Principles of Synchronous Digital Hierarchy

195Plesiochronous Digital Hierarchy

belonging to B channel is uncertain, and in the third set, the bit sequence has

become 3 2 3 3, meaning that the second bit of the third set has been picked

up from the second bit of B channel instead of the third bit, as in the case of

A, C, and D channels. Thus, the proper sequencing has been lost, and the

channel cannot be identied by the demultiplexer by the position of bits in

the bit stream. (The difference in the bit rate has been exaggerated for the

purpose of illustration. In actual practice, the difference in various E1 rates

will be a few parts per million only; however, it is enough to give us ...