Insensitivity in IP network performance

J. Roberts


Understanding the three-way statistical relationship between traffic, capacity and realized performance is vital not only for adequately provisioning IP network resources to satisfy anticipated demand but also for defining the service model and congestion control mechanisms that determine how those resources are shared. In expressing demand it is particularly important to know what set of traffic characteristics has a significant impact on performance and needs therefore to be monitored and controlled. This set clearly depends on the adopted network architecture: defined service classes, scheduling mechanisms, admission controls, traffic routing algorithms,... We argue that an essential criterion in designing the network architecture is that the resulting traffic-capacity-performance relationship be as simple as possible. In other words, resource sharing schemes should be such that performance is largely insensitive to detailed traffic characteristics.

Two resource sharing schemes which do meet the insensitivity criterion are so-called bufferless multiplexing for open-loop controlled streaming traffic and fair bandwidth sharing for closed-loop controlled elastic traffic. We review the powerful insensitivity results available for these multiplexing schemes and suggest that they indeed constitute the preferred basis for a network architecture offering guaranteed quality of service. Necessary congestion control mechanisms are described and their implementation is discussed.