Web Analytics Tutorial

Lesson 10 – Bandwidth Management

Total Bandwidth

Figure 1. The Monthly Bandwidth report shows bandwidth usage and rate for each month.

Web analytics can tell you precisely how many bytes you send to users over the course of any given period or for particular files, if your log files contain byte values (and most do). Summary’s time reports, like the Monthly Report, show you the number of bytes transferred for each period. As bandwidth is generally purchased on a monthly basis, Summary provides the Monthly Bandwidth report, Figure 1, that shows the number of bytes transfered and average transfer rate (BPS) for each month. Summary’s Overview : Bandwidth report also contains useful summaries regarding how much bandwidth is used, what speed connection is required to meet that volume (with adjustment for growth) and which requests are consuming the most bandwidth.

Most co-location facilities and Internet access providers limit your bandwidth usage in two ways. First, you are limited physically by the maximum available bandwidth on your Internet connection. This limitation is the peak number of bits per second (BPS) that you can transfer and affects transfer rates during your peak usage times. Second, you are generally charged on a monthly basis for the total amount of bandwidth you consumed (or the number of bytes you transferred) during that period. The monthly bytes in either the Monthly Bandwidth report or the Overview : Bandwidth summary are comparable to what you are charged for by your provider.

When someone makes a request for a page, he sends a small number of bytes over the network to your server. Then your server responds with a file or other object for the visitor. What Summary tracks is just the size of the file returned. The byte counts do not include the original request or the headers that may have been sent with the response. Generally these two items are not very significant, especially if your files are large. A typical request may be 120 bytes while a response, including the file sent, is more likely to be about 15,000 bytes. When you compare your byte totals in Summary to those your access provider or co-location facility give you, theirs will generally be higher. If you have just simple web traffic you can expect about a one or two percent increase. If you use cookies, or provide other services, like email or ftp, then the actual bandwidth usage could be significantly higher.

Suggested Bandwidth

When determining how much bandwidth you should have, you also want to decide on a monthly contract rate. Rather than using the peak usage, you should look at how many bytes you transfer, total, each month. In the Overview : Bandwidth report, Summary also tells you how many bytes per month you have transferred on average and gives transfer rates for the last few months. The average is a good place to start, but you should look at the last few complete months of traffic to see if your usage is growing. If you are analyzing in the middle of a month, the last month will have a low byte-count and skew the average down slightly. Alternately, you can look at the average bytes transfered per recent day to see what your usage was in the past two to three weeks. Multiply this number by 30 to get an approximate monthly usage requirement. Depending on your provider’s pricing you should probably choose the contract that offers slightly more than the greater of all these monthly usage numbers.