  We study the performance of Selective Acknowledgments with TCP over the
ATM-UBR service category. We examine various UBR drop policies, TCP mechanisms
and network configurations to recommend optimal parameters for TCP over UBR. We
discuss various TCP congestion control mechanisms compare their performance for
LAN and WAN networks. We describe the effect of satellite delays on TCP
performance over UBR and present simulation results for LAN, WAN and satellite
networks. SACK TCP improves the performance of TCP over UBR, especially for
large delay networks. Intelligent drop policies at the switches are an
important factor for good performance in local area networks.
