Look Twice Before Diversifying into Telephony
troubleshoot because they resemble background noise or hop frequencies quickly. In general, these difficulties have made spread-spectrum equipment more expensive. However, recent advances have made low-power, packet radio transceivers much less expensive.
Packet-Switching. Packet-switching is a communications technology widely available today in many different forms. The Internet is based upon a packet-switching protocol called TCP/IP (Transmission Control Protocol/ Internet Protocol). This protocol comes standard with any UNIX system. Another common packet-switching protocol, X.25, is typically used for lower-speed applications, (at or under 56 kilobits per second (Kbps)). X.25 is widely available and relatively inexpensive. The internal packet-switching protocol in most packet radio networks remains a proprietary format derived from the X.25 protocol. Packet-switching vendors have modified X.25 to optimize radio network transmission. As with any proprietary protocol, the user becomes dependent upon the manufacturer for equipment.
During the last four years, two new forms of packet-switching have developed. Frame relay, which operates from 56 Kbps to 1.544 megabits per second (Mbps), is commonly available as a wide-area networking protocol from local and long distance carriers. Frame relay improves upon X.25 by reducing overhead for error-checking to generate higher data throughput. The newest protocol, ATM (asynchronous transfer mode), first became available in 1993. ATM allows only fixed-size packets (cells), but these can be switched at very high line speeds (in the gigabit range).
While frame relay is now widely available in major metropolitan areas, ATM has just made its market debut. Currently, frame relay appears to have become the packet-switching protocol of choice because of its price/performance ratio (for equipment and service). In the future, most industry analysts agree that ATM will serve as the network technology for almost all voice, data, and video services because of its superior performance. However, since it is of limited availability and currently more expensive than frame relay, ATM is now only emerging in high-performance, niche applications.
Software. Any telecommunications network is built upon switches that require software for operation, administration, and maintenance. Certain software functions are essential to any public data network:
s Call setup, administration, and termination
s User configuration
s Network management (trouble identification, tracking, escalation, and resolution)
s Equipment and transmission media inventory
A utility network for internal use does not have to support billing, network management, and security at the same level as a public network. Users of a public network will expect these issues to be well defined before placing their own data at risk. Therefore, the software systems required of public carriers must be planned, developed, and tested before a transport service can be offered.
Exhibit 2 shows how an electric utility might set up a packet radio network as the backbone for telecommunications services. The diagram depicts a utility that has deployed a network management center and a wireless packet network in a specific geographic region. The utility may target certain regional industries in close proximity to the backbone (such as, military/government, water, oil/ gas, or other power companies). Some locations will lie close enough to serve without deploying any intervening packet radio nodes; others