Previous Table of Contents Next


B-ISDN Access

B-ISDN user access is broadband in nature, relying on SDH/SONET fiber optic transmission standards. There are two access interfaces specified at this time. User Network Interface A (UNI A) operates at OC-3 rates of 155 Mbps, while User Network Interface B (UNI B) operates at OC-12 rates of 622 Mbps. Network-to-Network Interfaces (NNIs) will be provided for network access to B-ISDN from Frame Relay, SMDS and N-ISDN networks.

B-ISDN Services

The ITU-T defines two types of B-ISDN services, interactive and distribution.

Interactive Services
involve bidirectional transmission and include three classes of service, conversational, messaging and retrieval. Conversational services include voice, interactive data and interactive video. Messaging services include compound document mail and video mail. Retrieval services include text retrieval, data retrieval, image retrieval, video retrieval and compound document retrieval.
Distribution Services
may or may not involve user presentation control. For example, interactive TV is a service requiring presentation control. Interactive TV lets the viewer interact with the program, perhaps to select a product marketed over TV, to influence the ending of a movie, or to change the camera angle in order to view a football play from a different perspective. Conventional broadcast TV exemplifies a service requiring no presentation control.

B-ISDN Equipment

B-ISDN user equipment is an extension of those that were explored in Chapter 8. Broadband Terminal Equipment 1 (B-TE1) is defined as B-ISDN-compatible CPE. While the exact nature of the B-TE1 is yet to be determined, it is likely that it will take the form of ATM-compatible B-ISDN communications servers. These servers will combine the functions of a PBX, data switch, and video switch. At the extreme, they will take the form of ATM-based multimedia communications servers.

Broadband Terminal Equipment Type 2 (B-TE2) is defined as terminal equipment that supports a broadband interface other than B-ISDN. Terminal Equipment Type 2 (TE2) continues to be defined as terminal equipment that supports an interface other than ISDN. Both B-TE2 and TE2 equipment will interface with the network through a Broadband Terminal Adapter (B-TA).

B-ISDN Costs

B-ISDN implementation costs cannot be determined at this point, although they will be very high. Carrier network costs will include investments in ATM switches and SDH/SONET fiber optic transmission facilities. User investments in totally new hardware and software will be nontrivial, to say the least.

B-ISDN Advantages

B-ISDN has the clear advantage of being standards-based. As previously noted, ISDN is based on probably the most carefully though-out and documented set of standards in the history of the planet. Unfortunately, the standards actually are standards recommendations that have not been applied universally on the same basis. Whether or not B-ISDN standards recommendations will suffer the same remains to be seen.

N-ISDN was intended to be universally available. This hasn’t happened. We also will have to wait and see if B-ISDN also suffers from lack of availability. In all likelihood, the high cost of implementing B-ISDN will restrict its availability and use to areas where there exist large concentrations of customers with pockets deep enough to afford the service. Where there is sufficient density of demand, carriers will certainly deploy the underlying technologies.

B-ISDN will support connections that are switched, permanent, semi-permanent, point-to-point, and multipoint. It will support services that are on-demand, reserved and permanent; and either connection-oriented or connectionless in nature.

Based on the foundation technologies of SS7, ATM, and SONET, B-ISDN will offer significant advantages. These advantages include broadband switching and transmission, bandwidth-on-demand and the ability to accommodate all forms of data on a highly flexible basis. Finally, B-ISDN is future-proof—there are no understudy service technologies waiting in the wings to supersede B-ISDN.

B-ISDN Disadvantages

If all this seems to be too good to be true, it’s because it is! As Aesop noted in the 6th century B.C.: “Every truth has two sides; it is well to look at both, before we commit ourselves to either.” So it is with Broadband ISDN. B-ISDN standards are in their developmental infancy. True enough, the underlying technologies are well on their way, but B-ISDN really hasn’t been well-defined at this point. When those standards recommendations are set over the next few decades, they likely will remain open to interpretation, as has been the case with N-ISDN. Additionally, the cost of implementing B-ISDN will be very high—it will not be for everyone.

B-ISDN Applications

B-ISDN applications are all futures, including virtually anything one can imagine, short of teleportation, which likely will be reserved for Star Trek reruns. B-ISDN certainly will support any form of data communications we can imagine—connectivity will be supported between any imaginable combination of hosts, workstations, LANs and servers, and across any distance. Voice, data, video and image communications will be supported in the ultimate form of high-resolution multimedia.

High-Definition TV (HDTV) will be supported along with the rest, and on an interactive basis. Large, high-resolution, digital display technologies will replace the TV set and computer monitor, allowing future generations to experience the unbridled joy of interacting with their favorite talk show host on a multimedia basis and live (in real time).


Previous Table of Contents Next