ISDN (Integrated Services Digital Network) - , , .
ISDN :
;
;
;
;
( frame relay);
.
ISDN
: , .
ISDN (. 21.1):
();
(TA);
();
();
().
ISDN T1 ( , , , /, ) ISDN.
( ISDN) T2 , , , , ISDN.
2 ISDN.
R 2
1 2 ISDN.
2 , S.
S .
T 1 2.
U 1 ISDN. ISDN . , , (NT). S/T.
ISDN
: N-ISDN B-ISDN.
N-ISDN (narrowband) 2048 /. B-ISDN (broadband) 155000 /. N-ISDN. ISDN (time division multiplexing - TDM).
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ISDN
ISDN .
ISDN (Basic Rate Interface- BRI) ISDN 64 / ( ). , 16 / ( D). , 2B+D 192 /.
ISDN (Primary Rate Interface- PRI) . PRI ISDN 30 B - D - (30B+D). PRI ISDN 23 B - D - (23B+D). 2048 / 1544 / - .
ISDN , , Internet, , . , ISDN-, - .
ISDN:
;
;
( 128 /) ;
.
ISDN:
;
, .
.25
X.25 . . X.25 ISDN :
( )
( )
.25
:
- (DTE, Data Terminal Equipment). , , ( , , ..), , (PAD, packet assembler/disassembler);
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- (DCE, Data Circuit-Terminating Equipment). ;
- PSE (Packet Switching Exchange), (). . X.25. . . , - .
.25 . , .
.25
X.25 , .
X.21 X.21bis ( V.24, V.35, RS-232C, RS-449, G.703). .
.25 , . HDLC (High-level Data Link Control)- LAP-B (Link Access Protocol - Balanced). LAP-B LLC2 (IEEE 802.2), .
X.25/3 (PLP, Packet Layer Protocol), . , , .
, (Call Request), , .
X.25 4096 , 128 .
X.25, , ( 16 ). . X.121 . : 0 - ( , , 250 251 - , , ), 9 - ( , , 7 - , , 14 ).
X.25 , . , X.25 , , LAP-B. . .25:
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;
;
, ;
.
.25:
( 56 64 /);
.