Measuring bandwidth

YouTube’s speed testing site gives a good estimate of how fast videos can play on a computer. Video streaming servers often have their bandwidth limited for a particular connection to 140% of the highest needed bandwidth for the video to play, so it’s normal for a video to not fill up its buffer as fast as a network connection could allow.

YouTube’s numbers for its customers show that typical bandwidth for the USA is 4.21 Mbps. This is more than enough for online video applications. As a comparison, today’s high quality “HD” web video is about 3 Mbps, regular DVD is 5 Mbps, and Blu-Ray DVD is 40 Mbps. In 2005, typical web video was 0.3 Mbps (300kbps).

Reproducing a low-bandwidth environment

The easiest way to test on a low-bandwidth environment is to use a macintosh and ask the Mac OS firewall to limit the speed on a specific network port. This will limit the network speed on that port for the entire computer.

The ports that should be limited to simulate low-bandwidth web video performance issues are:
Port 80: Non-encrypted HTTP traffic
Port 443: Encrypted HTTPS traffic
Port 1935: Streaming RTMP video

These are the only 3 ports required to limit. Note that this will reduce bandwidth for all applications using these ports, so you will notice the performance difference for all web pages, not just the ones you are testing.

O'Reilly's Mac Dev center has a good introduction to the Mac OS firewall, and MacTipsAndTricks.com has a good overview of using it to reduce bandwidth.

As an example, to limit network activity to 50K a second (400Kbps, 0.4 Mbps), open a Terminal window in the Mac OS and enter the following:

sudo ipfw pipe 1 config bw 50KByte/s
sudo ipfw add 1 pipe 1 src-port 80
sudo ipfw pipe 2 config bw 50KByte/s
sudo ipfw add 2 pipe 2 src-port 1935
sudo ipfw pipe 3 config bw 50KByte/s
sudo ipfw add 3 pipe 3 src-port 443

To remove the bandwidth limiting, enter the following:
sudo ipfw delete 1
sudo ipfw delete 2
sudo ipfw delete 3

The bandwidth limits are set per port, so the browser's true bandwidth will be is higher because multiple ports may be used to render a page. HTML content is almost always loaded on port 80; streaming video is usually on port 1935. Once an HTML page has loaded and the video is playing, the bandwidth limit on streaming video will be accurate.