Sorry for the cross-post. Having not really been following the whole
Neutrality Debate, this clarified some stuff for me. I hope you enjoy it.
Copied from: http://www.pbs.org/cringely/pulpit/pulpit20060622.html
June 22, 2006
Why don't they tell us ending Net Neutrality might kill BitTorrent?
By Robert X. Cringely
Last week's column was about Bill Gates' announced departure from
day-to-day management at Microsoft and a broad view of the Net
Neutrality issue. We'll get back to Microsoft next week with a much
closer look at the challenges the company faces as it ages and what I
believe is a clever and counter-intuitive plan for Redmond's future
success. But this week is all about Net Neutrality, which turns out to
be a far more complex issue than we (or Congress) are being told.
Net Neutrality is a concept being explored right now in the U.S.
Congress, which is trying to decide whether to allow Internet Service
Providers to offer tiers of service for extra money or to essentially be
prohibited from doing so. The ISPs want the additional income and claim
they are being under compensated for their network investments, while
pretty much everyone else thinks all packets ought to be treated equally.
Last week's column pointed out how shallow are the current arguments,
which ignore many of the technical and operational realities of the
Internet, especially the fact that there have long been tiers of service
and that ISPs have probably been treating different kinds of packets
differently for years and we simply didn't know it.
One example of unequal treatment is whether packets connect from
backbone to backbone through one of the public Network Access Points
(NAPs) or through a private peering arrangement between ISPs or backbone
providers. The distinction between these two forms of interconnection is
vital because the NAPs are overloaded all the time, leading to dropped
packets, retransmissions, network congestion, and reduced effective
bandwidth. Every ISP that has a private peering agreement still has the
right to use the NAPs and one has to wonder how they decide which
packets they put in the diamond lane and which ones they make take the bus?
Virtual Private Networks are another example of how packets can be
treated differently. Most VPNs are created by ISP customers who want
secure and reliable interconnections to their corporate networks. VPNs
not only encrypt content, but to a certain extent they reserve
bandwidth. But not all VPNs are created by customers. There are some
ISPs that use VPNs specifically to limit the bandwidth of certain
customers who are viewed as taking more than their fair share. My late
friend Roger Boisvert, a pioneer Japanese ISP, found that fewer than 5
percent of his customers at gol.com were using more than 70 percent of
the ISP's bandwidth, so he captured just those accounts in VPNs limited
to a certain amount of bandwidth. Since then I have heard from other
ISPs who do the same.
As pointed out last week, though, there is only so much damage that an
ISP can do and most of it seems limited to Voice-over-IP (VoIP)
telephone service where latency, dropouts, and jitter are key and
problematic. Since VoIP is an Internet service customers are used to
paying extra for (that, in itself, is rare), ISPs want that money for
themselves, which is the major reason why they want permission to end
Net Neutrality--if it ever really existed.
The implications of this end to Net Neutrality go far beyond VoIP,
though it is my feeling that most ISPs don't know that. These are bit
schleppers, remember, and the advantages of traffic shaping are only
beginning to dawn on most of them. The DIS-advantages are even further
from being realized, though that will start to change right here.
The key question to ask is what impact will priority service levels have
on the services that remain, those having no priority? In terms of the
packets, giving priority to VoIP ought not to have a significant impact
on audio or video downloads because those services are buffered and if
they take a little longer, well that's just the price of progress,
right? Wrong. Let's look at the impact of priority services on
BitTorrent, the single greatest consumer of Internet bandwidth.
Though e-mail and web surfing are both probably more important to
Internet users than BitTorrent, the peer-to-peer file transfer scheme
uses more total Internet bandwidth at something over 30 percent. Some
ISPs absolutely hate BitTorrent and have moved to limit its impact on
their networks by controlling the amount of bandwidth available to
BitTorrent traffic. This, too, flies in the face of our supposed current
state of blissful Net Neutrality. A list of ISPs that limit BitTorrent
bandwidth is in this week's links, though most of them are, so far,
outside the United States.
BitTorrent blocking or limiting can be defeated by encrypting the
torrents, but that increases overhead, causes a bigger bandwidth hit,
and defeats local caching schemes that might help reduce bandwidth
demand. So blocking BitTorrent actually makes life worse for all of us,
which may be why most U.S. ISPs aren't doing it.
So let's assume that ISPs are allowed to offer tiered services. What
impact will that have on BitTorrent? The answer lies in the nature of
the TCP/IP protocol. Here is an analysis from a friend who is far more
savvy about these things than I am:
"If you look at the amount of overhead TCP needs it's exponential to how
slow each connection is; the slower (the connection) the more overhead
because the window sizes are smaller and more control packets are being
used for verification. And you know what? BitTorrent is FAR WORSE.
Remember that for each file you download on BitTorrent you connect to
dozens, possibly even hundreds of people, and the slower each of those
connections is the more the overhead increases.
"About a month ago the amount of torrents I may (have been)
automatically downloading at any given time was between 10 and 30. This
means that I was getting no more than 1Kbps from every peer, which meant
about half of my bandwidth usage was in BitTorrent protocol overhead and
not in downloading file data. I brought this (overhead) down (by 40
percent) by just having five torrent downloads at a time and queuing the
rest, and I even got the files faster. I then did some more scheduling
and what not to get (my bandwidth use down by a total of 70 percent) and
I still downloaded about the same amount of real file data.
"So what happens when everyone's VoIP or other preferred packets get
preference over my torrent packets? Since I have no knowledge of the
other people's usage in my aggregate network I can't adjust well for
changes in the network. The BitTorrent traffic that is going will have
exponentially increased overhead due to the slow downs, increasing
overall Internet packet overhead (with BitTorrent already 30+ percent of
all Internet traffic). Which means that allowing the telco's to
subsidize the cost of improving their infrastructure by having preferred
packets could exponentially increase the cost accrued by the larger
internet and backbone providers just to keep costs down at the aggregate
To recap: Giving priority to some traffic puts a hurt on other types of
traffic and when that other traffic constitutes more than 30 percent of
the Internet, the results can be severe for all of us. On the Internet
everything is connected, and you can't easily ignore the impact of one
service on another.
With this new knowledge I did a simple test that you can do, too. I have
a Vicomsoft Internet Gateway that does very fine traffic shaping, though
there are many similar products available, like ClarkConnect and some
others that are open source. Many routers can do traffic shaping, too. I
did a couple BitTorrent downloads of specific files, measuring how much
time and total bandwidth was required. Then I deleted those files,
changed my Internet Gateway settings to give priority to my Vonage VoIP
packets, called my Mom on the phone and started downloading the same two
Vonage and many other VoIP services use an Analog Telephone Adapter
(ATA) device to connect your phone to the network. That ATA can do
traffic shaping, too, which requires that it be connected inline between
your broadband modem and router. Of course I didn't realize this until
AFTER my test was done.
My test results were clear. I had no problem downloading the same
BitTorrent files, but it took longer. That was no surprise. After all, I
WAS talking to my Mom, which would have taken some bandwidth away from
BitTorrent. But the more interesting result was that the total bandwidth
required to download the same files using traffic shaping versus not
using traffic shaping was almost 20 percent more, which undoubtedly came
down to increased BitTorrent overhead due to contention and
retransmissions involving the priority VoIP service.
Traffic shaping causes different patterns on the local network,
especially aggregate networks that use creative technologies to send
Ethernet frames over old telephone and cable infrastructure. It's taken
a very long time to get Internet technologies to where they are today,
and all the protocols built on top of those technologies operate under
certain assumptions. Just like a web site sent over TCP assumes that TCP
will make sure all the packets will get to their destination, rich
application protocols like BitTorrent operate under assumptions like
known patterns in bandwidth changes on aggregate networks.
Let's say Net Neutrality goes away and the broadband ISPs start offering
tiered services. My simple test suggests that one possible impact is
that Bit Torrent traffic, which currently uses, say, 30 percent of
Internet bandwidth, is going to expand to about 36 percent simply
because of inefficiencies created by the tiered services. This will
increase the backbone costs for ISPs and will take back at least some of
the very performance advantage they are supposedly selling to their
The result of ending Net Neutrality under this scenario, then, is that
the ISPs make money from tiered services but with higher overhead costs
and lower priority service levels than one might expect. The ISPs then
might try banning BitTorrent to keep it from messing with their tiered
services, but we've already establish this can't practically be done on
a technical level because torrent encryption can always get around the
ban. The only way, in fact, to limit BitTorrent traffic would be to have
it made illegal and now we're back again to the clueless Congress that
started this whole mess.
I don't think these latter ideas are even in the heads of broadband
ISPs. They simply haven't thought that far. But eventually, as they try
trimming this and expanding that to solve a problem that shouldn't have
existed in the first place and can't otherwise be solved, they'll come
up with something all of us will hate. I guarantee it.
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