KR100342248B1 - A wavelength division multiplexing system accepting tributary signals with different transmission rates by using time division multiplexing - Google Patents

Abstract

The present invention provides a time division multiplexing (TDM) for synchronous signals having different transmission rates in a wavelength division multiplexing (WDM) system in which multiple signals are modulated into optical signals having different wavelengths and transmitted to one optical fiber. Then, the method of allocating one light wavelength is disclosed.

The system uses the first frame format 22 to relate these signals when a plurality of low-speed dependent signals are input among synchronous digital hierarchy (SDH) signals, which are the main signals accepted by the WDM system. A first stage time division multiplexer (10) for TDM using a high-speed signal (stage 1 multi-signal) with an asynchronous digital hierarchy (PDH) method, and a dependent signal having a relatively high speed among major SDH signals is mixed. And the second stage time division multiplexer (20) for assigning one wavelength by TDM using a second frame format (24) using the second frame format (24) to make it at the highest rate to be accommodated together. In the second stage time division multiplexer, when the TDM is input at a relatively high speed and is input, it is converted into an optical signal having a predetermined wavelength. It comprises an optical multiplexer 40 for multiplexing a plurality of optical transponders ring 30 and the respective optical signals of different wavelengths input from each of the plurality of optical transponder.

Description

A wavelength division multiplexing system accepting tributary signals with different transmission rates by using time division multiplexing}

The present invention relates to a system for WDM multiplexed signals after TDM at high speed by mixing and receiving low-speed dependent signals having different speeds.

The WDM method is a data transmission method that improves bandwidth utilization efficiency of an optical fiber line by dividing and transmitting multiple wavelengths of a plurality of signals in one optical fiber. WDM systems have the advantage of accepting dependent signals with various transmission rates. Among the various signals, the main signals accepted by the WDM system are SDTM's 155.520 Mb / s STM-1, 622.080 Mb / s STM-4, and 2488.320 Mb / s STM-16 signals, which the WDM system can accept In general, one wavelength is allocated regardless of the signal speed. However, allocating one wavelength to a 155.520 Mb / s signal or 622.080 Mb / s signal to accommodate a variety of dependent signals results in lower bandwidth usage efficiency than allocating one wavelength to a 2488.320 Mb / s signal. There is this.

This relatively low speed 155.520Mb / s signal is TDM as 620Mb / s or 2.5Gb / s signal, or 622.080 Mb / s signal is TDM as 2.5Gb / s signal and then one wavelength is assigned. There is a need for a technology that can improve the efficiency of resource and line bandwidth usage.

As described above, the TDM scheme applied to the WDM system accommodates the frame overhead, multiplexing, and subordinate signals necessary for multiplexing in addition to the transmission rate corresponding to N times of the subordinate signals when multiplexing the input dependent signals having the same rate of N channels. An additional bit rate is needed for the bit to align. This is the same method used for multiplexing of the PDH method.

In the TDM scheme for increasing bandwidth use efficiency in a WDM system, it is common to combine only signals of the same type and multiplex them into high-speed signals. For example, in a WDM system that optically transmits 2.5Gb / s signals by assigning one wavelength, up to 16 S155-1 signals of 155.520Mb / s can be bundled and multiplexed into 2.5Gb / s signals or 622Mb / s STM-4 Only four signals are bundled and multiplexed into 2.5Gb / s signals. In this case, when the signal capacity to be transmitted from one point to another point and thus multiplexed to the optical signal assigned with one wavelength is not 16 with STM-1 dependent signal or 4 with STM-4 signal, The problem is that the 2.5Gb / s signal bandwidth is not used at all.

As described above, an object of the present invention is to provide a WDM system for mixing and accommodating dependent signals having different transmission rates in order to improve line bandwidth efficiency and secure diversity in accommodating dependent signals in the TDM scheme.

1 is a block diagram illustrating an embodiment of a system in which a 155.520 Mb / s channel and a 622.080 Mb / s channel are mixed and multiplexed and applied to a WDM device.

2 is a frame configuration diagram of multiplexing 155.520 Mb / s four channels into 620 Mb / s signals.

3 is a frame configuration diagram of receiving and multiplexing 155.520 Mb / s bundled signals and 622.080 Mb / s signals at the same time and multiplexing them into 2.5 Gb / s signals.

<Brief description of the main parts of the drawings>

10: first stage time division multiplexer 20: second stage time division multiplexer

22: frame format used for the first stage time division multiplexer

24: Frame format used for the second stage time division multiplexer

30: optical transponder 40: optical multiplexer

<Preferred embodiment of the present invention>

The WDM system of the present invention uses a time division multiplexer to mix dependent signals of different transmission speeds, multiplex them into one high-speed signal, and then allocate wavelengths and transmit the multiple optical signals modulated with different wavelengths to one optical fiber. When several dependent signals having a relatively low speed are input among SDH signals, which are the main signals accepted by the WDM system, the signals are converted into relatively high speed signals (one-stage multi-signal) using the first frame format 22. When the first stage time division multiplexer 10 for PDH TDM is input and the first stage multiplexing signal and a dependent signal having a relatively high speed among SDH signals are mixed and input, the second frame format 24 is used. The second stage time division multiplexer 20, the second stage time division multiplexer Multiplexing the optical signals of different wavelengths inputted from each of the plurality of optical transponders 30 and the plurality of optical transponders, which are converted to the optical signal of a predetermined wavelength when the TDM is input at a relatively high speed and then input. It comprises an optical multiplexer 40 for.

In the present invention, a signal having a relatively high rate of TDM by the first stage time division multiplexer is generated by the multiplexing, and the main transmission rate is an overhead bit and a signal for forming a multiframe in addition to the sum of the dependent signal rates to be multiplexed. The sum α of the bits necessary for alignment for clock adaptation of the signal is increased.

In the present invention, the second stage time division multiplexer attempts to simultaneously receive the output signal of the first stage time division multiplexer of 623.840 Mbps and the signal of 622.080 Mbps, and considers the frame based on the 623.840 Mbps signal in consideration of the speed difference between the two signals. When configuring and accepting 622.80 Mb / s signals, it is desirable to insert four rows of fixed fill enable bits.

Now, the principle of the present invention having the above-described configuration will be described in detail by taking a case where multiple reception signals of 155Mb / s and 622.080Mb / s are mixed and multiplexed into 2.5Gb / s signals.

1 shows a method of mixing W155 with a 155.520 Mb / s channel and a 622.080 Mb / s channel. The first stage time division multiplexer 10 of FIG. 1 multiplexes 155.520 Mb / s four channels with 620 Mb / s data. The multiplexing method here multiplexes 155.520 × 4 = 622.080 Mb / s in addition to the transmission rate of 155.520 × 4 = 622.080 Mb / s. The overhead bits to form and the bits needed for the justification for clock adaptation of the signal further increase the transmission rate. Therefore, the transmission rate R1 of the multiple signal becomes 622.080Mb / s + `alpha`.

The second stage time division multiplexer 20 of FIG. 1 multiplexes four channels into 2.5Gb / s signals by mixing and receiving the above R1 transmission signal and 622.080 Mb / s (R2) signal. Similarly to the first stage time division multiplexer 10, the second stage time division multiplexer 20 multiplexes the PDH multiplex to form multiple frames in addition to the transmission rate four times R1 or R2 and to position the dependent signals. bandwidth is needed for justification. In addition, in order to accommodate signals of R1 and R2 transmission rates in the same multi-frame, when a low transmission rate of R2 signals is accommodated, a fixed fill (Payload) is used to compensate for alpha, which is a difference from the R1 signal, in the payload in the frame. Fixed Stuff).

The signal multiplexed into a 2.5Gb / s-class signal by the second stage time division multiplexer 20 is totally converted into an optical signal having a specific wavelength in the optical transponder 30 of FIG. The optical signal is WDM via the optical multiplexer 40 of FIG.

When designing the frame structure for the first stage time division multiplexer 10 and the second stage time division multiplexer 20, the second stage time division multiplexer 20 is adjusted by correlating the transmission rate of the multiple signals with the frame structure. It is important to design for easy implementation of fixed fill within. Here, as an example of the frame structure design for the time division multiplexer of the first and second stages, a method of simultaneously receiving 155.520 Mb / s and 622.080 Mb / s signals will be described.

2 is a frame structure in which 155.520 Mb / s four channels are bundled and multiplexed into 620 Mb / s signals.

Among the overheads, the frame alignment signal (FAS) is a frame alignment signal bit used in demultiplexing. P is a parity check bit for monitoring transmission quality, and SV is a service channel bit allocated to an operator or supervisory control channel. Cji (i = 1 to 4, j = 1 to 5) is a Justification Control bit that controls the justification to adapt the dependent signal to the system clock speed, and JO is the justification that allows the alignment to occur. Justification Opportunity) bit, which is allocated to each channel of 8 bits, and is aligned with the alignment control bit.

The multi-rate of FIG. 2 is 623.840 Mb / s, and the frame structure is composed of 17,920 bits of total frame length with 2,560 subframes and 7 rows. Therefore, the frame rate is 34.813 kHz. The Justification Ratio is determined by the difference between the number of bits of the slave signal input during one frame and the number of bits allowed in one slave signal during one frame, and is determined by a signal of R1 transmission rate of 155.520 Mb / s. When accepting, statistically, 0.64 bits per frame from Equation 1 should be filled with dummy data.

4,468-155.520 * 10 ⁶ / (frame rate) = 0.64 bits

In this case, since two bits are allocated to each channel as the alignment bits, the alignment ratio is 0.32.

Only the multiple transmission rate of 623.840 Mb / s among the parameters for the first stage time division multiplexer affects the design of the second stage time division multiplexer frame structure.

3 illustrates an embodiment of a frame structure for simultaneously multiplexing an R1 transmission rate signal and a 622.080Mb / s signal in the same frame when the multiple transmission rate R1 is set to 623.840Mb / s in the first stage time division multiplexer. Where ** represents a fixed stuff seat when accepting a 622.080 Mb / s signal.

In FIG. 3, C1, C2, and C3 are alignment control bits, and JO is also a alignment enable bit, and 8 bits are allocated to each channel among 32 bits to perform alignment with the alignment control bits.

The multicast rate is 2,501,440 kb / s, and the frame structure is 11,264 subframes and 5 rows. The total frame length is 56,320 bits. Thus, the frame rate is 44.415 kHz. Frame overhead bits have been allocated 32 rows of bits. For the fixed fill bit, 32 rows of payload bits are allocated, and each channel is allocated 8 bits of 32 bits. When accepting R1 baud rate signals of 623.840 Mb / s, the fixed fill allowance bit is transmitted with a valid payload, i.e., an information bit, and when accepting a signal of R2 baud rate of 622.080 Mb / s, the corresponding channel among the fixed fill allowance bits. By inserting the dummy data into the 8-bit bit positions given in Fig. 6, the transmission rate difference from when accepting the 623.840 Mb / s signal is eliminated. Therefore, when accommodating 623.840 Mb / s, the number of bits allocated to each dependent signal is 14,048 bits including the alignment allowable bit and 14,008 bits when accommodating 622.080 Mb / s. This slight difference between the compensation and the remaining transmission rate is accepted as the difference in the alignment ratio.

When accommodating a signal of R1 transmission rate of 623.840 Mb / s, 2.22 bits per frame are statistically filled with dummy data from Equation 2.

14,048-623.840 * 10 ⁶ / (frame rate) = 2.22 bits

In this case, since the alignment bits are allocated 8 bits for each channel, the alignment ratio is 0.28.

In addition, when accommodating an R2 transmission rate signal of 622.080 Mb / s, the alignment ratio is 0.23 from Equation (3).

14,008-622.080 * 10 ⁶ / (frame rate) = 1.85 bits

According to the present invention, the efficiency of the line bandwidth can be improved by TDM of several dependent signals in the WDM scheme and then transmitting them by assigning one wavelength. In this case, in general, the dependent signal multiplexes signals having the same transmission speed, but in the present invention, when the number of signals having the same speed is not large by mixing and accommodating signals having different transmission speeds, the dependent signal is mixed with the signals having different speeds. Bandwidth usage efficiency can be improved. As an example, in the present invention, a mixed signal of two types of signals 155.520Mb / s and 622.080Mb / s among SDH signals is mixed and TDM, and a method of applying the same to a WDM device is presented.

Claims (3)

In a wavelength division multiplexing system that uses a time division multiplexer to assign a single wavelength by mixing subordinate signals having different transmission speeds and then transmits optical signals of various wavelengths to one optical fiber, When a relatively low speed signal is input among the synchronous digital hierarchy signals, which are the main signals accepted by the wavelength division multiplexing system, these signals are relatively high speed using a first frame format. A first stage time division multiplexer for time division multiplexing in a Plesiochronous Digital Hierarchy scheme; Among the synchronous digital rank signals, when a relatively high dependent signal is inputted, a time division multiplexing is performed using a second frame format using a second frame format to mix and accommodate the first-stage multiple signals to make the highest relative speed. A second stage time division multiplexer for allocating a wavelength; A plurality of optical transponders which are pre-converted into optical signals having a predetermined wavelength when inputted after time division multiplexing in the second stage time division multiplexer; And And an optical multiplexer for multiplexing optical signals of different wavelengths input from each of the plurality of optical transponders. The method of claim 1, wherein the multi-rate used when bundling four 155.520 Mbps channels into the 620 Mbps signal using the first stage time division multiplexer is 623.840 Mbps and has a length of 2,560 bits in 7 subframes. The total frame length is 17,920 bits, the frame rate is 34.813 kHz, and the second transmission rate is used to mix the output of the first time division multiplexer and the 622.080 Mbps channel with the second stage time division multiplexer. 2,501,440 kbps and the frame structure is characterized in that the server frame is 11,264 bits in length and 5 rows, the total frame length is 56,320 bits. The method of claim 2, wherein the second stage time division multiplexer configures a frame based on a 623.840 Mbps signal to simultaneously receive an output signal of the first stage time division multiplexer of 623.840 Mbps and a signal of 622.080 Mbps. A wavelength division multiplexing system, characterized in that it inserts eight rows of fixed fill bits per channel to accept a difference in transmission speed between two signals when accommodating a signal.