NO CARRIER

NO CARRIER (capitalized) is a text message transmitted from a modem to its attached device (typically a computer), indicating the modem is not (or no longer) connected to a remote system.
NO CARRIER is a response message that is defined in the Hayes command set. Due to the popularity of Hayes modems during the heyday of dial-up connectivity, most other modem manufacturers supported the Hayes command set. For this reason, the NO CARRIER message was ubiquitously understood to mean that one was no longer connected to a remote system.