Sergio Amadeu da Silveira - Cidadania e Redes Digitais

eng
c i t i z e n s h i p a n d d i g i t a l n e t w o r k s
million household connections on an average contracted bandwidth of 512 kb/s (kilobits
per second). If all these connections were active simultaneously and using the
full bandwidth for transit to the global Internet, TeleVirtua would have to contract
with Global Crossing’s something like 2.5 Tb/s (terabits per second), or 2.5 million
megabits per second.
In real life, it is not difficult to conclude that even if everyone was doing simultaneous
transit with the global Internet, the actual bandwidth effectively used would
be many times smaller than that. In fact, most users will be doing transit with servers
in Brazil, consulting Brazilian newspapers or blogs, or e-mailing from a Brazilian
provider, and the general transit will be rarely using the full bandwidth provided by
TeleVirtua. Good for TeleVirtua, but here we get to an imponderable territory. How
to calculate how much international transit bandwidth has to be hired not to risk the
quality of service to five million customers? And how much bandwidth should be
guaranteed at the national Internet Exchange Points (IXPs) through which TeleVirtua
exchanges traffic with other networks, for transit to other national Internet services?
Judging by the total amount of traffic of the twelve Brazilian IXPs operated by
CEPTRO 4 (which, today, is around 24 Gb/s, or gigabits per second), and also remembering
that not the entire country’s Internet transit passes through these IXPs,
these international contracts for transit shall be closer to gigabits than to terabits. If
TeleVirtua hires 25 Gb/s of international transit, that means 1% of the theoretical
maximum that can be used by its five million customers.
This case illustrates the solution of “underbuying transit bandwidth.” This practice
is adopted by the major suppliers of “broadband” in Brazil, who suppose that
the vast majority of consumers will rarely use, on average, more than a small fraction
of the bandwidth hired for international transit. In this sense, the “overselling”
of bandwidth is a menace to net neutrality: each client is at risk of not having
enough bandwidth at a time of high demand for transit, as it would happen in a
toll road that is often congested. In this situation you may verify, as often occurs,
that a Vimeo or YouTube streaming is much slower and choppier than an equivalent
streaming from the content provider associated to the broadband provider — in our
example, a GloboTerra video would continue to be delivered uninterruptedly.
4. CEPTRO is a division of NIC.br (Brazilian Network Information Center) that manages, among
other things, the twelve Internet Exchange Points which are located in the main Brazilian capitals. See
http://www.ceptro.br.
106