Network Bandwidth vs Traffic

In the discussion of web hosting, you will see two different units shown; 95 Percentile and Traffic. This is a brief explanation of them and how they (loosely) relate to each other. Note this is slightly technical.

In summary, bandwidth (referred to as 95 Percentile) is basically the (almost) highest speed of traffic you use over a one month period. Traffic is the total amount of bits and bytes you actually use each month. If that satisfies you, ignore the rest! Otherwise, read on.

The simplest real world example is a water hose. If you turn on the spigot at a water hose full bore, you are at the “capacity” of the water hose; you are using it at its full force. However, depending on whether you are watering delicate flowers or trying to wash mud off the sidewalk, you may need to adjust that flow.

Traffic, in our documents, describes the total amount of water which flows from the hose. Instead of gallons, we use the units gigabytes, which is may sound like a lot but is really not on an active web site. If you are looking at a plan that gives you 20 Gigabytes of traffic a month, it is the sum total of all traffic. Back to our example of the water hose, it is the number of gallons the water department will bill you for at the end of the month.

95 Percentile is a quirk based on the way the Internet works. In this, it is not the total amount of traffic, but the maximum speed with which the traffic was used. In other words, it is similar to the highest flow used by the water hose, with a twist.

95 Percentile gets its name because we are looking at the highest traffic you used in the slowest 95 percent of the time. This allows you to have a few, short bursts of very high speed, but not have to pay for them. If you download some really big files from your web site, and it takes an hour to download a few gigabytes of data, you do not get billed for those (assuming your traffic the rest of the month is lower).

The way it works, in reality, is this. We take a reading from our network devices every five minutes, looking at the amount of traffic which flowed from your server during that time. We keep track of this until the end of the month.

At the end of the month, we will have around 9,000 readings (average of 8284 if you must know). We then sort them by the values; largest number first, smallest on the bottom. Now, we throw away the top 5% of the values (so, out of 8284, we throw away 440). The largest value that is left is what you are billed. It is your “95 percentile.”

How do the two compare? That is really difficult, but under “normal” circumstances, you can estimate that 1Mb/s, used normally, is the equivalent to 320 gigabytes of data transferred during a month. Read on only if  you really want to know more.

Remember, we throw away the top 5 percent of the readings. Five percent of a month is approximately 36 hours. So, in one of the extreme scenarios, say you download a huge amount of information for 35 hours, and you do it at 10Mb/s.  That would result in about 156 Gigabytes of data downloaded. Then, in the remainder o  the month, you download continuously at 1Mb/s, which would result in approximately 290 gigabytes more, for a total of 446 Gigabytes. And, you only get charged for 1Mb/s.

However, and here is the warning, if you downloaded for 36 hours and 1 minute at 10Mb/s, you would be billed for 10Mb/s, or your base of 1Mb/s PLUS the “overage” charge for 9Mb/s.

Daily Data follows network services standard by billing for bandwidth in two ways. If you agree to be charged for a certain bandwidth (95 percentile), we bill a flat rate so long as you do not exceed that. It allows us to commit to our providers for a total bandwidth rate which gives us a better price. However, if you exceed your committed rate, we have to pay more per megabit for the overage, and thus we much charge you a higher price for the overage.

So, if you commit to 2 Megabits, we charge you $75/mo for the extra (one Mb/s is calculated into our colocation fee). If you exceed that, however, and use 3 Mb/s, we bill $95 for the extra above that, a $20 upcharge which reflects our liability to our providers.

If you are only going to have higher traffic for one month, or even two, it is simpler to just pay the surcharge. However, if you believe you will be using more bandwidth in the future, it is more cost effective to commit to the extra usage, even if you do not use it all in some months.