Here's how the service works:

Teligent, a Vienna company that is among the wave of new entrants to the telecommunications market, operates an independent wireless network in 28 metropolitan areas in the United States. The basic concept: Let clients use radio links to bypass the local telephone company for high-speed Internet connections and plain old telephone service.

Offering service at speeds up to 100 times as fast as those possible with a conventional dial-up connection, the service is aimed at customers in buildings equipped with Teligent dishes and transmission equipment. The company claims savings of up to 30 percent.

Wall Street has been hot on Teligent of late. Its stock was stuck in the $30 range through 1998, but earlier this year it jumped to the $50s.

1 Customer signs on to a computer in an office building to send a graphics file to a branch office. Expressed as a digital "bitstream," the signal travels to the roof over phone wires that have been upgraded to carry high-speed signals.

2 On the roof, the signal is converted to microwave form and sent over the air from a small dish to another building nearby that has a Teligent "base station." Signals from other buildings feed into the base station as well.

3 The signal flows by wire to a routing device known as a switch. Based on the destination addresses of the material, the switch puts the data onto different networks for forwarding to their destination.

4 Return signals travel by the same route.