Bill MacKenty

The bandwidth usage of Youtube

One of the lame excuses I hear about schools who block youtube is the “bandwidth-whaaaaaa” excuse. One of the reasons schools block youtube is because of bandwidth concerns.  I always thought this was suspect, so I decided to investigate this myself.

1. I downloaded and installed wireshark

2. I found a suitable disgusting youtube video entitled “HOW TO CARE FOR GIANT AFRICAN SNAILS” Really. Blech. Gross.  http://www.youtube.com/watch?v=weUGei2waw4 - it is 1 minute, 26 seconds.

3. I cleaned my browser cache, and made sure my school doesn’t use any type of proxy filtering - which would alter my results. I also made sure I didn’t have anything else running which uses bandwidth (although that isn’t as important, because the filtering on Wireshark is great.

4. I fired up wireshark and started capturing packets - I used Mozilla Firefox (3.5.5)I ran the test 4 times, each time thoroughly cleaning my browser cache. Here are the results:

a. 3679607 bytes (3.5 MB)
b. 26034 bytes (0.02 MB)
c. 153738 bytes (0.1 MB)
d. 23879 bytes (0.02 MB)

Hmmm. That’s rather odd. I’m quite certain my school doesn’t do any web caching, and I am also sure I nuked my browser cache, so these results may be from youtube’s content delivery network.  Needless to say, the first video was alarming, but subsequent views were really no problem.  I decided to test this with another video of about the same length, http://www.youtube.com/watch?v=ScLDQDKwzxs using the same methods above. Here are the results.

a. 8291621 (7.9 MB)
b. 8277143 (7.9 MB)
c. 8281093 (7.9 MB)

Alarming. 8 MB is significant - and that is only one person! In my school of 1600 end-users, I estimate at any one moment during the school day, there are 5 youtube streams being played (40 MB).  During a class, 25 streams (200 MB), and in the morning (when all the students and faculty are checking their email and watching a funny movie) I estimate about 100 streams (800 MB).

Result

My suspicious are unfounded. Youtube does eat massive amounts of bandwidth. I suspect a caching solution would really go a long way towards aleviating horrible bandwidth spikes. 

Thanks to Itai for helping out.