Samsung Ubigate iBG3026, Configuration Manual

Page: 219 / 718

Ubigate iBG3026 Configuration Guide/Ed.00
© SAMSUNG Electronics Co., Ltd.
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Policing Using Single Rate Three Color Marking
(srTCM)
The srTCM algorithm uses single rate CIR, and two burst sizes, i.e., CBS, and
EBS. The srTCM will be implemented using two token buckets, i.e., Tc of
size CBS, and Te of size EBS. A packet is ‘colored’ green if it doesn't exceed
the CBS, yellow if it does exceed the CBS but not the EBS, and red otherwise.
Coloring is just a means to convey the conformance level of packets.
An action can be configured for each color. The supported actions include:
Permit, Mark DSCP value and Drop.
The srTCM works as follows. Let the token buckets be represented by Tc(t)
whose maximum capacity is CBS bytes, and Te(t) whose maximum capacity
is EBS bytes. One token is the equivalent of one byte. Tc(0) is equal to CBS,
and Te(0) is equal to EBS. Thereafter tokens are replenished as follows. If Tc
< CBS then Tc is incremented by CIR bytes-per-second up to CBS else if Te <
EBS then Te is incremented by CIR bytes-per- second up to EBS.
When packet of size B bytes arrives for policing, if Tc(t)-B >= 0, then the
packet is marked green(transmit) and Tc is decremented by B else if Te(t)-B
>= 0 then packet is marked yellow and Te is decremented by B else packet is
marked red. This mode of operation is the default mode and is known as
color-blind mode.
In the color aware mode, packet is assumed to be pre-colored. In this case
when packet of size B bytes arrives for policing, if Tc(t)-B >= 0 and packet
color is green, then the packet color is unchanged(transmit) and Tc is
decremented by B else if Te(t)-B >= 0 and packet’s color is green then the
packet is marked yellow and Te is decremented by B else if packet color is
green or yellow, then the packet is marked red.