# Communication Fault Maintenance Decision of Information System Based on Inverse Symmetry Algorithm
## 2 Definition of Algorithm
### Failure Maintenance Decision
#### 2.4.2 Medium Problem  
Communication media can be a twisted pair cable, coaxial cable, optical fiber, infrared, and laser media, usually twisted pair and optical fiber. For the twisted pair cable, the key troubleshooting factors for communication failure are as follows:  
1. Polarity: It is necessary to ensure that the transmission, reception, and other signals of the media signal are connected one by one. Especially for the bus powered information system, the signal also has polarity, and reverse wiring will lead to communication interruption after the signal is reversed.
2. Shielding: The communication network cable screen layer shall be reliably grounded, and the grounding resistance shall be less than 10 N. Especially for systems with different bus equipment grounding points, the cable laying must be single ended grounded [20; 21]. It is recommendedto connect multiple cables in the sequence of \"shield out--shield person--shield out--shield person\" when bridging at nodes.
* Grounding: Grounding the signal line of communication medium anywhere will lead to communication failure of the information system. For places with intrinsic safety requirements, the cable shield shall be grounded outside the explosion-proof area and connected to the neutral point of a safety barrier [20; 21; 22; 23]. The grounding of the information system shall be separated from the protection grounding of the device, transmission system grounding, and power system grounding.
* Quality: The cable signal core of each network section shall not be short circuited or open circuited. Short circuit will lead to the interruption of all communication, and open circuits can cause most communication failures. At the same time, the cable impedance shall be generally less than 0.16 \(\Omega\)/m. Each signal line of the cable shall be well insulated, and the insulation resistance between them shall be greater than 200 k\(\Omega\). For important occasions, it is necessary to test the characteristic impedance (recommended: 100 kHz), electrostatic capacity (recommended: 1 kHz), withstand voltage (DC200 V), and other parameters of the cable.
* Terminal resistance: As an impedance matching element, two terminal resistors are required in each network segment of the bus. The purpose of using the terminal resistor is to reduce the signal attenuation and deformation by applying the principle of signal transmitting wave. Therefore, at the head and tail nodes of each network segment, it is important to check whether the connected terminal resistance or the node connector terminal is at the \"on\" position, and at the same time, other nodes in the middle segment shall not have the terminal resistance or the node connector terminal is at the \"off\" position.
* Others: In the information system, the number of repeaters in a bus shall be less than four, and the distance of network transmission shall not exceed the maximum length allowed by the theory of the communication cable used. For the mixed use of various cables, it is necessary to ensure that: \[L_{1}/Max_{1}+L_{2}/Max_{2}+\cdots+L_{n}/Max_{n}<1\] (19)  
In Equation (19), \(L_{1}\), \(L_{2}\), and \(L_{n}\) are the actual lengths of 1, 2, and \(n\) segments of the communication cables used; \(Max_{1}\), \(Max_{2}\), and \(Max_{n}\) are the longest distances allowed by the theory of communication cables used in 1, 2, and \(n\) segments, respectively.  
For optical fiber and other media signals, the processing of communication fault is similar. Although it is simple and effective to judge the quality of optical fiber by means of a flashlight and other tools, it is not a substitute for special inspection. When troubleshooting, it is also important to check the minimum bending radius of the optical fiber and the quality of the optical joint. It is very important to test the quality of optical cable by using a signal attenuation tester.