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Using the Autosense Mechanism
How Adaptive Mode Works
Copyright © 2010, Juniper Networks, Inc.
bandwidth map contains a set admission-bandwidth or set admission-bandwidth
adaptive action for that (S,G).
QoS adjustment is performed on the joining interface when an OIF is added to the mroute
for a given (S,G) data stream and the multicast bandwidth map contains a set
qos-bandwidth or set qos-bandwidth adaptive action for that (S,G).
You can prioritize the traffic by configuring a priority value for the <S, G> data stream on
a physical port by issuing the set priority command. Dynamic multicast admission control
enables only prioritized groups to join the interface after the configured priority limit is
reached on the physical port. The system records the priority when a new <S, G> entry
is created. For more information, see "Enabling Port Admission Bandwidth Control" on
page 28 .
NOTE: You can create a single route map with the set admission-bandwidth
command, the set qos-bandwidth command, or both. However, creating an
entry with only one of these set commands enables only that specific function
for the matched address (that is, only multicast traffic admission control or
only QoS adjustment). The same is true for the adaptive commands.
Video bandwidth is typically considered to be a constant rate—2 Mbps for standard
definition television (SDTV) and 10 Mbps for high definition television (HDTV). However,
in reality, and depending on achievable video compression, the bit rate can vary. For
example, HDTV streams (using MPEG4 or WM9 encoding) can vary between 6 Mbps
(for low-action programs) to 10 Mbps (for a fast-paced, high-action programs). The
autosense mechanism causes the bandwidth value, used for admission control and QoS
adjustment, to be the actual measured rate of the stream. Using this feature to measure
the actual bandwidth avoids the need to configure arbitrary bandwidth limits and enables
a channel to be reassigned to a different (S, G) without requiring a bandwidth map to
be changed.
You configure the auto-sense mechanism in the multicast bandwidth using the set
admission-bandwidth adaptive command, set qos-bandwidth adaptive command, or
both. For example:
host1(config)#route-map mcast-bandwidths permit 10
host1(config-route-map)#match ip address sdtv
host1(config-route-map)#set admission-bandwidth adaptive
host1(config-route-map)#set qos-bandwidth adaptive
host1(config-route-map)#end
In this example, any stream with an (S,G) that matches the sdtv access list performs
adaptive bandwidth detection for admission control and QoS adjustment.
A rate measurement mechanism runs on the ingress line card that polls the forwarding
controller (FC) to obtain statistics for each mroute. This mechanism then reports the
rate measurement to the SRP to update the bandwidth map. By computing the average
Chapter 1: Configuring IPv4 Multicast
11
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