The benefit of Class-of-Service (CoS) is an important topic in the "Network Neutrality" debate. Proponents of network neutrality suggest that over-provisioning is a viable alternative to CoS. 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 this Required Extra Capacity (REC). For realistic traffic distributions (e.g., long-range dependent), we find the REC using ns-2 simulations of the CoS and classless links. Our primary contribution is in using these link models to quantify the REC for realistic network topologies under various scenarios including "closed loop" environments with traffic generated by TCP sources that adapt to the available capacity. 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.

The benefit of Class-of-Service (CoS) is an important topic in the "Network Neutrality" debate. Proponents of network neutrality suggest that over-provisioning is a viable alternative to CoS. 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 this Required Extra Capacity (REC). For bursty and realistic traffic distributions, we find the REC using ns-2 simulation comparisons of the CoS and classless link cases. We use these link models to quantify the REC for realistic network topologies. We show that REC can be significant even when the proportion of premium traffic is small, a situation often considered benign for the over-provisioning alternative.

The desire or ability of an ISP to provide differentiated service is a current hotly debated topic. In this paper, we quantify the value of having differentiated service (i.e., class-of-service (CoS)) support in an IP backbone. We compare the capacity requirements of a Diffserv environment providing service for applications that require delay or loss assurances in comparison to a network that provides classless (i.e., best-effort) service and still has to meet the same performance assurances. Our modeling framework first develops a link model that quantifies the required extra capacity (REC) in order for a classless link to provide the same level of performance as experienced by premium class traffic passing through a fixed capacity CoS link. We develop the REC calculations for the cases when average delay or the average loss probability is the target performance goal with Poisson or Markov modulated Poisson process (MMPP) input traffic. Our primary contribution is in quantifying the value of the CoS support in a network setting.