JPH04329727A - Inter-equipment frame synchronization system - Google Patents

Abstract

PURPOSE:To prevent out of synchronism from giving effect onto a data receiver by sending a reception relay data including a pseudo frame synchronization pattern to the data receiver for a frame period when the out of frame synchronism is detected. CONSTITUTION:When a frame synchronization pattern is not detected in a signal data-in from a pre-stage device when a data relay transmitter and a post-stage device are in frame synchronization state, a pseudo frame signal transmission circuit 8 is started by a frame out of synchronism signal from a synchronization control circuit 3, a pseudo frame synchronization pattern is sent to an insert circuit 7 and a reception data including the pseudo frame synchronization pattern is sent as a data-out to the post-stage device. Thus, out of frame synchronism in the pre-stage data relay transmitter does not immediately give effect on the post-stage data relay transmitter or the data receiver and the post-stage data relay transmitter or the data receiver can easily recognize whether or not the pre-stage data relay transmitter is in the frame synchronization state.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to inter-device frame synchronization when data is transmitted in a frame format from a preceding data relay transmission device to a subsequent data relay transmission device or a data receiving device via a digital transmission path. In particular, inter-device frame synchronization methods that prevent frame synchronization in a preceding data relay device from being immediately affected by frame synchronization in a subsequent data relay transmission device or data receiving device; The present invention relates to an inter-device frame synchronization method that improves frame synchronization recovery characteristics in a data relay transmission device or a data reception device.

0002

[Prior Art] Generally, when data is transmitted and received in a frame format between devices via a digital transmission path, the data receiving side detects a frame synchronization pattern in the received data, thereby knowing the frame start position. The received data can only be meaningfully processed if the beginning position of the frame is known. To detect the beginning position of the frame,
Generally, a frame synchronization state is established for the first time when a frame synchronization pattern is detected continuously at a frame period equal to the number of backward protection stages set in consideration of the transmission quality in the middle of the transmission path. When a frame synchronization pattern is not detected continuously for the number of forward protection stages, it is assumed that the frame synchronization has been lost for the first time, and a frame synchronization pattern is searched for in order to return to the frame synchronization state (hunting state).

By the way, for a data transmission system in which one or more data relay transmission devices are serially interposed between a data transmission device as a data transmission source and a data reception device as a data reception destination, the frame synchronization method described above is useful. If the method is applied as is, frame synchronization loss in the preceding data relay transmission device will have a chain reaction effect on the subsequent data relay transmission device and data receiving device, and the overall data transmission system will suffer. It takes a lot of time to recover frame synchronization.

[0004] Regarding this type of technology, for example, Japanese Patent Laid-Open No. 2-67835 (Pseudo frame signal transmission system of digital wireless system) can be mentioned. In this case, when frame synchronization is detected, pseudo frame data is synchronized with the received signal and sent to the subsequent wireless device, while the subsequent wireless device transmits the pseudo frame data. By receiving this signal, frame synchronization is prevented from shifting to an out-of-frame state.

[0005]

[Problem to be Solved by the Invention] However, in the conventional technology, when frame synchronization occurs, pseudo frame data is sent to the subsequent device, causing the frame synchronization of the subsequent device to be lost. However, if the frame synchronization pattern in the pseudo frame data is the same as the regular one, the subsequent device indicates that the previous device is in the frame synchronization state. It is impossible to know whether it is true or not.

[0006] A first object of the present invention is that when data is transmitted in a frame format from a preceding data relay transmission device to a subsequent data relay transmission device or a data receiving device via a digital transmission path, the preceding data Frame synchronization in the relay transmission device is immediately transmitted to the subsequent data relay transmission device,
Or inter-device frame synchronization that does not affect the data receiving device and allows the subsequent data relay transmission device or data receiving device to easily know whether or not the preceding data relay transmission device is in frame synchronization state. There is a method to provide. In addition to the first object, the second object of the present invention is to prevent a subsequent data relay transmission device or a data receiving device from being in a pseudo frame synchronization state due to frame synchronization loss in the preceding data relay transmission device. An object of the present invention is to provide an inter-device frame synchronization method that can quickly shift to a normal frame synchronization state after a previous data relay transmission device recovers from frame synchronization.

[0007]

[Means for Solving the Problems] The first object is to synchronize frames at the frame synchronization pattern transmission timing in the frame synchronization state when frame synchronization is detected in the preceding data relay transmission device. The received relay data, which includes a pseudo frame synchronization pattern with a different bit pattern, is transmitted to the downstream data relay transmission device or data receiving device at frame intervals, while the downstream data relay transmission device or data receiving device uses the pseudo frame synchronization pattern. This is achieved by maintaining at least a pseudo frame synchronization state while the frame synchronization pattern is continuously detected.

[0008] The second purpose is to determine the frame synchronization pattern transmission timing in the frame synchronization state when frame synchronization is detected in the preceding data relay transmission device, and to determine whether the bit pattern is different from the frame synchronization pattern. While transmitting received relay data including different pseudo frame synchronization patterns to a downstream data relay transmission device or a data receiving device at frame intervals, a downstream data relay transmission device,
Alternatively, while the data receiving device maintains at least the frame synchronization state while the pseudo frame synchronization pattern is continuously detected, if the preceding data relay transmission device returns to the frame synchronization state, the received relay data is sequentially stored at least temporarily with a length slightly larger than one frame length, and when the temporarily stored received relay data including the frame synchronization pattern is transmitted to a subsequent data relay transmission device or data receiving device. This is achieved by transmitting the frame synchronization pattern with its transmission timing matched with the pseudo frame synchronization pattern transmission timing.

[0009]

[Operation] When frame synchronization is detected in the preceding data relay transmission device, a pseudo frame synchronization pattern with a bit pattern different from the frame synchronization pattern is included at the frame synchronization pattern transmission timing in the frame synchronization state. The received relay data is sent to the downstream data relay transmission device,
Alternatively, when data is transmitted to a data receiving device at frame intervals, the data receiving device not only knows that the subsequent data relay transmitting device or the preceding data relay transmitting device is out of frame synchronization, but also uses pseudo frame synchronization patterns. At least a pseudo frame synchronization state can be maintained while the frame synchronization is continuously detected. Also,
When the preceding data relay transmission device returns to the frame synchronization state from the frame out-of-frame state, when transmitting received relay data containing a normal frame synchronization pattern to the subsequent data relay transmission device or data receiving device, When the normal frame synchronization pattern is transmitted with its transmission timing matched with the previous pseudo frame synchronization pattern transmission timing, the subsequent data relay transmission device or data reception device in the pseudo frame synchronization state Since a regular frame synchronization pattern can be immediately detected at the same phase in place of the previous pseudo frame synchronization pattern, it is possible to return from the pseudo frame synchronization state to the regular frame synchronization state.

0010

[Example] The present invention will be explained below with reference to FIG. FIG. 1 shows the main circuit configuration of a data relay transmission device according to the present invention. For convenience of explanation, it is assumed that the data relay transmission device performs backward protection and forward protection, and its operation will be described as follows.

That is, assuming that the data relay transmission device and the subsequent device are in an initial state or a state out of frame synchronization, under the control of the synchronization control circuit 3,
Frame format data from the previous device
-in, the synchronization detection circuit 1 monitors/searches for a frame synchronization pattern, thereby establishing a frame synchronization state from an out-of-frame state through a backward protection state. Once a frame synchronization pattern is detected from the frame format data data-in, it enters the backward protection state, and if the frame synchronization pattern is detected continuously for the number of backward protection stages in the frame period in this backward protection state, , it is considered that the frame synchronization state has been established. In this frame synchronization state, the synchronization control circuit 3 outputs a frame synchronization state signal as a transition state signal, and based on this, the timing circuit 4 generates various timing signals including frame pulses.
On the other hand, the frame control circuit 3 controls the selector 10 to selectively output received data from the preceding device via the read/write timing circuit 6. Received data from the previous device is sent to the delay circuit 5.
After being delayed for a predetermined time, the data is passed through the insertion circuit 7 as it is, and is selectively output from the selector 10 as frame format data data-out to a subsequent device. This frame format data dat
Based on a-out, a frame synchronization state is similarly established in the downstream device.

Now, while the data relay transmission device and the subsequent device are in frame synchronization, for some reason the frame format data da from the preceding device is
Once the frame synchronization pattern is no longer detected from ta-in, the transition state shifts to the forward protection state, and if the frame synchronization pattern is not detected continuously for the number of forward protection stages in this forward protection state, the transition state is This is the first time that the frame is out of synchronization. In this state of frame synchronization, the synchronization control circuit 3
The pseudo frame signal sending circuit 8 is activated by the frame synchronization loss signal from the frame synchronization signal, and a pseudo frame synchronization pattern is sent to the insertion circuit 7. By inserting this pseudo frame synchronization pattern into the frame synchronization pattern position in the previous frame synchronization state, received data including the pseudo frame synchronization pattern is sent to the downstream device as frame format data data-out. It is something. The downstream device monitors/searches for the pseudo frame sync pattern at the same time as the frame sync pattern, but if a new pseudo frame sync pattern is detected in place of the previous frame sync pattern, the previous device As soon as it is known that the device in frame is out of frame synchronization, the transition state is placed in the forward protection state. If a frame synchronization pattern is not detected continuously for the number of forward protection stages in this forward protection state, the subsequent device is also put into an out-of-frame state in principle, but if a pseudo frame synchronization pattern from the previous device is detected, As long as the frames are continuously detected in the frame period, a search for a frame synchronization pattern toward a frame synchronization state is not performed. That is,
As long as the pseudo frame synchronization pattern is continuously detected, the subsequent device is placed in a pseudo frame synchronization state.

As described above, when the data relay transmission device eventually transitions from the frame out-of-frame state to the frame-synchronized state via the backward protection state while the pseudo frame synchronization state is maintained in the downstream device ( If frame synchronization recovery) is assumed, the received data in the frame synchronization state from the delay circuit 5 is controlled by the read/write timing circuit 6 and stored in a storage circuit (specifically, configured from an elastic memory, etc.). The storage capacity is set to be slightly larger than one frame.9). The storage circuit 9 is provided to absorb and match the difference in frame phase between the front and rear devices of this data relay transmission device.
In parallel with the storage of the received data into the storage circuit 9, the received data is read out from the storage circuit 9. When transitioning to the frame synchronization state, the sending of the pseudo frame synchronization pattern from the pseudo frame signal sending circuit 8 is stopped,
Transmission of the received data to the downstream device via the insertion circuit 7 is stopped, and instead, the received data read from the storage circuit 9 is transmitted to the downstream device via the selector 10; At this time, if the received data is read out from the memory circuit 9 so that a frame synchronization pattern is newly located at the position of the previous pseudo frame synchronization pattern, the subsequent device will immediately perform frame synchronization in place of the previous pseudo frame synchronization pattern. It is possible to detect patterns. The subsequent device detects the frame synchronization pattern and learns that the previous device has returned to frame synchronization, and at the same time, the state transitions from the pseudo frame synchronization state to the original frame synchronization state.

[0014]

As explained above, in the case according to claim 1, frame synchronization in the preceding data relay transmission device does not immediately affect the subsequent data relay transmission device or the data receiving device, and furthermore, The data relay transmission device or the data reception device can easily know whether or not the data relay transmission device is in the frame synchronization state. If the subsequent data relay transmission device or data receiving device is in a pseudo frame synchronization state due to frame synchronization loss, the frame synchronization state is immediately shifted to the normal frame synchronization state after the previous data relay transmission device recovers frame synchronization. It's something you can get.

The pseudo frame pattern detection circuit 2 shown in the figure is provided to detect a pseudo frame synchronization pattern from a preceding device. In the end, there is one
When the above-mentioned data relay transmission devices are interposed in a serial manner, the present invention can be applied to each data relay transmission device and its immediately subsequent device (including the data receiving device), thereby making it possible to apply the present invention to the entire system. The frame synchronization recovery characteristics can be considerably improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main circuit configuration of a data relay transmission device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Synchronization detection circuit, 2... Pseudo frame pattern detection circuit, 3... Synchronization control circuit, 4... Timing circuit, 5... Delay circuit, 6... Read/write timing circuit, 7... Insertion circuit, 8... Pseudo frame signal sending circuit , 9...Memory circuit, 10
…selector

Claims (2)

[Claims] Claim 1. An inter-device frame synchronization method when data is transmitted from a preceding data relay transmission device to a subsequent data relay transmission device or a data receiving device in a frame format via a digital transmission path, the method comprising: If a frame synchronization loss is detected in the data relay transmission device, the received relay data containing a pseudo frame synchronization pattern with a bit pattern different from the frame synchronization pattern is transmitted at the frame synchronization pattern transmission timing in the frame synchronization state. While transmitting to a subsequent data relay transmission device or data receiving device at frame intervals, the subsequent data relay transmission device or data receiving device is at least in a frame synchronization state while a pseudo frame synchronization pattern is continuously detected. An inter-device frame synchronization method that maintains Claim 2: When data is transmitted in frame format from a preceding data relay transmission device to a subsequent data relay transmission device or data receiving device via a digital transmission path, frame synchronization occurs in the preceding data relay transmission device. is detected, at the frame synchronization pattern transmission timing in the frame synchronization state, the received relay data containing a pseudo frame synchronization pattern whose bit pattern is different from the frame synchronization pattern is transmitted to the subsequent data relay transmission device or the data reception device. An inter-device frame that is transmitted to a device at frame intervals, while maintaining at least a frame synchronization state while a pseudo frame synchronization pattern is continuously detected in the subsequent data relay transmission device or data reception device. In the synchronous method, when the previous data relay transmission device returns to the frame synchronization state, from the point of return, the received relay data is sequentially stored at least temporarily with a length slightly larger than one frame length. When temporarily stored received relay data including a frame synchronization pattern is transmitted to a subsequent data relay transmission device or a data reception device, the transmission timing of the frame synchronization pattern matches the pseudo frame synchronization pattern transmission timing. An inter-device frame synchronization method in which the frame synchronization pattern is transmitted in place of the pseudo frame synchronization pattern.