(dial-up lines) . , ( ). ( ) 3,1 (300-3400 ), , . , , . 4- . , . , . RJ-11 6- , .
, (leased lines) . ( ) ( , ). , :
, , , . , , ( ). . ( , ) ( ).
( ), , . (3,1 ), ( ) ( ) ( , , -). 48 (60... 108 ), 12 ( 3,1 ) , ( ). , ( Private Branch eXchange).
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. .
. .
, .
DS0 64 / , G.711 (8 , 8 ). TDM (Time Division Multiplexing). (sequential byte interleaving). DS0 DS1, (, ) (1) (1). 1 2,048 / 30 DS0 64 /, .
1 1,544 / 24 DS0. 1/1 , . , . DS1 , . (). 1 1 .
DS1 , . , 10 N ( 64 /) .
/ PDH (Plesiochronous Digital Hierarchy). : , , . , , , . , , . (Justification bit), , . ( ) , ( ). . J-, , , . , DS1 DS2, (bit interleaving). . , . , , - J- . ( ) (DS0) DS1. ( ) PDH . / . , 1 4, : 4 3, 3 2 , , 1 2 ( ). , , . 24. ( ) .
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. 24. 1 PDH
, . SONET (Synchronous Optical NETwork ), ANSI, SDH (Synchronous Digital Hierarchy ), G.707-G.709. SONET -n (Optical Carter), STS- n, (Synchronous Transport Signal), n (51,84 /). SDH STM- n (Synchronous Transport Module), 3 , SONET, 155,52 / (. . 11). SONET/SDH (drop) (add), . , . : ( ) ( ). ( , ) , . : , , , ( ). SDH , . 25 ( ), ( ) ( 2-) SDH. , , add-drop multiplexer (ADM). , , SDH, (BOD bandwidth on demand).
. 25. SDH add-drop
SONET/SDH PDH DS-1, DS-3, DS-4. , . ( ) (, , ...) , SONET/SDH, (access contrller). , . . , PDH.
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11
SONET/SDH
CSU (Channel Service Unit ) DSU (Data Service Unit ). CSU / , . DSU RS-232C, RS-449, V.35, HSSI , . . DSU , TDM. CSU/DSU , / . CSU/DSU .
G.703 (Physical/electrical characteristics of hierarchical digital interfaces) (, ), STM-1 (G.703.12). G.703 (. . 10), :
(m parts per million);
;
( ), , ;
( ).
G.703.1 64 / ( 75 ) (2, 3 4 120 ) . :
(co-directional), 4- : , . .
(central-directional), 6-8- , ( ). AMI. .
(contra-directional), 8- . (DCE), (DTE). AMI.
BNC, RJ-45. 1/1 , 2 :
1 3 , ( ) 647 , AMI B8ZS. 1544 / 50 ppm (0,005%).
E1 3 ( ) 2,37 ( ), ( ) 488 , AMI HDB3. 2048 / 50 ppm (0,005 %).: