You'd think using an existing ISDN line would be simple
Last month, I described the tribulations I endured while trying to establish an ISDN connection in the small office/home office (SOHO) lab I maintain at home. I wanted to have the ISDN line installed so that I could connect my SOHO lab to the Windows NT Magazine Lab, which already had an ISDN Basic Rate Interface (BRI) line. Using this connection, I planned to examine many issues associated with remote branch office and SOHO connectivity.
However, US West has still not activated my home ISDN line. This month, I decided to try to configure the Lab's ISDN connection for X2 (up to 56 kilobits per second--Kbps) access, hoping to achieve higher-speed connections than my 28.8Kbps modem provides.
Defining the Connection
I'll bet you're wondering why I chose X2 instead of K56Flex technology. I wanted a Lab connection that would work well with Remote Access Service (RAS), support ISDN BRI (128Kbps) connections, support standard V.34 (or slower) analog connections, and support 56Kbps connections. When I reviewed my options, the 3Com/U.S. Robotics Courier I-modem appeared to be ideal; it met all my criteria. The fact that the I-modem uses X2 to obtain 56Kbps connections was incidental.
After deciding on X2 connectivity, I did what I always do when I approach a new ISDN implementation: I called my buddy Mel, who owns and operates an Internet Service Provider (ISP) based solely on ISDN and frame relay technology. When I told him my plan, Mel's first words were, "You're nuts to implement a modem-based solution. It'll limit you to the maximum rate of the serial interface on the server (115Kbps), not the maximum BRI rate (128Kbps). You'd be much better off with a LAN-attached solution."
I fully understood Mel's concerns, but his advice didn't take into account everything I wanted my I-modem to enable me to do. I wanted my connection to support NetBEUI and IPX. Most LAN-attached solutions for ISDN access are TCP/IP-based, which would seriously limit the software I could test between the Lab and my SOHO lab.
Still, I contacted 3Com/U.S. Robotics, which also offers a family of LAN-attached servers. The company's smallest unit, NETServer, includes integrated I-modems, supports multiple protocols, works well with RAS, and can attach to my Ethernet network. However, the smallest NETServer supports eight BRI connections. The Lab has only one BRI connection. The NETServer struck me as overkill, and I decided I was better off relinquishing the 13Kbps difference between the 128Kbps BRI speed and 115Kbps serial speed. Besides, using a standalone I-modem is much simpler than setting up a LAN-attached solution. You attach the I-modem to your RAS server as you would attach any other modem. The Windows NT driver database comes with support for the I-modem.
So, I set my course of action. I decided to ignore Mel's advice and go with a standalone I-modem that would attach to one of the RAS servers in the Lab.