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Chapter 4 QoS in an AVVID-Enabled Wide-Area Network
QoS Toolset
Figure 4-1
WAN Infrastructure
QoS Toolset
The challenges of packet loss, delay, and delay variation can be addressed through the application of
various QoS tools.
This section provides information about the use of QoS tools in WAN environments. For general
information about the QoS Toolset, see the
Classification
In a WAN environment, classification is generally DSCP-based. NBAR can also be used for
classification within the WAN. For information on these two tools, see the
.
Provisioning
With respect to provisioning tools in a WAN environment, special consideration should be given to the
following:
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Policers and Shapers
The principle drawback in strict traffic policing is that TCP will retransmit dropped packets and will
throttle flows up and down, until the all the data is sent (or the connection times-out). Such TCP ramping
behavior results in inefficient use of bandwidth (both over-utilizing and under-utilizing the WAN links).
Because shaping usually delays packets rather than dropping them, it smooths flows and allows for more
efficient use of WAN bandwidth. Therefore, shaping is more suitable in the WAN than policing. This is
especially in the case with NBMA WAN media where physical access speed can vary between two
endpoints, such as Frame Relay and ATM (as shown in
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