Write a note on Error-Detection Codes?

Answer 1

To make sure all the frames are delivered to the receiver in proper order a protocal calls for the receiver to send back special control frames bearing positive and negative acknowledgements about the incoming frames.If the sender receives a positivev acknowledgement it is termed that the frames have reached safely on the other hand if is negative the frame must be transmitted again. There are chances that due to hardware problems (i.e noise burst) some frames may get vanished. In this case, the protocol waiting for the acknowledgement, would hang forever. To nullify this effect a timer is introduced. When the sender transmits a frame it also starts the timer. The timer is set to go off long enough for the frame to reach the destination, be processed there, have an acknowledgement propagate back to the sender. If either the frame or the acknowledgement is lost the timer goes off automatically alerting the sender to transmit the frame again. Sequence numbers are provided to the frames so that the receiver can distinguish if the frames are repeated again.