The fragmentation of higher layer packets into ATM cells is a major problem in an ATM network when congestion arises. Once one cell is lost the remaining cells belonging to the same packet are not useful anymore, and thus, selective discarding mechanisms have been proposed in many papers.

The Active Cell Discarding mechanism is presented. Its goal is to guarantee a minimum QoS by allowing enough free space in the ATM switching buffer to queue a set of initial cells of the packet. If this is achieved, then a minimum flow of information may be guaranteed for a given connection. Critical information may be delivered in these initial cells of the packet.

Measurements on the ATM backbone network of the Spanish Academic network show the profile of IP traffic over ATM. Classical IP based protocols may benefit from this ACD mechanism, as well as new multimedia protocols over ATM.