dhhh - giao trinh truyen du lieu.2010

7/22/2019 DHHH - Giao Trinh Truyen Du Lieu.2010

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B GIAO THNG VN TITRNG I HC HNG HI

B MN: K THUT MY TNHKHOA: CNG NGH THNG TIN

BI GING

TRUYN DLIU

TN HC PHN : TRUYN DLIUM HC PHN : 17305TRNH O TO : I HC CHNH QUYDNG CHO SV NGNH : CNG NGH THNG TIN

HI PHNG - 2010


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MC LCChng I: CC KHI NIM C BN ................................................................................. 4

1.1. Tin tc - d liu - tn hiu ........................................................................................... 41.2 M ha d liu ............................................................................................................. 51.3 Cc phng php truyn tin ...................................................................................... 17

Chng II: H THNG TRUYN THNG ........................................................................ 192.1. Gii thiu v h thng truyn thng .......................................................................... 192.2 H thng truyn s liu .............................................................................................. 212.3. Cc h thng truyn s liu thng gp..................................................................... 222.4. Mi trng truyn tin ................................................................................................ 242.5. Cc chun giao tip truyn thng .............................................................................. 372.6. Mng truyn thng .................................................................................................... 49

Chng III: K THUT TRUYN S LIU ..................................................................... 503.1. Gii thiu v k thut truyn s liu.......................................................................... 503.2. K thut nh khung trong truyn s liu .................................................................. 503.3. K thut truyn ni tip khng ng b .................................................................... 513.4. K thut truyn ni tip ng b ............................................................................... 533.5. Cc k thut truy nhp ng truyn ........................................................................ 59

Chng IV: CC VN TRONG TRUYN S LIU .................................................. 634.1. Vn pht hin sai v sa sai .................................................................................. 63

..................................................................................................... 74............................................................................................. 87

u l ng .................................................................................... 87u khin khc phc li .............................................................................. 91

m bo cht lng dch v .......................................................................... 94Chng V: MNG TRUYN S LIU ............................................................................ 102

5.1. Tng quan............................................................................................................... 1025.2. Kin trc phn tng v m hnh OSI. TCP/IP .......................................................... 1045.3. Phn loi mng theo k thut chuyn mch ............................................................. 1065.4. K thut LAN ......................................................................................................... 109


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YU CU V NI DUNG CHI TIT

Tn hc phn:K thut Truyn dliu Loi hc phn:1B mn ph trch ging dy:K thut my tnh Khoa ph trch:CNTT

M hc phn: 17305 Tng sTC: 2

TS tit L thuyt Thc hnh/Xemina T hc Bi tp ln n mn hc

45 45 0 0 0 0

iu kin tin quyt:

Sinh vin phi hc xong cc hc phn sau mi c ng k hc phn ny:

Kin trc my tnh, Mch v tn hiu, L thuyt truyn tin, K thut Vi x l, Nguyn lhiu hnh, Cu trc d liu

Mc tiu ca hc phn:

- Cung cp cho sinh vin nhng khi nim tng quan v K thut truyn s liu, Mngtruyn thng...

Ni dung ch yu- Chng I: Tng quan

- Chng II: H thng truyn thng

- Chng III: K thut truyn s liu

- Chng IV: Cc vn c bn trong truyn thng

- Chng V: Mng truyn s liu

Ni dung chi tit ca hc phn:

TN CHNG MC

PHN PHI S TIT

TS LT BT TH KT

Chng I: Tng quan 9 9

1.1. Mt s khi nim v thng tin 2

1.2. M ho d liu 3

1.3. Cch truyn thng tin trn ng truyn 2

1.4. Nhng vn c bn trong truyn thng 2

Chng II: H thng truyn thng 6 5 1

2.1. H thng truyn thng 1

2.2. Phng tin truyn tin 3

2.3. Cc chun giao tip trong truyn thng 1 1

Chng III: K thut truyn s liu 8 8

3.1. Tng quan 1

3.2. Cc k thut truyn s liu 7

Chng IV: Cc vn c bn trong truyn thng 9 8 1

4.1. Tng quan 1

4.2. M ho pht hin sai, sa sai 4 14.3. Kim sot ng truyn 3

Chng V: Mng truyn s liu 13 12 1


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5.1. Tng quan 1

5.2. Kin trc phn tng v m hnh OSI, TCP/IP 2

5.3. Phn loi mng theo k thut chuyn mch 3

5.4. K thut mng cc b 2 1

5.5. Mng v tuyn v mng v tinh 2

5.6. Mng truyn d liu IDSN/ DSL 3

Nhim v ca sinh vin:

Tham d cc bui thuyt trnh ca gio vin, t hc, t lm bi tp do gio vin giao,tham d cc bi kim tra nh k v cui k.

Ti liu hc tp:

William Stalling, Data Computer and Communication

ng Vn Chuyt, L thuyt truyn tin, NXB Gio dc

Nguyn Vn Thng, C sk thut Truyn s liu, NXB Khoa hc k thut

Quch Tun Ngc, X l tn hiu s, NXB Gio dcNguyn Thc Hi, Mng my tnh v h thng m, NXB Gio dcNguyn Hng Sn,K thut truyn sliu, NXB Lao ngX hi

Hnh thc v tiu chun nh gi sinh vin:

- nh gi da trn tnh hnh tham d bui hc trn lp, cc bui thc hnh, imkim tra thng xuyn v im kt thc hc phn.

- Hnh thc thi cui k: thi vit rc phch, thi gian lm bi: 75 pht

Thang im: Thang im chA, B, C, D, F

im nh gi hc phn Z = 0.2X + 0.8Y.

Bi ging ny l ti liu chnh thc v thng nht ca B mn K thut my tnh, KhoaCng nghThng tin v c dng ging dy cho sinh vin.

Ngy ph duyt: 15 / 6 / 2010

Trng B mn: ThS. Ng Quc Vinh


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Chng I: CC KHI NIM C BN

1.1. Tin tc - d liu - tn hiu

D liu (Data):bao gm cc s kin, khi nim hay cc ch th c din t di mthnh thc thch hp cho vic thng tin, thng dch hay x l bi con ngi hay my mc.

Thng Tin (Information): ngha m con ngi qui cho d liu theo cc qui c cth.

Tin tc c th biu th bi ting ni, hnh nh, cc vn bn, tp hp cc con s, cc khiu, thng qua n con ngi hiu nhau . . .. Trong h thng truyn thng, thng ngi takhng phn bit d liu v tin tc.

Thng tin khi truyn: Theo cc dng nng lng khc nhau: m, in, sng quang,sng in

Vt mang tin: Mi trng dng mang thng tin (L dng nng lng - C kh nnglu tr, truyn gi thng tin...)

Tn hiu (Signal): l tin tc, d liu c chuyn i, x l (bi cc b phn m hav /hoc chuyn i) cho ph hp vi mi trng truyn thng. Bn cht tn hiu vn l mthm n tr bin thin theo thi gian hay tn s.

C hai loi tn hiu: tn hiu tngt v tn hiu s.

Tn hiu tng t(analog):

Tn hiu c bt c gi tr no trong mt khong thi gian xc nh.

Tn hiu tng t quen thuc c dng hnh sin. Mt tn hiu tng t c thc sha trthnh tn hiu s.

Ba c im chnh ca tn hiu tng t bao gm:

o Bin (Amplitute):

o mnh ca tn hiu, n v: decibel (dB) hay volts.

Bin cng ln th tn hiu cng mng.o Tn s (Frequency):

Tn s (f) ca tn hiu l sdao ng ca tn hiu trong mt n v thigian (thng tnh bng giy) hay cn gi l tc thay i ca tn hiutrong mt giy, n v Hz hay s chu k trong mt giy.

Mt chu k l s di chuyn sng ca tn hiu tim ngun bt ucho n khi quay trv li im ngun .

o Pha (Phase):

L n vo v tr tng i ti mt thi im trong mt chu kn

ca tn hiu, n c trng cho tnh tr. Tc thay i quan h ca tn hiu i vi thi gian, c m t theo

(degree). S dch pha xy ra khi chu k ca tn hiu cha kt thc,v mt chu k mi ca tn hiu bt u trc khi chu ktrc chahon tt.

Tn hiu s:L tn hiu m bin ch c mt trong hai gi tr duy nht, tng ng vihai trng thi logic c trng bi hai s 0 v 1 trong h nh phn. H thng truyn tn hiu nyl h thng truyn nh phn.


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Tn hiu s bao gm ch hai trng thi, c din t vi hai trng thi ON hay OFFhoc l 0 hay 1. Tn hiu s yu cu khnng bng thng ln hn tn hiu tng t

Cc vn khi truyn dliu:

Thng dng tn hiu s cho d liu s v tn hiu tng t cho d liu tng t

C th dng tn hiu tng t mang d liu s

C th dng tn hiu s mang d liu tng tBit Interval v Bit Rate:

Hu ht cc tn hiu s l khng tun hon, chu k v tn skhng xc nh. Hai khinim t ra y l Bit Interval v Bit Rate. Bit Interval l khong thi gian cn thit gimt bit. Bit Rate l slng Bit Interval trong 1 giy, theo cch ni khc, Bit Rate l s bitc gi i trong 1 giy (bps).

1.2 M ha d liuD liu lu tr trong mt my tnh l dng cc bt 0 v 1. c thmang c t

ni ny sang ni khc ( trong hoc ngoi my tnh), th d liu thng c chuyn isang dng tn hiu s. iu ny c gi l s chuyn i tn hiu s sang tn hiu s (digitalto digitalD/D) hoc m ho d liu s sang tn hiu s.

i lc chng ta cn chuyn i mt tn hiu tng t (v don ni chuyn trongin thoi) sang tn hiu s v mt vi l do no nh gim bt hiu ng ca ting n. iuny c gi l s chuyn tn hiu tng t sang tn hiu s (A/D) hoc s ho mt tn hiutng t.

Vo lc khc chng ta li cn chuyn mt tn hiu s tu ra ca mt my tnh quamt phng tin truyn thng c thit k cho dng tn hiu tng t. V dnh vic gi tnhiu tni ny n ni khc qua mng in thoi cng cng, tn hiu s cung cp bi mytnh sc chuyn sang tn hiu tng t. iu ny c gi l bin i tng t sang shay iu ch tn hiu s.

Thng th mt tn hiu tng t c truyn qua mt khong cch di s dngphng tin truyn thng tng t. V d m thanh, m nhc t mt trm radio, bn thn n

l mt tn hiu tng tc pht qua khng kh. Tuy nhin, tn s ca m thanh hoc mnhc khng thch hp cho vic truyn pht. Tn hiu pht i phi c mang bi mt tn hiuc tn scao hn. iu ny c gi l bin i tng tsang tng t(A/A) hay iu chtn hiu tng t.

Cc phng thc

chuyn i

S/s

(D/D)

Tng t/s

(A/D)

S/tng t

(D/A)

Tng t/tng

t (A/A)


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1.2.1D liu s-Tn hiu s

Chuyn i hoc m ho s / s l s miu t thng tin dng s sang mt tn hiu s. Vd khi chng ta truyn tn hiu t my tnh n my in, c hai d liu gc v d liu ctruyn u dng s. Trong kiu m ho ny cc s nh phn 0 v 1 pht ra bi my tnhc chuyn thnh cc xung in th, cc xung ny c th truyn c qua dy dn in.

Trong rt nhiu k thut m ho s / s, chng ta ch bn n nhng k thut hu dngnht cho vic truyn thng d liu. C 3 loi ph bin: n cc, cc v lng cc c ch ranh hnh di.

M ho n cc:l dng n gin vi ch mt k thut c s dng.

M ho cc: c 3 kiu con: NRZ, RZ, v biphase. Hai trong s chng c nhng s biti phc tp.

M ho lng ccc ba s bin i: AMI, B8ZS, v HDB3.1.2.1.1.M ho n cc

M ho n cc rt n gin v th s. Tnh n gin ca n cung cp s ch dn d

dng lm c s pht trin cho cc h thng m ho phc tp hn v cho php chng ta nghincu cc loi bi ton m bt k h thng truyn s no cng phi thc hin.

H thng truyn s lm vic da trn xung in cng vi mt kt ni trung gian, thngl dy dn hoc cp. Trong hu ht cc kiu m ho, mc in p cao thp ng vi gi tr nh

phn 1 hoc 0. Tnh c cc ca mt xung m ch vic la chn l cc dng hay cc m. Mho n cc c tn nh vy l bi v n ch s dng mt cc. Tnh c cc ny ch nh 1trong 2 trng thi 0 hoc 1 (thng l 1). Trng thi cn li (thng l 0) c i din biin p 0.

M ho n cc ch s dng mt mc in p(mc in p dng hoc m).

Trong v d ny, m nh phn 1 c m ho ng vi gi tr dng v m nh phn 0c m ho ng vi gi tr 0. Hn na vic m ho n cc khng phc tp v d thc hin.

Tuy nhin, m ho n cc c t nht 2 vn lm cho n t mong mun: thnh phnmt chiu v s ng b ho.

Thnh phn mt chiu (DC):Bin trung bnh ca mt tn hiu m ho n cc lkhc 0. iu ny to ra thnh phn dng mt chiu (DC) mt thnh phn c tn s bng 0.Khi mt tn hiu cha thnh phn DC, n khng th truyn i m khng x l.

01011101M ho s /s

thi gian

Bin

0 1 0 0 1 1 1 0

M ho s / s

n cc Cc Lng cc


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ng b ho:Khi mt tn hiu khng n nh, bn nhn khng th xc nh im uv im cui ca mi bit. V th vn ng b ho trong vic m ho n cc c th xy ra

bt c khi no dng d liu gm mt lot cc ch s 0 hoc 1. Qu trnh s ho dng s thayi mc in p ch ra s thay i gi tr bit. S thay i tn hiu cng ch ra rng mt bitva kt thc v mt bit mi bt u. Tuy nhin trong m ho n cc mt lot cc bt cnggi tr, nh 7 s 1, tc l khng c s thay i in p, mc in p dng khng b ph v

sau 7 ln min l nhn gi tr bit 1. Bt c khi no khng c tn hiu thay i ch ra imbt u ca bit tip theo trong chui, bn nhn phi da trn mt mc thi gian. Chng hnvi tc bit 1000 bps, nu bn nhn xc nh mt in p dng tr 0.005s, m tc c 1

bt l 0.001s, hay 5 bit.S thiu ng b gia ng h cabn nhn v bn gi lm sai lch thi gian ca tn

hiu, v d 5 bt 1 b ko di thnh 0.006s, v do bn nhn s hiu thnh 6 bt 1. Mt bitph trong dng d liu gy ra mi th sau khi n c gii m nhm. Mt gii php cpht trin iu khin vic ng b ho trong truyn pht mt cc l s dng mt du tch,mc song song mt ng mang mt xung ng h v cho php bn nhn phn chia ng

b ho li thi gian ca n. Nhng vic nhn i s ng s dng cho truyn pht ngngha vi viclm tng chi ph v v vy s khng kinh t.1.2.1.2. M ho cc:

M ho cc s dng 2 mc in th, mt in p dng v mt in p m. Bng vics dng c 2 mc, trong phng php m ho cc, mc in th trung bnh trn ng truync gim xung v vn v thnh phn DC ca m ho n cc v th c gim nh.Trong m ho Manchester v Manchester vi sai (xem trang sau), mi bit gm c c hai inth dng v in th m, v vy thnh phn DC hon ton c th loi ra.

M ho cc s dng 2 mc bin (mc dng v mc m)

Trong s rt nhiu kiu m ho cc a dng, chng ta s ch kim tra 3 kiu thng dngnht: nonreturn to zero (NRZ), return to zero (RZ), v biphase. M ho NRZ bao gm 2cch: nonreturn to zero, level (NRZ-L), v nonreturn to zero, invest (NRZ-I). Biphase cng c2 phng php. u tin, Manchester l phng php c s dng bi mng LAN. K n,Manchester vi sai, l phng thc c s dng bi mng Token Ring LAN

M ho Nonreturn to Zero (NRZ):

Trong m ho NRZ, mc ca tn hiu lun l dng hoc m. Hai phng thc thngdng nht ca vic truyn pht NRZ c trnh by nh sau:

M ho NRZ-L :

Trong m ho NRZ-L, mc ca tn hiu ph thuc vo kiu ca bit m n trnh by.in thdng quy c l bit 0, tn hiu in thm quy c l bit 1; theo cch mcca tn hiu ph thuc vo trng thi ca cc bit.

Trong NRZ-L mc ca tn hiu ph thuc vo trng thi ca bit

Polar

NRZ RZ Biphase

NRZ-L NRZ-I Manchester Manchester vi sai


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Mt vn c th ny sinh khi c mt dy di cc bit 0 v 1 trong d liu. Bn nhnnhn mt dng in th lin tc v c th xc nh c bao nhiu bit c gi da vong h ca chng, iu ny c thc ng b hoc khng c ng b vi ng hngi gi.

M ho NRZ-I :

Trong NRZ-I . Mt so ngc ca in th miu t mt bit 1. S chuyn i trngthi gia in thdng v in thm a ra mt bit 1. Mt bit 0 c miu tnh mtskhng thay i. NRZ-I tt hn NRZ-L v sng b ho cung cp bi sthay i tnhiu trong mi thi im mt bit 1 gp phi. Hin trng ca chui bit 1 trong lung dliu cho php bn nhn ng b ho thi gian ca n n ni nhn thc s ca victruyn. Mt chui bit 0 c th gy ra vn , tuy nhin do cc bt 0 khng hn nh vy,chng gim thiu vn xy ra.

Trong NRZ-I cc tn hiu c o ngc nu mt bit 1 c gp.

Trong chui NRZ-L, in thdng v m c ngha r rng; dng i vi 0 v mi vi 1. Trong chui NRZ-I , bn nhn tm kim sthay i t mt mc ny n mckhc nh l c s nhn ra bt 1.

M ho Return to Zero (RZ)

Nh chng ta c th thy, bt c thi im no th d liu gc cng cha ng cc s1 v khng lin tip nhau. Bn nhn c th mt v tr ca n. V nh chng ta cp ntrong phn tho lun v m ho n cc, mt cch m bo ng b ho l gi cc tn hiuthi gian phn tch trn mt knh phn tch. Tuy nhin gii php ny s lm tng chi phng thi d xy ra li ca bn thn chng. Mt gii php tt hn l bng cch no chang vic ng b ho trong tn hiu m ho. Mt vi th ging nh gii php c cung cp

bi NRZ-I, nhng kh nng trnh by trnh by chui 0 v 1 l nh nhau.

m bo vic ng b ho, cn phi c mt tn hiu thay i cho mi bit. Bn nhnc th s dng nhng thay i ny xy dng, cp nht v ng b ho ng h ca n.

Nh chng ta bit trn, NRZ-I thc hin iu ny cho mt chui tun t cc bt 1.Nhng thay i vi mi bit, chng ta cn phi c nhiu hn 2 mc. Mt gii php l mho theo kiu Return to Zero (RZ), bng vic s dng 3 gi tr: dng, m v khng. TrongRZ, nhng thay i tn hiu khng phi gia cc bt, nhng trong mi bit. Ging nh NRZ -

thi ian

thi ian

Bin

NRZ-L

NRZ-I

0 1 0 0 1 1 1 0

Thi gian

Gi tr

0 1 0 0 1 1 1 0


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L, in th dng c ngha l 0, v in th m c ngha l 1. Trong khong thi gian ca mtna bit, mt na tn hiu cn li tr v 0. Mt bit 1 thc t c miu t l dng-0 v mt bit0 cmiu t l m -0 s tt hn ch c mt mnh dng v m.

S bt li chnh ca m ho RZ l i hi 2 thay i tn hiu m ho 1 bit, v v vyn chim gi gii rng hn. Tuy nhin c ba kh nng chng ta kim tra tt hn, l hiuqu tt nht.

M ha Biphase:C l gii php tt nht cho n nay gii quyt vn ng b ho l m ho

Biphase. Trong phng php ny s thay i tn hiu trong khong thi gian ca mi bitnhng khng tr v 0. Thay vo n chuyn sang cc i din. Ging nh RZ, giakhong thi gian truyn cho php ng b ho.

M ho Biphase c bsung l: Manchester v Manchester vi sai.

Manchester:

M ho Manchester s dng cch o ngc mi bt trong khong thi gian can ng b v miu t bit. Vic chuyn trng thi m-dng tng ng vi bt 1 v

dng-m tng ng vi bt 0. y ta s dng vic mt chuyn trng thi n chohai mc ch. M ho Manchester t c theo mc ca ng bho nh RZ, nhngch c 2 gi trbin .

Manchester vi sai:

Trong Manchester vi sai vic o ngc trong khong thi gian ca mi bt cs dng cho vn ng bho, nhng s c mt hoc thiu vng ca vic bin ic thm vo u trong khong thi gian tm ngng c s dng xc nh cho

bit. Mt s bin i c ngha l bt 0 v s khng bin i c ngha l bt 1.Manchester vi sai yu cu 2 sthay i tn hiu trnh by bt 0 nhng chc 1 trnh by bit 1.

1.2.1.3M ho lng cc:M ho lng cc, ging nh RZ, s dng 3 mc in th: dng, m v 0. Tuy nhin

khng ging nh RZ, mc 0 trong m ho lng cc c s dng miu t bit 0, cn bt 1ng vi in th m hoc dng. Nu u tin mt bit c miu t bi bin dng, th bt1 th hai s c miu t bin m, cn bt 1 th ba li c miu t bng bin dng... Vic lun phin ny xut hin c khi cc bit 1 ri rc nhau.

Ba kiu ca m ho lng cc thng thng truyn thng d liu l: AMI, B8ZS, vHDB3

Thi gian

Thi gian

Manchester

Manchestervi sai

Bin

Lng cc

AMI B8ZS HDB3


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M ho AMI(o du xen klng cc):

M ha AMI l kiu m ho lng cc n gin nht; trong tn gi ca n; tduxut pht tin tn v c ngha l 1. V vy AMI c ngha l o 1 xen k nhau. Mt vtr trung lp, in th 0 s trnh by bt 0. Nhng bt 1 c miu t bi cc in p dngm an xen nhau. Hnh 5.10 a ra v d ny.

Mt s bin i ca AMI c gi l gi ba bc vi bt 0 nm xen k gia in thdng v in th m.

Vi vic o ln trong mi ln xut hin ca 1, AMI t c 2 mc ch: th nht

cc thnh phn DC l 0, v th 2 mt dy di cc s1 c ng b ho. Khng c kthut no chc chn vic ng b ho cho mt chui di cc s 0.

Hai bin i ca AMI va c pht trin gii quyt vn ng b ho chui 0,c bit cho vic truyn pht khong cch ln. u tin, c s dng Bc M, cgi l B8ZS (lng cc thay th 8-zero). Thhai, c s dng Nht v Chu u, cgi l HDB3 (lng cc mt cao 3). C hai kiu ny u l s thch nghi vi AMI mchthay i mu gc trong trng hp c nhiu chui 0 lin tip.

B8ZS:

B8ZS l mt s tho thun c chp nhn Bc M cung cp vic ng b hocho chui 0. Trong tt c cc tnh hung, cc chc nng B8ZS tng tnh ca AMI.AMI thay i cc vi mi 1 gp phi. Nhng thay i ny cung cp sng b ho cnthit bi bn nhn. Nhng tn hiu khng thay i trong sut chui 0, v vy vic ng bho thng b mt.

S khc nhau gia B8ZS v AMI xut hin bt c khi no c 8 hoc nhiu hn cc bt0 lin tip gp phi trong dng d liu. Gii php cung cp bi B8ZS l p t sthay itn hiu gi bn trong chui 0 (c gi l violation). mi thi im c 8 bit 0 xut hinlin tip, B8ZS a vo nhng thay i trong mu da trn s khc bit ca bit 1 trc (1 ch xut hin pha trc ca chui 0).

Nu bt 1 trc l dng, 8 bt 0 s c m ho l 0, 0, 0, +, -, 0, -, +. Hy nh rngbn nhn ang tm kim s thay i xc nh 1. Khi n thy c 2 in tch dng lin tipbao quanh 3 bt 0, n nhn ra mu, tnh ton v a vo violation khng gy ra li. Sau

Thi ian

Bin


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n tm kim phn cn li ca nhng violation trng i. Khi tm thy chng, bn nhn chuyn8 bt thnh 0 v quay tr li ch AMI thng thng.

Nu cc ca bt 1 trc l m, mu ca cc violation s l tng t nhng o ngcli cc. C mu dng v m c ch ra trong hnh 1.13.

HDB3:

Vn ng b ho chui lin tip cc s 0 c gii quyt Nht v Chu u khcvi M. Quy c ny, gi l HDB3, a s thay i vo mu AMI mi thi im 4 bt 0 lintip thay cho 8 bitnh ca Bc M. Mc d tn gi ca n l HDB3, cc mu thay i bt ckhi no c 4 bt 0 lin tip.

Nh trong B8ZS, mu ca cc violation trong HDB3 c da trn s phn cc cabt 1 trc . Tuy nhin khc vi B8ZS, HDB3 cng nhn vo s cc bt 1 va xut hintrong dng bt k t ln thay th cui cng. Bt c khi no s ca bt 1 k t ln thay th cuicng l l, B8ZS y mt violation vo v tr th 4 ca cc bt 0 lin tip. Nu s phn ccca bt trc l dng, violation l dng. Nu s phn cc ca bit trc l m,violation l m.

Bt c khi no s ca bt 1 k t ln thay th cui cng l chn, B8ZS y violation vo

v tr u tin v v tr th 4 ca cc bt 0 lin tip. Nu cc ca bt trc l dng, c haiviolation l m.Nu cc ca bit trc l m, c hai violation l dng.V d 1: S dng B8ZS, m ho dng bt 10000000000100; p dng vi cc ca bt 1 utin l 1.

V d 2: S dng HDB3, m ho dng bt 10000000000100; p dng vi s cc bt 1 trcn l chn v bt 1 u tin l dng.

Thi ian

Bin

Thi gian

Bin

1 0 0 0 0 0 0 0 0 0 0 1 0 0


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1.2.2.D liu tng t tn hiu s

i khi chng ta cn s ho mt tn hiu tng t. V d gi ging ni ca con ngitrong mt khong cch xa. Chng ta cn s ho n gim nhiu v n. Vn ny c gil chuyn i tn hiu tng t v tn hiu s hoc l s ho tn hiu tngt.

Trong s chuyn i t tn hiu tng t v tn hiu s, chng ta a ra cc thng tindi dng sng lin tc nh l mt dy nhp ca cc tn hiu s (1s hoc 0s).

Chuyn i tn hiu tng t v tn hiu s cn s dng mt vi tn hiu s ctrnh by ti phn 5.1. Cu trc ca s chuyn i l khng c vn g. Vn l lm nh

th no chuyn cc thng tin t s lng ln cc gi tr ti s ri rc ca cc gi tr mkhng nh hng ti gic quan con ngi v cht lng ca tn hiu.1.1.1.1.iu chbin xung (Pulse Amplitude Modulation - PAM)

Bc u tin trong qu trnh chuyn i tn hiu tng t v tn hiu s c gi liu ch bin xung. K thut ny thao tc vi tn hiu thng t, n gin n v to ranhng di ca xung c bn c kt qu mutn hiu tng t. Thut ng mu c ngha ln v bin ca tn hiu trong 1 khong thi gian l bng nhau.

L thuyt mu c dng trong iu ch bin xung l hiu qu hn trong cc vngkhc ca nng lng, n l d liu truyn thng. Tuy nhin PAM l nn tng quan trng trongchuyn i tn hiu tng t v tn hiu s l thuyt ny c gi l iu ch xung theo m

(pulse code modulation - PCM)Trong PAM, tn hiu ban du l mu ti thi gian ngh bng nhau

PAM gi l k thut mu v gi. hin ti, cp tn hiu l c, tip theo l tr giptng hp. Nhng mu gi tr xy ra ch trong s xut hin ca sng, nhng nhn chung kt qutrong PAM vn cn ngn.

L do PAM khng hu dng trong d liu truyn thng l, mc d n truyn i snggc t mt di ca xung, nhng xung ny vn cn c bin (vn l tn hiu tng t, khng

phi l tn hiu s). to ra tn hiu s chng ta phi sa i chng bng cch dng PCM.

Lu : PAM c mt vi ng dng, nhng bn thn n khng dng trong d liu truynthng. Tuy nhin y l bc quan trng ph bin u tin trong l thuyt chuyn i v cgi l PCM.1.2.2.2.iu chxung theo m (PCM)

PCM sa i vn to ra xung bng PAM hon thnh mt tn hiu s. Lm nhvy, PCM u tin lng t ho nhng xung ca PAM. S lng t l l thuyt tha hngnhng gi tr trong mt dy bit ti mu c bit.

Analog/Digital

conversion

(codec)

AmplitudeAmplitude

Time Time

a. Anaglog signal b. PAM signal


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Hnh 1.18 trnh by 1 mu phng thc ca tha ktn hiu v gi tr ln lng tho mu. Mi gi tr chuyn i vo tng ng 7 bt nh phn. Bt th 8 l bt du (+ l 0vl 1).

Tc ly mu (Sampling Rate).

Nh chng ta thy t cc hnh v trc, s chnh xc ca mi tn hiu s c ti toli t cc tn hiu tng t ph thuc vo s mu em theo. S dng PAM v PCM chngta ti to li sng chnh xc bng cch em theo s lng mu khng xc nh, hoc chng tac th ti to s pht ra trng khng ca chnh n. R rng chng ta mun tm mt s u trn trc s. Nh vy, cu hi l C bao nhiu mu th ?

Trn thc t, rt t thng tin ng ch cho vic gi v nhn to li cu trc ca tnhiu tng t. Theo nh l Nyquist m bo tnh chnh xc trong s ti to tn hiu tngt nguyn bn ta s dng PAM, s tc ly mu phi tin hnh hai ln tn s cao nht catn hiu gc. Nh vy, nu chng ta mun mu ging ni in thoi vi tn s ln nht 4000Hz, chng ta cn tc ly mu ca 8000 mu trn 1 giy.

Lu : Theo nh l Nyquist, s tc ly mu t nht phi tin hnh 2 ln tn s caonht.

Mt s tc ly mu hai ln tn s x Hz c ngha tn hiu phi c ly mu mi x giy. Dng ging ni qua ng dy in thoi trn l mt v d, iu ny c ngha l mtmu mi 1/8000 giy.

hiu r hn v nh l xt v d sau: Tc ly mu l bao nhiu di bng rng10000 Hz (1000 ti 11000)?

+024 00011000 -015 10001111 +125 01111101

+038 00100110 -080 11010000 +110 01101110

+048 00110000 -050 10110010 +090 01011010

+039 00100111 +052 00110110 +088 01011000

+026 00011010 +127 01111111 +077 01001101

Amplitude

Time

++38

+48 +39

+26

-15

-

-50

+52

++

+110+

+88+77


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Gii: Tc ly mu hai ln tn s cao nht ca tn hiu

Tc ly mu = 2(11000) = 22000 mu/giy.

Bao nhiu bit cho mt mu?

Sau khi chng ta tm c tc ly mu, chng ta cn xc nh s bit cn truyn chomi mu. iu ny phc thuc vo mc ca chnh xc cn thit. S bit l nhng lachn cho tn hiu gc cn ti to vi chnh xc mong mun trong bin .

V d:Mt tn hiu l mu, mi mu yu cu t nht 12 mc ca chnh xc (+0 n+5 v0 n -5). Bao nhiu bit s c gi cho mi mu?

Gii: Chng ta cn 4 bit: 1 bit cho du v 3 bit cho gi tr. 3 bit gi tr c th biu dinbng 23= 8 mc (000 n 111), iu l nhiu hn ci ta cn. Vi 2 bit gi tr l khng v 22= 4. Vi 4 bit gi tr th qu ln v 24= 16(tha qu nhiu).

Tc Bit (Bit Rate).

Sau khi tm c s bit trn mi mu, ta cn tnh ton Bit Rate theo cng thc:

Bit Rate = Tc ly mu x S bit trn mi mu

V d:Chng ta mun s ho ging ni con ngi. Bit Rate l g? vi gi thit 8 bit trnmt mu.

Gii:Ging ni bnh thng ca ngi thng tn s t 0 n 4000 nh vy tc ly mu l: Tc ly mu = 2 x 4000 = 8000mu/giy.

Bit Rate c th tnh ton nh sau:

Bit Rate = Tc ly mu x S bit trn mt mu

= 8000x8 = 64000 bit/s = 64 Kbps.

1.2.3.D liu s-Tn hiu tng t

Bin i D/A (hay cn gi l iu bin D/A) l qu trnh thay i mt trong nhng ctrng ca tn hiu tng t da vo thng tin trong tn hiu s (0 v 1). Khi truyn d liu tmt my tnh n my tnh khc qua ng in thoi cng cng, chng hn nh: d liu gc

l s, nhng v cc ng dy in thoi mang cc tn hiu tng t, nn d liu phi cchuyn i. D liu s phi c iu bin thnh tn hiu tng t, iu c thc hintrng nh hai gi tr phn bit tng ng vi s nh phn 0 v 1.

Amplitude

Time

Tn s cao nht = x Hz

Tc mu = 2x mu/giy

Thi gian gia 2 mu = x


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C nhiu thit b bin i D/A, nhng chng ta s ch bn n nhng thit b c li nht

cho vic truyn d liu.Mt tn hiu hnh sin c 3 c trng: bin , tn s v pha. Khi thay i mt trong 3

c trng ny, ta s to c phin bn mi ca tn hiu hnh sin . Chng hn tn hiu gcl mc 1, c th bin i thnh mc 0 hoc ngc li. V th, bng s thay i lin tc hnhdng ca mt tn hiu in n gin, ta c th dng n m t d liu s. Bt c ba ctrng trn c th c thay i theo cch ny, a cho ta t nht 3 thit b bin i d lius thnh tn hiu tng t: ASK (Amplitude Shift Keying - di bin ).

FSK (Frequency Shift Keying - di tn s).

PSK (Phase Shift Keying - di pha).

Hn na, thit b th t tt hn c l thay i hn hp ca c bin , tn s v pha

c gi l b iu ch bin cu phng QAM (Quadrature Amplitude Modulation).QAM l hiu qu nht so 3 thit b trc, v l thit b c dng trong tt c cc MODEMhin i (hnh 5.23).

Cc thnh phn ca b bin i D/A:

Trc khi tho lun cc phng php c th bin i D/A, c hai vn c bn phic nh ngha: tc truyn bit/baud v tn hiu mang.Bit Rate and Baud Rate:

Hai thut ng c dng thng xuyn trong vic truyn d liu l bit rate v baud rate.Bit rate l s bit c truyn trong mt giy. Baud rate ch ra s n v tn hiu trn mt giyc yu cu m t nhng bit . Khi tho lun v hiu qu my tnh, th bit rate l quantrng hn, v ta mun bit thi gian x l tng mu tin.Tuy nhin, trong vic truyn d liu,th ch trngn tnh hiu qu ca vic chuyn d liu t ni ny n ni khc trong cc mutin hay cc khi tin. Cc n v tn hiu t hn c yu cu l hiu qu hn cho h thng v

bng thng hp hn c yu cu truyn cc bit; v vy, chng ta ch trng hn vo baudrate. Baud rate xc nh bng thng yu cu gi tn hiu.

Baud rate = Bit rate / (s bt trn mt n v tn hiu)1.2.3.1iu chbin (ASK)

Cng tn hiu mang c bin i sang dng s nh phn 0 hoc 1. Trng hp nytn s v pha l khng i trong khi bin thay i. in p biu din mc 1 v m tmc 0 l sang tri vi h thng. Khong thi gian 1 bit l l giai on c nh ngha l 1

bit. nh bin ca tn hiu trong sut khong thi gian mi bt l khng i v s thay i

ca n ph thuc vo bit (0 hoc 1). Tc truyn dng ASK b gii hn bi cc tnh cht vtl ca mi trng truyn.


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Khng may, vic truyn ASK l nhy cm cao vi nhiu. Thut ng ting n (nhiu) mch n in p khng nh trc can thip vo ng truyn bi cc hin tng khc nh ls nng ln hay in t c sinh ra bi cc ngun khc. Cc in p khng nh trc nytrn ln vi tn hiu lm thay i bin . Mc 0 c th b i thnh mc 1 hoc ngc li. Rrng nhiu l vn kh gii quyt i vi ASK, do ch c da vo bin nhn bit.

Nhiu thng tc ng ln bin ; v th ASK l phng php iu ch b nh hng nhtbi nhiu.K thut ASK ph bin c gi l OOK (on-off-keying). Vi OOK, cc gi tr bit

c m t khng theo in p. S tin b l gim bt trong nng lc yu cu truyn thngtin.1.2.3.2iu chtn s(FSK)

Tn s tn hiu mang c bin i m t cc ch s nh phn 0 hoc 1. Tn s tnhiu mang trong sut thi gian mi bit l khng i, gi tr ca ph thuc vo bit 0 hoc 1:cn li bin v pha l khng i.

FSK trnh c hu ht cc vn nhiu ca ASK. Bi v thit b nhn coi tn s tiu

biu thay i qua s chu k cho, n c th b qua cc nh in p. Cc yu t gii hn caFSK l mi trng vt l ca sng mang. Bng thng FSK

Mc d FSK dch gia 2 tn s mang, n d phn tch thnh 2 tn s trong cng thiim. Ta c th ni ph FSK l s hn hp ca 2 ph ASK tp trung quanh tn s fc0 v fc1.

bng thng yu cu cho vic truyn FSK bng tc baud rate ca tn hiu cng vi tn sdch (khc nhau gia hai tn s mang): BW = (fc1-fc0) + Nbaud.

1.2.3.3iu chpha (PSK)

Pha ca sng mang c bin i biu din sang s nh phn 0 hoc 1. C bin v

tn s l khng i, cn pha th thay i. V d, nu ta bt u vi mt pha 0o

m t bt 0,th ta c th thay i pha sang 180o gi s nh phn 1. Pha ca tn hiu trong sut thi gianmi bt l khng i v gi tr ca n ph thuc vo bit 0 hoc 1.


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Phngphp trn thng c gi l 2-PSK hoc PSK nh phn, bi v 2 pha khcnhau (0o v 180o) c dng. Hnh 5.30 ch r iu ny bng mi quan h gia pha sang gitr bit. S th hai, c gi l chm sao (constellation) hoc s trng thi pha, ch racng mi quan h c minh ho ch bng cc pha.

1.3 Cc phng php truyn tin

1.3.1Cu trc knh truyn

Truyn song song (Parallel)

Mi bit dng mt ng truyn ring. Nu c 8 bits c truyn ng thi s yu cu 8ng truyn c lp

truynd liu trn mt ng truyn song song, mt knh truyn ring c dng thng bo cho bn nhn bit khi no d liu c sn (clock signal)

Cn thm mt knh truyn khc bn nhn bo cho bn gi bit l sn sng nhn d liu k tip

Truyn ni tip (Serial)Tt c cc bit u c truyn trn cng mt ng truyn, bit ny tip theo sau bit kia

Khng cn cc ng truyn ring cho tn hiu ng b v tn hiu bt tay (cc tn hiuny c m ha vo d liu truyn i)


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C hai cch truyn ni tip:

Bt ng b: Khi truyn bt ng b ngi ta pht tng k hiu ring r, cch bit nhauv phn bit cc k t ngi ta thm tn hiu u (start) v cui (stop) vo mi k t.

ng b: Khi truyn ng b nhn bit gi tr cc thi im l 0 hay 1 cn phi ctn hiu xung clock gi l tn hiu ng b. Tn hiu ng b c chu k l T, ngha l mi giy

ngun s cung cp T

1

bits.

1.3.2Ch truyn tinMch n cng (mt chiu: simplex): thng tin ch c th truyn t ngun sang thit b

thu m chiu ngc li khng th thc hin c. V d: d liu c truyn t my tnh sangmy in.

Mch bn song cng (hai chiu ngt qung: half duplex). Hai thit bu cui c thtruyn d liu cho nhau ti nhng thi im khc nhau.

Mch song cng (hai chiu ton phn: duplex). Hai thit bu cui c th truyn dliu cho nhau ng thi.

CU HI V BI TP

1.1. Anh ch hy trnh by v cc loi tn hiu c s dng trong truyn dn hin nay. Nucc c trng, u nhc im ca chng

1.2. Trnh by hiu bit ca anh ch vcc i lng lin quan n tn hiu truyn dn. Nucc khc phc cc nhc im (nu c)

1.3. Trnh by hiu bit ca anh ch vcc phng thc truyn dn hin nay. Cc u nhcim ca cc phng thc ny.

1.4. Cho chui bt cn truyn: 1001 0111 0011 1010 1101 1111 0101 1101. Anh ch hy mha chui bt trn theo phng php m ha NRZ-I, 3 bc, Manchester, FSK.

1.6.Cho chui k t cn truyn theo m ASCII m rng l TEST. Anh ch hy m hachui k ttrn theo phng php m ha NRZ, AMI, Manchester, FSK.

1.7.Tn hiu xung PAM c ly mu vi tc 12 KHz t tn hiu tng t dng sng hnhsin 1KHz. Hy xc nh xung PAM tnhin, xung PAM nh phng, Xung DM.

1.8. Mt my thu DM thu c chui bt nh phn: 1001 0111 0011 1010 1101 1111 01011101. Anh ch hy v tn hiu tng t tm kim xut hin ti u ra ca b tch phn

One-way only

Sim lex o eration

Half-duplex operation

Two-way but not atthe same time

Full-duplex operation

Both-way atthe same time


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Chng II: H THNG TRUYN THNG

2.1. Gii thiu v h thng truyn thng

H thng truyn thng c hiu l mt h thng ton din gip truyn s liu t niny n ni khc. Xt m hnh mt h thng truyn thng tiu biu :

Khi xt mt h thng truyn thng ta xt ti cc yu t sau:

Sender: h thng pht L h thng pht d liu.

Receiver: h thng thu L h thng thu d liu nhn c t h thng pht

Hnh trng mng (Topology): cu hnh chi tit ca ng truyn v cc hthng

Giao thc mng (Protocol): Tp hp cc qui tc, qui c v phng thc truyn, v

khun dng d liu m khi tham gia truyn thng cc thit b trong h thng phi tun th. Mi trng truyn: cc vt dn cho php d liu c truyn ti trn truynt niny sang ni khc.

D liu: Thng tin truyn c nh dng cc dng khc nhau. Cc dng thng thyca thng tin gm:

Text:H thng m ha u tin lin quan n vn bn l h thng m Morse, c sdng rng ri trc khi c my tnh.

yl mt b m nh phn s dng 2 k t chm (.) v gch (-) s ha vn bn (cth xem tng ng vi cc bit 0 v 1). Tuy nhin n c im bt li l ngho nn: t cc kt c m ha. N s dng s phi hp ca cc du gch v du chm vi di khc nhau,iu ny khng c tin li c bit cho cc k t c tn sut xut hin ging nhau. Chnh v

th n khng c dng s ha thng tin. Nu chng ta qui nh rng s bit dng mha cho mt k t phi bng nhau th vi p bit ta c th m ha cho 2pk t. Ngy nay, textc tn ti di dng 1 chui bit (0 hoc 1). Chui c s dng th hin 1 k t gi l

Lut 1

Lut 2

Lut n

Lut 1

Lut 2

Lut n

Sender ReceiverMi trng truyn

D liu


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m (code). Cc m Unicode thng s dng 16 hoc 32 bit biu din v m ASCII s dng 1byte biu din.

S: Biu din di dng1 chuibit c gi tr nh phn tng ng vi gi tr s (Khngbiu din di dng m ASCII)vd: 8 1000

Hnh nh tnh:nh s tht s l mt nh c v nn t cc ng thng v ming thng c xy dng bng cc im. Mt nh theo chun VGA vi phn gii640x480 c ngha l mt ma trn gm 480 ng ngang v mi ng gm 640 im nh(pixel).

Mt im nh c m ha ty thuc vo cht lng ca nh:nh en trng: s dng mt bit m ha mt im: gi tr 0 cho im nh mu en v

1 cho im nh mu trng.

nh gm 256 mc xm: mi im c th hin bng mt byte (8 bits ;

nh mu: ngi ta chng minh rng mt mu l s phi hp ca ba mu c bn l (Red), xanh l (Green) v xanh dng (Blue). V th mt mu bt k c th c biu bin

bi biu thc: x = aR + bG +cB Trong a, b, c l cc lng ca cc mu c bn. Thngthng mt nh p s c lng mu vi gi tr t 0 n 255. V nh th, mt nh mu thucloi ny c th hin bng 3 ma trn tng ng cho 3 loi mu c bn. Mi phn t camng c gi tr ca 8 bits. Chnh v th cn c 24 bit m ha cho mt im nh mu. Kchthc ca cc nh mu l ng k, v th ngi ta cn c phng php m ha gim kchthc ca cc nh.

m thanh v video:D liu kiu m thanh v video thuc kiu tn hiu tun t. Cctn hiu tun t c s ha theo cch thc sau y:

1 - Ly mu

Tn hiu c ly mu: vi tn s f,ta o bin ca tn hiu, nh th tac mt lot cc so.

2 - Lng haTa xc nh mt thang o vi ccgi tr l ly tha ca 2 (2p) vthc hin vic ly tng ng cc so vo gi tr thang o.

3- M ha

Mi mt gi tr sau c mha thnh cc gi tr nh phn v

t vo trong cc tp tin.111110101110110010......


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Dung lng tp tin nhn c ph thuc hon ton vo tn s ly mu f v s lng bitdng m ha gi tr thang o p (chiu di m cho mi gi tr).

2.2 H thng truyn s liu

DTE (Data Terminal Equipment):thit b u cui d liu vi chc nng truyn ccd liu t ngi(ti ngi dng)s dng di dng s hoc tng t

DCE (Data Circuit_Terminal Equipment):thit b chuyn i d liu vi chc nng

chuyn i cc tn hiu t DTE sang dng tng thch vi mi trng truyn.Nhiu:

.

.

.

.

.

, m

.

Trong h thng trn , cc tn hiu tng ng:

S(t) S(t)

M(t)M(t)

G(t) G(t)

Nu cc tn hiu tng ng cng khc xa nhau chng t s nh hng ca nhiu vih thng cng ln.

DTE DCE DCE DTE

Mi trng

S(t)

m(t)

G(t)G(t)

m(t)S(t)

Nhiu


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Vd: H thng internet ADSL s dng trn h thng thoi vn c :

Phn loi h thng truyn s liu:

A- Phn loi theo a l:

1) Mng cc b:

2) Mng din rng:

3) Mng ton cu:

B- Phn loi theo tnh cht s dng

1) Mng truyn s liu k sinh:2) Mng truyn s liu chuyn dng:

C- Phn loi theo hnh trng mng

1) Mng tuyn tnh:

2) Mng hnh sao:

3) Mng vng:

4) Mng hn hp

D- Phn loi theo k thut

1) Mng chuyn mch knh:

2) Mng chuyn mch thng bo:3) Mng chuyn mch gi:

E- Phn loi theo kin trc phn tng mng:

1) Mng OSI

2) Mng ring cng ty

3) Mng theo kin trc TCP/IP

4) .

2.3. Cc h thng truyn s liu thng gp

:

Model Model

Knh thoi


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: .

: )

:.

: .

.2.3.2.

2 bit 0-1)

thp

: .

.

(baud rate).

1 giy.

2.3.3. knh

Ch ny hot ng theo m hnh ca h thng in thoi. c th giao tip vi

my B, my A phi thc hin mt cuc gi (call). Nu my B chp nhn cuc gi, mt knho c thit lp dnh ring cho thng tin trao i gia A v B. Tt c cc ti nguyn ccp cho cuc gi ny nh bng thng ng truyn, kh nng ca cc b hon chuyn thngtin u c dnh ring cho cuc gi, khng chia s cho cc cuc gi khc, mc d c nhngkhong ln thi gian hai bn giao tipim lng. Ti nguyn (bng thng) s c chia thnhnhiu nhng phn bng nhau v s gn cho cc cuc gi. Khi cuc gi s hu mt phnti nguyn no , mc d khng s dng n n cng khng chia s ti nguyn ny cho cccuc gi khc. Vic phnchia bng thng ca knh truyn thnh nhng phn c th cthc hin bng mt trong hai k thut: Phn chia theo tn s (FDM Frequency Division MultiAccess) hay phn chia theo thi gian (TDMA- Time Division Multi Access).

thp /D

thp /A


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2.3.2

Trong phng php ny, thng tin trao i gia hai my tnh (end systems) c phnthnh nhng gi tin (packet) c kch thc ti a xc nh. Gi tin ca nhng ngi dngkhc nhau (v d ca A v B) s chia s nhau bng thng ca knh tr

hut lu v chuyn tip (store and forward), tclu li cc gi tin cha gigichng i.

2.4. Mi trng truyn tin

Trong h thng truyn d liu, mi trng truyn dn l ng truyn vt l gia nigi v ni nhn. Phng tin truyn thng c phn lm hai loi l c dn v khng dn.Trong c loi trn, truyn thng thc cht l truyn sng in t. Vi phng tin truyn cdn, sng in t c truyn dc theo mt phng tin truyn dn nh cp xon i, cp

ng trc hay cp quang. Kh quyn v khng gian xung quanh ta c xem nh l v d vphng tin truyn khng dn, iu c ngha l cc tn hiu in t c truyn i nhngkhng theo mt hng nht nh v n thng c gi l mng khng dy.

Cc c trng v cht lng ca vic truyn d liu c xc nh bng c cht lngca phng tin truyn dn v ca tn hiu truyn dn. i vi mi trng truyn c dn,

phng tin truyn dn l thnh phn quan trng xc nh gii hn truyn dn.

Vi phng tin truyn khng dn, bng thng ca tn hiu dc cung cp bi ng tenquan trng hn mi trng truyn dn. c tnh ca tn hiu c truyn bi ng ten l nhhng hoc a hng. Thng thng th cc tn hiu c tn s thp thng l a hng, iu c ngha l cc tn hiu c pht theo mi hng t ng ten. Vi cc tn hiu c tn scao, cc tn hiu c tp trung truyn theo mt ng thng.

Trong khi thit k mt h thng truyn d liu th vn cn c quan tm l tc truyn d liu v khong cch truyn d liu


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2.4.1 Mt s khi nim

Bng thng:Nu bng thng cng ln th tc truyn d liu t cng mt nguncng cao.

Cc h hi truyn dn:Cc h hi nh l s suy gim, gii hn khong cch, vi mitrng truyn c dy, thng thng th cp xon i c s h hi v tn hiu ln hn cp ngtrc, v cp ng trc li b h hi tn hiu nhiu hn cp quang.

Nhiu giao thoa:S xung t ca cc tn hiu trong cng mt di tn c th lam sailch hoc lm mt cc tn hiu. Nhiu giao thoa l c trng ring ca cc phng tin truynkhng dy, tuy nhin n cng l mt vn i vi phng tin truyn c dy. Vi phngtin truyn c dy, nhiu giao thoa c th gy ra bi cc cp gn nhau.V d cp xon ithng b li vi nhau, v mt ng dn thng cha nhiu cp do s dn n nhiu.

Nhiu giao thoa cng c xut hin trong truyn khng dn. Nu c bc tt th phng tintruyn c dn c th gim ti a vn ny.

S thit cc b nhn:Mt phng tin truyn dn c th c s dng to ra kt niim-im hoc c dng chia s ng truyn vi cc thit b khc. Trong trng hp

phi chia s ng truyn vi cc thit b khc, cc thit b c chia s s gy ra nhiu cng

nh s sai lch cc tn hiu trn ng truyn, v th s dn ti s gii hn khong cch cngnh tc truyn d liu.

2.4.2 Phng tin truyn c dn

Vi phng tin truyn c dn, kh nng truyn c th hiu theo ngha tc d liu

hoc bng thng, ph thuc ch yu vo khong cch v mi trng truyn thng trong kiu kt ni l im - im hay a im, nh trong mng LAN. Bng 2.1 di y cho ta

bit cc c im chung ca phng tin truync dn thng dng vi ng dng truyn im- im ng di.

Cc phng tin truyn c dn thng c s dng l cp xon i, cp ng trc vcp quang.


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2.4.2.1. Cp xon i

Phng tin truyn c dn r nht v c s dng nhiu nht l cp xoni

M t vt l:

Mt cp cp xon i bao gm hai dy bc ng cch in c sp xp theo mt quytc chun. Mi cp dy hot ng nh l mt kt ni truyn thng n. Mt s cp ny c

b li vi nhau thnh mt cp c bc trong mt v bo v. Mt dy cp c th cha hngtrm i dy dn. Vic xon cc dy li lm gim nhiu xuyn m, nhiu giao thoa gia cccp gn nhau trong dy cp. Nhng cp dy gn nhau trong cng mt b c di khcnhau gp phn lm gim nhiu xuyn m, nhiu giao thoa.Trn mt kt ni ng di, di ca cc cp dy thng khc nhau khong t 5 ti 15 cm.Cc dy trong mt cp c ngknh t 0,4 n 0,9 mm.ng dng:

Cp xon i c dng ph bin trong truyn dn c tn hiu s v tn hiu tng t.N thng c s dng trong mng in thoi v l phng tin truyn dn trong victruyn thng ca ni b mt to nh.

Trong mng in thoi, tp hp cc in thoi ca nhng gia nh ring l s c ktni ti mt tng i cc b bi dy cp xon i v c gi l ng thu bao. Trong mt

ta nh, mi in thoi s c kt ni bng cp xon i chy ti tng i con trong phnghoc ti tng i chnh ca ta nh. Cp xon i c thit k h tr truyn ting ni sdng tn hiu tng t. Tuy nhin, vi sh tr ca modem, cp xon i c th iu khintruyn d liu s vi tc va phi.

Cp xon i cng l phng tin thng dng nht trong vic truyn tn hiu s. Tc truyn d liu s ca mng cc b trong mt to nh thng vo khong 64kbps. Chng chc s dng rng ri trong mt to nh cho mng cc b kt ni cc my tnh c nhn.Tc truyn d liu ca mng ny thng l khong 10Mbps.Tuy nhin, mt s mng sdng cp xon i vi tc truyn t 100Mbps ti 1Gbps cng c thit k, mc dchng b hn ch v s lng cc thit b v phm vi ca mng. Vi cc mng xa nhau th tc

truyn d liu trn cp xon i khong 4Mbps.


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Cp xon i r hn nhiu so vi cc thit b truyn dn khc nh cp ng trc, cpquang v chng d s dng hn. Tuy nhin chng li b hn ch hn v tc truyn d liucng nh khong cch ca mng.

Cc c im truyn dn:

Cp xon i c th truyn c tn hiu s v tn hiu tng t. Vi tn hiu tng t, bkhuych i tn hiu truyn c lp t cch nhau khong t5 n 6 km. Vi d liu s(bng c tn hiu s v tn hiu tng t), cc b lp c t cch nhau 2-3 km.

So vi cc loi phng tin truyn dn khc(cp ng trc, cp quang), cp xon i bgii hn bi tc truyn d liu, bng thng v khong cch. Hnh 4.3 cho thy, s suygim tn hiu ca cp xon i l mt hm tng nhanh theo tn s. Cp xon i cng b nhhng mnh bi cc h hi khc. Phng tin ny d bi nhiu giao thoa v nhiu tp bi v nd xy ra hin tng giao thoa gia cc trng in t . V d, mt dy dn chy song songvi mt dng in xoay chiu s tng thm 60Hz nng lng. Nhiu xung cng d nh hng

n cp xon i.Cc dy c bc s lm gim s giao thoa. Cc dy c xon vo nhau lm gimgiao thoa ca sng c tn s thp v vic s dng cc dy c di khc nhau ca cc cplin k lm gim nhiu xuyn m.

Vi tn hiu tng t trong kt ni im im, mt bng thng c th ln ti 1 MHz, nh tr mt s knh. i vi vic truyntn hiu s im im ng di, d liu c th truynvi tc ln ti vi Mbps, vi khong cch ngn, tc truyn d liu c th ln ti 100Mbps thm ch ln ti 1 Gbps.

Cp xon i c v v khng v bc

Cp xon i c 2 loi: c v bc v khng c v bc. Cp xon i khng v bc

(UTP) u tin c s dng lm dy in thoi.y l phng tin truyn dn r tin nht thng c s dng trong cc mng LAN.

N rt d lp t v s dng.

Cp xon i khng v bc ch yu b nh hng bi nhiu giao thoa sng in t, baogm giao thoa t cc cp xon i gn nhau v t nhiu ca mi trng bn ngoi. Mt cch ci thin cc c trng ca cp xon i l ta bc si cp bng cc v bc li kim loinhm lm gim s giao thoa. Cp xon i c v bc cho php truyn d liu vi hiu sut tthn tc cao hn. Tuy nhin, n li t hn v kh lp t hn so vi cp khng bc.

Cp UTP loi 3 v loi 5

Hu ht cc vn phng u c lp t sn loi cp xon i 100 ohm thng c gi

l cp inthoi. V cp xon i in thoi thng c lp t sn, n cng thng c sdng cho cc ng dng LAN. Tuy nhin tc d liu v khong cch gia cc thit b cacp xon i in thoi l kh gii hn.


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Chun EIA-568-A phn bit ba loi cp UTP:

Loi 3: Cp UTP kt hp vi cc phn cng kt ni c cc c tnh truyn dn lnn 16 MHz.



Cp loi 3 v cp loi 5 c s dng ch yu trong cc ng dng LAN. Loi 3 s dngch yu cho cc ng in thoi trong cc vn phng. Loi 5 thng c s dng truynd liu v ang tr nn thng dng v c ci t sn trong cc cao c. im khc nhauchnh gia cp loi 3 v loi 5 l s vng xon trn mi n v khong cch. Loi 5 xon chthn vi bc xon thng thng khong 0.6 n 0.85 cm trong khi loi 3 l 7.5 n 10 cm.Loi 5 xon cht hn nn t hn v cung cp hiu sut cao hn loi 3.

Tham s u tin c s dng so snh s suy gim. Cng ca tn hiu suy gimtheo khong cch trn mi phng tin truyn dn. Trn cc phng tin c dn, s suy gim

thng theo hm logarit v thng c din t nh mt hng s theo decibel trn mi n vkhong cch.

Nhiu xuyn m gn cc thit b u cui trong cc h thng cp xon i l s kthp cc tn hiu t mt cp dy sang mt cp khc ti cc cht kim loi. S kt hp din rakhi tn hiu truyn xm nhp vo cht ni ca ng thu tn hiu nhn ti cng mt u cang truyn. (v d tn hiu c truyn b thu bi mt cp dy nhn gn ).

Cp xon i c

v bc chng nhiuCp xon i khng c

v bc chng nhiuCp xon i UTP v STP s

dng u ni RJ-11. RJ 45

2.4.2.2 Cp ng trc

M t vt l:

Cp ng trc, ging nh cp xon i bao gm hai ng dn in, nhng n c cutrc khc cho php n hot ng trong min tn s rng hn. N bao gm vng rng hnh tr

dn in bn ngoi bc ly mt dy kim loi dn in n bn trong. Dy kim loi bn trongc gi bi mt lot cc vng cch in xp cch u nhau hoc c bc bi mt cht inmi. Vng dn in bn ngoi c bc bi mt v bc. cp ng trc n c ng knh


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vo khong 1 n 2.5 cm. Do c bc kn, c cu trc ng tm, cp ngtrc chu nhiu vxuyn m tt hn cp xon i.ng dng:

Cp ng trc c l l phng tin truyn thng a nng nht v c s dng rng ritrong nhiu ng dng khc nhau. Cc ng dng quan trng nht l:

Phn phi tn hiu truyn hnh

Truyn tn hiu in thoi ng di

Kt ni cc h thng my tnh khong cch gn

Mng ni b

Cp ng trc nhanh chng c s dng rng ri phn phi tn hiu truyn hnh titng nh truyn hnh cp. Truyn hnh cp tr nn thng dng nh in thoi, s kn hln n hng trm v khong cch ln n vi chc kilomet. Trc y, cp ng trc c v trquan trng trong cc mng in thoi ng di. Ngy nay, n ang phi i mt vi s cnhtranh ngy cng tng ca cp quang, sng viba mt t v v tinh. Bng cch s dng vic

phn chia nhiu thnh phn tn s, cp ng trc c th mang ti 10000 knh ting ni cng

mt lc.Cp ng trc cng c s dng nhiu trong cc kt ni khong cch ngn gia ccthit b. Bng cch s dng tn hiu s, cp ng trcc th c s dng cung cp ccknh vo ra tc cao trn cc h thng my tnh.

Cc c tnh truyn dn:

Cp ng trc c s dng truyn c tn hiu tng t v tn hiu s. Cp ng trcc cc c tnh tn s cao hn so vi cp xon i v v vy c th s dng hiu qu vi cctn s v tc d liu cao hn. Do c v bc v cu trc ng tm, cp ng trc t chu nhhng bi nhiu v xuyn m hn cp xon i. Yu t nh hng ch yu n hiu sut ls suy gim, nhiu nhit v nhiu iu bin. Nhiu iu bin ch xut hin khi c mt viknh hoc di tn s c dng chung trn mt ng cp.

Vi cc ng truyn tn hiu tng t khong cch di, vic khuch i sau mt vikm l rt cn thit, tn s cng cao th khong cch cn khuch i tn hiu cng ngn. Ph cth s dng cho tn hiu tng t c th m rng n khong 500 MHz. i vi tn hiu s,cn s dng cc b lp sau 1km v nu tc d liu cao hn th khong cch cn lp licng gn hn.


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2.4.2.3. Cp quang

M t vt l:

Cp quang l mt phng tin mm do, ng knh nh c kh nng truyn tia sng.Cc cht liu thy tinh hoc cht do c th c s dng lm nn cp quang. Cp quangc ch to bi silic yoxit nng chy tinh khit c kh nng truyn tt nht nhng rt khch to. Cp quang ch to bng si thy tinh nhiu thnh phn khng tt bng nhng kinh thn v vn cho kt qu chp nhn c. Si cht do c gi r nht v c th s dng cho ccng truyn ngn v chp nhn mt mt cao.

Cp si quang c dng hnh tr v bao gm ba thnh phn ng tm: li, lp sn ph vv bc. Li l thnh phn trong cng v bao gm mt hoc nhiu si rt mnh lm bng thytinh hoc nha. Li c ng knh khong 8 n 100 m . Mi si c bc mt loi v c

bit lm bng thy tinh hoc cht do c c tnh quang hc khc vi li. B mt gia li vlp v bc c bit c tc dng to s khc x nh sng ton phn trong li. Lp ngoi cng

bc ly mt hoc mt vi si cp ph sn l v bc. V bc oc lm bng cht liu nhatng hp v cc cht liu khc nhm bo v li chng li hi m, s n mn, va p v ccnguy hi t mi trng bn ngoi.

ng dng:Mt trong cc cng nghc ngha nht trong truyn d liu l s pht trin ca cc

h thng truyn thng bng cp quang. Cp quang cn c s dng trong truyn thngng di v cc ng dng ca n trong lnh vc qun sang pht trin mnh. S ci thinlin tc trong hiu sut v gi thnh ngy cng gim cng vi cc u im vn c ca cpquang khin n c dng ngy cng nhiu kt ni mng ni b. Cc c tnh sau cacp quang phn bit n vi cp xon i v cp ng trc:

Dung lng ln hn: Tim nng vbng thng ca cp quang rt ln, v vy tc truyn d liu ca cp quang rt cao, ln ti hng trm Gbps trn qung nghng chc km. Ta c th so snh vi tc thc t cc i hng trm Mbps trn

qung ng 1 km ca cp ng trc v ch vi Mbps trn 1 km hay t 100Mbpsn 1 Gbps trn vi chc mt ca cp xon i.

Kch thc nhhn v nhhn: Mt si cp quang nhhn mt dy cp ngtrc v mt b cp xon i. chy trong cc ta nh hay di lng t, u imvkch thc rt c li v kch thc nhhn cng gim cc yu cu v cu trccng trnh.

t suy gim hn: S suy gim trong cp quang nhhn nhiu so vi cp ng trcv cp xon i, v l mt hng s trn mt min rng.

Khng bnh hng bi in t: Cc h thng cp quang khng bnh hng bicc trng in t bn ngoi. V vy h thng khng bnh hng bi s nhiu

giao thoa, nhiu xung v nhiu xuyn m. Si quang khng pht ra nng lng do t nh hng n cc thit b khc v c mc bo mt cao hn, trnh b nghetrm v kh b r r.

Khong cch cn lp tn hiu ln hn: S b lp cn s dng t hn lm gim githnh v t cc ngun gy li. Hiu sut ca cc h thng cp quang theo quanim ny c s pht trin vng chc. Khong cch thng thng gia cc b lpvo khong 10 km v c cc ghi nhn khong cch ln ti hng trm km. Cch thng cp ng trc v cp xon i thng phi dng b lp sau khong vikm.

C nm loi ng dng chnh ca cp quang tr nn quan trng:

Cc cp trc ng diCc cp trc trong thnh ph

Cc cp trc gia cc vng


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ng ni gia khch hng v tng i

Cc mng ni b

Vic s dng cp quang trong truyn tn hiu ng di ngy cng tr nn thng dngtrong cc mng in thoi. Cc qung ng ln n 1500 km v dung lng rt cao (thngthng khong 20000 n 60000 knh ting ni). Cc h thng ny ang cnh tranh v mtkinh t vi sng viba v c gi thp hn nhiu so vi cp ng trc. Cc ng cp quangchy di bin cng ang c s dng nhiu hn.

Cc ng trc trong thnh ph c di trung bnh khong 12 km v c th c khong100000 knh ting ni trong mi nhm trc. Cc ng trc ny c lp t trong ccng ng chn di t v khng c cc b lp tn hiu, c ni vi cc tng i inthoi.

Cc ng trc gia cc vng c di khong 40 n160 km kt ni cc thnh ph vcc vng qu hay l gia cc tng i in thoi ca cc cng ty khc nhau. Hu ht cc hthng ny c t hn 5000 knh ting ni. Cc k thut c s dng trong cc ng dng nyang cnh tranh vi cc k thut s dng sng vi ba

Cc ng ni gia khch hng v tng i l cc ng cp chy trc tip t tng itrung tm ti khch hng. Cc ng cp ny ang dn thay th cp xon i v cp ngtrc tr thnh cc mng c y dch v khng ch x l ting ni v d liu m cn chnh nh v video. Ban u ng dng ny ca cp quang l cho cc khch hng thng mi,nhng vic truyn dn n tng gia nh s sm xut hin.

ng dng quan trng cui cng ca cp quang l cho mng ni b. Cc chun angc pht trin v cc sn phm cho mng cp quang d c dung lng t 100 Mbps n 1Gbps v c th h tr hng trm, thm ch hng nghn trm trong mt to nh ln hoc mtkhu nhiu ta cao c.Cc c tnh truyn dn:

Cp quang truyn tn hiu c m ha thnh cc chm tia sng phn x ton phn

bn trong. iu ny c th xay ra trong bt cmi trng truyn dn no c ch s khc xcao hn mi trng bn ngoi. Trong thc t, cp quang hot ng nh mt sng truyn chng vi tn s trong khong t 1014n 1015 hertz, bao gm c nh sng hng ngoi v nhsng nhn thy c.


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Tia sng t mt ngun sng i vo trong li hnh tr bng thy tinh hoc cht do. Cctia c gc rng b phn x v truyn dc theo si cp, cc tia khc b hp thu bi cht bao bc.Hnh thc truyn ny gi l truyn a cch, nhy bc, theo ngha c nhiu gc khc nhau s

phn x.Khi truyn dn a cch, tn ti nhiu ng truyn khc nhau, mi ng truyn s c

di khc nhau dn ti thi gian truyn ca mi ng cng khc nhau. iu ny khin cc

thnh phn tn hiu (xung nh sng) tri ra theo thi gian v v vy gii hn tc truyn md liu c th nhn mt cch chnh xc. Hay ni cch khc yu cu khong cch gia ccxung gii hn tc d liu. Loi cp ny ph hp cho vic truyn khong cch rt ngn.Khi bn knh ca li cp gim i, s gc phn x cng t i. Bng cch gim bn knh ca litheo yu cu ca bc sng.Vic truyn theo kiu n cch (single-mode) cung cp hiu sutcao hn v cc l do sau. Vch c mt ng truyn nn cc sai lch nh khi truyn theokiu a phng thc khng th din ra. Kiu n cch thng c s dng cho cc ngdng ng di bao gm in thoi v truyn hnh cp. Cui cng, do cc ch s khc x cali khc nhau nn ta c th c kiu truyn th ba l a cch bin i dn. y l kiu trunggian gia hai kiu trn v mt c tnh. Ch s khc x cao hn ti trung tm khin tia sngcng gn trc th cng chm hn cc tia gn lp v. Tia sng trong li i theo ng con gxon c v ch s khc x c phn loi v gim khong cch phi truyn ca n. Khongcch c thu ngn v tc cao hn cho php tia sng pha ngoi bin ti thit b nhngn nh cng thi im vi cc tia truyn thng li. Cc cp c kiu a cch bin i dnthng c s dng trong cc mng ni b.

C hai loi ngun sng khc nhau c s dng trong cc h thng cp quang: dioedpht quang (LED) v diode bc x laser (ILD). C hai u l cc thit b bn dn pht ra ccchm sng ti mt hiu in th no . n LED r hn hot ng trong min nhit rnghn v c thi gian s dng lu hn. Trong khi ILD hot ng theo nguyn l laser hiuqu hn v c tc truyn d liu ln hn.

C mt mi lin h gia bc sng s dng, kiu truyn v tc d liu nhn c.

C hai kiu truyn n cch v a cch u h tr mt vi bc sng nh sng v c th sdng c ngun nh sng laser hay n LED. Trong cp quang, nh sng c truyn tt nhttrong ba ca s bc sng khc nhau, 850, 1300 v 1550 nanometer (nm). Tt c nhng

bc sng ny u nm trong vng hng ngoi ca ph tn s, nm pha di vng nh sngnhn thy c (t 400 n 700 nm). S mt mt s gim i khi bc sng tng ln v cho

php tc d liu cao hn trn cc khong cch di. Hu ht cc ng dng cc b hin nayu s dng ngun sng n LED. Mc d vic s dng n LED khng t nhng n giihn tc d liu di 100 Mbps v khong cch l vi km. c th c tc d liu caohn v khong cch xa hn phi s dng n LED pht nh sng c bc sng 100 nm hocngun sng laser. c tc d liu cao nht v khong cch truyn xa nht ta phi dngngun sng laser c bc sng 1500 nm

Dn thnh phn bc sng (Wavelength-Di vision Mul tiplexing):

Tim nngca cp quang s c s dng ton b khi nhiu chm sng vi cc tn skhc nhau c truyn trn cng mt si cp. y l cch truyn dn thnh phn tn s(FDM) nhng thng c gi l dn thnh phn bc sng (WDM). nh sng truyn trongsi cp baogm nhiu mu hay nhiu bc sng, mi bc sng mang cc knh d liu khcnhay. Nm 1997 phng th nghim Bell chng minh mt h thng WDM vi 100 chmsng s hot ng 10 Gbps vi tc d liu khong 1 t t bit mi giy. Hin nay cc hthng thng mi vi 80 knh v tc 10 Gbps i vo hot ng.

2.4.3. Truyn khng dyi vi cc phng tin truyn khng dy, vic truyn v nhn c thc hin bi mt

ng ten. Khi truyn i, ng tenpht ra nng lng sng in t vo trong mi trng (thngl khng kh) v khi thu, ng tenthu sng t mi trng xung quanh. C hai loi hnh c bntrong h thng truyn dn khng dy: truyn dn c nh hng v truyn theo mi hng.


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Vi loi truyn c nh hng, ng tens pht ra mt chm in t hi t, v th ng ten phtv ng tennhn phi c chnh sao cho hng thng vo nhau. Khi truyn theo mi hng,tn hiu truyn pht ra theo mi hng v c th thu bi nhiu ng ten. Nhn chung, tn s catn hiu cng ln th kh nng tp trung chng vo mt tia c nh hng cng cao.

C 3 loi tn s chnh c quan tm. Tn s trong khong 2GHz n 40GHz c gil sng viba. tn s ny, c th to ra tia c nh hng tt v sng viba ph hp vi vic

truyn im - im. Sng viba cng c s dng trong truyn thng v tinh. Tn s trongkhong 30MHz n 1GHz ph hp vi truyn thng theo mi hng. Ta c th thy tn sny ging nh tn s ca i pht thanh. Bng 2.3 tm tt cc c tnh ca truyn dn khngdy ti nhiu di tn. Sngviba l 1 phn ca di UHF v ton b di SHF, sng pht thanhgm di tn VHF v mt phn ca di UHF. Mt loi tn s quan trng khc, dnh cho ccng dng cc b , l tia hng ngoi ca quang ph. Loi ny bao gm cc tn s xp x t3.1011ti 2.1014. Tia hng ngoi c s dng trong vic truyn thng im im v a imtrong mt phm vi hp nh mt phng n.

2.4.3.1 Sng viba mt t

M t vt l:

Hu ht nhng loi ng ten pht sng viba l parabol (hay ng tencho). Cc ng tennay thng c ng knh khong 3m. ng tenc lp c nh v tp trung cc tia li trongkhong hp truyn chng ti ng tennhn. ng tenpht sng viba thng t ti im caotrn mt t c th m rng khong cch gia cc ng tenv c th truyn qua nhng vtcn gia. Nu nh khng c chng ngai vt no th khong cch ln nht gia hai ng ten:

d=7.14. hK.

Trong d: khong cch gia hai ng tentnh bng km, h: cao ca ng tentnh bngm, K: H s iu chnh tnh ton, trong thc t sng viba b un cong hoc b khc x dotri t cong v v th vic truyn i c xa hn vic truyn cc tia thng. Theo kinh nghimth K nn bng 4/3.

V d hai ng tensng viba cao 100m c th truyn i 13314,7 =82 km

truyn c vi khong cch xa, cn s dng mt lot cc trm chuyn tip v cckt ni im im l mt chui cc trm lin tip c th vt qua c gii hn khongcch..

ng dng:

Cc h thng s dng sng viba mt t u tin l cc dch v vin thng ng dibn cnh vic s dng cc cp ng trc hay cp quang. Sng viba yu cu cc b khuych


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i v b lp c t gn nhau hn cp ng trc vi cng mt ng truyn v i hi nmtrong tm nhn. Sng viba s dng ph bin trong pht thanh v truyn hnh.

Mt ng dng ph bin khc ca sng viba l kt ni im im vi khong cch ngngia cc to nh. N cn c s dng trong cc mch nh ca ti vi hoc trong vic trao id liu ca mt mng cc b. Sng viba khong cch ngn cng c th c s dng chonhng ng dng ng vng.Mt doanh nghip cng c th s dng sng viba trong vic kt

ni vi tng i xa trong cng thnh ph t tng i cc b ca cng ty.c tnh truyn dn:

Truyn dn sng viba bao gm mt phn nh ca ph in t. Tn s ph bin c sdng truyn l t 2GHz n 40GHz. Tn s cng cao th bng thng ca v tc truyncng cao.Nh vy vi bt k h thng truyn thng no, nguyn nhnchnh ca s mt mt ls suy yu cc tn hiu. Vi sng viba (v c cc tn s radio) s suy yu c tnh theo cngthc sau:

dBd

L

24

log10

trong : d: khong cch truyn: di bc sng cc di trong cng mt n v

Do s suy yu gim theo bnh phng khong cch. V th, b lp khuych i cth lm cho h thng sng viba pht xa hn t 10 n 100 km. S suy yu c th tng ln doma, s nh hng ca lng ma c bit ng lu .

2.4.3.2.Sng vi ba v tinhCc c trng vt l:

Trong thc t, v tinh truyn thng l mt trm chuyn tip sng vi ba. N c sdng kt ni hai hay nhiu hn cc trm pht v thu sng mt t. V tinh thu sng trnmt bng tn (uplink), khuch i hoc lp li tn hiu, sau truyn chng trn mt tn skhc (downlink). Mt v tinh trn quo siu khin mt s loi di tn v c gi l btip v tch sng.

Trong hnh th nht, vtinh ang c s dng cho mt kt ni im im gia haing ten mt t. Trong hnh th hai, v tinh h trtruyn thng tin t mt trm pht trn mtt ti nhiu tram nhn.


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vic truyn thng c hiu qu th v tinh phi gi c v tr tnh so vi mt t. Tuynhin s di chuyn ca v tinh s khin n khng nm trong tm nhn ca cc trm trn mtt ti mi thi im. gi c v tr tnh so vi mt t th v tinh phi quay cng qyo vi tri t v cn gi cao khong 35.784 km so vi mt t.

Hai v tinh s dng cng mt di tn s, nu qu gn nhau th s gy ra nhiu. trnh s nh hng ln nhau, cc chun hin nay yu cu khong cch l 40(gc gia hai v

tinh c o t mt t) i vi di tn 4/6 GHz v khong cch l 3 0i vi di tn 12/14GHz. V th, s v tinh l c gii hn.

ng dng:

V tinh truyn thng l mt cuc cch mng cng ngh c tm quan trng nh cpquang. Mt s ng dng quan trng ca v tinh:

Truyn hnh

in thoi ng di

Mng thng mi ring

Do tnh cht truyn qung b t nhin ca n, v tinh rt ph hp cho truyn hnh nn

n ang c s dng rng ri M v nhiu ni trn th gii.Theo cch truyn thng,chng trnh c pht t mt im trung tm sau s c truyn ti v tinh v s cpht qung b ti cc trm nhn. Cc trm ny li phn phi chng trnh n tng ngidng ring l. Mt mng cung cp dch v qung b cng cng (PBS) phn phi cc chngtrnh truyn hnh hu nh l thng qua cc knh v tinh. Cc mng thng mi khc cng mt

phn s dng v tinh, cc h thng truyn hnh cp hin nay ang cn i vic tng ccchng trnh nhn t v tinh. ng dng mi nht ca cng ngh v tinh trong truyn hnh lv tinh qung b trc tip, tn hiu video t v tinh s c truyn trc tip n nh ca ngis dng. Vic gim gi thnh v kchthc ca anten khin iu ny tr nn kh thi vmt kinh t, hin nay mt s knh i vo hot ng v mt s khc c ln k hoch

Vic truyn v tinh cn c s dng kt ni im im cc ng trc gia cc

tng i in thoi ca mng in thoi cng cng. y l phng tin truyn ti u cho ccng trc quc t c mc s dng cao v ang cnh tranh vi cc h thng mt t trongvic kt ni quc t ng di.

Ngoi ra v tinh cn mt s ng dng trong truyn d liu thng mi. V tinh c thchia tng dung lng ra thnh thnh mt s knh v cho nhng khch hng thng mi ringl thu cc knh ny. Mi khch hng c trang b mt angten ti mt s v tr v c th sdng cc knh ca v tinh cho mng ring ca mnh. Cc ng dng ny kh t v ch giihn trong cc t chc ln c yu cu cao. Pht trin gn y v cc h thng u cui m rtnh (VSAT) cung cp mt s la chn gi thnh thp. Hnh 2.6 m t mt h thng VSATthng thng. Mt s trm khch hng c trangb cc angten VSAT gi thnh thp. Theo

mt s quy tc, nhng trm ny chia s mt dung lng truyn v tinh truyn ti mt trmtrung tm. Trm trung tm c th trao i hay tip nhn thng bo gia cc khch hng.Cc c tnh truyn dn:

Khong tn s ti u cho truyn v tinh l trong khong 1 n 10 GHz. Tn s di 1GHz s b nh hng bi nhiu t cc ngun t nhin nh t ngn h, mt tri v kh quynv c cc nh hng gy ra bi con ngi do cc loi thit b in khc nhau. Nu tn s trn 10 GHz, tn hiu s b nh hng d di bi sc ht v ma ca kh quyn.

Hu ht cc v tinh cung cp cc dch v truyn im im ngy nay u s dng bngtn c rng trong khong t 5.925 n 6.425 GHz truyn t mt t ln v tinh (uplink)vbng thng trong khong 2.7 n 4.2 GHz truyn t v tinh v mt t (downlink). S

kt hp ny c gi l di tn 4/6 GHz. Ch rng tn s uplink v downlink l khc nhau. hot ng lin tc m khng xy ra xung t, v tinh khng th nhn v truyn trn cngmt tn s. V vy tn hiu nhn t trm mt t trn mt tn s c truyn li trn mt tns khc.


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Di tn 4/6 GHz nm trong vng ti u t 1 n 10 GHz nhng b s dng bo ha.Cc tn s khc trong vng ny li khng th s dng do cc ngun xung t vi cc tn s

ny thng l cc sng vi ba trn mt t. V vy, di tn 12/14 GHz c pht trin (uplink:t 14 n 14.5 GHz; downlink: t 11.7 n 14.2 GHz). Trong di tn s ny, c th b quavn nhiu. Tuy nhin, ta c th s dng cc trm thu mt t nh hn v r hn. C ththy rng di tn trn s b bo ha do phi ln k hoch cho vic s dng di tn 19/29GHz. Khi s dng di tn ny, s suy gim s ln hn nhng li cho php bng thng rnghn v cc thit b thu nh v r hn.

Ta cn cp n mt s tnh cht ca truyn thng v tinh. Th nht, do khong cchln, tr do truyn vo khong mt phn t giy gia hai trm mt t. tr ny c thnhn thy khi ni chuyn in thoi. Ta cng phi quan tm n iu khin li v iu khinlu lng. Th hai, sng ngn v tinh rt hu hiu truyn qung b. Nhiu trm c thtruyn tn hiu n v tinh v tn hiu t mt v tinh c th c nhn bi nhiu trm.

2.4.3.3. Sng v tuyn qung bM t vt l:

S khc nhau c bn gia sng v tuyn qung b v sng ngn l sng v tuyn qungb s truyn theo mi hng cn truyn sng ngn th c nh hng. V vy sng v tuynqung b khng yu cu phi s dng anten cho v anten cng khng cn phi quay theomt hng chnh xc.Ccng dng:

Sng v tuyn l thut ng chung c s dng, bao gm cc tn s trong khong t 3kHz n 300 GHz. Thut ng sng v tuyn qung b c s dng bao gm c bng tnVHF v mt phn ca UHF: 30 MHz n 1 GHz. Min tn s ny bao gm c bng tn FMca radio v bng tn UHF v VHF ca tivi. Min tn s ny cng c s dng cho mt ving dng mng truyn d liu.Cc c tnh truyn dn:

Min tn s trong khong t 30 MHz n 1 GHz ph hp cho vic sng v tuyn qungb. Khng ging nh trng hp ca cc sng in t tn s thp, tng in ly khng phn xcc sng v tuyn c tn s trn 30 MHz. V vy vic truyn b gii hn trong phm vi tmnhn v cc cc my pht s khng b cn tr bi cc my pht khc do s phn x t tng khquyn nh khi truyn sng ngn. Khng ging nh cc tn s cao ca sng ngn, sng truynqung b t b hng do nhiu t cc cn ma hn.

Truyn sng v tuyn tun theo cng thc (2.1), tc l khong cch cc i gia mypht v my thu ln hn khng ng k so vi kh nng nhn ca mt ngi. Nh i visng ngn, suy gim theo khong cch tun theo cng thc (2.2). Bc sng cng di thsng v tuyn cng t chu nh hng ca s suy gim.


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Nguyn nhn chnh gy h hi cho sng v tuyn qung b l s giao thoa ca nhiu tnhiu. S phn x t mt t, nc, t t nhin hoc t cc i tng do con ngi to ra cth gy nn nhiu loi tn hiu gia cc anten. Mt v d l TV s thu v pht nhiu hnh nhkhc nhau lc c my bay bay qua.2.4.3.4 Tia hng ngoi

Truyn thng bng tia hng ngoi s dng cc my thu pht c th iu chnh cc nh

sng hng ngoi. Hai my thu pht phi nm trong tm nhn ca nhau trc tip hoc thngqua phn x t cc b mt c mu sng nh trn nh.

S khc nhau quan trng gia truyn sng hng ngoi v sng ngn l truyn sng hngngoi khng th xuyn qua tng. V vy ta khng cn quan tm n vn bo mt v nhiunh trong cc h thng truyn sng ngn. Hn na, khng c mt yu cu no trong vic sdng di tn s khi truyn sng hng ngoi.

2.5. Cc chun giao tip truyn thng

2.5.1. Cc chun chungHu ht cc thit b x l tn hiu c kh nng truyn nhn tn hiu hn ch, thng

thng cc thit b ny c gn trc tip vi cc thit b chuyn nhn tn hiu hoc quamng, chng c gi l cc thit b truyn nhn d liu u cui (DTE, DCE).

Mi thit b x l tn hiu (trm) thng c kt hp vi mt cp gm mt DTE vmt DCE.

Hai trm truyn tn hiu cho nhau qua hai DCE ca mi bn c kt ni vi nhau.

Hai DCE trao i tn hiu vi nhau trn mng hoc ng truyn phi tng t nhau,ngha l b phn nhn tn hiu bn ny phi tng ng vi b phn pht tn hiu ca bn kia.

DTE v DCE truyn nhn tn hiu vi nhau do cng phi tng thch vi nhau v dliu v thng tin iu khin (cc chun)

Cc chun v giao din ga DTE vDCE bao gm:

Chun v cu trc: xc nh kt ni vt l gia DTE v DCE (tn hiu v mch iukhin thng qua cp ni v gic cm)

Chun v tn hiu: xc nh mc hiu in th, thi gian bin i tn hiuChun v chc nng

).

Chun v th tc: xc nh th t thao tc trong truyn d liu da trn chun chcnng ca cc ng tn hiu.

Chun EIA-RS 232 (Electronic I ndustry AssociationRecomand Standard): chun giaotip truyn thng cng nghip

EIA cng b tiu chun RS-232C vi n lc nhm to ra khnng ghp ni ccthit b do nhiu nh sn xut lm ra m khng i hi c mt tiu chun k thut c bit chotng trng hp.

tng xy dng tiu chun RS-232 l phi s dng cng loi ni dy, th d loiu ni 25 chn hoc 9 chn, c ni theo cng mt cch v s dng cng mc in p khi

biu din cc s nh phn 1 v 0 tng ng. Vi tng ny, nu nh mi ngi u tham


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gia vo tiu chun theo cng mt cch th c th ni cc thit b vi cng RS-232 ca cchng khc nhau, cc mu m khc nhau m khng cn c thm iu kin no. Cc mdem,cc my in v nhiu thit b khc c th c ni vo giao din RS-232.

Ngy nay, hu ht cc my tnh u trang b mt hoc hai cngni tip RS-232, v ttc u c kh nng s dng RS-232, t nht l nh mt kh nng tu chn t nh sn xutmy tnh hoc t pha ngi s dng my tnh.

Cc mch in tch hp c b pht v b nhn RS-232C c cc nh sn xut khcnhau thit k v ch to, th d Motorola, National, Semiconductors. Cc chip b pht/ bm RS-232 tip nhn mc in p TTL li vo v bin i chng thnh cc mc dnhring cho RS-232C truyn. Cc b nhn RS-232 lm vic theo cch ngc li: tip nhntn hiu li vo theo chun RS-232 v bin i cc tn hiu sang cc mc TTL tng ng. Cc

b phn ny u nm trn bn mch chnh hoc trn mt Card vo/ ra, ngha l pha sau cacng RS-232.Tn hiu truyn theo chun RS-232 ca EIA

Chun RS-232 quy nh mc logic 1 ng vi in p t -3V n -25V (mark), mclogic 0 ng vi in p t 3V n 25V (space) v c kh nng cung cp dng t 10 mA n

20 mA.Ngoi ra, tt c cc ng ra u c c tnh chng chp mch.

Chun RS-232 cho php truyn tn hiu vi tc n 20.000 bps nhng nu cp truyn ngn c th ln n 115.200 bps.Cc phng thc ni gia DTE vDCE:

n cng (simplex connection): d liu chc truyn theo 1 hng.

Bn song cng (half-duplex): d liu truyn theo 2 hng, nhng mi thi im chc truyn theo 1 hng.

Song cng (full-duplex): s liu c truyn ng thi theo 2 hng.

Hnh 2.26: nh dng khung truyn dliu theo chun RS 232

Khi khng truyn d liu, ng truyn s trng thi mark (in p -10V). Khi btu truyn, DTE s a ra xung Start (space: 10V) v sau ln lt truyn t D0 n D7 vParity, cui cng l xung Stop (mark: -10V) khi phc trng thi ng truyn. Dng tnhiu truyn m t nh sau (truyn k t A):


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Cc c tnh kthut ca chun RS-232 nh sau:

Tc d liu cc i : 20 Kbpsin p ng ra cc i : 25Vin p ng ra c ti : 5V n 15VTrkhng ti : 3K n 7K in p ng vo : 15V nhy ng vo : 3VTrkhng ng vo : 3K n 7KMc logic 1 (mc du) nm trong khong: -3 V n12 V; trong khong t5 Vn12 V l tin cy, mc logic 0 (mc trng) nm trong khong: +3 V n +12 V,khong t+ 5 V n +12 V l tin cy.Tr khng ti v pha b phn ca mch phi ln hn 3.000 nhng khng cvt qu 7.000 .Cc li vo ca b nhn phi c in dung phi nhhn 2.500 pF. di ca cp ni gia my tnh v thit b ghp ni qua cng ni tip khng thvtqu 15m nu khng s dng mdem.

Cc gi tr tc truyn d liu chun l 50, 75, 110, 150, 300, 600, 1200, 2400,4800, 9.600, 19.200, 28.800,, 56.600 baud. Cc tc truyn d liu thng dngtrong cng ni tip l: 1200 bps, 4800 bps, 9600 bps v 19200 bps.

Nh vic quy nh thng nht s dng mt u ni 25 chn v v sau b sung thmu ni 9 chn cho cng ni tip RS-232, c th hn l cm v pha dy cp cn cm v

pha my tnh, m tt c cc sn phm u tng thch vi nhau. Quy nh ny cng p dng

thng nht cho cc thit b ghp ni vi cng RS-232. Hnh trn ch ra cch sp xp chn cau ni 25 chn v 9 chn dng cho RS-232C, cn vic nh ngha chc nng ca cc chnc lit k bng k tip. Tiu chun RS-232C quy nh r vic s dng u ni thng nht tt c cc sn phm u tng thch vi nhau. V vy th t v chc nng ca cc chn c quy nh rt c th v phi tun th mt cch nghim ngt. d dng nhn ra th tcc chn, bn cnh cc chn u c in r s th t trn phn nha ca phch cm cng nh cm. Nhn xt ny cn c lu khi kim tra cp ni hoc t hn mt cp mi.

Cc chn v chc nng trn u ni 25 chn v 9 chn.

25

chn

9

chn

Tn Vittt

Chc nngCh : =>: Li vo


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25

chn

9

chn

Tn Vittt

Chc nngCh : =>: Li vo

Tnh hot ng ging vi CTS nhng c kchhot bi DTE khi n sn sng nhn d liu.

7 5 Signal Ground

(t ca tn hiu)SG Tt c cc tn hiu c so snh vi t tn hiu

(GND).

8 1 Data Carrier Detect DCD=>

Pht hin tn hiu mang d liu.

20 4 Data Terminal

Ready (u cui dliu sn sng)

DTR

Ch cho thy l DCE ang nhn tn hiu rungchung.

Truyn thng gia hai nt:

Cc s khi kt ni dng cng ni tip:

Khi thc hin kt ni nh trn, qu trnh truyn phi bo m tc u pht v thuging nhau. Khi c d liu n DTE, d liu ny s c a vo b m v to ngt. Ngoi

ra, khi thc hin kt ni gia hai DTE, ta cn dng s sau:


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Khi DTE1 cn truyn d liu th cho DTR tch cc => tc ng ln DSR ca DTE2 chobit sn sng nhn d liu v cho bit nhn c sng mang ca MODEM (o). Sau ,DTE1 tch cc chn RTS tc ng n chn CTS ca DTE2 cho bit DTE1 c th nhn dliu.

Khi thchin kt ni gia DTE v DCE, do tc truyn khc nhau nn phi thchin iu khin lu lng. Qu trinh iu khin ny c th thc hin bng phn mm hay

phn cng. Qu trnh iu khin bng phn mm thc hin bng hai k t Xon v Xoff. K tXon c DCE gii khi rnh (c th nhn d liu). Nu DCE bn th s gik t Xoff. Qutrnh iu khin bng phn cng dng hai chn RTS v CTS. Nu DTE mun truyn d liuth s giRTS yu cu truyn, DCE nu c kh nng nhn d liu (ang rnh) th gi li C

2.5.2.

thc hin cc phng php truyn mt cch c th, cc nh ch to cung cp mtlot cc IC chuyn dng, cc IC ny chnh l phn cng thuc lp vt l trong mt h thngthng tin,chng hot ng theo nguyn tc ca k thut s v v vy ch truyn ng bhay bt ng b ph thuc vo vic s dung ng h chung hay ring khi truyn tn hiu s ixa.

Cc IC u l cc vi mch c th lp trnh. u tin lp trnh ch hot ng mongmun bng cch ghi mt byte c ngha vo thanh ghi ch mode register. Sau ghi tip

byte iu khin vo thanh ghi lnh command register vi mch theo m hot ng. Vcc giao tip truyn ni tip c dng kh rng ri trong cc thit b in t hin i, cc vimch ngoi vi LSI c bit c pht trin cho php thc hin cc loi giao tip ny. Tntng qut ca hu ht cc IC ny l:

UART (Universal Asynchronous Receiver Transmitter)USRT (Universal Synchronous Receiver Transmitter): mch ng bthin hngk t.USART c th hot ng theo UART hay USART tu chn.

BOPs (Bit-Oriented Protocol Circuits) mch ng bthin hng bit.UCCs (Universal Communication Control circuits) c th lp trnh cho c 3 loitrn.

C UART v USART u c kh nng thc hin nhu cu chuyn i song song sangni tip truyn s liu i xa v chuyn i ni tip sang song song khi tip nhn s liu.i vi s liu truyn bt ng b, chng cng c kh nng ng khung cho k t mt ccht ng vi START bit, PARITY bit v cc STOP bit thch hp.

Cc a ch c s v ngt

Cng a chc bn IRQ

COM1 3F8h IRQ4

COM2 2F8h IRQ3COM3 3F8h (IRQ4)

COM4 2F8h (IRQ3)

Cc cng ni tip t th nht n th t u c phn bit qua cc v tr a ch trongvng vo/ ra ca my tnh v cc s ngt tng ng (IRQ). a ch u tin ca UART, c thl ca thanh ghi m truyn/ nhn, c tnh l a ch c s. Thng thng, a ch c s vIRQ c quy nh nh cc u ni (Jumper) trn Card vo/ ra hoc trn bn mch chnh.

Mch iu khin truyn thng db vn nng UART(VXL 8250A)

Vi mch 8250A l mt UART c dng rng ri trong cc my IBM PC ti v phi

ghp ni tip c u ni ra cng thng tin ni tip theo chun RS 232C


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Cc thanh ghi c th chia lm 3 loi:

Thanh ghi iu khin (Control Register): dng nhn v thc hin cc lnh tCPU.

Thanh ghi trng thi (Status Register): dng thng bo cho CPU bit v trngthi ca UART hay UART ang lm g.

Thanh ghi m (Buffer Register): dng gi k t trong lc truyn hoc x l.

Cc thanh ghi ny cng gi cc k t nh phn c truyn v nhn. Vic truy nhp lncc thanh ghi c thc hin thng qua a ch v khi iu khin. Mi thanh ghi c gnmt a ch tnh theo cch so snh tng i (Offset) vi a ch c s ca cng ni tip. Cca ch ca hai cng ni tip u tin trong hu ht cc my tnh c tiu chun ho. vit phn mm ghp ni qua cng ni tip ta cn lu l: ton b hot ng ca giao din nitip u c iu khin qua cc thanh ghi ca UART, trong thanh ghi m truyn/ nhnd liu thng c tnh l hai thanh ghi. Do ch c 8 a ch nn cn n s chuyn mch

bn trong thng qua bit DLAB (Division Latch Access Bit, bit 7 ca thanh ghi iu khinng truyn). Cc a ch ca tng thanh ghi u c tnh theo khong cch n a ch cs, khong cch ny thng c gi l Offset. Tu theo cc thanh ghi, Offset nhn gi tr cth trong khong t 0 n 7.

DLAB A2 A1 A0 Thanh ghi a ch

0 0 0 0 Bm c/ghiRBH 3F8 (2F8)0 0 0 1 Cho php ngt - IER 3F9 (2F9)

X 0 1 0 Nhn dng ngt (chc)IIR 3FA (2FA)

X 0 1 1 iu khin ng truynLCR 3FB (2FB)

X 1 0 0 iu khin modemMCR 3FC (2FC)

X 1 0 1 Trn thi ng truynLSR 3FD (2FD)

X 1 1 0 Trng thi modemMSR 3FE (2FE)

X 1 1 1 Khng dng

1 0 0 0 Cht s chia (LSB) 3F8 (2F8)

1 0 0 1 Cht s chia (MSB) 3F9 (2F9)


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Vi mch UART 8250 c tt c 10 thanh ghi, sau y ta s ln lt tm hiu cc thanhghi ny:

Cc thanh ghi lu tr:

Nh thy r t tn gi, cc thanh ghi ny thc cht l cc b m c chuyn dng gi mt k t, k t ny hoc l c nhn nhng cha c c, hoc l c gi ticng ni tip nhng cn cha c truyn i. Khi m t qu trnh truyn d liu qua cng nitip, thanh ghi gi (Holding Register) thng c gi l b m nhn hoc b m truyn.

Vic trang b cc b m nhn v truyn cng l mt c im ca vi mch 8250. cim ny cho php mt k t th hai c gi ti cng ni tip trc khi k t th nht c truyn hoc c c xong xui bi b x l. Trong thi gian ch k t th nht ctruyn hoc c c, k t th hai c gi trong b m. Sau y ta s thy r hn l:trng thi ca b m truyn v b m nhn c quy nh bi thanh ghi trng thi ngtruyn, c th hn l bit 7 ca thanh ghi iu khin ng truyn LCR (Line ControlRegister). Khi bit ny c t bng '0' th thao tc c t a ch c s s c t b m nhnRX v thao tc vit s vit vo b m truyn TX

Thanh ghi iu khin ng truyn:

Mt thanh ghi khc trong vi mch 8250 c gi l thanh ghi iu khin ng truynLCR (Line Control Register). Thanh ghi ny lu tr cc tham s c ngi lp trnh thit lpv xc nh khun mu khung truyn ca cuc trao i thng tin. Cc thng tin v: s cc bit

d liu, s lng bit dng v kiu chn l c s dng trong khung truyn u c ct gitrn thanh ghi ny. D liu c th c vit vo thanh ghi ny v c c ra sau y. Chcnng cc bit ca thanh ghi LCR.

Cc bit 0 v 1. Gi trc ct gi trong hai bit nhi phn ny ch r s cc bit dliu trong tng k t c truyn. S cc bit trn mt k t c th nm trongkhong t5 n 8 bit, cho php xc nh di ca t (Word). Li gii thch cho

bit 0 v 1 trn hnh v 12 lm sng t thm vai tr ca cc bit ny.Bit 2 ch r s cc bit dng trong mi khung truyn. Nu nh bit 2 c mt gi trlogic bng 0 th s bit dng sc vi mch 8250 to ra. Nu k tc truyn csu, by hoc tm bit d liu v bit 2 c t vo mt logic 1 th hai bit dng s

c to ra v "nh km" vo tng tc truyn. Nu nh nm bit d liu cchn lm h thng m dng cho mt k t th cn n 1,5 bit dng chn vo trongt d liu. Yu cu ny cn thit thch ng vi cc thit b c trn sdng nm bit d liu.Bit 3. c quy nh l bit cho php chn l, ngha l c s dng bit chn l haykhng. Nu bit ny c gi tr logic 1 th bit chn l sc to ra v chn vo tngxu k t. Do tnh chn l c cho php nn bt k k t no nhn c cngu b kim tra v tnh chn l.Bit 4. Kiu chn l c chn, l hoc chn, c xc nh bng cch t bit 4.Khi ct gi mt trng thi logic 0 vtr ny c ngha l t tnh chn l l l vngc li, ct gi mt trng thi logic 1 bit 4 c ngha l t tnh chn l l chn.

Nu nh bit 3, tc l bit cho php chn l, b cm bng cch t mt gi tr logic 0vo v tr ny th bt k l gi trbit nh thno c t vtr bit 4 cng khngc tc dng.


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Bit 5. (Bit stick parity). Nu nh bit 3 v bit 5 c t gi tr logic 1 th khi btruyn xut ra mt k t, b nhn ti ch (local) s pht hin nh mt gi trlogic 3.Bit 6. c quy nh l bit BREAK (dng). Khi bit ny c t mt gi tr logic1 th n bt buc SOUT (Serial out hay TxD) chuyn sang mc logic trng (mcLOW) cho n khi mt gi tr logic 0 c ct gi vo bit 6. Nhc bit ny m

my tnh c th bo hiu cho thit bu cui bit l c ni nh mt phnca h thng truyn thng.Bit 7. Phi c t mt gi tr logic 1 truy nhp cc cht s chia (divisorlatches). Cc cht ny l nhng thanh ghi ct gi schia i vi tn hiu gi nhp(ng h), sny quy nh tc baud ca h thng truyn thng ni tip. Miln tc baud c t li th bit ny (bit 7) li c t v gi tr logic 0.

Thanh ghi tc baud:Tc baud c t bng cch np mt s chia chim 16 bit, trong 8 bit thp hn

ca s chia c t trn a ch b m TX/ RX v 8 bit pha trn t ach k tip sau bm TX/ RX. S tng gp i s cc thanh ghi l cn thit v khi bit 7 hoc thanh ghi LCR(thng vit tt l DLAB) c li v gi tr logic 0 hai a ch ny gn lin vi b m nhnv b m truyn. Khi bit DLAB c t vo mt gitr logic 1 th hai a ch ny gn linvi hai cht s chia. Cc cht s chia bao gm 16 bit hay hai byte, c sp xp thnh cc bitc gi tr thp LSB (Least Significant byte) v bit c gi tr cao hn MSB (Most Significant

bit), c s dng trong vic t tc baud ca h thng truyn thng.Bi v cc cht s chia c rng l hai byte, gi tr 060 Hex cn c chia ra ct

gi trn hai thanh ghi LSB v MSB. Vi gi tr tc baud bng 1200 trong th d ny, 60Hex c ct gi trong LSB (bitc gi tr thp) v gi tr 0 c ct trong MSB (bit c gi trcao hn).

Tc baudmun c

Schia c dng to ra: 16 x ng h Sai s theo phn trm(sai khc gia mong

mun v thc t)Thp phn Hex

50 2304 90075 1536 600

110 1047 417 0,026134,5 857 359 0,058150 768 300 -

300 384 180 -600 192 0C0 -1200 96 060 -


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Tc baudmun c

Schia c dng to ra: 16 x ng h Sai s theo phn trm(sai khc gia mong

mun v thc t)Thp phn Hex

1800 64 040 -2000 58 03A 0,692400 48 030 -

3600 32 020 -4800 24 018 -7200 16 010 -9600 12 00C -

Mt s tc baud v cc gi tr s chia tng ng di chai dng thp phn v thplc phn (Hex). Gi tr ny ca s chia c np vo b m TX/ RX khi bit DLAB c mtgi tr logic 1 t vo.

Thanh ghi trng thi ng truyn:

Thanh ghi trng thi ng truyn (LSR: Line Status Register) thanh ghi 8 bit, chathng tin v qu trnh d liu qua cng ni tip cn cung cp cho b vi x l.

Bit 0, c dng thng bo cho bit d liu nhn c (DR: Data Received).Khi bit 0 c gi trlogic 1 c ngha l d liu c nhn v sn sng b xl c.Bit 1: Mt gi tr logic 1 bit ny c ngha l k t nhn trc b mt v nkhng c c trc khi mt k t mi c nhn nn k t mi ghi ln kttrc.Bit 2: Mt gi tr logic 1 bit li chn lc ngha l k t c nhn c tnhchn l sai. Khi thanh ghi trng thi ng truyn (LSR) c c th bit ny li

c t v gi tr logic 0.Bit 3: y l bit li khung truyn. Nu k t nhn khng c mt bit dng hpl, ngha l c li khung truyn, th bit 3 trong thanh ghi LSR c t vo mt gitr logic 1.Bit 4: c quy nh l bit gin on ngt (break interrupt bit). Bit ny c tng t vo mt gi tr logic 1 khi d liu nhn c c gimt mctrng trn ton b chiu di ca mt t d liu.Bit 5: c quy nh l bit bo hiu trng thi rng ca bm truyn (THRE:Transmit Holding Register Empty). Bit ny bo hiu l cng ni tip sn sng tipnhn k tkhc c truyn ti.

Bit 6: Bit ny l mt bit chc. Khi bit ny c gi tr logic 1 th bm truynang cn trng.Bit 7: khng c s dng v lun c t gi tr logic 0.


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Khi vit phn mm truy nhp thanh ghi ln thanh ghi trng thi ng truyn ta cn lu ti mt s chc nng ca thanh ghi ny. Thanh ghi trng thi ng truyn (LSR: LineStatus Resgister) xc nh trng thi ca b m truyn v b m nhn. Thanh ghi ny chdng c ra, ni dung tt c cc bit c t ng t bng phn cng.

Mt iu ri ro c th xy ra khi truyn d liu mt k t mi c th c vit vo bm truyn trc khi k t trc y c gi. Khi k t mi ny s vit ln ni

dung ca k t ang c truyn. trnh tnh trng ri ro ny S5 c giao nhim v thngbo kt qu kim tra xc nh liu vn cn mt k t trong b nh. Nu c th n c tthnh '1', cn nu nh bit ny c gi tr bng 0 th c ngha l b m truyn ang trong trngthi trng rng.

truyn mt k t:- Kimtra bit 6 cho n khi c t;(Test Bit 6 until set;)- Truyn k t; (Send character;)

nhn k t:- Kim trabit 0 cho n khi c t; (Test Bit 0 until set;)- c k t; (Read character;)

Thanh ghi cho php ngt:

Vi mch 8250 c mt nhiu kh nng ngt. C hai thanh ghi c s dng iukhin v xc nh cc ngun ngt. Thanh ghi u tin trong hai thanh ghi l thanh ghi cho

php ngt IER (Interrupt Enable Register) cn thanh ghi th hai l thanh ghi nhn dng ngtIIR (Interrupt Identification Register).

Bit 0: Mi ln nhn mt k t th mt ngt li c to ra. Bit ny c t li(Reset) sau khi k t c b xl c.Bit 1: Nu bit ny c t mt gi tr logic 1 th bm truyn (thanh ghi gitruyn) trng v mt ngt xut hin.


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Bit 2: cho php c sthay i trong trng thi ng truyn b nhn theo cch gyra mt ngt.Bit 3: cho php c sthay i trong trng thi modem ngt b x l.Bit 4- 7: Cc bit ny lun c t gi tr logic 0.

Nu nh kh nng ngt ca vi mch cho php v mt ngt xut hin th bit xut rangt t 8250 chim ly mc logic 1. Tn hiu ny c ni vi bus ngt cng ca my tnh.

Logic 1 trn bus ny bo hiu cho b x l bit l cn phi ch ti cng ni tip. Hnh 15minh ho s phn b ca cc bit trn thanh ghi IER.

Thanh ghi nhn dng ngt

Nu nh mt ngt xut hin th phn mm chng trnh phi thc hin c chc nngkim tra thanh ghi xc nh xem s kin no ang gy ra ngt. Thanh ghi nhn dng ngtIIR cha ng m, nhn dng iu kin (ngt) no ang yu cu ch .

Mt im cn ch l: gia cc ngt cng c mc u tin khc nhau, ni khc i lc mt vi ngt t ra l "quan trng" hn so vi cc ngt khc. V nguyn tc, ngt no quan

trng hn s c u tin x l trc.Thanh ghi nhn dng ngt Cc ngt v t li chc nngBit2

Bit1

Bit0

Mcu tin

Kiu ngt Ngun ngt iu khint li ngt

0 0 1 - Khng dng Khng dng -1 1 0 Cao nht Trng thi

ng nhnLi trn hoc li chnl hoc li khungtruyn hoc breakinterrupt

c thanh ghi trngthi ng truyn

1 0 0 Th hai C d liu nhn

C d liu nhn c thanh ghi mb nhn

0 1 0 Th ba Bmtruyn trng

Bm truyn trng c thanh ghi IR(nu l ngun ngt)hoc ghi vo bmtruyn

0 0 0 Tht Trng thimodem

Xo gi hoc dliu sn sng hoc bochung hoc pht hintn hiu ng nhn

c thanh ghi trngthi modem

Bng trn lit k cc mc u tin ca tng ngt. Ct t li ngt lit k tc ng no lcn n t li ngt c cht.

Mch iu khin truyn thng ng b - db vn nng USART (VXL 8251A)Vi mch 8251A l mt USART c dng rng ri trong cc my IBM PC ti v phighp ni tip c u ni ra cng thng tin ni tip theo chun RS 232C


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S :

Cc thanh ghi c th chia lm 3 loi:- Thanh ghi iu khin (Control Register): dng nhn v thc hin cc lnh t

CPU.- Thanh ghi trng thi (Status Register): dng thng bo cho CPU bit v trng thi

ca UART hay UART ang lm g.- Thanh ghi m (Buffer Register): dng gi k t trong lc truyn hoc nhnThanh ghi t ch

D7 D6 D5 D4 D3 D2 D1 D0S2 S1 EP PEN L2 L1 B2 B1

Bit 0,1 c dng ng b v h s nhn tc 00 ng b 10 nhn 1601 nhn 1 11 nhn 64

Bit 2,3: s bit m k t00 5 10 7

01 6 11 8Bit 4: cho php dng Parity hay khngBit 5: Parity bitBit 6,7: s bit STOP

00 khng hp l 01 110 11/2 11 2

Thanh ghi t lnh

D7 D6 D5 D4 D3 D2 D1 D0EH IR RTS ER SBRK RxE DTR TxEN

Bit 0: cho php pht tn hiuBit 1: DTE sn sngBit 2: Cho php thu

m

d liu

m

Pht

iukhinpht

m

Thu

Logiciukhinghic

Reset

Clk

C/D

RD

WR

RxD

RS232

iukhinthu

TxD

i ukhinmode

mDSR

DTR


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Bit 3: Gi k tgin on (k t vi tt c cc bit la 0)Bit 4: Xo cliBit 5: Yu cu truynBit 6: Reset ni bBit 7: tm kim k tng b

Thanh ghi trng thi:

D7 D6 D5 D4 D3 D2 D1 D0DSR SYNDET FE OE PE TxEMPTY RxRDY TxRDY

Bit 0: bn pht sn sngBit 1: bn thu sn sngBit 2: m pht rngBit 3: li ParityBit 4: li thu Bit 5: li FrameBit 6: k tng b

Bit 7: modem sn sng2.6. Mng truyn thng

Nhng h thng truyn thng c th m con ngi s dng v khai thc:

H thng in tn dng nng lng in mt chiuH thng thng tin v tuyn in dng nng lng sng in tH thng thng tin quang nngH thng thng tin dng sng mH thng truyn s liuH thng truyn hnh

H thng thng tin thoiTrong phm vi ca h thng truyn s liu

Mng chuyn mch knhMng chuyn mch giMng dch v tch hp sMng cc bMng v tuynMng v tinh

CU HI V BI TP2.1. Anh ch hy trnh by v thng truyn thng tng qut.

2.2. Anh ch hy trnh by vcc ng truyn hu tuyn c s dng hin nay. Nu cim v phm vi ng dng ca chng.2.3. Trnh by hiu bit ca anh, ch v chun EIA-RS232C2.4. Trnh by hiu bit ca anh, ch v mch iu khin truyn thng d b vn nng

UART8250A2.6. H thng truyn mt k t m ASCII chun l A thng qua mch iu khin truyn

thng d b UART8250A. Anh ch hy cho bit gi tr cc bt ca thanh ghi iu khinng truyn, thanh ghi tc Bound. Bit rng h

dhhh - giao trinh truyen du lieu.2010

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