TABLE OF CONTENTS Operators of carrier-scale IP networks are faced with the constant challenge of providing a consistent service in the most cost-effective way while dealing with rapid network expansion and traffic growth, the introduction of new services, and the deployment of new technologies.
This is particularly challenging for networks that offer quality of service (QoS). Such networks support a wide range of application with very different requirements on performance. They enable customers to prioritise their applications according to performance and business need byoffering multiple classes of service with different targets on delay and throughput, backed by service level agreements (SLAs) or service level guarantees (SLGs). For example, voice applications should be assigned to a high priority class to ensure the low delay and loss that is necessary for a satisfactory call quality. On the other hand, Web browsing and e-mail are usually considered to be lower priority and tolerate a 'best-effort' service.
Since businesses are increasingly moving towards one IP-based platform for all their applications, there is a growing demand for IP quality of service, particularly in enterprise networks and IP virtual private networks (VPNs). The latter provide the customer with a highly flexible and secure corporate IP network between geographically dispersed sites via a shared and managed infrastructure.
The underlying mechanisms that enable service differentiation in an IP network gave already been discussed in Chapter 4. However, the QoS mechanisms on their own do not guarantee that contracted performance levels are delivered. That chapter highlighted...
