Moving toward ISDN interoperability - ISDN interface devices in a nonstandardized industry - Technology Information

Communications News, Sept, 1997

There is a wide and varying array of ISDN services and products waiting to service today's band-width-hungry road warriors and telecommuters, but it's easy to get confused by the choices.

Though ISDN was created more than 10 years ago, it is just now seeing mass deployment internationally and throughout the U.S. As a result, standards to enhance the usability of ISDN are still being developed and deployed, in some cases without adequate interoperability testing.

The formal CCITT standards consider all ISDN interface devices to be terminal adapters (TAs), but the reality is that ISDN products providing data capabilities fall into one of three categories: ISDN routers, asynchronous/synchronous TAs, and fully synchronous TAs.

ISDN routers are small devices that route ISDN traffic to and from a local LAN such as Ethernet. They can usually support multiple clients on the LAN interface, often providing dynamic IP addressing for these clients. Shiva's AccessPort is an example.

Asynchronous/synchronous TAs often connect to the client via a serial connection and are configured via the popular AT command set. They are usually easy to install, configure, and use, but often suffer from the performance limitations of a serial connection. Examples of these devices are 3Com's 3ComImpact IQ, Motorola's BitSURFR Pro, and Adtran's Express XRT.

Fully synchronous devices tend to be internal to the client and are programmed via a software application programming interface (API) allowing direct control of the ISDN B-channels. This often comes at the cost of ease of installation and configuration. Eicon's DIVA Pro 2.0 PCI U Interface is an example.

STANDARDS & INTEROPERABILITY

Over the past few years, the Internet Engineering Task Force (IETF) has been busy creating standards for ISDN. But before standards are proposed and ratified, vendors often create products to non-ratified specifications, perpetuating interoperability difficulties until products can be updated to newly passed standards.

This happened as the IETF's standard for the multilink protocol (MLP) evolved from a draft proposal to the final, accepted standard. Fortunately, most ISDN vendors have now implemented the ratified MLP standard and have also ensured proper interoperability with other ISDN vendor products.

But there are still many products in users' hands that have old MLP implementations. Draft proposals for the bandwidth allocation control protocol (BACP), data compression, tariff management, and security are working through the IETF standards process. As a result, we may see products delivered with implementations of these draft proposals, causing further interoperability concerns.

Determining which device to buy can be difficult. As a general guide, first evaluate your needs and resources. Do you need to support multiple client PCs or just one? How many ISDN lines do you have available? Do you have an open slot in your PC and the expertise to install an internal ISDN device? What is your budget?

Stay in touch with your ISDN device vendor. As ISDN standards and implementations evolve, vendors are sure to create updates to add features and resolve bugs in product firmware and drivers.

Search for vendors who are driving standards while they support current releases with added value and backwards-compatible solutions where there are no standards.