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122 Summit 300-48 Switch Software User Guide
Quality of Service (QoS)
Summit 300-48 switches support up to four physical queues per port.
NOTE
As with all Extreme switch products, QoS has no impact on switch performance. Using even the most
complex traffic groupings has no cost in terms of switch performance.
Applications and Types of QoS
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 40. 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.
Voice Applications
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.
Video Applications
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 can 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).
Critical Database Applications
Database applications, such as those associated with ERP, typically do not demand significant
bandwidth and are tolerant of delay. You can establish a minimum bandwidth using a priority less than
that of delay-sensitive applications.