PXF4333 Datasheet, PDF (68/361 Pages) Infineon Technologies AG – ABM 3G ATM Buf fer Manager

ABM-3G
PXF 4333 V1.1
Functional Description
The following maximum fill thresholds are available:
BufMax, and QueueLimit are determined by physical limits.
BufMaxNg, SBMax, TrafClassMax, QueueMax are configured per traffic class.
3.4.1.6.2 Selective CLP1 Discard
Selective discard is based on the CLP marking found in the arriving cells and is enabled
by the CLP transparency flag (CLPT) stored per connection in the LCI table.
In cell discard mode, the mechanism triggers tail drop for CLP=1 cells only. In this mode,
the mechanism is used to limit the buffer space provided for the non-guaranteed part of
VBR.2/.3 traffic.
In packet discard mode, the mechanism triggers EPD for CLP=1 frames only. According
to the GFR conformance definition, a CLP1 frame is assumed when the first cell of the
frame is a CLP1 cell. In this mode, the mechanism is used mainly for the GFR service.
The following discard thresholds are available to control selective CLP1 discard:
BufCiCLP1, SBCiCLP1, QueueCiCLP1.
Note: There is no selective CLP1 discard threshold available for the traffic class view.
3.4.1.6.3 Packet Discard
Packet discard mechanisms rely on the AAL5 End Of Packet (EOP) indication in the PTI
field of the cell header. The ABM-3G implements two packet discard mechanisms:
• Early Packet Discard (EPD)
• Partial Packet Discard (PPD).
Packet discard can be enabled individually per traffic class by setting the flags EPDen
and PPDen in the TCT respectively. The dynamic status of an ongoing packet discard is
stored per connection in the fields LastCellOfPacket, DiscardPacket and DiscardRestOf-
Packet in the LCI table.
Both mechanisms are provided to avoid or reduce the volume in the transmission of
corrupted packets and therefore improve utilization of buffer and bandwidth resources.
Early Packet Discard (EPD)
The Early Packet Discard (EPD) mechanism drops all cells of a packet if it decides to
drop the first cell of that packet. In packet discard mode, if at cell arrival the related cell
counter exceeds this threshold, and the flag LastCellOfPacket is enabled in the LCI
table, indicating that the arriving cell is the first cell of a packet, then the cell is discarded
and the flag DiscardPacket is enabled in the LCI table. All subsequently arriving cells of
the packet are discarded without taking into consideration the cell counter.
EPD may only be applied to non real-time connections. The mechanism is enabled by
the software configurable flag EPDen, specified per traffic class in the TCT.
Data Sheet
68
2001-12-17