JPH0654917B2 - Loop transmission system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a loop transmission system in a loop transmission system used for local communication.

2. Description of the Related Art FIG. 3 shows a configuration example of a loop transmission system to which a conventional loop transmission method is applied. In FIG. 3, reference numeral 6 denotes a master station that generates a synchronous clock for a frame that circulates on the transmission line 10 for a fixed time, and 7 indicates a master station when the synchronous clock generating function of the master station 6 does not operate normally. It is a sub-master station that generates a frame synchronization clock instead of 6. 3 to 5 are remote stations,
A terminal device for packet switching or a terminal device for circuit switching is connected to these remote stations to transmit data by bucket switching or circuit switching.

The frame transmission / reception in the remote station is performed in synchronization with the synchronization clock generated in the master station 6 or the sub master station 7. At the remote station, the data is stored in fixed-length slots existing in the frame circulating on the transmission path, and after writing various information in the frame header, it is transmitted together with the switching signal for packet switching and circuit switching. It is sent out on the road and captured by the destination remote station.

FIG. 4 shows a block diagram of a conventional remote station.
In FIG. 4, reference numeral 21 is a receiving unit for taking in signals on the transmission line 10, and 22 is a transmitting unit for sending out signals on the transmission line 11. 23 distributes the signal on the transmission path taken in by the receiving section to the slot for packet switching and the slot for circuit switching, and sends each to the packet switching section 24 or the circuit switching section 25, and vice versa. This is a TDMA unit that combines the signals from the line switching unit 25 into a series of slots and sends them to the transmitting unit 22 together with their switching signals.
The packet switching unit 24 interfaces with a terminal device for packet switching. The circuit switching unit 25 interfaces with a terminal device for circuit switching.

Problems to be Solved by the Invention In the conventional loop transmission system configured as described above, when the synchronization clock of the frame generated in the master station 6 of FIG. Although the frame synchronization clock is generated, if out-of-sync occurs in this case as well, the cyclic frames cannot be synchronized at each remote station, making it impossible to perform circuit switching as well as packet switching. All communication of will stop.

It is an object of the present invention to provide a loop transmission method capable of preventing a complete communication stoppage of the transmission system.

A means for solving the problem By connecting a center station that manages and controls the frames that circulate on the transmission path at regular intervals and a terminal device that performs packet switching or circuit switching, to a common transmission path configured in a loop. Forming a loop transmission system with multiple remote stations that perform data transmission as components,
When a frame composed of a frame header and a plurality of fixed-length slots circulates through the loop-shaped transmission line for data transmission together with a switching control signal for packet switching and circuit switching, the remote station is set to the center station. It is equipped with both a synchronizing means for transmitting and receiving a cyclic frame in synchronization with the synchronous station, and an asynchronous means for controlling to perform only packet exchange without synchronizing with the center station when detecting the out-of-sync of the cyclic frame. A loop transmission method characterized in that data transmission is performed using a synchronization means, and when out-of-synchronization of a cyclic frame occurs, switching to the asynchronous means prevents a complete communication stop of the loop transmission system.

With the above-described structure, the present invention controls each remote station existing on the loop transmission system to perform packet exchange asynchronously with the center station when out-of-sync of the cyclic frame is detected, and loop transmission is performed. Prevents overall system outage.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows a loop transmission system to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a center station that manages and controls a frame that circulates on a transmission path at a constant cycle by generating a synchronous clock. 2 to 5 are remote stations for data transmission / reception arranged on the loop-shaped transmission line 10. A packet switching terminal device and a circuit switching terminal device are connected to each remote station, and packet switching and circuit switching are performed via these remote stations. At the remote station, the data is stored in slots that are divided into fixed lengths that exist in the frame that is circulating on the transmission path, and after writing various information in the frame header, along with a switching signal for packet switching and circuit switching. It is sent out on the transmission line and taken in by the destination remote station.

A block diagram of the remote station is shown in FIG. In FIG. 2, reference numeral 21 is a receiving unit that takes in signals on the transmission line 10, and 22 is a transmitting unit that sends out signals on the transmission line 11. 23 distributes the signal on the transmission path taken in by the receiving section to the slot for packet switching and the slot for circuit switching,
Each is a packet switching unit 24 or a circuit switching unit 25.
Is a TDMA unit that sends signals to and from the packet switching unit 24 and the line switching unit 25, and conversely synthesizes them as a series of slots and outputs them together with their switching signals. The packet switching unit 24 interfaces with a terminal device for packet switching. The circuit switching unit 25 interfaces with a terminal device for circuit switching. Reference numeral 26 denotes an out-of-synchronization detection controller which detects out-of-frame synchronization of the signal received by the receiving unit 21 and sends a control signal to the multiplexer 27. The multiplexer 27 is the out-of-sync detection controller 2
Controlled by the switch 6, the signal to be input to the packet switching unit 24 is switched.

The operation of the present embodiment configured as described above will be described below. In FIG. 1, it is assumed that the frame synchronization clock generated by the center station 1 has lost synchronization. In this case, in each remote station having the configuration as shown in FIG. 2, the circuit switching slots in the TDMA unit 23 cannot be synchronized, and circuit switching on the loop transmission system becomes impossible. However, this out-of-frame synchronization is detected by the out-of-sync detection controller 26 of FIG. 2, and the input to the packet switching unit 24 is TDMA.
The multiplexer 27 is controlled so as to bypass the unit 23 and be directly connected to the receiving unit 21. That is, when the frame synchronization loss occurs, the signal received by the reception unit 21 of each remote station is controlled to be transmitted to the packet switching unit 24 as it is. At this time, the packet switching unit 24 extracts a data area for packet switching from the received signal based on the packet switching and circuit switching switching signals, and interfaces with the packet switching terminal device. Further, the output signal from the packet switching terminal device is transmitted to the TDMA unit 2
It is sent to the transmission unit 22 together with the packet switching and circuit switching switching signal created in 3, and sent out on the transmission line 11.
In the normal state, the frame is transmitted and received in synchronization with the center station without avoiding the TDMA unit.

As described above, according to the present embodiment, the frame out-of-sync detection controller is provided, and when the out-of-sync is detected, the signal received from the transmission line is transmitted to the packet switching section as it is without passing through the TDMA section, so that it is asynchronous with the center station. It is possible to enable packet switching in the loop transmission system and prevent a complete stoppage of communication in the transmission system.

Advantageous Effects of Invention As described above, according to the present invention, even if the frame synchronization is lost due to the failure of the center station, the communication between the packet switching terminal devices existing in the loop transmission system is possible, Since the worst case of the total stoppage of communication can be escaped, its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a loop transmission system according to an embodiment of the present invention, FIG. 2 is a block diagram of a remote station in the system, FIG. 3 is a block diagram of a conventional loop transmission system, and FIG. It is a block diagram of an example remote station. 1 ... Center station, 2-5 ... Remote station, 6 ... Master station, 7 ... Sub-master station, 10-11 ... Transmission line, 21 ...
Reception unit, 22 ... Transmission unit, 23 ... TDMA unit, 24 ...
... packet switching unit, 25 ... line switching unit, 26 ... out-of-sync detection controller, 27 ... multiplexer.

Claims (1)

[Claims] 1. A data transmission is performed by connecting a center station, which manages and controls frames circulating on a transmission path at a fixed cycle, and a terminal device, which performs packet switching or circuit switching, to a common transmission path configured in a loop. A loop transmission system is formed by using a plurality of remote stations as constituent elements, and a frame composed of a frame header and a plurality of fixed-length slots, together with a switching control signal for packet switching and circuit switching, is used for the loop transmission line. When performing data transmission by circulating the
It has both a synchronization means for transmitting and receiving a cyclic frame in synchronization with the center station and an asynchronous means for controlling to perform only packet exchange without synchronization with the center station when the out-of-sync of the cyclic frame is detected. Loop transmission characterized by performing data transmission using the synchronizing means at the time, and switching to the asynchronous means when out-of-synchronization of the cyclic frame occurs, thereby preventing complete communication stop of the loop transmission system. system.