Switching device for connecting a data transmission system to th

Details Switching device for connecting a data transmission system to th Switching device for connecting a data transmission system to th

1989-03-13

1990-03-20

George, Keith E.

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

375 36, H04M 1106

Patent

active

049107631

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.

REFERENCES:
patent: 4076961 (1978-02-01), Holsinger et al.
patent: 4607139 (1986-08-01), Froment et al.
IBM Technical Disclosure Bulletin, vol. 28, No. 8, Jan. 1986, pp. 3250-3251, New York, U.S.; "Adapter for Connecting a Multipoint Moden Network to the Public Switched Network".
Patent Abstracts of Japan, vol. 12, No. 65 (E-586) (2912), Feb. 27, 1988; & JP-A-62 208 746 (Fujitsu Ltd.) 14-09-1987.
IBM Technical Disclosure Bulletin, vol. 24, No. 8, Jan. 1982, pp. 4268-4269, New York, U.S.; M. Cukier et al.: "Non-disruptive Switched Network Back-up".

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