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Class Information
Number: 379/250
Name: Telephonic communications > Centralized switching system > Four-wire switching
Description: Subject matter for connecting two lines, each of which has a physically separate pair for each direction of transmission.
Patents under this class:
| Patent Number |
Title Of Patent |
Date Issued |
| 6728309 |
Method and apparatus for high speed data transmission over a four-wire subscriber line |
Apr. 27, 2004 |
| 5414763 |
Apparatus and method for providing echo suppression to a plurality of telephones |
May. 9, 1995 |
| 5325428 |
Automatic switching-back device for telephone circuit |
Jun. 28, 1994 |
| 5034978 |
Universal channel unit switchable between two wire and four wire configurations |
Jul. 23, 1991 |
| 5027347 |
Intercom system |
Jun. 25, 1991 |
| 4953055 |
System and a protection and remote power-feeding device for equipment connected by two transformers to a four-wire transmission link |
Aug. 28, 1990 |
| 4598172 |
Telecommunication terminal |
Jul. 1, 1986 |
| 4538033 |
Data bridge with gating and/or testing |
Aug. 27, 1985 |
| 4403119 |
DTMF Activated remote telephone line switching and testing |
Sep. 6, 1983 |
| 4347409 |
Key telephone system |
Aug. 31, 1982 |
| 4288664 |
Neutralization signal developing device for an echo suppressor |
Sep. 8, 1981 |
| 4258236 |
Remote telephone line switching and testing |
Mar. 24, 1981 |
| 4156114 |
Telephone network for verifying operator-initiated calls |
May. 22, 1979 |
| 4097690 |
Intercommunication and alarm telephone system |
Jun. 27, 1978 |
| 4008376 |
Loudspeaking teleconferencing circuit |
Feb. 15, 1977 |
| 3978290 |
Digital private automatic branch exchange |
Aug. 31, 1976 |
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