Chapter 32: Packet Throttling
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Quality of Service Mechanisms
With the rapid convergence of different types of Internet traffic flows (voice, video, data, gaming, streaming media, and
the like), the various forms of Quality of Service (QoS) mechanisms are being called upon to better manage the bandwidth
that is shared by these various traffic flows.
Proper application of QoS is essential if statistical multiplexing is employed in the network.
Statistical Multiplexing
Statistical multiplexing permits X subscribers (each requiring a bandwidth of W) to share a single channel providing a total
bandwidth T, even if T < XW. On average, this is possible due to the fact that many subscribers are idle for some fraction of
their operating time.
However, in a system that capitalizes on statistical multiplexing, the total bandwidth converging on a link may periodically
exceed the total bandwidth T that can be supported by the link. Under these overload conditions, QoS mechanisms must
make decisions about which packets to drop, which packets to route, and what order to use when routing those successful
packets.
Weighted Random Early Detection and Traffic Policing
Currently, the C4/c CMTS uses a congestion avoidance mechanism known as Weighted Random Early Detection (WRED) in
conjunction with traffic policing, to decide which packets to drop.
Traffic Shaping
Traffic shaping is another QoS mechanism used with the C4/c CMTS. In general, traffic shaping and traffic policing both
accomplish very similar goals. Both mechanisms change the handling of packet streams in a particular service flow to
better match the service for which the customer subscribed. However, the two mechanisms accomplish this task in slightly
different ways.