The throughput an application achieves is dependant on the amount of buffer space available in the sending and receiving hosts, packet loss due to errors or congestion, packet size (usually limited to 1500 bytes by Ethernet), and the round trip time between the 2 hosts. If this test reports that the sender or receiver buffer size is the limiting factor, increase the buffer size by changing the default buffer size on your computer. Win 95/98/NT users can easily set and change their default buffer size by using the TCPtune application developed by the NLANR MOAT group. Windows users may find that they perfer the DrTCP tool from the dslreports.com web site.

If a large number of retransmissions occur, check the duplex and speed setting on your host and the network switch it attaches to (duplex mismatches are a serious problem due to broken autonegoation protocols). Extremely long round trip times (over 1 sec) ususally indicate that a network router or switch is congested leading to long queuing times. Contact your local network administrator for help in solving this problem

The Bandwidth * Delay product is reported at the bottom of the "more details" page. Throughput limits for the NDT server's transmit buffer, your clients receive buffer, and the network infrastructure. You may use these numbers as a guide to determining what your client's receive buffer is currently set to. Divide the buffer size by the reported round trip time (RTT) to calculate the throughput value.

For more info on TCP tuning, visit cable/dsl tuning or dslreports.com tweaks or UNIX and Windows TCP/IP tuning tips.

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