Switching device for connecting a data transmission system to the telephone switched network
US4910763A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 13, 1989 |
| Grant date | Mar 20, 1990 |
| Priority date | — |
| Expiry date | Mar 13, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L12/00
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A data transmission system is described which includes a switching circuit that enables the connection of a tributary modem to a control modem via the public switched network. Switching occurs when it is no longer possible to transmit data on the leased network because the line connected to the tributary modem has failed. The switching circuit can connect either the permanent leased line or the switched network to the receiver of the control modem. It comprises a narrow pass-band filter and detector which is permanently connected between the reception side of the switched network and the control modem receiver. When the tributary modem answers a call from the control modem, it sends a tone ahead of the data message, the frequency of which tone corresponds to the frequency of the pass-band filter and is out of the data band. When such a tone is detected by the detector and pass-band filter, the control modem toggles a two position switch which isolates the leased line and connects the switched network to the receiver of the control modem.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.