Chapter 8: ISDN & Transaction Processing

The excitement ISDN brings to what is broadly called POS (for Point-of-Sale or Point-of-Service) transaction processing flows directly from the capabilities and technologies involved.

The Power of the D Channel

The ISDN D channel is, by definition, an X.25 packet-switched channel designed for call signaling and set-up. Yet because it is packet-switched, it can also be used for hundreds of other purposes: caller-to-caller messages, for commands that can control the telephone network, and - most important here - for user interconnection to the worldwide X.25 packet network.

This direct interconnection of the D channel to the X.25 network gives virtually any data device, from a telephone to a cash register, a dedicated, full-time connection to the NYNEX X.25 packet network - and thus, through interexchange carriers and public networks, to any other computer or data device, anywhere in the world. The potential uses are almost limitless:

Transfer files and messages.
Users can send and receive electronic mail, as well as share many smaller computer files. For these small messages and files, the speed of X.25 is quite acceptable.

Access information services.
Most users today access data and information services through dialed analog connections to either the public packet network or the private X.25 networks of major services. Direct ISDN D-channel connections, however, mean lower costs and faster response times. Several of today's most popular services, including Compuserve and GEnie, are instituting special direct packet connections to accommodate ISDN users.

Access databases.
Many systems, including those for work-at-home and call-center applications, offer access to a mainframe database through the D channel. Data most often consists of small alphanumeric files where packet speeds are more than adequate. A typical 500-character customer purchase record, for example, could be transmitted in less than half a second.

Real-time information.
A number of brokerages use D-channel connections to their brokers' PCs for up-to-the-second stock prices and other data.

Security and telemetry.
Buildings across the country use D-channel telephone connections for entry devices and alarms, as well as fire, heat and motion sensors.

Sales and Service Call Center Processing.
Many ISDN-based call centers now use D-channel access to the packet network to control and direct the worldwide telephone network.

Point-of-Sale/Point-of-Service transaction processing.
These range from credit card authorizations and medical insurance processing to bank-card debiting and gasoline sales.

Subsequent Sections Of This Chapter:

Understanding Packet Switching
X.25 & ISDN
Virtual Transaction