Attachments to the Public Switched Telephone Network (PSTN) Category II Attachment Requirements for 2400 Bits per Second Duplex Modems Standardized for Use on the PSTN
"This ETS specifies the technical characteristics to be met by modems seeking Category II approval for duplex operation over the PSTN at 2400 bits per second. The modulation scheme specified is that described in CCITT Recommendation V.22bis [7]. The term ""modem"" in the context of this ETS includes all physical implementation practices for voice band modems@ which are galvanically connected to the PSTN. This ETS specifies four modes of operation each with five modes of use (see subclause 5.2). This ETS also contains descriptions of the tests to be performed in order to confirm compliance with the functional requirements contained herein. A general description of the test conditions and test requirements is given in Annex A."