Ever wondered what the small boxes placed by the phone company around your neighborhood are for? Here's an explanation.

In neighborhoods with underground phone lines, as opposed to overhead wiring on poles, these small boxes are commonly seen scattered throughout the area. Typically, one box is located for every two or three houses. In the southeastern United States, a common sight might look like this:

These boxes generally stand about two or three feet (around a meter) tall and are approximately 8 inches (20 cm) wide and square in shape.

For those familiar with the HSW article 'How Telephones Work,' you’ll know that each phone line to your home consists of a pair of copper wires. However, the thick underground cables running through your neighborhood can hold anywhere from 25 to 50 pairs of copper wires. The small green box is where the cable emerges from the ground, allowing a phone company worker to splice into it. Here’s what one looks like during construction, near a new subdivision:

The installation is straightforward. The cable’s outer sheath is stripped off to expose the wires, and several pairs are spliced for the homes that share the box (the clear plastic blocks are the splices). Two-pair cables then run underground to connect the houses. In some cases, the splicing setup may be more intricate, with a plastic or ceramic plate and a junction block instead of direct splices.

So, where does the 25-pair or 50-pair cable originate? If you explore your neighborhood, you might come across a larger box that looks like this:

This box stands around 4 to 5 feet (1.5 meters) tall. A larger cable with hundreds of wire pairs passes through here, with one or more 25-pair or 50-pair cables branching off. Inside the box, there’s a large punch-down panel where phone company technicians connect each smaller cable pair to the corresponding larger cable pairs.

The larger cable often begins at a box like this one:

This box is approximately 6 feet (2 meters) tall and 12 feet (4 meters) wide. On the right, you can spot its power meter, indicating it has its own power source, unlike the smaller boxes that only contain passive splices. Inside this powered box, digitizers convert the pairs from each house so that phone calls in the area are transmitted using a much smaller set of wires. This box can also handle larger lines, such as T1 or T3 lines, which carry voice data, with digitizers breaking down multiplexed lines into individual pairs. These multiplexed lines might travel along the road as copper, fiber optic, or coaxial cables.

Eventually, the multiplexed lines reach a switch, which could look something like this:

This structure has no windows and is roughly 50 feet (15 meters) on each side. For more information on what happens at the switch, refer to Question 354!