Digital data communication techniques use asynchronous or synchronous transmission. Asynchronous transmission sends data one character at a time, while synchronous transmission sends data in blocks without start/stop codes. Error detection codes like parity and CRC are added to detect errors, while error correction codes can correct errors by adding redundancy. Line configurations consider topology (star, bus, etc.) and duplex mode (half duplex uses one path while full duplex uses two simultaneous paths).