User guide
9-4 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
Q
UALITY
OF
S
ERVICE
(Q
O
S)
C
RITICAL
D
ATABASE
A
PPLICATIONS
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.
W
EB
B
ROWSING
A
PPLICATIONS
QoS needs for Web browsing applications cannot be generalized into a single category.
For example, ERP applications that use a browser front-end may 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 may 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 may have a large impact on perceived performance due to
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. In addition, RED
may be used to reduce session loss if the queue that floods web traffic becomes
over-subscribed.
F
ILE
S
ERVER
A
PPLICATIONS
With some dependencies on the network operating system, file serving typically poses
the greatest demand on bandwidth, although file server applications are very tolerant of
latency, jitter, and some packet loss, depending on the network operating system and
the use of TCP or UDP.
Full-duplex links should be used when deploying policy-based QoS. Half-duplex
operation on links can make delivery of guaranteed minimum bandwidth
impossible.
Tab le 9-1 summarizes QoS guidelines for the different types of network traffic.