Method and apparatus for testing in FDM system
US3952163A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 3, 1975 |
| Grant date | Apr 20, 1976 |
| Priority date | — |
| Expiry date | Mar 3, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L1/243
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A data communication system is described in which dial access control signals such as RING, DATA SET READY, DATA TERMINAL READY, CARRIER DETECT, and OUT OF SERVICE are transmitted between a central processing unit (CPU) and remote terminals in the form of frequency-modulated signals. A special frequency signal is transmitted from a remote terminal whenever a RING or DATA SET READY control signal is present and a CARRIER DETECT signal is not. Preferably, this special frequency is midway between the center frequency used for data communication and the frequency of either the MARK or the SPACE signal. Upon reception, this special frequency signal is processed in a particular fashion to generate signals comparable to the RING or DATA SET READY signals of the prior art. DATA TERMINAL READY and CARRIER DETECT control signals are transmitted as carrier signals and the OUT OF SERVICE signal is transmitted as a center frequency signal. Suitable processing at the receiver forms these signals into signals comparable to those of the prior art. Advantageously, the OUT OF SERVICE signal is used with appropriate apparatus to initiate testing of the remote terminal. Circuitry in this apparatus per…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.