JP2768586B2 - Transmission data conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asynchronous transfer mode (ATM) for converting a format signal of a synchronous digital hierarchy (SDH) into a full cell stream signal.
e) It relates to a transmission data conversion method in the processing device.

[0002]

2. Description of the Related Art A transfer mode used in a broadband ISDN (B-ISDN) is an ATM mode. ATM cell-based transmission and SDH-based transmission are available as ATM cell transmission modes. Some ATM processors for SDH-based transmission include a transmission data conversion circuit that converts an input SDH format signal into a full cell stream signal. Here, the SDH format signal is A
The transmission data conversion circuit includes various overheads in addition to the TM cells, and the transmission data conversion circuit converts the SDH format signal into a full cell stream signal including only cells including no overhead.

FIG. 2 is a block diagram showing a configuration example of a conventional transmission data conversion circuit. In FIG. 2, the SDH format signal is supplied to a cell storage buffer 1, and data of an ATM cell portion excluding overhead is stored in the cell storage buffer 1 under the control of the control means 2, and stored in the cell storage buffer 1. The data in the ATM cell portion is read under the control of the control means 2 and converted into a full cell stream signal.

Here, the control means 2 sends a cell synchronization signal for clarifying the insertion position of the ATM cell in the SDH format signal or whether the data of the SDH format signal given to the cell storage buffer 1 is data of the ATM cell. A mask signal for clarifying whether the data is overhead data is provided, and the control means 2 controls writing and reading based on these signals as follows.

(1) As shown in FIG. 3A, when a frame head overhead SOH1 representing the head of one frame of the SDH format signal is input to the cell storage buffer 1 in accordance with the ATM cell phase, the cell storage The writing to the buffer 1 is not executed, and the empty cell B is output from the cell storage buffer 1 immediately from this phase.

(2) As shown in FIG. 3B, when the frame head overhead SOH1 is inserted so as to divide the ATM cell C2 into two, that is, the frame head overhead SOH1 matches the phase of the ATM cell. If the input is not made, the writing to the cell accumulation buffer 1 is not executed, and the frame head overhead SOH
After the ATM cell C2 in which 1 is inserted in the middle is output from the cell storage buffer 1, the empty cell B is output.

(3) Frame head overhead SOH1
Other overhead OHs are discarded at the entrance side of the cell storage buffer 1, and as shown in FIG. 3C, if there is one cell of data (53 bytes) in the cell storage buffer 1 at the time of discarding, , The ATM cell C2 is output from the cell storage buffer 1.

(4) As described above, overhead OHs other than the frame head overhead SOH1 are discarded at the entrance side of the cell storage buffer 1, but as shown in FIG. If there is no data (53 bytes) for one cell in the accumulation buffer 1, the empty cell B is sent out, and then the ATM cell C2 is output from the cell accumulation buffer 1.

Since the overhead of the SDH frame signal is removed and converted to a full cell stream signal, it is inevitable that an empty cell is generated in the full cell stream signal. Therefore, when the frame head overhead SOH1 is input, Has been designed to absorb the difference in the effective data amount by transmitting an empty cell. Further, since a cell is used as a unit, the next cell is transmitted from the cell storage buffer 1 when there is data for one cell or more in the cell storage buffer 1.

In order to convert the SDH frame signal into a full cell stream signal without discarding the ATM cells by the control by the control means 2 as described above, the capacity of the cell storage buffer 1 needs to be approximately 3 ATM cells (149). Bytes) required.

FIG. 4 is an explanatory diagram of the required capacity of the cell storage buffer 1. If the storage amount of the cell storage buffer 1 is 52 bytes, which is slightly insufficient for one cell at the time T1 when the transmission of a certain cell C1 from the cell storage buffer 1 is completed, the control means 2 sends the empty cell B1 from the cell storage buffer 1 Output. If a 9-byte frame head overhead SOH1 is input during or immediately after the output of the empty cell B1, the empty cell B2 is output following the empty cell B1. While outputting such empty cells B1 and B2, the input S
The ATM cell data of the DH frame signal is stored in the cell storage buffer 1, and the frame head overhead SOH1
Data is discarded. Therefore, at the time T2 when the empty cell B2 has been transmitted, 149 (= 52 + 53 + 53)
-9) Byte data is accumulated. In such a situation where data is accumulated most, 149 bytes of data are accumulated. Therefore, the capacity of the cell accumulation buffer 1 needs to be at least 149 bytes or more.

[0012]

However, in the conventional transmission data conversion method, an empty cell is sent out every time the frame head overhead SOH1 is input.
Since empty cells are transmitted even when the accumulation amount of the cell accumulation buffer 1 is less than one cell (53 bytes) at the time when transmission of the previous cell is completed, empty cells are frequently output. As a result, the continuity of the data has been reduced, and the transmission delay has been increased through the conversion processing of the transmitted data.

As described above, the capacity of the cell storage buffer 1 is required to be about 3 ATM cells, and the memory capacity is large.

The present invention has been made in view of the above points, and it is possible to significantly reduce the frequency of transmitting empty cells and to use an SDH format signal which requires a small amount of memory as a cell storage buffer. Is intended to provide a transmission data conversion method for converting the data into a full cell stream signal.

[0015]

In order to solve the above-mentioned problems, the present invention comprises a cell storage buffer and control means for controlling access to the cell storage buffer.
In a transmission data conversion method in which a synchronous digital hierarchy frame signal is input to a cell storage buffer and a full cell stream signal consisting of only cells included in the frame signal is transmitted from the cell storage buffer, access to the cell storage buffer is as follows. Like.

That is, all the overhead data included in the frame signal is discarded at the entrance of the cell storage buffer, and only the data of the cell included in the frame signal is written into the cell storage buffer. . On the other hand,
At least one byte larger than the amount of overhead that occurs most in one cell period is set as a threshold for determining whether or not to transmit an empty cell. At the time of starting transmission of a new cell,
The cell data is read from the cell accumulation buffer when the accumulation amount of the cell accumulation buffer is equal to or larger than the judgment threshold, and empty cells are sent out when the accumulation amount of the cell accumulation buffer is smaller than the judgment threshold.

[0017]

In the present invention, the frame head overhead is handled without being distinguished from other overheads. That is, all overhead data included in the frame signal is discarded at the entrance of the cell accumulation buffer, and only the data of the cell included in the frame signal is written into the cell accumulation buffer.

Further, when a certain cell (including an empty cell) has been transmitted from the cell storage buffer, the threshold value for determining whether or not to transmit an empty cell is set to a small amount, so that the transmission of the empty cell is performed. We decided to reduce the frequency. That is,
An amount that is at least one byte larger than the amount of overhead that occurs most in one cell period is set as a threshold for determining whether or not to transmit an empty cell. In such a case, when the transmission of a valid cell other than an empty cell starts, the accumulated amount may be less than one cell. However, even during this transmission, the cell data is transmitted from one cell to the next. Since the data is input to the storage buffer, the transmitted cell becomes a valid cell completely filled with data.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. Note that the SDH frame is STM-1 (Sync
It is described as a frame according to the hronous Transport Module-1).

In this embodiment, similarly to the conventional system, a cell storage buffer 1 and a control means 2 are provided (see FIG. 2). An SDH format signal is supplied to the cell storage buffer 1 and controlled under the control of the control means 2. The data of the ATM cell portion excluding the overhead is stored in the cell storage buffer 1, and the data of the ATM cell portion stored in the cell storage buffer 1 is read under the control of the control means 2 and converted into a full cell stream signal. Is done.

However, the point that the cell storage buffer 1 has a small capacity (the point realized by a small memory) and the specific control method by the control means 2 are different from those of the conventional method.

FIG. 1 is a flowchart showing the control processing executed by the control means 2 of this embodiment. The control means 2 executes a write control process for the cell storage buffer 1 and a read control process from the cell storage buffer 1 in parallel.

First, a write control process for the cell storage buffer 1 executed by the control means 2 will be described.

The control means 2 includes a cell synchronizing signal for clarifying the insertion position of the ATM cell in the SDH format signal and the data of the SDH format signal supplied to the cell storage buffer 1 when the data of the ATM cell or the data of the overhead. A mask signal for clarifying this is provided. The control means 2 determines whether the data currently given to the cell storage buffer 1 is overhead data or ATM data.
It is determined whether the data is cell data (step 100). In addition,
In the STM-1, the overhead includes a section overhead SOH of 9 × 8 bytes, a management unit pointer AU of 9 bytes, and a path overhead POH of 1 × 9 bytes, and the first section overhead SOH1 of one frame is a frame. It is the head overhead.

If the data currently provided to the cell storage buffer 1 is any of these overheads, the overhead data is discarded and writing to the cell storage buffer 1 is not executed (step 101).

On the other hand, if the data currently supplied to the cell storage buffer 1 is ATM cell data, the control means 2 writes the data of the ATM cell into the cell storage buffer 1 (step 102).

The control means 2 repeatedly executes such determination of the type of input data and discarding or writing processing according to the data type.

In the case of the above-described conventional system, it is necessary to confirm whether or not the frame head overhead SOH1 has been input, and perform a process for instructing the read control process to transmit an empty cell. In this example,
The frame head overhead SOH1 is handled in the same way as other overheads. That is, the data of the frame head overhead SOH1 is simply discarded.

Next, a read control process from the cell storage buffer 1 executed by the control means 2 will be described.

When it is time to transmit a new cell from the cell storage buffer 1, the control means 2 determines whether or not 10 bytes or more of data (ATM cell data) is stored in the cell storage buffer 1 (step 200). ). For example, the amount of storage can be determined by the difference between the write address and the read address.

When data of 10 bytes or more is stored in the cell storage buffer 1, the control means 2 repeatedly outputs data from the cell storage buffer 1 until the next cell transmission timing (steps 201 and 202). . At the start of transmission, there may be a case where an amount smaller than one cell is stored. However, even during transmission, data of one cell is written in the cell storage buffer 1 as described above. Can be sent.

On the other hand, if it is determined in step 200 that only data of 9 bytes or less is stored in the cell storage buffer 1, the control means 2 causes the cell storage buffer 1 to send empty cells (step 20).
3). For example, the control means 2 has a 53-byte counter, which manages the idle cell period and the like.

As described above, at the timing when the transmission of the ATM cell or the empty cell is completed, the storage amount of the cell storage buffer 1 is confirmed, and when the storage amount is 10 bytes or more, the transmission of the ATM cell data is performed. The control means 2 controls the cell storage buffer 1 so as to transmit an empty cell when the number of bytes is equal to or less than the byte.
Control.

Here, 10 bytes, which is a threshold value for determining whether or not to transmit an empty cell, include 53 bytes in the transmitted ATM cell.
This is the minimum amount required to completely insert the byte data. It is assumed that x bytes have been stored in the cell storage buffer 1 at the time when the transmission of a certain ATM cell is completed. During the transmission period (one cell period) of the next ATM cell,
If 9-byte section overhead SOH (or management unit pointer AU) and 1-byte path overhead POH data are included in the SDH format signal input to the cell storage buffer 1, these data are discarded. The ATM cell data input to the cell storage buffer 1 is 43 (= 53-9-1).
Bytes. The input 43 bytes of data,
From the stored x-byte data, 53 for one cell
If the byte data is not secured, A
The TM cell cannot be transmitted. Therefore, even in a state where overhead is most discarded, if at least 10 bytes of data are stored in the cell storage buffer 1, A is inserted in the next cell transmission period.
A TM cell can be transmitted, and 10 bytes serve as a threshold for determining whether to transmit an empty cell.

The maximum storage amount at which empty cells are transmitted is 9 bytes, and the maximum possible amount of ATM cell data input to the cell storage buffer 1 during one cell transmission period during which empty cells are transmitted is as follows. It is 53 bytes for one cell. Therefore,
Even when the largest amount of data is accumulated in the cell accumulation buffer 1, the accumulation amount is 62 bytes. Therefore, in the case of this embodiment, the cell accumulation buffer 1 has at least 62 cells.
What is necessary is just to have the capacity of bytes.

FIG. 5 shows an example of changes in the SDH format signal input to the cell storage buffer 1 and the full cell stream signal transmitted from the cell storage buffer 1.

FIGS. 5A1 and 5A2 show a case where no empty cell is transmitted even if overhead is discarded. For example, it is assumed that 26 bytes of data of the ATM cell C12 have been accumulated in the cell accumulation buffer 1 at the time point t1 when the transmission of the ATM cell C11 is completed. In this case, immediately after the transmission of the ATM cell C11, the transmission of the ATM cell C12 is executed. During this transmission, the data input to the cell storage buffer 1 is switched to the data of the next ATM cell C13. It is assumed that a 9-byte overhead OH is inserted in the middle of the data of the ATM cell C13. Therefore, at the time point t2 when the ATM cell C12 has been transmitted from the cell storage buffer 1, the storage amount of the cell storage buffer 1 is increased by 1 from 26 bytes up to that point.
It changes to 7 bytes, but this storage amount (17 bytes) is 1
Since it is 0 bytes or more, the transmission of the ATM cell C13 is executed immediately after the transmission of the ATM cell C12.

FIGS. 5 (B1) and 5 (B2) show a case where an empty cell is transmitted due to the discard of the overhead. For example, the time t when the ATM cell C21 is completely transmitted
3, assume that 16-byte data of the ATM cell C22 has been stored in the cell storage buffer 1. In this case, immediately after the transmission of the ATM cell C21, the ATM cell C
22 is executed. During this transmission, the data input to the cell storage buffer 1 is changed to the next ATM cell C.
It is assumed that the data is switched to the data 23 and the 9-byte overhead OH is inserted in the middle of the data of the ATM cell C23. However, the insertion position of the overhead OH is
It is assumed that the time is after the time t4 when the cell C22 has been transmitted from the cell storage buffer 1. Therefore, immediately after the transmission of the ATM cell C22, the transmission of the ATM cell C23 is executed. At time t5 when the ATM cell C23 has been transmitted from the cell storage buffer 1, the cell storage buffer 1
Changes from 16 bytes to 7 bytes as the overhead OH is discarded. This storage amount (7
Byte) is less than 10 bytes, so the ATM cell C2
After the transmission of No. 3, the empty cell B11 is transmitted. Empty cell B1
At the transmission end time point t6 of 1, the accumulated amount is 60 bytes, and the transmission of the ATM cell C24 is executed.

Therefore, according to the above-described embodiment, empty cells are transmitted from the cell storage buffer 1 only when the storage amount of the cell storage buffer 1 at the start of transmission is less than 10 bytes. Occurs much less frequently than in the past. That is, the frame head overhead SOH1 is discarded at the entrance of the cell storage buffer 1 and no empty cell transmission function is provided for it, and the threshold value for determining whether or not to transmit an empty cell is smaller than in the past. The frequency of transmission is reduced. As a result, the continuity of the data is increased as compared with the conventional case, and the transmission delay of the ATM cell due to the conversion processing of the transmission data can be reduced on average on average.

According to the above embodiment, the threshold value for determining whether or not to transmit an empty cell is reduced, and the overhead O
Since the empty cell sending function for H is not provided, the required minimum capacity of the cell storage buffer 1 can be reduced.
The cell storage buffer 1 can be realized with a small number of memories.

Further, according to the above embodiment, since the function of transmitting an empty cell is not provided for the frame head overhead SOH1, the processing of the control means 2 is simplified as shown in FIG. High-speed SDH even if 2 is realized by CPU-centered software
The structure of the control means 2 can be simplified if it can support frame signals and is realized by hardware.

In the above embodiment, the SD according to STM-1 is used.
Although the present invention is applied to an ATM processing device for processing an H frame signal, the present invention can be applied to an ATM processing device for processing other SDH frame signals such as STM-4 and STM-16.

[0043]

As described above, according to the present invention, even if the head of the frame is input to the cell storage buffer, the transmission of the empty cell is stopped, and the data of all the overhead is transmitted at the entrance of the cell storage buffer. Along with discarding,
Since the storage amount that is at least one byte larger than the amount of overhead that occurs most frequently during one cell period is used as a threshold value for determining whether or not to transmit empty cells, the frequency of transmitting empty cells is remarkably reduced and data continuation is performed. Performance can be improved, and the amount of memory used as a cell storage buffer can be reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a process of converting an SDH format signal into a full cell stream signal according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a transmission data conversion circuit.

FIG. 3 is an explanatory diagram showing a conventional conversion process from an SDH format signal to a full cell stream signal.

FIG. 4 is an explanatory diagram of a required capacity of a conventional cell storage buffer.

FIG. 5 is an explanatory diagram illustrating a conversion example of the embodiment.

[Explanation of symbols]

 1. Cell storage buffer 2. Control means

Continuation of the front page (56) References JP-A-2-32644 (JP, A) JP-A-2-90834 (JP, A) JP-A-3-174837 (JP, A) JP-A-5-244129 (JP) , A) JP-A-5-260076 (JP, A) IEICE Technical Report, SSE 90-36 (1990-7-25), p. 31-36 (58) Field surveyed (Int. Cl. ⁶ , DB name) H04L 12/28 H04L 12/56

Claims (1)

(57) [Claims] 1. A cell storage buffer and control means for controlling access to the cell storage buffer, wherein a frame signal of a synchronous digital hierarchy is input to the cell storage buffer, and only a cell included in the frame signal is input. In the transmission data conversion method for transmitting the full cell stream signal from the cell accumulation buffer, discarding all overhead data included in the frame signal at the entrance of the cell accumulation buffer,
Only the data of the cells included in the frame signal are written into the cell accumulation buffer, and a threshold value for determining whether or not to transmit an empty cell by an amount at least one byte larger than the amount of overhead generated most in one cell period. At the start of transmission of a new cell,
When the storage amount of the cell storage buffer is equal to or greater than the determination threshold, the cell storage buffer sends out cell data,
A transmission data conversion method characterized by transmitting an empty cell when the accumulation amount of the cell accumulation buffer is less than a judgment threshold.