Wiring fault diagnosis
11.1 Common wiring construction failure modes
There are many kinds of network cable faults. Generally speaking, there are two types of faults: one is connection faults, and the other is electrical faults.
Connection failure: mostly due to construction reasons or accidental damage to network cables, such as wiring errors, short circuits, open circuits, etc .;
Electrical characteristics failure: It is the cable that fails to meet the requirements of the wiring standard during signal transmission.
1. Line break
1) Fault type: physical damage to the cable or connector.
2) Cause of failure: mostly caused by improper construction methods or accidental damage to network cables. The main performance is that the connection between the connector and the cable is broken (the connection end of the cable is not inserted in place), the cable is broken from a certain position due to excessive pulling, and the cable is cut due to external construction forces.
3) Failure phenomenon: The connectivity test of the cable fails. The lighter will cause the communication of the network equipment connected to the wiring to be terminated, and the worst will cause the entire network to be paralyzed.
2. Short circuit
1) Fault type: physical damage to the cable.
2) Cause of failure: mostly caused by improper construction methods or damage to the insulation layer of network cables. It is mainly caused by short circuit between cables due to excessive tight binding, damage to the insulation layer when gold shaving nails are embedded in the cable, the stripping head, and the insulation material of multiple wires of the cable is broken, resulting in bare wires and so on.
3) Failure phenomenon: The cable signal is short-circuited, and the network device connected to the cable cannot obtain the correct communication signal.
3. Bending, bending and breaking
1) Fault type: The cable is partially damaged.
2) Causes of failure: mostly caused by improper construction techniques and design or brutal construction. The main performance is that the cable is damaged due to the twisting of the cable, the bending radius is too small, and the force of pulling the cable exceeds its mechanical strength. It appears in new wiring projects.
3) Failure phenomenon: The connectivity test of the cable is unqualified and the cable parameter test is unqualified. In severe cases, the communication of the network equipment connected to the cable will be terminated. For example, in copper cable systems, excessive return loss usually indicates that the bend radius is not properly controlled in the cable routing. In fiber optic systems, high attenuation may result.
Fourth, the connector is open
1) Type of failure: partial failure of the connector.
2) Failure reason: If the RJ-45 connector is faulty, the cable connectivity test fails. If the fiber is open at the connector, the fiber connectivity test fails. The main reason for this type of failure is the breakage of connectors and cables due to improper force during construction. In the process of optical fiber connector docking, the fiber core diameter, numerical aperture, differential conductance of the refractive index distribution, and the optical fiber's lateral misalignment, angle tilt, end face gap, end face shape and other factors will affect the link performance to varying degrees. In severe cases, the link will open. In a wiring system, it is best to use optical fibers produced by the same manufacturer, so as to basically ensure the consistent numerical aperture and refractive index distribution.
3) Symptom: The link is unavailable or has large attenuation.
Five, pin output error
1) Fault type: wrong line diagram.
2) The cause of the failure: the four pairs of twisted pair cables were not inserted into the RJ-45 crystal head according to the standard arrangement during production. The main performance is: reverse connection, wrong pair and cross-winding.
3) Failure phenomenon: lead to incorrect wiring diagram of the cable, network failure, and cable parameter test failure (mainly crosstalk and excessive return loss). It will cause a drop in network performance or a deadlock on the device.
6. Other faults
1) Lower the level of the wiring cable and charge it second. 2) Cut corners. 3) Use inferior connectors.
These faults will seriously affect the performance and life of the entire integrated wiring system. Of course, as long as a comprehensive inspection and certification test of the wiring project is carried out in strict accordance with the acceptance standard of the integrated wiring system, these failures can be found and claims can be made against the illegal wiring company.
11.2 Wiring fault diagnosis method and its elimination
1. Wiring fault diagnosis technology
1. High precision time domain reflection technology
2. High-precision time-domain crosstalk analysis technology
3. Compensation technology
4. Optical time domain reflection technology
Second, wiring fault diagnosis
1. Coil fault diagnosis
There are several types of line diagram faults, such as short circuit, reverse connection, wrong pair, and cross winding. General test equipment can easily find the first two faults, such as using Fluke DSP-4300, the test technology is also very simple.
2. Length troubleshooting
After the cable is too long (exceeds the specified limit length of the link), the link has a large impedance change, which will cause a large signal attenuation. HDTDR technology can be used for positioning.
3. Cross-winding fault diagnosis
Cross-winding faults are difficult to find. The main reason for the cross-winding error is that the connection module or connector is not made in compliance with the ANSI / TIA / EIA 568-B regulations. Although the 1-1, 2-2, ..., 8-8 connections are physically achieved, There is no guarantee for the twisting of 1-2, 3-6, 4-5, 7-8 wire pairs; or the pair is too loose when connecting modules or connectors. The HDTDX technology of the tester can be used to find such errors. It can accurately report the start and end points of the serial cable, even if the serial cable exists in a certain part of the link.
4. Fault diagnosis of return loss
The return loss failure is mainly due to link impedance mismatch. The mismatch mainly occurs at the connector, but may also occur at the place where the characteristic impedance of the cable changes. Especially in Gigabit Ethernet, the four pairs of twisted pairs need to be bidirectionally transmitted at the same time (full duplex), so the reflected signal will be mistaken for the received signal and cause confusion and cause failure. Using HDTDR technology can accurately locate the return loss fault. For example, a link that does not qualify for a certain return loss.
5. Fault diagnosis of optical cable link
The factors that affect the optical cable link include laying optical cables, the termination of optical double-ended connectors, the connection of double-ended jumpers and network equipment. The termination has the greatest impact on the link loss, and will cause mode interference on the multimode optical cable.
The effective method to reduce the failure of optical cable in wiring engineering is: ①remember the strength coefficient of the optical cable, do not drag the optical cable vigorously, and do not excessively bend the optical cable; ② clean the connector during the installation process according to the requirements of the manufacturer; ③ use OLTS according to the standard Test the installed optical cable with OTDR; ④ When testing the optical cable link, use a clean jumper and always keep it clean; ⑤ Install dust caps on all connectors.
3. Wiring troubleshooting
1. Elimination of broken lines
2. Elimination of open circuit faults
3. Elimination of faults with excessive return loss
4. Elimination of impedance discontinuity
5. Elimination of ultra-long link faults
6. Elimination of faults caused by the slow speed of the entire network due to fiber links
7. Rumination of daisy chain effect
4. Network health maintenance technology
1. What is network health maintenance
The so-called mission-critical network refers to the application that the network owner fully trusts in the network. Once the network is shut down and the efficiency is reduced due to failure or poor performance, the owner company will suffer huge losses. Such as air traffic control network, financial securities exchange network, national defense and military command network, and hospital medical network are typical mission-critical networks.
Minimize the frequency of network failures and the impact of failures. Specifically, it includes the following measures: ①management should participate in network decision-making; ② make emergency preparations and plans when failures occur; ③ implement preventive measures for possible problems; ④ comprehensively monitor the network and try to achieve network failures Early detection; ⑤ rapid fault isolation and troubleshooting; ⑥ the use of advanced network monitoring equipment and training managers to improve the quality of network management and maintenance. Among them, "overall monitoring of the network" and "quick fault isolation and troubleshooting" are the essence of the "network health maintenance strategy", and "the use of advanced network monitoring equipment and good quality network management personnel" is the realization of the "network health maintenance strategy "Means and methods. The ultimate goal is to achieve zero failures in network operation.
2. Implementation of network health maintenance
The implementation of network health maintenance is mainly to use advanced network testing equipment to regularly test and monitor the network system, and report the network operation in time, and then quickly eliminate network faults based on the results of the report.
Network health maintenance requires that the test instruments used have the ability to identify bad frames without a frame start identifier (SFD), "short frame" monitoring capabilities, and related network performance automatic testing capabilities.
Shenzhen Powercom Electronics Co., Ltd. , https://www.expowercome.com