JPH03104446A - Duplicate system for bus type network - Google Patents

Abstract

PURPOSE:To offer a bus type network duplicate system with high reliability without limit of degree of freedom and a change in a transmission control protocol by forming MODEMs and MAC(medium access control) layers in duplicate, connecting the MODEM to different 2 systems of transmission lines and connecting the transmission lines with a repeater. CONSTITUTION:Plural branching devices 13 are used for a main system transmission line 10 to connect MODEMs 11A, 11B, 11C with MAC layers 14A, 14B, 14C. On the other hand, plural branching devices 23 are used for a standby system transmission line 20 to connect MODEMs 21A, 21B, 21C with MAC layers 24A, 24B, 24C, and a resistor 22 with equal characteristic impedance to the impedance of the transmission line is used to terminate both ends of the standby system transmission line. When the MODEM 11A of a station 3A is failed, only the station 3A uses the MAC layer 24A and the MODEM 21A of the standby system to send and receive the data and the data transmission reception between the station 3A and other stations 3B, 3C are implemented via a repeater 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a redundant system for bus-type networks. [Conventional technology] Conventionally, LANs with bus-type structures using coaxial cables, such as CSMA/CD (IEEE 802.3) LANs and Tokoun Bus (IEEE 802.4) LANs, have existed for a long time. There is. These bus-type LANs, like the ring-type LANs that have been around for a long time in Japan, have the characteristic that even if the power to a node station is cut off, it does not affect the entire system. However, the disadvantage is that when the transmission line is cut or when adding stations, the entire system may go down or the system must be stopped. On the other hand, in a ring-type LAN, the transmission path is duplicated and the loop pack function is incorporated, so that even if a transmission path is disconnected at one point, the system will not go down. Therefore, even in bus-type networks, attempts have been made to make the transmission line and modem redundant so that the system can operate normally even if the transmission line is disconnected or the modem fails. Figure 2 shows a conventional duplex system in a bus-type LAN using coaxial cables. The modem 11^,
118.1 IC, modem 2 1A, 2 18.2
IC is connected and selector switch 4 A, 4 B, 4
C to each station 3^. 3B and 3C can be switched to the main transmission line 10 or the protection transmission line 20. 12.22 is a terminating resistor equal to the characteristic impedance of the transmission line. During normal operation, station 3 A
, 3 8. 3C, for example, 3^, passes through the main modem 11A and is sent to the main transmission line l.
0 to separate stations 3B and 3C, respectively. If a modem, for example IIA, fails, all stations' switches 4A, 4B,
4C are brought down to the dotted line LULL all at once, and data transmission is resumed via the backup transmission line 20. [Problems to be Solved by the Invention] However, this method has the following problems.

(1) Stations 3B to 3C other than 3A will switch the entire system to the standby system even if one modem fails.
Even if the modem is operating normally, it will be switched to a standby system whose operation is not guaranteed, which does not necessarily improve reliability. {2} If a modem or drop cable fails, it will not affect information transmission between other stations.
On the contrary, it is difficult for all stations to recognize this failure. If this recognition is not possible, switching to the backup system cannot be performed. To avoid this situation, special information must be transmitted to confirm the operating status of each station. (3) Even if a transmission method were adopted to solve problem (2) above, it would be difficult to distinguish between a station power outage and a modem failure. For this reason, the greatest advantage of the bus network, which is the ability to freely turn on and off power to stations, is somewhat limited.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a highly reliable bus-type network duplexing method that does not require changes to transmission control procedures or restrict degrees of freedom. [Means for Solving the Problems] The bus-type network redundancy system of the present invention is a bus-type network in which a transmission path is provided with a plurality of branch sections, stations are connected to each branch section, and data is transmitted to each other via the transmission path. In a network, the modem and MAC (medium access control) layer, which is the data input/output section of each station, are duplicated, each modem is connected to two different transmission lines, and the transmission lines are connected using a repeater. In the event of a minor failure, such as a failure of one modem, only the affected station was switched to a different transmission line, and data transmission between that station and other stations was performed via a repeater. It is something.

This bus type network can also be duplicated by duplicating part or all of the layer from the LLC (Theoretical Link System II) layer to the application layer. [f￥! Each station only has a modem and the MAC layer is redundant, so the standby system can also be monitored during normal operation. In the event of a minor local failure, such as a failure of one modem, only the station in question will have access to the modem and MAC.
It is switched to another system of transmission H via the layer. Therefore,
Data can be transmitted from the backup transmission line to the main transmission line via a repeater, or vice versa. Only the modem at the abnormal location is switched, and the pond stations are in the same state as when normal, so reliable data transmission is guaranteed as before the abnormality occurred.

[Example] Hereinafter, a specific example of the present invention will be described using FIG. 1. In FIG. 1, a plurality of branchers 13 are used in the main transmission line 10, and the MAC (medium access control) layer 1 4
A, 1 48.1 Modem 11A, 11B with 4C,
IIC is connected, and both ends of the main transmission line are terminated by a resistor 12 whose characteristic impedance is equal to the transmission line. On the other hand, the protection transmission line 20 similarly uses a plurality of branchers 23 to connect the MAC layers 2 4 A, 2 4 B, 2
A modem 2 LA, 2 18.2 IC with 4C is connected, and both ends of the protection transmission line are terminated by a resistor 22 having the same characteristic impedance as the transmission line.

Stations 3^ and 38.3C, which transmit and receive data, are connected to the main and backup MAC layers, and can operate both MAC layers and modems simultaneously. The main transmission line 10 and the protection transmission line 20 are connected by a repeater 5, so that data in the main system can be transmitted to the protection system, and data generated in the protection system can be transmitted to the main system. It has become. First, under normal conditions, each station is connected to the main MA
Data is sent and received using C114A to 14C and modems IIA to 11C. At the same time, the backup MAC layer 2
Modems 4A to 24C and modems 21A to 21C are made to perform only reception operations, and receive main system data transmitted to the backup system via repeater 5. By comparing the received data from the main and backup systems, both systems are monitored. If the main modem used is 11^, 118.1 IC
For example, if a failure occurs in the modem 11^ of station 3^ as shown by an Transmission and reception of data between the station 3A and other stations 38.3C is performed via the repeater 5. In addition, if the main transmission line 10 becomes an FT line, data transmission and reception on the main side will be impossible due to the reflection of the signal at the break point, so all stations will switch transmission to the backup system and transmit the backup system. Data is sent and received using a network. In this way, in the event of a partial failure, such as a modem failure at one station or an abnormality in the branch terminal of a branch switch, only the relevant station is switched to the standby system and data transmission and reception is performed in the same way as during normal operation. Since the other stations are in the same state as normal, it is possible to guarantee reliable data transmission as before the abnormality occurred. In the above embodiment, the MAC layer is duplicated, but part or all of the layer from the LLC (logical link control) layer to the application layer can also be duplicated.
It can be applied to both (IEEE 802.3) type LAN and Tokoun Bus (IEEE 802.4) type LAN. In particular, in the case of the token bus method, it is also possible to join the backup MAC layer and modem to the theoretical ring and exchange tokens. In the case of only receiving operations, the modem can only monitor the receiving section, but by exchanging tokens, it can also monitor the transmitting section. In addition, when the standby system also joins the logical ring in this way, the following two methods of switching in the event of a failure are possible. (1) Temporarily remove the protection system from the logical ring, change the MAC layer station address of the protection system to the address of the main system, rejoin the logical ring, and send and receive data. (2) The standby MAC layer station address is that. By t, the primary address is used only as the source address of the transmitted data frame. Communication system W for MAC layer of token bus
This method is possible because some LSIs allow the source address of the data frame to be set independently of the station address for token delivery. By adopting methods (1) and (2), stations with no faults can maintain the network without having to be conscious of moving to the standby system. [Effects of the Invention] According to the present invention, since the operation of the standby system can be constantly monitored,
The reliability of the entire network can be increased. Furthermore, when a certain failure occurs, the stations that need to be switched to the standby system are limited to those that are unable to communicate due to the failure, which has the advantage of minimizing the impact on the network.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a conventional duplex bus type network. In the figure, 3A, 3B, 3C are stations, 4
^, 48.4G is a switch, 5 is a repeater, 10 is a main transmission line, 11^, 11B, IIC is a main modem, 12 is a main transmission line terminating resistor, 13 is a main transmission line branch , l4 is the main MAC layer, 20 is the protection transmission line, 2 1A, 2 18
．． 2 IC is a protection modem, 22 is a protection transmission line termination resistor, 23 is a protection branch, and 24 is a protection MAC layer.

Claims (1)

[Scope of Claims] 1. A modem serving as a data input/output unit of each station in a bus-type network in which a transmission line has multiple branches, stations are connected to each branch, and data is transmitted to each other via the transmission line. The MAC (medium access control) layer is duplicated, each modem is connected to two different transmission lines, and the transmission lines are connected using a repeater to prevent minor failures such as a failure of one modem. This is a bus-type network redundancy system characterized by switching only the relevant station to a different transmission path, and transmitting data between the relevant station and other stations via a repeater. 2. The duplex bus network system according to claim 1, wherein a part or all of the layer from the LLC (theoretical link control) layer to the application layer is duplexed.