Hybrid Mode - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Hybrid Mode

926
This mode, which is a combination of the bandwidth-guarantee and bandwidth-protection
modes, enables the capabilities of bandwidth restriction and the per-flow bandwidth
moderation to be accomplished simultanouesly. Bandwidth-guarentee or
bandwidth-restriction mode controls the guaranteed rates for a given micro-flow.
However, it does not adminster or manage the manner in which the excess aggregate
bandwidth can be shared among the micro-flows. A certain micro-flow can potentially
use all the excess aggregate bandwidth starving the other micro-flows of any excess
bandwidth.
Bandwidth-protection or peak mode controls the amount of bandwidth that a particular
micro-flow can consume, thereby protecting other flows from being starved. However,
it does not specify any guaranteed rates for the micro-flows. For example, if micro-flow
rates for flows f1, f2 and f3 are 50 Mbps, 60 Mbps, 50 Mbps respectively, and the aggregate
rate is 70 Mbps, it is possible that f1 and f2 flows might be provided 50 Mbps and 20
Mbps respectively, with no bandwidth allocated for f3.
Hybrid mode implements the benefits of the peak and guaranteed modes to overcome
their individual limitations. In hybird mode, the micro-flow policer specifies two rates,
CIR and EIR, for the micro-flow. The CIR specifies the guaranteed portion out of the total
macro-flow bandwidth for a micro-flow, and the PIR specifies the maximum portion of
the total macro-flow bandwidth for a micro-flow. This mechanism is analogues to CIR
functioning in guarantee mode and EIR functioning in peak mode, thereby combining the
advantages of both models. In hyrbid mode, both color-aware and color-blind modes
are supported for child policers.
Child policers operate in compliance with the RFC 4115 mode of two-rate three color
markers. Normal two-rate three color markers on ACX routers operate in compliance
with the RFC2698 mode.
Consider a sample configuration in which the maximum allowed rate for a user is 140
Mbps. A total of four services or applications called expedited forwarding (EF), Gold,
Silver and Bronze are defined for the hybrid mode of the policer with PIR values of 55Mbps,
60 Mbps, 130 Mbps, and 140 Mbps respectively. The defined CIR values are 50 Mbps, 40
Mbps, 30 Mbps, and 20 Mbps for EF, Gold, Silver, and Bronze services respectively. For
example, when 140 Mbps of traffic is received for each of the four services, then the
permitted green-colored traffic is 50, 40, 30 and 20 Mbps respectively for the four services.
If only 140 Mbps of EF traffic is received, 50 Mbps of EF traffic as green and 5 Mbps of
EF traffic as yellow are permitted. In the same scenario, assume the macro-policer rate
to be 26 Mbps. Also, assume two child policers in color-aware mode, namely, child
policer-1 with a CIR of 10 Mbps and an EIR of 10 Mbps. Child policer-2 has a CIR of 15
Mbps and an EIR of 5 Mbps. When flow-1 is a 100 Mbps stream of yellow traffic, and
flow-2 is an 100 Mbps stream of green traffic, the output of this policer hierarchy is as
follows:
Flow-1 has 0 Mbps of green traffic and has less than or equal to 5 Mbps of yellow traffic.
Flow-2 has 10 Mbps of green traffic and has greater than or equal to 10 Mbps of yellow
traffic.
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