SD+: improving TCP performance over ATM UBR service using modified selective drop buffer management scheme

A new packet discard scheme called selective drop with a forgiveness mechanism that can be plugged into the existing selective drop buffer management scheme is developed. The new scheme that we call SD+ remarkably enhanced both the throughput and fairness of TCP running over an ATM-UBR service. Our scheme does not require per VC accounting but per VC-state where only one bit is needed. The focus is on demonstrating and analyzing the effect of the forgiveness mechanism when plugged into the SD scheme in low latency networks. The SD scheme is selected because it is evolved as an improvement over both PPD and EPD policies that can be practically applied to existing ATM switches. This paper explains the concepts behind the new scheme and demonstrates its effect on TCP performance using simulation.