9 .25
.25 OSI, . .25 . () , , . .25 DTE (Data Terminal Equipment) DCE (Data Circuit-Terminating Equipment), .
.25 6- 1976 ., 1980 1984 . 80- .25 , .
.25 LAPB (Link Access Protocol Balanced), . , LAPB , 2 (), , , . , .25, , , , , . , , .
.25 ( 60- ) , . .25 , . , , .25 , , , Frame Relay ( ).
. 1 .25 .75 - PAD, (SNA, ..) .25. .25 , .75 . , .75 , . , .75 , .25 , .
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. 1.
.25
.25 , OSI (. 2). .25 DTE DCE. .25 2121-.
, HDLC (High-level Data Link Control Procedure), . .25 LAPB. , . HDLC 25 . LAPB DCE DTE. ( LAPD) . LAPB 3 .25, ISDN. 3 .25 LAPD.
. 2. OSI .25
, , . , . .
.25 , . 6. / 3 , . 3 . 4 DTE, . . ( 16 ).
. 3. .25:
.25 OSI , , .25 . .25 , . DTE 4095 . , 15 255 . , . . DTE DCE. , DTE, . . , (Virtual Call service, VC) (Permanent Virtual Circuit service, PVC).
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(virtual calls) , .. , . DTE, DCE . 25 . . DCE DCE, DTE, . DTE , DTE , , DTE. DTE . , - , DTE , . DTE, .
(permanent virtual circuit) DTE . , , , .
.25
.25 , , .
.25 . , (MMSW) DX-200 (Nokia) -90 ().
.25 , . .
ISDN , .25 ISDN. .25 ISDN 1. , .25 ISDN ( ISDN).
, Case , ISDN .25 ( ) .25. DTE X.25 ISDN DCE .25 . ISDN D- ISDN. D- ISDN , DCE DTE - ISDN 3 .25. - .25.
Case .25 ISDN. DTE ISDN, ISDN DCE X.25. ISDN. ISDN LAPB -, LAPB LAPD D-.
, ISDN X.25, , . ISDN, 1988 ., X.25 Frame Relay, . .