ISDN and Analog Access in One PackageWith ISDN services becoming more available, users who crave higher-speed access are quickly making the move to such services. But most people soon discover there are still many situations where they need to connect to traditional analog modems.
One way to get both forms of access is to have two access lines--an ISDN link and an analog phone line--each with the appropriate termination equipment (an ISDN terminal adapter and a modem, respectively). But from a financial perspective, that hardly makes sense, especially when you consider that you can use an ISDN link for both voice and data connections.
For those users who truly need both types of access, a new solution is starting to emerge: hybrid devices that connect to an ISDN line and also support analog modem communications. Such products are essentially enhanced ISDN terminal adapters, but a more apt name for them would be ISDN/analog modems. Products in this category include the Courier I-modem with ISDN/V.34 from U.S. Robotics, the Elite Series ISDN modems from Zy-Xel, the Hybrid Modem TA 200 (also known as the HMTA 200) from Motorola, the ISDN System Adapter from Hayes, and the WaveRunner from IBM.
These devices typically cost more than modems that incorporate V.35 technology, and they're usually just a bit more pricey than standard ISDN terminal adapters. However, they sell for less than what a combination ISDN terminal adapter/high-performance modem would cost. For instance, the ZyXel Elite Series ISDN modems start at just $549.
These hybrid products allow you to take advantage of an ISDN link's higher bandwidth when ISDN is available at the other end of the line. For example, they enable you to connect to an Internet service that offers ISDN connections. And if the endpoint on the connection doesn't support ISDN, these devices can also support a link to a traditional modem (see the figure "Simplifying Digital Access").
These new devices can be regarded as modem replacements. However, they should not be confused with higher-end products, such as access routers that can combine ISDN and analog access into one device through separate ports.
The new ISDN/analog modem-like products are just that: modem-like. For example, for analog access they use the same communications software programs as a regular analog modem. Also, many use standard AT commands (with slight modifications) for ISDN connections.
The biggest difference between ISDN/analog devices and regular modems is that the former are more difficult to configure. This is because of the complexity involved in making an ISDN connection. If you don't have your equipment configured correctly for your local exchange carrier's central-office equipment, an ISDN/analog hybrid modem will not work. This is an ISDN-specific problem common to all ISDN modems, not just the hybrid products.
That's in contrast to the case of two regular modems attempting to establish a connection. If the two devices are configured differently--say, to operate at different data rates--they are capable of negotiating at the start of the call and settling on a default transmission rate that both can handle.
When you use an ISDN/analog modem, however, you are typically required to enter information about the type of switch that the central office is using, the SPIDs (service provider identifications) associated with the channels over which the connection is being made, and the telephone numbers of the SPIDs. All this information varies, depending on the local exchange carrier whose equipment you are connecting with.
There are other parameters that sometimes require setting when you are establishing an ISDN connection. But the switch type, SPIDs, and telephone numbers are the ba-sic ones you need to get an ISDN/analog modem up and running. To help, manufacturers of these hybrid devices include configuration tools to make the setup process easier. For example, U.S. Robotics offers an easy-to-use configuration menu and includes a test routine that checks to see if you can establish a connection. Motorola includes a Windows-based configurations manager with the HMTA 200.
All these products support connections with the major ISDN switches you are likely to find in a local exchange carrier's central office. These switches include AT&T's 5ESS, Northern Telecom's DMS-100, and those that are compatible with the National ISDN-1 specifications.
Varying Uses
ISDN/analog modems can have many uses. One place where they are likely to be installed is in homes that have ISDN services. For instance, a telecommuter might use one to dial in to the corporate network at high speeds or to access the Internet over an ISDN link. Using the same device, that person can also make a connection to CompuServe or another corporate site where analog modems are used to accept incoming calls.
The first step you must take to use an ISDN/analog modem is to obtain ISDN services. Most telecommuters are likely to get BRI (Basic Rate Interface) service, the basic ISDN residential offering of most carriers. BRI service provides two B (i.e., bearer) channels, each of which offers 64-Kbps rates, and one D (i.e., data) channel that carries signaling information at 16 Kbps.
You can configure the B channels in any one of several ways. For example, you can combine them to achieve a resulting aggregate bandwidth of 128 Kbps. At this rate, videoconferencing and transferring large files become realistic options for the telecommuter. In addition, connections to high-overhead protocols, such as the X Window System, become more tolerable. You can, of course, choose to allocate the B channels so that one is for data and one is for voice. This gives you between two and four times as much bandwidth than you could obtain using the fastest modems.
Driving the Market
ISDN has been around for many years. However, not until the past two or three years have a significant number of the RBOCs (Regional Bell Operating Companies) made the services more widely available throughout their territories.
Fueling the growing demand for ISDN services are applica-tions such as remote LAN access, personal videoconferencing, and collaborative work-sharing programs. Before ISDN, of course, most users simply relied on analog-modem connections to the LAN. But the main reason people are now buying the new ISDN/analog modem devices is to obtain Internet access, according to the vendors. Anyone who regularly surfs the Internet can probably understand why this is so. It all has to do with WWW-site (World Wide Web) access. Such access involves receiving many data types (e.g., graphics, audio, and movie clips) that are difficult to compress. This makes it painfully slow to access them using even a high-end analog modem.
Many Internet service providers are now offering ISDN links to their service. And in April, another on-line service, Prodigy, announced that it, too, would offer its users ISDN access, primarily to improve Internet and WWW-site access.
But Internet access aside, many users are now moving to ISDN because it has become much more affordable than it was in the past. Some RBOCs, for example, are pricing ISDN services attractively to entice home users. For instance, Pacific Bell, which has been one of the most aggressive carriers in terms of rolling out ISDN services to its customers, is offering residential ISDN services for about $25 per month, plus per-minute charges of 3 cents for the first minute of a local call and 1 cent for each additional minute. Even better, these per-minute residential charges apply only during prime times--there's no charge during the weekends or at night.
Basically, everything seems to be coming together for ISDN access. The telecommunications charges for ISDN services are getting reasonable, and user demand for higher-speed access to LANs--and the Internet--is growing.
PRODUCT INFORMATION
Courier I-modem with ISDN/V.34from......$595 U.S. Robotics, Inc. Skokie, IL (708) 982-5010 fax: (708) 933-5800 BBS: (708) 982-5092 Elite Series ISDN modems................$549-$749 ZyXel Anaheim, CA (714) 693-0808 fax: (714) 693-8811 BBS: (714) 693-0762 Hybrid Modem TA 200.....................$895 Motorola, Inc. Transmission Products Division Huntsville, AL (800) 451-2369 (205) 430-8000 fax: (205) 430-8926 ISDN System Adapter.....................$999 Hayes Microcomputer Products, Inc. Norcross, GA (800) 964-2937 (404) 840-9200 fax: (404) 441-1213 WaveRunner..............................$545 IBM Armonk, NY (800) 426-3333 (914) 765-1900
Telecommuters can use an ISDN/analog modem device to dial in to the corporate network at high speeds or to access the Internet over an ISDN link.
Devices that combine ISDN and analog-modem functions into a single unit give you the flexibility to connect to a variety of services and devices.
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