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    M ng truy n s li u chuy n m ch gi X25

    Cc thnh ph n c a m ng chuy n m ch gi X.25 - Giao th c m ng chuy n m ch gi B o m t trong cc m ng chuy n m ch gi Khi no s d ng chuy n m ch gi Cc giao ti p v t l c a m ng chuy n m ch gi Trang b cho cc m ng chuy n m ch gi

    3. Cc thnh ph n c a m ng chuy n m ch gi

    3.1. M u 3.2. Cc tuy n lin l c c a m ng 3.3. Thi t b chuy n m ch gi

    o 3.3.1. Giao ti p l p v t l o 3.3.2. Giao ti p l p tuy n o 3.3.3. Modul chuy n m ch gi o 3.3.4. Modul qu n l m ng o 3.3.5. C u trc ph n c ng c a cc b chuy n m ch

    gi

    o 3.3.6. c tnh c a thi t bi chuy n m ch gi 3.4. Cc PAD

    o 3.4.1. Giao ti p khng ng b o 3.4.2. Module chuy n i k t - gi o 3.4.3. Module giao th c l p m ng o 3.4.4. Giao ti p l p tuy n o 3.4.5. Giao ti p v t l o 3.4.6. Module qu n l m ng o 3.4.7. C u trc ph n c ng c a PAD o 3.4.8. Ch t l ng c a PAD

    3.5. Cc giao ti p ch o 3.5.1. C u trc ph n c ng c a giao ti p ch o 3.5.2. Hi u qu c a giao ti p ch

    3.6. Cc ng n i c ng m ng o 3.6.1. Ph n c ng c a c a c ng o 3.6.2. Hi u ch c a c a c ng

    3.7. H th ng qu n l m ng

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    o 3.7.1. Giao ti p qu n l m ng NMS o 3.7.2. Ph n c ng v ph n m m c a NMS

    3.8. K t lu n

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    Tu thu c vo t ng ki u chnh xc c a tuy n thng tin, c th c m t tn hi u ng h ring cho m i h ng chuy n tin; ch m t ng h c dng cho c hai h ng ho c khng c tn hi u ng h no c . tr ng h p sau, lu ng s li u cng mang theo c thng tin v ng h nh p. C nhi u ph ng php ring m ho lu ng s li u cho php ng h ny c th tch ra t s li u m t lo i k thu t c g i l "m ho Manchester".

    h u h t cc tr ng h p c s khc bi t gi a cc giao ti p m i pha c a tuy n lin l c. M t u g i l "thi t b k t cu i m ch i n s li u", hay DCE. Cn u kia g i l

    "thi t b u cu i s li u", hay DTE. Ni chung cc thi t b trong m ng (t c l cc nt chuy n m ch gi) l cc DCE giao ti p v i cc thi t b u cu i pha ngoi vnh ai m ng. Cn cc thi t b u cu i i di n cho DTE u n i v i cc giao ti p DCE. Khi u n i vo m ng thng tin th lun ph i c m t CDE c a m ng v thi t b ng i s d ng ph i c m t giao ti p DTE.

    m c ny th gi a DCE v DTE khc g nhau? h u h t cc tr ng h p, giao ti p DCE cung c p cc tn hi u ng h nh th i cho tuy n. DTE c n s d ng thng tin nh th i do DCE cung c p khi l y m u s li u thu c v pht s li u. Cn c s khc bi t v v t l gi a cc giao ti p DCE v DTE. Cc giao ti p DCE lun s d ng cc b u chuy n ci, "trong khi cc giao ti p DTE th s d ng cc b u chuy n c". i u ny l i lin quan n tnh

    tr ng m ng cng c ng, v an ton i n, cc m ch i n n i tr c ti p vo giao ti p m ng cng c ng khng bao gi c l chn ra. i u ny s x y ra n u s d ng b n i chuy n c cho cc DCE.

    ng dy ph thng nh t cho cc tuy n c a m ng chuy n m ch gi l cc i dy xo n ho c cp nhi u s i thng th ng. Cc i dy xo n l ki u c bi t c a cp nhi u s i. y cc c p dy c a cp c xo n quanh nhau d c theo s i cp. i v i m t s lo i tn hi u i n

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    (v d nh giao ti p X.21) th cp c s d ng ph i l dy cp xo n v n r t quan tr ng cho thao tc c a thi t b i u khi n v thi t b thu m i u cp.

    Ki u dy n i ny c th dng cho b t k t c s l ng no t i 10 tri u bit m i dy c ly r t ng n. Cp di t i a 1 km cng c th c s d ng cc t c th p h n. N u c n c t c cao h n ho c c ly di h n th th ng s d ng cp quang. T t c cc giao ti p v t l cho cc m ng chuy n m ch gi s c p chi ti t ch ng 10.

    3.3. Thi t b chuy n m ch gi

    Thi t b chuy n m ch gi l trung tm c a m ng chuy n m ch gi. Chng t o ra cc phn vng c a m ng (nh m t nhi u s m ng) v t o ra m ng chuy n m ch gi hon ch nh c nhi u c tnh khai thc quan tr ng. V v y c n ph i m b o ch c ch n r ng, cc thi t b chuy n m ch gi c ch n cho m t m ng ph i c c tnh v kh n ng chu n xc cho nh ng g m m ng c n s d ng.

    3.3.1. Giao ti p l p v t l

    Hnh 3.2 m t cc ph n t c b n c a m t thi t b chuy n m ch gi. Cc tuy n thng tin c a m ng d n vo thi t b chuy n m ch c n i vo cc giao ti p v t l c a thi t b chuy n m ch. Chng cung c p cc i m n i v t l (t c l cc b u chuy n) v cc i m n i i n (cc b i u khi n v b thu bo hi u ng i n ang s d ng).

    V ki u giao ti p c th thay i nn cc giao ti p ny th ng d ng cc phi n n i ki u ch u c m. Nhi u ki u giao ti p khc nhau c s d ng cho cc m ng chuy n m ch gi s c bao qut chi ti t ch ng 10. M c tiu c a ch ng ny l gi i thi u tn cc giao ti p m khng i su vo chi ti t.

    Giao ti p v t l ph thng nh t (t c l giao ti p l p v t l)

    g i l X.21. BIS, i khi cn g i l V.24. Cn giao ti p bo hi u i n th ng l V.28, cn g i l RS.232. Cc c c u

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    ch c n ng c a module l p m ng c a cc thi t b chuy n m ch gi. C hai ki u module chuy n m ch gi khc nhau tu thu c b chuy n m ch gi ki m tra nh th no cc gi ang c n chuy n m ch.

    Ki u th nh t th c hi n cng vi c chuy n "thng su t" cc gi. C ngha l cc gi thu v c nh tuy n, n u c th khng ki m tra n i dung c a chng c ngha hay chng vi ph m th th c l p m ng theo cch no . Ki u chuy n m ch ny th ng di n ra cc m ng kh i s li u, b i v thi t b chuy n m ch ch xem tiu kh i s li u c a b n tin. V n khng c thng tin tr ng thi nh

    m ng g i th c hi n b chuy n m ch gi ch ti n hnh ki m tra r t t. u i m c a ki u chuy n m ch ny l thao tc r t nhanh. Cng vi c x l tiu cc gi ch duy tr m c r t th p nn t c chuy n m ch cao. i u ny cng c ngha l ph n m m c a thi t b chuy n m ch t ng i n gi n.

    Nh c i m c a ph ng th c chuy n qua ny l cc thi t

    b chuy n m ch gi c th cho l i qua m ng. i u ny s khng h tr ng n u m i thi t b trn m ng c th x l c t ng tr ng thi l i c th nh n bi t c. Kinh nghi m cho th y m c d cc thi t b v n lm vi c chu n xc i u ki n thng th ng nh ng ngoi tr ng thi thng th ng cn c l i ph n m m hay ph n c ng v d n t i s c , th m ch r t nghim tr ng. Tr ng h p x u nh t ton b m ng c th b nh tr . Khi th c hi n ph n m m

    t o l p m ng, m t t l l n ph n m m dnh i ph khi l i x y ra. N l chu n m c ki m tra l i v ph c h i ph n m m v i i u ki n th c t khi kh c th do ki m m i tr ng thi l i sinh ra. R rng l cng ngh so n th o ph n m m hon thi n th c th kh ng nh r ng s n ph m ph n m m c a t ng m ng c th lm vi c chu n xc m i tnh hu ng. Tuy v y th i i m ny v n cn v ng m c.

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    N u cc thi t b chuy n m ch gi ki m tra kh t khe t ng gi m t, th cc l i c th c nh v v ng n ng a khng a vo m ng. i u ny c hi u qu nh t cc m ng g i th c. V cc b chuy n m ch gi c n c tr ng thi c a cc cu c g i th c chuy n qua chng nn chng ph i c ton b thng tin c n ki m tra xem t ng gi c thch h p v tr ng thi c a cu c g i th c cho n hay khng.

    m t vi c ny c th th c hi n ra sao, ta xem xt tr ng h p m t thi t b u cu i ch u c m t ki u l i ph n m m ring. L i ny gy cho thi t b khng tun th

    cng vi c i u khi n lu ng l p m ng d n t i vi c pht i m t dy lin ti p cc gi theo m t cu c th c vo m ng. N u nt chuy n m ch gi c a thi t b u cu i ny chuy n m ch cho cc gi ny qua th dy gi s c a vo m ng. N c th lm m t nhi u ti m n ng cc nt chuy n m ch gi theo ng n i c a cu c g i th c v c th d n t i s c nt chuy n m ch gi, ho c t nh t cng lm gi m ch t l ng cng vi c.

    V b chuy n m ch gi c thng tin v tr ng thi c a cu c g i th c nn n c th t kh ng ch cng vi c i u khi n lu ng c a giao th c l p m ng. M t khi thi t b u cu i khng tun th giao th c l p m ng th thi t b chuy n m ch gi c th b y cc gi khng h p l v thng bo cho thi t b u cu i l n gy l i. V v y l i b sa b y ngay khi n t i m ng, nn khng th lan qua m ng. Ki u

    phng v ny c bi t quan tr ng i v i cc m ng chuy n m ch gi cng c ng v chng c hi u su t s d ng r...