[Cu-wireless] roll your own dsl

Paul Riismandel 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:

from: http://www.pbs.org/cringely/pulpit/pulpit20010823.html

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 
beautiful thing.

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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