pxf4336 Infineon Technologies Corporation, pxf4336 Datasheet - Page 73

• Manufacturer Part Number: pxf4336
• Description: Abm Premium Atm Buf Fer Manager
• Manufacturer: Infineon Technologies Corporation

ABM-P
PXF 4336 V1.1
Functional Description
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-P 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.
The Buffer Manager attempts not to corrupt a packet, once it has accepted the first cell.
This means that for EPDen=1, the maximum thresholds TrafClassMax, SBMax and
QueueMax are disabled for the rest of the packet. Only the thresholds BufMax,
BufMaxNg and QueueLimit can corrupt an accepted packet.
Partial Packet Discard (PPD)
Under the rare circumstances described at the end of the previous section, it may
happen that a cell is discarded from within a packet although the EPD algorithm has
accepted it. In this case it is meaningful to discard also all following cells of the packet.
However, the last cell of a partially discarded packet should be buffered if possible, since
the reassemble mechanism at the receiver is triggered by the last cells of user data
packets. This mechanism is referred to as Partial Packet Discard (PPD).
In packet discard mode, if at cell arrival the related cell counter exceeds this threshold,
and the exceeding cell is not an end of packet or an OAM cell, then the cell is discarded
and the flag DiscardRestOfPacket is enabled in the LCI table. All subsequently arriving
cells of the packet, excluding the last cell of the packet, are discarded without taking into
consideration the cell counter.
Data Sheet
73
2001-12-17