CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
NEC confidential and Proprietary
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3.2.2 Receive ATM function
(a) Cell synchronization
Cell synchronization is used to identify a cell boundary and extract an ATM cell from the bit string accommodated
in the SPE payload area. The cell boundary is identified by using the header error control (HEC) area for a cell
header. The position of a cell is identified by checking CRC calculation of a bit string accommodated in the SPE
payload area, shifting the bit string one byte at a time, to check the point at which the syndrome becomes 0. The
following polynomial expression is used for this purpose.
G (X) = X
8
+ X
2
+ X + 1
Figure shows the status transition of cell synchronization by means of header error control.
Figure 3-17. Cell Synchronization Status Transition
Cell synchronization status
(SYNC)
Hunting status
(HUNT)
Preceding synchronization status
(PRESYNC)
No HEC error
HEC error
HEC without error
δ
times in row
HEC error
α
times in row
Summary of Contents for NEASCOT-P65
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