User guide

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XTREME
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9-3
A
PPLICATIONS AND
T
YPES OF
Q
O
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A
PPLICATIONS AND
T
YPES OF
Q
O
S
Different applications have different QoS requirements. The following applications are
ones that you will most commonly encounter and need to prioritize:
• Voice applications
• Video applications
• Critical database applications
• Web browsing applications
• File server applications
General guidelines for each traffic type are given below and summarized in Table 8-1.
Consider them as general guidelines and not strict recommendations. Once QoS
parameters are set, you can monitor the performance of the application to determine if
the actual behavior of the applications matches your expectations. It is very important
to understand the needs and behavior of the particular applications you wish to protect
or limit. Behavioral aspects to consider include bandwidth needs, sensitivity to latency
and jitter, and sensitivity and impact of packet loss.
V
OICE
A
PPLICATIONS
Voice applications typically demand small amounts of bandwidth. However, the
bandwidth must be constant and predictable because voice applications are typically
sensitive to latency (inter-packet delay) and jitter (variation in inter-packet delay). The
most important QoS parameter to establish for voice applications is minimum
bandwidth, followed by priority.
V
IDEO
A
PPLICATIONS
Video applications are similar in needs to voice applications, with the exception that
bandwidth requirements are somewhat larger, depending on the encoding. It is
important to understand the behavior of the video application being used. For example,
in the playback of stored video streams, some applications may transmit large amounts
of data for multiple streams in one “spike,” with the expectation that the end-stations
will buffer significant amounts of video-stream data. This can present a problem to the
network infrastructure, because it must be capable of buffering the transmitted spikes
where there are speed differences (for example, going from Gigabit Ethernet to Fast
Ethernet). Key QoS parameters for video applications include minimum bandwidth,
priority, and possibly buffering (depending upon the behavior of the application).