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Setting up a V.90 / 56K Analog Modem Pool Server

February 20th--Victoria Chan


How do you set up a low cost V.90 / 56K dial in modem pool for telecommuters, into your network? There are undoubtedly several good hardware solutions, such as fine products from Intel's Shiva, Livingstone and many more, costing in the tens of thousands of dollars. How does a small company get a Dial-In solution that is affordable, for accessing our Business System, Email and Web, mobile Order Entry system or for Time Slips entry, and etc.

Urban Legends

You will not get 56K connect speeds when two V.90 / 56K modems are each end. That is an urban legend as the best connect speed is 33.6K. For a primer on how V.90 / 56K modem technology works, check out this article at First and foremost, you need Digital Telephone lines preferably on the Server end. This would be ISDN, acronym for Integrated Services Digital Network. As it's name implies it is definitely well integrated. The cost per line, comparing POTS, acronym for Plain Old Telephone Service, shows ISDN costing less.

ISDN for Flexibility

ISDN can carry Voice as well as Data over the same medium. Sure POTS can too, but at much lower tonal quality and data throughput. Unfortunately for us in North America, ISDN did not enjoy the popularity of Europe. The standards in North America for ISDN is also different when compared with Europe, but that is a whole different subject.

An example of ISDN strength is flexibility. Let us take a closer look at ISDN BRI, acronym for Basic Rate Interface, consisting of two 64K B Channel (Bearer for Data), and one 16K D Channel (Data for Control). You need to have a UPS to power the ISDN device especially if there is no other POTS line, as ISDN lines will go down in a power failure. With the right ISDN Modem or Router that supports POTS compatibility, the single ISDN BRI can be your only phone line. You can be connected with both ISDN BRI channels, yielding a full connect speed of 128K ISDN BRI to ISDN BRI. With ISDN BRI you actually get two telephone numbers. Even when both B-channels are connected, yielding 128K, an Analog POTS phone can still dial, connect and carry out a voice or fax conversation. There is magic happening on the D-channel as this will force one of the B-channels to be diverted to carry out this other voice or fax conversation, while maintaining a 64K data connect. Another benefit with ISDN is it's instantaneously connect speed.

V.90/56K Dial - In requires ISDN

To offer V.90 / 56K connection from any V.90 / 56K modem dialing through POTS, you need to have a minimum of an ISDN BRI at the server end. The modem could be the USRobotics I-Courier modem, but the disadvantage of this modem is only one B channel is dedicated to V.90 / 56K and the other is for Voice POTS. This could be the dedicated fax line, but we outgrew that solution and required two or more V.90 / 56K simultaneous connections. To build a V.90 / 56K modem pool, you need the MultiTech ISI Hybrid Modem Adapter. These hybrid modems can support any combination of V.90 / 56K connections or ISDN connections. On researching for our Dial-In requirements, I found this product to be unique in the market place. The cost for a MultiTech ISIHP-2U hybrid modem server card supporting four V.90 / 56K connections with two ISDN BRI lines (4 Bearer Channels), is US$1400. The ISIHP-4U is US$2400, supporting eight V.90 / 56K connections with four ISDN-BRI. Multitech also has one that hooks up to ISDN PRI supporting thirty V.90 / 56K connections, but that is material for another white paper.

Now that you have the right modem for the job, you will need to build a server. This could be any existing File Server in the office, running either Unix, Linux, Novell 4.2 and higher, Windows NT4 / 2000 Server & etc. Microsoft RAS supports this modem very well under NT and 2000, and you need to be familiar with setting up TCP/IP, some basic routing and RAS.

Our Dial - In RAS Solution

For us, we needed a quick solution so we stuck to Windows NT4 server as it was already set up with our retiring USRobotics I-Courier modem. It worked so well that we did not bother to move it to our new Win2K server or Novell 5.1 box. Future direction for us? I may try this Modem in FreeBSD using Linux compatibility, even though it is not supported. This is because we are BSD wing-nuts. I would prefer to see full FreeBSD support, however.


Writing a How To for installing these MultiTech Hybrid Modems is outside the scope of this article. We have used this for over two years and I have been meaning to write up an article on this Modem. The modem has worked flawlessly for us and I would recommend this Hybrid Modem to any company that is searching for a reliable solution for RAS, instead of those high priced hardware solutions. We are authorized to sell MultiTech Products and offer expert systems consultation.