This attribute specifies the low priority Early Packet Discard (EPD)
offset for connection queues. On ATM IP FPs a given connection
queue is associated with one of eight emission priorities (EP). These
include six unshaped EPs, one exclusive VBR shaper EP and one
ABR/VBR shaper EP. This attribute specifies the EPD offset for the
exclusive ABR/VBR shaper EP and the last two (lower priority)
unshaped EPs.
This offset is used to derive a connection EPD threshold for a given
Congestion Control (CC) level by subtracting the offset from the
All Packet Discard (APD) threshold at the same CC level. The APD
thresholds are themselves derived from the transmit queue limit.
The EPD threshold only applies to a connection if the
txPacketWiseDiscard feature is requested. The
txPacketWiseDiscard feature can be enabled only if the transmit
queue limit is at least 5.71 times the EPD offset. This ensures that
the derived EPD threshold will never be less than 17.5 % of the
transmit queue limit. If this condition is not satisfied,
txPacketWiseDiscard for the connection will be automatically
disabled.
Due to the above constraint, if the operator wishes to decrease the
transmit queue limit and still have txPacketWiseDiscard enabled on
the connection then this offset must be set to a lower value that
meets the above requirement.
Due to hardware granularity the actual value of the EPD offset may
not match exactly the value provisioned. The actual value is
displayed under the ATM Connection Administrator service
category subcomponents on ATM IP FPs.
This attribute does not apply to CQC FPs.