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Understanding Color-Aware Mode for Single-Rate Tricolor Marking

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

Summary of PLP Changes

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

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

Incoming PLP

Packet Metered Against

Possible Cases

Outgoing PLP

low

CIR, CBS, and EBS

Conforming

low

Packet exceeds the CIR and CBS but does not exceed the EBS.

medium-high

Packet exceeds the EBS.

high

medium-low

EBS only

Packet does not exceed the EBS.

medium-low

Packet exceeds the EBS.

high

medium-high

EBS only

Packet does not exceed the EBS.

medium-high

Packet exceeds the EBS.

high

high

Not metered by the policer.

All cases.

high

The following sections describe single-rate color-aware 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 PLP unchanged or increase it to medium-high or high, so these packets are therefore metered against both the CBS and the EBS. 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, packets remain marked as low PLP.

  • If bursts exceed the CBS but not the EBS, some of the packets are marked as medium-high PLP, and some of the packets remain marked as low PLP.

  • If bursts exceed the EBS, 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, so these packets are therefore metered against the EBS only. For example, if a behavior aggregate or multifield classifier marks a packet with medium-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 CBS, the packets remain marked as medium-low PLP.

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

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

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

  • If the rate of traffic flow is greater than the EBS, some of the packets are marked as high PLP and some 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 CBS or the EBS.

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