60- AT&T . , -, . FDM 12 60 , . , , , , .
1, , ( ) 24 . - , , 1 8000 - (Pulse Code Modulation, PCM). 64 /. 1 , . 1 - 2, 6,312 /, 2 , 44,736 /. T1, T2 , .
70- , T1, , . T1, T2 , , , - , , . .
CCITT. , . ( ), . El, E2 - 2,048 /, 8,488 / 34,368 /. ANSI.
, - DSn (Digital Signal n). . 6.2 .
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6.2.
1/1 /.
1 24- 1,544 / , . , 24- . 1 ( , 1,544 /) , . 1, 2 . , . , - . 24 64 = 1,536 /, 8 / .
1 .
1 24 , ( ) . 1 8- , 56 / ( , , , . .). . , pax , - .
1 23 , 24- , - . , 24 , 56 /. (bit robbing).
4- 1 2 DS-1 - , DS-2 ( 4- DS-1) 12 , , . , DS-3 7 DS-2, .
G.700-G.706. , . , 4 . 1 2 32. 30 64 / .
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64 / (56 /) 1/1. (fractional) 1/1. - .
PDH : , - . 1/1 RJ-48. 1,544/2,048 /. : 1 B8ZS, El- HDB3. 1 1800 ( ) .
2/2 4 1/1. / , - , .
G.703, , 1. 1.
, PDH .
. , , - . . . , 64 / , 2, - 1, 1. PDH , . , (back hauling). 1 , 672 , , , 2, 64 /. 1 , , 1. , , , .
PDH . , . . , , . , , .
PDH. - , , PDH - 139 /.
, - Synchronous DigitalHierarchy, SDH.