How To Deploy New Optical Cables In Crowded Underground Communication Pipes?

As a communication infrastructure resource, communication pipelines play an important role in today's rapid development of information and communication networks. The scale of operators' communication networks continues to expand, and the development of communication services continues to diversify. In particular, the growing demand for optical cable resources for new services represented by 5G has gradually revealed the shortage of existing network resources, which is reflected in the communication pipelines as pipe holes. There is a shortage of resources, so how to deploy new optical cables?

The "pipe hole occupancy rate" indicator measures the usage of pipe hole resources in a certain pipeline segment. At present, the pipe hole occupancy rate of many roads exceeds 90%, and some road sections even reach 100%. It is difficult to add new optical cables to the existing pipe holes, and it is urgent to reduce the pipe hole occupancy rate of existing pipelines. Here are some ways to reduce tube hole occupancy.

1. Use Textile Sub-tubes

The pipe group combination of underground communication pipelines generally includes some single-hole pipes with an inner diameter of about 100mm or 90mm. When laying optical cables in a single-hole tube, multiple plastic sub-tubes should be laid to improve tube hole utilization. Four 32mm/28mm sub-tubes are usually placed in a single-hole tube with an inner diameter of 100mm, and an optical cable is placed in each sub-tube. In this way, four optical cables can be placed in a single-hole tube with an inner diameter of 100mm.

However, in this case, the cross-sectional utilization rate of the single-hole tube (Σ cable cross-sectional area/single-hole tube cross-sectional area) is too low, only about 10%. In order to make full use of pipe hole resources. Textile sub-tubes are usually soft, ribbon-shaped sub-tubes sewn from polyester and nylon mesh that have a low coefficient of friction and contain a traction rope.

The textile sub-tubes that are put through at one time are called a belt. Each textile sub-tube has 3 different combinations, one with 1 hole, one with 2 holes, and one with 3 holes, which can accommodate 1, 2, and 3 optical cables respectively. The use of textile sub-tubes can increase the number of optical cables laid in each single-hole tube several times, thereby correspondingly reducing the tube hole occupancy rate. The tensile strength of textile sub-tubes exceeds 1000kg, which is several times that of ordinary pipe optical cables. Directly laying or removing the optical cable in the tube hole of the existing optical cable will easily cause damage to the optical cable. If the textile sub-tube is laid out first and then the optical cable is threaded through the textile sub-tube, it is easier to implement and will not cause damage to the optical cable.

However, the application of textile sub-tubes faces the following problems: (1) The price is high; (2) When laying out optical cables in single-hole tubes, the sub-tubes are often not laid out, but the cables are directly superimposed, so the use of textile sub-tubes cannot Increase the number of optical cables that the tube hole can carry. This is also the reason why textile sub-tubes have not been widely used across the country.

2. Use Microtubes And Microcables

Under the condition that air blown fiber optic cables are easy to lay, replace and manage, compared with laying ordinary optical cables, the solution of manually laying HDPE pipe for fiber optic cable in urban pipelines and then blowing the microcables through HDPE multi ducts has a better tube hole occupancy rate. It can be reduced by nearly 1 times compared with laying general cables. Micro cables need to be laid by air blowing, and construction is required to have relevant equipment, such as air blowing machines, micro duct Bundle,micro duct connecter, micro tube distribution closures, etc. For more information about air-blown microcables, please read “How Air Blown Fiber System Can Contribute To Urban Expansion?”.

3. Use Compact Fiber Optic Cables

Compact optical cable is a high-density optical cable whose mechanical properties meet the requirements of ordinary optical cables, but whose outer diameter is much smaller than ordinary optical cables with the same number of cores. Unlike microcables, compact fiber optic cables can be laid like regular fiber optic cables and do not need to be laid in specific microducts. For the same type of optical cable, the "minimum allowable tensile force" index is mainly proportional to the cross-sectional area of the optical cable. In order to achieve the lowest tensile performance of ordinary optical cables, the minimum outer diameter of compact optical cables is usually equivalent to that of ordinary optical cables, about 9.5mm. The minimum number of cores of compact optical cables is usually not less than 96 cores. Taking the GYTA 144-core optical cable from a major optical cable manufacturer as an example, the cross-sectional area of the compact optical cable is only 40.5% of that of ordinary optical cables.

Comparison Of Compact And Ordinary Optical Cable Cross-sections

Due to the small cross-sectional area, the use of compact optical cables in single-hole tubes can reduce the tube hole occupancy rate by more than 50%. For example, usually each porous tube can be mixed with about 10 ordinary optical cables of various outer diameters. If the large-core optical cable is a compact optical cable, each porous tube can be mixed with more than 20 hybrid optical cables with various outer diameters.

4. Incorporate Small Core Count Optical Cables

Multiple small-core optical cables terminated at the same location (the same or adjacent ODF, the same optical exchange) and the same route. If these optical cables are at the same optical cable level, multiple small-core optical cables can be merged into one large-core cable. Count optical cables to reduce pipe hole occupation. The optical cable layer here refers to: core layer, backbone aggregation layer, ordinary aggregation layer, as well as base station access, trunk section, distribution section, introduction section, etc. of the access layer. If the starting point, end point and routing of optical cables at different levels are the same, it will also Merging is possible.

Combined Small Core Count Optical Cable Diagram

The number of cores of small-core optical cables is relative to the number of cores of new optical cables, and there are no strict core number requirements. However, from the perspective of controlling project investment, the number of cores of a single dismantled optical cable should not exceed 48 cores. Among the currently laid optical cables, 24 cores and below account for more than 60%. Even if 10% of them can be merged, it can greatly alleviate the current shortage of pipe hole resources.

5. Reduce The Length Of New Optical Cables By Reusing Existing Optical Cable Cores

Although the occupancy rate of existing tube holes is very high, the fiber core utilization rate of in-use optical cables is very low. For example, the overall optical cable core utilization rate in a certain area of operator M (Σ In-use fiber core/Σ In-use optical fiber core ) is only 27.7%, while the overall optical cable core utilization rate of operator T in the same area exceeds 50%. Operator M can reduce the laying length of optical cables by making a little use of the spare fiber cores of existing optical cables, thus Reduce the occupation of pipe hole resources.

For example, current customer access usually lays 12-core optical cables directly from the transfer box (or computer room) to customer users. Since each user actually needs only 1 to 2 cores, this leads to the loss of the fiber core of the customer access optical cable. Usage is too low. When new inbound users are added, if only 2 to 4 cores are allocated to the users and multiple users share one optical cable, the core utilization rate of inbound access optical cables can be greatly improved.

In the figure below, the numbers in collection point 1 to collection point 5 indicate the time sequence for collection point users to place installations. In Figure B, when Inbound customers 2 to Inbound customers 5 are placing installations, only the optical cables from the joint box to collection point users need to be laid.

Summarize

Newly added optical cables use compact optical cables or Direct Buried tube bundle or air blow fiber, which can reduce the occupation of remaining pipe hole resources by optical cables. However, as more and more new optical cables are added, if the original optical cables in the pipe group are not sorted out, the pipe group will eventually remain will be filled. Therefore, for sections with high pipe hole occupancy rates, before adding new optical cables, the original optical cables should be properly reconnected and adjusted to ensure that after the new optical cables are added in this phase of the project, there will still be a certain number of vacant sub-holes in the pipe group.

For sections where the tube hole occupancy rate reaches 100%, textile sub-tubes can be laid out through the gaps in the original tube holes, and then compact optical cables with large core numbers can be laid out from the textile sub-tubes, and the original multiple small-core optical cables can be merged. , and then add optical cables after freeing up pipe hole resources. Through these methods, the efficiency of underground pipeline resource utilization can be improved.

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