A METHOD OF PROVIDING SECURE TRANSMISSION FOR FACSIMILE DATA MODEM SIGNALS

摘要

A method of operating a security device to secure the transmission of data between authorized modems and against interception by A method of operating a security device to secure the transmission of data between authorized modems and against interception by an unauthorized modem. The modems each implement a defined protocol that includes negotiation and data transport portions of a communications session that is conducted over a network utilizing signals selectively occurring in a plurality of frequency channels. The security device includes a first interface coupleable to a modem to exchange first predetermined signals occurring in a first plurality of frequency channels and a second interface coupleable to a network to exchange second predetermined signals occuring in a second plurality of frequency channels. A signal processor is coupled between the first and second interfaces, to implement a bi-directional conversion of the signals between the first and second plurality of frequency channels by frequency shifting the first and second predetermined signals between the first and second pluralities of frequency channels. Further, the security device can provide for a first frequency shift of greater than a predetermined frequency tolerance specified by the defined protocol for a first portion of said communications session and a second frequency shift for a second portion of the communications session.