Chapter 31 Differentiated Services

Two Rate Three Color Marker (TRTCM, defined in RFC 2698) is a type of traffic policing that identifies packets by comparing them to two user-defined rates: the Committed Information Rate (CIR) and the Peak Information Rate (PIR). The CIR specifies the average rate at which packets are admitted to the network. The PIR is greater than or equal to the CIR. CIR and PIR values are based on the guaranteed and maximum bandwidth respectively as negotiated between a service provider and client.

Two Rate Three Color Marker evaluates incoming packets and marks them with one of three colors which refer to packet loss priority levels. High packet loss priority level is referred to as red, medium is referred to as yellow and low is referred to as green. After TRTCM is configured and DiffServ is enabled the following actions are performed on the colored packets:

•Red (high loss priority level) packets are dropped.

•Yellow (medium loss priority level) packets are dropped if there is congestion on the network.

•Green (low loss priority level) packets are forwarded.

TRTCM operates in one of two modes: color-blind or color-aware. In color-blind mode, packets are marked based on evaluating against the PIR and CIR regardless of if they have previously been marked or not. In the color-aware mode, packets are marked based on both existing color and evaluation against the PIR and CIR. If the packets do not match any of colors, then the packets proceed unchanged.

31.2.1 TRTCM-Color-blind Mode

All packets are evaluated against the PIR. If a packet exceeds the PIR it is marked red. Otherwise it is evaluated against the CIR. If it exceeds the CIR then it is marked yellow. Finally, if it is below the CIR then it is marked green.

Figure 151 TRTCM-Color-blind Mode

 

Exceed NO

 

 

Exceed NO

 

 

Low Packet

 

 

PIR?

 

 

 

 

CIR?

 

 

 

Loss

 

 

 

 

 

 

 

 

 

 

 

 

 

YES

 

 

 

 

YES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

High Packet

 

 

 

Medium Packet

 

 

 

 

 

 

Loss

 

 

 

Loss

 

 

 

 

 

 

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MGS-3712/MGS-3712F User’s Guide