Quantum and Evolution Series Installation and Operating Handbook
8-48
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Fair-weighting queuing: higher priority transmitted first but lower priority
packets are given a percentage of the bandwidth to stop total starvation.
The 8 QoS priority levels are mapped to three TCP/IP queues. Packets with highest QoS
priority (level 7) are sent to high priority TCP/IP queue. Delay-sensitive packets (QoS
levels 6 and 5) are sent to the medium priority queue. The remainder (QoS levels 4 to 0)
are sent to the low priority TCP/IP queue. For Strict priority queuing, all packets in high
priority queue are processed before any in medium priority queue which in turn are
processed before any in the low priority queue. For Fair-weighting queuing, for every 4
packets sent from high priority queue, 2 are sent from medium queue and 1 from low
priority queue.
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The following example shows a traffic shaping scheme based on priority tagging.
8.12.9.4.4 MPLS EXP
Stream classification may be based on MPLS QoS, specifically the 3-bit EXP field in the
MPLS header. This is often used to support Diffserv in MPLS networks. The MPLS EXP
field has eight possible values, mapping directly to equivalent internal modem classes (0 to
7) each of which can be shaped using its own CIR, BIR, etc.
