Why Implement Qos - Avaya P580 User Manual

Chapter 25

Why implement QoS?

Purpose of QoS
Prerequisites
Implementation
Example
25-2
In a network that has time-sensitive traffic (VoIP) or bandwidth-intensive
traffic (real-time or near-real-time streaming-video), QoS makes it possible
for you to prioritize the time-sensitive traffic and assign larger amounts of
bandwidth to those applications that require it.
VoIP traffic has relatively low bandwidth requirements, but cannot tolerate
latency or frame loss. Therefore, this traffic needs a high priority to ensure
its timely delivery. On the other hand, streaming video is bandwidth-
intensive but has large "jitter buffers" so can tolerate some latency. Thus,
you can assign streaming video traffic a lower priority than voice, but must
assign streaming video more bandwidth than voice.
To successfully implement QoS, you must have a thorough knowledge of
the traffic patterns in the network. You need this information to:
Classify traffic and assign it the required priority and bandwidth.
Identify the areas of the network where bottlenecks might occur and
that therefore need bandwidth limiting.
Identify the areas of the network where time-sensitive traffic is
being delayed and needs to be prioritized better.
An example of managing QoS across the network is to define traffic classes
and manage these on a network-wide basis. The four classes and their
priorities might look like those outlined in
* Note: For information about DSCP (DiffServ Code Point), see
"Diffserv" later in this chapter.
Table 25-1. Examples of Classes of Service
Service Class Priority
Highest Priority 7
Time Sensitive 5
Traffic
High Priority 1
Data
Best Effort 0
User Guide for the Avaya P580 and P882 Multiservice Switches, v6.0
Table 25-1.
DSCP Type of Traffic
Value
56 Network Management
Traffic, OSPF, Spanning
Tree, etc.
40 Real-time voice, video
conferences.
8 SAP, Web, etc. Dependent
upon your business.
0 Everything else.