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Throughput is the right performance metric for the Internet!

Logo of the United States Federal Communicatio...
Logo of the United States Federal Communications Commission, used on their website and some publications since the early 2000s. (Photo credit: Wikipedia)
Many people thing that it's enough to have a fiber to the home (FTTH) connection to guarantee that Internet browsing becomes super fluid, with webpage loading time below 1 second. That's unfortunately completely wrong, as shows the figure below from a study led by FCC in 2012.

FCC's 2012 study of web page load time in the US. X axis is the advertised Internet access speed, Y axis is the actual webpage load time. As you can see, from 6 Mb/s there is almost not improvement in the webpage load time!

This figure shows that it's useless to have even a 10Gb/s connection from your ISP if you use it to download a movie from a server based very far. There are two reasons for this:

  1. Bottlenecks outside of the access network:
    • For instance, congested peering points or slow servers
  2. TCP troughput limitations

English: Establishing a TCP connection Fran├žai...
TCP connection establishment - the three way handshake. All messages are acknowledged thanks to the ACK flag, which TCP uses for congestion control too.
I will detail the second point about TCP throughput, because very few people understand it correctly. TCP properties do not permit you to use your connection at its maximum speed. The reason for this ? The exponential growth of TCP throughput depends on how fast the client and the server exchange "ack" acknowledgements, and this, in turn, depends  directly on the round trip time (RTT) between the server and the client! So, the closer the server, the more efficient TCP will use the available bandwidth.

Remember this: in the Internet, it's not bandwidth that matters. It's throughput!


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