[Cu-wireless] roll your own dsl
p-riism at uiuc.edu
Mon Aug 27 00:32:10 CDT 2001
Some interesting ideas here. I know copper pairs are still around here in C-U:
Roll Your Own
Not Only Can You Do Your Own DSL, Here's How to Become a Broadband Tycoon
at the Same Time
By Robert X. Cringely
This is the week I said we'd roll our own DSL. On the surface it looks like
a daunting task, but it is actually not that hard at all if you can get
past the many regulatory loopholes. But why would you even want to do such
a thing? Well maybe DSL isn't available in your area. Maybe you want a
significantly cheaper alternative to a T-1 line. Or just maybe you and the
kid down the block want to play networked games at warp speed. Well here is
how to do it.
DSL is nothing but a pair of copper wires down which bits are pushed. DSL
companies go to great lengths to explain how hard this is, but it really
isn't. The trick is grabbing the signal off the phone line before it gets
to the local phone switch where a band-pass filter limits the frequencies
that pass through to 3300 Hz. Outfits like Covad and the other fast-fading
national DSL providers use their CLEC (Competitive Local Exchange Carrier)
status and presence at the local telco Central Office (CO) to do just that
-- grab the signal before it gets wacked.
But there is another way to keep the signal from being messed with and
that's by ordering-up from the phone company what's generally called a "dry
copper pair." This is just a pair of wires that connect one location with
another as long as both locations are served by the same CO. Most telephone
companies have (or had) a tariff for dry copper pairs varying from $15-45
per month, though they'll often lie and say it isn't available. Parts of
Verizon still have this tariff, which is usually called a "Series 1100
circuit." Historically these dry pairs were used either for the old "leased
lines" that connected serial terminals down at the local airline office or
they were used by security companies for alarm circuits. A dry pair is just
that -- a pair of wires with no dialtone down which you could send a
current to ring a bell on the other end. When you go looking for one, try
asking first for an alarm circuit (the cheapest way when available), then
an OPX (off-premise extension) line, then a paging circuit, or finally LADS
(local area data service). Keep running down the list until the phone
company says "yes."
In our set-up, we'll be using the pair to send data. This means you have to
put devices at each end of the line. One friend of mine in the East uses
gear from Telmax while my friend Brett Glass from Wyoming uses PairGain/ADC
"Megabit" modems. "These cost about $300 wholesale and can get up to two
megabits-per-second, full duplex," says Brett, who lives for this stuff.
"It's SDSL technology, so the link is symmetrical. Pairgain's boxes have
built-in 'smart' bridges, so you just plug Ethernet into them and they
automatically learn which MAC addresses are on each side. We connect our
two houses (the one we live in and my wife's computerized weaving workshop)
with these. We also connect a few businesses without radio line of sight to
LARIAT that way."
LARIAT is Brett's clever wired/wireless cooperative ISP that you can reach
through one of the links you'll find under "I Like It."
So now we have a two megabit circuit but no Internet. It's just like buying
a T-1 line (E-1, actually -- the European data standard that runs at 2.048
megabits-per-second) for, say $30. But to turn that into an Internet
connection, one end has to be plugged to an Internet backbone. There are
many ways to do this. Put one end of the circuit at your business. Put one
end at your school. Put one end in the machine room at a local ISP.
Of course the local telephone companies hate this whole idea because they
want to sell you that T-1 line for $500-600 per month. That's why they will
tell you dry pairs don't exist when they usually do exist. And that's why
phone companies are trying to get rid of dry pairs as quickly as they can.
Now let's make life worse for the phone companies by being even more
clever. Install an 802.11b access point at your end of the line and use it
to offer high-speed Internet access to the neighborhood. This is the part
of the column that feels to me like the last couple minutes of the song
"Alice's Restaurant." What if everyone got a dry pair, made an Internet
connection, then offered wireless service to their neighbors. It's a
And speaking of offering wireless service to the neighbors, there has been
a great advance in that area from Linksys, the hyper-aggressive hub makers.
This news comes courtesy of Stuart Winokur, technical support manager here
at PBS. Linksys has come out with a firmware upgrade for its WAP 11
Wireless Access point that allows two of them to function as
Ethernet-to-Ethernet bridges. The firmware is free on the Linksys Website.
The firmware also allows use of Ethernet MAC address access lists to
restrict connections to a list that is uploaded into flash ROM. That way it
is much harder for people to just cruise down your street with a notebook
computer, surfing on your bandwidth and stealing your files.
The street price of these Linksys boxes is now down around $250, which is
half the price of the next cheapest bridge, from SMC. And the Linksys units
have removable antennas, too, so you can add your own high-gainer. Since
there are three 802.11b channels in the U.S. that don't interfere, I'm
guessing you could put the bridges on Channel 1, 6 or 11, and use an
additional Access point in your house set to one of the other
non-interfering channels as a standalone access point for wireless
connections in your house and to the neighbors.
But let's say you have even grander ambitions. Not content to be a
socialist Internet Service Provider, you want to be a capitalist ISP, too.
All this dry pair stuff means that anyone who already has dry pairs -- LOTS
of dry pairs -- suddenly has an asset they never knew had value. Quick like
a bunny, buy-up that stodgy old burglar alarm company that's been limping
along in your town for 50 years. They have a dry pair (often more than one)
going to every building. Switch the dry pairs to digital, make the alarm
service digital, too, then use the old alarm panel and all that excess
bandwidth to offer both wired and wireless Internet access to the whole
town. With the lowest circuit cost and more circuits than a regular ISP
could ever afford, you'll soon be a broadband tycoon.
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