Identifying Callers

When a call completes successfully (the modem detects a valid signal carrier from the other modem), the DUP task uses binary synchronous (BSC) protocols to identify the caller. The DUP task issues ACK or NAK control characters in response to any BSC information received from the modem, until a data buffer is received (indicated by a STX control character). When the call is detected, the DUP task sets a 5 minute timer and waits for a data buffer to arrive.