Why Did Broadband-ISDN Really Die?

There are positive reasons for the smooth uptake of IP, such as the easy availability of the TCP/IP stack as compared with competing proprietary data protocols, the relative simplicity of the basic Internet architecture, and the prior existence of enterprise multiprotocol routers that could be used directly as Internet routers.

Perhaps more important, though, were the problems with ATM. In the 1980s when ATM was being designed, the dominant usage mode was seen to be the multimedia successor to the phone call—human beings making videophone calls. As we saw above, interactive multimedia is the most challenging application for packet networks, requiring a complex infrastructure of signaling, terminal capability negotiation, and QoS-aware media transport. It was not until the mid-nineties that large ATM switches capable of supporting the required signaling and media adaptation came to market—too expensive and too late.

Even worse, the presumed videophone usage model for B-ISDN was highly connection-oriented, assuming relatively long holding times per call. So ATM was designed as a connection-oriented protocol with substantial call set-up and tear-down signaling required for every call to reserve resources and establish QoS across the network. This required per-call state to be held in each of the transit network switches. For comparison, millions of concurrent calls (sessions or flows) transit a modern Internet core router and that router knows nothing whatsoever about them.

It turned out that critical enabling technologies for the Internet, such as DNS, require brief, time-critical interactions for which a connection-oriented protocol is inappropriate. Even for connection-oriented applications such as file transfer, which use TCP to manage the connection, connection state is held only in the end systems, not in the network routers, which operate in a connectionless fashion. This has allowed the Internet to scale.

So in summary, ATM had too narrow a model for how end-systems would network, and backed the wrong connection-oriented solution that couldn’t scale. Because ATM was designed against a very sophisticated set of anticipated, predicted requirements, it was very complex, which led to equipment delays, expense, and difficulty in getting it to work. The world moved in a direction not anticipated by the framers of B-ISDN and it was stranded, and then discarded.

Why Broadband ISDN?

The carriers knew they had to packetize their networks, and that they needed a new architecture (B-ISDN) supported by a number of new protocols. Here are some of the functions carriers thought they wanted to support.

§  Set up a multimedia video-telephony call between two or more people (involves signaling).

§  Carry the call between two or more people (involves media transport).

§  Permit access to music, TV programs and varied computer applications.

§  Allow computers to communicate efficiently at high speeds.

Each of the above functions would be a chargeable service, leading to billing the customer. Carriers also needed to provision, operate, assure, manage, and monitor their networks as per usual.

When carriers contemplate network transformation or modernisation, they like to huddle amongst themselves in the standards bodies to agree their target services and design a standardized architecture. The latter consists of a number of components, implemented using switches and servers, plus standardized message formats (protocols) to provide the intercommunication. It’s easy to see why this ends up as a monolithic and closed activity—it all has to be built by the vendors, slotted together and then work properly. Getting the architecture into service is usually a highly complex and multi-year activity, and the cost will have to be covered by more years of revenue-generating service. Supporters of the model have pointed to the scalability and reliability of modern networks, the accountability, which comes from centralized control, and the sheer functionality that can be put in place by organizations with access to large capital resources and internal expertise.

Critics point to the monopolistic tendencies of capital-intensive industries with increasing returns to scale, the resistance of carriers to innovation and the overall sluggishness and inflexibility of the sector. They note that circuit-switched networking began in the 1860s and that it had taken a further 130 years to automate dialling and digitise calls. By the time I was asking my question in Canada, B-ISDN had already been in gestation for around 15 years with no significant deployment.

The Internet, of course, also took its time to get started. TCP/IP came into service in 1983 and by the late eighties research groups were using e-mail and remote log-in. The fusion of hypermedia and the Internet gave us Web browsers and Web servers in 1993–94 and launched the explosion in general Internet usage. By 1996 there was already a debate within the vendor and carrier community: was the future going to be IP and was the B-ISDN vision dead? It took a further ten years for the industry to completely take on board the affirmative response.

The Internet always ran on carrier networks. More precisely, the basic model of the Internet comprised hosts (computers running an IP stack and owned by end users) and routers (sometimes called gateways) forwarding IP packets to their correct destinations. The routers could be operated by any organization (often maverick groups within carriers) and were interconnected using standard carrier leased lines. Almost all hosts connected to the routers by using dial-up modems at each end across switched telephone circuits. So from a carrier perspective, the Internet was simply people buying conventional transport and switched services—the specificity of the Internet was invisible. In truth, the Internet was beneath the radar of the B-ISDN project.