MPLS-Enabled Applications: Emerging Developments and New Technologies

8.8. QoS IN A VPN SCENARIO

From a QoS point of view, a BGP/MPLS VPN has to provide at least the same guarantees as a private network. Because it is sold as a premium service with QoS guarantees, the customer expectations from the QoS performance of a BGP/MPLS VPN are high.

As seen in the Traffic Engineering chapter (Chapter 2), QoS guarantees can be readily translated into bandwidth requirements. The question is, how are these requirements expressed? When discussing bandwidth requirements, two conceptual models exist:

1. Pipe model. A pipe with certain performance guarantees exists between two specific VPN sites. Therefore, the customer must know the traffic matrix and must translate it into a set of pipes that meet these requirements. For example, for a VPN where branch offices connect to a central site, the amount of traffic between each branch office and the central site must be known. This approach is difficult to implement in practice because the traffic matrix is typically not known in advance. Furthermore, changes to connectivity (such as two branch offices starting to exchange traffic) require changing the pipe definitions.

2. Hose model. The bandwidth requirements are expressed as the aggregate bandwidth going out of and coming into a site. (This is similar to a hose because traffic is 'sprayed' from one point to multiple points.) It is much easier to define the bandwidth requirements in this case because the estimate is for the aggregate traffic rather than individual flows ...