Apple Broadband Tuner for Mac

The Broadband Tuner allows you to take full advantage of very high speed FiOS based Internet connections that have a high latency. The installer tweaks some system parameters. There is an optional uninstaller that can be used to restore the settings that were in effect at the time just before the system parameters were changed.

The installer increases the default values for the size of the TCP send and receive buffers. With larger buffers more data can be in transit at once. A startup configuration file is also updated so that these changes will persist across restarts.
The system parameters are sysctl variables that are set as follows:
net.inet.tcp.sendspace: 131072
net.inet.tcp.recvspace: 358400
kern.ipc.maxsockbuf: 512000

This change has a system wide effect and is applied even if the network is not high speed connection with a high latency, with the exception of modem connections for which the system uses small default TCP buffer sizes.