JPH01136439A - Frame synchronizing system - Google Patents

Abstract

PURPOSE:To establish the synchronization in the ATDM system without fail by not changing the position of synchronization detection when number of times of synchronization pattern dissidence is a preset value or below. CONSTITUTION:When information to be sent does not exist, a synchronizing cell F is always sent and when the information to be sent exists, the information is split into small fixed length to form general information part D and at least an address part A is added and sent while being incorporated into the cell. When the synchronizing pattern detection position signal is inputted, it is collated with the synchronizing pattern and when they are coincident, the number of counted dissidence is reset to zero to hold the synchronizing pattern detection position. In case of dissidence, the number of dissidence is carried up by one and it is compared with a preset value. When the count is below the set value, the synchronizing detection position is kept and when the count is more than the set value, the synchronizing detection position is changed to other position. Thus, the synchronization of cell is established.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is an asynchronous method in which address bits, etc. are added to subdivided information, and the resulting information is placed in unused fixed length cells and multiplexed and transmitted as information transmission cells. Time division multiplexing (Asynchronous
ous Time Division Multipl
In the exing (hereinafter abbreviated as ATDM) system,
The present invention relates to a frame synchronization method for synchronizing transmitted cells, and more specifically, to a frame synchronization method characterized by a hunting method in the synchronization method.

[Conventional technology]

Conventionally, synchronous time division multiplexing (Synchronous Ti
me Division Multiplexing
In the frame synchronization method (hereinafter abbreviated as STDM), a frame synchronization bit is always inserted at a certain position in a frame, so the frame synchronization bit periodically arrives at the receiving side. Therefore, in the conventional hunting method in the frame synchronization circuit, the bit at the synchronization pattern detection timing position is checked against the synchronization pattern every cycle, and if they match, the synchronization pattern detection position is held; The synchronization pattern detection position is immediately changed to another position and a hunting operation for detecting the synchronization pattern is performed.

On the other hand, in the ATDM system, the insertion position of the synchronization bit is a fixed position within one cycle (in the STDM system, it refers to one frame, and in the ATDM system, it refers to one cell), but the synchronization bit is only specified to be inserted within a certain maximum interval (the unit is a cell), and is not necessarily inserted at double cycles as in the STDM system (Figure 2 shows information transmission in the ATDM system). This is an explanatory diagram showing an example of a multiplexing format of a synchronization cell I and a synchronization cell F, and this will also be recognized in the same diagram).

[Problem to be solved by the invention] Therefore, the conventional hunting method that detects a synchronization pattern at one location within one cycle assumes that a synchronization bit is always inserted at a true synchronization position. Therefore, there is a drawback that when a synchronization pattern mismatch is detected at a true synchronization position where no ATDM synchronization bit is inserted, the synchronization pattern detection position moves immediately, and cell synchronization may not be established.

The object of the present invention is to solve the drawbacks of such prior art and to
Provides a frame synchronization method that enables cell synchronization to be established without immediately moving the synchronization pattern detection position even if a synchronization pattern mismatch is detected at the true synchronization position where no DM synchronization bit is inserted. It's about doing.

[Means for solving problems]

In order to achieve the above object, in the present invention, even if a synchronization pattern mismatch is detected, the synchronization pattern detection position is not moved immediately.

[Effect]

In the present invention, even if a synchronization pattern is not detected at the synchronization pattern detection position during hunting, the synchronization pattern detection position is not immediately changed, but the synchronization cells as the synchronization pattern are set to a certain preset number of cells. If the synchronization pattern detection position is exceeded and not detected, the synchronization pattern detection position is changed to another position.

〔Example〕

The present invention will now be described in detail with reference to the drawings.

FIG. 2 is an explanatory diagram showing an example of a multiplex format of an information transmission cell I and a synchronization cell F in the ATDM system. As seen in the figure, when there is no information to be transmitted, the synchronization cell F is always transmitted, and when there is information to be transmitted, the information is subdivided into fixed lengths and divided into general information parts. After that, at least address part A is added thereto, and the data is assembled into a cell (information transmission cell I) and transmitted. The format is such that when a certain number of information transmission cells (2) are successively transmitted, a synchronization cell (F) is forcibly transmitted next.

FIG. 1 is a chart showing an operation algorithm of a hunting method according to an embodiment of the present invention, and the parts within the dotted line frame are different from the conventional hunting method.

In the hunting method according to the present invention, when a signal of a synchronization pattern detection position is input, it is checked against the synchronization pattern, and if they match, the number of mismatches counted up to that point is reset to zero, and the synchronization pattern detection position is held. . If there is a mismatch, the number of mismatches is incremented by 1 and compared with a preset value. If the count value is less than the set value, the synchronization detection position is held, and if the count value is greater than or equal to the set value, the synchronization detection position is changed to another position.

Because of this algorithm, in the hunting method according to the present invention, even if a mismatch of synchronization patterns is detected at the synchronization detection position, if the number of consecutive mismatches is less than a certain set value, the synchronization detection position will not be changed. Cell synchronization can be established by using the hunting method according to the present invention in an ATDM system in which the bit position is a fixed position within one cycle, but a synchronization bit is not necessarily inserted in the double cycle.

As an example of the setting value used for comparison with the unmatched count value,
There is a maximum interval for synchronization cell insertion (see FIG. 2 for the synchronization cell insertion interval). Unless a bit error occurs in the transmission path, synchronization cells should always be inserted within the maximum insertion interval, so if synchronization cells are not detected within the maximum insertion interval, that is, pattern mismatch detection If the number of times exceeds the set value, it becomes clear that the synchronization detection position at that time is not the true synchronization position, and at this point the synchronization detection position is changed to another position.

〔Effect of the invention〕

As described above, according to the present invention, since the synchronization detection position is not changed when the number of synchronization pattern mismatches is less than a certain set value, there is an advantage that cell synchronization can always be established in the ATDM system.

[Brief explanation of the drawing]

FIG. 1 is a chart showing a hunting operation algorithm in an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing an example of a format for multiplexing information transmission cells and synchronization cells in the ATDM system. Explanation of symbols A...Address part, D...General information part, F...
・Synchronization cell,■...Information transmission cell agent Patent attorney Akio Namiki Patent attorney Kiyoshi Matsuzaki figure

Claims (1)

[Claims] 1) When there is information to be transmitted, the information is divided into small pieces, address bits are added, and fixed-length information transfer units (hereinafter referred to as cells) are assembled, and then multiplexed and transmitted. In a transmission method in which a synchronization cell carrying a specific bit string for establishing cell synchronization is created and transmitted when there is no relevant information, or when a certain number of cells carrying information have been transmitted, During a hunting operation in which a synchronization cell is detected from among transmitted cells in order to establish cell synchronization, a synchronization cell, which is a synchronization pattern, is detected in advance at a predetermined timing position where a synchronization pattern should be detected. A frame characterized in that when a set number of cells are not detected, the timing position where a synchronization pattern should originally be detected is changed to another position, and a hunting operation is performed again to detect cells for synchronization. Synchronous method.