Cordless phone

Cordless telephones are telephones that include a base unit which is coupled to a telephone network via a telephone line, and a handset that communicates with the base unit via an RF link. Cordless telephones are similar to conventional corded telephones in that they are connected by wire to a local central office. However, they differ in that there is no cord between the base unit of the cordless telephone and the handset. Cordless telephones allow considerable freedom and mobility to the user, allowing the user to move about while engaged in a call, and to conduct a call at a considerable distance from the base station. Cordless telephone headsets offer hands-free roaming. Most homes and office have multiple telephone extensions with different types of telephone instruments selected to meet users' desires. Many users have both a wire-line telephone and a wireless telephone. Typically, a cordless telephone is comprised of two units: a base unit and a handset both of which are transceivers. The base unit connects to the public switched telephone network typically using a standard RJ-11 connector. The base unit provides a wireless connection to a handset. The handset is capable of receiving and transmitting signals over a wireless RF link to the base unit. The RF link either transmits the voice signals between the base unit and the remote handset using analog techniques (e.g., frequency modulation (FM), or using digital techniques (e.g., quadrature amplitude modulation (QAM) or frequency shift keying (FSK), etc.). When not in use, the handset is typically cradled in a receiving portion of the base unit for battery charging purposes, or simply left on a table or other piece of furniture. In such cordless telephone sets, a discrimination code, e.g. a base unit number or a terminal unit number, is set in order to discriminate a relationship between the base unit and terminal unit. Radio connection will be made when the discrimination code registered in the base unit matches that registered in the terminal unit. Unlike conventional consumer corded telephones, which typically operate solely from power supplied by the PSTN, cordless telephones typically require an external power source to enable their operation. Specifically, such telephones are typically supplied with a DC power adapter which must be connected to a wall power outlet.