PXB4330 Datasheet, PDF (47/201 Pages) Infineon Technologies AG – ICs for Communications

PXB 4330
Functional Description
3.1.5 EPD/PPD Handling
These functions can be enabled individually per traffic class. The dynamic flags of these
functions are stored in the connection specific (LCI) table. For both functions, the ABM
looks at the PTI bits of the cells to determine the packet borders of the upper SAR layer.
EPD Threshold Behavior
If the cell fill exceeds an EPD threshold, and EPD is enabled, new packets will not be
accepted but will be discarded completely. Cells belonging to packets which have been
transmitted partially are accepted.
PPD Threshold Behavior
If the cell fill exceeds a PPD (=max) threshold, the next cell is discarded and, if PPD is
enabled, all subsequent cells of the packet are discarded except the last cell. The sub-
sequent cells are discarded even if the cell fill might have dropped below the PPD
threshold in the meantime. The last cell is accepted again to convey the discard informa-
tion to the terminal (cell acceptance is possible only if the queue fill level dropped below
the threshold in the meantime). By checking the CRC-32 checksum of AAL5, the termi-
nal can determine rapidly that cells were lost and can immediately ask for
retransmission. Otherwise, the terminal would need to wait for a time-out.
3.1.6 Global Thresholds
The following global thresholds are provided:
• Global maximum buffer threshold
Cells exceeding the threshold will be discarded
• Global maximum threshold for non-real-time cells
• Global congestion indication threshold for ABR
• Global EPD threshold for GFR CLP1 frames (CLPT bit is false)
If the cell fill reaches a maximum threshold, cells are discarded as long as the overflow
condition prevails. If the cell fill drops below the maximum threshold, the cells are accept-
ed again immediately.
3.1.7 Scheduler Thresholds
For each upstream direction Scheduler, two individual thresholds can be programmed
which are continuously compared by the ABM. The results of all comparisons are pro-
vided bit-mapped into microprocessor registers, so that the external controller can
rapidly check the fill state of the Schedulers. This feature is provided to enhance the
throughput over a switching network by dynamic re-programming of the Scheduler out-
put rates, depending on the actual load. This is more efficient than the static rate
adjustment.
Data Sheet
3-47
09.99