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Lesson 11 Server transfer load
Objective Calculate server transfer load.

Server Transfer Load

In addition to calculating transfer speed to determine a Web page's download time, it is equally important to calculate the transfer load. Transfer load is the bandwidth needed to accommodate all the users expected to download web pages from a site you have designed. How do I calculate how much data the server must transfer to the client?

Calculating the amount of data the server must transfer to the client involves estimating the total bandwidth requirements based on the expected user traffic and the size of the web pages. This calculation is crucial for ensuring that the server infrastructure can handle the expected load without compromising the user experience. Follow these steps to calculate the server's data transfer requirements:
  1. Determine Average Page Size: Assess the average size of the web pages on your site. This includes all elements that constitute the page, such as HTML, CSS, JavaScript files, images, videos, and other multimedia content. The average size should be measured in bytes (B), kilobytes (KB), or megabytes (MB).
  2. Estimate User Traffic: Estimate the expected number of users (U) who will access your site within a given time frame. This could be measured in users per second, minute, hour, or day, depending on your needs and the expected traffic patterns.
  3. Consider Page Views per User: Estimate the average number of page views per user (V). This is how many different pages you expect a single user to view in a session.
  4. Calculate Total Data Transfer: Multiply the average page size by the estimated number of users and the average number of page views per user. This will give you the total data transfer required to accommodate the expected user traffic. The formula for total data transfer (T) is:

Convert the following formula from TeX to MathML so that I can publish it on the web. T = Average Page Size × User Traffic × Page Views per User
Ensure that all components of the formula are in consistent units, particularly the average page size and the resulting total data transfer, which should both be in bytes (or a consistent multiple thereof).
If your site has an average page size of 1.5 MB, you expect 1,000 users per hour, and you estimate that each user will view an average of 3 pages per session:
  1. Convert the average page size to bytes:

    1.5 MB × 1,000,000 = 1,500,000 bytes
  2. Calculate the total data transfer:
    1,500,000 bytes/page × 1,000 users/hour × 3 pages/user = 4,500,000,000 bytes/hour
  3. Convert the total data transfer to gigabytes (GB) for easier interpretation:
    4,500,000,000 1,000,000,000 = 4.5 GB/hour

Therefore, to accommodate the expected user traffic, the server must be capable of transferring approximately 4.5 GB of data per hour. This calculation is fundamental for planning server bandwidth and infrastructure requirements. It's also important to account for peak traffic times, which may significantly exceed the average estimates, and to plan for scalability to handle unexpected increases in user traffic. Regular monitoring and adjustments based on actual usage patterns are essential for maintaining optimal performance and user experience.

Estimating the server's transfer load

Transfer load is the bandwidth needed to accommodate all the users expected to download web pages from a site you have designed. To calculate how much data the server must transfer, follow the steps below:
  1. Add the sizes, in bytes, of all the components of the Web page (HTML text, images, video, audio, and JavaScript code, for example).
  2. Multiply by 8 to convert bytes to bits.
  3. Multiply by the number of hits (accesses) expected on the Web page in a specified time.
  4. Divide by the number of seconds in the specified time period (for example, 86,400 seconds per day).

For example, the components of a particular Web page add up to a total of 30K. That number equals 240K. If 100,000 visitors were expected to view the page per day, that would mean a total of 24,000,000,000 bits transferred per day. There are 86,400 seconds in a day. Dividing the bits per day by the number of seconds in a day equals 277,777 bits per second or 277Kbps MINIMUM.
Why minimum? Because it's very likely some visitors will arrive at roughly the same time, increasing bandwidth requirements during those moments. For this reason, fast Web sites operate at only about 40 percent of their maximum (peak) bandwidth capacity.
In the next lesson, you will learn about network diagnostic tools for troubleshooting.

Server Transfer Load - Exercise

Click the Exercise link below to review calculating bandwidth speeds of various pipes.
Server Transfer Load - Exercise

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