Optical cable line failure

The interruption of the optical cable line caused by external factors or the optical fiber itself, which affects the communication service, is called the optical cable line fault. The interruption of optical cables does not necessarily lead to service interruption. Those that cause service interruption due to a fault are handled according to the fault repair procedure, and those that do not affect the service are dealt with according to the cutover procedure.

fiber optic line

1 Classification of optical cable line faults

According to the interruption of the optical fiber of the faulty optical cable, the fault types can be divided into three types: complete optical cable interruption, partial bundle pipe interruption, and partial optical fiber interruption in a single bundle pipe.

1.1 The fiber optic 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;

If there is a connector near the fault point and there is enough reservation on site, take the method of pulling the reservation and using the original connector to deal with it;

There are neither reservations nor joints near the fault point, so it should be solved by means of continuation of the cable.

1.2 Part of the bundled tube in the optical cable is interrupted or part of the optical fiber in the single bundled tube is interrupted

The repair is based on the premise of not affecting other fibers in use. It is recommended to use the skylight connection method to repair the faulty fiber.

2 Analysis of the causes of optical cable line failures

The reasons for the failure of optical cable lines can be roughly divided into four categories: external factors, natural disasters, defects of the optical cable itself and human factors.

2.1 Line faults caused by external factors

(1) Excavation by external force: To deal with the failure of excavator construction, the optical cable of the pipeline is opened to check whether the optical cable is damaged in the manual well, and the two-way test interrupts the optical cable. , you should first conduct a bidirectional test on the optical cable at the fault point to confirm the number of blocked optical cables, and then deal with them in a targeted manner.

(3) Shooting: This type of fault generally does not interrupt all optical fibers, but damages some parts of the optical cable or optical fibers, but it is more difficult to find such faults.

2.2 Line failure caused by natural disasters

Rat bites and bird pecks, fires, floods, strong winds, ice, lightning strikes, electric shocks

2.3 Line failure caused by the fiber itself

(1) Natural fiber breaking: Since the optical fiber is drawn from glass and plastic fibers, it is relatively fragile, and static fatigue will occur over time, and the optical fiber will gradually age, resulting in natural fiber breaking. Or water enters the splice box, resulting in increased fiber loss or even fiber breakage.

(2) Influence of ambient temperature: If the temperature is too low, the water in the splice box will freeze, and the optical cable sheath will shrink longitudinally, and the pressure will be applied to the optical fiber to generate micro-bending, which will increase the attenuation or interrupt the optical fiber. If the temperature is too high, it is easy to damage the cable sheath and other protective materials and affect the characteristics of the optical fiber.

2.4 Line faults caused by human factors

(1) Work failure: human failure caused by technicians in maintenance, installation and other activities. For example, when the optical fiber is spliced, the optical fiber is scratched, and the bending radius of the optical fiber is too small; the running optical cable is cut off by mistake when the optical fiber is cut; the connection is not firm when the optical fiber is spliced, and the reinforcing core is not tightly fixed when the splice box is packaged. Broken fiber.

(2) Stealing: criminals steal and cut the optical cable, causing the optical cable to be blocked.

(3) Destruction: Deliberately sabotage, causing optical cable blocking.

3 Troubleshooting principles

The purpose is to give priority to the replacement of the in-use system, and to compress the fault duration as the fundamental, regardless of day and night, weather conditions, maintenance boundaries, and use the fastest method to temporarily seize the transmission system in use.

The general principles of fault handling are: rush through first, then repair; first core, then edge; first local end, then peer end; first in the network, then out of the network, and deal with fault levels. When two or more faults occur at the same time, priority will be given to major faults. The inspection and repair shall not be suspended until the line obstacle is removed.

4 Develop line emergency dispatch plan

Before formulating an emergency dispatch plan, a careful investigation of the system opening of all optical cable lines should be carried out, and a plan for optical fiber rushing and replacement should be reasonably formulated according to the optical fiber resources of the same cable and the same route.

The emergency rushing and replacement plan should be revised and updated in a timely manner according to the circuit opening and fiber core occupancy, so as to keep the plan consistent with the actual opening situation and ensure the feasibility of the emergency plan.

The content of the emergency dispatch plan should include the participating personnel, leading organizations, specific measures and detailed circuit dispatch plans.

5 Optical cable fault repair process

1. The processing after the fault occurs, different types of line faults, the focus of processing is different.

(1) There is a total resistance fault that can be replaced by an optical cable in the same route. The personnel on duty in the computer room should use other good fiber cores to block services on the optical fiber in accordance with the emergency plan as soon as possible, and then repair the faulty fiber as soon as possible.

(2) If there is no optical fiber that can be replaced by the total block fault, the emergency plan is implemented to replace the connection or the direct repair of the obstacle point. The principle of "first important circuit, second secondary circuit" should be followed during the first replacement or repair.

(3) The optical cable has non-total resistance, and there are remaining optical fibers available. Use spare fiber cores or other optical cables with the same route to replace the services on the faulty fiber cores. If there are many faulty cores, there are not enough spare cores, and there are no other optical cables with the same route, the secondary circuit can be sacrificed to replace the important circuit, and then the faulty core can be repaired by the method without interrupting the circuit.

(4) The optical cable is not fully resisted, and there is no remaining optical fiber or optical cable with the same route. If the blocked optical fiber opens an important circuit, use other non-important circuit optical fibers to replace the blocked optical fiber, and use the method of uninterrupted cutover to repair the faulty fiber core urgently.

(5) The transmission quality is unstable, and the system is good and bad. If there is a spare fiber core that can be replaced or other optical cables with the same route, the services on the optical fiber can be transferred to other optical fibers. Find out the cause of the degradation of transmission quality and deal with it in a targeted manner.

2. Fault location

If it is determined that the optical cable line is faulty, you should quickly determine which relay segment the fault occurred 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 receiving the fault notification, the line maintenance unit should quickly load the repair tools, instruments and equipment, and at the same time notify the relevant maintenance line staff to find the cause and fault point in the nearby area. The preparation time for emergency repair of optical cable lines shall be carried out according to 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 maintenance department shall be the business leader in the emergency repair of optical cable line failures. During the emergency repair period, we shall pay close attention to the emergency repair situation on site, and do a good job of cooperation. The emergency repair site shall be commanded 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 fault point is found, emergency optical cable or other emergency measures should be used. Observe and analyze the situation on site, make records, take pictures, 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 resumed as soon as possible after verification is available.

8. On-site treatment after emergency repair. After the repair work is over, inventory tools and equipment, sort out test data, fill in relevant registrations, deal with the site, and stay behind a certain number of people to protect the site.

9. Line data update. After the repair work is completed, organize the test data, fill in the relevant forms, update the line information in time, summarize the emergency repair situation, and report to the higher authorities.

6 Common fault phenomenon 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. Estimation of possible causes

According to the curve displayed by the OTDR test, the cause of the fault can be preliminarily judged, and the fault treatment can be carried out in a targeted manner.

According to the fault analysis, there are many problems in the splice box due to the failure of the optical cable not caused by external force.

(1) The fiber in the fiber accommodating disk is loose, causing the fiber to spring up and be squeezed at the edge of the fiber accommodating disk or the screws on the disk. In severe cases, the fiber will be crushed and broken.

(2) When the residual fiber in the splice box is placed in the coil, the local bending radius is too small or the optical fiber is seriously twisted, resulting in large bending loss and static fatigue. The change in the 1310nm wavelength test is not obvious, and the 1550nm wavelength test joint loss is significant increase.

(3) When the fiber end face is made, the bare fiber is too long or the fiber protection position of the heat shrinkable protection tube is improper when heated, resulting in a part of the bare fiber outside the protection tube, and the bare 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 joint loss increases with the increase, which will cause fiber breakage in severe cases.

(5) Because the optical cable is not fixed tightly, the displacement of the optical cable due to stress or external force leads to the distortion or bending of the remaining fiber of the optical cable, which causes the optical fiber attenuation.

(6) Water enters the splice box, and freezing in winter leads to 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 due to obvious external forces such as natural disasters or external construction, the inspection and repair personnel will carefully inspect the optical cable route according to the fault phenomenon and approximate fault location provided by the tester, and it is generally easier to find the fault location. Otherwise, it is not easy for the inspectors to find the fault location from the abnormal phenomenon on the route. At this time, the distance from the fault point measured by the OTDR to the test terminal must be checked with the original test data to find out which two markers (or which two joints) the fault point is between. After necessary conversion, Find the exact location of the point of failure. If conditions permit, two-way testing can be performed, 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 distances have different deviations. When the test range is 150km, the test error is ±40m.

(2) Errors caused by improper operation of the test instrument

In the optical cable fault location test, the correctness of the OTDR is directly related to the accuracy of the obstacle test. Factors such as improper setting of instrument parameters or inaccurate vernier settings will lead to errors in test results.

(3) Calculation error

The distance of the fault point measured by the OTDR can only be the length of the optical fiber, and the skin length of the optical cable and the ground distance between the test point and the obstacle point cannot be directly obtained. Compliant or unclear about the shrinkage rate of the optical cable used, there will also be certain errors.

(4) Errors caused by inaccurate completion data of optical cable lines

Due to the lack of attention to the accumulated data or the low reliability of the recorded data during the line construction, the completion data of the line are inconsistent with the actual situation. Based on such data, it is impossible to accurately determine the obstacle points.

For example, the reeling length of the remaining fibers in the splice box when the optical cable is connected, the reeling length of the optical cable at various special points, and the fluctuation of the optical cable with the terrain, etc. The accuracy of these factors directly affects the positioning accuracy of the obstacle point.

5. Methods to improve the accuracy of fault location of optical cable lines

(1) Correct and proficient in the use of the instrument

Accurately set the parameters of the OTDR, select the appropriate test range file, apply the amplification function of the instrument, and accurately place the cursor on the corresponding inflection point, such as the inflection point of the fault point, the start point of the fiber, and the inflection point of the fiber end, so that a more accurate measurement can be obtained. Test Results.

(2) Establish accurate and complete original data

Accurate and complete optical cable line data is the basic basis for obstacle measurement and determination. Therefore, attention must be paid to the collection, arrangement and verification of line data, and a true, credible and complete line data must be established.

(3) Establish accurate line routing data, including marker (pole number) - length (cable length) comparison table (refer to the appendix), "fiber length accumulation" and "fiber attenuation" records, after establishing "fiber length accumulation" The distance from the end station to each connector should be measured from both ends. In order to obtain accurate test results, transition fibers can be used according to the situation. On-the-job acceptance personnel collect and record various reserved lengths. The more carefully registered, the smaller the error in obstacle determination.

(4) Establish complete and accurate line information

The building line information not only includes many data in the line construction, as-built technical documents, drawings, test records and pictures of the backscattered signal curve of the optical fiber in the relay section, etc., but also retains some original data of the optical cable and optical fiber provided by the manufacturer when the optical cable leaves the factory. (such as the shrinkage rate of the optical cable, the refractive index of the optical fiber, etc.), these data are the basis and comparison basis for future obstacle testing.

(5) Make the correct conversion

To accurately determine the location of the fault point, it is also necessary to convert the length of the fiber tested to the ground length from the test end (or a joint point) to the fault point.

The ground length from the test end to the fault point can be calculated by the following formula (the unit of length is m):

L = [(L1-L2)/(1+P)-L3]/( 1+a )

In the formula, L is the ground length from the test end to the fault point (in meters), L1 is the optical fiber length from the test end to the fault point measured by the OTDR (in meters), and L2 is the length of the optical fiber reserved in each splice box (unit is meter), L3 is the length (unit is meter) of the optical cable and all coils at each joint, P is the shrinkage rate (ie twist coefficient) of the optical fiber in the optical cable, it is best to use the value provided by the manufacturer, generally is 7‰, and a is the natural bending rate of the optical cable (0.5% for pipeline laying or overhead laying, and 0.7%-1% for direct burial laying). With accurate and complete original data, the faulty fiber length measured by the OTDR can be compared with the original data, and the location of the fault point can be accurately identified.

(6) Keep the obstacle test consistent with the test conditions on the data

During the fault test, try to maintain the consistency of the test instrument's signal, operation method and instrument parameter setting. Because the optical instrument is very precise, if there is a difference, it will directly affect the accuracy of the test, resulting in the difference between the two tests themselves, making the test results incomparable.

(7) Flexible testing, comprehensive analysis

Under normal circumstances, two-way fault testing can be performed at both ends of the optical cable line, and the location of the fault point can be calculated based on the original data. Then comprehensively analyze and compare the test and calculation results in the two directions to make the judgment of the specific location of the fault point more accurate. When there are no obvious features on the route near the obstacle point, and the specific obstacle point cannot be determined on site, methods such as measuring at the nearest joint can also be used, or excavation at the obstacle point of the preliminary test, and the test instrument of the terminal station is in a real-time measurement state. Find the change of the curve at any time, so as to find the exact fiber fault point.

7 Matters needing attention when judging and handling optical cable faults

1. Matters needing attention when troubleshooting

(1) When the long-distance optical cable line fails, the two adjacent maintenance units should check and repair at the same time.

(2) The maintenance units of optical cable lines at all levels should accurately grasp the information of their optical cable lines. Proficient in the testing method of the obstacle point of the optical cable line, and can accurately analyze and determine the position of the obstacle point. Always maintain a certain emergency repair force, and be proficient in the operation procedures of line emergency repair and the use of emergency equipment.

(3) Optical cable maintenance personnel should be familiar with optical cable line information, be proficient in line emergency repair operation procedures, obstacle testing methods and optical cable connection technology, strengthen emergency repair vehicle management, and be ready for emergency repairs at any time.