ISDN is now a mature technology but will it ever replace leased lines? Or will it be overtaken by new technologies, such as DSL? Geoff Marshall investigates

Rhetorik, the network market intelligence company, reports a huge rise in corporate use of ISDN technology over the wide area. When comparing today's installed base with that of one year ago, Rhetorik finds that the number of sites using ISDN has soared from 50% to 65%. During the same period the percentage of sites using leased lines has decreased from 80% but still leads the market with a huge base of 78%.

The main justification for the shift towards ISDN is the reduction in installation cost and lower call charges now available. This trend is likely to continue over the coming year and Rhetorik expects ISDN to take the top slot by October 2000. Richard Foskett, Managing Director of Rhetorik, commented on some of the key findings, "It has taken many years for ISDN to build its installed base. This is mainly due to British Telecom historically demanding high charges for ISDN in comparison to other European countries.

As a WAN technology, it is ideal in that it is now increasingly cost-effective and provides reliable, high-speed connection as and when required. Over the next twelve months we expect that it will steal the top slot from leased line technology in the wide area. Other technologies in this space have had little impact. We see X.25 disappearing, although it is hanging on with a share of 4.7%. Frame Relay is gaining ground, rising from a share of 14% to 17% in the space of a year. However, ATM is making little or no progress and it remains at the bottom of the league table being used by a mere 3.7% of the sites surveyed."

If you want to host your own web-site, or call charges have gone through the roof, a leased line is the logical choice. Some local operators are offering a wireless alternative, giving 2 Mbits/sec throughput at a better price than the corresponding Megastream line.

On the other hand, analogue is still surprisingly popular for home and SOHO business users. A low-tariff analogue dial-up line for Internet access must offer the best value until ADSL matures, as the installation, rental, and usage charges are a fraction of the corresponding BT Highway alternative, with a minimal reduction in performance (48k average for a V.90 modem, vs. 64k ISDN). NTL is offering a second line upgrade, with 1p per minute local connection aimed directly at the Internet user. Black Box, a major catalogue-based vendor, offers products to aggregate data over several analogue telephone lines if 48k is not sufficient.

We spoke to Patrick Hudgell, Managing Director of Black Box, regarding the possible impact of ADSL on the ISDN market: "From the point of view of performance, ADSL is obviously a far more attractive proposition than ISDN. The only problem is that it is not yet available in most areas and is still prohibitively expensive for most users. The only reason that I can think of why BT are being so slow about introducing ADSL is that they are waiting to re-coup the investment that they've made in ISDN infrastructure.

Having said that, the latest Black Box Network Industry survey (June 1999) shows that 88% of organisations now use ISDN (compared with 67% in September 1997) so perhaps it is the home user that still needs to be attracted to the ISDN world? If this is true then I suppose one way to get ADSL would be for everyone to rush out and get ISDN, thus fulfilling BT amortisation costs for ISDN. But, of course, then they wouldn't want ADSL!"

According to John Porter, Product Development Manager at Eicon Technology, a major vendor of ISDN hardware: "The European ISDN market today -- for data CPE (customer premises equipment) units -- is estimated by Dataquest at between 4 and 5 million units annually, and growing at 20% per annum. Eicon has nearly 20% of this market, and is a leading vendor in eight countries across Europe. Depending on the country, and essentially local tariffing, ISDN is being used both as a consumer service - primarily in Germany, Scandinavia, and Benelux - and an SME business service everywhere."

Why ISDN?
Businesses require faster access -- ISDN works at 64K or 128K both ways so is between 2 and 8 times the speed of the fastest modem and will give a full 64K or 128K throughput. In many instances this can be further enhanced through the use of software compression. Quality of Service -because ISDN is digital the quality of the link is almost totally error free.

Breadth of Service - ISDN, in both Primary and Basic Rate format, is available to nearly all the population. Although BT Highway has certain restrictions, it is still widely available.

Compatibility - ISDN is a standard, which means any manufacturer's device can talk to another manufactu er's product using PPP or Multi PPP.

Flexibility - ISDN is very flexible in that it can be used for a large number of different requirements from the user at home; a small office of peer-to-peer users that require to have a phone, fax, email and Internet access from one device using MSN; the remote notebook user requiring GSM access to the ISDN router at HQ, to the WAN network.
Proven Technology - ISDN has been around for 10 years and is widely used for WAN connectivity and remote access to a corporate network. The technology is very effective and well proven, with over 2 million ISDN channels supplied by BT. In most scenarios the users do not have to 'make' a call using ISDN -- it happens in the background, unlike a modem connection. The more sophisticated devices also 'drop' the connection if no traffic is going over the connection thereby reducing costs.

ADSL
DSL stands for Digital Subscriber Line, and is a local-loop technology that can achieve higher speeds than ISDN over the installed base of traditional copper pairs. There are many variants of DSL, but the one being talked about most is Asymmetric DSL (ADSL), which provides a fast (upwards of 2 Mbits/sec) downlink to the customer, but a slower uplink that is ideally suited to Internet browsing. ADSL is, however, not really suitable for WAN links, which would be better served by the other DSL variants, such as HDSL, SDSL, and VDSL.

ADSL is today in advanced trials in most European countries, and in some cases is actually being delivered in low volumes, offering greater bandwidth than ISDN in any format, Primary Rate or otherwise, and supporting plain old telephone copper cable. However, there are still serious technical, commercial and competitive issues to overcome, and even from an application viewpoint it is not clear how ADSL services will be finally positioned.

Whilst it is expected that ADSL will become a mainstream offering by regional PTTs, it is not expected to replace ISDN -- where returns on considerable recent investment still need to be realised -- rather, it will provide a higher bandwidth service where customers require this. This is indeed similar positioning to analogue modems and ISDN, where the analogue modem is far from dead but customers requiring a higher service level are upgrading to ISDN.

The main reason that ADSL is being hailed as the 'next technology' is its speed capability (up to 8 Mbits/sec downstream). Once ADSL becomes available, it will change the way users access the Internet. However, it is point-to-point technology not point to multi-point. Users requiring point to multi-point will still buy ISDN as will those users who will find ADSL too expensive in its initial stages.

SAS Distribution is the UK distribution channel for AVM and BinTec Communications. Stephen Stanway from SAS Distribution says, "Although ADSL is going to make a large impact on the market, this will be for users requiring very fast Internet Access and large volume downloads, but do not want to pay for a leased-line connection. For those users who have a lower volume requirement, ISDN will remain the preferred choice. ISDN is also ideal for users who require point to multi-point communications or access to a Corporate Network using GSM technology." Many of the vendors offering DSL products are the same a those with an ISDN portfolio - for example, Ramp Networks now has a DSL router as well as traditional ISDN and modem products.

CONCLUSION   
For business use, ISDN is the technology of choice thanks to the immediate connection, aggregation, routability, and reliability - until the connection stays open for over 4 hours per day - or ADSL matures, as it has in the North American market, leap-frogging ISDN.

So, the ISDN market is increasing at a very fast rate and will continue to do so even with the advent of technologies like ADSL. The technologies are very different and ISDN will certainly not cease in the short-to-medium term. The main reason that ISDN is growing at such a pace is that businesses need point to multi-point access to data stores or remote access. The current growth of ISDN is 50% more than this time last year. The sales of BT's Business Highway are similar to Home Highway but both are far exceeded by ISDN-2e. BT is promoting ISDN very heavily and the cost is now such that virtually any user can access the service without thinking of the cost as being a limiting factor.

BT is also providing its customers with ISDN products (like BT SpeedWay from AVM, a very low-cost, easy-to-use, internal or external controller). The take up by users of this type of service is estimated to have exceeded 100,000 in a year. Because ISDN technology has been around for some years the routers and software that are on the market today are very good and, if used in the right way, are very effective for business.