Structure of the Telephone User Network
Sections of the User Network
The user network is divided into three main parts: the main network, the distribution network, and the dispersion network.
The user network encompasses the path from the central plant’s main distribution point until the connection reaches the user’s telephone equipment. These stages are:
- Outdoor Line: This section covers the path from the central terminal to the distribution box. This connection typically uses high-capacity cables. The outdoor line is further divided into two sections: power cables and distribution cables.
- Dispersion Network Attack Line: This is the single cable connecting the terminal with the Primary Termination Point (PTR) box located at the user’s home.
Power Network (Main Distribution)
The power network consists of cables, usually of high capacity, starting from the central wire gallery. It branches throughout the service area and terminates at the side.
The side is the point where the cable leaves the base of a pole, using conduits or underground cables to extend outward.
In small towns, the power cable installation is entirely aerial, stapled to fronts or supported by lines of posts.
In larger towns, due to urban planning requirements and the large size of the cables, it is often necessary to use underground conduits, especially near the central plants where there is a greater concentration of pairs.
An advantage of underground installation is the ability to install, replace, or repair cables without extensive trenching.
Underground conduits for the main lines are interspersed along small routes, separated by no more than 200m, and accessible from the street via structures known as access chambers (or manholes). These chambers are where wires are spliced with others, where loading coils are installed, and from where access to the side is provided. The entire set of power cables is called the feeding network.
Distribution Cables
The main lines branch out into the access chambers, leading through lateral conduits. These connect to external cables, which may be smaller, running on pole lines or stapled inside building walls. This entire set of cables constitutes the distribution network.
These distribution cables branch further, ending at interconnection organs that physically cut the conductors coming from the central office.
The interconnection organs are terminal boxes for a small number of pairs and connection boxes for a larger number of pairs, often located inside buildings.
Dispersion Network Attack Line
This is the single cable that connects the interconnection body with the PTR at the entrance of the user’s home.
For outdoor installations—whether via walls, aerial lines, or underground pipes—various types of service entrance cables are used to suit the environmental conditions (e.g., mesh-protected cable for rodent protection in pipelines, high-strength bimetallic rush for facades and aerial facilities). In all cases, the service entrance cable is coated in special black plastic to protect the internal conductors from temperature and humidity changes without affecting their electrical characteristics.
All these final connection lines form what is called the dispersion network or connection network.
Cable Terminal
The cable terminal is located in the gallery of the power cables, linking the main distribution cables.
It may consist of wire pairs, with capacities ranging between 5 and 1200 pairs, using a 0.5 mm gauge, and reinforced plastic casings.