PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
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Each AAL1 cell is either 46 or 47 bytes, depending upon whether or not the cell contains a
structure pointer.
2.8.2 Peak Cell Rates (PCRs) for Unstructured Cell Formats
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PCR ≤ 4,107 cells per second for T1 (assuming 47 bytes for each AAL1 cell).
PCR ≤ 5,447 cells per second for E1 (assuming 47 bytes for each AAL1 cell).
PCR ≤ 118,980 cells per second for T3 (assuming 47 bytes for each AAL1 cell).
PCR ≤ 91,405 cells per second for E3 (assuming 47 bytes for each AAL1 cell).
If all lines are at the same rate, the aggregate PCR ≤ 53,191 cells per second for
multiple-line unstructured data format (assuming 47 bytes for each AAL1 cell). If all lines
are not at the same rate, the aggregate PCR ≤ 46,542.
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PCR ≤ 1,000 cells per second for OAM cells. This rate of OAM cells is calculated on the
basis of up to four cells per second per VC. Transmitting and receiving OAM cells at this
rate consumes 20% of the microprocessor accesses.
2.8.3 Peak Cell Rates and Partial Cells
Partial Cells can be used to minimize the amount of delay required to assemble a cell. However,
the amount of overhead required for the same amount of TDM data increases when partial cells
are used. This overhead increases as the number of data bytes per cell decreases. The following
equations can be used to determine the PCR when partial cells are used.
First, the maximum average cell generation time (MACGT) is calculated. The MACGT value is
equal to the maximum average number of cycles to generate a cell, times the length of the clock
cycle. Second, the maximum average cell generation time is multiplied by the number of cells
required per second to give the total cell generation time (TCGT).
The following equations are given for different modes of operation. Each equation is calculated
on a per-queue basis. If all the queues are configured the same, then the total for a queue can be
multiplied by the number of queues. Otherwise, the sum of the calculations for each queue needs
to be totaled. The sum must be less than one. The following variables are used:
K = # of data bytes per cell
N = number of timeslots assigned to queue
L = length of clock cycle
NOTE: If OAM cells are used, add the following equation for the OAM cells:
TCGT
= 212 × L × (maximum number of OAM cells per second)
OAM
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PMC [ PMC-SIERRA, INC ]
