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Why are FTTH cables divided into multiple cables
Release Date: 2023-01-04

The optical fiber to the home (FTTH) cable line from the office to the customer is generally divided into main section, distribution section, lead-in section and the home section.

Generally speaking, the fewer sections an optical fiber link passes through, the higher the security of the link. Why should FTTH optical fiber lines be divided into so many sections?

1.If the optical fiber link from the office to the user passes through only one section of optical cable (excluding jumper), that is, each user will have a direct cable to the office, as shown in Figure 

2. What is the problem?

There are two main problems. (1) The number of incoming optical cables is large, and the number of incoming optical cables allowed by an office is limited; (2) when the user is installed, the distance of laying optical cable is longer, which is not easy to install.

Restricted by the above two aspects, the maximum number of users allowed to access such an office is only dozens of households, of course, there is no application scenario.

2.To solve the above problems, we made two improvements.

(1) The cable is out of the large number of fiber optic cables, and then the cable connector box is divided into a number of small number of fiber optic cables; Of course, if a cable branch points too much, will affect the cable life and transmission index.

(2) To set up fibre distribution boxes in places where users are concentrated as the dividing point between engineering and loading; When the user is installed, only a small section of optical cable needs to be laid from the fiber distribution box to the user.

It is estimated that the number of service users of an office is 480 ~ 960, with 10 optical cables out of one office, 6 ~ 12 sub-fiber boxes for each optical cable, and 8 users for each sub-fiber box. At this time, from the office to the user of the optical cable line has become two optical cable sections: office ~ sub box, sub box ~ user. Because of the cable junction, the connection relationship of the optical fiber is fixed, and the decay is small, generally do not take the cable connector box as the starting point of the segment.

Compared with Figure 1, the number of service users in Figure 2 has increased several times, but the capacity is still too small. In addition, user development is dynamic, if a location needs to add a fiber box, you need to re-lay the cable from the office.

3.From the comparison of Figure 3 and Figure 2, it can be seen that from the perspective of reducing the number of outgoing optical cables and convenient installation, the capacity of the office can be improved by adding branch points on the optical cable. Optical cable bifurcation point mainly has optical cable handover box (hereinafter referred to as "optical") and connector box 2.

One optical cable can be divided into several optical cables by optical crossing, and the number of diverging cables is mainly limited by the laying conditions of optical cables. The connection relationship between each fiber cable is flexible, but it will increase the loss of active connection and increase the difficulty of fiber core management.

Cable through the connector box can be divided by a small number, generally not more than 6 (1 point 5). The two sides of the connector box generally have cable remaining, if the number of different cables in a connector box is more, the cable will appear messy, not beautiful, as shown in Figure 4; Therefore, in general, the number of different optical cables in a cable connector box will be controlled within 4 (1 point 3).

After adding a cable handover box on the basis of Figure 3, the cable network structure from the office to the user is shown in Figure 5. It is estimated that the number of service users of a handover box is 480 ~ 960 households, with 10 incoming optical cables at the end of one handover box and 6 ~ 12 sub-boxes for each sub-box and 8 users for each sub-box.

So how many optical exchanges can a bureau set up? It is estimated that there are 10 optical cables out of one office and each optical cable is connected to an average of 3 optical intersections. 30 optical intersections can be set. In this way, the capacity of a bureau is about: 14400 ~ 28800 households; This large capacity can basically meet the needs of a large number of scenarios.

4.Construction is always limited by construction conditions. For example, if the optical cable network is to cover a residential district, the optical communication is best set in the residential district. However, when the main optical cable construction is carried out in a bureau, most residential properties will not allow the construction in their residential district. The main cable project has long been completed.

Urban residential communities, commercial buildings, and other cluster markets have uncertain demand for engineering construction, and the construction of main cable must be completed within a certain time (generally in 2 ~ 3 months). In order to solve this contradiction, in the construction of the main optical cable, the main optical intersection is set in the distance from the potential user group, convenient optical cable layout, with installation conditions. When construction conditions are available in residential communities, commercial buildings and other cluster markets, distribution optical communication is installed in these locations, and distribution optical cables from trunk optical communication to distribution optical communication are laid for communication, as shown in Figure 6. In this way, the cable line from the office to the customer is divided into the main section, the distribution section, the incoming section, and the incoming section.

The number of users that can be covered by an office can be further increased by configuring the cable optical communication. How many wiring optical links can be brought under a trunk optical link? Lao Ding Tou thinks 5 ~ 10 is appropriate; If you only take 2 ~ 3 wiring optical intersection, it is better to change the trunk optical intersection into a joint box.

5.At present, the optical fiber to the home (FTTH) optical cable line from the office to the user mainly consists of four sections. However, we should also see that too many sections of optical fiber will deteriorate the quality of optical fiber link and make the connection relationship of optical fiber link complicated.

The separation of trunk optical communication and distribution optical communication is mainly to solve the problem of different construction timing of trunk optical cable and lead-in optical cable. In the scene where the construction timing is not affected, for example, when the coverage of a bureau belongs to the same township or the same residential area, it is of no significance to set trunk optical communication and distribution optical communication separately.

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