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Single-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 43.

Table 43: Color-Aware Mode TCM PLP Mapping

Incoming PLP	Packet Metered Against	Possible Cases	Outgoing PLP
low	CBS and EBS	Packet does not exceed the CBS.	low
		Packet exceeds the CBS but not the EBS.	medium-high
		Packet exceeds the EBS.	high
medium-low	EBS only	Packet does not exceed the CBS.	medium-low
		Packet does not exceed the EBS.	medium-low
		Packet exceeds the EBS.	high
medium-high	EBS only	Packet does not exceed the CBS.	medium-high
		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.

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 CBS and the EBS.

For example, if a BA or MF classifier marks a packet with low PLP according to the type-of-service (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 CBS, packets remain marked as low PLP.
If the rate of traffic flow is greater than the CBS but less than the EBS, 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 EBS, 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 EBS 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 CBS, packets remain marked as medium-low PLP.
If the rate of traffic flow is greater than the CBS but less than the EBS, 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 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 CBS, packets remain marked as medium-high PLP.
If the rate of traffic flow is greater than the CBS but less than the EBS, 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 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 CBS or the EBS and all the packets remain marked as high PLP.

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