This is a human-to-human communication protocol used for error correction ie resending missed words and letters!
This usually happens during a telephone conversation where the person on the other side cannot clearly hear you due to noise on the line.
If your telephone cannot hold a normal phone, chances are that things like ADSL will not work or you will have horrible download experience. Causes of noise on the line can be load coils, long distance from the CO or just high voltage across a local loop connection.
Checking the quality of your line will reduce the pain of slow broadband speeds
