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JUNOSe 11.1.x Policy Management Configuration Guide
Table 10: TCP-Friendly One-Rate Rate-Limit Profile Algorithms (continued)
Two-Rate Rate-Limits Overview
The two-rate rate limiter enables you to build tiered rate-limit services and to specify
different treatments for packets at different rates.
Token buckets control how many packets per second are accepted at each of the
configured rates and provide flexibility in dealing with the bursty nature of data
traffic. At the beginning of each sample period, the two buckets are filled with tokens
based on the configured burst sizes and rates. Traffic is metered to measure its
volume. When traffic is received, if tokens remain in both buckets, one token is
removed from each bucket for every byte of data processed. As long as tokens are
still in the committed burst bucket, the traffic is treated as committed.
When the committed burst token bucket is empty but tokens remain in the peak
burst bucket, traffic is treated as conformed. When the peak burst token bucket is
empty, traffic is treated as exceeded.
In color-blind mode, if the committed token bucket has enough tokens when a packet
is received, the packet is green and tokens are subtracted from both the committed
and the peak token buckets. If the peak bucket does not have enough tokens left, it
is allowed to go negative. Green packets are the committed traffic.
If the committed bucket does not have enough tokens for the packet, the peak bucket
is tested (and the committed bucket is not changed). If there are enough tokens in
the peak bucket, it is decremented and the packet is yellow. Yellow packets are the
conformed traffic. If the peak bucket does not have enough tokens either (because
the committed bucket did not have enough tokens), the packet is red. Red packets
are the exceeded traffic.
The two-rate rate-limit profile attributes are:
86
Two-Rate Rate-Limits Overview
Step
If CD < Extended Burst
If CD >= Extended Burst
If incoming packet color is (only occurs in
color-aware operation)
ATM cell mode ATM cell tax accounted for in statistics and rate calculations
Color-aware Color-aware rate action (only for hierarchical rate limits)
Committed rate Target rate for a packet flow
Committed burst Amount of bandwidth allocated to accommodate bursty traffic
in excess of the committed rate
Result
Packet is colored yellow
T(t) is decremented by B (allow T(t) < 0, if
necessary)
Packet is colored
CD is reset to 0
Packet is colored red
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