Pulse or digital communications – Repeaters – Testing
Patent
1990-03-28
1992-09-08
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
34082531, 375 13, 375121, 380 23, H04L 2908
Patent
active
051464721
ABSTRACT:
Methods for embedding additional information (e.g. a password function) in a handshake of communicating modems is provided. An auxiliary packet containing the additional information is placed in the handshake sequence of an originating modem in such a manner that it cannot be confused by the receiving modem with other signals which are required to be sent by the originating modem in the modem handshake. The answering modem looks for the auxiliary packet, and if the auxiliary packet is not received, or if the information in the auxiliary packet is not sufficient to establish authorization, the answering modem causes the call to be dropped. In V.32 type modems, the auxiliary packet is placed by the originating modem somewhere in the training sequence (TRN) after the required twelve hundred eighty symbol intervals, and before the R2 sequence, and the auxiliary packet is generated in such a manner that it cannot be confused with the R2 sequence. In order to guarentee that the auxiliary packet is discernible and that no confusion with other signals is possible, the auxiliary packet is comprised of two multiplexed signals; an information signal at a 2400 bit/second rate which includes a burst flag, and an HDLC formatted start flag, password, check sum, and stop flag; and a 2400 bit/second R2 prevention signal which is coded to be compatible with the burst flag and to guarentee that regardless of the HDLC formatted signal, the composite auxiliary packet cannot constitute an R2 sequence.
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Data Communication over the Telephone Network, CCITT Red Book, vol. VIII--Fascicle VIII.1; Oct. 8-19, 1984; p. 161 and diagram page.
General Datacomm, Inc.
Gordon David P.
Safourek Benedict V.
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