Past exam of the computer science course of the University of Oxford / 2015 / Computer networks / 1 / b

In differential Manchester encoding, every data bit still has a compulsory transition at its midpoint for clock recovery. The data value is specified by whether a transition occurs at the beginning of the bit, rather than by the direction of the midpoint transition. One convention is beginning transition for zero and no beginning transition for one; interchanging the meanings consistently also works.

Reversing the signal polarity exchanges high and low everywhere, but preserves both the presence and the absence of transitions. A receiver using differential Manchester encoding therefore decodes the same data after a polarity reversal, provided it has acquired the timing and boundary reference. Ordinary Manchester encoding with a fixed low–high/high–low interpretation would exchange the two data values. The advantage is