Lesson 4	Transfer loads
Objective	List the Steps for Estimating the Server's Transfer Load.

Server Transfer Load

Steps for Estimating the Server's Transfer Load

The transfer load refers to the quantity of data the server will need to transfer in order to accommodate the number of users that are likely to download Web pages from the site. Calculating the anticipated transfer load helps identify the bandwidth requirements for the server and the site. To calculate the bandwidth requirements for a server:
Transfer Load = (Web Page Size x 8 x Visitors) / 86,340secs

Add the sizes, in bytes, of all the components of the Web page visited (including HTML text, images, video, audio, and JavaScript code).
Multiply by 8 to convert bytes to bits.
Multiply by the number of visitors expected for the Web page in a specified time (usually a 24-hour period).
Divide by the number of seconds in the specified time period (e.g. 86,400 seconds per 24-hour period).

Be aware that this formula only calculates the AVERAGE load over a 24 hour period. Most Web sites experience peak load times whose maximum transfer load requirements should be recalculated for just that specific period (such as 6 p.m. to 8 p.m.).
The following series of images illustrates how a server'a bandwidth requirements are calculated

1) When you add all the different files on the web page, you get a total page size of 30 KB

2) To convert bytes into bits, you multiply by 8

3) If 100,000 visitors are expected each day, the total number of bits per day will be 24,000,000

4) Dividing 24,000,000 (which is the number of bits per day) by 86,400 which is the number of seconds within a 24-hour period leads to 277,777 bit per second or 277 Kbps.

5) xDSL would be insufficient, given your needs. You would have to choose a T1 or E1 lines.

Estimating the Server's Transfer Load

If you are launching a new site, calculating your bandwidth is difficult to determine. The best approach is to keep careful track of your website's activity for the first few months after it goes live so you can determine your actual monthly usage, and adjust the required bandwidth accordingly. For more established sites, calculating your estimated bandwidth goes as follows:

Estimate the average page size of your site, in kilobytes (KB).
Multiply this value by the monthly average number of visitors.
Multiply the result from step 2. by the average number of pageviews per visitor.

Keep in mind that your calculations must include every one of your sites hosted on the server. If you run twelve domains on the same VPS account, take the time to add up the page sizes, visitors and pageviews across all domains.
These simple calculations should give you an idea of how much bandwidth you can expect to use, but some math is required. Basing your usage allotment solely on these rough estimates will not give you the entire picture.

Server Response Time

Server response time measures how long it takes to load the necessary HTML to begin rendering the page from your server, subtracting out the network latency between the search engine and your server. There may be variance from one request to the next, but the differences should not be that big. Highly variable server response time may indicate an underlying performance issue and may require you to optimize CSS and Javascript.

Understanding Hardware Requirements- Quiz

Click the Quiz link below to check your understanding of server hardware.
Understanding Hardware Requirements - Quiz

Transfer Loads - Exercise

Click the Exercise link below to determine bandwidth requirements for Asteron.com.
Transfer Loads - Exercise
In the next lesson, you will learn about connectivity devices.