client signals that can be accommodated in the digital frame by increasing the bit rate of the client signals by inserting a dummy pattern including a frame synchronization pattern into the fixed frame. Transparent rate to range And rate adjustment means for, on the receiving side, using the frame synchronization pattern to determine the area of the dummy pattern, to remove the dummy pattern, and a rate restoring means for rate restoring the bit rate of the original client signal The number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are set to M: N (for client signals other than the client signal having the highest bit rate among the plurality of types of client signals. M, if N is to constitute the specific fixed frame by inserting the dummy pattern at a ratio of natural numbers), and the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a N and as _{C) × (M + N)} / N is capable of accommodating a bit-rate range of the digital frame And sets the value. Here, in order to ensure the transparency of the client signal, the rate adjustment is performed by applying no overhead to the bit sequence of the client signal, for example, by adding a new overhead.

According to a second aspect of the invention, in a digital transmission system according to claim 1, wherein the frame synchronization pattern is characterized by a different pattern from the frame synchronization pattern of the client signal. The frame synchronization pattern for determining the dummy pattern insertion position can be, for example, an inverted pattern of F628.

According to a third aspect of the invention, in a digital transmission system according to claim 1, wherein the dummy pattern is characterized in that it comprises a scrambling pattern.

According to a fourth aspect of the present invention , a plurality of types of client signals having different bit rates are accommodated or multiplexed in a digital frame and transmitted, and the accommodated or multiplexed signal is separated from the received digital frame and the client is separated. A digital transmission system for outputting a signal, wherein a fixed pattern is used for a client signal other than the client signal having the highest bit rate among the plurality of types of client signals, and a dummy pattern is used for the fixed frame. A rate adjusting unit that transparently adjusts the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame by increasing the bit rate of the client signal by inserting Kind of client signal Among the client signals other than the client signal having the highest bit rate, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are in a ratio of M: N (M and N are natural numbers). by inserting the dummy pattern constituting said specific fixed frame, when the bit rate and frequency accuracy of the client signal and the B _C and ± a _C, is _{(B C ± a C) ×} (M + N) / N It said set the value of N and M such that accommodate possible bit rate range of the digital frame, characterized by error monitoring using a specific region of the dummy pattern. Here, CRC (Cyclic Redundancy Check) and BIP (Bit Interleaved Parity) used in Ethernet (registered trademark) and SDH can be inserted into the specific area of the dummy pattern to perform error monitoring.

According to a fifth aspect of the present invention , a plurality of types of client signals having different bit rates are accommodated or multiplexed in a digital frame and transmitted, and the accommodated or multiplexed signal is separated from the received digital frame and the client is separated. A digital transmission system for outputting a signal, wherein a fixed pattern is used for a client signal other than the client signal having the highest bit rate among the plurality of types of client signals, and a dummy pattern is used for the fixed frame. A rate adjusting unit that transparently adjusts the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame by increasing the bit rate of the client signal by inserting Kind of client signal Among the client signals other than the client signal having the highest bit rate, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are in a ratio of M: N (M and N are natural numbers). by inserting the dummy pattern constituting said specific fixed frame, when the bit rate and frequency accuracy of the client signal and the B _C and ± a _C, is _{(B C ± a C) ×} (M + N) / N When the values of N and M are set so as to be within the bit rate range that can be accommodated in the digital frame and the client signal is rate-adjusted, the performance of the client signal is monitored, and when an abnormality is detected, the rate is The adjusting means inserts a specific pattern corresponding to the abnormal state into the dummy pattern or the client signal accommodating area. And notifies the abnormal state to the receiving side.

Invention according to claim 6, when the digital transmission system according to claim 1, when performing rate recovery, from the processing unit of the digital frame on the reception side, detects a maintenance signal indicating abnormality of the upstream signal, The rate restoration means transmits a maintenance signal at a bit rate after rate restoration.

According to a seventh aspect of the present invention, a plurality of types of client signals having different bit rates are accommodated or multiplexed in a digital frame and transmitted, and the accommodated or multiplexed signal is separated from the received digital frame, thereby the client. A digital transmission method for outputting a signal, wherein a dummy pattern including a frame synchronization pattern is used by using a specific fixed frame for a client signal other than the client signal having the highest bit rate among the plurality of types of client signals. Is inserted into the fixed frame to increase the bit rate of the client signal and transparently adjust the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame ; On the receiving side, the frame Using the period pattern to determine the area of the dummy pattern, wherein by removing the dummy pattern, and a possible rate-restored to the bit rate of the original client signal, the highest bit rate among the plurality of types of client signals The dummy pattern is inserted at a ratio of M: N (M and N are natural numbers) between the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment for client signals other than client signals having to constitute the specific fixed frame, in the case where the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a C) × (M + N) / N is the digital frame The N and M values are set so that the bit rate range can be accommodated.

  According to the present invention, it is possible to transparently accommodate or multiplex a plurality of types of client signals having different bit rates with low cost and improved accommodation efficiency, and perform transmission using digital frames having the same bit rate. It becomes possible.

  Further, according to the present invention, it is possible to specify where an error has occurred in the system by including error monitoring information in the dummy pattern inserted for rate adjustment.

  Furthermore, according to the present invention, the client device is notified by the maintenance signal that there is an abnormality in the upstream signal, and the client device can detect the abnormal state.

  Hereinafter, embodiments to which the present invention can be applied will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 2 shows a basic block configuration of a digital transmission system that multiplexes and transmits a plurality of types of client signals having different bit rates according to the first embodiment to which the present invention can be applied. The client signals are two STM-64 signals 201a and 201b and two 10GbE-LANPHY signals 202a and 202b. The STM-64 signals 201a and 201b are transparently transmitted to the vicinity of the bit rate of 10.3125 Gbit / s of the 10 GbE-LANPHY signal using the fixed frame in which the dummy pattern is inserted in the rate adjustment units 203 and 204 which are circuits for performing rate adjustment. The rate is adjusted. The rate adjustment of the STM-64 signal will be described later with reference to FIG.

  In the OTN transmission device 205 on the transmission side, the rate-adjusted STM-64 signals 201 a and 201 b and the 10 GbE-LANPHY signals 202 a and 202 b are multiplexed and transmitted to the reception side via the transmission path 206. In the reception-side OTN transmission apparatus 207, the rate-adjusted STM-64 signal and the 10 GbE-LANPHY signal are separated from the received signal and output. For the rate-adjusted STM-64 signal, the dummy pattern is deleted from the fixed frame in the rate restoration units 208 and 209 which are circuits for restoring the bit rate of the rate-adjusted client signal to the original bit rate, It is output after being restored to the original client signal bit rate (201a ', 201b'). This OTN transmission apparatus 205 applies an overclocking method in order to accommodate 10.3125 Gbit / s 10 GbE-LANPHY signals, and the bit rate of an OTN signal in which four client signals are multiplexed is 44.6 Gbit / s s.

  In order to accommodate or multiplex multiple types of client signals with different bit rates in a digital frame for transmission at one bit rate, the bit rate of the client signal is set to the highest bit among the client signals using a specific fixed frame. Increase to near the rate. Usually, a certain range of the bit rate of the client accommodation area of the digital frame for transmission is allowed. For example, according to the specification of the OTN system, a bit rate error in the range of ± 20 ppm is allowed. This may be specified within a certain range of the bit rate of the digital frame, or may be allowed by a frequency synchronization function such as justification processing of the digital frame. Therefore, the rate adjustment of a plurality of types of client signals having different bit rates may be performed by converting the rate to an allowable range of the digital frame without completely matching the bit rates. At this time, in order to ensure the transparency of the client signal, the bit sequence of the client signal is not subjected to any processing, and the rate adjustment is performed by adding, for example, a new overhead.

  In the international standard OTN, a frequency shift of up to ± 65 ppm can be absorbed by the justification process. However, since the frequency accuracy of the 10 GbE-LANPHY signal is ± 100 ppm, in the present embodiment, for the justification process. In the byte area (that is, OPU), the frequency adjustment range is expanded by changing the number of bytes per OTU frame from 1 byte to 2 bytes.

  FIG. 3 shows an example of a process in which the bit rate is converted in the process of accommodating the client signal. The bit rates of the STM-64 signal and the 10 GbE-LANPHY signal as client signals are 9.95328 Gbit / s ± 20 ppm and 10.3125 Gbit / s ± 100 ppm, respectively. The 10 GbE-LANPHY signal is accommodated in the digital frame as it is without being processed. The STM-64 signal is accommodated in the digital frame by increasing the bit rate within a range of 10.3125 Gbit / s ± 100 ppm using a fixed frame so that the STM-64 signal falls within the bit rate range that can be accommodated in the digital frame. Here, since the OTN transmission apparatus accommodates the 10 GbE-LANPHY signal, the justification processing function is expanded to allow a bit rate deviation of ± 100 ppm. In order to accommodate 10 GbE-LANPHY with a frequency accuracy of ± 100 ppm, the frequency adjustment range of the justification function is expanded by expanding the justification byte range of the OTU frame as described above. But it is possible. In this embodiment, since the number of bytes per OTU frame is changed from 1 byte to 2 bytes for the OPU, a frequency shift of ± 65 ppm × 2 = ± 130 ppm can be allowed as shown in FIG. it can. Using this justification function, the 10 GbE-LANPHY signal and the rate-adjusted STM-64 signal are accommodated in frequency synchronization. As a result, the frequency synchronization of a plurality of client signals can be achieved, and it becomes possible to time-division multiplex them into a higher-speed OTU frame.

  FIG. 4 shows an example of a fixed frame configuration for rate adjustment of the STM-64 signal. Here, for each N bits 402b of the STM-64 signal 401 before rate adjustment, an M-bit dummy pattern 402a is inserted (N and M are natural numbers), and the dummy pattern M bits and the client signal N bits are set as one set. It constitutes a fixed frame. Here, the values of M and N are (9.995328 ± 20 ppm) × (M + N) / N using the bit rate of 9.95328 Gbit / s of the STM-64 signal 401 and its frequency accuracy of ± 20 ppm, It is necessary to set the bit rate range that can accommodate the transmission digital frame. The STM-64 signal 402 and the 10 GbE-LANPHY signal 403, which are rate-adjusted by inserting the dummy pattern 402a, are accommodated or multiplexed after the bit rate is adjusted within the range that can be accommodated by the digital frame for transmission. . In this specification, the ratio M / N for inserting an M-bit dummy pattern for every N bits of the STM-64 signal is referred to as a dummy pattern insertion ratio.

  In the OTN standardized by ITU-T, the frequency accuracy of the client signal is ± 20 ppm, but the frequency accuracy of the 10 GbE-LANPHY signal is ± 100 ppm. In order to allow the frequency accuracy of ± 100 ppm and map the client signal of the 10 GbE-LANPHY signal to the OTU frame, there is a method that allows the bit rate of the OTU frame to ± 100 ppm. Accordingly, considering the frequency accuracy of ± 20 ppm of the STM-64 signal and the frequency accuracy of ± 100 ppm of the 10 GbE-LANPHY signal, the dummy pattern insertion ratio M / N is included in the bit rate range that can be accommodated in the digital frame. (9.953328-20 ppm) / ((10.3125 + 100 ppm)-(9.95328-20 ppm)) or more, (9.95328 + 20 ppm) / ((10.3125-100 ppm)-(9.953328 + 20 ppm)) or less Needs to be set in the range.

  As shown in the lower part of FIG. 4, the M-bit dummy pattern 402a includes a frame synchronization pattern 404a. In order to separate the client signal from the fixed frame, restore the rate and output it on the receiving side, it is necessary to determine the position of the dummy pattern. For this reason, the rate adjustment units 203 and 204 set the frame synchronization pattern 404a in the dummy pattern, and the rate restoration units 208 and 209 determine whether or not the frame synchronization pattern 404a appears in a fixed frame period. The pattern insertion position is determined, and the dummy pattern 402a is deleted. Normally, a signal of a digital communication system includes a frame synchronization pattern for performing frame synchronization. This is the same for a client signal. In order to prevent the dummy pattern from being erroneously detected due to the frame synchronization pattern used in the client signal, a frame synchronization pattern different from the client signal is used as a frame synchronization pattern for determining the dummy pattern insertion position. For example, in this embodiment, the frame synchronization pattern for determining the dummy pattern insertion position can be an inverted pattern of F628, but is not limited thereto.

  Further, by setting the area other than the frame synchronization pattern 404a in the dummy pattern 402a as the scramble pattern 404b, it is possible to avoid the same code continuity. When serial data signal connection or optical signal connection is used as an interface between a circuit that performs rate adjustment (that is, a rate adjustment unit) and a circuit that performs digital frame processing for transmission (that is, an OTN transmission device on the transmission side) The clock is extracted on the side, and the subsequent digital processing is performed with the extracted clock. In this case, if the same code continues, the clock cannot be extracted. As shown in the present embodiment, by including the scramble pattern 404b in the dummy pattern 402a, the same sign continuity can be avoided, and the requirement condition of the same sign continuous proof strength of the timing extraction circuit can be relaxed.

  Table 1 below shows examples of dummy pattern insertion ratios. In order to rate-convert a 9.95328 Gbit / s signal to a 10.3125 Gbit / s signal, the least common multiple becomes very large, and it is necessary to perform rate adjustment using a very long frame, which is not practical. However, by using the frequency adjustment function of the digital frame for transmission (in this embodiment, the OTU frame of OTN), it is possible to match a plurality of types of client signals having different bit rates completely without matching the bit rates. It can be accommodated or multiplexed in digital frames of the same bit rate. In this embodiment, four client signals are time-division multiplexed and transmitted as an OTN signal of 44.6 Gbit / s. However, four OTN signals are wavelength-multiplexed without time-division multiplexing. It may be transmitted. In this case, since the transmission bit rate of the transmission device can be made the same for each wavelength, the cost of the optical transceiver module and the frame processing circuit can be reduced. In the present embodiment, the rate adjustment unit is shown as being outside the OTN transmission apparatus. However, the rate adjustment unit includes a client accommodation unit (not shown) and a frame processing unit (not shown) in the OTN transmission apparatus. ) May be included.

[Embodiment 2]
FIG. 5 shows a basic block configuration of a digital transmission system that multiplexes and transmits a plurality of types of client signals having different bit rates according to the second embodiment to which the present invention can be applied. In the present embodiment shown at the bottom of FIG. 5, the rate adjustment units 503-2 and 504-2 perform the rate adjustment executed in the rate adjustment units 203 and 204 of the first embodiment, and the client signal 501a- 2 and 501b-2 when the rate is adjusted, error detection of the client signal is performed, and error monitoring information is inserted into a specific area of the dummy pattern, so that the rate adjustment units 503-2 and 504-2 on the transmission side Error monitoring is performed up to the rate restoration units 508-2 and 509-2 on the reception side.

  In FIG. 5, an error has occurred between a circuit that performs rate adjustment processing using a fixed frame (that is, a rate adjustment unit) and a circuit that performs digital frame processing for transmission (that is, an OTN transmission apparatus on the transmission side). In this case, the system operation is compared between when there is no error monitoring (FIG. 5A) and when there is error monitoring (FIG. 5B).

  When there is no error monitoring, no error is detected in the reception-side OTN transmission apparatus 507-1, and only the client apparatuses 500e-1 and 500f-1 detect the error. Since only the client devices 500e-1 and 500f-1 can detect the error, it is impossible to specify where the error has occurred on the system.

  When there is error monitoring, the rate adjustment units 503-2 and 50-2 can confirm that there is no error in the accommodated client signal by monitoring the error of the client signal. Next, in the OTN transmission apparatus 507-2 on the receiving side, no error is detected, and rate restoration units 508-2, 509-2 having the same functions as the rate restoration units 208, 209 of the first embodiment, and An error is detected in the client devices 500e-2 and 500f-2. Since no error is detected in the section of the OTN transmission apparatus, the transmission side rate adjustment units 503-2, 504-2, between the transmission side OTN transmission apparatuses 505-2, or the reception side OTN transmission apparatuses 507-2- It can be determined that an error has occurred in any of the rate restoration units 508-2 and 509-2. CRC or BIP used in Ethernet or SDH can be applied as error monitoring information to be inserted into a specific area of the dummy pattern.

  In the present embodiment, the rate adjustment unit is shown as being outside the OTN transmission apparatus. However, the rate adjustment unit includes a client accommodation unit (not shown) and a frame processing unit (not shown) in the OTN transmission apparatus. ) May be included.

[Embodiment 3]
FIG. 6 shows a basic block configuration of a digital transmission system that multiplexes and transmits a plurality of types of client signals having different bit rates according to a third embodiment to which the present invention can be applied. When there is an abnormality such as a high error rate of the client signal, it is necessary to determine where the abnormality has occurred. In the present embodiment, the rate adjustment units 603 and 604 perform the rate adjustment executed in the rate adjustment units 203 and 204 of the first embodiment, and at the time of rate adjustment of the client signals 701a and 701b, When performance monitoring is performed and an abnormality is detected, the rate adjustment units 603 and 604 insert a specific pattern corresponding to the abnormal state into a dummy pattern or a client signal accommodation (payload) area, and set the abnormal state on the receiving side. Notify. By notifying the receiving side of the abnormal state, the receiving side device, that is, the rate restoring units 608 and 609 and the client devices 600e and 600f having the same functions as the rate restoring units 208 and 209 of the first embodiment, The location of occurrence can be recognized, and it can be determined whether maintenance action needs to be taken.

  In the present embodiment, the rate adjustment unit is shown as being outside the OTN transmission apparatus. However, the rate adjustment unit includes a client accommodation unit (not shown) and a frame processing unit (not shown) in the OTN transmission apparatus. ) May be included.

[Embodiment 4]
FIG. 7 shows a basic block configuration of a digital transmission system for multiplexing and transmitting a plurality of types of client signals having different bit rates according to a fourth embodiment to which the present invention can be applied. In the present embodiment, the rate adjustment units 603 and 604 may be the same as the rate adjustment unit of the first, second, or third embodiment. When the reception-side OTN transmission apparatus 707 detects that a signal interruption has occurred in the transmission path 706, the OTN transmission apparatus 707 sends out generic-AIS (Alarm Indication Signal) signals 701a ′, 701b ′, 702a ′, and 702b ′ to the reception client side. Thus, the client device 700e, 700f, 700g, 700h is notified that there is an abnormality in the upstream signal. When rate restoration processing is performed in the rate restoration units 708 and 709 having the same functions as the rate restoration units 208 and 209 of the first embodiment, the Generic-AIS signals (that is, maintenance signals) 701a ′ and 701b ′ are It is necessary to transfer to the client devices 700e and 700f. When rate restoration is performed in the rate restoration units 708 and 709, the rate restoration is performed when a maintenance signal indicating an abnormality in the upstream signal is detected from the transmission digital frame processing unit (that is, the OTU transmission apparatus 707 on the reception side). The same maintenance signals 701a ′ and 701b ′ are sent to the client devices 700e and 700f at a later bit rate. As a result, the client devices 700e and 700f can detect an abnormal state.

  When an SDH apparatus is used instead of the OTN transmission apparatus, an MS-AIS (Multiplex Section-Alarm Indication Signal) signal is used as a maintenance signal. Even when the rate adjustment processing and the rate restoration processing are performed in the rate adjustment unit and the rate restoration unit, the maintenance signal must be transmitted to the reception-side client device. Therefore, when the rate restoration unit detects the maintenance signal, the maintenance signal that is the same as the detected maintenance signal is output with the bit rate of the client signal that has been restored, and the failure status is notified to the reception-side client device.

  In the present embodiment, the rate adjustment unit is shown as being outside the OTN transmission apparatus. However, the rate adjustment unit includes a client accommodation unit (not shown) and a frame processing unit (not shown) in the OTN transmission apparatus. ) May be included.

[Embodiment 5]
FIG. 8 shows a configuration diagram of an ODU frame structure used in a digital transmission system for multiplexing and transmitting a plurality of types of client signals having different bit rates according to a fifth embodiment to which the present invention can be applied. In the present embodiment, unlike the previous embodiments, a frame processing unit (not shown) in the transmission-side OTN transmission apparatus also performs rate adjustment, and the transmission-side OTN transmission apparatus operates in a specific area of the transmission digital frame. A fixed frame is formed by inserting a dummy pattern into the frame, and the rate adjustment of the client signal is realized. In the transmitting OTN transmission apparatus, in the process of multiplexing the client signal in the OTU frame, the client signal is first accommodated in the ODU frame, and then accommodated or multiplexed in the OTU frame. The 10 GbE-LANPHY signal is not processed and is accommodated in an overclocked ODU frame as it is. In the present embodiment, since the OTN transmission apparatus performs processing integrally with the transmission digital frame in order to adjust the rate, there is no need to newly synchronize the frame, and it is not necessary to have performance monitoring or a failure status notification function. The rate can be adjusted with a minimum number of circuits.

  An example of a configuration diagram of the ODU frame structure is shown in the lower part of FIG. In the ODU frame, in order to match the bit rate of the multiplexed signal of the ODU frame that accommodates the slower client signal with the bit rate when the client signal is accommodated in the payload area without multiplexing, the payload area is specified. An FS byte can be inserted at the position as a dummy pattern. Normally, when accommodating a 10 Gbit / s client signal, the FS byte is inserted in a payload area of 3808 bytes × 4 rows in a range of 16 bytes × 4 rows. However, when accommodating an STM-64 signal, rate adjustment is performed by expanding the FS byte area from 16 bytes to 148 bytes. By changing the FS byte area to a 148 byte string, the STM-64 signal is rate-converted at a ratio of (3808-16) / (3808-148) and a bit rate of 10.3125 Gbit / s-24.2 ppm. Thus, it can be multiplexed with an ODU frame containing a 10 GbE-LANPHY signal. Thus, by changing the insertion range of the FS byte, the rate can be adjusted with a minimum circuit change. In this embodiment, the FS byte is inserted into one area, but it may be divided and inserted into a plurality of locations. Also, the insertion range can be set in byte units without inserting FS bytes in byte string units. By this rate adjustment, the rate-adjusted STM-64 signal falls within the range of the 10 GbE-LANPHY signal bit rate of 10.3125 Gbit / s ± 100 ppm and is handled or accommodated in the same manner as the 10.3125 Gbit / s client signal. Multiplexing is possible.

  As described above, in the various embodiments, the example in which the client signal is transmitted by time division multiplexing has been described. However, the client signal may be transmitted by wavelength multiplexing without being time division multiplexed. In this case, since the transmission bit rate of the transmission device can be made the same for each wavelength, the cost of the optical transceiver module and the frame processing circuit can be reduced.

FIG. 2 is a configuration diagram showing a digital transmission system in which an STM-64 signal and a 10 GbE-LANPHY signal are directly accommodated in a payload area of an OTU frame and transmitted by wavelength multiplexing, and a configuration diagram of an OTU frame structure. It is a figure which shows the basic block structure of the digital transmission system which multiplexes and transmits the multiple types of client signal with a different bit rate by 1st Embodiment which can apply this invention. It is a figure which shows the example of the process in which a bit rate is converted in the process which accommodates a client signal. It is a figure which shows the example of a fixed frame structure for the rate adjustment of a STM-64 signal. It is a figure which shows the basic block structure of the digital transmission system which multiplexes and transmits the multiple types of client signal with a different bit rate by 2nd Embodiment which can apply this invention. It is a figure which shows the basic block structure of the digital transmission system which multiplexes and transmits several types of client signals with a different bit rate by 3rd Embodiment which can apply this invention. It is a figure which shows the basic block structure of the digital transmission system which multiplexes and transmits the multiple types of client signal with a different bit rate by 4th Embodiment which can apply this invention. It is a block diagram which shows an example of the ODU frame structure used in the digital transmission system which multiplexes and transmits the multiple types of client signal with a different bit rate by 5th Embodiment which can apply this invention.

Explanation of symbols

101a, 101a ′ STM-64 signal 102a, 102a ′ 10GbE-LANPHY signal 103, 104, 108, 109 OTN transmission device 105, 107 Wavelength multiplexing device 201a, 201b, 201a ′, 201b ′ STM-64 signal 202a, 202b, 202a ', 202b' 10GbE-LANPHY signal 203, 204 Rate adjustment unit 205, 207 OTN transmission device 208, 209 Rate restoration unit 401, 402 STM-64 signal 402a Dummy pattern 402b, 404c Client signal 403 10GbE-LANPHY signal 404a Frame synchronization pattern 404b Scramble pattern 500a-1 to 500h-1 Client device 501a-1, 501b-1, 501a-1 ', 501b-1' STM-64 signal 02a-1, 502b-1, 502a-1 ′, 502b-1 ′ 10GbE-LANPHY signal 503-1, 504-1 Rate adjustment unit 505-1, 507-1 OTN transmission device 508-1, 509-1 Rate recovery Unit 500a-2 to 500h-2 Client device 501a-2, 501b-2, 501a-2 ', 501b-2' STM-64 signal 502a-2, 502b-2, 502a-2 ', 502b-2' 10GbE- LANPHY signal 503-2, 504-2 Rate adjustment unit 505-2, 507-2 OTN transmission device 508-2, 509-2 Rate restoration unit 600a-600h Client device 601a, 601b, 601a ', 601b' STM-64 signal 602a, 602b, 602a ′, 602b ′ 10GbE-LANPHY signal 60 , 604 Rate adjustment unit 605, 607 OTN transmission device 608, 609 Rate restoration unit 700a to 700h Client device 701a, 701b STM-64 signal 701a ', 701b' Maintenance signal 702a, 702b 10GbE-LANPHY signal 702a ', 702b' Maintenance signal 703, 704 Rate adjustment unit 705, 707 OTN transmission device 708, 709 Rate restoration unit 706 Transmission path

Claims (7)

A digital transmission system that accommodates or multiplexes a plurality of types of client signals having different bit rates in a digital frame, and separates the accommodated or multiplexed signals from the received digital frame and outputs the client signal. And
For a client signal other than the client signal having the highest bit rate among the plurality of types of client signals, a dummy pattern including a frame synchronization pattern is inserted into the fixed frame using a specific fixed frame, Rate adjusting means for increasing the bit rate of the client signal and transparently adjusting the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame ;
On the receiving side, the frame synchronization pattern is used to determine the area of the dummy pattern, the dummy pattern is deleted, and rate restoration means for rate restoration to the bit rate of the original client signal is provided,
For client signals other than the client signal having the highest bit rate among the plurality of types of client signals, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are expressed as M: N (M, If N is the constituting said specific fixed frame by inserting the dummy pattern at a ratio of natural numbers), and the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a C ) × (M + N) / N is set to a value of N and M so that the bit rate range of the digital frame can be accommodated. The digital transmission system according to claim 1 , wherein
The digital transmission system according to claim 1, wherein the frame synchronization pattern is a pattern different from the frame synchronization pattern of the client signal. The digital transmission system according to claim 1 , wherein
The digital transmission system according to claim 1, wherein the dummy pattern includes a scramble pattern. A digital transmission system that accommodates or multiplexes a plurality of types of client signals having different bit rates in a digital frame, and separates the accommodated or multiplexed signals from the received digital frame and outputs the client signal. And
A bit rate of the client signal is obtained by inserting a dummy pattern into the fixed frame using a specific fixed frame for a client signal other than the client signal having the highest bit rate among the plurality of types of client signals. Rate adjustment means for transparently adjusting the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame,
For client signals other than the client signal having the highest bit rate among the plurality of types of client signals, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are expressed as M: N (M, If N is the constituting said specific fixed frame by inserting the dummy pattern at a ratio of natural numbers), and the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a C ) × (M + N) / N is set so that the values of N and M are within the bit rate range that can be accommodated in the digital frame ,
An error monitoring is performed using a specific area of the dummy pattern . A digital transmission system that accommodates or multiplexes a plurality of types of client signals having different bit rates in a digital frame, and separates the accommodated or multiplexed signals from the received digital frame and outputs the client signal. And
A bit rate of the client signal is obtained by inserting a dummy pattern into the fixed frame using a specific fixed frame for a client signal other than the client signal having the highest bit rate among the plurality of types of client signals. Rate adjustment means for transparently adjusting the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame,
For client signals other than the client signal having the highest bit rate among the plurality of types of client signals, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are expressed as M: N (M, If N is the constituting said specific fixed frame by inserting the dummy pattern at a ratio of natural numbers), and the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a C ) × (M + N) / N is set so that the values of N and M are within the bit rate range that can be accommodated in the digital frame ,
When adjusting the rate of the client signal, if the client signal performance is monitored and an abnormality is detected, the rate adjustment unit may specify a specific pattern according to the abnormal state as the dummy pattern or the payload area of the client signal. A digital transmission system that is inserted into the receiver and notifies the receiving side of an abnormal state . The digital transmission system according to claim 1 , wherein
When performing a rate restoration, if a maintenance signal indicating an upstream signal abnormality is detected from the digital frame processing unit on the receiving side, the rate restoration means sends out a maintenance signal at the bit rate after the rate restoration. A featured digital transmission system. This is a digital transmission method in which a plurality of types of client signals having different bit rates are accommodated or multiplexed in a digital frame, and the received or multiplexed signal is separated from the received digital frame to output the client signal. And
For a client signal other than the client signal having the highest bit rate among the plurality of types of client signals, a dummy pattern including a frame synchronization pattern is inserted into the fixed frame using a specific fixed frame, Transparently adjusting the bit rate of the plurality of types of client signals to a bit rate range that can be accommodated in the digital frame by increasing the bit rate of the client signal ;
The receiving side determines the area of the dummy pattern using the frame synchronization pattern, deletes the dummy pattern, and restores the bit rate of the original client signal ; and
For client signals other than the client signal having the highest bit rate among the plurality of types of client signals, the number of bits of the dummy pattern and the number of bits of the client signal before rate adjustment are expressed as M: N (M, If N is the constituting said specific fixed frame by inserting the dummy pattern at a ratio of natural numbers), and the bit rate and frequency accuracy of the client signal and the B _C and _{± a C, (B C ±} a C ) × (M + N) / N, wherein the values of N and M are set such that the bit rate range that can be accommodated in the digital frame is set.

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