A gracious cell discard scheme in ATM multiplexer

An analytical model for the gracious cell discard (GCD) control of a finite capacity queue in ATM output multiplexer is proposed. We put a gracious cell throttle (GCT) in front of a queue (main queue: MQ). The GCT is composed of a temporary queue (TQ) and a nonlinear filter (NLF). In every time slot, a burst of cells composed of HP (high priority) and LP (low priority) arrives. Cells are classified and HP cells are not governed by the NLF and go directly to TQ, whereas LP cells are governed by the NLF. When the length of MQ is greater than zero, the NLF discards a part of LP cells based on a nonlinear filter function. The remaining LP cells are admitted to MQ along with all the HP cells within the available space of MQ. As a cell rejection policy for the overflow in MQ, we propose a partial rejection with prioritized selection (PR-PS). PR-PS operates as follows: when the number of cells in TQ exceeds the vacant space in MQ, the HP cells are accepted first within the limit of the remaining space in MQ. If there remains any vacant space in MQ after the HP cells are accepted, the LP cells can enter within the limit of the updated remaining space in MQ. Finally, we evaluate performance of the QoS (quality of service) measures related to the cell loss and delay.