Content

| Overview

Increasingly data networks are being called upon to support communications for traffic with varied delivery requirements. Previously an organization used separate networks for voice, video, and data traffic. It is now common practice to combine these into a single multiservice network in which the varied traffic types coexist. There are many circumstances where these Quality of Service (QoS) requirements have not been met or even addressed at a rudimentary level:

- The long delay in speech transmission when calling by way of an international satellite link
- Stop-start and choppy Internet streaming video performance
- Harsh audio when using an Internet-based IP phone
- Messenger applications are all examples of inadequate QoS

For many applications such as file and print services, Internet browsing, email and peer-to-peer messaging products, the “best effort” delivery attempts of the Internet and many corporate networks may be adequate. However, for organizations seeking to integrate their voice and data networks using Voice over IP (VoIP), IP telephony or high quality streaming video for corporate communications, it is essential that QoS be built into the design of the network.

In order to provide QoS within a network it is critical to have an understanding of the network characteristics that make up quality of service and the QoS requirements of the varied traffic and applications using the network. Once application and traffic requirements can be stated in QoS terms, classification techniques are used to identify streams of traffic as having a particular QoS requirement. For example, a standard access-list could be used to identify a user who requires priority access to the network resources. Once traffic has been classified into classes of service, there are many scheduling and congestion management techniques that can be used to provide the desired service characteristics. The key to effective QoS design is knowing how these techniques operate and the benefits and limitations of each.