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Two-Rate Tricolor Marking, Color-Aware Mode

In color-aware mode, the metering treatment the packet receives depends on its classification. Metering can increase a packet’s preassigned PLP, but cannot decrease it, as shown in Table 45.

Table 45: Color-Aware Mode TCM 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 CIR.	medium-low
		Packet does not exceed the PIR.	medium-low
		Packet exceeds the PIR.	high
medium-high	PIR only	Packet does not exceed the CIR.	medium-high
		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.

Incoming PLP Low

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. Therefore, these packets are metered against both the CIR and the PIR.

For example, if a BA or MF classifier marks a packet with low PLP according to the ToS bits in the IP header, 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 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.

Incoming PLP Medium-Low

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 packet’s PLP unchanged or increase the PLP to high. Therefore, these packets are metered against the PIR only.

For example, if a BA or MF classifier marks a packet with medium-low PLP according to the ToS bits in the IP header, 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 medium-low PLP.
If the rate of traffic flow is greater than the CIR/CBS but less than the PIR, 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.

Incoming PLP Medium-High

For example, if a BA or MF classifier marks a packet with medium-high PLP according to the ToS bits in the IP header, 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 medium-high PLP.
If the rate of traffic flow is greater than the CIR but less than the PIR, 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.

Incoming PLP High

Packets belonging to the red class have already been marked by a classifier with high PLP. The marking policer can only leave the packet’s PLP unchanged. Therefore, these packets are not metered against the CIR or the PIR and all the packets remain marked as high PLP.

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