Required Extra Capacity: Estimating Overprovisioning in a Single Class-of-Service IP Backbone

The benefit of Class-of-Service (CoS) is an important topic in the “Network Neutrality” debate. Some proponents of network neutrality suggest that over-provisioning is a viable alternative to CoS, and that there is no need for differentiated services in an IP backbone for users needing better-than-besteffort service. In this paper, we quantify the extra capacity requirement for an over-provisioned classless (i.e., best-effort) network compared to a CoS network providing the same delay or loss performance for premium traffic. We first develop a link model that quantifies the Required Extra Capacity (REC). To illustrate key parameters involved in analytically quantifying REC, we start with simple traffic distributions. Then, for more bursty and realistic traffic distributions (e.g., long-range dependent), we find the REC using ns-2 simulations of CoS and classless links. We, then, use these link models to quantify the REC for realistic network topologies under various scenarios including situations with “closed loop” traffic generated by many TCP sources that adapt to the available capacity. We also study the REC under link and node failures. We show that REC can be significant even when the proportion of premium traffic requiring performance assurances is small, a situation often considered benign for the over-provisioning alternative. We also show that the impact of CoS on best-effort traffic is relatively small while still providing the desired performance for premium traffic.