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.

ISDN : SDN pricing, ISDN loose traffic

ISDN
The most common type of circuit switching used in business today is an ISDN. “Integrated services” means that a user can send voice, data, and video across the network at the same time. “Digital” refers to the fact that the lines provided by the telephone company transmit digital, not analog, signals. Digital is cleaner and faster than analog. Computers using a normal analog phone line use modems to convert between the computer’s digital signal and the phone line’s analog capabilities. ISDN, being digital, requires no modem but does require the use of a network adapter. It looks just like an external modem but costs three times as much.

ISDN comes in two sizes: large and really large. Basic rate interface (BRI) is normally used by a single person, while dozens of employees may use one primary rate interface (PRI) connection for voice and data traffic. BRI is used for applications such as telecommuting, Internet access for a single user, and, occasionally, videoconferencing. PRI has the same bandwidth as a T-1 and is used for similar purposes: to connect multiple users to the Internet or to carry voice calls from a PBX to a carrier.

BRI
ISDN technicians say BRI is “2B + D,” meaning the service has two separate bearer channels for transmitting information and one data channel used behind the scenes for signaling. The bearer channels have 64-Kbps bandwidth each, and the data channel has 16-Kbps bandwidth.

PRI
PRI is “23B + D.” There are 23 bearer channels and 1 data signaling channel. These 24 channels are the standard used in the United States and in Japan. Elsewhere in the world, PRI ISDN uses 30 channels. One of the main advantages of the D channel used in PRI ISDN is that an inbound caller’s phone number can be passed along to the PBX, which is very helpful for call centers.

ISDN pricing
ISDN installation costs vary widely from carrier to carrier and can sometimes be waived. After the customer has purchased the equipment and paid for the installation, the following monthly recurring charges apply with both types of ISDN: line charges, local calls (if measured service), and longdistance toll calling.

Monthly line charges for BRI ISDN are between $50 and $150. PRI ISDN line charges are normally between $300 and $1,000. The charges for local calling and long-distance calling are about the same as standard voice telephone call rates.

ISDN began to be widely offered by the telephone companies in the late 1980s. Although the service promised many improvements over previous technologies, customers were not eager to subscribe. Some blamed poor marketing by the telephone companies, but the real reason is probably because the initial service offerings were too confusing to business people. The phone companies required prospective ISDN customers to be too involved in minor technical decisions. The whole process was a turnoff to business people, and ISDN got a bad name. Some said ISDN really stood for “innovations subscribers don’t need.” Over the past few years, the telephone companies have made new activations less painful, and the demand for fast connections to the Internet has breathed new life into ISDN service.

ISDN loose traffic
ISDN is a measured service, and users pay for each minute of calling in addition to a flat monthly fee. If a new ISDN customer does not inform the long distance carrier of the new ISDN line, then the calls will be billed on the LEC’s ISDN bill. The calls will be billed at casual rates, which may be $0.35 to $3 per minute. Customers whose ISDN calls are being billed at casual rates on their LEC bill should inform their long-distance carrier, which can move the ISDN loose traffic to the long-distance bill. This should result in much lower pricing.

Although circuit switching was an improvement over dedicated private lines, phone company upper management still was not satisfied and continued to worry about traffic jams on their telephone network. The biggest problem with circuit switching, from a telephone company perspective, is that, similar to regular voice calls, the phone company circuit is tied up for the entire length of the phone call. During a regular voice call, if one person sets the phone down to check the roast in the oven or answer the doorbell, the phone line is still tied up. Even though the line is quiet and no data is being passed across it, the line is still tied up and no one else can use it.

When thousands of businesses across the country make simultaneous circuit switching calls, there may eventually be a shortage of capacity. Once again, phone companies sent their engineers back to the drawing board with a similar charge “to figure out a way to send even more data across the existing phone network.” The end result was packet switching.