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Helpful Stuff/The Art of Measuring Download Times
While working at the Unitied States Mint, a friend of mine wrote this short explanation of how files are downloaded as well as a formula
to figure out download time. Enjoy. Thanks Ciarán.
Measuring the connection speed is not a straightforward process and there are many factors to consider. The benchmark metric to compare
against would be as follows:
S = Size of file download (in KB or Kilobytes)
C = Connection Speed (in KBps or kilobits per second known as Bandwidth)
Note: “8” represents the number of bits in a byte. All variables are converted to bits.
Optimum Download Time = (S * 1024 * 8)/(C * 1000) seconds
For example: 157 Kbytes download at a 56 KBps connection would take (157*1024*8)/(56*1000) = 22.96 seconds. In other words, you measure the
size of all objects (images, flash, HTML etc) associated with a page and plug this value along with the connection speed into the above
formula and this is the optimum download time at your connection speed. Any other test has to be considered inaccurate, as you will see.
The optimal download time with any connection can easily be calculated. But this is next to impossible to achieve based on a number of
factors. Below is a list of some of these factors and while I am not a Network engineer, these factors are based on the nature of any
connection to the Internet or World Wide Web.
The speed you connect to the Internet is the speed with which you are connected to your Internet Service Provider (ISP), and ISP only. For
example, if you are visiting the CNN home page and the connection to your ISP is 56KBps, you are by no means connected to CNN at 56KBps. In
other words, your connection speed does not represent the speed at which you will download pages/images from anywhere on the Internet. When
you request a page from a web site anywhere in the world, you are asking your ISP to find that page and serve it back to you over the
connection that you have with your ISP. To get that page for you, there a number of things that must happen;
- The ISP does a reverse lookup to resolve the text address to an Internet Protocol (IP) address using a DNS (Domain Name Server) and
figures the optimum path to that address. Depending on how your ISP achieves this, you may never use the same path to get to the same
address or your ISP may record the path and route all request to that address using that recorded path. This is not factored into your
connection to your ISP.
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