Lesson
10: Understanding Quality of Service
QoS is important to many network applications. Voice/data
integration is not possible without. Nor is effective multimedia…
or even VPNs. In this module, we’ll discuss what QoS
is and some of its building blocks. Will also look at some
specific examples of how QoS can be used.
The
Agenda
- What
Is QoS?
- QoS
Building Blocks
- QoS
in Action
What Is Quality of Service (QoS)?
Basically, QoS comprises the mechanisms that
give network managers the ability to control the mix of bandwidth,
delay, variances in delay (jitter), and packet loss in the
network in order to deliver a network service such as voice
over IP; define different service-level agreements (SLAs)
for divisions, applications, or organizations; or simply prioritize
traffic across a WAN.
QoS provides the ability to prioritize traffic and allocate
resources across the network to ensure the delivery of mission-critical
applications, especially in heavily loaded environments. Traffic
is usually prioritized according to protocol.
So what does this really mean...
An analogy is the carpool lane on the highway.
For business applications, we want to give high priority to
mission-critical applications. All other traffic can receive
equal treatment.
Mission-critical applications are given the right of way at
all times. Multimedia applications take a lower priority.
Bandwidth-consuming applications, such as file transfers,
can receive an even lower priority.
What Is Driving the Need for QoS?
There are two broad application areas that
are driving the need for QoS in the network:
- Mission-critical applications need QoS to ensure delivery
and that their traffic is not impacted by misbehaving applications
using the network.
- Real-time applications such as multimedia and voice
need QoS to guarantee bandwidth and minimize jitter. This
ensures the stability and reliability of
existing applications when new applications are added.
Voice and data convergence is the first compelling application
requiring delay-sensitive traffic handling on the data network.
The move to save costs and add new features by converging
the voice and data networks--using voice over IP, VoFR, or
VoATM--has a number of implications for network management:
- Users will expect the combined voice and data network
to be as reliable as the voice network: 99.999% availability
- To even approach such a level of reliability requires
a sophisticated management capability; policies come into
play again
So what are mission critical applications?
Enterprise Resource Planning (ERP) applications
- Order entry
- Finance
- Manufacturing
- Human resources
- Supply-chain management
- Sales-force automation
What else is mission critical?
- SNA applications
- Selected physical ports
- Selected hosts/clients
QoS Benefits
QoS provides tremendous benefits. It allows
network managers to understand and control which resources
are being used by application, users, and departments.
It ensures the WAN is being used efficiently by the mission-critical
applications and that other applications get “fair”
service, but take a back seat to mission-critical traffic.
It also provides an infrastructure that delivers the service
levels needed by new mission-critical applications, and lays
the foundation for the “rich media” applications
of today and tomorrow.
Where Is QoS Important?
QoS is required wherever there is congestion. QoS has been
a critical requirement for the WAN for years. Bandwidth, delay,
and delay variation requirements are at a premium in the wide
area.
LAN QoS requirements are emerging with the increased reliance
on mission critical applications and the growing popularity
of voice over LAN and WAN.
The importance of end-to-end QoS is increasing due to the
rapid growth of intranets and extranet applications that have
placed increased demands on the entire network.
QoS Example
Hopefully this Image provides a little context. It demonstrates
a real example of how QoS could be used to manage network
applications.
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