JPH0319445A - Cell synchronization control system - Google Patents

Abstract

PURPOSE:To shorten the time deciding synchronization establishment and synchronizing step-out when the line state is favorable and to ensure the decision of synchronization establishment and synchronizing step-out even when the line state is unfavorable by varying a forward and backward protection stage number responding to an address error rate at the cell synchronization. CONSTITUTION:An address error detection section 1 and a cell synchronization processing section 2 are provided. The error detection section 1 detects an error in a destination address included in a header part to generate the signal of the error rate, and the cell synchronization processing section 2 varies the forward and backward protection stage number at the cell synchronization in response to the address error rate detected by the address error detection section 1 to apply cell synchronization processing. When the line state is excellent, the deciding time of synchronization establishment and synchronizing step- out is shortened, thereby ensuring the decision of the synchronization establishment and synchronizing step-out.

Description

[Detailed Description of the Invention] (Summary) Regarding the cell synchronization control method in the ATV transmission system, synchronization is achieved when the line condition is good by changing the number of forward protection stages and the number of backward protection stages according to the address error rate during cell synchronization. The purpose is to shorten the determination time for establishment and loss of synchronization, and to ensure that determination of establishment and loss of synchronization can be made reliably even in poor line conditions. A cell consisting of a data part inserted with the transmission information and an empty cell that does not contain transmission information are continuously transmitted, and a frame pattern is inserted into the empty cell at a predetermined interval, and the receiving side performs a predetermined forward protection using the frame pattern. and an ATM transmission system that synchronizes cells by performing backward protection, an address error detection section that detects address errors in the header section, and changing the number of stages of the forward protection and backward protection according to the address error rate. It is constructed by providing a cell synchronization processing section that performs cell synchronization processing. [Industrial Application Field] The present invention relates to a cell synchronization control system in an ATM transmission system. In broadband ISDN communication method 2, voice, image, etc., which have conventionally been carried out over multiple networks, are used. All information transmission such as data is handled centrally and transmitted using digital signals.

ATM (Asynchronous Trat) is one of the information transmission methods in the broadband ISDN communication system.
+sferMode) transmission method. The ATV transmission method transmits information by dividing generated information data into short pieces, adding headers to them to form short packets called cells, and transmitting these to the other party via a line. , STM (Sync
This is attracting attention as a future transmission method to replace the chronous transfer mode) transmission method.

In the ATM transmission system, a cell is sent out and transmitted to the other party only when information is generated on the terminal side. Therefore, the efficiency of line usage is increased, and information on all speeds from low to high speeds can be handled centrally.

In such an ATM transmission system, when cell synchronization is performed, the time required to determine synchronization establishment and synchronization loss is shortened when line conditions are good, and synchronization establishment and synchronization loss judgments can be reliably performed even when line conditions are poor. It is requested that the

[Prior Art] In the ATM transmission system, information generated on the transmitting side is divided into short pieces, a header is added, and the cells are formed and sent. Figure 3 shows line information in the ATM transmission system, where 1., n-1, n, n+l,... indicate cells of fixed length, and these cells are sent out continuously. , these cells contain a certain percentage of cells that do not contain information (vacant cells), as indicated by diagonal lines. Also, Figure 4 shows the structure of an ATM cell.
(a) shows a normal cell, with a header section 21 and a data section 2.
It has been shown that it consists of 2. In the header section 21,
It includes an address indicating the destination of the cell and check bits such as parity for error checking this address.

Further, (1)) indicates an empty cell, and the data section 22 is empty.

In the ATM transmission system, cell synchronization control is a problem when transmitting a large number of short cells.

Cell synchronization is the process of finding the beginning and end of a cell, or the dividing position between a header section and an information section. Without cell synchronization, the receiving side cannot correctly extract the transmitted information.

In order to achieve cell synchronization, it is common for the transmitting side to send out a predetermined frame pattern at certain intervals, and the receiving side to synchronize based on this pattern. In addition, as a method for synchronizing cells without reducing the efficiency of the transmission path, a frame pattern F is inserted into the header section 21 of the above-mentioned empty cell as shown in FIG. 4(b), and the receiving side The most appropriate method is to detect this frame pattern and synchronize based on it.

[Problem to be solved by the invention]

However, as the empty cell rate, that is, the percentage of empty cells included in all transmitted cell packets, decreases, frame patterns arrive less frequently on the receiving side, making it difficult to determine whether synchronization is established or out of synchronization. There is a problem with becoming.

The present invention is an attempt to solve the problems of the prior art, and is to change the number of forward protection stages and the number of backward protection stages according to the address error rate during cell synchronization, and to establish synchronization when the line condition is good. It is an object of the present invention to provide a cell synchronization control method that shortens the time required to determine synchronization and loss of synchronization, and can reliably determine synchronization establishment and loss of synchronization even in poor line conditions.

(Means for solving the problem) In the ATM transmission system, on the transmitting side, a cell consisting of a header section including a destination address and a data section into which transmission information is inserted, and an empty cell that does not contain transmission information are successively separated. At the same time, a frame pattern is inserted into an empty cell at a predetermined interval, and cells are synchronized on the receiving side using the frame pattern extracted from the empty cell. Predetermined forward protection and backward protection are performed during cell synchronization.

FIG. 1 shows the basic structure of the present invention, in which on the receiving side of such an ATM transmission system, an address error detection section 1 and . A cell synchronization processing section 2 is provided.

The address error detection section 1 detects an error in the destination address included in the header section and generates an error rate signal.

The cell synchronization processing section 2 performs cell synchronization processing by changing the number of stages of forward protection and backward protection during cell synchronization according to the address error rate detected by the address error detection section 1.

[Effect]

In the present invention, in addition to a normal frame pattern search, the state in which an address error occurs in the header section is monitored, and the number of forward protection stages and the number of backward protection stages are changed depending on the magnitude of the address error rate. Here, the number of forward protection stages refers to the value of how many times a frame pattern must be found to determine that synchronization is out, and the number of backward protection stages refers to the value of how many times a frame pattern must be found to establish synchronization. ing.

As shown in FIG. 4(b), an ATM cell is divided into two parts: a header part and a data part. A destination address called VCI or VPI is written in the header part. This address includes bits for error checking, so it can be used to measure the error rate of the line.

From the error rate obtained in this way, the number of forward protection stages and the number of backward protection stages are determined using a statistical method, and the establishment of synchronization and the synchronization loss are determined based on the number of forward protection stages and the number of backward protection stages found, and synchronization control information and synchronization Outputs the signal.

〔Example〕

In order to implement the method of the present invention, a circuit for inserting a fixed format frame pattern into empty cells is used on the transmitting side.

FIG. 2 shows an embodiment of the present invention, and shows the circuit configuration on the receiving side.

The reception termination circuit 11 terminates the line and provides an interface between the line signal and the parts subsequent to the cell synchronization processing section 12. The cell synchronization processing section 12 performs operations for establishing and losing cell synchronization, and passes signals to the header conversion processing section 13. The header conversion processing unit l3 performs processing such as header conversion, extracts received data, and outputs it to the next stage.

The transmission signal from the line undergoes processing such as serial-to-parallel conversion in the reception termination circuit 11, and is input to the cell synchronization processing section 12. The cell synchronization processing unit 12 has a synchronization protection circuit, and determines whether cell synchronization is established or out of cell synchronization according to the predetermined number of forward protection stages and the number of backward protection stages.
When synchronization is established, the cell is passed to the one-ferder conversion processing unit l3. The header conversion processing section 13 performs header conversion processing, and at this time also performs an error check on the destination address, measures the error rate, and outputs the value to the cell synchronization processing section 12.

In the cell synchronization processing section 12, by receiving the error rate value as feedback from the header conversion processing section 13,
Based on a calculation formula given in advance according to the value, the protection circuit changes the number of forward protection stages and the number of backward protection stages to values that are optimal for the state of the line. Establishment of synchronization and loss of synchronization are then determined based on the determined number of forward protection stages and the determined number of backward protection stages. Note that at this time, synchronization control information and synchronization signals are output.

(Effects of the Invention) As described above, according to the present invention, frame patterns can be transmitted using only empty cells in the ATM transmission system, so that line usage efficiency can be improved.

In addition, the number of forward protection stages and backward protection stages during cell synchronization is changed according to the address error rate, so when the line condition is good, the time for synchronization establishment and synchronization loss processing is shortened, and even when the line condition is bad, synchronization can be performed. It becomes possible to reliably determine establishment and out-of-synchronization.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the first principle of the present invention, Fig. 2 is a diagram showing the structure of an embodiment of the present invention, Fig. 3 is a diagram showing line information in the ATM transmission system, and Fig. 4 (a ), (b) are ATMs
It is a diagram showing the configuration of a cell. 2 is an address error detection section, and 2 is a cell synchronization processing section.

Claims (1)

[Claims] On the transmitting side, a cell consisting of a header section including a destination address and a data section into which transmission information is inserted, and an empty cell that does not include transmission information are continuously transmitted, and the empty cell is sent out at a predetermined interval. In an ATM transmission system that inserts a frame pattern into a cell and synchronizes the cell by performing predetermined forward protection and backward protection using the frame pattern on the receiving side, an address error detection section (1) that detects an address error in the header section is used. ), and a cell synchronization processing unit (2) that performs cell synchronization processing by changing the number of forward protection and backward protection stages according to the address error rate.