Engineering budget for attenuation testing in FTTH access projects

 In the article “FTTH Access Project Attenuation Test”, mentioned that the loss test in FTTH access project includes: single reel inspection of optical cable, loss test of optical cable line, local test of optical splitter, and full test of ODN optical fiber link. So how should these tasks be applied in the project budget?

Single drum inspection of optical cable

Although the quality of current cables is relatively good, if the optical cables are not inspected on a single reel before construction, and the quality problems are found after laying and installation, the cost of replacement will be relatively high; moreover, if quality problems are found after laying, it is difficult to obtain the approval of the optical cable manufacturer. Therefore, single reel inspection of optical cables is necessary.

Single reel inspection of optical cables should apply “TXL1-006 Single Reel Inspection of Optical Cables”. Although FTTx requires to use two wavelength windows, single reel inspection only needs to test the attenuation of any wavelength window. It is almost impossible for the attenuation of optical fiber in one window to be normal while the attenuation of the other window is abnormal.

Polarization mode dispersion does not need to be tested in FTTH access projects, so there is no need to use a polarization mode dispersion tester for single reel inspection.

Loss test of optical cable line

The attenuation test of the optical cable line should apply the corresponding sub-item of “user optical cable test”. The instruments in the user optical cable test involve light source, optical power meter and OTDR. The light source and power meter are mainly used in the test process, but when the attenuation of the fiber link is abnormal, OTDR is needed to determine the fault. Therefore, all 3 instruments will be used.

2.1 Trunk Section Cable Testing

The fiber cores of trunk cables are usually divided into exclusive fiber cores, shared fiber cores, and reserved fiber cores. Since the fiber distribution structure of trunk cable is relatively complex, testing is also more troublesome.

The following is an example of a 144-core trunk cable ring. In this example, each trunk fiber cross-connect has 24+24 (48 in total in both directions) cores, and each fiber cross-connect and service aggregation point share 24 cores, and 24 cores are reserved, as shown in Figure 1.

Exclusive fiber cores are tested at the service convergence point and trunk optical crossover. Four trunk optical crossovers test a total of 48 cores x 4 sections. The “TXL 6-106 User optical fiber cable test for less than 48 cores 4 sections” should be applied;

Shared fiber cores need to be tested section by section. The shared optical fiber in the figure is divided into 5 sections. The “TXL 6-104 User optical cable test for less than 24 cores 5 sections” should be applied;

Reserved fiber cores only need to be tested at the service convergence point. The “TXL 6-104 User optical cable test for less than 24 cores 1 section” should be applied.

2.2 Distribution Section Optical Cable Test

When the distribution section optical cable is a star-shaped network structure, as shown in Figure 2, the engineering volume of the optical cable test should be applied to “TXL 6-106 48-core or less user optical cable test 2 sections”;

When the distribution cable segment is a star-shaped network structure, as shown in Figure 2, the engineering volume of the optical cable test should be applied to “TXL 6-106 48-core or less user optical cable test 2 sections”;

When the distribution cable segment is a tree-shaped networking structure, as shown in Figure 3, it is necessary to test between the trunk optical cross-connect and GP01, and between the trunk optical cross-connect and GP02. It is more appropriate to apply the “2-section test for user optical cables with less than 48 cores” than the “1-section test for user optical cables with less than 96 cores”.

2.3 Introduction cable test

The introduction cable also needs to be tested at the distribution optical intersection and each fiber optic distribution box, as shown in Figure 4. Should we apply “12 core or less drop cable test 1 section” or “2 core or less drop cable test 6 sections”?

Since the distance between the fiber splitter boxes connected to the same drop cable wire is usually short, and at the same splitter distribution box, the attenuation test of the fiber core (to the distribution optical cross-connect) terminated in the fiber splitter box can often be completed at one time with the full ODN link test (no need to go to the same place many times), so it is more reasonable to apply the “1 section test for user optical cables with less than 12 cores”.

Local test of optical splitter

It is not necessary to perform local testing of optical splitters in a project for the following reasons:

(1) The quality of the fiber splitters is good enough, and it is sufficient to perform spot checks on some of the splitter ports during equipment inspection;

(2) If the quality problem of the splitter is discovered after it is installed in the ODN link, it is easy to replace the plc splitter;

(3) The quality problem of the replaced splitter will not be questioned by the fiber optic splitter manufacturer.

It is recommended that Party A make it clear before construction that local testing of the optical splitter is not required in the project.

4. ODN fiber link full-length test

When using primary splitting, the ODN fiber link full-length test is determined by the split ratio and number of newly added splitters. For example, if a 1:64 splitter is added, the “TXL6-137 1:64 fiber link attenuation test 1 link group” is applied.

When using secondary splitting, the ODN fiber link full-length test is determined by the split ratio and number of newly added second-level splitters, regardless of whether the first-level splitters need to be added. For example, in Figure 4, in addition to the 6 pcs 1:8 splitters installed in the 6 fiber distribution boxes, 1 more was added at the wiring optical intersection, and a total of 7pcs 1:8 splitters were added, so the “TXL6-134 1:8 fiber link attenuation test 6 link groups” is applied. 

When secondary splitting is used, whether the first-stage splitter is new or existing, the optical fiber link attenuation from the service aggregation point ODF to the output port of the first-stage splitter should be tested and recorded.

Conclusion

Only fiber links with analog signals need to test return loss, so the sub-item “TXL6-139 Fiber Link Return Loss Test” should not appear in FTTH access projects.

The above is just humble opinion on the application of budget quotas for attenuation test related work in FTTH access projects. If the construction contract or Party A has other provisions for this, the provisions of the contract and Party A should be followed.