As seen in the February/March 2002 issue of
LAW OFFICE COMPUTING
www.lawofficecomputing.com
O
rganizations with seve ral offices
located in the same city usually
want to link them into a single secure
n e t work. Although, not applicable for all
situations, if your organizations are with-
in the same city, you might be able to
set up a “campus” type system using sin-
gle-line Digital Subscriber Line (SDSL )
modems connected by a single pair of
phone wires.
This pair of wires, re f e r red to by
various names by different phone com-
panies, is most often called a “dry pair.”
This is an unconditioned telephone wire
c i rcuit from one location to another
without telephone equipment connect-
ed to it. These circuits are often much
less expensive than other alternative s
offered by the phone company, and can
a c h i e ve synchronous speeds of 2
Megabits per second
(Mbps) in each direction within dis-
tances not exceeding two miles.
Connection speed begins to drop after
distances exceeding two miles, but
respectable speeds can be achieved at
distances of four to five miles.

t h rough a telephone wire center or
switch office unless you are running
your own direct wire.)
The Wide Area Network (WA N )
was constructed to share netwo r k
re s o u rces and to minimize the number
of Internet Service Provider (ISP )
accounts and the need to secure each
access point (including emergency ser-
vice providers), which is best done using
h a rd - w i red land line communications
using a single broadband access point
that is shared by all offices and secured
with a firewall and antivirus system. We
looked at seve ral options, including a
virtual private network (VPN) and wire-
less networking, before deciding to use
SDSL modem bridging.
Although 80 2 .11b wireless net-
working was feasible and could provide
11 Mbps basic Ethernet performance,
80 2 .11b is expensive, with pre l i m i n a r y
Create a WAN Using
SDSL Modems
These bridging devices can connect to remote
segments of your LAN.
By Joseph L. Kashi and Thomas Boedeker
Bridging the Gap: The 300S modem was plugged in at each end point and connected phone
cords to wall jacks on each end for this installation.
As seen in the February/March 2002 issue of

locations, and then had the phone com-
p a ny install four regular phone jacks in
our central office, one for each end of
e very dry pair link. Then, we simply
plugged in a 300S modem at each end
point and connected the phone cord s
to the wall jacks on each end. Wi t h i n
about 30 seconds, the modem indica-
tor lights showed good circuits. We then
connected the SDSL modem to our net-
work using Ethernet cables.
Initially, we had some internal net-
work problems until we determined that
we needed to use an uplink port on our
hub or switch or use a cro s s over cable if
connecting the modems to a standard
Ethernet port. Once the modems we re
p roperly connected to our main net-
work, individual segments we re able to
see each other. No other configura t i o n
was re q u i red. Although you give up
some flexibility, security and contro l ,
simple WAN bridges are an easier
method of connecting network seg-
estimates at about $25,000, and it’s
also potentially less secure. VPN wa s
also possible, but in our local market,
a vailable VP N options we re not syn-
c h ronous with an $8,000 estimated
setup charge. VPN also had a re c u r r i n g

consistently obtained better thro u g h p u t
for a given line distance than the ve n-
dors’ published estimates.
We installed an ADC Megabit
Modem 300S (www.adc.com) with
switch selectable speed options of up to
2 Mbps, partly because we knew some-
one who already had good experience
with this product. The 300S has an RJ -
45 port to connect to the network and
an RJ-11 port to connect to the dry pair
using a standard phone to wall cord. It
uses an external power supply and is
priced at around $400.
S e ve ral other SDSL modem models
a re available, including the NetTo N e t
SNE 2000-S, the MuLogic DSL - 2048
and the Netopia R7200. Howe ve r ,
some models are limited to 1.54 Mbps.
Some other models also offer differe n t
connector options, so we suggest yo u
check carefully to be sure you have the
correct parts and connections on hand.
Our plan to connect five separa t e
locations required us to choose our cen-
t ral office, where the main servers are
located, as the WAN’s common point.
Benefits and Downsides of SDSL
The benefits we achieved using dry pair SDSL WAN were:
1. Simple setup and maintenance.

to six computers we found no significant
reduction in speed.
As we extended to three and a half
miles we saw throughput speed drop to
about 1.5 Mbps, still T-1 speed at a
small fraction of the cost. These re s u l t s
e n c o u rage us to consider a longer link
of five miles. Although that longer link
has not been installed and tested, we
h a ve read about similar SDSL bridges
achieving T-1 speeds over distances of
four to five miles, but these longer dis-
tances work better if the copper wire is
the heavier 24 AWG rather than the
26-gauge wire that is common in older
areas.
S e ve ral other points should be
noted. If you have been using a
Dynamic Host Configuration Pro t o c o l
( DHCP) server on each LAN segment
to assign Internet Protocol (IP) addre s s-
es, you need to shut off all but one in
o rder to avoid potential conflicts in
a d d ress assignment. And, with many
security systems, you are limited to one
range of IP addresses. This will limit yo u
to 255 devices connected to the net-
work on all segments combined.
If you have a need to connect sev-
e ral offices located within two to seve n

University in 1976. He is admitted to prac-
tice before the Alaska Supreme Court, the
U.S. Supreme Court and the U.S. Court of
Appeals for the 9th Circuit and speaks fre-
quently on legal automation topics.