Wiring troubleshooting

11.1 Common wiring construction failure modes

There are many types of network cable failures, which can generally be divided into two categories: one is connection failure, and the other is electrical characteristic failure.

Connection failure: mostly caused by construction reasons or accidental damage to the network cable, such as wiring errors, short circuits, open circuits, etc.

Electrical characteristic failure: The cable fails to meet the wiring standard requirements during signal transmission.

1. Line break

1) Fault type: Physical damage to the cable or connector.

2) Cause of the fault: Most of them are caused by improper construction methods or accidental damage to the network cables. The main manifestations are disconnection between the connector and the cable (the cable connection end is not fully inserted), the cable is broken at a certain position in the middle due to excessive pulling, and other external forces during construction cause the cable to be cut.

3) Fault phenomenon: The cable connectivity test fails. In the least, the communication of the network equipment connected to the cable is interrupted, and in the worst case, the entire network will be paralyzed.

2. Line short circuit

1) Fault type: Physical damage to the cable.

2) Causes of failure: Most of them are caused by improper construction methods or external damage to the insulation layer of the network cable. Mainly due to short circuits between cables caused by over-tight bundling, gold nails embedded in the cables, damage to the insulation layer when stripping the wire heads, and the insulation material of multiple wires of the cable breaking, resulting in exposed wires, etc.

3) Fault 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: Partial damage to the cable.

2) Cause of failure: Most of the failures are caused by improper construction technology and design or rough construction, etc. The main manifestations are cable damage due to cable tangling, too small bending radius, and cable pulling force exceeding its mechanical strength, etc., which often occurs in new wiring projects.

3) Fault phenomenon: The cable fails the connectivity test and the cable parameter test. In severe cases, the communication of the network equipment connected to the cable is terminated. For example, in a copper cable system, high return loss usually indicates that the bending radius is not properly controlled during the cable routing. In a fiber optic system, it may cause high attenuation.

4. Connector open circuit

1) Fault type: Partial connector failure.

2) Cause of failure: If the RJ-45 connector fails, the cable connectivity test fails. If the optical fiber is open at the connector, the optical fiber connectivity test fails. The main cause of this type of failure is the breakage of the connector and cable due to improper force during construction. During the docking process of optical fiber connectors, factors such as the optical fiber core diameter, numerical aperture, differential conductivity of the refractive index distribution, and the lateral misalignment, angle tilt, end face gap, and end face shape of the optical fiber will have varying degrees of impact on the link performance, and in severe cases will cause the link to be open. In a wiring system, it is best to use optical fibers produced by the same manufacturer to basically ensure that the numerical aperture and refractive index distribution are consistent.

3) Fault phenomenon: The link is disconnected or has severe attenuation.

5. Pin output error

1) Fault type: Line graph error.

2) Cause of the fault: The four pairs of twisted-pair cables were not inserted into the RJ-45 connector in the standard arrangement during production. The main manifestations are: reverse connection, wrong pairing, and cross-wiring.

3) Fault phenomenon: The cable wiring diagram is incorrect, the network is unavailable, and the cable parameter test fails (mainly due to excessive crosstalk and return loss). This will cause a decline in network performance or a deadlock in the device.

6. Other faults

1) Downgrading wiring cables. 2) Cutting corners. 3) Using inferior connectors.

These faults will seriously affect the performance and life of the entire integrated wiring system. Of course, as long as the wiring project is fully inspected and certified according to the integrated wiring system acceptance standards, these faults can be discovered and claims can be made against illegal wiring companies.

11.2 Wiring Fault Diagnosis and Troubleshooting

1. Wiring Fault Diagnosis Technology

1. High-precision time domain reflectometry technology

2. High-precision time domain crosstalk analysis technology

3. Compensation technology

4. Optical Time Domain Reflectometry

2. Wiring Fault Diagnosis

1. Coil fault diagnosis

There are several types of line diagram faults, such as short circuit, reverse connection, wrong pair, series winding, etc. The first two faults can be easily found by general test equipment, such as Fluke DSP-4300, and the test technology is also very simple.

2. Length fault diagnosis

When the cable is too long (exceeds the maximum length specified for the link), the link will have a large impedance change, which will cause a large signal attenuation and can be located using HDTDR technology.

3. Series winding fault diagnosis

A cross-link fault is difficult to detect. The main reason for a cross-link error is that the ANSI/TIA/EIA 568-B specification is not followed when making the connection module or connector. Although the 1-1, 2-2, ..., 8-8 connection is physically achieved, the twisting of the 1-2, 3-6, 4-5, 7-8 wire pairs is not guaranteed; or the wire pairs are twisted too long when connecting the module or connector. This type of error can be found using the tester's HDTDX technology, which can accurately report the start and end points of the cross-link cable, even if the cross-link exists in a part of the link.

4. Return loss fault diagnosis

Return loss failure is mainly caused by link impedance mismatch. Mismatch mainly occurs at the connector, but it can also occur where the characteristic impedance changes in the cable. Especially in Gigabit Ethernet, the four pairs of wires in the twisted pair need to transmit in both directions at the same time (full duplex), so the reflected signal will be mistaken for the received signal and cause confusion and failure. HDTDR technology can be used to accurately locate the return loss fault. For example, for a link with unqualified return loss.

5. Optical cable link fault diagnosis

Factors that affect the optical cable link include laying the optical cable, termination of the optical cable double-ended connector, double-ended jumper and connection of network equipment. Termination has the greatest impact on link loss and will cause mode interference for multimode optical cables.

Effective methods to reduce optical cable failures in wiring projects are: ① Remember the strength coefficient of the optical cable, do not drag the optical cable too hard, and do not bend the optical cable excessively; ② Clean the connectors during installation according to the manufacturer's requirements; ③ Use OLTS and OTDR to test the installed optical cables according to the standards; ④ When testing the optical cable link, use clean jumpers and always keep them clean; ⑤ All connectors must be equipped with dust covers.

3. Wiring troubleshooting

1. Troubleshooting of line damage

2. Troubleshooting of open circuit faults in network cabling

3. Troubleshooting of excessive return loss

4. Troubleshooting of impedance discontinuity faults

5. Troubleshooting of excessive link length

6. Troubleshooting of the entire network slowing down due to optical fiber links

7. Eliminate the daisy chain effect

4. Network Health Maintenance Technology

1. What is network health maintenance?

Mission-critical networks refer to applications where the network owner completely relies on the network. Once the network is shut down and efficiency is reduced due to a failure or poor performance, it will cause huge losses to the owner's company. Typical mission-critical networks include air traffic control networks, financial securities exchange networks, national defense and military command networks, and hospital medical networks.

Minimize the frequency of network failures and the impact of failures. Specifically, the following measures are included: ① Management 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 find network failures at an early stage; ⑤ Quickly isolate and troubleshoot failures; ⑥ Use advanced network monitoring equipment and train management personnel to improve the quality of network management and maintenance. Among them, "comprehensively monitor the network" and "quickly isolate and troubleshoot failures" are the essence of the "network health maintenance strategy", while "using advanced network monitoring equipment and well-qualified network management personnel" are the means and methods to achieve the "network health maintenance strategy". The ultimate goal is to achieve zero network failures.

2. Implementation of network health maintenance

The implementation of network health maintenance mainly involves using advanced network testing equipment to regularly test and monitor the network system, and promptly report the network operation status, and then quickly troubleshoot network faults based on the report results.

Network health maintenance requires that the test instruments used have the ability to identify bad frames without a frame start identifier (SFD), the ability to monitor "short frames", and the ability to automatically test related network performance.