How to limit the speed or access to the Internet by influencing the cable from the outside?

Question

Burglary protection

How can you disrupt the transmission of data (signals) over a cable, both copper and fiber, influencing it from the outside without violating its integrity? Maybe something like a ferrite ring or some kind of coil

Answer 1

There are definitely no optics, there are two states: either there is a signal or not.
Copper 5e is a big question. I only know on 100Mbps channels that with bad connections (that is, when there are many errors), the cable starts to fall off or the duplex is turned off, as well as the transition to 10Mbps.
If “magic-hypothetical” coils existed, they caused such a panic. Because I didn’t particularly notice the speed loss with a 110m cable (I remind you that this is the limit), and at the same time, the cards on both sides were 150 rubles in total. Issued on the torrent as usual 95-98Mbps

Answer 2

With copper, it is quite simple - to introduce interference. It can be an electric discharge, you can induce current with an external magnetic field (wind the solenoid around a piece of cable). Thus, affect the very medium of propagation of an electrical signal, up to the failure of network equipment.
With optics, such a number will not work. It can be done mechanically, but no one would guess. Bending or longitudinal rotation (glass strongly dislikes longitudinal rotation deformations). Mice and rats can also spoil the optics quite well - this is a headache for FOCL installers.