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Documento extraído de http://www.isa.uniovi.es/docencia/redes/Apuntes/tema3.pdf. Universidad de Oviedo

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La capa de enlace

  1. 1. ! " # $ %$ &" ( $ ) $ * $ + ) ! , ) - . - " # $ ! " - ! / 0 1 %1/2 ! 30 4 / 4 5 ) 6 * ) ) " 7 3" ! 8 ! % & (&$$ % ) * &( + % , $ - ! 9$, -$ ! 2" #$ % !&
  2. 2. - 0 + * % < + / 7= + + 0 ; 0 - - > %? < 7 + 3 = 0 = 3 0 > - + @ ; = ? ? 7 %" ! 3 !!! + ? 0 7 ? + A - $ * : 0 - : 3 6 * - + 0 = * + ; + ; A "B1 = $!=" = C = 3 0 ; - D 0 !!!= ; - < 3? @ 7 + + @ 0 ? > "& -: =3 0 ( ) * ? 7 $; = D ; ",E," = 0 ! F% 4! F =F ! - 1! F %1 5 4 !F = :! F %: ! F = * @? + ? F 0 = ? @ ? * ; ; 0 = + + 7 - = ? 7 7 3 + 0 ? + / ;= @ ? ? 0 + + ? + / + * * + - + ? + : & ;
  3. 3. = ? % *= 0 % = ? -> < - ? @ ; 7 G" ,$/1 8.H ./ / % 0 1 0 2 $ - $ ",$ 3 * 4 1 " " "1 ,3 * 4 " " " " " " " "% 1 " 1 1 * 0 0 1 " 1 1 ) " " " " )% % " " " " * " " " " - 0 7 - 0 7 F D F D5 * 6 & )E & ) & :: & :: %( E %C I F - 0 7 I : : 7 * > * ! 3 ( ; 1 ( ; 1 ( ; 1 @ 7 8 .E . .E .9 +. ** 2 1 " " " 2 /" = - = /" % ? ? : : $ @ - = -1J= "B1= 6 6 ",C$ 1 % % % - 0 7 - 0 70 2 > >8 >8 1 * ; < "B1 "B1 6 6 $ 6:9E-: 6 6 , 1 = 6 : 1 = 3 2 9 - < 7 *% + " @ 0 K > 0 = : & ;
  4. 4. F * "B1 $? * /" ; 0 0 D = 0 , *C > , L LL LLLLLLL ",C 7 0 L LL LLLLLL L ":9 7 > L LL LLLLLL -:9 6 > L LL LLLLL LL -,: 6 L) ) LL) LLLLL L / 2 / 0 L ) L L LLL LLLL - " L LLL L L 1/2 / 0 ) L ) LLL L L "B1 ; F 0 + "B1 = = + 0 K3 0 ? 7 ":9 3 -:9 ? = + 3 = ? +"B1 "B1 "B1 "B1 ",C M 0 N ":9 M N -:9 ! ? =@ 3? ? ? ? 7 ! * = ; -:9 3 ? + ! ; - ? ? + - = ? ; - 3 ; F - 0< < - 9 ; O ":9 / 2 ) - -:9 3 9 * ; O - ":9 -/ 2 ) - - - -:9 3 7 0 ; O ":9 / 2 ) - -:9 3 0 = * ; -3 ; @ = = 7 3@ ? < + ? + > 0 * 0 2 - 0 ? * = ? ? 03 ? : & ;
  5. 5. F ? 7 < $! - % -? - 0 ? +* 3 + " + - * @ ? + 0 =3 ? < 0 ; =3 + ; @ 3 ? 0 "B1 "B1 6 1 1 M N 8 8 8 8 8 8 ) 1>8 ) ; : * ; 1D$ 2; ; 1D 0 ; 1D ; . - < 7 % +0 = - C = " !!! " + D = = ? 7 7 3 + " L L ! = ? 6 ? @ ? 7 0 3+ ? 0L < A - 7 ? 0 0 - 7 ? 0 0 0 = > = L= 3 " > 0 0 0 = < = L - ; 6 ? + " < 0 = @ 0; % 0 = = 7 ; L L LL L L L LL 9 ,) ; L L L LL LL L L L L L LL L L 7 * ; L L LL L L L LL = < 0 = ? 7 !!! @ + 0 =@ 0 - < 0 !!! : & ;
  6. 6. / ? + 0 0 = 3 @ ; ? < + +5" 0 = 3 3 0 % " ? + + < < ; 3+ 0 - + 3? + %-: = * 1 = 3 0 > > + 3E *) - > = ? + 7 ? ; > - ? 3 > * % - 0 = ---& 88 % 0 ? C!& = D 3 = = % 3 % - D + * @ > 3 = 3 ? D = 5 3 9 6 - @ ; = = > D ? + % 3 ; % : 0 3 1 @ 3 0 " @ 0 + = @ < - @ > = * @ : & ;
  7. 7. " > - ? ? - @ > 3 ,+ @ 0 * + " = = =3 - 0 > =? + = 3 = ? ? + + 0 ! * = @ 0 +? + -- 0 = ? - = 0 * = - 7 = * = + ? " 0 3 0 0 = 0 L % 7 = = 3 0 LO% +0 / ;= * = @ 0 @ ? 7 ; @ 0 0 = 7 + 3 3 + ? ; - = + = < ; 3 K 0 + / 3 2 + + 7 A ; = 3 3 > = 3 = ? + * : & ; )
  8. 8. K 3 < 0 < 3 < ? ; @ ; * = ? + 0 / = + + 7 P 0 0 * 0 * P 3 + + - = 0 + K 7 ? D ; +; 3 ; + < 3 ; < - + +< % 3 = < = + = 0 < = 0 + = + A = + = = - ; D = + = ;+%0 - ; + ? = 7 = 3 0 = 3 ? + 0 0 = ? ; > 3 ! * = L=L LL 0 ;+ 0 - = 3 0 + < = ? ? + 0 = + ;+ 0 - =@ 3 ; + ? = * = = * ; ; 0 + = = 0 ? D * =3? * * / ? D < ? = < 3 + = D - = = = ?0 < ? 0 + + ,- . F = 7 = K 0 % 3 8= 0 ;L D ? D 0 % % / * = 0 * = ML LLLL N : & ; .
  9. 9. + ML LLLL N ? D ? 03 D ! = 0 *;ML LLLL ?N $ < D 0 " 0 = 0 0 ? + 0 L = ? @ - = D ? + D 0 * 0 K ? = ; ? 00 ? / - < 0 7 = 00 ? = D 0 3 D =3 ? * = 0 K M9N+ ; 0< ;+ 0 + 8F ;+ 0 ? 0 ;+ @ 3 0 = ? 3 D ;+ ; Q R 9 9 R S 9 9 R ) R . R 8 E T& @ 7 & T&&&&& - * + ? K < 0 ? A % IOE%8U " 0 ? 8 > V + 0 ? - , $ * - 0 - 0 + + LLLL LLLL LLLL + L LL L L LL L L LL L 3 LL ??LL ??LL F L L L L L L L L L L? L LLLL LL LLLL LL LLLL LL - LLL LLL LLLL LL % % : & ; 8
  10. 10. 3 0 -E" 7= ? +; @ 5 / 0 / 1 - 7 03 - 7 @ 0 )) )= ;8 )0 + =? K ; + ? W = K 0 ? 0 + = 03 > + ? " 0 3 < @ 7 - < 0 + + = + D 0 : 0< K ? < 7 A = < * ? 7 - , $ * - 0 - 0 - 0 + + LLLL LLLL LLLL LLLL ? + LL L LL L LL L LL 3 LL ??LL ??LL LLLL F L L L L L L L? L LL L L L L L L L L L - L L L L L L L % % % ( % 2 & 2 - = ;% = ; 3 > ! 0 + 1 K ) 0 + - < 0; ? + 0 =3 0 % + - 0 ? = 3 % = ; + + % K F ; 0 - ; % + 3 * 3 ; : & ; O
  11. 11. ? " = @ 0; , 9 ; L L L L > LI>8I>.I> I> I> I% 2 ; LL > I>I% 9 ; L L L L LLLL %> LI>8I>.I> I> I> I U> > I> I> I>OI>.I>)I> 9 ;L L L L LLLL R LL > > > >O >. >) > R > I>I LLL L L L LL L > > > > LI>8I>)I> I>L L > > L >OLLLLL > >O >8 L L L > >8 >. >) L LL > >. >) 8 L L > > LLLLL >8 > > L > LL > > > L LLL > > LLLLL LLL LL LL LL LLLLL L LLL LLLLL LLLL LL LL L LLLLL L L 7 ; L L > I> ; L L L L L L > I> I> I>OI>.I>)I> I> I> - * 7 ? 0 GC/ "/O H " 0 ? 0 7 < 3? = = ; 0 = @ = 0 - > 0 +5 = 0 + 3 3 = @ 5 = 7 7 ; ? - :: 3 ---= ) )0 A > I> I> IF ; 0 3 ;A : 0 : & ; L
  12. 12. 0 : 0 : D 0 : ;+ + 0 %& L= 0 0 ;+ 0 + L= 0 0 ;+ ; 0 ! D = )0 8 03 = =) V ! 0 )0 A - 0 A LL V - 0 A LL V - D 0 A LL V - ;+ )0 A LL V - ;+ .0 A OO=OO)O V : ; ;+ A OO=OO8 V " + ! ( # " 7 + = ? * ? =? ? @ @ 0 D = - ? 0 = ? - 0 @ 7 D < - < ; 3 7 K 3 ? " 0 = + ? ? K LV / ; = + K ? 0 ;+ 3 + +% < = ! 0 3 ? = < 3 - < ? 3 * = ? @ : & ;
  13. 13. " ( , * - * + @ + 0 ? 0 ?+ @ 0 = = +5 ,0 D + + ? ? @ 3 ? @ 0; A < 0 + " = ; < + =+ ; 3 < ; " % * " ? 0 * ? + = 0 0 > " = 3 # 0 = 3 0 G" ,$/1 8.H ! 7 = / 2 ? ;0 ? 3 3 ; ; - / - / : : / 2 / 2 : : / 2 : - +; 0 0 7D @ 0 / 2 7 0 / 3 3 = 3 : & ;
  14. 14. - / - / : : / 2 / 2 0 : : :: : / 2 0 : : : / 2 / 2 : : : / : / * = ? < / 2 + A 0 ? + " ? D 0 = = D L= D = ; DL= D % < + ; = @ + + * - / - / : %L : %L : / 2 0 : 0 : / 2 : % : %L / 2 0 :: : % D / 2 %L : % / 2 : %L : / 2 D / 2 : %L % D : % %L 0 : / : - 0< + < 7 / 2- / 2 K % 0 ? / 2=@ < ? %? @ @ <>/ @ 0 D 7 D %L= ? 0 =? D ? = % - @ 0 0 + : & ;
  15. 15. - / : %L : 0 : / 2%L : %L : % D / 2%L %L " / 2 : : % / 2% 0 : : %L 0 : - / - : %L : %L / : %L : - / 2%L / 2%L : %L : %L : %L / / 2%L : % - / 2%L - : % / : % / 2% - / 2% / / 2% - : %L : %L / 2%L / / 2%L - : % : % : % % ? : % / 2% - / 2% : %L / : %L % ? : %L / 2%L - / 2%L ,0 = 7 D ; ; +? 7 - %L 3 8% L .= 8% L .= ! > * 3@ 3? ? @ 3 ; ? / 2 0< D ? 0 3 : & ;
  16. 16. ? + ;0 * ? 3 0 = 7 < /D 0 = + = ? D + ? - 0 D + * ? 0 = * 0 7 = @ " %* 2 - < ; 0 0" ; 0 0 / ? ? D K0 ++ =3 ? @ @ 0 =3 =? @ + ; ? / ? 0 @ * = ; D = / 2 + ; " 7 2 9 5 +6 " = ; 1/2 ? ? + 7 " - 1/2 0< @ 7 0* 7 ? / 1/2 + " + 3 ! "# " @ 0 D = = ) 3 .= 3 0 1/2 = = ) 3 .= ? D @ 0 " 2 ( 4 ; + = ; / ? 0 @ = * * + : & ;
  17. 17. " " % 22#7 @ @ A 2 - + + 3 0 = 0 + & >= 0 ? + 0 ? @ 0 - ? @ 3 + ?/ 2 ; D A ?? 3 0 D 0 " $ - + * 0 ? @ 3 0 3 ? ; 0 7 7 ? ; " = ; ? 0 ; @ @ 3 = = " 0 = 0 7 ? = ? , 0 ? ? = ? < D = < - 0 +; = + ? /$ ? / ;= ? + =+ 0 0 ++ = ? ? < ? 0 ++ = " @ 0 * ?? > 0 ? = < > 0 ++ = ? 3< > + 0 ++ = 3< + * = < 3 @ !F 3 ; + ?+ * -> + + @ + * A $ 3 %$ " - 5 7 + ? > "& & - < + * 7 + * 3 0 = ; : & ; )
  18. 18. + > A = 3 =@ D @ ; K - ; ? = * =0 7 ; - 0 3 ;+ ! * = 7 < ? "& & = ; ( %L ? ; 0 =3 ; & ( % ? 0 ; " 0 = = ? ;+ 3 @ ? 3 = ? ; 3 ; 0 7 ? "& & + " !5 + + * < + ? 7 +5 3 3 3 + 7 / * = > @ 5 0 + @ + =3? K > ? + ; + * +5 9,1E9,66 ? ; ; + / 2 0 * L ) . L ) . L 1D %1 1 D 1X 0 1 X =? + + F D + ? 0 + 7 A1X 1X = = 0 1X F ; + 3 3 * + 3 K * 0 ++ - K ;> ; ; K D ? 7 " 0 % 8= L .= ; @ 0 3 ? + " D .0 % 8= L . ; @ . ? 0 ++ 1 = K +* = 0 3 ; K? + GC/ "/ O H : & ; .
  19. 19. "! < # * 9 % 7 3 0 ? ? 0 3 0 > -? + = ? - W = D ? + = ? " + A - 0 > A = = ; = 0 $ > A @ ? = 3 7 + = 0 > A 0 = = - !!!= & & & = ? =! ! ! = 0 ? YJ + @ Z %C =" = " + ; ? K = ; < 3 " ? D 3 ? 0 = 3 0 / ? 0 C = * = ; ; 3 = ? + + C " ; ; 0 6 % ? 6 = ? * ; 0 0< *" != ; 7 ? 0 3 + / > 6 = + !!! ? 6 )) =)) = )) 3 . . : & ; 8
  20. 20. ! " # $%& $ ( # ) * )+ ,$% --+ . / 0 0/ / 1 ( 2///3 " . $ " , ( 0 1 ( $ $ $ 4 / 0 0/ $ " . , . 1 " $ 5 6 $ &$ & $1 1 ( " . 5 1 %* $ & ! & 1 $ & " 4 /( $ " . 1 & " . 75 6 "" 1 $( / 1 ( $ &$ & 7 " . $ &$ & 8$ $ $ & $ " . 1 ( " . ( & $1 . / 0 0/ / 1 ( 2///3 4 & $ . & " $ &$ $ $ 4 $( 0 0 ( /// 1 & " . $ 1 # . & " 1$ ($ &$ $ $ 4 $( ( + ( / 1 ( 2 /3 " $( . * 1 " * $ & . &$ $0( 1 1 "$ (% " ( / 1 ( 2 / 3 " $( . $ & 1 " & "" 0($% 1 ( . & 1 & " . /// 1$ ($ 1. * . . . /// ( / 1 ( 2 /3* $ 9 ( $ 1 ( . 1. $( $ $ 1. $ " 1 " $ $ $ $ & 4 & $&& $( $ $ " 1 . $ & 1 " . / 0 0/ / 1 ( " . 5 $ 1 25 3 . . (& & . "0 : 1&$4 & $ ( ( ;/$ < : & ; O

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