Owner's Manual

360 | Chapter 15. QoS
NETGEAR 8800 User Manual
• Voice Applications on page 360
• Video Applications on page 360
• Critical Database Applications on page 360
• Web Browsing Applications on page 360
• File Server Applications on page 361
Voice Applications
Voice applications, or voice over IP (VoIP), 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 the
network 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 and priority, and possibly buffering
(depending upon the behavior of the application).
Critical Database Applications
Database applications, such as those associated with Enterprise Resource Planning (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.
Web Browsing Applications
QoS needs for Web browsing applications cannot be generalized into a single category. For
example, ERP applications that use a browser front-end might be more important than
retrieving daily news information. Traffic groupings can typically be distinguished from each
other by their server source and destinations. Most browser-based applications are
distinguished by the dataflow being asymmetric (small dataflows from the browser client,
large dataflows from the server to the browser client).
An exception to this might be created by some Java
™
-based applications. In addition,
Web-based applications are generally tolerant of latency, jitter, and some packet loss;
however, small packet loss might have a large impact on perceived performance because of
the nature of TCP. The relevant parameter for protecting browser applications is minimum
bandwidth. The relevant parameter for preventing non-critical browser applications from
overwhelming the network is maximum bandwidth.