Configure the ATM 2 EPD Threshold

By default, the ATM 2 PIC allows PVCs to consume all the buffers they require. If the sustained traffic rate for a PVC exceeds its shaped rate, buffers are consumed. Eventually, all buffers on the PIC are consumed, and the other PVCs are starved. This results in head-of-line blocking.

For each PVC, you prevent this situation by configuring the early packet discard (EPD) threshold of the PVC. The EPD threshold is a limit on the number of transmit packets that can be queued. Packets that exceed the limit are discarded.

To set the EPD threshold of a PVC, include the epd-threshold statement at the [edit interfaces interface-name unit logical-unit-number] or [edit interfaces interface-name unit logical-unit-number family family address address multipoint-destination destination-address] hierarchy level:

epd-threshold cells; 

For one-port and two-port OC-12 interfaces, the allowable range is 1 through 425,984 cells. For two-port OC-3 interfaces, the allowable range is 1 through 212,992 cells.

You should include the epd-threshold statement in the configuration of all the PVCs that you configure on an ATM 2 PIC. The epd-threshold statement performs two functions:

• It prevents head-of-line blocking because it limits the number of packets and therefore buffers that can be consumed by each configured PVC.
• It sets the maximum lifetime that can be sustained by packets over the PVC when traffic has oversubscribed the configured shaping contract.

Example: Configure the ATM 2 EPD Threshold

Configure the EPD threshold for a point-to-point ATM 2 interface and a point-to-multipoint ATM 2 interface.

On a point-to-point ATM 2 interface

[edit interfaces at-1/0/0]

unit 0 {

    vci 0.123;

    epd-threshold 1300;

    ...

}

On a point-to-multipoint ATM 2 interface

[edit interfaces at-1/0/1]

unit 0 {

    multipoint;

    family inet address 12.12.12.12/24 {

        multipoint-destination 12.12.12.14 vci 0.123 epd-threshold 1300;

        ...

    }

}