Diagnosing a TCP/ATM performance problem: a case study

This paper describes our efforts in analyzing a TCP/ATM performance problem, wherein two SGI Indy workstations with OC-3 (155 Mbps) connectivity to a wide-area ATM network achieve a disappointing end-to-end throughput of 4.3 Mbps for file transfers. The problem is diagnosed using cell-level measurements from the operational ATM network. Surprisingly, the performance problems are not due to send and receive socket buffer size problems, heterogenous ATM equipment, or cell loss within the ATM network. Rather, the poor performance is caused by an overrun problem at the sending workstation for the ftp transfer, and TCP's lack of robustness in the presence of multiple lost packets.