In the course of researching my article on Dynamic Streaming in Flash, I ended up doing way more testing than I’d initially intended. But things didn’t work the way I expected right away, and being the way I am (foolish? glutton for punishment?), I had to find out why.
There’ll be more on that in the article when it comes out on streamingmedia.com, but for now, I wanted to make a note about how to simulate fluctuating bandwidth conditions.
On Windows, Netlimiter 3 Lite works OK, especially if you’re just doing bandwidth detection to select the appropriate stream at startup. Shunra VE Desktop seemed to create more realistic test conditions for fluctuating bandwidth and stream-switching during playback, an impression that was validated by colleagues I spoke with. At $850 a pop, it certainly ought to be better than the $20 NetLimiter.
But on the Mac, it all worked for free. It’s already built in to the OS’s Unix roots. It’s in the ipfw command. You set it up by creating filters with bandwidth limits, then associating those filters with the ports you want limited. Here’s how to set up a bandwidth limiter for testing streaming over all ports. Note that if you’re not logged in as root, you will need to use sudo to run these:
sudo ipfw add 10 pipe 1 tcp from any to me
sudo ipfw add 11 pipe 1 tcp from any to me
Change it at will by issuing the pipe command again…
Or remove the filters like this…
sudo ipfw delete 11
You can also introduce simulated network latency, control outbound bandwidth separately from inbound, and control bandwidth to or from a single IP address or subnet. There’s great documentation at Luigi Rizzo’s Dummynet site. Thanks also to Ask Bjorn Hansen for his mini-tutorial on this.