PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
While in the SYNC state, if another cell is received with a valid and correct SN, the RALP
remains in the SYNC state. Otherwise, if an invalid SN is received, the RALP goes to the
INVALID state; or if a valid but incorrect SN is received, the OUT_OF_SEQUENCE state is
entered. All cells received while in the SYNC state are accepted.
While in the INVALID state, four possibilities can occur.
•
If the cell received has an invalid SN, the START state is re-entered and the cell is
dropped.
•
If the cell received has a valid SN and is in sequence with the last valid SN, then a
misinserted cell is detected and RALP returns to the SYNC state, but the cell is dropped to
keep SN integrity because the previous cell has already been sent.
•
•
If the cell received has a valid SN and is equal to SN + 2 with respect to the last valid SN,
then the RALP returns to the SYNC state and the cell is accepted.
Otherwise, if the SN is valid but does not meet any of the previous criteria, then the cell is
dropped and the OUT_OF_SYNC state is entered.
While in the OUT_OF_SEQUENCE state, five possibilities can occur.
•
If the cell received has an invalid SN, the START state is re-entered and the cell is
dropped.
•
If the SN is valid and in sequence with the last valid, in sequence SN, then a misinserted
cell is detected and RALP returns to the SYNC state, but the cell is dropped to keep SN
integrity because the previous cell has already been sent.
•
If the SN is valid and the SN is in sequence with the SN of the previous cell, the RALP
assumes cells were lost; it inserts a number of dummy cells identical to the number of lost
cells, accepts the cell and returns to SYNC. If the number of lost cells is greater than
MAX_INSERT, then no cells are inserted and a forced underrun occurs. If an underrun
occurred when cells were lost, no cells are inserted.
•
•
If the received SN is valid and the SN has a value equal to SN + 2 with respect to the last
SN received in sequence, then the cell is accepted and the RALP returns to the SYNC
state.
And finally, if the SN is valid but does not meet any of the previous criteria, then the cell
is dropped and the RALP enters the OUT_OF_SYNC state.
See Figure 32 on page 51 for the flow of the “Fast SN Algorithm”.
Anytime a cell is dropped, the R_DROPPED_CELLS counter (refer to “R_DROPPED_CELLS
Word Format” on page 161) is incremented and the SN_CELL_DROP sticky bit (refer to “SN_
CELL_DROP” on page 158) is set. Anytime a cell is detected lost, the R_LOST_CELLS counter
(refer to “R_LOST_CELLS Word Format” on page 162) is incremented by the number of lost
ꢄꢉ
PMC [ PMC-SIERRA, INC ]
