QUESTION: Can we generally claim that PDH links deals with synchronization transfer only if we abuse some bandwidth on a low hierarchy as DS1 or E1 for the sync derivation (that is not being used for traffic transfer simultaneously as well)?
ANSWER: You are correct in observing that PDH multiplexing preserves the tributary clock (of the DS1) by ensuring that there is adequate extra bandwidth available (for example, at the DS2 level) and using bit-stuffing techniques to "fill" this extra bandwidth. These stuff bits are unavailable for traffic transfer. The entire bandwidth of the tributary (of the DS1) is preserved and none "stolen" from the DS1 for frequency adjustment purposes.
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