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Quality of Service in Network

QoS is important to many network applications. Voice/data integration is notpossible 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 lookat some specific examples of how QoS can be used.


-WhatIs QoS?

-QoSBuilding Blocks

-RandomEarly Detection (RED)

-ResourceReservation Protocol (RSVP)

-QoSin Action

What Is Quality of Service (QoS)?

Basically, QoS comprises the mechanisms that give network managersthe 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 voiceover 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 thenetwork to ensure the delivery of mission-critical applications, especially inheavily 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 businessapplications, 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. Multimediaapplications take a lower priority. Bandwidth-consuming applications, such asfile transfers, can receive an even lower priority.

What Is Driving the Needfor QoS?

There are two broad application areas that are driving theneed for QoS in the network:

- Mission-critical applications need QoS to ensure delivery and that theirtraffic is not impacted by misbehaving applications using the network.

- Real-time applications such as multimedia and voice need QoS to guaranteebandwidth and minimize jitter. This ensures the stability andreliability of existing applications when new applications are added.

Voice and data convergence is the first compelling application requiring delay-sensitivetraffic handling on the data network. The move to save costs and add new featuresby converging the voice and data networks--using voice over IP, VoFR, or VoATM--hasa number of implications for network management:

- Users will expect the combined voice and data network to be as reliableas the voice network: 99.999% availability

- To even approach such a level of reliability requires a sophisticatedmanagement 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 managersto 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 applicationsand that other applications get “fair” service, but take a back seatto mission-critical traffic.

It also provides an infrastructure that delivers the service levels needed bynew mission-critical applications, and lays the foundation for the “richmedia” applications of today and tomorrow.

Where Is QoS Important?

QoS is required wherever there is congestion. QoS has been a critical requirementfor the WAN for years. Bandwidth, delay, and delay variation requirements areat a premium in the wide area.
LAN QoS requirements are emerging with the increased reliance on mission criticalapplications 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 intranetsand extranet applications that have placed increased demands on the entire network.

QoS Example

Hopefully this Image provides a little context. It demonstrates a real exampleof how QoS could be used to manage network applications.

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