The present invention generally pertains to a conference calling arrangement for a digital switching network and more particularly to a time shared three-port conference circuit for use in conjunction with a T-S-T digital switching network.
Historically, switching systems were equipped with a number of conference circuits. When a request for a conference call is detected by such a switching system, this system would select an unused conference circuit to connect each of the conferees in a conference call arrangement. In this scheme, one conference call would require one conference circuit.
With the advent of time division switching systems, conference circuits are required to manipulate PCM voice samples in an associated time slot switching environment. Time division switching systems utilize common equipment for a number of subscribers. One conference circuit for each conference call is inefficient.
One such conference circuit for manipulating PCM voice samples is taught by U.S. Pat. No. 4,126,766, issued on Nov. 21, 1978, and having the same successor in interest as the assignee of the present application. This conference circuit is a three-port device for use in a private automatic branch exchange. This conference circuit handles only a single conference call at a time. Each conference call requires a separate conference circuit. Threshold level detection and last speaker retention features are provided by this circuit In addition, all three conferees' voice samples are compared before outputting the resultant loudest speakers' samples.
Another digital multiport conference circuit is taught by U.S. Pat. No. 4,175,215, issued on Nov. 20, 1979, and having the same successor in interest as the assignee of the present application. This circuit provides for handling a single conference call at a time. In addition, threshold level detection and last speaker retention features are provided.
Another multiport conference circuit is taught by U.S. Pat. No. 4,274,155, issued on June 16, 1981, and having the same successor in interest as the assignee of the present application. Similar to the above mentioned circuits, this circuit also handles one conference call at a time.
Each of the above mentioned circuits suffers from the same deficiency of operating in a time shared switching system, while not itself being a time shared circuit.
Accordingly, it is the object of the present invention to provide an efficient time shared conference circuit for use with a digital time division switching system.