truyen du lieu -...

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Unformatted text preview: ____________________________________________________Ch ng 1 Nh ng khi ni m c b n I - 1 _____________________________________________________________________________________________________ Nguy n Trung L p Truy n d li u Z CH NG 1 NH NG KHI NI M C B N VI DNG L CH S NH NG KHI NI M CHUNG H TH NG TRUY N T NG T H TH NG TRUY N S H TH NG M V M HNH OSI ___________________________________________________________________________ 1.1 VI DNG L CH S Thng tin d li u l ph ng php truy n thng dng m nh phn thay cho tn hi u. C th coi l ch s thng tin d li u b t u vo n m 1837 v i s pht minh i n tn c a Samuel F. B. Morse. l h th ng truy n cc xung i n bi u di n cho cc d u ch m, v ch (t ng ng v i cc s nh phn 1, 0) trn cc ng dy ng nh cc my c i n. Cc t h p khc nhau c a cc m ny thay cho cc ch , s , d u.... c g i l m Morse. B n i n tn u tin c pht hi n Anh do Charles Wheatstone v William Cooke th c hi n nh ng h th ng c a h ph i dng 6 ng dy. N m 1840, Morse ng k sng ki n v i n tn M v n n m 1844 th ng dy i n tn u tin c thi t l p gi a Baltimore v Washington D.C. . N m 1849, b n tin u tin c in nh ng v i v n t c r t ch m, cho n n m 1860 v n t c in t c l 15 bps. Cng ty i n tn Mi n Ty (Western Union Telegraph Company) c thi t l p n m 1850 Rochester, New York cho php th c hi n vi c trao i thng tin gi a cc c nhn. N m 1874, Emile Baudot thi t k c my pht dng ph ng php a h p, c th truy n cng lc 6 b n tin trn cng m t ng dy. N m 1876, Alexander Graham Bell a i n tn ln m t b c pht tri n m i: s ra i c a i n tho i. Thay v chuy n b n tin thnh cc chu i m Morse, Bell cho th y r ng ng i ta c th truy n th ng tn hi u i n c tr ng cho ti ng ni trn cc ng dy. Nh ng h th ng i n tho i u tin c n cc c p ng dy khc nhau cho hai ng i mu n trao i thng tin v i nhau, m t ng i ph i n i i n tho i c a mnh vo ng ng dy n i v i i n tho i c a ng i m mnh mu n lin l...
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truyen du lieu -...

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