Quality Of Service (Qos) - Siemens optiPoint 410 entry Administrator's Manual

Technical Overview

Quality of Service (QoS)

Modern networks can be used to provide various Qualities of Service to
network endpoints based upon the importance of the endpoint and its
generated traffic. Quality of Service is a term used to describe this catago-
risation of network traffic in networks based on the importance of the data
and the treatment of that prioritized traffic.
A typical example of use of QoS in a network is that of an IP Phone. Tele-
phone Voice traffic is more important that for HTTP related traffic for a PC.
Prioritization of voice traffic over that of the HTTP traffic means that during
periods of heavy network load that voice service is maintained, whereas
the response times for a user's Web Broweser will degrade and possibly
stop working.
Quality of Service can be supported in networks at both Layer 2 and Layer
3. At Ethernet layer 2 the MAC header is extended to provide VLAN infor-
mation and Quality of Service priorities. Ethernet layer 2 allows for prioriti-
sation of traffic from 0 (lowest) to 7 (highest). At the layer 3, the IP layer
traffic can be prioritized using information embedded in the IP Type of ser-
vice (DiffServ) field that allows for 64 levels of prioritization.
To utilize Quality of Service features the network infrastructure (switch fab-
ric) must support prioritized delivery of traffic based on layer 3 and/or layer
2.
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