allotment is an important consideration in choosing
a dedicated or colocated server host. There are different
methods of allocation, and it is important to understand
the differences among them.
let us begin by defining bandwidth. What is often referred
to as bandwidth is really data transfer, which is the
total of how much data has been transferred from a site
over a certain period of time. Every time someone makes
a request for an HTML page (views it in a browser),
that HTML file is transferred to the user's computer,
which takes bandwidth. If there are any images on that
page, each of those images must also be transferred
to the users browser, which takes more bandwidth. Bandwidth
consumption on specific sites can be minimized by making
the data set to be transferred smaller. Some of the
ways to accomplish this include removing extraneous
tags and spaces in your HTML code, compressing images
more, using less colors in them, and using fewer images.
Also, not using Microsoft Front Page. Not only does
it generate sloppy and bloated code, but it adds unnecessarily
to bandwidth consumption.
helps to understand the nomenclature regarding sizes.
bits = 1 byte.
bytes = 1 kilobyte (Kb).
kilobytes (Kb) = 1 megabyte (mb or meg)
megabytes = 1 gigabyte (gb or gig)
gigabytes = 1 terabyte. (tb)
above are the correct and exact definitions. Note, however,
that some hosts will use 1000 as the multiplier rather
than 1024. Be sure to check with any host regarding
how they define these terms.
usage will vary from hour to hour, day to day, and even
by season. Viewed on a graph, peaks and valleys are
typical of most any site and server. Traffic drops off
sharply during night time hours (over many time zones)
for most sites, week-ends, and even during summer for
Thus, spikes in bandwidth usage are normal and to be
expected. In some cases, those spikes may be well beyond
the typical traffic pattern, which can affect the server
and attendant costs in various ways.
allocation and costs
amount of bandwidth usage allocated by various hosting
companies can vary considerably. Some of the monthly
amounts seen among well known companies are 10 gb, 20
gb, 50 gb, 65 gb, 100 gb and others. Some even quote
in megabytes, sometimes to hide the high cost of their
bandwidth. One host advertises $40 for 500 mb additional
bandwidth. That's $80 per gb, an exorbitant amount.
Reasonable rates from $3 to $10 per gb can be found
at better companies.
Bandwidth allocation methods
are three basic methods used in the allocation of bandwidth.
They are the capped line (or rate limited) method, average
usage method, and the x percentile method. It is important
to understand each one and what the differences among
them are. One in particular, the percentile method,
is greatly misunderstood and there is much false information
spread about it by people who simply do not understand
is a flat fee based on the size of the dedicated line
you get. The amount of bandwidth that can be transferred
is capped, or limited, to a specified amount. This can
contain the cost of bandwidth to the specified limit
and keep it at a flat fee. You get a data pipe of a
specified (limited) size. A peak in bandwidth (several
users accessing the site simultaneously) would mean
slowdown or inaccessibility of the server. Some users
would have to wait longer to access sites and some might
get a "server timed out" message and not reach
method is also referred to as rate limiting as the rate
of transfer is limited.
measurements are taken at various intervals and averaged
together to provide the bandwidth consumption figure.
Any bandwidth in excess of the allotted amount is charged
the stated amount per gigabyte. Some hosts have bandwidth
plans in blocks, whereas others charge per gb. Crossing
the threshold into the next level could add substantially
to the costs in block plans, especially for those hosts
with a high cost per gb, so be especially aware of the
cost of higher levels.
also that some hosts charge an estimated usage amount
which may be higher than actual usage. Some may choose
to use an average figure, others might use the median.
costs tend to be higher at hosts that use the average
usage method. You are either subsidizing someone else's
high usage, or they are subsiding yours, and you are
all paying higher costs on other services to cover the
costs to the host.
probably averages out for the hosting companies if they
have enough customers. The way bandwidth traffic patterns
usually work out, some 75% of them will probably overpay
and cover the other 25% that underpay.
is the most misunderstood of the bandwidth methods.
Though any percentile can be used, the 95th percentile
method is most frequently mentioned. Here's the reason
providers use the 95th percentile system - If you let
your customers burst, it doesn't matter if you're paying
for X bandwidth, or paying for X with burstable.
your customers burst, then you must make sure that you
have bandwidth available above their highest burst rate,
not just equal to it, above it. If a customer uses 5
kbit for 5 minutes, you have to have 6 kbit for the
entire month as they can burst at any time. If a customer
uses 5 MBit for 5 minutes, you have to have 5.1 Mbit
the entire month. Again, they can burst at any time.
order to do that, you must either subsidize bandwidth
elsewhere, or bill them based on that burst rate. There
is no in-between, not if you want to last as a business.
of the upper end bandwidth companies such as AboveNet,
Exodus Communications, and UUNet use it. They do so
in order to prevent situations where they're getting
congestion due to lack of bandwidth. They must always
keep the 100th percentile amount of bandwidth in reserve.
percentile method allows a server to accommodate most
any increase in traffic without slowing access speeds
for the visitors. The chart below is an actual one from
the port of a host using the 95%ile method. In this
case, it also indicates a change in clients, which is
why there is no real activity from about July 21 to
July 31 (the new customer took over on the 31st).
Note the fairly level blue line at its bottom range
(just above the green, which is incoming bandwidth).
This is what most people would probably think of as
their typical usage, or in that general area. This is
what they will say they "really used".
there are several spikes driving usage way up on a repeated
basis. Basically, what happens is that more bandwidth
is allocated so that traffic is not slowed down when
it increases, even as much as it did here (and in other
spikes). Essentially, the 95th percentile system is
close to your maximum sustained bandwidth usage for
any part of the month, and you are billed for that amount
for the entire month if you are on this system.
top 5% on the spikes is knocked off. Note the highest
point in this graph is 1.21m Multiply that by 30 days
and you would have 36.3 gb for the month. However, the
maximum bandwidth is 33 gb. Obviously, part of that
1.21m spike is the 5% lopped off the top end.
What's the alternative? Systems that limit the bandwidth.
They can contain your bandwidth costs to what you expect,
but at the drawback of slowing access at peak periods.
Imagine a hosting company with capped bandwidth and
several sites at peak demand simultaneously.
care to read War and Peace or Hawaii while waiting for
a web site to load in your browser?
we have another actual example (taken on May 30, 2001).
Note the overall more uniform level than the example
to recap, we have 95%ile, with the advantage of fairly
uniform access speed regardless of the increase in traffic
and the disadvantage that the price of bandwidth will
rise commensurately with that increase.
most hosting companies don't want the reputation of
having slow servers, you should understand why they
would prefer this method, even if they have a choice.
However, many bandwidth providers charge by the 95th%ile
method, so some of the hosting companies charge their
customers the same way.
About the Percentile Method
Is the 95%ile system unfair? No. It is a system that
ensures that no matter how much increased bandwidth
you have (which is related to traffic but not synonymous
with it), that the speed will not be impaired. It can
keep companies and servers from getting a reputation
as a "slow server". In some cases, that could
be detrimental for business. If you try people's patience,
they may try other sites.
then, do some people think this method is unfair? Aside
from not understanding it, it is probably because they
are billed for near the highest amount of usage for
the entire month.
discriminates against high bandwidth usage sites.
It does no such thing. It is the high spikes in bandwidth,
not high bandwidth usage of itself, that trigger the
charges some people don't understand. High usage sites
pay more because they use more. There is nothing the
least bit discriminatory about that very fair practice.
triples your "real" bandwidth usage.
Another falsehood. Some people have had sustained spikes
triple, or even quadruple, that of their level usage,
in excess of the allotted amount, and state this as
fact. It simply isn't true. The variation from level
use to sustained spike height can vary from server to
thing must happen in order to incur additional bandwidth
charges under the 95th %ile method. The sustained spike
level must exceed the allotted amount of bandwidth.
If that doesn't happen, it doesn't matter how high the
the sustained spike level does exceed the allotted amount,
then the height of the sustained spikes is a factor
in additional charges. The frequency of the spikes,
their height, and how long they spike, all help determine
to what extent additional charges are incurred. It is
far from so simple a statement as tripling one's usage.