System and method for embedding digital information in a dial tone signal

In a private branch exchange system which provides a dial tone that is similar to a public dial tone provided by a public telephone system, a method for providing a user with access information through the dial tone, the method comprising the steps of:

• encoding, by the private branch exchange, the access information into the dial tone such that the dial tone is altered,
• receiving the encoded dial tone at a connecting device;
• decoding the access information from the encoded dial tone by detecting the encoded access information;
• providing the decoded access information to the user.

In a private branch exchange system capable of emulating a central office, a method for downloading access information from the private branch exchange system without interfering with the central office, the method comprising the steps of:

• detecting zero crossings of a signal provided by the private branch exchange;
• embedding access information at the zero crossings of the signal;
• providing the signal to a receiving device;
• sampling, by the receiving device, the signal at a frequency higher than a modulating frequency of the signal;
• examining samples of the signal at times determined by a phase locked loop having a frequency approximately equal to the modulating frequency of the signal;
• extracting the access information from the signal;
• and
• displaying the access information to a user.

In a private branch exchange system, a method for embedding access information in a signal, the method comprising the steps of:

• generating a dial tone comprising a modulating signal and a carrier signal;
• detecting zero crossings of the modulating signal;
• embedding access information at the zero crossings of the signal by:
• zeroing the signal at zero crossings for those portions of the access information represented by digital zeros;
• and
• refraining from zeroing the signal at zero crossings for those portions of the access information represented by a digital one.

In a system having a modem capable of connecting with a private branch exchange system, a method for downloading access information from the private branch exchange system, the method comprising the steps of:

• causing a dial tone to be received by the modem from the private branch exchange system;
• sampling the dial tone received by the modem at a frequency greater than a modulating frequency of the dial tone;
• extracting the access information from the samples at times determined by phased locked loop having a frequency substantially equal to the modulating frequency of the dial tone;
• and
• displaying the extracted access information to a user.

In an environment including a private branch exchange system, wherein the private branch exchange system generates one or more signals including a dial tone that are similar to public signals generated by a public telephone system wherein the public signals cannot be altered, a system for providing access information to a user over the dial tone, the system comprising:

• a dial tone generator of the private branch system;
• an encoder that embeds access information in the dial tone generated by the dial tone generator, wherein the encoder comprises:
• a zero crossing detector that detects zero crossings of the dial tone, wherein the access information is embedded at the zero crossings of the dial tone by the encoder;
• a decoder included in a receiving device, wherein the receiving device receives the dial tone and wherein the decoder extracts the access information from the dial tone, the decoder comprising:
• a phase locked loop;
• a digital detector, wherein the digital detector accesses the embedded access information using the phase locked loop, and a display device for displaying the access information.