This ETS contains the technical characteristics required for end-to-end interworking over the Public Switched Telephone Network (PSTN) of 2400 bits per second (bit/s) duplex modems standardized for use over the PSTN, in accordance with CCITT Recommendation V.22bis [2]. The term ""modem"" in the context of this ETS includes all physical implementation practices for voice band modem, which is conductively connected to the PSTN.