Configuring QoS Traffic Policing and Shaping
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 26-23
The TCM policier meters each packet and passes the metering result along with the packet to the Marker.
Depending upon the result sent by the Meter, the packet is then marked with either the green, yellow, or
red color. The marked packet stream is then transmitted on the egress based on the color-coded priority
assigned.
The TCM Meter operates in Color-Blind mode (the Color-Aware mode is not supported). In the Color-
Blind mode, the Meter assumes that the incoming packet stream is uncolored.
There are two types of TCM marking supported:
• Single-Rate TCM (srTCM)—Packets are marked based on a Committed Information Rate (CIR) value
and two associated burst size values: Committed Burst Size (CBS) and Peak Burst Size (PBS).
• Two-Rate TCM (trTCM)—Packets are marked based on a CIR value and a Peak Information Rate
(PIR) value and two associated burst size values: CBS and PBS.
Both srTCM and trTCM operate in the same basic manner, as shown in the above diagram. The main
difference between the two types is that srTCM uses one rate limiting value (CIR) and trTCM uses two
rate limiting values (CIR and PIR) to determine packet marking.
The type of TCM used is determined when the policier is configured; depending on which rates and burst
size values are configured, TCM functions in ether single-rate or two-rate mode. There is no explicit
command to select the type of TCM. See “Configuring Tri-Color Marking” on page 26-24 for more
information.
Based on the TCM type used, packets are marked as follows:
TCM Type Meter Compliance Marker Color Result
Single-Rate
(srTCM)
Packet is CIR/CBS compliant. GREEN Packet is transmitted with the Drop
Precedence set to LOW.
Packet is not CIR/CBS
compliant but is CIR/PBS
compliant.
YELLOW Packet is transmitted with the Drop
Precedence set to HIGH (packet is
dropped first when congestion
occurs on the egress queue.
Packet is neither CIR/CBS nor
CIR/PBS compliant.
RED Packet is dropped at the ingress.
Two-Rate
(trTCM)
Packet is CIR/CBS compliant. GREEN Packet is transmitted with the Drop
Precedence set to LOW.
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