Cell discarding mechanisms with minimum flow quality

Abstract

The fragmentation of higher layer packets into ATM cells is a major problem in an ATM network if congestion arises. Once one cell is lost, the remaining cells belonging to the same packet are not useful, and thus, the interest of selectively discarding such cells is the focus of many papers. When dealing with multimedia real-time interactive services, their stringent QoS requirements demand the use of effective congestion control mechanisms to guarantee a minimum QoS. The Active Cell Discard (ACD) mechanism and some modifications presented in this paper try to guarantee a minimum QoS by making sure that there is always enough free space in the buffer to queue a set of initial cells of the packet. Even if the tail of the packet is cut out by a cell discarding mechanism, the initial set of cells may be useful to maintain the QoS of the application. It provides a minimum flow of information, and critical information may be delivered in these initial cells of the packet. In this paper, we present some of the results obtained for the performance of the ACD mechanisms and compare them with other known proposals. The traffic model used for this evaluation follows the characteristics of the ATM traffic measured in the Spanish academic ATM network.