Supermicro SSE-G2252 User Manual page 262

SSE-G2252/SSE-G2252P Switches User's Manual
• The PHB label is composed of five bits, three bits for per-hop behavior, 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 green if it doesn't
exceed the committed information rate and committed burst size, yellow if it does
exceed the committed information rate and committed burst size, but not the excess
burst size, and red otherwise.
• 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, C
and E, which both share the common rate CIR. The maximum size of the token
bucket C is BC and the maximum size of the token bucket E is BE.
The token buckets C and E are initially full, that is, the token count Tc(0) = BC and
the token count Te(0) = BE. Thereafter, the token counts Tc and Te are updated CIR
times per second as follows:
• If Tc is less than BC, Tc is incremented by one, else
• if Te is less then BE, Te is incremented by one, else
• neither Tc nor Te is incremented.
When a packet of size B bytes arrives at time t, the following happens if srTCM is
configured to operate in Color-Blind mode:
If Tc(t)-B ≥ 0, the packet is green and Tc is decremented by B down to the
•
minimum value of 0, else
if Te(t)-B ≥ 0, the packets is yellow and Te is decremented by B down to the
•
minimum value of 0,
• else the packet is red and neither Tc nor Te is decremented.
When a packet of size B bytes arrives at time t, the following happens if srTCM is
configured to operate in Color-Aware mode:
If the packet has been precolored as green and Tc(t)-B ≥ 0, the packet is green
•
and Tc is decremented by B down to the minimum value of 0, else
• If the packet has been precolored as yellow or green and if
Te(t)-B ≥ 0, the packets is yellow and Te is decremented by B down to the
minimum value of 0, else
• the packet is red and neither Tc nor Te is decremented.
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