This type of event is signalled with a DLE message, which is a single-character message preceded by a Data Link Escape code. DLE is a character sent from the modem to the computer whose definition is unrelated to either command or data mode, and which uses a specific ASCII code (0x10) which never occurs in any AT commands or responses, so that it can be isolated from the command/response stream on that merit alone. In these modes, whenever a DLE (0x10) is sent, the character following it has a special non-command and non-data meaning. For example, a DLE followed by the number 2 means the caller pressed the number 2 on his telephone keypad. This could happen in either command or data mode so long as the phone line is in use by the modem and someone is on the other end of the line.