ISDN voice

Many people looking at ISDN, especially in the price range of these products, are interested in reducing their costs as much as possible. Since ISDN has two B channels and supports both voice and data applications, using the ISDN connection for both is attractive.

ISDN phones are available and powerful, but they are relatively expensive. Most people considering this class of products want to keep their costs to a minimum and are looking for ways to use low-cost analog phones.

3Com's Impact includes a port for an analog telephone. It supports simple calling and does not support any of the sophisticated voice features that are available for ISDN.

Since the line power for NT1 and Impact are provided from a wall outlet, the phone service provided by Impact disappears when there is a power failure. A battery backup system is required if you want to maintain your ISDN telephone service during a power failure.

We had a number of problems with Impact's telephone port. We are served by a Northern Telecom, Inc. central office switch using their pre-National ISDN-1 implementation, which is Windows NT's ISDN release that came before its National ISDN-1 release at the end of 1992. While pre-National ISDN-1 is common in California, it is rare in other parts of the country. Occasionally, it would take us several seconds to get a dial tone. Also, we were not able to get voice and data to work alternately when we had entered only one Service Profile ID into Impact. 3Com said these problems are unique to the pre-National ISDN-1 implementation on the DMS-100 and they do not occur under National ISDN or on the AT&T 5ESS central office switch.

IBM provided us with its 7845 NT1 to support our voice testing. The 7845 provides an analog telephone interface in addition to the S/T interface. It also includes a 12-volt, 2.2-ampere-hour sealed lead-acid battery that will lasts 18 hours with the phone on-hook and 6 hours if the phone is used continuously. This is more than enough for anything other than a major disaster.

The 7845 supports many of the sophisticated ISDN features using hook flashes and tones. These features include speed dialing as well as call hold and multiple call appearances. It even lets you block incoming calls based on the telephone number of the calling party as delivered by the ISDN network.

The 7845 worked flawlessly for us. At $350, the 7845 costs $200 more than the street price of the lowest cost NT1, but it makes an attractive package that provides sophisticated voice capabilities when it is used with S/T products such as IBM's WaveRunner or ISDNtek's CyberSpace Internet.

Digi International, Inc. has recognized that many users will want to use the DataFire along with a product like the 7845 and will be introducing an S/T version of the DataFire in June.