Correct application of the hottest optical fiber t

2022-08-15
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Correct application of optical fiber tester in maintenance

nowadays, optical cables can be seen everywhere in data centers and information centers, and almost the backbone of the network is dominated by optical fibers. When we are happy with the improvement of network speed, we have to face all kinds of fiber failures that accompany it. This experience exists not only in the new network, but also in the process of network transformation and upgrading. Sometimes, optical fiber failures pester IT personnel like stubborn diseases. The network is upgraded to 1g or 10g, but it may only be on the physical interface. Sometimes, the actual traffic can't be reached at all, and even the basic connectivity has hidden dangers, often causing packet loss

therefore, we thought of the optical fiber tester, so it is inevitable to equip the optical fiber tester in the large network to help maintain. Therefore, the strain gauge is connected to the working principle of the tension machine of Jinan testing machine factory into the measuring circuit, but the situation is not very ideal, and the faults are reduced a lot, but there will be many inexplicable problems, such as packet loss. Can't these problems be solved with maintenance tools? How to apply these testing tools

1 precautions for optical fiber tester

if you want to be good at something, you must first sharpen it. We can introduce all kinds of optical fiber testers into the maintenance of optical fiber path, which in itself confirms the continuous development of technology. Recalling the network links of 10m and 100m optical fibers, we can safely use them without much testing

with the development of technology, the requirements of optical fiber for loss are becoming more and more strict. The total optical fiber link loss of 10G network is required to be controlled below 2.6d. Cultivate 1-2 leading new material enterprises B in the field of electronic polysilicon and large-size monocrystalline silicon, while the requirements of 10m and 100m network optical fiber loss will be relatively relaxed, which makes it almost easy to implement the optical fiber link in the original network. However, if the rate is increased to 1g and 10g, the original minimum loss may not be suitable for new applications. It is necessary to quantify the loss parameters with optical fiber testing to determine whether it can support the standard requirements. In addition, the high-speed network also puts forward requirements for the optical fiber itself, and the optical fiber is also divided into different categories. In order to improve the speed, the optical fiber itself needs to support higher mode bandwidth, especially for the multimode optical fiber widely used in local areas. As shown in Table 1, the link length corresponding to different mode bandwidth (MBW) is different, and their corresponding maximum loss is also different, in other words, Only qualified loss cannot guarantee that the tested link can support 10G network, and there must be corresponding mode bandwidth

in addition to the loss, length and mode bandwidth mentioned above, we also need to pay attention to dispersion. Many of our switch interface light sources have been changed from LED light sources to VCSEL light sources, which is also used in the test to reduce dispersion and avoid excessive signal broadening. In order to more truly evaluate the performance of optical cables, it is recommended to use VCSEL light sources in the test for 50 m optical fibers

finally, we should also pay attention to the analysis of event faults. Some faults are caused by a part of the optical fiber, such as poor matching of couplers and excessive bending. For such event type faults, we need to locate them. Simple test loss is not enough. We need to cooperate with OTDR tester to locate the event point

therefore, if you want to make good use of the optical fiber tester and really give full play to its efficiency, you need to master some usage methods when applying the tester

select the correct test standards, component standards and application standards. If you know the current network application, such as the link under test is running 1000base SX, then use the application standard to test. If you don't know the application, then use the component standard to test, such as the corresponding standards in ISO and TIA

pay attention to the mode bandwidth. When upgrading the link, it is necessary to consider whether the currently used optical cable meets the requirements of minimum mode bandwidth

choose the right light source. The light source selected during the test should be consistent with the light source of the actual light emission port

depending on the test requirements, decide which level of test to choose. Tsb-140 standard defines two types of tests, one is OLTS test, that is, the test method of light source optical power meter, and the other is OTDR test, that is, optical time domain reflection and single ended test. Category 1 is applicable to the test of optical loss, and category 2 is applicable to the location test of optical fiber fault

2 technology application: how to use the tester to solve the optical fiber fault

the following part gives examples for the common problems in optical fiber testing

(1) in case 1, why does the optical fiber test pass, but the packet is still lost when the network is running

in the selection of standards, many users will make some obvious mistakes, such as not paying much attention to whether the tested fiber is 50 m or 62.5 M

the difference between the requirements for the maximum loss value of optical fibers with two apertures is relatively large, and the wrong selection of optical cable test standard will directly lead to the change of decision threshold. For example, if the measured link is 50 m optical fiber, and the selected test standard is 62.5 m, and the application is 100bas, we should first take the resource-saving development path E-FX. Assuming that the test result is 10dB, the tester will get the result of pass, and the real situation should be unqualified, because it exceeds the judgment threshold of 6.3db. This answers the previous question. The test passed, but why does the running data still lose packets

(2) case 2: after passing the 10 Gigabit standard, why can't we support the 10 Gigabit rate

there are such users. When upgrading the backbone of the network, they will upgrade the module of the switch and the module of the server. Of course, they will also test the loss of optical fiber in the network. It seems that there is no problem in the method. The measured optical fiber meets the requirements of 10 Gigabit network, and the loss is less than the standard limit value, but the actual operation effect is still not ideal

the main reason for the analysis is that the mode bandwidth of optical cables is not considered. The mode bandwidth of different optical cables represents the maximum bandwidth that can be provided within a certain distance. The larger the mode bandwidth, the greater the transmission rate within a certain distance. However, since many optical fibers were laid in earlier years, the mode bandwidth is generally relatively low, less than 160, resulting in a long distance, and the rate cannot go up, Although the loss is qualified at this time

(3) case 3: the test loss is up to standard, and the mode bandwidth is no problem. Why is there still a problem in the actual operation

there is another misunderstanding in our test. As long as the loss passes, we think the optical fiber is OK, but this is not the case. Suppose such a situation, the standard design requires the link loss to be 2.6db, but during the test, due to the adapter failure, the loss of an adapter reaches more than 0.75db, but the total link loss is still less than 2.6db. At this time, if the test loss is simple, the adapter problem may not be found, However, in real network use, the transmission error rate will be greatly increased due to adapter problems

3 conclusion

to ensure the normal operation of the optical fiber network, it is recommended to often do some maintenance tests on the backbone link and the upgraded link to ensure the performance of the optical fiber link. Attention should be paid to the selection of the tester. According to its own requirements, if it only needs to test the loss, it can be achieved generally, such as flukedtx series with optical modules. However, if it is necessary to accurately locate fault events, professional event analysis equipment such as flukeoptifiber tester may be more suitable. For general Gigabit networks, test loss is generally enough, while for 10 Gigabit networks, both loss and event location should be taken into account

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