To help you identify your bandwidth requirements, two different methods are described in this section. For information on other methods, you can search Internet sites, as discussed later in this section.
The first method you can use to estimate bandwidth requirements is based on historical data from existing Internet sites. The number of bytes transferred is a commonly recorded statistic about Internet sites, and typical transfer statistics are available by searching the Internet. Many organizations publish statistics about data transferred and user connections on the World Wide Web, and the World Wide Web consortium at http://www.w3.org provides information about tools for gathering Web server statistics.
The following example illustrates this first estimation method. It calculates the kilobits per second (Kbps) of bandwidth required for a Web site that transfers approximately 250,000,000 bytes in an average 12-hour period:
250,000,000 ´ (8 bits data + 4 bits overhead) / ((12 hours ´ 60 minutes ´ 60 seconds) ´ 1024) = 67.8 Kbps
This example site requires a minimum of two 56 kilobits per second dedicated lines or one ISDN line.
When examining data from historical sites, remember to correctly convert different units of measure to bits (the unit of measurement for bandwidth). To obtain the number of bits contained in one transferred byte, multiply the number of bytes by 12; there are 8 bits per byte, plus 4 bits of overhead data. You also need to express the results in terms of seconds. If your data is recorded as bytes per hour, multiply the number of hours by 3,600 (60 minutes per hour ´ 60 seconds per minute).
The second method you can use to estimate bandwidth requirements is based on the estimated number of simultaneous user connections and the average size of documents transferred. The following example illustrates this method:
(Average connections per day / Number of seconds per day) ´ (Average document size in kilobytes ´ (8 bits data + 4 bits overhead))
Because there are 86,400 seconds in one day, 8 bits in a byte, and 4 bits overhead per byte of data, the formula can also be written as:
(Average connections per day / 86,400) ´ (Average document size in kilobytes ´ 12)
For example, if you predict 3,000 connections per day and the average file size accessed by remote users to be 85K, your bandwidth requirements can be estimated as follows:
(3,000 / 86,400) ´ (85 ´ 1,024 ´ (8+4)) = 36.3 Kbps
You can search sites on the Internet to find discussions of bandwidth estimation methods used, or recommended, by other users with experience in establishing Internet and Web server sites. Considerations other than those discussed previously might arise. For example, bandwidth requirements should also account for a minimum acceptable transfer rate per user, based on a projected load per remote user accessing the Internet Information Server. In other words, you should consider whether your server will be able to transfer data to all users at a rate that is acceptable to remote users.
To predict a peak load on your Internet Information Server, you need to estimate the number of users who will simultaneously connect to your server and consider the type of service they will access. If your users will primarily access your Web service for HTML documents with audio and graphics, you need a much higher bandwidth connection than if your users will primarily access the Web server to browse text documents.