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Understanding Color-Aware Mode for Two-Rate Tricolor Marking

In color-aware mode, the treatment the packet receives depends on its classification. Marking can increase the preassigned PLP but cannot decrease it

Summary of PLP Changes

Table 1 shows how a packet’s incoming priority can be modified with two-rate marking.

Table 1: Color-Aware Mode Two-Rate PLP Mapping

Incoming PLP

Packet Metered Against

Possible Cases

Outgoing PLP

low

CIR and PIR

Packet does not exceed the CIR.

low

Packet exceeds the CIR but not the PIR.

medium-high

Packet exceeds the PIR.

high

medium-low

PIR only

Packet does not exceed the PIR.

medium-low

Packet exceeds the PIR.

high

medium-high

PIR only

Packet does not exceed the PIR.

medium-high

Packet exceeds the PIR.

high

high

Not metered by the policer.

All cases.

high

The following sections describe color-aware two-rate PLP mapping in more detail.

Effect on Green Packets (Low PLP)

Packets belonging to the green class have already been marked by a classifier with low PLP. The marking policer can leave the packet’s PLP unchanged or increase the PLP to medium-high or high. These packets are therefore metered against both the CIR and the PIR. For example, if a behavior aggregate or multifield classifier marks a packet with low PLP and the two-rate TCM policer is in color-aware mode, the output loss priority is as follows:

  • If the rate of traffic flow is less than the CIR, the packets remain marked as low PLP.

  • If the rate of traffic flow is greater than the CIR but less than the PIR, some of the packets are marked as medium-high PLP and some of the packets remain marked as low PLP.

  • If the rate of traffic flow is greater than the PIR, some of the packets are marked as high PLP and some of the packets remain marked as low PLP.

Effect on Yellow Packets (Medium PLP)

Packets belonging to the yellow class have already been marked by a classifier with medium-low or medium-high PLP. The marking policer can leave the PLP unchanged or increase it to high. These packets are therefore metered against the PIR only. For example, if a behavior aggregate (BA) or multifield classifier marks a packet with medium-low PLP and the two-rate TCM policer is in color-aware mode, the policer assigns output loss priority as follows:

  • If the rate of traffic flow is less than the CIR, the packets remain marked as medium-low PLP.

  • If the rate of traffic flow is greater than the CIR but less than the PIR, the packets remain marked as medium-low PLP.

  • If the rate of traffic flow is greater than the PIR, some of the packets are marked as high PLP and some of the packets remain marked as medium-low PLP.

If a BA or multifield classifier marks a packet with medium-high PLP and the two-rate TCM policer is in color-aware mode, the policer assigns output loss priority as follows:

  • If the rate of traffic flow is less than the CIR, the packets remain marked as medium-high PLP.

  • If the rate of traffic flow is greater than the CIR but less than the PIR, the packets remain marked as medium-high PLP.

  • If the rate of traffic flow is greater than the PIR, some of the packets are marked as high PLP and some of the packets remain marked as medium-high PLP.

Effect on Red Packets (High PLP)

Packets belonging to the red class have already been marked by a classifier with high PLP. Because the policer cannot decrease the PLP, it does not change it, and these packets are not metered against the CIR or the PIR.

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