This ETS contains the technical characteristics required for end-to-end interworking over the Public Switched Telephone Network (PSTN) of 1200 bits per second (bit/s) duplex modems standardized for use over the PSTN, in accordance with CCITT Recommendation V.22 [1]. NOTE: CCITT Recommendation V.22 [1] also describes a method of transmitting data at 600 bit/s. This ETS specifies the characteristics to be met by such modems and, if requested by the applicant, this feature can also be tested against the specifications.