1 Classification of optical cable line faults
According to the interruption of the optical fiber of the faulty cable, the fault types can be divided into three types: total interruption of the optical cable, interruption of part of the bundle tube, and interruption of part of the fiber in a single bundle tube.
1.1 The optical cable is completely broken
If there are reservations on both sides of the site, take centralized reservations and add a joint to deal with them;
There are joints near the fault point and there are enough reservations on site, use the method of pulling reservations and using the original joints;
There is neither reservation nor joint near the fault point, so it should be solved by cable extension.
1.2 Partial bundle tube interruption in fiber optic cable or partial fiber optic interruption in single bundle tube
The repair is based on the premise that it does not affect other optical fibers in use. It is recommended to use the skylight connection method to repair the faulty optical fiber.
Optical cable line failure
2 Analysis of the Causes of Optical Cable Line Failures
The causes of cable line failure can be roughly divided into four categories: external force factors, natural disasters, defects of the cable itself and human factors.
3 Troubleshooting principles
With the purpose of prioritizing the transmission of the active system, and based on the compression of the fault duration, regardless of day or night, regardless of whether the weather is good or bad, and regardless of maintenance boundaries, the fastest method is used to temporarily clear the active transmission system.
The general principle of fault handling is: get through first, then repair; first the core, then the edge; first the local end, then the opposite end; When two or more failures occur at the same time, the major failures shall be dealt with first. Before the line obstacle is removed, the inspection and repair shall not be suspended.
4 Formulate line emergency dispatch plan
Before formulating the emergency dispatch plan, it is necessary to conduct a thorough investigation of the system opening conditions of all optical cable lines, and reasonably formulate an optical fiber emergency communication plan according to the optical fiber resource conditions of the same cable and route.
The emergency emergency communication plan should be revised and updated in a timely manner according to the opening of the circuit and the occupancy of the fiber core, keeping the plan consistent with the actual opening situation, and ensuring the feasibility of the emergency plan.
The content of the emergency dispatch plan should include the participating personnel, leading organization, specific measures and detailed circuit dispatch plan.
5 Optical cable line fault repair process
1. The processing after the fault occurs, different types of line faults, the focus of processing is different.
(1) The same route has a total resistance fault that can be replaced by an optical cable. The personnel on duty in the computer room should use other good fiber cores to block the services on the fiber according to the emergency plan at the first time, and then repair the faulty fiber as soon as possible.
(2) For a total resistance fault where there is no optical fiber to replace it, follow the emergency plan to implement emergency communication or direct repair of the obstacle point.
(3) There is non-total resistance in the optical cable, and there are remaining optical fibers available. Use spare fiber cores or other optical cables on the same route to pass through services on faulty fiber cores. If there are many faulty fiber cores, not enough free fiber cores, and no other optical cables with the same route, the secondary circuit can be sacrificed to pass through the important circuit, and then the faulty fiber core can be repaired without interrupting the circuit.
(4) There is non-total resistance in the optical cable, and there is no remaining optical fiber or optical cable with the same route. If the blocked fiber is an important circuit, use other non-important circuit fibers to pass through the blocked fiber, and use the method of continuous cutover to repair the faulty fiber core urgently.
(5) The transmission quality is unstable, and the system is up and down. If there is a spare fiber core or other fiber optic cable with the same route, the service on this fiber can be transferred to other fibers. Find out the reason for the decline in transmission quality and deal with it in a targeted manner.
2. Fault location
If it is determined that the optical cable line is faulty, it should quickly determine which relay section the fault occurs in and the specific situation of the fault, and ask the network management room in detail. According to the judgment result, immediately notify the relevant line maintenance unit to judge the fault point.
3. Preparation for emergency repair
After the line maintenance unit receives the failure notice, it should quickly load the emergency repair tools, instruments and equipment and set off, and at the same time notify the relevant maintenance lineman to find the cause and failure point in the nearby area. The preparation time for emergency repair of optical cable lines shall be implemented in accordance with regulations.
4. Establish a communication system
After the repair personnel arrive at the fault point, they should immediately establish a communication system with the transmission room.
5. Organization and command of emergency repairs
The emergency repair of optical cable line failure is led by the maintenance department. During the emergency repair period, it pays close attention to the on-site emergency repair situation and cooperates well. The emergency repair site is directed by the leader of the optical cable line maintenance unit.
While testing the fault point, the emergency repair site should designate a special person (usually an optical cable operator) to organize the excavation personnel to stand by, and arrange the logistics service work.
6. Emergency repair of optical cable lines
When the point of failure is found, emergency optical cable or other emergency measures should be used, firstly, the main optical fiber channel should be cleared, and the communication can be quickly restored. Observe and analyze the situation at the scene, make records, take photos, and report to the public security organs.
7. Business recovery
After the on-site optical cable repair is completed, the computer room should be notified in time for testing, and communication should be restored as soon as possible after verification is available.
8. On-site treatment after emergency repair. After the emergency repair work is over, check the tools and equipment, sort out the test data, fill in the relevant registration, handle the scene, and stay with a certain number of personnel to protect the scene of the rescue.
9. Line data update. After the repair work is over, sort out the test data, fill in the relevant forms, update the line information in time, summarize the repair situation, and report to the superior department in charge.
6 Common failure phenomena and possible cause analysis
1. Distance judgment
When the computer room determines that the fault is an optical cable line fault, the line maintenance department should test the faulty optical cable line in the computer room as soon as possible, and use the OTDR test to determine the location of the line fault point.
2. Possible cause estimation
According to the curves displayed by the OTDR test, the cause of the fault is preliminarily judged, and the fault is handled in a targeted manner.
According to the fault analysis, there are many problems in the splice box for optical cable faults caused by non-external forces, and the reasons for fiber breakage or increased attenuation in the splice box are divided into the following situations:
(1) The optical fiber in the fiber tray is loose, causing the optical fiber to bounce up and be squeezed at the edge of the fiber tray or the screw on the tray. In severe cases, the optical fiber will be crushed or broken.
(2) The local bending radius of the remaining fibers in the splice box is too small or the fibers are seriously twisted when they are stored in the reel, resulting in large bending loss and static fatigue. The test at 1310nm wavelength does not change significantly, but the test at 1550nm wavelength shows significant splice loss. increase.
(3) When making the end face of the optical fiber, the bare optical fiber is too long or the optical fiber protection position is improper when the heat-shrinkable protective tube is heated, causing a part of the bare optical fiber to be outside the protective tube, and the bare optical fiber is broken when the splice box is subjected to external force.
(4) The bare optical fiber is injured when the coating is stripped, and the damage expands after a long time, and the loss of the joint increases, and in severe cases, the fiber will be broken.
(5) Because the optical cable is not fixed tightly, the displacement of the optical cable due to stress or external force causes the remaining fiber of the optical cable to be twisted or bent to cause attenuation of the optical fiber.
(6) Water enters the splice box and freezes in winter, resulting in increased fiber loss and even fiber breakage.
3. Find the specific location of the fault point of the optical cable line
When the optical cable line is blocked by obvious external forces such as natural disasters or external construction, the inspection and repair personnel will carefully inspect along the optical cable line route according to the fault phenomenon and approximate fault location provided by the tester, and it is generally easier to find the fault location. If it is not the above situation, it is not easy for inspectors to find the fault location from the abnormal phenomenon on the route. At this time, according to the distance from the fault point to the test end measured by OTDR, it must be checked with the original test data to find out which two markers (or which two joints) the fault point is between, and after necessary conversion, Find the specific location of the fault point. If conditions permit, a two-way test can be carried out, which is more conducive to accurately judging the specific location of the fault point.
4. The main reasons that affect the accurate judgment of the obstacle point of the optical cable line
(1) OTDR has inherent bias
The inherent deviation of OTDR is mainly reflected in the distance resolution. Different test distance deviations are different. When the test range is 150km, the test error reaches ±40m.
(2) Errors caused by improper operation of test instruments
When testing optical cable fault location, the correctness of OTDR use is directly related to the accuracy of obstacle testing. For example, factors such as improper instrument parameter setting or inaccurate cursor setting will lead to errors in test results.
(3) Calculation error
The distance to the fault point measured by OTDR can only be the length of the optical fiber, and the skin length of the optical cable and the ground distance from the test point to the obstacle point cannot be obtained directly. If it matches or is unclear about the shrinkage rate of the optical cable used, certain errors will also occur.
5. A method to improve the accuracy of cable line fault location
(1) Correctly and proficiently master the use method of the instrument
Accurately set the parameters of the OTDR, select the appropriate test range file, and use the amplification function of the instrument to accurately place the cursor on the corresponding inflection point, such as the inflection point of the fault point, the beginning and end points of the optical fiber, and the inflection point at the end of the optical fiber, so that more accurate results can be obtained. Test Results.
(2) Establish accurate and complete original data
Accurate and complete optical cable line information is the basic basis for obstacle measurement and judgment. Therefore, we must pay attention to the collection, sorting and checking of line information, and establish true, credible and complete line information.
(3) Establish accurate line routing information, including marker stone (rod number) - fiber length (cable length) comparison table (refer to the appendix), "fiber length accumulation" and "fiber attenuation" records, in the establishment of "fiber length accumulation" When collecting data, the distance from the end station to each connector should be measured from both ends. In order to test the results accurately, transition optical fibers can be used according to the situation. The on-the-job inspection personnel collect and record various reserved lengths. The more detailed the registration is, the smaller the error of obstacle judgment will be.
7 Matters needing attention when judging and handling optical cable faults
1. Matters needing attention when troubleshooting
(1) When a long-distance optical cable line fails at the provincial boundary or at the junction of two maintenance units, the two adjacent maintenance units should check out and carry out emergency repairs at the same time.
(2) Optical cable line maintenance units at all levels should accurately grasp the data of their optical cable lines. Familiar with the test method of the obstacle point of the optical cable line, can accurately analyze and determine the location of the obstacle point. Always maintain a certain repair force, and master the line repair procedures and the use of emergency equipment.
(3) Optical cable maintenance personnel should be familiar with the optical cable line information, master the line emergency repair operation procedures, obstacle test methods and optical cable connection technology, strengthen the management of emergency repair vehicles, and be ready for emergency repair at any time.
Special equipment, tools, instruments, machinery and vehicles for emergency repairs must be relatively concentrated, and a list must be listed to be ready at any time. Generally, they are not allowed to be borrowed or embezzled.
2. Matters needing attention during processing
(1) During the emergency repair process of the optical cable line, attention should be paid to the safe operation and use of instruments and equipment. Before performing the optical fiber fault test, the optical fiber under test should be physically disconnected from the optical terminal at the opposite end.
(2) Once the fault is eliminated and passed the strict test, immediately notify the maintenance department to verify the transmission quality of the optical cable and restore communication as soon as possible.
(3) Do a good job of troubleshooting records. After troubleshooting, the line maintenance department should promptly organize relevant personnel to analyze the cause of the failure in accordance with relevant regulations, sort out technical information and report it. Summarize lessons learned and propose improvement measures.
(4)When intervening or replacing the optical cable, the optical cable of the same manufacturer and the same model as the faulty optical cable should be used, and the optical cable joints and optical fiber connection loss should be minimized as much as possible. The length of the fiber optic cable inserted or replaced during the fault handling should generally not be less than 200m, and the fiber optic cable of the same manufacturer and type should be used as much as possible, and the average joint loss of the single-mode fiber should not be greater than 0.2dB/piece. The bending radius of the optical cable after troubleshooting and modification should not be less than 15 times the cable diameter.
