Study of TCP and UDP Interaction for the AF PHB

This informational draft presents results of a study on using different drop precedence assignments to address fairness issues when UDP and TCP traffic share the same Assured Forwarding (AF) PHB class. In particular, five different possible combinations of drop precedence assignment were explored with two different models of RED parameter settings. We present results showing that the type of RED model utilized can play a role in the nature of bandwidth sharing between TCP and UDP flows. The results also show that with the current four Class, three Drop Precedence AF specification, fairness between TCP and UDP in an under-provisioned network cannot be completely achieved by using separate drop precedence marking. Certain drop precedence mapping schemes are beneficial to TCP while others are beneficial for UDP. None are completely fair to both. The pdf version of this document is available at: http://www7.nortel.com:8080/CTL/draft-nsbnpp-diffserv-tcpudpaf-00.pdf