Effect of number of drop precedences in assured forwarding

This paper explores the issue of fair allocation of excess network bandwidth between congestion sensitive and insensitive flows in an Assured Forwarding traffic class. In the absence of any mechanism to distinguish between out-of-profile traffic of congestion sensitive and insensitive flows, congestion insensitive flows will get most of the excess network bandwidth. However, if out-of-profile packets of congestion sensitive and insensitive flows are `colored' differently, network can be configured so as to give better treatment to excess packets of congestion sensitive flows and achieve fair allocation of excess network bandwidth. With a view to clearly distinguish between out-of-profile packets of congestion sensitive and insensitive flows, three levels of drop precedence are required. However, if the network operates close to its capacity, three levels of drop precedence are redundant as there is not much excess bandwidth to be shared.