Giao Trinh Nhap Mon Mang May Tinh

8/3/2019 Giao Trinh Nhap Mon Mang May Tinh

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Khoa Cng Ngh Thng Tin Trung Cp Kinh T K Thut QuangTrung

Chng I Nhng khi nim c bn ca mng my tnh ...........5I. nh ngha mng my tnh ..........................................................................5

II. Phn loi mng my tnh ...........................................................................6II.1. Da theo v tr a l .............................................................................................. 6

II.2. Da theo cu trc mng ...........................................................................................6

II.2.1 Kiu im - im (point - to - point) ................................................................6

II.2.2 Kiu khuych tn .............................................................................................. 7

II.3. Da theo phng php chuyn mch ......................................................................7

II.3.1 Mng chuyn mch knh (Line switching network) .........................................7

II.3.2 Mng chuyn mch thng ip (Message switching network) .........................7

II.3.3 Mng chuyn mch gi (Packet switching network) ........................................8

III. So snh gia mng cc b v mng din rng ..........................................8

IV. Cc thnh phn ca mng my tnh ........................................................10

IV.1. Mt s b giao thc kt ni mng ...................................................................... 10

IV.2. H iu hnh mng - NOS (Network Operating System) ................................... 10

V. Cc li ch ca mng my tnh ...............................................................11

V.1. Mng to kh nng dng chung ti nguyn cho cc ngi dng. .......................11

V.2. Mng cho php nng cao tin cy. ...................................................................12V.3. Mng gip cho cng vic t hiu sut cao hn. ................................................ 12

V.4. Tit kim chi ph. ................................................................................................. 12

V.5. Tng cng tnh bo mt thng tin. ..................................................................... 12

V.6. Vic pht trin mng my tnh to ra nhiu ng dng mi ............................. 12

VI. Cc dch v ph bin trn mng my tnh ............................................ 12

Chng II M hnh truyn thng ...............................................14

I. S cn thit phi c m hnh truyn thng ............................................... 14II. Cc nhu cu v chun ha i vi mng .................................................15

III. M hnh OSI (Open Systems Interconnection) ....................................... 16

III.1. Nguyn tc s dng khi nh ngha cc tng h thng m .................................. 16

III.2. Cc giao thc trong m hnh OSI ....................................................................... 17

III.3. Cc chc nng ch yu ca cc tng ca m hnh OSI....................................... 18

III.3.1 Tng 1: Vt l (Physical) ...............................................................................18

III.3.2 Tng 2: Lin kt d liu (Data link) .............................................................. 18III.3.3 Tng 3: Mng (Network) ............................................................................... 19

III.3.4 Tng 4: Vn chuyn (Transport) ....................................................................21

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III.3.5 Tng 5: Giao dch (Session) .......................................................................... 22

III.3.6 Tng 6: Trnh by (Presentation) ...................................................................22

III.3.7 Tng 7: ng dng (Application) ................................................................... 23

IV. Qu trnh chuyn vn gi tin ...................................................................23IV.1. Qu trnh ng gi d liu (ti my gi) ............................................................23

IV.2. Qu trnh truyn d liu t my gi n my nhn. ...........................................25

IV.3. Chi tit qu trnh x l ti my nhn ................................................................... 25

V. Phng thc truyn tn hiu .....................................................................26

VI. M hnh TCP/IP ......................................................................................26

VI.1. Tng quan v b giao thc TCP/IP .................................................................... 26

VI.2. So snh TCP/IP vi OSI .................................................................................... 28VII. Cc giao thc truy cp ng truyn trn mng LAN ..........................29

VII.1. Giao thc chuyn mch (yu cu v chp nhn) ................................................29

VII.2. Giao thc ng dy a truy cp vi cm nhn va chm .................................29

VII.3. Giao thc dng th bi vng (Token ring) .........................................................30

VII.4. Giao thc dng th bi cho dng ng thng (Token bus) .............................. 30

VIII. Cc phng tin kt ni mng lin khu vc (WAN) ...........................30

Chng III a ch IP ..................................................................32I. Giao thc TCP/IP .......................................................................................32II. a ch IP ..................................................................................................32

II.1. Tng qut ...............................................................................................................32

II.2. Cu trc ca cc a ch IP ....................................................................................32

III. Mt s khi nim v thut ng lin quan ................................................36

III.1. Cc giao thc trong mng IP ............................................................................... 37

III.2. Cc bc hot ng ca giao thc IP .................................................................37

IV. Giao thc iu khin truyn d liu TCP ...............................................38

IV.1. Cc bc thc hin thit lp mt lin kt TCP/IP: ........................................39

IV.2. Cc bc thc hin khi truyn v nhn d liu ...................................................40

IV.3. Cc bc thc hin khi ng mt lin kt ...........................................................41

IV.4. Mt s hm khc ca TCP ...................................................................................41

V. Giao thc UDP (User Datagram Protocol) ...............................................43

VI. a ch IPv4 ............................................................................................45

VI.1. Thnh phn v hnh dng ca a ch IP ..............................................................45

VI.2. Cc lp a ch IP .................................................................................................45

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VII. IPv6 ........................................................................................................47

VII.1. Giao thc lin mng th h mi (IPv6) ............................................................. 47

VII.2. Mt s c im mi ca IPv6: .........................................................................47

VII.3. Kin trc a ch trong IPv6: ............................................................................. 48VII.3.1 Khng gian a ch: ..................................................................................... 48

VII.3.2 C php a ch: .......................................................................................... 49

Chng IV Thit b mng ........................................................... 50I. Mi trng truyn dn ............................................................................... 50

I.1. Khi nim .............................................................................................................. 50

I.2. Tn s truyn thng ............................................................................................... 50

I.3. Cc c tnh ca phng tin truyn dn .............................................................. 50I.4. Cc kiu truyn dn. .............................................................................................. 51

II. ng cp truyn mng .......................................................................... 51

II.1. Cp xon cp ......................................................................................................... 51

II.2. Cp ng trc ........................................................................................................ 52

II.3. Cp si quang (Fiber - Optic Cable) ..................................................................... 53

II.4. Cc yu cu cho mt h thng cp ........................................................................ 53

III. ng truyn v tuyn ............................................................................54

III.1. Sng v tuyn (radio) ...........................................................................................54

III.2. Sng viba ............................................................................................................. 54

III.3. Hng ngoi ........................................................................................................... 54

IV. Cc k thut bm cp mng ....................................................................55

V. Cc thit b lin kt mng .........................................................................56

V.1. Repeater (B tip sc) ...........................................................................................56

V.2. Bridge (Cu ni) ....................................................................................................57

V.3. Router (B tm ng) .......................................................................................... 60

V.3.1 Cc phng thc hot ng ca Router .........................................................63

V.3.2 Mt s giao thc hot ng chnh ca Router ................................................ 63

V.4. Gateway (cng ni) ............................................................................................... 64

V.5. Hub (B tp trung) ................................................................................................ 64

V.6. B chuyn mch (switch) ......................................................................................65

Chng V M hnh mng .......................................................... 66

I. Kin trc mng (Topology) .......................................................................66II. Nhng cu trc chnh ca mng cc b .................................................. 66

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II.1. Dng ng thng (Bus) ....................................................................................... 66

II.2. Dng vng trn (Ring) .......................................................................................... 67

II.3. Dng hnh sao (Star) ..............................................................................................67

II.4. Mng dng kt hp ................................................................................................69Chng VI Cc dch v ca mng din rng (WAN) .............70I. Mng chuyn mch (Circuit Swiching Network) ......................................70

II. Mng thu bao (Leased line Network) .....................................................73

III. Mng chuyn gi tin (Packet Switching NetWork) ................................74

IV. Mng X25 ...............................................................................................75

V. Mng Frame Relay ...................................................................................75

VI. Mng ATM (Cell relay) ..........................................................................76

Chng VII CC DCH V MNG THNG DNG ...........77I. DCH V WEB .........................................................................................77

I.1. Mt s thut ng c bn. ....................................................................................... 77

I.2. Gii thiu m hnh hot ng ca Web. ................................................................79

II. DCH V FTP ..........................................................................................80

II.1. M hnh hot ng ca FTP ..................................................................................80

II.2. Tp hp cc lnh FTP ........................................................................................... 81

III. E-MAIL...................................................................................................82

III.1. M hnh hot ng .............................................................................................82

III.2. Cc loi mail. ..................................................................................................... 83

III.3. S dng WebMail. ..............................................................................................83

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Chng I Nhng khi nim c bn ca mngmy tnh

Mng my tnh ngy nay pht trin mt cch nhanh chng v a dng. H iu hnhcng cc ng dng ca mng ngy cng phong ph, cc li ch ca mng ngy cng c khngnh. Mng my tnh bao gm rt nhiu loi, nhiu m hnh trin khai. Trong mt mng my tnhli c nhiu thnh phn cu thnh. Trc khi i chi tit v mng my tnh, chng ta s tm hiucc khi nim c bn ca mng my tnh.

I. nh ngha mng my tnh

Mng my tnh l mt tp hp cc my tnh c ni vi nhau bi ng truyn theo mtcu trc no v thng qua cc my tnh trao i thng tin qua li vi nhau.

ng truyn l h thng cc thit b truyn dn c dy hay khng dy dng chuyncc tn hiu in t t my tnh ny n my tnh khc. Cc tn hiu in t biu th cc gi trd liu di dng cc xung nh phn (on - off). Tt c cc tn hiu c truyn gia cc my tnhu thuc mt dng sng in t. Ty theo tn s ca sng in t c th dng cc ng truynvt l khc nhau truyn cc tn hiu. y ng truyn c kt ni c th l dy cp ngtrc, cp xon, cp quang, dy in thoi, sng v tuyn ... Cc ng truyn d liu to nn cutrc ca mng.

Hnh I-1 Mng my tnh

Vi s trao i qua li gia my tnh ny vi my tnh khc phn bit mng my tnhvi cc h thng thu pht mt chiu nh truyn hnh, pht thng tin t v tinh xung cc trmthu th ng... v ti y ch c thng tin mt chiu t ni pht n ni thu m khng quan tmn c bao nhiu ni thu, c thu tt hay khng.

c trng c bn ca ng truyn vt l l gii thng. Gii thng ca mt ngchuyn chnh l o phm vi tn s m n c th p ng c. Tc truyn d liu trnng truyn cn c gi l thng lng ca ng truyn - thng c tnh bng s lng

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bit c truyn i trong mt giy (Bps). Thng lng cn c o bng n v khc l Baud (lyt tn nh bc hc - Emile Baudot). Baud biu th s lng thay i tn hiu trong mt giy.

y Baud v Bps khng phi bao gi cng ng nht. V d: nu trn ng dy c 8

mc tn hiu khc nhau th mi mc tn hiu tng ng vi 3 bit hay l 1 Baud tng ng vi 3bit. Ch khi c 2 mc tn hiu trong mi mc tn hiu tng ng vi 1 bit th 1 Baud mitng ng vi 1 bit.

II. Phn loi mng my tnh

C nhiu cch phn bit mng my tnh nhng ngi ta thng phn bit mng mytnh theo v tr a l, cu trc mng, phng php chuyn mch.

II.1. Da theo v tr a l

Da vo phm vi phn b ca mng ngi ta c th phn ra cc loi mng nh sau:

GAN (Global Area Network) - Kt ni my tnh t cc chu lc khc nhau. Thngthng kt ni ny c thc hin thng qua mng vin thng v v tinh.

WAN (Wide Area Network) - Mng din rng, kt ni my tnh trong ni b cc qucgia hay gia cc quc gia trong cng mt chu lc. Thng thng kt ni ny c thchin thng qua mng vin thng. Cc WAN c th c kt ni vi nhau thnh GAN hayt n l GAN.

MAN (Metropolitan Area Network) - Kt ni cc my tnh trong phm vi mt thnhph hay gia cc thnh ph vi nhau.

LAN (Local Area Network) - Mng cc b, kt ni cc my tnh trong mt khu vc bnknh hp thng thng khong vi trm mt. Kt ni c thc hin thng qua cc mitrng truyn thng tc cao v d cp ng trc thay cp quang. LAN thng c sdng trong ni b mt c quan/t chc... Cc LAN c th c kt ni vi nhau thnhWAN.

Trong cc khi nim ni trn, thng c s dng nht hin ny l khi nim Mng dinrng WAN v mng cc b LAN.

II.2. Da theo cu trc mng

II.2.1 Kiu im - im (point - to - point)

ng truyn ni tng cp nt mng vi nhau. Thng tin i t nt ngun qua nt trunggian ri gi tip nu ng truyn khng b bn. Do , cn c tn l mng lu tr v chuyntip (store and forward).

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Hnh I-2 Cu trc im im

II.2.2 Kiu khuych tn

Bn tin c gi i t mt nt s c tip nhn bi cc nt cn li (cn gi l

broadcasting hay point to multipoint). Trong bn tin phi c vng a ch cho php mi nt kimxem c phi tin ca mnh khng v x l nu ng bn tin c gi n.

Hnh I-3 Cu trc kiu khuych tn

II.3. Da theo phng php chuyn mch

II.3.1 Mng chuyn mch knh (Line switching network)

Chuyn mch knh dng trong mng in thoi. Mt knh c nh c thit lp giacp thc th cn lin lc vi nhau. Mng ny c hiu sut khng cao v c lc knh b khng.

Hnh I-4 Mng chuyn mch knh

II.3.2 Mng chuyn mch thng ip (Message switching network)

Cc nt ca mng cn c vo a ch ch ca thng ip chn nt k tip. Nh vycc nt cn lu tr v c tin nhn c, qun l vic truyn tin. Trong trng hp bn tin qudi v nu sai phi truyn li. Phng php ny ging nh cch gi th thng thng.

Mng chuyn mch thng bo thch hp vi cc dch v thng tin kiu th in t (Email)hn l i vi cc ng dng c tnh thi gian thc v tn ti tr nht nh do lu tr v x lthng tin iu khin ti mi nt.

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Hnh I-5 Mng chuyn mch thng ip

II.3.3 Mng chuyn mch gi (Packet switching network)

Bn tin c chia thnh nhiu gi tin (packet) c di 512 bytes, phn u ca gi tinthng l a ch ch, m tp hp cc gi. Cc gi tin ca cc thng ip khc nhau c th

c truyn c lp trn cng mt ng truyn. Vn phc tp y l to li bn tin banu, c bit l khi truyn trn cc con ng khc nhau. Chuyn mch gi mm do, hiu sutcao. S dng hai k thut chuyn mch knh v chuyn mch gi trong cng mt mng thngnht gi l mng ISDN (Integrated Services Digital Network Mng thng tin s a dch v)

Hnh I-6 Mng chuyn mch gi

III. So snh gia mng cc b v mng din rng

Mng cc b v mng din rng c th c phn bit bi: a phng hot ng, tc ng truyn v t l li trn ng truyn, ch qun ca mng, ng i ca thng tin trnmng, dng chuyn giao thng tin.

a phng hot ng

Lin quan n khu vc a l th mng cc b s l mng lin kt cc my tnh nm trong mt khu vc nh. Khu vc c th bao gm mt ta nh hay l mt khu nh...iu hn ch bi khong cch ng dy cp c dng lin kt cc my tnhca mng cc b (Hn ch cn l hn ch ca kh nng k thut ca ng truynd liu). Ngc li mng din rng l mng c kh nng lin kt cc my tnh trongmt vng rng ln nh l mt thnh ph, mt min, mt t nc, mng din rngc xy dng ni hai hoc nhiu khu vc a l ring bit.

Tc ng truyn v t l li trn ng truyn

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Do cc ng cp ca mng cc b c xy dng trong mt khu vc nh cho nn nt b nh hng bi tc ng ca thin nhin (nh l sm chp, nh sng...). iu cho php mng cc b c th truyn d liu vi tc cao m ch chu mt t l linh. Ngc li vi mng din rng do phi truyn nhng khong cch kh xa vi

nhng ng truyn dn di c khi ln ti hng ngn km. Do vy mng din rngkhng th truyn vi tc qu cao v khi t l li s tr nn kh chp nhn c.

Mng cc b thng c tc truyn d liu t 4 n 16 Mbps v t ti 100 Mbpsnu dng cp quang. Cn phn ln cc mng din rng cung cp ng truyn c tc thp hn nhiu nh T1 vi 1.544 Mbps hay E1 vi 2.048 Mbps.

n v bps (Bit Per Second) l mt n v trong truyn thng tng ng vi 1 bitc truyn trong mt giy, v d nh tc ng truyn l 1 Mbps tc l c thtruyn ti a 1 Megabit trong 1 giy trn ng truyn .

Thng thng trong mng cc b t l li trong truyn d liu vo khong 1/107-108cn trong mng din rng th t l vo khong 1/106 - 107

Ch qun v iu hnh ca mng

Do s phc tp trong vic xy dng, qun l, duy tr cc ng truyn dn nn khi xydng mng din rng ngi ta thng s dng cc ng truyn c thu t cc cngty vin thng hay cc nh cung cp dch v truyn s liu. Ty theo cu trc ca mngnhng ng truyn thuc c quan qun l khc nhau nh cc nh cung cp ngtruyn ni ht, lin tnh, lin quc gia. Cc ng truyn phi tun th cc quy nhca chnh ph cc khu vc c ng dy i qua nh: tc , vic m ha.

Cn i vi mng cc b th cng vic n gin hn nhiu, khi mt c quan ci tmng cc b th ton b mng s thuc quyn qun l ca c quan .

ng i ca thng tin trn mng

Trong mng cc b thng tin c i theo con ng xc nh bi cu trc ca mng.Khi ngi ta xc nh cu trc ca mng th thng tin s lun lun i theo cu trc xc nh . Cn vi mng din rng d liu cu trc c th phc tp hn nhiu do vics dng cc dch v truyn d liu. Trong qu trnh hot ng cc im nt c th thay

i ng i ca cc thng tin khi pht hin ra c trc trc trn ng truyn hay khipht hin c qu nhiu thng tin cn truyn gia hai im nt no . Trn mng dinrng thng tin c th c cc con ng i khc nhau, iu cho php c th s dngti a cc nng lc ca ng truyn hay nng cao iu kin an ton trong truyn dliu.

Dng chuyn giao thng tin

Phn ln cc mng din rng hin nay c pht trin cho vic truyn ng thi trnng truyn nhiu dng thng tin khc nhau nh: video, ting ni, d liu... Trong khi cc mng cc b ch yu pht trin trong vic truyn d liu thng thng. iu ny

c th gii thch do vic truyn cc dng thng tin nh video, ting ni trong mt khuvc nh t c quan tm hn nh khi truyn qua nhng khong cch ln.

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Cc h thng mng hin nay ngy cng phc tp v cht lng, a dng v chng loiv pht trin rt nhanh v cht. Trong s pht trin s lng nhng nh sn xut t

phn mm, phn cng my tnh, cc sn phm vin thng cng tng nhanh vi nhiusn phm a dng. Chnh v vy vai tr chun ha cng mang nhng ngha quan

trng. Ti cc nc cc c quan chun quc gia a ra cc nhng chun v phncng v cc quy nh v giao tip nhm gip cho cc nh sn xut c th lm ra cc snphm c th kt ni vi cc sn phm do hng khc sn xut.

IV. Cc thnh phn ca mng my tnh

Mng my tnh bao gm cc thit b phn cng, cc giao thc v cc phn mm mng.Khi nghin cu v mng my tnh, cc vn quan trng cn c xem xt l giao thcmng, cu hnh kt ni ca mng v cc dch v mng.

IV.1. Mt s b giao thc kt ni mng

1. TCP/IP

u th chnh ca b giao thc ny l kh nng lin kt hot ng ca nhiuloi my tnh khc nhau.

TCP/IP tr thnh tiu chun thc t cho kt ni lin mng cng nh kt ni Internetton cu.

2. NetBEUI

B giao thc nh, nhanh v hiu qu c cung cp theo cc sn phm cahng IBM, cng nh s h tr ca Microsoft.

Bt li chnh ca b giao thc ny l khng h tr nh tuyn v s dng gii hn

mng da vo Microsoft.3. IPX/SPX

y l b giao thc s dng trong mng Novell.

u th: nh, nhanh v hiu qu trn cc mng cc b ng thi h tr kh nng nhtuyn.

4. DECnet

y l b giao thc c quyn ca hng Digital Equipment Corporation.

DECnet nh ngha m hnh truyn thng qua mng LAN, mng MAN v WAN. H

tr kh nng nh tuynIV.2. H iu hnh mng - NOS (Network Operating System)

Cng vi s nghin cu v pht trin mng my tnh, h iu hnh mng c nhiucng ty u t nghin cu v cng b nhiu phn mm qun l v iu hnh mng chiu qu nh:NetWare ca cng ty NOVELL, LAN Managerca Microsoftdng cho ccmyserverchy h iu hnh OS/2, LAN server ca IBM (gn nh ng nht vi LANManager), Vines ca Banyan Systems l h iu hnh mng dng choserverchy h iuhnh UNIX,Promise LAN ca Mises Computerchy trn cardiu hp mng c quyn,Windows for Workgroups ca Microsoft, LANtastic caArtisoft, NetWare Lite ca

Novell,....

Mt trong nhng s la chn c bn m ta phi quyt nh trc l h iu hnh mng nos lm nn tng cho mng ca ta, vic la chn tu thuc vo kch c ca mng hin ti v

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s pht trin trong tng lai, cn tu thuc vo nhng u im v nhc im ca tng hiu hnh.

Mt s h iu hnh mng ph bin hin nay:

H iu hnh mng UNIX: y l h iu hnh do cc nh khoa hc xy dng v cdng rt ph bin trong gii khoa hc, gio dc. H iu hnh mng UNIX l h iuhnh a nhim, a ngi s dng, phc v cho truyn thng tt. Nhc im ca n lhin nay c nhiu Version khc nhau, khng thng nht gy kh khn cho ngi sdng. Ngoi ra h iu hnh ny kh phc tp li i hi cu hnh my mnh (trcy chy trn my mini, gn y c SCO UNIX chy trn my vi tnh vi cu hnhmnh).

H iu hnh mng WindowsNT: y l h iu hnh ca hng Microsoft, cng l hiu hnh a nhim, a ngi s dng. c im ca n l tng i d s dng, htr mnh cho phn mm WINDOWS. Do hng Microsoftl hng phn mm ln nht

th gii hin nay, h iu hnh ny c kh nng s c ngy cng ph bin rng ri.Ngoi ra, Windows NT c th lin kt tt vi my chNovell Netware. Tuy nhin, chy c hiu qu, WindowsNT cng i hi cu hnh my tng i mnh.

H iu hnh mng Windows for Workgroup: y l h iu hnh mng ngang hng nh,cho php mt nhm ngi lm vic (khong 3-4 ngi) dng chung a trn my canhau, dng chung my in nhng khng cho php chy chung mt ng dng. H ddng ci t v cng kh ph bin.

H iu hnh mngNetWare ca Novell: y l h iu hnh ph bin nht hin nay nc ta v trn th gii trong thi gian cui, n c th dng cho cc mng nh (khongt 5-25 my tnh) v cng c th dng cho cc mng ln gm hng trm my tnh.Trong nhng nm qua, Novell cho ra nhiu phin bn caNetware: Netware 2.2,

3.11. 4.0 v hin c 4.1.Netware l mt h iu hnh mng cc b dng cho cc myvi tnh theo chun ca IBM hay cc my tnhApple Macintosh, chy h iu hnh MS-DOS hoc OS/2.

H iu hnh ny tng i gn nh, d ci t (my ch ch cn thm ch AT386) do ph hp vi hon cnh trang thit b hin ti ca nc ta. Ngoi ra, v l mt phnmm ph bin nn Novell Netware c cc nh sn xut phn mm khc h tr (theongha cc phn mm do cc hng phn mm ln trn th gii lm u c th chy tttrn h iu hnh mng ny).

V. Cc li ch ca mng my tnh

V.1. Mng to kh nng dng chung ti nguyn cho cc ngi dng.

Vn l lm cho cc ti nguyn trn mng nh chng trnh, d liu v thit b, c bit l ccthit b t tin, c th sn dng cho mi ngi trn mng m khng cn quan tm n v tr thcca ti nguyn v ngi dng.

V mt thit b, cc thit b cht lng cao thng t tin, chng thng c dng chung chonhiu ngi nhm gim chi ph v d bo qun.

V mt chng trnh v d liu, khi c dng chung, mi thay i s sn dng cho mi thnh

vin trn mng ngay lp tc. iu ny th hin rt r ti cc ni nh ngn hng, cc i l bnv my bay...

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V.2. Mng cho php nng cao tin cy.

Khi s dng mng, c th thc hin mt chng trnh ti nhiu my tnh khc nhau, nhiu thitb c th dng chung. iu ny tng tin cy trong cng vic v khi c my tnh hoc thit b b

hng, cng vic vn c th tip tc vi cc my tnh hoc thit b khc trn mng trong khi chsa cha.

V.3. Mng gip cho cng vic t hiu sut cao hn.

Khi chng trnh v d liu dng chung trn mng, c th b qua mt s khu i chiukhng cn thit. Vic iu chnh chng trnh (nu c) cng tit kim thi gian hn do ch cnci t li trn mt my.

V mt t chc, vic sao chp d liu phng h tin li hn do c th giao cho ch mt ngithay v mi ngi phi t sao chp phn ca mnh.

V.4. Tit kim chi ph.

Vic dng chung cc thit b ngoi vi cho php gim chi ph trang b tnh trn s ngi dng. Vphn mm, nhiu nh sn xut phn mm cung cp c nhng n bn cho nhiu ngi dng, vichi ph thp hn tnh trn mi ngi dng.

V.5. Tng cng tnh bo mt thng tin.

D liu c lu trn cc my phc v tp tin (file server) s c bo v tt hn so vi t ticc my c nhn nh c ch bo mt ca cc h iu hnh mng.

V.6. Vic pht trin mng my tnh to ra nhiu ng dng mi

Mt s ng dng c nh hng quan trng n ton x hi: kh nng truy xut cc chng trnhv d liu t xa, kh nng thng tin lin lc d dng v hiu qu, to mi trng giao tip thunli gia nhng ngi dng khc nhau, kh nng tm kim thng tin nhanh chng trn phm viton th gii,...

VI. Cc dch v ph bin trn mng my tnh

- Dch v tp tin (File services)

Cho php chia s ti nguyn thng tin chung, chuyn giao cc tp tin d liu t my ny sangmy khc. Tm kim thng tin v iu khin truy nhp. Dch v th in t E_Mail (Electronicmail) cung cp cho ngi s dng phng tin trao i, tranh lun bng th in t. Dch v thin t gi thnh h, chuyn pht nhanh, an ton v ni dung c th tch hp cc loi d liu.

- Dch v in n

C th dng chung cc my in t tin trn mng. Cung cp kh nng a truy nhp n my in,phc v ng thi cho nhiu nhu cu in khc nhau. Cung cp cc dch v FAX v qun l ccc trang thit b in chuyn dng.

- Cc dch v ng dng hng i tng

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S dng cc dch v thng ip (Message) lm trung gian tc ng n cc i tng truynthng. i tng ch bn giao d liu cho tc nhn (Agent) v tc nhn s bn giao d liu choi tng ch.

- Cc dch v ng dng qun tr lung cng vic trong nhm lm vic:nh tuyn cc ti liu in t gia nhng ngi trong nhm. Khi ch k in t c xc nhntrong cc phin giao dch th c th thay th c nhiu tin trnh mi hiu qu v nhanh chnghn.

- Dch v c s d liu

L dch v ph bin v cc dch v ng dng, l cc ng dng theo m hnh Client/Server. Dchv x l phn tn lu tr d liu phn tn trn mng, ngi dng trong sut v d s dng, png cc nhu cu truy nhp ca ngi s dng.

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Chng II M hnh truyn thng

I. S cn thit phi c m hnh truyn thng

mt mng my tnh tr mt mi trng truyn d liu th n cn phi c nhng yu t sau:

Mi my tnh cn phi c mt a ch phn bit trn mng. Vic chuyn d liu t my tnh ny n my tnh khc do mng thc hin thng qua

nhng quy nh thng nht gi l giao thc ca mng.

Khi cc my tnh trao i d liu vi nhau th mt qu trnh truyn giao d liu c thchin hon chnh. V d nh thc hin vic truyn mt file gia mt my tnh vi mt my tnhkhc cng c gn trn mt mng cc cng vic sau y phi c thc hin:

My tnh cn truyn cn bit a ch ca my nhn. My tnh cn truyn phi xc nh c my tnh nhn sn sng nhn thng tin Chng trnh gi file trn my truyn cn xc nh c rng chng trnh nhn file trn

my nhn sn sng tip nhn file. Nu cu trc file trn hai my khng ging nhau th mt my phi lm nhim v chuyn

i file t dng ny sang dng kia. Khi truyn file my tnh truyn cn thng bo cho mng bit a ch ca my nhn cc

thng tin c mng a ti ch.

iu trn cho thy gia hai my tnh c mt s phi hp hot ng mc cao. By githay v chng ta xt c qu trnh trn nh l mt qu trnh chung th chng ta s chia qu trnh

trn ra thnh mt s cng on v mi cng on con hot ng mt cch c lp vi nhau. y chng trnh truyn nhn file ca mi my tnh c chia thnh ba module l: Moduletruyn v nhn File, Module truyn thng v Module tip cn mng. Hai module tng ng sthc hin vic trao i vi nhau trong :

Module truyn v nhn file cn c thc hin tt c cc nhim v trong cc ng dngtruyn nhn file. V d: truyn nhn thng s v file, truyn nhn cc mu tin ca file,thc hin chuyn i file sang cc dng khc nhau nu cn. Module truyn v nhn filekhng cn thit phi trc tip quan tm ti vic truyn d liu trn mng nh th no mnhim v c giao cho Module truyn thng.

Module truyn thng quan tm ti vic cc my tnh ang hot ng v sn sng trao i

thng tin vi nhau. N cn kim sot cc d liu sao cho nhng d liu ny c th traoi mt cch chnh xc v an ton gia hai my tnh. iu c ngha l phi truyn filetrn nguyn tc m bo an ton cho d liu, tuy nhin y c th c mt vi mc an ton khc nhau c dnh cho tng ng dng. y vic trao i d liu gia haimy tnh khng ph thuc vo bn cht ca mng ang lin kt chng. Nhng yu culin quan n mng c thc hin module th ba l module tip cn mng v numng thay i th ch c module tip cn mng b nh hng.

Module tip cn mng c xy dng lin quan n cc quy cch giao tip vi mng vph thuc vo bn cht ca mng. N m bo vic truyn d liu t my tnh ny nmy tnh khc trong mng.

Nh vy thay v xt c qu trnh truyn file vi nhiu yu cu khc nhau nh mt tin trnh phctp th chng ta c th xt qu trnh vi nhiu tin trnh con phn bit da trn vic trao i

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gia cc Module tng ng trong chng trnh truyn file. Cch ny cho php chng ta phntch k qu trnh file v d dng trong vic vit chng trnh.

Vic xt cc module mt cch c lp vi nhau nh vy cho php gim phc tp cho vic

thit k v ci t. Phng php ny c s dng rng ri trong vic xy dng mng v ccchng trnh truyn thng v c gi l phng php phn tng (layer).

Nguyn tc ca phng php phn tng l:

Mi h thng thnh phn trong mng c xy dng nh mt cu trc nhiu tng v uc cu trc ging nhau nh: s lng tng v chc nng ca mi tng.

Cc tng nm chng ln nhau, d liu c ch trao i trc tip gia hai tng k nhau ttng trn xung tng di v ngc li.

Cng vi vic xc nh chc nng ca mi tng chng ta phi xc nh mi quan h giahai tng k nhau. D liu c truyn i t tng cao nht ca h thng truyn ln lt

n tng thp nht sau truyn qua ng ni vt l di dng cc bit ti tng thp nhtca h thng nhn, sau d liu c truyn ngc ln ln lt n tng cao nht cah thng nhn.

Ch c hai tng thp nht c lin kt vt l vi nhau cn cc tng trn cng th t ch ccc lin kt logic vi nhau. Lin kt logic ca mt tng c thc hin thng qua cctng di v phi tun theo nhng quy nh cht ch, cc quy nh c gi giao thcca tng.

Hnh II-7 M hnh phn tng

II. Cc nhu cu v chun ha i vi mngTrong thc t vic phn chia cc tng nh trong m hnh trn thc s cha . Trn th gii hinc mt s c quan nh chun, h a ra hng lot chun v mng tuy cc chun c tnh chtkhuyn ngh ch khng bt buc nhng chng rt c cc c quan chun quc gia coi trng.

Hai trong s cc c quan chun quc t l:

ISO (The International Standards Organization) - L t chc tiu chun quc t hotng di s bo tr ca Lin hp Quc vi thnh vin l cc c quan chun quc giavi s lng khong hn 100 thnh vin vi mc ch h tr s pht trin cc chun trn

phm vi ton th gii. Mt trong nhng thnh tu ca ISO trong lnh vc truyn thng lm hnh h thng m (Open Systems Interconnection - gi tt l OSI).

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CCITT (Commit Consultatif International pour le Telegraphe et la Tlphone) -T chc t vn quc t v in tn v in thoi lm vic di s bo tr ca Lin HipQuc c tr s chnh ti Geneva - Thy s. Cc thnh vin ch yu l cc c quan buchnh vin thng cc quc gia. T chc ny c vai tr pht trin cc khuyn ngh trong

cc lnh vc vin thng.III. M hnh OSI (Open Systems Interconnection)

M hnh OSI l mt c s dnh cho vic chun ho cc h thng truyn thng, n c nghincu v xy dng bi ISO. Vic nghin cu v m hnh OSI c bt u ti ISO vo nm 1971vi mc tiu nhm ti vic ni kt cc sn phm ca cc hng sn xut khc nhau v phi hpcc hot ng chun ho trong cc lnh vc vin thng v h thng thng tin. Theo m hnh OSIchng trnh truyn thng c chia ra thnh 7 tng vi nhng chc nng phn bit cho tngtng. Hai tng ng mc khi lin kt vi nhau phi s dng mt giao thc chung.

Vic nghin cu v OSI c bt u ti ISO vo nm 1971 vi cc mc tiu nhm ni kt ccsn phm ca cc hng sn xut khc. u im chnh ca OSI l ch n ha hn gii php chovn truyn thng gia cc my tnh khng ging nhau. Hai h thng, d c khc nhau u cth truyn thng vi nhau mt cc hiu qu nu chng m bo nhng iu kin chung sau y:

Chng ci t cng mt tp cc chc nng truyn thng. Cc chc nng c t chc thnh cng mt tp cc tng. cc tng ng mc

phi cung cp cc chc nng nh nhau. Cc tng ng mc khi trao i vi nhau s dng chung mt giao thc

M hnh OSI tch cc mt khc nhau ca mt mng my tnh thnh by tng theo m hnh phn

tng. M hnh OSI l mt khung m cc tiu chun lp mng khc nhau c th khp vo. Mhnh OSI nh r cc mt no ca hot ng ca mng c th nhm n bi cc tiu chun mngkhc nhau. V vy, theo mt ngha no , m hnh OSI l mt loi tiu chun ca cc chun.

III.1. Nguyn tc s dng khi nh ngha cc tng h thng m

Sau y l cc nguyn tc m ISO quy nh dng trong qu trnh xy dng m hnh OSI

Khng nh ngha qu nhiu tng vic xc nh v ghp ni cc tng khngqu phc tp.

To cc ranh gii cc tng sao cho vic gii thch cc phc v v s cc tng tcqua li hai tng l nh nht. To cc tng ring bit cho cc chc nng khc bit nhau hon ton v k thut s

dng hoc qu trnh thc hin. Cc chc nng ging nhau c t trong cng mt tng. La chn ranh gii cc tng ti cc im m nhng th nghim trong qu kh

thnh cng. Cc chc nng c xc nh sao cho chng c th d dng xc nh li, v cc

nghi thc ca chng c th thay i trn mi hng. To ranh gii cc tng m cn c nhng mc tru tng khc nhau trong

vic s dng s liu. Cho php thay i cc chc nng hoc giao thc trong tng khng nh hng n

cc tng khc. To cc ranh gii gia mi tng vi tng trn v di n.

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III.2. Cc giao thc trong m hnh OSI

Trong m hnh OSI c hai loi giao thc chnh c p dng: giao thc c lin kt (connection -oriented) v giao thc khng lin kt (connectionless).

Giao thc c lin kt: trc khi truyn d liu hai tng ng mc cn thit lpmt lin kt logic v cc gi tin c trao i thng qua lin kt ny, vic c linkt logic s nng cao an ton trong truyn d liu.

Giao thc khng lin kt: trc khi truyn d liu khng thit lp lin kt logic vmi gi tin c truyn c lp vi cc gi tin trc hoc sau n.

Nh vy vi giao thc c lin kt, qu trnh truyn thng phi gm 3 giai on phn bit:

Thit lp lin kt (logic): hai thc th ng mc hai h thng thng lng vinhau v tp cc tham s s s dng trong giai on sau (truyn d liu).

Truyn d liu: d liu c truyn vi cc c ch kim sot v qun l km theo(nh kim sot li, kim sot lung d liu, ct/hp d liu...) tng cng tin cy v hiu qu ca vic truyn d liu.

Hy b lin kt (logic): gii phng ti nguyn h thng c cp pht cho linkt dng cho lin kt khc.

i vi giao thc khng lin kt th ch c duy nht mt giai on truyn d liu m thi.

Gi tin ca giao thc: Gi tin (Packet) c hiu nh l mt n v thng tin dng trong viclin lc, chuyn giao d liu trong mng my tnh. Nhng thng ip (message) trao i gia cc

my tnh trong mng, c to dng thnh cc gi tin my ngun. V nhng gi tin ny khich s c kt hp li thnh thng ip ban u. Mt gi tin c th cha ng cc yu cuphc v, cc thng tin iu khin v d liu.

Hnh II-8 Phng thc xc lp cc gi tin trong m hnh OSI

Trn quan im m hnh mng phn tng tng mi tng ch thc hin mt chc nng l nhn dliu t tng bn trn chuyn giao xung cho tng bn di v ngc li. Chc nng ny thc

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cht l gn thm v g b phn u (header) i vi cc gi tin trc khi chuyn n i. Ni cchkhc, tng gi tin bao gm phn u (header) v phn d liu. Khi i n mt tng mi gi tin sc ng thm mt phn u khc v c xem nh l gi tin ca tng mi, cng vic trntip din cho ti khi gi tin c truyn ln ng dy mng n bn nhn.

Ti bn nhn cc gi tin c g b phn u trn tng tng tng ng v y cng l nguyn lca bt c m hnh phn tng no.

Ch :Trong m hnh OSI phn kim li ca gi tin tng lin kt d liu t cui gi tin

III.3. Cc chc nng ch yu ca cc tng ca m hnh OSI.

III.3.1 Tng 1: Vt l (Physical)

Tng vt l (Physical layer) l tng di cng ca m hnh OSI l. N m t cc c trng vt lca mng: Cc loi cp c dng ni cc thit b, cc loi u ni c dng , cc dy cpc th di bao nhiu v.v... Mt khc cc tng vt l cung cp cc c trng in ca cc tn hiuc dng khi chuyn d liu trn cp t mt my ny n mt my khc ca mng, k thutni mch in, tc cp truyn dn.

Tng vt l khng qui nh mt ngha no cho cc tn hiu ngoi cc gi tr nh phn 0 v 1. cc tng cao hn ca m hnh OSI ngha ca cc bit c truyn tng vt l s c xcnh.

V d:Tiu chun Ethernet cho cp xon i 10 baseT nh r cc c trng in ca cp xoni, kch thc v dng ca cc u ni, di ti a ca cp.

Khc vi cc tng khc, tng vt l l khng c gi tin ring v do vy khng c phn u(header) cha thng tin iu khin, d liu c truyn i theo dng bit. Mt giao thc tng vtl tn ti gia cc tng vt l quy nh v phng thc truyn (ng b, phi ng b), tc truyn.

Cc giao thc c xy dng cho tng vt l c phn chia thnh phn chia thnh hai loi giaothc s dng phng thc truyn thng d b (asynchronous) v phng thc truyn thng ng

b (synchronous).

Phng thc truyn d b: Khng c mt tn hiu quy nh cho s ng b gia

cc bit gia my gi v my nhn, trong qu trnh gi tn hiu my gi s dng ccbit c bit START v STOP c dng tch cc xu bit biu din cc k t trongdng d liu cn truyn i. N cho php mt k t c truyn i bt k lc no mkhng cn quan tm n cc tn hiu ng b trc . Phng thc truyn ng b: S dng phng thc truyn cn c ng b giamy gi v my nhn, n chn cc k t c bit nh SYN (Synchronization), EOT(End Of Transmission) hay n gin hn, mt ci "c " (flag) gia cc d liu camy gi bo hiu cho my nhn bit c d liu ang n hoc n.

III.3.2 Tng 2: Lin kt d liu (Data link)

Tng lin kt d liu (data link layer) l tng m ngha c gn cho cc bt c truyntrn mng. Tng lin kt d liu phi quy nh c cc dng thc, kch thc, a ch my gi

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v nhn ca mi gi tin c gi i. N phi xc nh c ch truy nhp thng tin trn mng vphng tin gi mi gi tin sao cho n c a n cho ngi nhn nh.

Tng lin kt d liu c hai phng thc lin kt da trn cch kt ni cc my tnh, l

phng thc "mt im - mt im" v phng thc "mt im - nhiu im". Vi phng thc"mt im - mt im" cc ng truyn ring bit c thit lp ni cc cp my tnh li vinhau. Phng thc "mt im - nhiu im " tt c cc my phn chia chung mt ng truynvt l.

Hnh II-9 : Cc ng truyn kt ni kiu "mt im - mt im" v "mt im - nhiuim"

Tng lin kt d liu cng cung cp cch pht hin v sa li c bn m bo cho d liunhn c ging hon ton vi d liu gi i. Nu mt gi tin c li khng sa c, tng linkt d liu phi ch ra c cch thng bo cho ni gi bit gi tin c li n gi li.

Cc giao thc tng lin kt d liu chia lm 2 loi chnh l cc giao thc hng k t v cc giao

thc hng bit. Cc giao thc hng k t c xy dng da trn cc k t c bit ca mt bm chun no (nh ASCII hay EBCDIC), trong khi cc giao thc hng bit li dng cccu trc nh phn (xu bit) xy dng cc phn t ca giao thc (n v d liu, cc th tc.)v khi nhn, d liu s c tip nhn ln lt tng bit mt.

III.3.3 Tng 3: Mng (Network)

Tng mng (network layer) nhm n vic kt ni cc mng vi nhau bng cch tm ng(routing) cho cc gi tin t mt mng ny n mt mng khc. N xc nh vic chuyn hng,vch ng cc gi tin trong mng, cc gi ny c th phi i qua nhiu chng trc khi nc ch cui cng. N lun tm cc tuyn truyn thng khng tc nghn a cc gi tin n

ch.

Tng mng cung cc cc phng tin truyn cc gi tin qua mng, thm ch qua mt mngca mng (network of network). Bi vy n cn phi p ng vi nhiu kiu mng v nhiu kiudch v cung cp bi cc mng khc nhau. hai chc nng ch yu ca tng mng l chn ng(routing) v chuyn tip (relaying). Tng mng l quan trng nht khi lin kt hai loi mng khcnhau nh mng Ethernet vi mng Token Ring khi phi dng mt b tm ng (quy nh

bi tng mng) chuyn cc gi tin t mng ny sang mng khc v ngc li.

i vi mt mng chuyn mch gi (packet - switched network) - gm tp hp cc nt chuynmch gi ni vi nhau bi cc lin kt d liu. Cc gi d liu c truyn t mt h thng mti mt h thng m khc trn mng phi c chuyn qua mt chui cc nt. Mi nt nhn gid liu t mt ng vo (incoming link) ri chuyn tip n ti mt ng ra (outgoing link)

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hng n ch ca d liu. Nh vy mi nt trung gian n phi thc hin cc chc nng chnng v chuyn tip.

Vic chn ng l s la chn mt con ng truyn mt n v d liu (mt gi tin chng

hn) t trm ngun ti trm ch ca n. Mt k thut chn ng phi thc hin hai chc nngchnh sau y:

Quyt nh chn ng ti u da trn cc thng tin c v mng ti thi im thng qua nhng tiu chun ti u nht nh.

Cp nht cc thng tin v mng, tc l thng tin dng cho vic chn ng, trnmng lun c s thay i thng xuyn nn vic cp nht l vic cn thit.

Hnh II-10 M hnh chuyn vn cc gi tin trong mng chuyn mch gi

Ngi ta c hai phng thc p ng cho vic chn ng l phng thc x l tp trung v x

l ti ch.

Phng thc chn ng x l tp trungc c trng bi s tn ti ca mt(hoc vi) trung tm iu khin mng, chng thc hin vic lp ra cc bngng i ti tng thi im cho cc nt v sau gi cc bng chn ng titng nt dc theo con ng c chn . Thng tin tng th ca mng cndng cho vic chn ng ch cn cp nhp v c ct gi ti trung tm iukhin mng.

Phng thc chn ng x l ti chc c trng bi vic chn ng cthc hin ti mi nt ca mng. Trong tng thi im, mi nt phi duy tr ccthng tin ca mng v t xy dng bng chn ng cho mnh. Nh vy ccthng tin tng th ca mng cn dng cho vic chn ng cn cp nhp v cct gi ti mi nt.

Thng thng cc thng tin c o lng v s dng cho vic chn ng bao gm:

Trng thi ca ng truyn. Thi gian tr khi truyn trn mi ng dn. Mc lu thng trn mi ng. Cc ti nguyn kh dng ca mng.

Khi c s thay i trn mng (v d thay i v cu trc ca mng do s c ti mt vi nt, phchi ca mt nt mng, ni thm mt nt mi... hoc thay i v mc lu thng) cc thng tintrn cn c cp nht vo cc c s d liu v trng thi ca mng.

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Hin nay khi nhu cu truyn thng a phng tin (tch hp d liu vn bn, ho, hnh nh,m thanh) ngy cng pht trin i hi cc cng ngh truyn dn tc cao nn vic pht trincc h thng chn ng tc cao ang rt c quan tm.

III.3.4 Tng 4: Vn chuyn (Transport)Tng vn chuyn cung cp cc chc nng cn thit gia tng mng v cc tng trn. n l tngcao nht c lin quan n cc giao thc trao i d liu gia cc h thng m. N cng cc tngdi cung cp cho ngi s dng cc phc v vn chuyn.

Tng vn chuyn (transport layer) l tng c s m mt my tnh ca mng chia s thng tinvi mt my khc. Tng vn chuyn ng nht mi trm bng mt a ch duy nht v qun ls kt ni gia cc trm. Tng vn chuyn cng chia cc gi tin ln thnh cc gi tin nh hntrc khi gi i. Thng thng tng vn chuyn nh s cc gi tin v m bo chng chuyntheo ng th t.

Tng vn chuyn l tng cui cng chu trch nhim v mc an ton trong truyn d liu nngiao thc tng vn chuyn ph thuc rt nhiu vo bn cht ca tng mng. Ngi ta chia giaothc tng mng thnh cc loi sau:

Mng loi A: C t sut li v s c c bo hiu chp nhn c (tc l chtlng chp nhn c). Cc gi tin c gi thit l khng b mt. Tng vnchuyn khng cn cung cp cc dch v phc hi hoc sp xp th t li.

Mng loi B: C t sut li chp nhn c nhng t sut s c c bo hiu likhng chp nhn c. Tng giao vn phi c kh nng phc hi li khi xy ra sc.

Mng loi C: C t sut li khng chp nhn c (khng tin cy) hay l giaothc khng lin kt. Tng giao vn phi c kh nng phc hi li khi xy ra li vsp xp li th t cc gi tin.

Trn c s loi giao thc tng mng chng ta c 5 lp giao thc tng vn chuyn l:

Giao thc lp 0 (Simple Class - lp n gin): cung cp cc kh nng rt ngin thit lp lin kt, truyn d liu v hy b lin kt trn mng "c lin kt"loi A. N c kh nng pht hin v bo hiu cc li nhng khng c kh nng

phc hi.

Giao thc lp 1 (Basic Error Recovery Class - Lp phc hi li c bn) dng vicc loi mng B, y cc gi tin (TPDU) c nh s. Ngoi ra giao thc cnc kh nng bo nhn cho ni gi v truyn d liu khn. So vi giao thc lp 0giao thc lp 1 c thm kh nng phc hi li.

Giao thc lp 2 (Multiplexing Class - lp dn knh) l mt ci tin ca lp 0 chophp dn mt s lin kt chuyn vn vo mt lin kt mng duy nht, ng thic th kim sot lung d liu trnh tc nghn. Giao thc lp 2 khng c khnng pht hin v phc hi li. Do vy n cn t trn mt tng mng loi A.

Giao thc lp 3 (Error Recovery and Multiplexing Class - lp phc hi li cbn v dn knh) l s m rng giao thc lp 2 vi kh nng pht hin v phchi li, n cn t trn mt tng mng loi B.

Giao thc lp 4 (Error Detection and Recovery Class - Lp pht hin v phc hili) l lp c hu ht cc chc nng ca cc lp trc v cn b sung thm mt skh nng khc kim sot vic truyn d liu.

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III.3.5 Tng 5: Giao dch (Session)

Tng giao dch (session layer) thit lp "cc giao dch" gia cc trm trn mng, n t tn nhtqun cho mi thnh phn mun i thoi vi nhau v lp nh xa gia cc tn vi a ch ca

chng. Mt giao dch phi c thit lp trc khi d liu c truyn trn mng, tng giao dchm bo cho cc giao dch c thit lp v duy tr theo ng qui nh.

Tng giao dch cn cung cp cho ngi s dng cc chc nng cn thit qun tr cc giaodnh ng dng ca h, c th l:

iu phi vic trao i d liu gia cc ng dng bng cch thit lp v giiphng (mt cch lgic) cc phin (hay cn gi l cc hi thoi - dialogues)

Cung cp cc im ng b kim sot vic trao i d liu. p t cc qui tc cho cc tng tc gia cc ng dng ca ngi s dng. Cung cp c ch "ly lt" (nm quyn) trong qu trnh trao i d liu.

Trong trng hp mng l hai chiu lun phin th ny sinh vn : hai ngi s dng lun phinphi "ly lt" truyn d liu. Tng giao dch duy tr tng tc lun phin bng cch bo chomi ngi s dng khi n lt h c truyn d liu. Vn ng b ha trong tng giao dchcng c thc hin nh c ch kim tra/phc hi, dch v ny cho php ngi s dng xc nhcc im ng b ha trong dng d liu ang chuyn vn v khi cn thit c th khi phc vichi thoi bt u t mt trong cc im

mt thi im ch c mt ngi s dng quyn c bit c gi cc dch v nht nh catng giao dch, vic phn b cc quyn ny thng qua trao i th bi (token). V d: Ai c c

token s c quyn truyn d liu, v khi ngi gi token trao token cho ngi khc thi cng cngha trao quyn truyn d liu cho ngi .

Tng giao dch c cc hm c bn sau:

Give Token cho php ngi s dng chuyn mt token cho mt ngi s dngkhc ca mt lin kt giao dch.

Please Token cho php mt ngi s dng cha c token c th yu cu token . Give Controldng chuyn tt c cc token t mt ngi s dng sang mt

ngi s dng khc.

III.3.6 Tng 6: Trnh by (Presentation)

Trong giao tip gia cc ng dng thng qua mng vi cng mt d liu c th c nhiu cchbiu din khc nhau. Thng thng dng biu din dng bi ng dng ngun v dng biu dindng bi ng dng ch c th khc nhau do cc ng dng c chy trn cc h thng honton khc nhau (nh h my Intel v h my Motorola). Tng trnh by (Presentation layer) phichu trch nhim chuyn i d liu gi i trn mng t mt loi biu din ny sang mt loikhc. t c iu n cung cp mt dng biu din chung dng truyn thng v cho

php chuyn i t dng biu din cc b sang biu din chung v ngc li.

Tng trnh by cng c th c dng k thut m ha xo trn cc d liu trc khi c

truyn i v gii m u n bo mt. Ngoi ra tng biu din cng c th dng cc k thutnn sao cho ch cn mt t byte d liu th hin thng tin khi n c truyn trn mng, u nhn, tng trnh by bung tr li c d liu ban u.

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III.3.7 Tng 7: ng dng (Application)

Tng ng dng (Application layer) l tng cao nht ca m hnh OSI, n xc nh giao din giangi s dng v mi trng OSI v gii quyt cc k thut m cc chng trnh ng dng dng

giao tip vi mng. cung cp phng tin truy nhp mi trng OSI cho cc tin trnh ng dng, Ngi ta thitlp cc thc th ng dng (AE), cc thc th ng dng s gi n cc phn t dch v ng dng(Application Service Element - vit tt l ASE) ca chng. Mi thc th ng dng c th gmmt hoc nhiu cc phn t dch v ng dng. Cc phn t dch v ng dng c phi hptrong mi trng ca thc th ng dng thng qua cc lin kt (association) gi l i tng linkt n (Single Association Object - vit tt l SAO). SAO iu khin vic truyn thng trongsut vng i ca lin kt cho php tun t ha cc s kin n t cc ASE thnh t ca n.

IV. Qu trnh chuyn vn gi tin

IV.1. Qu trnh ng gi d liu (ti my gi)

ng gi d liu l qu trnh t d liu nhn c vo sau header (v trc trailer) trn milp. Lp Physical khng ng gi d liu v n khng dng header v trailer. Vic ng gi dliu khng nht thit phi xy ra trong mi ln truyn d liu ca trnh ng dng. Cc lp 5, 6, 7s dng header trong qu trnh khi ng, nhng trong phn ln cc ln truyn th khng cheader ca lp 5, 6, 7 l do l khng c thng tin mi trao i.

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Hnh II-11 B sung phn u thng ip & tn d liu s dng

Cc d liu ti my gi c x l theo trnh t nh sau:

- Ngi dng thng qua lp Application a cc thng tin vo my tnh. Cc thng tin ny cnhiu dng khc nhau nh: hnh nh, m thanh, vn bn

- Tip theo cc thng tin c chuyn xung lp Presentation chuyn thnh dng chung,ri m ho v nn d liu.

- Tip d liu c chuyn xung lp Session b sung cc thng tin v phin giao dchny.

- D liu tip tc c chuyn xung lp Transport, ti lp ny d liu c ct ra thnh nhiuSegment v b sung thm cc thng tin v phng thc vn chuyn d liu m bo tincy khi truyn.

- D liu tip tc c chuyn xung lp Network, ti lp ny mi Segment c ct ra thnhnhiu Packet v b sung thm cc thng tin nh tuyn.

- Tip d liu c chuyn xung lp Data Link, ti lp ny mi Packet s c ct ra thnhnhiu Frame v b sung thm cc thng tin kim tra gi tin ( kim tra ni nhn).

- Cui cng, mi Frame s c tng Vt L chuyn thnh mt chui cc bit, v c y lncc phng tin truyn dn truyn n cc thit b khc.

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IV.2. Qu trnh truyn d liu t my gi n my nhn.

Bc 1: Trnh ng dng (trn my gi) to ra d liu v cc chng trnh phn cng, phn mmci t mi lp s b sung vo header v trailer (qu trnh ng gi d liu ti my gi).

Bc 2: Lp Physical (trn my gi) pht sinh tn hiu ln mi trng truyn ti truyn dliu.

Bc 3: Lp Physical (trn my nhn) nhn d liu.

Bc 4: Cc chng trnh phn cng, phn mm (trn my nhn) g b header v trailer v xl phn d liu (qu trnh x l d liu ti my nhn).

Gia bc 1 v bc 2 l qu trnh tm ng i ca gi tin. Thng thng, my gi bit ach IP ca my nhn. V th, sau khi xc nh c a ch IP ca my nhn th lp Network camy gi s so snh a ch IP ca my nhn v a ch IP ca chnh n:

- Nu cng a ch mng th my gi s tm trong bng MAC Table ca mnh c c a chMAC ca my nhn. Trong trng hp khng c c a ch MAC tng ng, n s thc hingiao thc ARP truy tm a ch MAC. Sau khi tm c a ch MAC, n s lu a ch MACny vo trong bng MAC Table lp Datalink s dng cc ln gi sau. Sau khi c a chMAC th my gi s gi gi tin i.

- Nu khc a ch mng th my gi s kim tra xem my c c khai bo Default Gatewayhay khng.

+ Nu c khai bo Default Gateway th my gi s gi gi tin thng qua Default Gateway.

+ Nu khng c khai bo Default Gateway th my gi s loi b gi tin v thng bo"Destination host Unreachable"

IV.3. Chi tit qu trnh x l ti my nhn

Bc 1: Lp Physical kim tra qu trnh ng b bit v t chui bit nhn c vo vng m.Sau thng bo cho lp Data Link d liu c nhn.

Bc 2: Lp Data Link kim li frame bng cch kim tra FCS trong trailer. Nu c li th frameb b.

Sau kim tra a ch lp Data Link (a ch MAC) xem c trng vi a ch my nhn haykhng. Nu ng th phn d liu sau khi loi header v trailer s c chuyn ln cho lp

Network.

Bc 3: a ch lp Network c kim tra xem c phi l a ch my nhn hay khng (a chIP) ? Nu ng th d liu c chuyn ln cho lp Transport x l.

Bc 4: Nu giao thc lp Transport c h tr vic phc hi li th s nh danh phn on cx l. Cc thng tin ACK, NAK (gi tin ACK, NAK dng phn hi v vic cc gi tin c gi n my nhn cha) cng c x l lp ny. Sau qu trnh phc hi li v sp tht cc phn on, d liu c a ln lp Session.

Bc 5: Lp Session m bo mt chui cc thng ip trn vn. Sau khi cc lung hontt, lp Session chuyn d liu sau header lp 5 ln cho lp Presentation x l.

Bc 6: D liu s c lp Presentation x l bng cch chuyn i dng thc d liu. Sau kt qu chuyn ln cho lp Application.

Bc 7: Lp Application x l header cui cng. Header ny cha cc tham s tho thun giahai trnh ng dng. Do vy tham s ny thng ch c trao i lc khi ng qu trnh truynthng gia hai trnh ng dng.

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V. Phng thc truyn tn hiu

Thng thng c hai phng thc truyn tn hiu trong mng cc b l dng bng tn c s(baseband) v bng tn rng (broadband). S khc nhau ch yu gia hai phng thc truyn tn

hiu ny l bng tng c s ch chp nhn mt knh d liu duy nht trong khi bng rng c thchp nhn ng thi hai hoc nhiu knh truyn thng cng phn chia gii thng ca ngtruyn.

Hu ht cc mng cc b s dng phng thc bng tn c s. Vi phng thc truyn tn hiuny ny tn hiu c th c truyn i di c hai dng: tng t (analog) hoc s (digital).Phng thc truyn bng tn rng chia gii thng (tn s) ca ng truyn thnh nhiu gii tncon trong mi di tn con cung cp mt knh truyn d liu tch bit nh s dng mt cpmodem c bit gi l b gii / iu bin RF cai qun vic bin i cc tn hiu s thnh tn hiutng t c tn s v tuyn (RF) bng k thut ghp knh.

VI. M hnh TCP/IPVI.1. Tng quan v b giao thc TCP/IP

TCP/IP l b giao thc cho php kt ni cc h thng mng khng ng nht vi nhau.Ngy nay, TCP/IP c s dng rng ri trong cc mng cc b cng nh trn mngInternet ton cu.

TCP/IP c xem l gin lc ca m hnh tham chiu OSI vi bn tng nh sau:

Tng lin kt mng (Network Access Layer)

Tng Internet (Internet Layer)

Tng giao vn (Host-to-Host Transport Layer) Tng ng dng (Application Layer)

Hnh II-12 : Kin trc TCP/IP

Tng lin kt:

Tng lin kt (cn c gi l tng lin kt d liu hay l tng giao tip mng) l tngthp nht trong m hnh TCP/IP, bao gm cc thit b giao tip mng v chngtrnh cung cp cc thng tin cn thit c th hot ng, truy nhp ng truyn vt lqua thit b giao tip mng .

Tng Internet:

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Tng Internet (cn gi l tng mng) x l qua trnh truyn gi tin trn mng. Cc giaothc ca tng ny bao gm: IP (Internet Protocol), ICMP (Internet ControlMessage Protocol), IGMP (Internet Group Messages Protocol).

Tng giao vn:

Tng giao vn ph trch lung d liu gia hai trm thc hin cc ng dng ca tngtrn. Tng ny c hai giao thc chnh: TCP (Transmission Control Protocol) v UDP(User Datagram Protocol)

TCP cung cp mt lung d liu tin cy gia hai trm, n s dng cc c ch nh chianh cc gi tin ca tng trn thnh cc gi tin c kch thc thch hp cho tng mng bndi, bo nhn gi tin,t hn ch thi gian time-out m bo bn nhn bit c ccgi tin gi i. Do tng ny m bo tnh tin cy, tng trn s khng cn quan tm nna.

UDP cung cp mt dch v n gin hn cho tng ng dng. N ch gi cc gi d liu

t trm ny ti trm kia m khng m bo cc gi tin n c ti ch. Cc c ch mbo tin cy cn c thc hin bi tng trn.

Tng ng dng:

Tng ng dng l tng trn cng ca m hnh TCP/IP bao gm cc tin trnh v cc ngdng cung cp cho ngi s dng truy cp mng. C rt nhiu ng dng ccung cp trong tng ny, m ph bin l: Telnet: s dng trong vic truy cp mng txa, FTP (File Transfer Protocol): dch v truyn tp, Email: dch v th tn in t,WWW (World Wide Web).

Hnh II-13: Qu trnh ng/m gi d liu trong TCP/IP

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Cng tng t nh trong m hnh OSI, khi truyn d liu, qu trnh tin hnh t tngtrn xung tng di, qua mi tng d liu c thm vo mt thng tin iu khin cgi l phn header. Khi nhn d liu th qu trnh xy ra ngc li, d liu c truyn ttng di ln v qua mi tng th phn header tng ng c ly i v khi n tng trn

cng th d liu khng cn phn header na. Hnh v sau cho ta thy lc d liu quacc tng. Trong hnh v ny ta thy ti cc tng khc nhau d liu c mang nhngthut ng khc nhau:

Trong tng ng dng d liu l cc lung c gi l stream.

Trong tng giao vn, n v d liu m TCP gi xung tng di gi l TCP segment.

Trong tng mng, d liu m IP gi ti tng di c gi l IP datagram.

Trong tng lin kt, d liu c truyn i gi l frame.

Hnh II-14: Cu trc d liu trong TCP/IP

VI.2. So snh TCP/IP vi OSI

Mi tng trong TCP/IP c th l mt hay nhiu tng ca OSI.

Bng sau ch r mi tng quan gia cc tng trong m hnh TCP/IP vi OSI

OSI TCP/IP

Physical Layer v Data link Layer Data link Layer

Network Layer Internet Layer Transport Layer Transport Layer

Session Layer, Presentation Layer,

Application Layer

Application Layer

S khc nhau gia TCP/IP v OSI ch l:

Tng ng dng trong m hnh TCP/IP bao gm lun c 3 tng trn ca m hnh OSI

Tng giao vn trong m hnh TCP/IP khng phi lun m bo tin cy ca victruyn tin nh trong tng giao vn ca m hnh OSI m cho php thm mt

la chn khc l UDP

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VII. Cc giao thc truy cp ng truyn trn mng LAN

truyn c d liu trn mng ngi ta phi c cc th tc nhm hng dn cc my tnh camng lm th no v lc no c th thm nhp vo ng dy cp gi cc gi d kin. V d

nh i vi cc dng bus v ring th ch c mt ng truyn duy nht ni cc trm vi nhau,cho nn cn phi c cc quy tc chung cho tt c cc trm ni vo mng m bo rng ngtruyn c truy nhp v s dng mt cch hp l.

C nhiu giao thc khc nhau truy nhp ng truyn vt l nhng phn thnh hai loi: ccgiao thc truy nhp ngu nhin v cc giao thc truy nhp c iu khin.

VII.1.Giao thc chuyn mch (yu cu v chp nhn)

Giao thc chuyn mch l loi giao thc hot ng theo cch thc sau: mt my tnh ca mngkhi cn c th pht tn hiu thm nhp vo mng, nu vo lc ny ng cp khng bn th mch

iu khin s cho trm ny thm nhp vo ng cp cn nu ng cp ang bn, ngha l angc giao lu gia cc trm khc, th vic thm nhp s b t chi.

VII.2.Giao thc ng dy a truy cp vi cm nhn va chm

Giao thc ng dy a truy cp (Carrier Sense Multiple Access with Collision Detection hayCSMA/CD ) cho php nhiu trm thm nhp cng mt lc vo mng, giao thc ny thng dngtrong s mng dng ng thng. Mi trm u c th c truy nhp vo ng dy chungmt cch ngu nhin v do vy c th dn n xung t (hai hoc nhiu trm ng thi cngtruyn d liu). Cc trm phi kim tra ng truyn gi d liu i qua c phi ca n haykhng. Khi mt trm mun truyn d liu n phi kim tra ng truyn xem c rnh hay khng gi gi d liu ca, nu ng truyn ang bn trm phi ch i ch c truyn khi thyng truyn rnh. Nu cng mt lc c hai trm cng s dng ng truyn th giao thc phi

pht hin iu ny v cc trm phi ngng thm nhp, ch i ln sau cc thi gian ngu nhinkhc nhau.

Khi ng cp ang bn trm phi ch i theo mt trong ba phng thc sau:

Trm tm ch i mt thi gian ngu nhin no ri li bt u kim tra ng truyn. Trm tip tc kim tra ng truyn n khi ng truyn rnh th truyn d liu i. Trm tip tc kim tra ng truynn khi ng truyn rnh th truyn d liu i vi

xc sut p xc nh trc (0 < p < 1).

Ti y phng thc 1 c hiu qu trong vic trnh xung t v hai trm cn truyn khi thyng truyn bn s cng rt lui v ch i trong cc thi gian ngu nhin khc nhau. Ngc li

phng thc 2 c gng gim thi gian trng ca ng truyn bng cc cho php trm c thtruyn ngay sau khi mt cuc truyn kt thc song nu lc c thm mt trm khc ang ith kh nng xy ra xung t l rt cao. Phng thc 3 vi gi tr p phi la chn hp l c thti thiu ha c kh nng xung t ln thi gian trng ca ng truyn.

Khi lu lng cc gi d liu cn di chuyn trn mng qu cao, th vic ng c th xy ravi s lng ln c gy tc nghn ng truyn dn n lm chm tc truyn tin ca h

thng.

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VII.3.Giao thc dng th bi vng (Token ring)

y l giao thc truy nhp c iu khin ch yu dng k thut chuyn th bi (token) cppht quyn truy nhp ng truyn tc l quyn c truyn d liu i. Th bi ay l mt n

v d liu c bit, c kch thc v ni dung (gm cc thng tin iu khin) c quy nhring cho mi giao thc. Theo giao thc dng th bi vng trong ng cp lin tc c mt thbi chy quanh trong mng Th bi l mt n v d liu c bit trong c mt bit biu dintrng thi s dng ca n (bn hoc ri). Mt trm mun truyn d liu th phi i n khi nhnc mt th bi rnh. Khi trm s i bit trng thi ca th bi thnh bn, np gi d liu ckm theo a ch ni nhn vo th bi v truyn i theo chiu ca vng.

V th bi chy vng quang trong mng kn v ch c mt th nn vic ng d liu khng thxy ra, do vy hiu sut truyn d liu ca mng khng thay i.

Trong cc giao thc ny cn gii quyt hai vn c th dn n ph v h thng. Mt l vic

mt th bi lm cho trn vng khng cn th bi lu chuyn na. Hai l mt th bi bn luchuyn khng dng trn vng.

VII.4.Giao thc dng th bi cho dng ng thng (Token bus)

y l giao thc truy nhp c iu khin trong cp pht quyn truy nhp ng truyn chocc trm ang c nhu cu truyn d liu, mt th bi c lu chuyn trn mt vng logic thitlp bi cc trm . Khi mt trm c th bi th n c quyn s dng ng truyn trong mtthi gian xc nh trc. Khi ht d liu hoc ht thi on cho php, trm chuyn th bi ntrm tip theo trong vng logic.

Nh vy trong mng phi thit lp c vng logic (hay cn gi l vng o) bao gm cc trmang hot ng ni trong mng c xc nh v tr theo mt chui th t m trm cui cng cachui s tip lin sau bi trm u tin. Mi trm c bit a ch ca cc trm k trc v saun trong th t ca cc trm trn vng logic c th c lp vi th t vt l. Cng vi victhit lp vng th giao thc phi lun lun theo di s thay i theo trng thi thc t ca mng.

VIII. Cc phng tin kt ni mng lin khu vc (WAN)

Bn cnh phng php s dng ng in thoi thu bao kt ni cc mng cc b hocmng khu vc vi nhau hoc kt ni vo Internet, c mt s phng php khc:

ng thu bao (leased line). y l phng php c nht, l phng php truynthng nht cho s ni kt vnh cu. Bn thu ng dy t cng ty in thoi (trc tiphoc qua nh cung cp dch v). Bn cn phi ci t mt "Chanel Service Unit"(CSU) ni n mng T, v mt "Digital Service Unit" (DSU) ni n mng ch(primary) hoc giao din mng.

ISDN (Integrated Service Digital Nework). S dng ng in thoi s thay v ngtng t. Do ISDN l mng dng tn hiu s, bn khng phi dng mt modem nivi ng dy m thay vo bn phi dng mt thit b gi l "codec" vi modem ckh nng chy 14.4 kbit/s. ISDN thch hp cho c hai trng hp c nhn v t chc.Cc t chc c th quan tm hn n ISDN c kh nng cao hn ("primary" ISDN)

vi tc tng cng bng tc 1.544 Mbit/s ca ng T1. Cc ph khi s dngISDN c tnh theo thi gian, mt s trng hp tnh theo lng d liu c truyni v mt s th tnh theo c hai.

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CATV link. Cng ty dn cp trong khu vc ca bn c th cho bn thu mt "ch" trnng cp ca h vi gi hp dn hn vi ng in thoi. Cn phi bit nhng thit

b g cn cho h thng ca mnh v rng ca di m bn s c cung cp l baonhiu. Cng nh vic ng gp chi ph vi nhng khch hng khc cho knh lin lc

l nh th no. Mt dng k l hn c a ra vi tn gi l mng "lai" ("hybrid"Network), vi mt knh CATV c s dng lu thng theo mt hng v mtng ISDN hoc gi s s dng cho ng tr li. Nu mun cung cp thng tin trnInternet, bn phi xc nh chc chn rng "knh ngc" ca bn kh nng phc vcho nhu cu thng tin ca khch hng ca bn.

Frame relay. Frame relay "uyn chuyn" hn ng thu bao. Khch hng thu ngFrame relay c th mua mt dch v c mc xc nh - mt "tc thng tin uthc" ("Committed Information Rale" - CIR). Nu nh nhu cu ca bn trn mng lrt "bt pht" (burty), hay ngi s dng ca bn c nhu cu cao trn ng lin lctrong sut mt khong thi gian xc nh trong ngy, v c t hoc khng c nhu cuvo ban m - Frame relay c th s kinh t hn l thu hon ton mt ng T1 (hoc

T3). Nh cung cp dch v ca bn c th a ra mt phng php tng t nh lphng php thay th l Switched Multimegabit Data Service.Ch truyn khng ng b (Asynchoronous Trangfer Mode - ATM). ATM l mt

phng php tng i mi u tin bo hiu cng mt k thut cho mng cc b vlin khu vc. ATM thch hp cho real-time multimedia song song vi truyn d liutruyn thng. ATM ha hn s tr thnh mt phn ln ca mng tng lai.

ng vi sng (Microware links). Nu cn kt ni vnh vin n nh cung cp dch vnhng li thy rng ng thu bao hay nhng la chn khc l qu t, bn s thymicroware nh l mt la chn thch hp. Bn khng cn tr qu t cho cch ny camicroware, tuy nhin bn cn phi u t nhiu tin hn vo lc u, v bn s gpmt s ri ro nh tc truyn n mng ca bn qu nhanh.

ng v tinh (satellite links). Nu bn mun c chuyn mt lng ln d liu cbit l t nhng a im t xa th ng v tinh l cu tr li. Tm hot ng canhng v tinh cng v tr a l vi tri t cng to ra mt s chm tr (hoc "b chedu") m nhng ngi s dng Telnet c th cm nhn c.

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Chng III a ch IP

I. Giao thc TCP/IP

Giao thc TCP/IP c pht trin t mng ARPANET v Internet v c dng nh giao

thc mng v vn chuyn trn mng Internet. TCP (Transmission Control Protocol) lgiao thc thuc tng vn chuyn v IP (Internet Protocol) l giao thc thuc tng mngca m hnh OSI. H giao thc TCP/IP hin nay l giao thc c s dng rng ri nht lin kt cc my tnh v cc mng.

Hin nay cc my tnh ca hu ht cc mng c th s dng giao thc TCP/IP lin ktvi nhau thng qua nhiu h thng mng vi k thut khc nhau. Giao thc TCP/IP thccht l mt h giao thc cho php cc h thng mng cng lm vic vi nhau thng quavic cung cp phng tin truyn thng lin mng.

II. a ch IP

II.1. Tng qutNhim v chnh ca giao thc IP l cung cp kh nng kt ni cc mng con thnh linkt mng truyn d liu, vai tr ca IP l vai tr ca giao thc tng mng trong mhnh OSI. Giao thc IP l mt giao thc kiu khng lin kt (connectionlees) c ngha lkhng cn c giai on thit lp lin kt trc khi truyn d liu.

S a ch ha nh danh cc trm (host) trong lin mng c gi l a ch IP 32bits (32 bit IP address). Mi giao din trong 1 my c h tr giao thc IP u phi cgn 1 a ch IP (mt my tnh c th gn vi nhiu mng do vy c th c nhiu a chIP). a ch IP gm 2 phn: a ch mng (netid) v a ch my (hostid). Mi a ch IPc di 32 bits c tch thnh 4 vng (mi vng 1 byte), c th biu th di dng

thp phn, bt phn, thp lc phn hay nh phn. Cch vit ph bin nht l dng k phpthp phn c du chm (dotted decimal notation) tch cc vng. Mc ch ca a chIP l nh danh duy nht cho mt my tnh bt k trn lin mng.

Do t chc v ln ca cc mng con (subnet) ca lin mng c th khc nhau, ngita chia cc a ch IP thnh 5 lp, k hiu l A, B, C, D v E. Trong lp A, B, C cha ach c th gn c. Lp D dnh ring cho lp k thut multicasting. Lp E c dnhnhng ng dng trong tng lai.

Netid trong a ch mng dng nhn dng tng mng ring bit. Cc mng lin ktphi c a ch mng (netid) ring cho mi mng. y cc bit u tin ca byte u tinc dng nh danh lp a ch (0 - lp A, 10 - lp B, 110 - lp C, 1110 - lp D v

11110 - lp E).

y ta xt cu trc ca cc lp a ch c th gn c l lp A, lp B, lp C.

II.2. Cu trc ca cc a ch IP

Mng lp A: a ch mng (netid) l 1 Byte v a ch host (hostid) l 3 byte. Mng lp B: a ch mng (netid) l 2 Byte v a ch host (hostid) l 2 byte. Mng lp C: a ch mng (netid) l 3 Byte v a ch host (hostid) l 1 byte.

Lp A cho php nh danh ti 126 mng, vi ti a 16 triu host trn mi mng. Lp ny

c dng cho cc mng c s trm cc ln.Lp B cho php nh danh ti 16384 mng, vi ti a 65534 host trn mi mng.

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Lp C cho php nh danh ti 2 triu mng, vi ti a 254 host trn mi mng. Lp nyc dng cho cc mng c t trm.

Hnh III-15: Cu trc cc lp a ch IP

Mt s a ch c tnh cht c bit: Mt a ch c hostid = 0 c dng hng timng nh danh bi vng netid. Ngc li, mt a ch c vng hostid gm ton s 1

c dng hng ti tt c cc host ni vo mng netid, v nu vng netid cng gmton s 1 th n hng ti tt c cc host trong lin mng

Hnh III-16: V d cu trc cc lp a ch IP

Cn lu rng cc a ch IP c dng nh danh cc host v mng tng mng cam hnh OSI, v chng khng phi l cc a ch vt l (hay a ch MAC) ca cc trmtrn mt mng cc b (Ethernet, Token Ring.).

Trong nhiu trng hp, mt mng c th c chia thnh nhiu mng con (subnet), lc

c th a thm cc vng subnetid nh danh cc mng con. Vng subnetid cly t vng hostid, c th i vi lp A, B, C nh v d sau:

Hnh III-17: V d a ch khi b sung vng subnetid

n v d liu dng trong IP c gi l gi tin (datagram), c khun dng

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Hnh III-18: Dng thc ca gi tin IP

ngha ca thng s nh sau:

VER (4 bits): ch version hin hnh ca giao thc IP hin c ci t, Vic c ch sversion cho php c cc trao i gia cc h thng s dng version c v h thng s

dng version mi.

IHL (4 bits): ch di phn u (Internet header Length) ca gi tin datagram, tnh theon v t ( 32 bits). Trng ny bt but phi c v phn u IP c th c di thay ity . di ti thiu l 5 t (20 bytes), di ti a l 15 t hay l 60 bytes.

Type of service (8 bits): c t cc tham s v dch v nhm thng bo cho mng bit dchv no m gi tin mun c s dng, chng hn u tin, thi hn chm tr, nng suttruyn v tin cy. Hnh sau cho bit ngh ca trng 8 bits ny.

Precedence (3 bit): ch th v quyn u tin gi datagram, n c gi tr t 0 (gi tin bnhthng) n 7 (gi tin kim sot mng).

D (Delay) (1 bit): ch tr yu cu trong

D = 0 gi tin c tr bnh thng

D = 1 gi tin tr thp

T (Throughput) (1 bit): ch thng lng yu cu s dng truyn gi tin vi la chntruyn trn ng thng sut thp hay ng thng sut cao.

T = 0 thng lng bnh thng v

T = 1 thng lng cao

R (Reliability) (1 bit): ch tin cy yu cu

R = 0 tin cy bnh thng

R = 1 tin cy cao

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Total Length (16 bits): ch di ton b gi tin, k c phn u tnh theo n v byte vichiu di ti a l 65535 bytes. Hin nay gii hn trn l rt ln nhng trong tng laivi nhng mng Gigabit th cc gi tin c kch thc ln l cn thit.

Identification (16 bits): cng vi cc tham s khc (nh Source Address v DestinationAddress) tham s ny dng nh danh duy nht cho mt datagram trong khong thigian n vn cn trn lin mng.

Flags (3 bits): lin quan n s phn on (fragment) cc datagram, Cc gi tin khi i trnng i c th b phn thnh nhiu gi tin nh, trong trng hp b phn on thtrng Flags c dng iu khin phn on v ti lp ghp b d liu. Ty theo gi trca Flags s c ngha l gi tin s khng phn on, c th phn on hay l gi tin

phn on cui cng. Trng Fragment Offsetcho bit v tr d liu thuc phn ontng ng vi on bt u ca gi d liu gc. ngha c th ca trng Flags l:

bit 0: reserved - cha s dng, lun ly gi tr 0.

bit 1: (DF) = 0 (May Fragment) = 1 (Don't Fragment)

bit 2: (MF) = 0 (Last Fragment) = 1 (More Fragments)

Fragment Offset (13 bits): ch v tr ca on (fragment) trong datagram tnh theo n v

8 bytes, c ngha l phn d liu mi gi tin (tr gi tin cui cng) phi cha mt vngd liu c di l bi s ca 8 bytes. iu ny c ngha l phi nhn gi tr caFragment offset vi 8 tnh ra lch byte.

Time to Live (8 bits): qui nh thi gian tn ti (tnh bng giy) ca gi tin trong mng trnh tnh trng mt gi tin b qun trn mng. Thi gian ny c cho bi trm gi vc gim i (thng qui c l 1 n v) khi datagram i qua mi router ca lin mng.Thi lng ny gim xung ti mi router vi mc ch gii hn thi gian tn ti ca ccgi tin v kt thc nhng ln lp li v hn trn mng. Sau y l 1 s iu cn lu vtrng Time To Live:

Nt trung gian ca mng khng c gi 1 gi tin m trng ny c gi tr= 0.

Mt giao thc c th n nh Time To Live thc hin cuc ra tm ti nguyntrn mng trong phm vi m rng.

Mt gi tr c nh ti thiu phi ln cho mng hot ng tt.

Protocol (8 bits): ch giao thc tng trn k tip s nhn vng d liu trm ch (hin tithng l TCP hoc UDP c ci t trn IP). V d: TCP c gi tr trng Protocol l6, UDP c gi tr trng Protocol l 17

Header Checksum (16 bits): M kim sot li ca header gi tin IP.

Source Address (32 bits): a ch ca my ngun.

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Destination Address (32 bits): a ch ca my ch

Options ( di thay i): khai bo cc la chn do ngi gi yu cu (tu theo tngchng trnh).

Padding ( di thay i): Vng m, c dng m bo cho phn header lun ktthc mt mc 32 bits.

Data ( di thay i): Trn mt mng cc b nh vy, hai trm ch c th lin lc vinhau nu chng bit a ch vt l ca nhau. Nh vy vn t ra l phi thc hin nhx gia a ch IP (32 bits) v a ch vt l (48 bits) ca mt trm.

III. Mt s khi nim v thut ng lin quan

a ch mng (Network Address): l a ch IP m gi tr ca tt c cc bits phn

nhn dng my tnh u l 0, c s dng xc nh mt mng.V d : 10.0.0.0; 172.18.0.0 ; 192.1.1.0

a ch qung b (Broadcast Address) : L a ch IP m gi tr ca tt c cc bits phn nhn dng my tnh u l 1, c s dng ch tt c cc my tnh trong mng.

V d : 10.255.255.255, 172.18.255.255, 192.1.1.255

Mt n mng chun (Netmask) : L a ch IP m gi tr ca cc bits phn nhn dngmng u l 1, cc bits phn nhn dng my tnh u l 0. Nh vy ta c 3 mt n mng

tng ng cho 3 lp mng A, B v C l :- Mt n mng lp A : 255.0.0.0

- Mt n mng lp B : 255.255.0.0

- Mt n mng lp C : 255.255.255.0 Ta gi chng l cc mt n mng mc nh (Default Netmask)

Lu : a ch mng, a ch qung b, mt n mng khng c dng t a ch chocc my tnh

a ch mng 127.0.0.0 l a ch c dnh ring t trong phm vi mt my tnh. Nch c gi tr cc b ( trong phm vi mt my tnh). Thng thng khi ci t giao thc IP thmy tnh s c gin a ch 127.0.0.1. a ch ny thng thng kim tra xem giao thcIP trn my hin ti c hot ng khng. a ch dnh ring cho mng cc b khng ni kt trc tip Internet: Cc mng cc

b khng ni kt trc tip vo mng Internet c th s dng cc a ch mng sau nh ach cho cc my tnh trong mng ca mnh :0 - Lp A : 10.0.0.01 - Lp B : 172.16.0.0 n 172.32.0.02 - Lp C : 192.168.0.03 ngha ca Netmask

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Vi mt a ch IP v mt Netmask cho trc, ta c th dng php ton AND BIT tnhra c a ch mng m a ch IP ny thuc v. Cng thc nh sau :

Network Address = IP Address & Netmask

V d : Cho a ch IP = 198.53.147.45 v Netmask = 255.255.255.0. Ta thc hin phpton AND BIT (&) hai a ch trn:

Biu din thp phn Biu din nh phn

IP Address 198.53.147.45 11000110 00110101 10010011 00101101

Netmask 255.255.255.0 11111111 11111111 11111111 00000000

Network Address 198.53.147.0 11000110 00110101 10010011 00000000

III.1. Cc giao thc trong mng IP

mng vi giao thc IP hot ng c tt ngi ta cn mt s giao thc b sung, ccgiao thc ny u khng phi l b phn ca giao thc IP v giao thc IP s dng nchng khi cn.

Giao thc ARP (Address Resolution Protocol): y cn lu rng cc a ch IP cdng nh danh cc host v mng tng mng ca m hnh OSI, v chng khng phil cc a ch vt l (hay a ch MAC) ca cc trm trn mt mng cc b (Ethernet,Token Ring.). Trn mt mng cc b hai trm ch c th lin lc vi nhau nu chng bita ch vt l ca nhau. Nh vy vn t ra l phi tm c nh x gia a ch IP (32

bits) v a ch vt l ca mt trm. Giao thc ARP c xy dng tm a ch vtl t a ch IP khi cn thit.

Giao thc RARP (Reverse Address Resolution Protocol): L giao thc ngc vigiaothc ARP. Giao thc RARP c dng tm a ch IP t a ch vt l.

Giao thc ICMP (Internet Control Message Protocol): Giao thc ny thc hin truyncc thng bo iu khin (bo co v cc tnh trng cc li trn mng.) gia cc gatewayhoc mt nt ca lin mng. Tnh trng li c th l: mt gi tin IP khng th ti ch ca

n, hoc mt router khng b nh m lu v chuyn mt gi tin IP, Mt thngbo ICMP c to v chuyn cho IP. IP s "bc" (encapsulate) thng bo vi mt IPheader v truyn n cho router hoc trm ch.

III.2. Cc bc hot ng ca giao thc IP

Khi giao thc IP c khi ng n tr thnh mt thc th tn ti trong my tnh v btu thc hin nhng chc nng ca mnh, lc thc th IP l cu thnh ca tng mng,nhn yu cu t cc tng trn n v gi yu cu xung cc tng di n.

i vi thc th IP my ngun, khi nhn c mt yu cu gi t tng trn, n thchin cc bc sau y:

To mt IP datagram da trn tham s nhn c.

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Tnh checksum v ghp vo header ca gi tin.

Ra quyt nh chn ng: hoc l trm ch nm trn cng mng hoc mt gateway sc chn cho chng tip theo.

Chuyn gi tin xung tng di truyn qua mng.

i vi router, khi nhn c mt gi tin i qua, n thc hin cc ng tc sau:

1) Tnh chesksum, nu sai th loi b gi tin.

2) Gim gi tr tham s Time - to Live. nu thi gian ht th loi b gi tin.

3) Ra quyt nh chn ng.

4) Phn on gi tin, nu cn.

5) Kin to li IP header, bao gm gi tr mi ca cc vng Time - to -Live, Fragmentationv Checksum.

6) Chuyn datagram xung tng di chuyn qua mng.

Cui cng khi mt datagram nhn bi mt thc th IP trm ch, n s thc hin bicc cng vic sau:

1) Tnh checksum. Nu sai th loi b gi tin.

2) Tp hp cc on ca gi tin (nu c phn on)

3) Chuyn d liu v cc tham s iu khin ln tng trn.

IV. Giao thc iu khin truyn d liu TCP

TCP l mt giao thc "c lin kt" (connection - oriented), ngha l cn phi thit lp linkt gia hai thc th TCP trc khi chng trao i d liu vi nhau. Mt tin trnh ngdng trong mt my tnh truy nhp vo cc dch v ca giao thc TCP thng qua mtcng (port) ca TCP. S hiu cng TCP c th hin bi 2 bytes.

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Hnh III-19: Cng truy nhp dch v TCPMt cng TCP kt hp vi a ch IP to thnh mt u ni TCP/IP (socket) duy nhttrong lin mng. Dch v TCP c cung cp nh mt lin kt logic gia mt cp u niTCP/IP. Mt u ni TCP/IP c th tham gia nhiu lin kt vi cc u ni TCP/IP xakhc nhau. Trc khi truyn d liu gia 2 trm cn phi thit lp mt lin kt TCP giachng v khi khng cn nhu cu truyn d liu th lin kt s c gii phng.

Cc thc th ca tng trn s dng giao thc TCP thng qua cc hm gi (function calls)trong c cc hm yu cu yu cu, tr li. Trong mi hm cn c cc tham sdnh cho vic trao i d liu.

IV.1. Cc bc thc hin thit lp mt lin kt TCP/IP:Thit lp mt lin kt mi c th c m theo mt trong 2 phng thc: ch ng(active) hoc b ng (passive).

Phng thc b ng, ngi s dng yu cu TCP ch i mt yu cu lin kt gin t xa thng qua mt u ni TCP/IP (ti ch). Ngi s dng dng hm

passive Open c khai bo cng TCP v cc thng s khc (mc u tin, mc anton)

Vi phng thc ch ng, ngi s dng yu cu TCP m mt lin kt vi mtmt u ni TCP/IP xa. Lin kt s c xc lp nu c mt hm Passive Opentng ng c thc hin ti u ni TCP/IP xa .

Bng III-1 Lt k mt vi cng TCP ph bin

S hiu cng M t

0 Reserved

5 Remote job entry

7 Echo

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9 Discard

11 Systat

13 Daytime

15 Nestat

17 Quotd (quote odd day)

20 ftp-data

21 ftp (control)

23 Telnet

25 SMTP

37 Time

53 Name Server

102 ISO - TSAP

103 X.400

104 X.400 Sending

111 Sun RPC

139 Net BIOS Session source

160 - 223 Reserved

Khi ngi s dng gi i mt yu cu m lin kt s c nhn hai thng s tr li tTCP.

Thng s Open ID c TCP tr li ngay lp tc gn cho mt lin kt cc b (localconnection name) cho lin kt c yu cu. Thng s ny v sau c dng thamchiu ti lin kt . (Trong trng hp nu TCP khng th thit lp c lin kt yu cuth n phi gi tham s Open Failure thng bo.)

Khi TCP thit lp c lin kt yu cu n gi tham s Open Sucsess c dng thngbo lin kt c thit lp thnh cng. Thng bo ny dc chuyn n trong c haitrng hp b ng v ch ng. Sau khi mt lin kt c m, vic truyn d liu trnlin kt c th c thc hin.

IV.2. Cc bc thc hin khi truyn v nhn d liu

Sau khi xc lp c lin kt ngi s dng gi v nhn d liu. Vic gi v nhn dliu thng qua cc hm Send v receive.

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Hm Send: D liu c gi xung TCP theo cc khi (block). Khi nhn c mtkhi d liu, TCP s lu tr trong b m (buffer). Nu c PUSH c dng thton b d liu trong b m c gi, k c khi d liu mi n s c gi i.

Ngc li c PUSH khng c dng th d liu c gi li trong b m v s

gi i khi c c hi thch hp (chng hn ch thm d liu na gi i vi hiuqu hn).

Hm reveive: trm ch d liu s c TCP lu trong b m gn vi mi linkt. Nu d liu c nh du vi mt c PUSH th ton b d liu trong b m(k c cc d liu c lu t trc) s c chuyn ln cho ngi s dng. Cnnu d liu n khng c nh du vi c PUSH th TCP ch ti khi thch hpmi chuyn d liu vi mc tiu tng hiu qu h thng.

Ni chung vic nhn v giao d liu cho ngi s dng ch ca TCP ph thuc vo vicci t c th. Trng hp cn chuyn gp d liu cho ngi s dng th c th dng c

URGENT v nh du d liu bng bit URG bo cho ngi s dng cn phi s lkhn cp d liu .

IV.3. Cc bc thc hin khi ng mt lin kt

Vic ng mt lin kt khi khng cn thit c thc hin theo mt trong hai cch: dnghm Close hoc dng hm Abort.

Hm Close: Yu cu ng lin kt mt cch bnh thng. C ngha l vic truynd liu trn lin kt hon tt. Khi nhn c mt hm Close TCP s truyni tt c d liu cn trong b m thng bo rng n ng lin kt. Lu rng khimt ngi s dng gi i mt hm Close th n vn phi tip tc nhn d liu

n trn lin kt cho n khi TCP bo cho pha bn kia bit v vic ng linkt v chuyn giao ht tt c d liu cho ngi s dng ca mnh.

Hm Abort: Ngi s dng c th ng mt lin kt bt v s khng chp nhn dliu qua lin kt na. Do vy d liu c th b mt i khi ang c truyn i.TCP bo cho TCP xa bit rng lin kt c hy b v TCP xa s thng bocho ngi s dng ca mnh.

IV.4. Mt s hm khc ca TCP

Hm Status: cho php ngi s dng yu cu cho bit trng thi ca mt lin ktc th, khi TCP cung cp thng tin cho ngi s dng.

Hm Error: thng bo cho ngi s dng TCP v cc yu cu dch v bt hp llin quan n mt lin kt c tn cho trc hoc v cc li lin quan n mitrng.

n v d liu s dng trong TCP c gi l segment (on d liu), c cc tham s vi ngha nh sau:

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Hnh III-20: Dng thc ca segment TCP

Source Por (16 bits): S hiu cng TCP ca trm ngun.

Destination Port (16 bit): S hiu cng TCP ca trm ch.

Sequence Number (32 bit): s hiu ca byte u tin ca segment tr khi bit SYN cthit lp. Ny bit SYN c thit lp th Sequence Number l s hiu tun t khi u(ISN) v byte d liu u tin l ISN+1.

Acknowledgment Number (32 bit): s hiu ca segment tip theo m trm ngun ang ch nhn. Ngm bo nhn tt (cc) segment m trm ch gi cho trm ngun.

Data offset (4 bit): s lng bi ca 32 bit (32 bit words) trong TCP header (tham s nych ra v tr bt u ca ngun d liu).

Reserved (6 bit): dnh dng trong tng lai

Control bit (cc bit iu khin):

URG: Vng con tr khn (Ucgent Poiter) c hiu lc.

ACK: Vng bo nhn (ACK number) c hiu lc.

PSH: Chc nng PUSH.

RST: Khi ng li (reset) lin kt.

SYN: ng b ha s hiu tun t (sequence number).

FIN: Khng cn d liu t trm ngun.

Window (16 bit): cp pht credit kim sot ngun d liu (c ch ca s). y chnh ls lng cc byte d liu, bt u t byte c ch ra trong vng ACK number, m trmngun sn sng nhn.

Checksum (16 bit): m kim sot li cho ton b segment (header + data)

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Urgemt Poiter (16 bit): con tr ny tr ti s hiu tun t ca byte i theo sau d liukhn. Vng ny ch c hiu lc khi bit URG c thit lp.

Options ( di thay i): khai bo cc option ca TCP, trong c di ti a ca vng

TCP data trong mt segment.Paddinh ( di thay i): phn chn thm vo header m bo phn header lun ktthc mt mc 32 bit. Phn thm ny gm ton s 0.

TCP data ( di thay i): cha d liu ca tng trn, c di ti a ngm nh l 536byte. Gi tr ny c th iu chnh bng cch khai bo trong vng options.

V. Giao thc UDP (User Datagram Protocol)

UDP (User Datagram Protocol) l giao thc theo phng thc khng lin kt c s

dng thay th cho TCP trn IP theo yu cu ca tng ng dng. Khc vi TCP, UDPkhng c cc chc nng thit lp v kt thc lin kt. Tng t nh IP, n cng khngcung cp c ch bo nhn (acknowledgment), khng sp xp tun t cc gi tin(datagram) n v c th dn n tnh trng mt hoc trng d liu m khng c c chthng bo li cho ngi gi. Qua ta thy UDP cung cp cc dch v vn chuyn khngtin cy nh trong TCP.

Khun dng UDP datagram c m t vi cc vng tham s n gin hn nhiu so viTCP segment.

Hnh III-21: Dng thc ca gi tin UDP

UDP cng cung cp c ch gn v qun l cc s hiu cng (port number) nh danhduy nht cho cc ng dng chy trn mt trm ca mng. Do t chc nng phc tp nnUDP thng c xu th hot ng nhanh hn so vi TCP. N thng c dng cho ccng khng i hi tin cy cao trong giao vn.

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Hnh III-22: M hnh quan h h giao thc TCP/IP

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VI. a ch IPv4

VI.1. Thnh phn v hnh dng ca a ch IP

a ch IP ang c s dng hin ti (IPv4) c 32 bit chia thnh 4 Octet ( mi Octet c 8 bit,tng ng 1 byte ) cch m u t tri qua phi bit 1 cho n bit 32, cc Octet tch bit nhau

bng du chm (.), bao gm c 3 thnh phn chnh.

Bit 1......................................................................Bit 32

* Bit nhn dng lp ( Class bit )

* a ch ca ng mng ( Net ID )

* a ch ca my tnh ( Host ID ).

Bit nhn dng lp (Class bit) phn bit a ch lp no.

1. a ch Internet biu hin dng bit nh phn:

x y x y x y x y. x y x y x y x y. x y x y x y x y. x y x y x y x y

x, y = 0 hoc 1.

V d:

0 0 1 0 1 10. 0 1 1 1 1 0 1 1. 0 1 1 0 1 1 1 0. 1 1 1 0 0 0 0 0Bit nhn dng Octet 1 Octet 2 Octet 3 Octet 4

2. a ch Internet biu hin dng thp phn:

xxx.xxx.xxx.xxx

x l s thp phn t 0 n 9

V d: 146. 123. 110. 224

Dng vit y ca a ch IP l 3 con s trong tng Octet. V d: a ch IP thng thy trnthc t c th l 53.143.10.2 nhng dng y l 053.143.010.002.

VI.2. Cc lp a ch IP

a ch IP chia ra 5 lp A,B,C, D, E. Hin ti dng ht lp A,B v gn ht lp C, cn lp D

v E T chc internet ang dnh cho mc ch khc khng phn, nn chng ta ch nghin cu3 lp u.

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