For the last several years there has been a great deal of publicity about FDDI (Fiber Distributed Data Interface). The prospect of 100 Megabit per second transmission is of increasing importance as organizations begin to move graphics and multimedia over their LANs and WANs. While FDDI is being implemented via satellite, microwave, and cable, recently we have been asked whether it will be possible to realize these higher data transmission rates over telephone company circuits, especially local circuits which still are primarily unshielded twisted pair wires. The answer is yes, but probably not over voice-grade circuits.
There has been an ANSI (American National Standards Institute) Committee (X3T9.5) working on a standard for carrying computer data at FDDI rates over voice-grade unshielded twisted-pair circuits, the ubiquitous type used for most telephone conversation, but the group recently decided that support of FDDI data rates over voice-grade twisted pair circuits would require complex and expensive circuitry that could make the technology too expensive to be practical. Instead, the effort will be directed toward the development of specifications for 100-megabit-per-second data transmissions over data-grade unshielded and shielded twisted-pair wiring. Data grade telephone company and LAN circuits, which are more reliable than voice-grade circuits, are now generally available, and are rapidly dropping in price.
The ANSI Committee's working group on FDDI is still split between competing proposals for supporting FDDI data rates over data-grade twisted pair, therefore, it may be 1993 before the differences are resolved. The standard, when completed, will also be important for LANs as many older installations rely on shielded twisted pair rather than coaxial cable. Some vendors are not waiting for the completion of the standard, however. Microdyne Corporation has unveiled a LAN controller that gives users 100 megabits per second of bandwidth at the desktop using only shielded twisted-pair cable and standard IBM multi-station access units. The controller, designated the EXOS BOSS, is based on the latest draft proposal for ANSI's Copper Distributed Data Interface. The controller required works with IBM Type 1 shielded twisted-pair cable. The controller supports IBM's Personal Computer Industry Standard Architecture data bus interface, and fits into a PC like any Ethernet or token-ring controller. The card costs $1,495.
