Ferrite bead in cable or in device?
Ferrite beads around a cable raise the impedance for common mode signals. That is the main reason that they are external to any device, on the cable.

Common mode signals can be present on differential pairs and in this case a common mode choke inside a device would suffice. But common mode signals can just as well be present on e.g. the ground signal towards the cable. In that case only a bead around the whole cable section will help.

And in case you are not aware: only a few microvolts  of common mode signal suffice to violate EMC compliance rules in case they are present on a cable. This is because the device ground (e.g. metal case or PCB GND plane) in combination with the cable combine to an almost perfect antenna.