LWC Training Corp.
Voice over IP Online Course
Lesson 4 - Quality of Service
When you pick up a telephone, you expect to converse in a clear and understandable way. The ubiquitous public
system telephone network provides this service. A voice over IP system needs to provide the same. Anything less
would provide an excuse to avoid the technology. The public Internet is notoriously haphazard. Watching a web
page stall as it loads is a fine example of the pitfalls of this complex technology. Quality of service is an
issue with Voice over IP and is usually listed as one factor in the slow adoption of the technology. In the case
of VoIP, QoS means that the telephone conversation sounds as close to real life as possible, or at least similar to a conversation over the public telephone network.
This module looks at the factors that affect quality of service for VoIP and then examines the techniques that
may be applied to a VoIP system that can give the users a true high quality telephone experience.
A. QoS factors
B. Bandwidth: Share or restrict
C. Providing QoS
D. Packet Level Techniques for Providing QoS
Review and Final Exercise
Upon completion of this section, students will:
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- Understand what factors influence QoS and how this affects voice quality.
- Appreciate that two approaches can be taken for QoS: restrict the number of sessions to the
available bandwidth or share what bandwidth there is but give priority to services that need
- Know some of the techniques used to provide QoS to VoIP. These include 802.1p, ToS, DiffServ,
RSVP and MPLS.