Data modem having line verification and automatic disconnect features
US3979559A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 2, 1975 |
| Grant date | Sep 7, 1976 |
| Priority date | — |
| Expiry date | Sep 2, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B3/20
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
Modems having line verification circuitry for automatically advising that a direct distance dialed network has been connected between the communicating modems with the echo suppressors in the network disabled, is disclosed. The line verification circuitry is either identical for all modems or may be master/slave equipment. The line verification circuitry includes a first tone generator for emitting a unique tone for disablingthe echo suppressors in the telephone line. A communicating modem, upon receiving this unique tone activates a second tone generator that emits a different second tone which is not capable of disabling the echo suppressors but is capable of transmission through the telephone line when the echo suppressors are disabled. (63)disabling the at both modems respond to the first and second tones for automatically verifying the existence of the desired communication link. The modem provides a data set ready signal to the data terminal equipment upon a telephone line being established between the communicating modems until completion of data transmission, in spite of gaps between data messages.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.