Business Notes Communications

In a country with the world's most renowned phone system, plain old breakdowns aren't supposed to happen. But lately America has been coming unhooked. The most recent epidemic began on June 26, when 6.3 million customers in Washington, Maryland, Virginia and West Virginia lost service for up to eight hours. The same day, phone circuits went haywire in two Southern California area codes. Then, last week, 1 million Bell of Pennsylvania customers temporarily lost service, as did dialers in San Francisco. The scourge of breakdowns was eerily reminiscent of the January 1990 collapse of AT&T's long- distance system.

Most of the outages were quickly corrected, but repairing confidence may take a while longer. After discounting sabotage or a computer virus, investigators focused on the common thread shared by the stricken areas * -- they all use a computerized super-operator dubbed Signaling System 7, which automatically chooses the most efficient route for each call.

At week's end the maker of the SS7 network, DSC Communications, declared that flaws in its own software had triggered the plague of busy signals and dial tones. The Texas-based company said it would make alterations in the affected phone systems that should act "like a fuse on a power line" and prevent small glitches from escalating into major breakdowns.