d by the signal 111 in one frame and 000 in the next frame. Bits 5, 6, 7, and 8 in Set IV (Table 6.3) are used for negative justification of tributaries 1, 2, 3, and 4, respectively, and bits 9 to 12 for positive justification of the same tributaries. Table 6.2 Higher-Level PCM Multiplex Comparison Level System Type North American T/D type Number of voice channels Line bit rate (Mbps) 1.544 6.312 44.736 274.176 Japan Number of voice channels Line bit rate (Mbps) 1.544 6.312 32.064 97.728 400.362 Europe Number of voice channels Line bit rate (Mbps) 2.048 8.448 34.368 139.264 Source: Ref. 11. 10 Positive/zero/negative justification. This refers to stuffing to compensate for input channel bit rates that are either too slow, none necessary, or too fast. DIGITAL NETWORKS Table 6.3 8448-kbps Digital Multiplexing Frame Structure Using Positive/Zero/Negative Justification Tributary bit rate (kbit/s) 2048 Number of tributaries 4 Frame Structure Bit Number Set / Frame-alignment signal (11100110) 1 to 8 Bits from tributaries 9 to 264 Set // Justification control bits Cj1 (see Note) 1 to 4 Bits for service functions 5 to 8 Bits from tributaries 9 to 264 Set III Justification control bits C (see Note) 1 to 4 Spare bits 5 to 8 Bits from tributaries 9 to 264 Set IV Justification control bits Cj3 (see Note) 1 to 4 Bits from tributaries available for negative justification 5 to 8 Bits from tributaries available for positive justification 9 to 12 Bits from tributaries 12 to 264 Frame length 1056 bits Frame duration 125 us Bits per tributary 256 bits Maximum justification rate per tributary 8 kbps Note: Cjn indicates nth justification control bit of the jth tributary. Source: Table 1/G.745, CCITT Rec. G.745, p. 437, Fascicle III.4, IXth Plenary Assembly, Melbourne, 1988 (Ref. 6). Besides, when information from tributaries 1, 2, 3, and 4 is not transmitted, bits 5, 6, 7, and 8 in Set IV are available for transmitting information concerning the type of justifi- cation (positive or negative) in frames containing commands of positive j