Method for transmitting data signals on analog subscriber lines

Abstract

A method for transmitting data signals on analog subscriber lines wherein bilateral data transmission between subscriber terminal equipment and exchange is intended to occur, with relative ease and with low outlay, even during speech signal transmission. A signal, preferably the charge pulse signal, that is already generated at least in the exchange for some other use is employed as a carrier signal wherein, accordingly, it is possible to exploit an already existing infrastructure.

I claim as my invention  
     
         1 . A method for transmitting data signals on analog subscriber lines between a subscriber terminal equipment and a telephone exchange, preferably during speech signal transmission of an existing telephone connection, comprising the step of modulating the data signals in a subscriber circuit and in the subscriber terminal equipment onto a signal with periodic characteristics serving as a carrier signal that has a frequency lying outside the speech band and that is already generated at least in the telephone exchange for some other use.  
     
     
         2 . A method for transmitting data signals as claimed in  claim 1 , wherein the signal with periodic characteristics generated in the telephone exchange for some other use is a signal transmitted from the telephone exchange to the subscriber terminal equipment for purposes of charge display and charge debiting at the subscriber.  
     
     
         3 . A method as claimed in  claim 1 , wherein information which serves for authentication of the subscriber terminal equipment is transmitted as data signals.  
     
     
         4 . A method as claimed in  claim 1 , further comprising the step of transmitting as data signals information serving the specification of the charge display or the charge debiting at the subscriber.  
     
     
         5 . A method for transmitting data signals as claimed in  claim 1 , further comprising the steps of: 
 providing a carrier signal generator in the telephone exchange;    providing a data source in the telephone exchange;    providing a modulator in the telephone exchange;    modulating the data signals delivered by the data source onto a carrier signal delivered by the carrier signal generator;    filtering out modulation products falling in the speech signal range at a transmit side;    superimposing the modulated carrier signal and the speech signal;    filtering out the modulated carrier signal at a receive side;    connecting a demodulator downstream of the filtering step;    connecting a data evaluation circuit to the demodulator; and    blocking the carrier signal frequency connected to the telephone terminal of the subscriber terminal equipment upstream with a filtering means.    
     
     
         6 . A method for transmitting data signals as claimed in  claim 5 , further comprising the steps of: 
 providing a pulse formation step to the carrier signal generator of the subscriber circuit downstream; and    prolonging the transient response time and delay time of pulse edges arising in the activation and deactivation of the carrier frequency generator, so as to avoid clicks in the telephone terminal.    
     
     
         7 . A method for transmitting data signals as claimed in  claim 6 , further comprising the steps of: 
 providing an authentication module preferably allocated to groups of subscriber circuits;    generating data serving for subscriber identification to be transmitted to the subscriber terminal equipment with the authentication module; and    evaluating data received by subscriber terminal equipment in this connection and interrupting telephone connections potentially determined to be non-authenticated.