Receive Atm Function - NEC UPD98413 User Manual

CHAPTER 3 FUNCTIONAL OUTLINE

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.
8 2
G (X) = X + X + X + 1
Figure shows the status transition of cell synchronization by means of header error control.
Figure 3-17. Cell Synchronization Status Transition
Hunting status
(HUNT)
No HEC error
HEC error
α
times in row
HEC error
Preceding synchronization status
(PRESYNC)
Cell synchronization status
HEC without error
(SYNC)
δ
times in row
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