STU III operation over 2.4 kbps links

The STU III phones are designed to work over public switched telephone networks and not over a digital link, such as a satellite 2.4-kb/s data link. Two interfaces, the STel 9610 and 9620, which enable two STU III phones to operate over synchronous 2.4 kb/s channels, are described. The STel 9610 STU III digital link interface unit provides an interface to the STU III phone that functions like a central office or PBX interface. It provides loop current, dial tone, ring back, busy signals, and can detect and process dual-tone multifrequency (DTMF) signals. The STel 9620 STU III Telco gateway interface is treated as a normal phone by the public switched network. The applications of these products are discussed