REIN (short for Repetitive Electrical Impulse Noise) is a term applied to some interference found on problematic broadband connections. The interference can be detected as electrical impulses on the physical telephone line on which the internet connection operates.
REIN can cause interference with modems and routers, which in turn causes errors to mount up, eventually leading to the loss of synchronisation.
REIN is often caused by faulty electrical equipment in the vicinity of the broadband line and/or router. Usually the equipment is emitting a radio frequency which causes electrical impulses along the telephone line carrying the broadband service.
The cause of the REIN can be traced by using a directional radio frequency analyser, as the source of the REIN is often broadcasting the interference on 612 kHZ (AM).