Following on from my last post about Virgin Broadband and their traffic management, I came to a realisation. I phoned them up and asked about the current usage for our account over the last few weeks or so. They gave me this data:<\/p>\n
Daily Downstream Total:
Period Total (GB)
26\/03\/2011 0.432 GB
27\/03\/2011 0.362 GB
28\/03\/2011 0.748 GB
…
17\/04\/2011 0.591 GB
18\/04\/2011 0.863 GB
20\/04\/2011 9.496 GB
21\/04\/2011 9.912 GB<\/span><\/p><\/blockquote>\nWhat is apparent is that around about the 18th of April, our usage dramatically increased. I couldn’t account for this usage in general browsing terms, especially as we were away for a few days over that period. Thinking back, I looked over the iperf commands I was using to measure the bandwidth. On the client side, I was running this command every ten minutes:<\/p>\niperf -c www.example.com -P 4 -f k -w 256k -t 60<\/span><\/p><\/blockquote>\n
This was using a TCP window of 256k, a transmit window of 60 seconds and four threads in parallel (-P 4<\/span>). The net result of this is that I was sending 70MB of data from the client to the server six times an hour. Multiply this by 24, and you get a number very close to 10GB (which is what Virgin indicated we were downloading). So, after a bit of reading, I changed the client iperf options:<\/p>\n
iperf -c www.example.com -P 1 -f k -t 5 -x CMSV<\/span><\/p><\/blockquote>\n
Now, I only have one thread running for five seconds with a default TCP window length and a single thread. The addition of -x CMSV<\/span> reduces the output from iperf and means I don’t have to grep SUM<\/span> to get the relevant line. Furthermore, I think a 10 minute sampling frequency is a little on the high side, so I changed the cronjob to only run the iperf script every half an hour, which should still give the granularity I wanted.<\/p>\n
Of note is that with a smaller TCP window and a shorter transmit time, the results are slightly more erratic. They are, however, still showing the same pattern as before.<\/p>\n
So, it seems Virgin were correctly measuring our downloads and managing our traffic accordingly. What caused the initial slow-down that prompted me to measure the bandwidth remains a mystery.<\/div>\n","protected":false},"excerpt":{"rendered":"
Following on from my last post about Virgin Broadband and their traffic management, I came to a realisation. I phoned them up and asked about the current usage for our account over the last few weeks or so. They gave me this data: Daily Downstream Total:Period Total (GB)26\/03\/2011 0.432 GB27\/03\/2011 0.362 GB28\/03\/2011 0.748 GB…17\/04\/2011 0.591 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/posts\/18"}],"collection":[{"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/comments?post=18"}],"version-history":[{"count":0,"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/posts\/18\/revisions"}],"wp:attachment":[{"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/media?parent=18"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/categories?post=18"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cazenave.co.uk\/wp-json\/wp\/v2\/tags?post=18"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}