The text approved is:

Fascicle VII.3 - Rec. T.4

4.3	Extended two-dimensional coding scheme

The basic facsimile coding scheme specified in S 2.2 of Recommendation T.6 may be used as an option in Group 3 facsimile. This coding scheme is limited to the use of the Error Correction Mode specified in S 3.3.

4.4	Error limiting mode

One-dimensional coding scheme with the division of scan line into parts.

The one-dimensional coding scheme with the division of scan line into parts is an optional extension of the one-dimensional coding scheme specified in Annex B.

5	Modulation and demodulation

Group 3 apparatus operating on the general switched telephone network shall utilize the modulation, scambler, equalization and timing signals defined in Recommendation V.27 ter, specifically SS 2, 3, 7, 8, 9, 11 and the Appendix.

5.1	The training signal to be used shall be the long training sequence with protection against talker echo (see Recommendation V.27 ter, S 2.5.1, Table 3/V.27 ter).

5.2	The data signalling rates to be used are 4800 bit/s and 2400 bit/s as defined in Recommendation V.27 ter.

Note 1 ù Some Administrations pointed out that it would not be possible to guarantee the service at a data signalling rate higher than 2400 bit/s.

Note 2 ù It should be noted that there are equipments in service using, inter alia, other modulation methods.

Note 3 ù Where quality of communication service can successfully support higher speed operation, such as may be possible on leased circuits or high-quality switched circuits. Group 3 apparatus may optionally utilize the modulation, scrambler, equalization and timing signals defined in Recommendations V.29, V.33 and V.17. For V.29 this specifically refers to SS 1, 2, 3, 4, 7, 8, 9, 10 and 11. Under this option the data should be non-multiplexed and limited to the data signalling rates of 9600 bit/s and 7200 bit/s. For V.33 this specifically refers to SS 1, 2, 3, 4, 7 and 8. Under this option the data should be non-multiplexed. For V.17 this specifically refers to SS 1 through 5.

Note 4 ù When V.33 signalling is used the training signal shall be preceded by a Talker Echo Protection signal. The Talker Echo Protection signal shall consist of an unmodulated carrier for a duration of 185 ms to 200 ms followed by a silent period of 20 to 25 ms.

Note 5 ù When V.17 signalling is used the training signal shall include the Talker Echo Protection (TEP) signal defined in S 5.3/V.17.

6	Power at the transmitter output

The average power should be adjustable from ù15 dBm to 0 dBm but the equipment should be so designed that there is no possibility of this adjustment being tampered with by an operator.

Note ù The power levels over the international circuits will conform to Recommendation V.2.