Why is FTTH divided into multiple optical cables

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

Generally speaking, the fewer optical cable sections an optical fiber link passes through, the higher the security of the link. Why is the FTTH optical cable line divided into so many optical cable sections?

If the optical fiber link from the office to the user only passes through one optical cable section (excluding fiber jumpers), that is, a direct optical cable is directly laid out from each user to the office.

There are two main problems here. (1) The number of optical cables entering the office is large, and the number of incoming optical cables that can be allowed by one office is limited; (2) The distance for laying the optical cables when the user installs is long, which is inconvenient for installation.

Due to the limitations of the above two aspects, the maximum number of users that such an office can allow access to is only a few dozen, and of course there is no application scenario.

fiber to the home

In order to solve the above problems, we have made two improvements:

(1) Optical cables with large core counts are used for outgoing optical cables, and then branched into multiple small-core optical cables with optical cable splice boxes; of course, if an optical cable has too many divergence points, it will affect the life and transmission indicators of the optical cable.

(2) Set up a fiber distribution box at a location where users are concentrated, as the demarcation point between engineering and installation; when users place and install, they only need to lay a short section of optical cable from the fiber distribution box to the user.

Assuming that there are 10 optical cables out of an office, 6 to 12 fiber distribution boxes are set up for each optical fiber cable, and 8 users are placed in each fiber distribution box, the number of users served by one office is 480 to 960. At this time, the optical cable line from the office to the user has become two optical cable segments: the office to the fiber distribution box, and the fiber distribution box to the user. Since the connection relationship of the optical fibers is fixed at the optical cable joint, and the attenuation is small, the optical cable joint box is generally not used as the starting point of the segmentation.

The number of service users has increased several times, but the capacity is still too small. In addition, the development of users is dynamic. If a fiber distribution box needs to be added at a certain location, the optical cable needs to be re-laid from the office.

From the perspective of reducing the number of outgoing optical cables and facilitating placement and installation, increasing the capacity of the office can be achieved by adding branch points on the optical cables. The divergence points of optical cables mainly include two types of optical cable junction boxes (hereinafter referred to as "optical junctions") and splice boxes.

An optical cable can be branched into multiple optical cables through optical crossover, and the number of branched optical cables is mainly limited by the laying conditions of the optical cables; the connection relationship between the optical cables is flexible, but it will increase the loss of the active connection and increase the fiber optic cable. Difficulty in core management.

The number of optical cables that can be branched through the splice box is small, generally no more than 6 (1 point 5). There are generally remaining optical cables on both sides of the splice box. If there are many different optical cables in a splice box, the optical cables will appear messy and unsightly, as shown in Figure 4; therefore, under normal circumstances, an optical cable joint The number of split optical cables in the box will be controlled within 4 (1 point 3).

Optical cable network structure from office to user. It is estimated that a junction box has 10 drop optical cables at each end, each drop cable is equipped with 6 to 12 fiber distribution boxes, and each fiber distribution box is placed with 8 users.

So how many optical crosses can be set in one office? It is estimated that there are 10 optical cables out of one office, and each optical cable is connected to 3 optical crosses on average, and 30 optical crosses can be set. In this way, the capacity of a bureau is about 14,400 to 28,800; such a large capacity can basically meet the needs of many scenarios.

Project construction is always limited by construction conditions. For example, if the optical cable network is to cover a residential area, it is best to set up the optical communication in the residential area. However, when constructing the backbone optical cable of a bureau, most residential properties will not. It is allowed to carry out construction in their community, and when the market department negotiates the construction conditions with a certain community, the trunk optical cable project has already been completed.

The demand for engineering construction in residential quarters, commercial buildings, and other cluster markets in the city is uncertain, and the construction of trunk optical cables must be completed within a certain period of time (usually within 2 to 3 months). In order to solve this contradiction, during the construction of the trunk optical cable, the trunk optical cross-connection should be set up in a location that is close to the potential user group, convenient for optical cable laying and installation conditions. When the residential quarters, commercial buildings, and other cluster markets are ready for construction, the distribution optical cross-connects are installed in these locations, and the distribution optical cables from the trunk optical cross-connection to the distribution optical cross-connection are laid out for communication, as shown in Figure 6. In this way, the optical cable line from the office to the user is divided into as shown in Figure 1: the trunk section, the distribution section, the lead-in section and the home section.

The setting of wiring optical communication can further increase the number of users that the office can cover. So how many wiring optical switches can be brought under a trunk optical switch? Lao Dingtou thinks 5 to 10 are suitable; if only 2 to 3 wiring optical switches are carried, it is better to change the trunk optical switch into a splice box Woolen cloth.

At present, the fiber-to-the-home (FTTH) fiber optic cable line from the office to the user is mainly a 4-segment structure as shown in Figure 1, but we should also see that too many segments of the fiber optic cable will make the quality of the fiber optic link worse, making the fiber optic The connection relationship of the link becomes complicated.

The main purpose of separating the trunk optical cross and the distribution optical cross is to solve the problem of different construction timing of the trunk optical cable and the drop optical cable. The construction timing is not affected, such as when the coverage of a bureau belongs to the same town or the same residence It does not make sense to set up the trunk and distribution optical crosses separately.