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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 1 Overview
What is the Quality of Service Toolset?
Call Admission Control
After performing the calculations to provision the network with the required bandwidth to support voice,
video and data applications, it's important to ensure that voice or video do not oversubscribe the portion
of the bandwidth allocated to them. While most QoS mechanisms are used to protect voice from data,
Call Admission Control (CAC) is used to protect voice from voice (and video from video).
CAC is illustrated in
Figure 1-17
, which shows an environment where the network has been provisioned
to support only two voice calls. However, if a third voice call is attempted, the quality of all calls will
degrade.
Figure 1-17 Call Admission Control--Protects Provisioned Bandwidth for Voice from Voice
Tip
A detailed discussion of CAC is not in the scope of this document, but it is and important consideration
in successful AVVID rollouts. The details of CAC are covered in the "Call Admission Control" chapter
of the IP Telephony Solution Reference Network Design Guide.
Management Tools
Implementing a QoS solution is not a one-time task that is complete upon policy deployment. A
successful QoS deployment is followed by ongoing monitoring of service levels and periodic
adjustments and tuning of QoS policies, as shown in
Figure 1-18
.
IP
IP
IP
IP WAN
81032
V
M
IP WAN link provisioned for 2 VoIP calls
CAC limits number of VoIP calls on each WAN link
No physical limitation on IP links.
If third call accepted, voice quality
of all calls degrades.
CallManager
IP WAN
link
Router/
Gateway