A Five Minute Guide to ISDN

Integrated Services Digital Network (ISDN) was specified by the CCITT standards body (now known as ITU-T) as long ago as 1984. It was originally designed as a "next generation" telephone system, integrating voice and data into one connection. The ISDN Basic Rate Interface (or BRI) is a standard connection you would have in any home or small business, offering two simultaneous connections (any mix of fax, voice and data). When used as a data connection, ISDN BRI can offer two independent data channels of 64kbps each, or 128kbps when combined into one connection. The ISDN Primary Rate Interface (or PRI) offers 30 channels (of 64kbps each), giving a total of 1920kbps. As with BRI, each channel can be connected to a different destination, or they can be combined to give a larger bandwidth. These channels, known as "bearer" or "B" channels, are at the heart of the flexibility of ISDN.

As we know, the standard telephone connection did not die, and in fact increasing demand for extra phone lines (and fax lines) has made the telco business very profitable. However, ISDN has grown into a premium service, which the telcos like to target towards high-end or highvolume telephony users, typically businesses rather than home users. Let's look at some of the advantages that have given ISDN its unique niche:

• Dialup is fast. ISDN calls typically dial and connect in 1 to 3 seconds.
• It's digital. 64kbps bandwidth for each "B" channel is guaranteed.
• It's multi-mode. A "B" channel can carry data, voice, fax or video.
• It concentrates calls: a PRI connection can deliver 30 concurrent calls through one cable. A BRI delivers 2 calls through one cable.
• Through MSN you can associate many telephone numbers to the same line (at a fraction of the cost of separate, multiple telephone lines).

The ISDN Primary Rate connection is well suited for server-end or central-site tasks, where many concurrent connections or calls will be handled in one place. As well as acting as a central point for incoming connections, a server-based connection to ISDN can (at the same time) act as a Gateway offering telephony services to users on the local area network (LAN) in the office. For example, a server connected to ISDN can accept incoming faxes, and route them to individual users on the LAN: this is a growing application today, since it is convenient for users to receive fax and voicemail messages in the same way that they receive email.

Most of the whitepaper discusses the central site, but it's worth focusing briefly on ISDN Basic Rate, and the user-side of the equation. ISDN BRI can be used for many purposes from a standard desktop or laptop PC. Applications are comparable to a modem, although there are some key advantages for ISDN, for example:

• 64kbps or 128kbps Internet connection, with 1-3 second dialup
• Send/Receive fax: Group 3 and Group 4 (64kbps digital)
• Concurrent Internet access and phone/fax use
• Telephony with multiple phone numbers
• Point-to-point video conferencing

ISDN BRI is ideal for remote working (teleworking), since it gives access to most of the services available in an office including: telephony; fax; email; Internet. The fast dialup speed and high throughput (when compared to a conventional modem) offers a more effective remote working environment.

Eicon Networks offers one of the largest product families for ISDN, both for teleworkers and for central site applications, such as we will see in the next sections. Eicon Networks' remote access products, DIVA, are widely known across the world, and the server-end (or central site) products are known by the name DIVA Server.