ZyXEL Communications Plumbing Product metrogigabit switch User Manual

 Chapter 36 Differentiated Services

MGS3700-12C User’s Guide

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. 

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 172   TRTCM-Color-blind Mode 

Exceed
   PIR?

    

Exceed
   CIR?