CHAPTER 10. QoS
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Traffic Policing
Policing controls the traffic by dropping packets or marking down their
priority when the configured profile is exceeded. Shaping controls the traffic
by delaying packets using a queuing mechanism when they arrive faster than
the configured rate. Therefore shaping can smooth out the burstiness in a flow,
helping to minimize buffer overruns in intermediate routers. Policing does not
smooth out bursts, but it can control bursts by dropping packets or marking
them down.
Since shaping delays packets, thereby throttling the packet rate instead of
dropping them, adaptive applications(those using TCP) perform better.
Dropping packets can cause exponential back off of TCP, which can adversely
affect the throughput. This problem with policing can be minimized by
configuring the burst parameter of the policer to be a sufficiently large value.
Policing has the advantage of providing low latency since it does not queue
packets. This makes policing a good choice for interactive and streaming
voice and video applications. Policing also uses much less resources in the
router than shaping. It is a better method to provide QoS for incoming traffic
on an interface.
In the iBG2016 system, policing can be enabled in both the ingress and egress
directions, on the WAN interfaces, MAN interfaces, FE interfaces and the GE
interfaces on the main board. For LAN GE interfaces, traffic policing will be
done in hardware. The policing feature can be more appropriately described as
‘Class Based Policing’. Traffic Policing can be enabled individually for each
traffic class that defines a flow. This includes any inbound or outbound ‘leaf’
class created on an interface. Policing can be enabled in either srTCM or
trTCM mode.
The supported policing features in software enables to rate limit the traffic
corresponding to micro flow, aggregate flow, or behavior flow. For example,
VLAN ID based policing can be enabled on ingress traffic by configuring
traffic class with VLAN ID is the classification key and setting appropriate
policing parameters for traffic class. Similarly for application-based rate
limiting, configuring traffic class with application identifier as a classification
key and configuring policing parameters for traffic class can achieve rate
limiting.
Summary of Contents for Ubigate iBG2016
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