A quantitative study of Differentiated Services for the internet

The Differentiated Services architecture provides router mechanisms for agg regate traffic, and edge mechanisms for individual flows, that together can be used to build services with varying delay and loss behaviors, In this p aper, we compare the loss and delay behaviors that can he provided using th e services based on combinations of two router mechanisms, threshold droppi ng and priority scheduling and two packet marking mechanisms, edge-discardi ng and edge-marking. In the first part of our work, we compare the delay an d loss behaviors of the two router mechanisms coupled with edge-discarding for a wide range of traffic arrivals. We observe that priority scheduling p rovides lower expected delays to preferred traffic than threshold dropping, In addition, we find that a considerable additional link bandwidth is need ed with threshold dropping to provide same delay behavior as priority sched uling. We further observe little difference in the loss incurred by preferr ed traffic under both router mechanisms, except when sources are extremely bursty, in which case threshold dropping performs better. In the second par t of our work, me examine the throughput of a TCP connection that uses a se rvice built upon threshold dropping and edge-marking. Our analysis shows th at a significant improvement in throughput can be achieved. However, we fin d that in order to fully achieve the benefit of such a packet marking, the TCP window must take the edge-marking mechanism into consideration.