Two lines are better than one: Breakthrough multiplies modem speed

Integrated Services Digital Network modems have long used channel bonding to boost
their connectivity speeds by spreading data over a pair of wires. Why not apply the same
idea to analog modems and phone lines?

Several vendors are doing just that. U.S. Robotics Access Corp. of Skokie, Ill., Hayes
Microcomputer Products Inc. of Atlanta and Ramp Networks Inc. of Santa Clara, Calif., are
working on multiline analog devices that will arrive by the end of summer, before final
standards are thrashed out for the current crop of 56-kilobit/sec modems.

But that doesn't mean you'll be able to enjoy the multiline benefits anytime soon.
Internet service providers still have to embrace the idea.

In the meantime, you can try making your existing modems work together. Visit the World
Wide Web site at to see
how MidCore Software Inc. of Middlebury, Conn., developed what it calls modem-teaming
software to manage up to four individual connections to an Internet provider.

The MidCore product is specifically for small LANs with access to multiple modems. The
teaming software routes your Internet requests through the least-busy modem.

Analog modems with channel bonding could bring high-bandwidth Internet connectivity to
small offices at about half the price of an ISDN connection. But ultimate success depends
on whether Internet providers-not just their customers-support it and buy it.

Here's how it works. A multiline modem essentially merges the bandwidth of two or more
analog phone lines. It spreads the data you send and receive across multiple lines for
reassembly at the other end.

That's a breakthrough, because modems have already reached the physical limits of
analog phone lines. Buying a faster single-line modem no longer speeds up your throughput
because the line itself is the bottleneck.

A two-line modem that supports dual 56-kilobit/sec connections could yield nearly
112-kilobit/sec throughput. Your costs would be about $700 for the modem, $50 to $150 for
line installation, the monthly cost of the additional telephone line (about $30 depending
on location) plus your Internet provider's monthly charges. The latter would likely be
about double the cost of a single-line connection.

In contrast, an ISDN connection costs as much as $500 to install and has a monthly
service fee of about $80, depending on location. On top of that, the local phone company
charges you ISDN connect rates that average 2 cents to 5 cents per minute.

Modems that support multiple analog lines sound wonderful, but there's a hitch. Many
Internet providers have hundreds of ports that answer on a single phone number. If your
multiline modem connects to two or more of those ports at once, the provider's system must
know which two are yours, so it can divide and route the data properly. Most providers
aren't set up for that.

This problem could be solved with software so providers would not face expensive
hardware upgrades. But it's a much different approach to the way they do business. I
suspect they'll change only if there's a strong demand for it, and that's not going to
happen overnight.

Besides serving as a double Internet connection, U.S. Robotics' new LANLinker Dual
Analog router can even be attached to a LAN like two separate modems to dial out to two
separate locations. For information on LANLinker, visit

For a look at other high-bandwidth alternatives, see the High Bandwidth Web Page at
There's a good collection of technical papers and non-techie reviews of cable modems,
ISDN, 56-kilobit/sec analog modems, digital subscriber lines, wireless cable connections
and satellite Internet connectivity.

Shawn P. McCarthy is a computer journalist, webmaster and Internet programmer for
GCN's parent, Cahners Publishing Co. E-mail him at [email protected].

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