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Configuring QoS QoS General Overview
OmniSwitch 6600 Family Network Configuration Guide April 2006 page 24-3
QoS General Overview
Quality of Service (QoS) refers to transmission quality and available service that is measured and some-
times guaranteed in advance for a particular type of traffic in a network. QoS lends itself to circuit-
switched networks like ATM, which bundle traffic into cells of the same length and transmit the traffic
over predefined virtual paths. In contrast, IP and other packet-switched networks operate on the concept of
shared resources and best effort routing, using bandwidth as needed and reassembling packets at their
destinations. Applying QoS to packet-switched networks requires different mechanisms than those used in
circuit-switched networks.
QoS is often defined as a way to manage bandwidth. Another way to handle different types of flows and
increased bandwidth requirements is to add more bandwidth. But bandwidth can be expensive, particu-
larly at the WAN connection. If LAN links that connect to the WAN are not given more bandwidth,
bottlenecks may still occur. Also, adding enough bandwidth to compensate for peak load periods will
mean that at times some bandwidth will be unused. In addition, adding bandwidth does not guarantee any
kind of control over network resources.
Using QoS, a network administrator can gain more control over networks where different types of traffic
(or flows) are in use or where network congestion is high. Preferential treatment may be given to individ-
ual flows as required. Voice over IP (VoIP) traffic or mission-critical data may be marked as priority traf-
fic and/or given more bandwidth on the link. QoS can also prevent large flows, such as a video stream,
from consuming all the link’s bandwidth. Using QoS, a network administrator can decide which traffic
needs preferential treatment, and which traffic can be adequately served with best effort.
QoS is implemented on the switch through the use of user-defined policies. The following simplified illus-
tration shows how video traffic may receive priority over email traffic.
The Internet
email server
video feed
Best Effort
OmniSwitch
Sample QoS Setup
OmniSwitch 6648
OmniSwitch 6648
OmniSwitch 6648
OmniSwitch 6648
Prioritization
policy