Multimode modem with automatic negotiation of operational mode

Abstract

Apparatus and methods for determining an operational mode of a far-end modem are disclosed. Where the multimode modem is a call initiator, a method according to the invention includes transmitting a V.8 ANS am tone to the far-end modem, receiving a response signal from the far-end modem, and determining from the response signal whether the far-end modem is a commercial modem or a secure modem. Where the multimode modem is a call responder, a method according to the invention includes transmitting to the far-end modem a P1800 Hz tone with phase reversals, receiving a response signal from the far-end modem, and determining from the response signal whether the far-end modem is a commercial modem or a secure modem.

I claim:  
     
         1 . A method for identifying a far-end modem type, comprising: 
 transmitting a V.8 ANS am  tone to the far-end modem;    receiving a response signal from the far-end modem in response to the transmitted V.8 ANS am  tone; and    determining from the response signal whether the far-end modem is a commercial modem or a secure modem.    
     
     
         2 . The method of  claim 1 , wherein determining whether the far-end modem is a commercial modem or a secure modem comprises determining whether the far-end modem is a V.series modem or an FSVS modem.  
     
     
         3 . The method of  claim 2 , wherein determining whether the far-end modem is a commercial modem or a secure modem comprises: 
 determining whether the response signal is a V.8 CM tone; and    if the response signal is a V.8 CM tone, determining that the far-end modem as a V.8 modem.    
     
     
         4 . The method of  claim 1 , wherein determining whether the far-end modem is a commercial modem or a secure modem comprises: 
 determining whether the response signal has a nominal frequency of about 1800 Hz; and    if the response signal has a nominal frequency of about 1800 Hz, determining from the response signal whether the far-end modem is a V.32 modem or a secure modem.    
     
     
         5 . The method of  claim 4 , wherein determining whether the far-end modem is a V.32 modem or a secure modem comprises: 
 determining whether the response signal includes phase shifts; and    if the response signal does not include phase shifts, determining that the far-end modem is a V.32 modem.    
     
     
         6 . The method of  claim 4 , wherein determining whether the far-end modem is a V.32 modem or a secure modem comprises: 
 determining whether the response signal includes phase shifts; and    if the response signal includes phase shifts, determining that the far-end modem is a secure modem.    
     
     
         7 . The method of  claim 1 , further comprising: 
 determining from the response signal, an operational mode of the far-end modem.    
     
     
         8 . The method of  claim 7 , wherein determining the operational mode of the far-end modem comprises: 
 determining whether the response signal includes phase reversals; and    if the response signal includes phase reversals, determining that the far-end modem is an FSVS modem in alternate mode.    
     
     
         9 . The method of  claim 7 , wherein determining the operational mode of the far-end modem comprises: 
 determining whether the response signal includes a 128 dibit gap; and    if the response signal includes a 128 dibit gap, determining that the far-end modem is an FSVS modem in half-duplex mode.    
     
     
         10 . The method of  claim 7 , wherein determining the operational mode of the far-end modem comprises: 
 determining whether the response signal includes phase reversals;    determining whether the response signal includes a 128 dibit gap; and    if the response signal does not include phase reversals or a 128 dibit gap, determining that the far-end modem is an FSVS modem in interoperable mode.    
     
     
         11 . A method for determining a far-end modem type, comprising: 
 transmitting to the far-end modem a P1800 Hz tone with phase reversals;    receiving a response signal from the far-end modem in response to the transmitted P1800 Hz tone; and    determining from the response signal whether the far-end modem is a commercial modem or a secure modem.    
     
     
         12 . The method of  claim 11 , wherein determining from the response signal whether the far-end modem is a commercial modem or a secure modem comprises: 
 determining whether the far-end modem is a V.32 modem or a secure modem.    
     
     
         13 . The method of  claim 12 , wherein determining whether the far-end modem is a V.32 modem or a secure modem comprises: 
 determining whether the response signal includes a V.32 AC; and    if the response signal includes a V.32 AC, determining that the far-end modem is a V.32 modem.    
     
     
         14 . The method of  claim 11 , further comprising: 
 determining whether the response signal includes an FSVS Message A; and    if the response signal includes an FSVS Message A, determining that the far-end modem is an FSVS modem in alternate signaling mode.    
     
     
         15 . The method of  claim 11 , further comprising: 
 determining whether the response signal includes a V.32 AC;    determining whether the response signal includes an FSVS Message A; and    if the response signal includes neither a V.32 AC nor an FSVS Message A, determining that the far-end modem is an FSVS modem in interoperable mode.    
     
     
         16 . The method of  claim 11 , further comprising: 
 monitoring an incoming channel for energy at 2100 Hz; and    if 2100 Hz energy is present in the incoming channel for at least about one second, then determining whether the far-end modem is a V.32 compliant commercial modem or a secure modem in interoperable mode or alternate mode.    
     
     
         17 . A method for determining a far-end modem type, comprising: 
 monitoring an incoming channel for the presence of any of 1800 Hz energy or 2100 Hz energy;    if 1800 Hz energy is present in the incoming channel for at least about one second, then determining that the far-end modem is a secure modem in half-duplex mode; and    if 2100 Hz energy is present in the incoming channel for at least about one second, then determining whether the far-end modem is a V.32 modem or a secure modem in interoperable mode or alternate mode.    
     
     
         18 . The method of  claim 17 , further comprising: 
 monitoring the incoming channel for the presence of a V.8 ANS am  tone; and    if a V.8 ANS am  tone is present in the incoming channel, then determining that the far-end modem is a V.8 modem.    
     
     
         19 . A computer-readable medium having stored thereon computer executable instructions for performing a method for identifying a far-end modem type, comprising: 
 transmitting a V.8 ANS am  tone to the far-end modem;    receiving a response signal from the far-end modem in response to the transmitted V.8 ANS am  tone; and    determining from the response signal whether the far-end modem is a commercial modem or a secure modem.    
     
     
         20 . A computer-readable medium having stored thereon computer executable instructions for performing a method for identifying a far-end modem type, comprising: 
 transmitting to the far-end modem a P1800 Hz tone with phase reversals;    receiving a response signal from the far-end modem in response to the transmitted P1800 Hz tone; and    determining from the response signal whether the far-end modem is a commercial modem or a secure modem.