A quantitative study of differentiated services for the Internet

The differentiated services architecture provides router mechanisms for aggregate traffic, and edge mechanisms for individual flows, that together can be used to build services with varying delay and loss behavior. We compare the loss and delay behavior that can be provided using the services based on combinations of two router mechanisms, threshold dropping and priority scheduling and two packet marking mechanisms, edge-discarding and edge-marking. We compare the delay and loss behavior of the two router mechanisms coupled with edge-discarding for a wide range of traffic arrivals. We observe that priority scheduling provides lower expected delays to preferred traffic than threshold dropping. In addition, we find that a considerable additional link bandwidth is needed with threshold dropping to provide same delay behavior as priority scheduling. We further observe little difference in the loss incurred by preferred traffic under both router mechanisms, except when sources are extremely bursty, in which case threshold dropping performs better. We examine the throughput of a TCP connection that uses a service built upon threshold dropping and edge-marking. Our analysis shows that a significant improvement in throughput can be achieved. However, we find that in order to fully achieve the benefit of such a packet marking, the TCP window must take the edge-marking mechanism into consideration.