(. 2.1) , , . (line) (channel).
. 2.1.
(medium) , , , , .
(. 2.2.):
();
( -);
.
. 2.2.
() - , . , . . .
. , : , , , , , . , , . : , , - .
(twisted pair). (Shielded Twistedpair, STP), , (Unshielded Twistedpair, UTP), . , . (coaxial) , . , - , , . . - (optical fiber) (5-60 ) , . - ( 10 / ) .
. , , . , (KB, ), (Amplitude Modulation, AM) , , . , (), (Frequency Modulation, FM), ( microwaves). ( 4 ) . , , .
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, -. , . , , . 100 . , - , , , , , . .
( DCE - Data Circuit terminating Equipment) , , . . DCE , ISDN, , . DCE , .
, , (00 DTE - Data Terminal Equipment). DTE . .
DCE DTE . , , DTE, , DCE.
. :
;
.
, - - , . .
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. , , . - , . , - . , . 2.1 , , , - , ( ). . , - , . - , , , , , . .
, . , . , , (, ) , , .
. , , . . , , (Frequency Division Multiplexing, FDM).
. , , , , 2 3 , . , . , , . (, , ) (Time Division Multiplexing, TDM), (- ) .
, , - . , , - .