This is not a direct answer, but a few observations that might be clues.
- The additional pictures help, but you still haven't answered where this is. The purpose of the question was to get some idea of how formally things are done in your area.
This pictures show a mess, hinting at this being some third world location where seemingly anyone can hang stuff from the utility poles. That makes it harder to narrow down.
- The boxes are definitely not on the power lines. They are on telephone, internet, cable TV, or similar communication lines.
- The boxes look deliberate and orderly enough that they seem to be put there by the company owning the particular communication line. These are not bootleg taps for stealing cable TV, for example.
- Picture 4 clearly shows the cable looping thru the box, but not in a way that implies just a splice. That means these boxes are in-line with whatever signal pass thru them.
- Here is a crop of the 4th picture with the detail written on the box. This picture is flipped upside down since that seems to be the orientation of the writing. Maybe this means something to someone familiar with your area (wherever that is):
My guess based on the above is that the boxes are some kind of repeaters. Any signal degrades over distance in a cable. These boxes are probably at regular intervals. That interval is short enough that the signal can still be received intact. The boxes do so, recover the bits, then repeat them with restored amplitude, clean edges, and de-jittered.
The DC power to run the boxes is either included in the cable separately, or there is a DC bias added to the signals just for this purpose.