Explanation : A half-duplex (HDX) system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying (antennas are of trans-receiver type in these devices, so as to transmit and receive the signal as well).
A full-duplex (FDX), or sometimes double-duplex system, allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex, since they allow both callers to speak and be heard at the same time, the transition from four to two wires being achieved by a hybrid coil. A good analogy for a full-duplex system would be a two-lane road with one lane for each direction
Explanation : Bit stuffing is required when there is a flag of bits to represent one of the incidents like start of frame, end of frame, etc, If same lag of bits appear in the data stream, a zero can be inserted. The receiver deletes this zero from the data stream.