Edge-Core ECS4810-12M Layer 2 Management Manual page 264

| Quality of Service
C 12
HAPTER
Creating QoS Policies
information rate (PIR), and their associated burst sizes – committed burst
size (BC, or burst rate), and peak burst size (BP). Action may taken for
traffic conforming to the maximum throughput, exceeding the maximum
throughput, or exceeding the peak burst size.
The PHB label is composed of five bits, three bits for per-hop behavior,
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and two bits for the color scheme used to control queue congestion. In
addition to the actions defined by this command to transmit, remark
the DSCP service value, or drop a packet, the switch will also mark the
two color bits used to set the drop precedence of a packet for Random
Early Detection. A packet is marked red if it exceeds the PIR. Otherwise
it is marked either yellow or green depending on whether it exceeds or
doesn't exceed the CIR.
The trTCM is useful for ingress policing of a service, where a peak rate
needs to be enforced separately from a committed rate.
The meter operates in one of two modes. In the color-blind mode, the
◆
meter assumes that the packet stream is uncolored. In color-aware
mode the meter assumes that some preceding entity has pre-colored
the incoming packet stream so that each packet is either green, yellow,
or red. The marker (re)colors an IP packet according to the results of
the meter. The color is coded in the DS field [RFC 2474] of the packet.
The behavior of the meter is specified in terms of its mode and two
◆
token buckets, P and C, which are based on the rates PIR and CIR,
respectively. The maximum size of the token bucket P is BP and the
maximum size of the token bucket C is BC.
The token buckets P and C are initially (at time 0) full, that is, the token
count Tp(0) = BP and the token count Tc(0) = BC. Thereafter, the token
count Tp is incremented by one PIR times per second up to BP and the
token count Tc is incremented by one CIR times per second up to BC.
When a packet of size B bytes arrives at time t, the following happens if
trTCM is configured to operate in Color-Blind mode:
If Tp(t)-B < 0, the packet is red, else
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if Tc(t)-B < 0, the packet is yellow and Tp is decremented by B, else
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the packet is green and both Tp and Tc are decremented by B.
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When a packet of size B bytes arrives at time t, the following happens if
trTCM is configured to operate in Color-Aware mode:
If the packet has been precolored as red or if Tp(t)-B < 0, the
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packet is red, else
if the packet has been precolored as yellow or if Tc(t)-B < 0, the
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packet is yellow and Tp is decremented by B, else
the packet is green and both Tp and Tc are decremented by B.
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