QUESTION:
What attributes determine the data rate of 148.608Mbits/s that are derived from SONET OC-3 parameters?
ANSWER:
In SONET there is the notion of a "frame" that is 125 microseconds in duration. The SONET assembly in a frame can be viewed as (for OC-3) a rectangular array of width 270 octets and height 9 lines (9x270=2430 octets in a frame) (hence 155.52 Mbps).of the 270 octets, 9 are relegated to overhead and 261 for payload. Therefore the payload bit rate for OC-3 is, nominally, 150.336 Mbps. The actual traffic signals are first resynchronized using the SONET clock using bit-stuffing mechanisms that also require some overhead. That is why the "information" data rate is 148.608 Mbps.
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