JP2573560B2 - Frame synchronization method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frame synchronization system for transmitting digital information through a transmission line, and more particularly to obtaining a better synchronization characteristic even when the number of control bits is limited. This is related to the frame synchronization method used.

[Conventional technology]

2. Description of the Related Art Conventionally, as one type of transmission system for transmitting digital information, a digital transmission system having a fixed-length frame, synchronizing with a frame pattern, and transmitting signals having different transmission speeds by a staff control has been used. In this digital transmission system, control bits such as a frame pattern for synchronizing frames and a stuff control bit for transmitting stuff information are required in a frame for transmission control. These control bits and the frame synchronizing circuit on the receiving side need to determine the system so that transmission can be performed as stably as possible with respect to errors occurring in the transmission path and the like. That is, (a) frame synchronization is not unnecessarily deviated, (b) frame synchronization is not stopped, and (c) frame pattern bits are set so that synchronization recovery can be performed promptly. Determining the number, arrangement, synchronization protection circuit, etc.
(D) To make it difficult for destuff errors to occur, the staff control bits should have a redundant configuration.

[Problems to be solved by the invention]

In the above-described conventional frame synchronization method, when the method is determined, it is difficult to satisfy all the conditions because the requirements of each condition may conflict. In particular, good characteristics cannot be obtained when the number of control bits is limited given the transmission path and signal speed. In general, when there is only one type of frame pattern, if there is a signal or circuit in the device system that has a correlation with the frame synchronization in the system,
There is a risk of false synchronization. Therefore, a method of arranging a plurality of different frame patterns in one frame has been adopted. However, there is a problem (defect) that the number of required bits is increased.

[Means for solving the problem]

In the frame synchronization method according to the present invention, a plurality of frame patterns having frame synchronization information and staff control information are defined, and one of the frame patterns is transmitted on the transmission side in accordance with the status of the staff control for each frame. Thus, the frame synchronization information and the staff control information are transmitted synchronously, and the reception side detects any one of the plurality of frame patterns to detect the frame pattern. The control state is determined and the staff information is obtained to perform the destuff control.

[Action]

In the present invention, since the frame pattern changes according to the characteristics of the staff information, a better synchronization characteristic can be obtained even when the number of control bits is limited. In addition, even when the staff information deviates from a certain range defined by the method, it is determined that the synchronization has been lost, and the frame synchronization circuit can be operated.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the frame synchronization system according to the present invention, and is a diagram showing a receiving side circuit of a transmission apparatus for transmitting one digital signal by a staff control. In the figure, reference numeral 1 denotes an input terminal to which a received transmission path signal is input, 2 denotes a first frame pattern detection circuit for detecting a first frame pattern ABCDE indicating presence of a staff pulse, and outputting a first frame pattern signal; Is a second frame pattern detection circuit for detecting a second frame pattern abcde indicating no stuffing pulse and outputting a second frame pattern signal. Is determined and the staff control signal 5 is output. On the other hand, the ratio of detecting the presence / absence of the staff pulse is within a certain range in a normal state. And a staff control judging circuit including a redundancy judging circuit for outputting an out-of-synchronization detection signal 6; An adder circuit comprising an OR gate for outputting a synchronization detection signal 8; a frame synchronization circuit 9 for performing control such as synchronization recovery and synchronization protection by inputting the out-of-synchronization detection signal 6 and the frame pattern detection signal 8; This is a control output circuit that outputs various control signals from terminals 11a to 11n.

The frame pattern abcde indicating the absence of the stuff pulse is the frame pattern A indicating the presence of the stuff pulse.
This is the opposite pattern from BCDE.

Next, the operation of the frame synchronization system having the above configuration will be described. First, the received transmission path signal is input to a first frame pattern detection circuit 2, a second frame pattern detection circuit 3, and a staff control determination circuit 4 via an input terminal 1. Accordingly, the first frame pattern detection circuit 2 detects the first frame pattern ABCDE and outputs a first frame pattern signal, and the second frame pattern detection circuit 3 detects the second frame pattern abcde, A frame pattern signal is output, and a staff control judging circuit 4 judges the bit of the frame pattern by using a majority decision method with or without a staff pulse, and outputs a staff control signal 5. That is, with regard to the staff control, the frame pattern is a 2-bit error correction code. Then, in a transmission system that performs staff control,
Since the rate of detection of the presence / absence of the staff pulse falls within a certain range in a normal state, the staff control judging circuit 4 outputs an out-of-synchronization detection signal 6 based on the normal / abnormality of this rate. On the other hand, the addition circuit 7 adds the first frame pattern signal and the second frame pattern signal to output a frame pattern detection signal 8. Accordingly, the frame synchronization circuit 9 outputs the out-of-sync detection signal 6
Based on this and the frame pattern detection signal 8, control such as synchronization recovery and synchronization protection is performed. In this case, the frame synchronization circuit 9 receives the out-of-synchronization detection signal 6, and
Since the frame pattern changes according to the characteristics of the staff control, the risk of erroneous synchronization can be reduced regardless of the small number of bits. The control output circuit 10 is provided with the staff control signal 5 and the frame synchronization circuit 9.
Receiving these output signals, various control signals can be output from the output terminals 11a to 11n.

〔The invention's effect〕

As described in detail above, according to the frame synchronization method of the present invention, the frame pattern and the staff control bits can be shared, so that a smaller number of control bits is required and the risk of erroneous synchronization is reduced. There are effects such as being able to do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the frame synchronization system according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... First frame pattern detection circuit, 3 ... Second frame pattern detection circuit, 4 ... Stuff control determination circuit, 5 ... Stuff control signal, 6 ... Out of synchronization detection signal, 7 ... Addition circuit, 8 frame pattern detection signal, 9 frame synchronization circuit, 10 control output circuits, 11a to 11n output terminals.

Claims (1)

(57) [Claims] A digital transmission system having fixed-length frames, synchronizing frames by frame patterns, and transmitting signals having different transmission speeds by stuff control, wherein a plurality of frame patterns are defined, and a stuff for each frame is defined. In a frame synchronization system for transmitting frame synchronization information and stuff control information simultaneously by transmitting one of a plurality of patterns corresponding to the control state, the frame synchronization information is received upon detection of any of the plurality of frame patterns. While the detected frame pattern is detected, the received frame pattern is determined to be in any one of the stuff control states, stuff information is obtained and destuff control is performed, and based on the detected and undetected state of the frame pattern. , The obtained staff information should be out of a certain range determined by the method Frame synchronization method according to claim also determine the synchronization loss when the.