QUESTION:
What are the implications of this calculation?
ANSWER:
In SONET multiplexing, frequency offsets are accommodated by a method referred to as "pointer adjustments". In essence, data is considered not in bits but in octets (bytes). In the OC-1 case, when the accumulated movement is equivalent to 1 octet (8 bits) a pointer event is initiated. This implies that either one octet in the overhead section is actually data (information), called "positive justification", or one octet in the payload section is "don’t care", referred to as negative justification. The impact on the traffic being carried in the payload is a abrupt phase change of 8 bits (~160 nsec at OC-1) and this translates to jitter and wander in the traffic signal post-demultiplexing. In the STM-1 case (STM-1 is like OC-3), each pointer movement involves 3 octets at a time ( 24 bits at OC-3 is about 8 bits at OC-1 or ~160 nsec).
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