8.10 QoS Support

When we defined the term VPN in Section 8.1, we said that a VPN is defined by a set of administrative policies that control both connectivity and Quality of Service (QoS) among sites. In this section we look at the mechanisms that a service provider would use to implement the QoS aspects of the policies. This section uses material from both Chapter 6 and Chapter 7.

In the area of QoS, the challenge is to develop a set of mechanisms that supports QoS in a way that is flexible enough to support a wide range of VPN customers and scalable enough to support a large number of VPN customers. For example, a service provider should be able to offer its VPN customers multiple Classes of Service per VPN, where different applications within the same VPN would receive different Classes of Service. This way, for example, email would get one Class of Service while some real-time application could get a completely different Class of Service. Moreover, the Class of Service that a particular application would get within one VPN could be quite different from the Class of Service that precisely the same application would get within another VPN. That is, the set of mechanisms in support of QoS should allow the decision about what traffic gets a specific Class of Service to be made on a per-VPN basis. Moreover, not all VPNs have to use all the Classes of Service that a VPN service provider offers. Therefore, the...