:
# " - " (point-to-point);
# "" (cloud).
" - " , N N(N - 1)/2 . .
WAN "". .
"" :
( );
( E-mail);
( IP, X.25), ( Frame Relay), ( ATM).
. .
, ( ), - , , ( ).
(PSN - Packet-Switched Network) , . : , , .
( ), , . ( ), , - .
. , . : IP; X.25; Frame Relay; ATM.
PSN :
1) . : . , , .
( ), . , , .
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2) , .. . . , . , , , .
TCP/IP IP-, .. . : X.25, Frame Relay, ATM , , .. .
X.25
.25 , . X.25 . .25 ( ) 64 /. .25 .
.25 " - " , . .25 ( ) DTE DCE.
X.25, :
# DTE (data terminal equipment) ( , , , , .. ).
# DCE (data circuit-terminating equipment) ( , ).
# PSE (packet switching exchange) .
.25 :
1) ;
2) ;
3) .
.25 OSI: , . . , .
.25 , . , . . .25 X.21 X.21bis.
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.25 , . . . . LAP-B, , .
.25 PLP (Packet-Layer Protocol - ). , . PLP . DTE . . DTE, .
PLP :
# DTE. . DTE DCE, . DCE PSE, . , PSE, DCE, DTE , . DTE DCE, DCE DTE. , .
# , . .
# , , .
# , .
.25:
# , ;
# , ( ).
:
, .
