Apple introduced a useful tool with Lion that allows you to test application performance under various network conditions. The Network Link Conditioner (NLC) is primarily designed for testing iOS apps, though it can also be used for testing websites via Safari in the iOS simulator.
Once you install XCode on Lion, you will find the NLC preference pane installer located within /Developer/Applications/Utilities/Network Link Conditioner/. A reboot is required before the NLC daemon will run.
Once you have installed the Network Link Conditioner you can find the NLC icon in the “other” section of the system preferences. Once activated the NLC tool applies to the network interface of your Mac so it will impact ALL traffic on your computer when you turn it on. The nice thing about using NLC is that you can change the bandwidth profile on the fly.
The NLC is a nice addition to OS X and might just come in handy when running performance profiling from Lion.
