Virtual dropping for endpoint admission control

Endpoint admission control is a scalable QoS mechanism that relies on measuring the amount of lost or marked packets of a probing stream before allowing user data flows to enter the network. The existing approaches can be classified based on whether or not they use a separate traffic class for probing traffic, and whether or not they rely on a marking mechanism. Approaches that use a separate traffic class and rely on a marking mechanism are called out-of-band marking approaches and have proven to be most reliable but are also hard to deploy. As an alternative for out-of-band marking the approach of virtual dropping has been proposed, which discards packets that would have been marked otherwise, based on a virtual queue algorithm, thus removing the requirement of a common marking scheme. This paper compares the behavior of virtual dropping and out-of-band marking. Both mechanisms do not behave exactly the same, but differ slightly.