Any local-area network system must assure the accurate transmission of data between the devices it interconnects. To do so, it must communicate betweern them in a common electronic vocabulary, detecting and correcting possible transmission errors and safeguarding against mistimed transmissions that might result in garbles or errors. Differences in the choice of transmission methods, error-trapping, and signal timing make one system's electronic equipment or wiring incompatible with another.

For instance, Xerox Corp.'s Ethernet system is based on the transmission of rapid bursts of electronically encoded data at the rate of 10 million bits per second. Any device on the line can directly communicate with any other device, but only one message can be sent at a time. To prevent elcctronic collisions on the Ethernet cable, every interface circuit includes program routines to detect transmission problems and delay transmission of data until the line is clear. So far, about 100 companies worldwide have licensed Ethernet technology for use with their office equipment, but because of the growing number of competing systems it may never become a standard.

A recent count put the number of different systems on the market at 65 and still growing. One basic distinction among network systems is whether they transmit one message at a time (a "baseband" system) or several signals simultaneously ("broadband"). A modest system like Nestar Systems Inc.'s Cluster/One, designed to bring the speed and error-checking capabilities of Ethernet to Apple II computers, is a baseband network. Wang Laboratories Inc.'s WangNet, which can carry several signals simultaneously, including computer, telephone, and video transmissions, is a broadband network.

Another important distinction is whether all the stations on a network connect to a main cable like branches on a tree or whether they connect directly to one another in a ring configuration. In a tree-type configuration, the network can continue to function if one terminal stops functioning. But a ring-type system, proponents say, is more generally reliable.

Datapoint's ARC system has been rated among Ethernet's top rivals, since the announcement last year of Tandy Corp.'s development of hardware and software to link as many as 255 TRS-80 business computers on a single ARC network. As of this writing, a year later, Tandy is still said to be plagued by software bugs that prevent the marketing of these long-awaited network additions.

The availability of appropriate interface circuitry often determines the choice of the local-area network; few systems interconnect with a broad range of makes and models of office equipment. At the moment, for instance, only Corvus's Omniriet offers plug-in interface cards for both IBM Personal Computers and Apple II systems, making this the only network that can interconnect these microcomputer systems. Omninet and Nestar are among a handful of major systems that will link Apples. Digital Microsystems, which had the CP/M-based computer market all to itself with the HiNet local-area network, now faces a direct rival, CPUnet, from yet another garage-spawned enterprise, CPU Computer Corp., in Charlestown, Mass.

Competition from outside the computer industry is also expected to increase. The cable used by Ethernet was specifically designed for local-area networking, yet it resembles the coaxial wiring used by cable television systems. ln a handful of communities, local cable TV franchises already offer data transmission services, and more are expected to follow suit. The telephone company could also provide local-area networking as deregulation allows American Bell lnc., the new AT&T subsidiary, to pursue aggressively the market in office data transmission. Fiber-optics technology is being developed for use in the higher-speed office networks of the 1990s, but the odds seem to favor the flexibility of electronically wired networks.

Any dealer selling business systems will offer information on networks. Or you can check with individual manufacturers or systems houses. When selecting a local area network, consider its compatibility with existing office devices. Choices will be limited by the availability of compatible interface circuitry. If more than one system is available, consider how far the network can extend and how many devices it can interconnect. Expandability is of major importance. Reliable operating software and applicatioris programs are also essential. The following supply local-area networks:

Corvus Systems Inc./Omninet

2029 O'Toole Ave.

San Jose, CA 95131

(408) 946-7700

CPU Computer Corp./CPUnet

420-438 Rutherford Ave.

Charlestown, MA 02129

(617) 242-3350

Datapoint Corp,/ARC

9725 Datapoint Dr.

San Antonio, TX 78284

(512) 699-7000

Digital Microsystems Inc,/ HiNet

1840 Embarcadero

Oakland, CA 94606

(415) 532-3686

Nestar Systems Inc./Cluster/One

2585 E. Bayshore Rd.

Palo Alto, CA 94303

(415) 493-2223

Wang Laboratories Inc./WangNet

1 Industrial Ave.

Lowell, MA 01851

(617) 459-5000

Xerox Corp,/Ethernet

Marketing Services Dept. MS 105

1341 W. Mockingbird Lane

Dallas, TX 75247

(214) 689-6045

Zilog Inc./Z-Net

1315 Dell Ave.

Campbell, CA 95008

(408) 370-8000