HC VIN CNG NGH BU CHNH VIN THNG KHOA CNG NGH THNG TIN 1 BI GING H THNG PHN TN (Dng cho cng INT 1 4 05) Ngi son bin: ThS. Nguyn Xun Anh n v cng tc: B mn H thng thng tin Khoa CNTT 1 H ni12/2014 H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 2 MC LC CHNG 1:TNG QUAN V CC H THNG PHN TN....................................... 6 1.1H thng phn tn l g............................................................................................... 6 1.2Phnloi cc h thng phn tn ................................................................................ 7 1.2.1Cc h thng in ton phn tn............................................................7 1.2.1.1H thng in ton cm.................................................................................. 7 1.2.1.2H thng in ton li .................................................................................. 8 1.2.2Cc h thng thng tin phn tn............................................................9 1.2.3Cc h thng lan ta phn tn..............................................................10 1.3Cc c trng v mc tiu thit k c bn ca cc h thngphn tn .................... 11 1.3.1Kt ni ngi s dng v ti nguyn h thng....................................11 1.3.2Trong sut i vi ngi s dng .......................................................11 1.3.3Tnh m ca h thng..........................................................................12 1.3.4Qui m m rng h thng....................................................................12 1.4Cc kin trc ca cc h thng phn tn .................................................................. 12 1.4.1Cc kiu h thng phn tn..................................................................12 1.4.2Phn loi kin trc h thng phn tn .................................................15 CHNG 2:VN V GII PHP TRONG H THNG PHN TN................... 20 2.1Truyn thng ............................................................................................................ 20 2.1.1C s truyn thng ..............................................................................20 2.1.1.1Giao thc mng ............................................................................................ 20 2.1.1.2Phn loi truyn thng.................................................................................. 23 2.1.2Gi th tc xa ......................................................................................25 2.1.2.1C ch hot ng ca phng php gi th tc t xa .................................. 25 2.1.2.2Vn truyn tham s.................................................................................. 28 2.1.2.3Gi th tc t xa bng phng php khng ng b ................................... 29 2.1.2.4M hnh i tng phn tn ......................................................................... 29 2.1.3Truyn thng hng thng ip ..........................................................32 2.1.3.1Tnh bn b v tnh ng b trong trao i thng tin.................................... 32 2.1.3.2Truyn tin nhanh hng thng ip ............................................................. 33 2.1.4Truyn thng hng lung ..................................................................34 2.1.5Truyn thng theo nhm......................................................................34 2.2t tn ...................................................................................................................... 34 2.2.1Tn, nh danh v a ch.....................................................................34 2.2.2t tn phng.......................................................................................35 2.2.2.1Cc gii php n gin ................................................................................. 35 2.2.2.2Cch tip cn da trn ngun gc ................................................................ 35 2.2.2.3Bng bm phn tn ....................................................................................... 35 2.2.2.4Cch tip cn phn cp................................................................................. 40 2.2.3t tn c cu trc...............................................................................40 2.2.3.1Khng gian tn ............................................................................................. 40 2.2.3.2Phn gii tn ................................................................................................. 41 2.2.3.3Ci t khng gian tn.................................................................................. 42 2.2.3.4V d v h thng tn min........................................................................... 42 H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 3 2.2.4t tn da trn thuc tnh ..................................................................47 2.2.4.1Dch v th mc ........................................................................................... 48 2.2.4.2Ci t phn cp LDAP................................................................................ 48 2.2.4.3Ci t khng tp trung ................................................................................ 49 2.3ng b .................................................................................................................... 49 2.3.1ng b ng h .................................................................................49 2.3.1.1ng h vt l .............................................................................................. 50 2.3.1.2H thng nh v ton cu............................................................................. 50 2.3.1.3Cc gii thut ng b ng h.................................................................... 51 2.3.2ng h logic ......................................................................................52 2.3.2.1ng h logic Lamport ................................................................................ 52 2.3.2.2ng h vector ............................................................................................. 53 2.3.2.3Cc trng thi ton cc ................................................................................. 54 2.3.3Loi tr tng h.................................................................................56 2.3.3.1Gii thut tp trung....................................................................................... 56 2.3.3.2Gii thut khng tp trung............................................................................ 57 2.3.3.3Gii thut phn tn........................................................................................ 57 2.3.3.4Gii thut th bi .......................................................................................... 58 2.3.3.5So snh cc gii thut loi tr....................................................................... 58 2.3.4nh v ton cu cc nt ......................................................................58 2.3.5Cc gii thut bu chn .......................................................................59 2.3.5.1Cc gii thut bu chn truyn thng........................................................... 59 2.3.5.2Bu chn trong mi trng khng dy......................................................... 60 2.3.5.3Bu chn trong cc h thng qui m ln...................................................... 61 2.4Tin trnh trong cc h thng phn tn..................................................................... 61 2.4.1Cc lung.............................................................................................62 2.4.1.1Khi nim lung ........................................................................................... 62 2.4.1.2Lung trong cc h thng c lp ................................................................ 63 2.4.1.3Ci t lung................................................................................................. 64 2.4.1.4Lung trong cc h thng phn tn .............................................................. 65 2.4.2o ha..................................................................................................67 2.4.2.1Vai tr o ha trong cc h thng phn tn.................................................. 67 2.4.2.2Kin trc ca cc my o.............................................................................. 68 2.4.3My khch ...........................................................................................69 2.4.3.1Cc giao din ngi dng mng................................................................... 69 2.4.3.2Tnh trong sut phn b ti nguyn.............................................................. 69 2.4.4My ch ...............................................................................................70 2.4.4.1Cc vn thit k chung............................................................................. 70 2.4.4.2Cm my ch................................................................................................ 71 2.4.4.3Qun l cm my ch................................................................................... 72 2.4.5Ditr m.............................................................................................72 2.4.5.1Cc gii php di tr m................................................................................. 72 2.4.5.2Di tr v ti nguyn cc b........................................................................... 74 2.4.5.3Di tr trong h thng khng ng nht......................................................... 74 2.5Qun tr giao tc v iu khin tng tranh ............................................................. 74 2.5.1Cc giao tc .........................................................................................75 2.5.2Cc giao tc lng nhau.........................................................................76 2.5.3Cc kha ..............................................................................................76 H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 4 2.5.4iu khin tng tranh ti u..............................................................77 2.5.5Trnh t nhn thi gian........................................................................77 2.6Phc hi v chu li .................................................................................................. 78 2.6.1Gii thiu tnh chu li.........................................................................78 2.6.1.1Mt s khi nim c bn .............................................................................. 78 2.6.1.2Cc m hnh li ............................................................................................ 78 2.6.1.3Che giu li bng bin php d tha............................................................ 79 2.6.2Tin trnh bn b ..................................................................................80 2.6.2.1Nhng vn thit k................................................................................... 80 2.6.2.2Che giu li v nhn bn .............................................................................. 80 2.6.2.3Tha thun trong cc h thng li ................................................................ 81 2.6.2.4Pht hin li .................................................................................................. 82 2.6.3Truyn thng khch/ch tin cy ..........................................................82 2.6.3.1Truyn thng im im ........................................................................... 82 2.6.3.2Cc tnh hung li trong gi th tc t xa.................................................... 82 2.6.4Truyn thng nhm tin cy..................................................................84 2.6.4.1Lc truyn thng theo nhm tin cy c bn.......................................... 84 2.6.4.2Truyn tinnhm tin cy trong cc h thng ln.......................................... 85 2.6.5Cam kt phn tn.................................................................................86 2.6.5.1Cam kt hai pha ............................................................................................ 87 2.6.5.2Cam kt ba pha ............................................................................................. 87 2.6.6Phc hi ...............................................................................................88 2.6.6.1Gii thiu...................................................................................................... 88 2.6.6.2im kim tra............................................................................................... 88 2.7Bo mt..................................................................................................................... 88 2.7.1Khi nim chung..................................................................................89 2.7.1.1Tn cng thm d ......................................................................................... 89 2.7.1.2Truy nhp tri php ...................................................................................... 89 2.7.1.3Tn cng t chi dch v.............................................................................. 90 2.7.1.4Phn mm c hi ........................................................................................ 90 2.7.2Cc knh bo mt ................................................................................91 2.7.2.1Xy dng bc tng la............................................................................... 91 2.7.2.2Xy dng mng ring o .............................................................................. 91 2.7.2.3H thng pht hin v ngn chn t nhp................................................... 91 2.7.2.4Xc thc truy nhp ....................................................................................... 91 2.7.2.5Gii thiu mt s phng php m ha ....................................................... 93 2.7.3Kim sot truy cp...............................................................................94 2.7.4Qun l bo mt...................................................................................95 2.7.4.1Qun lkha................................................................................................ 95 2.7.4.2Qun tr nhm an ton .................................................................................. 96 2.7.4.3Qun l y quyn.......................................................................................... 96 2.8Tnh nht qun v vn nhn bn.......................................................................... 96 2.8.1Khi nim chung..................................................................................97 2.8.2Cc m hnh nht qun ly d liu lm trung tm ..............................97 2.8.2.1Nht qun lin tc......................................................................................... 97 2.8.2.2Nht qun th t cc thao tc ....................................................................... 98 2.8.3Cc m hnh nht qun ly my khch lm trung tm......................102 2.8.3.1Nht qun sau cng .................................................................................... 102 H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 5 2.8.3.2Nht qun c u...................................................................................... 102 2.8.3.3Nht qun ghi u....................................................................................... 103 2.8.3.4Nht qun c kt qu ghi .......................................................................... 103 2.8.3.5Nht qun ghi sau khi c .......................................................................... 104 2.8.4Qun l cc bn sao...........................................................................104 2.8.4.1t v tr my ch nhn bn ....................................................................... 104 2.8.4.2Nhn bn ni dung v v tr lp t ............................................................ 104 2.8.4.3Phn b ni dung........................................................................................ 105 2.8.5Cc giao thc nht qun ....................................................................106 2.8.5.1Nht qun lin tc....................................................................................... 106 2.8.5.2Cc giao thc da trn bn chnh ............................................................... 106 2.8.5.3Cc giao thc nhn bn ghi ........................................................................ 108 2.8.5.4Cc giao thc gn vi cache....................................................................... 109 2.8.5.5Ci t nht qun ly my khch lm trung tm........................................ 109 CHNG 3: CNG NGH V CCH TIP CN PHT TRIN H THNG PHN TN.................................................................................................................... 111 3.1M hnh gi th tct xa ...................................................................................... 111 3.2M hnh DCOM..................................................................................................... 114 3.3Kin trc CORBA .................................................................................................. 115 3.3.1Cc thnh phn c bn ca CORBA.................................................115 3.3.2Kin trc Corba v cc yu cu phn mm trung gian......................135 3.3.3p dng CORBA trong xy dng ng dng phn tn ......................135 3.4Gi phng thc t xa............................................................................................ 136 3.5Dch v web............................................................................................................ 138 3.5.1Cc thnh phn trong kin trc dch v Web ....................................139 3.5.2Cch thc trao i thng tin ca dch v Web ..................................139 3.5.3Quy trnh xy dng ng dng dch v Web ......................................141 3.6Kin trc hng dch v......................................................................................... 141 3.6.1Gii thiu v kin trc hng dch v...............................................141 3.6.2Cc dch v ........................................................................................142 3.6.3M hnh cp lng...............................................................................143 3.6.4Chu k sng dch v..........................................................................144 3.6.5Phn loi dch v ...............................................................................144 3.6.6Trc dch v doanh nghip................................................................145 3.6.7Cc m hnh kin trc da trn SOA ................................................145 3.6.8Cc mu trao i thng ip..............................................................145 TI LIU THAM KHO...................................................................................................... 147 H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 6 CHNG 1:TNG QUAN V CC H THNG PHN TN 1.1H thng phn tn l g Hthngphntnbaogmccmytnh(baogmcccthitbkhcnh PDA, in thoi di ng) c kt ni vi nhau thc hin nhim v tnh ton. H thngphntnxutphttnhucusdngkhnngtnhtontthnvhiuqu hnbngcchkthpkhnngtnhtoncatngmytnhclp,iutr thnh hin thc da trn nhng tin b v cng ngh mng. Ba yu t quyt nh tc tnh ton trong cc my tnh bao gm: Tc ca b vi x l trung tm (CPU), b nh (RAM) v ng truyn trong bo mch ch (Bus). i vi h thng phn tn, mt yu cu mi quan trng ny sinh l vn trao i thng tin gia cc my tnh, thiuyutnythnhimvtnhtontrnmitrngphntnskhngththc hinc.Tctruyndntrongcccngnghmngngycngtngtoiu kin cho s pht trin cc ng dng phn tn, cc my tnh c th trao i thng tin v chia s d liu vi nhau m khng ph thuc vo khong cch a l.H thng phn tn l h thng cc thnh phn c t trn cc my tnh mng, chngtraoithngtinvphihpcchotngchbngcchtruyntinbov ngi s dng cm gic nh l mt h thng n l. Khi nim phn tn c th hin bi tnh c lp catng my tnh nhng phi phi hp lm vic vi nhau ngi s dng khng c cm gic cc thnh phn ri rc. V d, mt h thng bn hng bao gm nhiu ca hng t ti nhng v tr khc nhau, vic nhp thng tin hng ha c thc hin ti nhiu v tr khc nhau (cc ca hng, nh kho, ) , tuy nhin cc nhn vin khai thc u c th tm thy thng tin theo yu cu ca mnh nh thcc thng tin ang c lu tr trn my tnh ca ngi s dng. Nhn chung vic xy dng cc ng dng phn tn phc tp hn nhiu so vi cc ng dng tp trung, trong nhiu trng hp bt buc phi xy dng cc ng dng phn tn v nhng l do sau: -Yu cu tnh ton phn tn: ng dng chy trn nhiu my tnh khc nhau nhm tn dng kh nng tnh ton song song hoc nhm mc ch s dng kh nng tnh ton ca cc my tnh chuyn dng. -Yu cu v kh nng x l li: Yu cu ny lin quan ti cc h thng cn phi mboantontuytingayckhicscxyra,iunycthchin bngcchtngslntnhtonchocngmtnhimvnhmmcchkpthi pht hin v x l li. -Chia s ti nguyn: Nhngngi s dng trao i thng tin vi nhau thng quamt ng dng trn mng. Mi ngi s dng chy mt ng dng phn tn trn my tnhcamnhvchiasccitngsdng.Mtsngdngphichytrn nhiu my tnh v d liu c t phn tn trn mng lin quan n quyn qun l v quyn s hu d liu: cho php truy nhp d liu t xa nhng khng cho php sao chp lu gi cc b. Trong cc h thng phn tn, mi trng mng ng vai tr quan trng trong vic phnphtthngtinnccthnhphnvtphpktqutnhtoncaccthnh phn . Cc my tnh kt ni vi nhau trn mng m nhim chc nng truyn thng cho cc ng dng, chng khng chia s b nh cho nhau do khng th s dng cc H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 7 bin ton cc trao i thng tin, thng tin trao i gia cc my tnh ch c thc hin thng qua c ch trao i tin bo. Mng l ti nguyn chung ca h thng do khi xy dng h thng phn tn cn phi xem xt n cc vn nh: Bng thng, cc im c th xy ra s c, bo mt v an ton d liu, ng b tin trnh. Qu trnh trin khai cc ng dng trong h thng phn tn thng gp mt s kh khn sau: -Trn mng c nhiu loi my tnh v thit b mng ca nhiu nh sn xut khc nhau v cc my tnh c ci t cc h iu hnh khc nhau. -Khtchhpccphnmmvchngcphttrintrnccngnngkhc nhau. -Thi gian pht trin phn mm ln do thng ko theo chi ph xy dng h thng cao. Thc t vic xy dng nn tng cho cc h thng phn tn vn da trn m hnh 7 lp OSI, trong 4 lp thp (vt l, lin kt d liu, mng v lp giao vn) gii quyt ccvnnhphthinvsali,nhtuyn....,nhngvnnythngdoh iu hnh m nhim. Tuy nhin vic p dng 3 lp trn (phin lm vic, trnh din v lp ng dng) c s dng trong cc sn phm nn ca h thng phn tn nhm mc ch x l cc th tc kt ni gia cc thnh phn phn tn v th hin cu trc d liuphctpcaccngdng,ccsnphmnhvygilphnmmtrunggian. Ccngdngphntnthng cxydngdatrnnnhiuhnhvccth vin h tr vic x l phn tn, chng thc hin cc nhim v xc nh v tr ca cc my tnh, ng b v m ha thng tin.1.2Phnloi cc h thng phn tn 1.2.1 Cc h thng in ton phn tn in ton phn tn thng c s dng trong cc tc nghip yu cu hiu nng cao, n bao gm hai nhm: in ton cm v in ton li. Trong h thng in ton cm, cc my tnh s dng cng h iu hnh v kt ni vi nhau qua mng ni b tc cao. in ton li bao gm nhiu h thng phn tn thuc v nhiu min qun l khc nhau v thng khng ng nht v phn cng cng nh h iu hnh. 1.2.1.1H thng in ton cm T l gia gi thnh v hiu sut x l ca my tnh c nhn ngy cng gim l chixydnghthngintoncm.Ccmytnhcnhnccitmt loi h iu hnh v kt ni vi nhau trong mng tc cao. in ton cm s dng k thut x l song song trn nhiu my tnh thc hin tnh ton. Mt v d kh quen bit ca in ton cm l h thngBeowulfc xy dng da trn h iu hnh Linux (hnh 1.1),mi cm bao gm nhiu nt trong c mt ntch(Master)mnhimchcnngxptvtrcaccthnhvinkhctrong chngtrnhsongsong,qunlhngi cc cng vic v giao tipvingi dng trong h thng. Nh vy, nt ch ch vic chy phn mm trung gian cn thit cho cc chng trnh thc hin v qun l cm, trong khi cc nt tnh ton s khng cn g khc ngoi h iu hnh chun. Mt thnh phn quan trng ca phn mm trung gian l th vin thc thi chng trnh song song, nhng th vin ny cung cp cc phng tin trao i thng tin da trn thng ip nhng cha c kh nng x l li, bo mt... H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 8 Hnh 1.1 H thng in ton cm Mt v d khc ca in ton cm l h thng MOSIX c xy dng da trn cch tip cn i xng, ngha l n cung cp mt hnh nh n ca h thng cm. trong sut rt cao ca MOSIX t c bng cch di tr tin trnh, ngi dng c th khi to mt tin trnh trn mt nt nhng tin trnh c th di tr sang nt khc thc hin nhm tn dng ti a tim nng x l ca mi nt trong h thng. 1.2.1.2H thng in ton liHthngintonlikhngihitnhngnhtcattcccnt,mi thnhvincthkhcvcphncnglnhiuhnhvccchnhschqunl. Vn ct li trong h thng in ton li l vic ly ti nguyn (my tnh, thit b ngoivi,csdliu...)tcccquankhcnhaunhngphichophpccnhm ngidngthuccccquancngtcvi nhau,nhvyscngtcc thc hin da trn c quan o, ngi dng thuc v mt c quan o th c quyn truy nhp n cc ti nguyn ca c quan o . Vi c tnh , nhiu phn mm h thng in ton li pht trin xung quanh victruynhptinguyntccvngquntrkhcnhauchonhngngidngvngdngthucvmtcquano,dotiuimcahthngintonli thng l nhng vn lin quan ti kin trc h thng. Hnh (..) l mt mu kin trc phn tng thng c ng dng trong cc h thng in ton li. Kin trc ny bao gm 04 tng: -Tng kt cu (Fabric): Cung cp giao din truy nhp ti nguyn cc b tri mttrangring.Ccgiaodinnyclmthchngvivicchophp chia s ti nguyn bn trong mt c quan o, n thng cung cp cc chc nng truyvntrngthivkhnngcatinguyn,ccchcnngqunlti nguyn thc (v d kha ti nguyn) -Tng kt ni (Connectivity): Bao gm cc giao thc truyn thng h tr cho cc giao tc li bao trm ton b cc ti nguyn, v d cc giao thc truy cp di chuyn ti nguyn hoc n gin ch l truy cp ti nguyn t mt v tr no . Tng kt ni s phi bao gm cc cc giao thc bo mt, tnh nng bo mtcthchomttikhonvcngcth chomtngdng(ttcnhng ngi dng s dng ng dng ). H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 9 -Tngtinguyn(Resource):Qunltinguynnl,nsdngccchc nng do tng kt ni cung cp v gi trc tip cc giao din tng kt cu cung cp thc hin cc chc nng iu khin truy nhp, v d cc chc nng thit lp cu hnh ti nguyn, khi to tin trnh c/ghi d liu -Tng tp trung (collective): X l cc yu cu truy nhp n nhiu ti nguyn khc nhau, thng cung cp cc chc nng nh: thm d, nh v, lp lch truy nhp , nhn bn ti nguyn... Cc giao thc thuc tng ny kh nhiu v thng khng phi l nhng giao thc c chun ha ( mbo cung cp dch v theo yu cu ca tng ng dng) -Tngngdng(Application):Baogmccngdngvnhnhbntrongc quan o v s dng mi trng in ton li. Hnh 1.2 Kin trc phn tng cho h thng in ton li Trongcchthngintonli,cctngtptrung,ktnivtinguyn thng c gp li v gi chung l tng trung gian, n c nhim v qun l v cung cpchcnngtruynhptrongsutnttccctinguynphnbtrncctrang mng khc nhau. Quan st cho thy, vic cung cp cc thng tin ring l trong cc h thng in ton kh ph bin, iu ny dn dn ti quan im v kin trc dch v li m (Open Grid Service Architecture) . 1.2.2Cc h thng thng tin phn tn Mt trng hp khc trong h thng phn tn l cc ng dng mng qui m ln, d liu c t nhiu ni nhng vic x l mi ni lin quan n nhng ni khc.Trong nhiu trng hp, cc my ch chy tin trnh cung cp dch v x l cho my khch, my khch n thun ch gi yu cu v nhn v kt qu c my ch x l. Tuy nhin mt yu cu t ra l cn phi c s phi hp x l gia cc my ch, mtyucu caratphamykhchnccmychd liuthyucu phic thcthi trntt c cc my chhoc chi cn mtmychkhngthc thi c yu cu ca my khch th tt c cc my ch khc cng khng c php thc thi yu cu ny. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 10 Hnh 1.3 Phn mm trung gian l phng tin truyn tin trong EAI Cc phn mm ngy cng tinh xo hn v chng ln lt tch chng thnh cc thnh phn (v d phn bit thnh phn c s d liuvi thnh phn x l), nh vy victchhphthngphichophpccthnhphntraoithngtintrctipvi nhau,tdnnngnhcngnghiplptchhpngdngdoanhnghip (Enteprise Application Integration - EAI). Thc t, cc thao tc thc hin trong c s dliu(CSDL),thngcthchindidngccgiaotc.Phnmmngdng cng tch bit vi d liu th cng cn phi c cc phng tin tch hp chng c lp vi CSDL, c bit cc thnh phn ng dng phi c kh nng trao i thng tin trc tip vi nhau ch khng phi ch l nhng phng tin Yu cu/Tr li nh trong cc h thng x l giao tc. 1.2.3Cc h thng lan ta phn tn Cc h thng in ton phn tn v h thng thng tin phn tn u c chung c im l tnh n nh ca chng, ngha l cc nt mng u c nh v ng truyn ktnimngchtlngcaotnginnh.mtmcno,tnhnnh ny c thc hin bng nhiu k thut khc nhau (s trnh by trong cc chng tip theocamnhcny)nhmtctnhtrongsutphntn.Vdviscmnh ca cc k thut che giu li v phc hi s cho chng ta cm gic thnh thong mi c mt vi li xy ra. Tng t nh vy chng ta cng c th che giu cc kha cnh lin quannvtrccnttrnmng,thctchophpngidngvccngdngtin rng cc nt vn ang hot ng. Tuynhin,vntrnnrtphctpkhixuthinccthitbdingv thit b nhng, chng ta phi ng u vi cc h thng phn tn m tnh khng n nh l iu tt yu. Cc thit b trong h thng loi ny thng l nhng thit b di ng vi c trnglvtrkhngnnhvktnimng khngdy,docch thngnycgilhthnglantaphntn(Distributedpervasivesystem).H thng ny thiu vng s kim sot nhn cng, cu hnh ca cc thit b ny do ch s hu thit b qui nh, nu khng th thit b s t ng khm ph mi trng v la chn cu hnh c cho l ph hp nht. s la chn c chnh xc nht, Grimm a ra cc yu cu sau cho cc h thng lan truyn phn tn: H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 11 -Baoqutnhngthayingcnh:Thitbphilintcnhnbitcmi trngcththayibtkthigianno.Vdkhiphthinthymtktni mng th thit b s t ng tm mng khc thay th. -Cung cp giao din cu hnh mc nh: Mi ngi dng c thi quen ring bit, do cn phi cung cp giao din cu hnh sao cho n gin nht ph hp vi tt c mi ngi hoc mt cu hnh c ci t t ng. -T ng nhn bit chia s ti nguyn: Mt kha cnh quan trng ca h thng lan ta l cc thit b thamgia h thng theo th t truy nhp thng tin, iu ny i hi phi cung cp cc phng tin d dng c, lu tr, qun l v chia s thng tin. Vi quan nim vic kt ni mng ca cc thit b thng gin on hoc thay ithkhnggianlutrthngtincthtruynhpccngsphithayi theo thi gian. Vi s hin din ca kh nng di ng th cc thit b phi d dng thchnghivimitrngccb,chngphickhnngddngphthincc dch v v phn hi theo cc dch v . S trong sut v mt phn b khng ch trong h thng lan ta m thc t cn s phn b v d liu, x l v iu khin, v l tt hn ht l phi phi by ch khng nn che giu chng. 1.3Cc c trng v mc tiu thit k c bn ca cc h thngphn tn Ngi s dng lun mong mun c c cc phn mm thn thin, tc x l nhanh,ddngcnhnhaccchcnngvmboantonthngtin.Sauy chng ta s tm tt bn mc tiu c bn khi xy dng mt h thng phn tn. 1.3.1Kt ni ngi s dng v ti nguyn h thng Mctiuchnhcahthngphntnlktningisdngvtinguyn mng.Nhimvchnhcamththngphntnlchophpngisdngc khai thc thng tin m khng ph thuc v tr a l ca ngi . Nh vy ny sinh hng lot vn lin quan n vic khai thc v s dng thng tin: ai c php truy nhp, truy nhp thng tin mc no, thi gian no c php truy nhp, tn sut truy nhp thng tin. 1.3.2Trong sut i vi ngi s dng Mc tiu trong sut i vi ngi s dng nhm che giu v tr thc ca thng tin i vi ngi s dng, ngi s dng khng bit c thng tin c lu tr u v x l trn my tnh no. Tnh trong sut i vi ngi s dng th hin cc c im sau: -Truy nhp (Access): n cch th hin d liu v phng php truy nhp. -V tr (Location): n ni lu tr thng tin. -Di chuyn (Migration): n qu trnh chuyn v tr lu tr d liu -tlivtr(Relocation):nqutrnhdichuyndliumkhnglmgin on hot ng ca ngi s dng. -Nhn bn (Replication): Che giu vic to ra bn sao d liu -Tng tranh (Concurrency): Che giu vic chia s ti nguyn cho nhiu ngi s dng -Li (Failure): Che giu li v phc hi ti nguyn-Bn b (Persistence): Che giu ti nguyn phn mm c ti vo b nh hay trn a. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 12 1.3.3Tnh m ca h thng c tnh m, h thng phn tn phi c chun giao tip vi h thng, nh vy s d dng hn trong vic trao i ti nguyn. Mt h thng m phi tun th cc tiu chun giao tip no c cng b, ngha l sn phm ca cc nh sn xut khc nhau c th tng tc vi nhau theo tp cc lut v cc qui tc hoc cc tiu chun c cng b, v d: ngn ng IDL, XML, giao thc dch v Web. 1.3.4Qui m m rng h thng H thng phn tn cn phi m bo d dng thm cc my tnh m khng cn phi sa i h thng, nh vy chng ta c th m rng hay thu hp h thng phn tn theo yu cu thc t, y l mt c tnh quan trng nht ca h thng phn tn. Khi mrnghthng,slngmytnhvslngngisdngtngthmnhng khng c php gim hiu sut hot ng ca h thng. Tng t nh vy, vic m rng h thng theo phm vi a l cn bo m t nhhng ti hiu sut hot ng ca h thng.Trong c hai trng hp m rng trn, cn phi bo m kh nng qun tr h thng. 1.4Cc kin trc ca cc h thng phn tn Datrncchktnivcchtraoithngtingiaccthnhvin,hthng phn tn c th phn thnh hai loi: H thng nhiu b vi x l (cc b vi x l dng chung b nh) v h thng nhiu tnh my tnh (mi b vi x l c b nh ring). H thngnhiumytnhccoilngnhtnuccmytnhcngchungnntng (phn cng, h iu hnh, mng) ngc li gi l h thng khng ng nht. 1.4.1Cc kiu h thng phn tn Tronghthngnhiubvixl,ccbvixldngchungbnhRAM, victraoithngtingiaccbvixlcthchinbngcchc/ghicc nh. Ngoi cc chc nng truyn thng ca h iu hnh (x l gi h thng, qun l b nh, qun l tp tin, qun l thit b vo ra), h iu hnh ca h thng nhiu b vi xlphithchinccchcnngcbitnh:ngbtintrnh,qunlti nguyn, lp lch lm vic. Trc ht, chng ta s tm hiu s b v phn cng ca h thng nhiu b vi x l sau s cp ti cc vn v h iu hnh trong cc h thng ny. H thng nhiu b vi x l u c c im chung l cc n v x l trung tm u c kt ni vo knh kt ni chung trong bo mch ch v truy nhp trc tip vo b nh dng chung.Hnh 1.4-a minh ha h thng nhiu b vi x l da trn mt knh truyn, cc n v x l trung tm v cc m-dun b nh dng chung mt knh truyn trao i thng tin. Trc khi truy nhp nh, n v x l trung tm phi kim tra xem knh truyn c bn hay khng. Nu ri, n v x l trung tm t a ch nh ln knh, pht tn hiu iu khin v ch cho n khi b nh t gi tr ca nh yu cu ln knh truyn. Nu knh truyn bn, n v x l trung tm phi ch cho n khi knh truyn ri, nh vy ny sinh vn v qun l tng tranh. i vi h thng ch c hai hoc ba n v x l trung tm th vic qun l tng tranh tng i n gin, vn s trnnkhphctpivihthngc32hoc64nvxltrungtm.Ni chung, h thng s b gii hn bi bng thng ca knh truyn v hu ht cc CPU s lng ph thi gian ch c nh. gii quyt vn ny, ngi ta thm b nh m H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 13 vo mi CPU (xem hnh 1.4-b), b nh m c th c tnh hp trong CPU, bn cnh, nm trn bo mch b vi x l hoc t hp cc phng n trn. B nh m trao i thng tin vi b nh dng chung theo phng php c/ghi tng khi (cc khi 32 hoc 64 byte), n v x l trung tm s c/ghi cc nh trong b nh m, nh vy s gim ng k lu lng trn knh truyn chung. (a) Khng c b nh m.(b) C b nh m.(c) C b nh m v b nh ring. Hnh1.4Ba loi h thng nhiu b x l da trn mt knh Mi khi b nh m c nh du bi mt trong hai trng thi: ch c hoc c/ghi. Nu CPU mun ghi mt nh m nh xut hin trong cc b nh m khc, phn cng ca knh truyn s pht hin tnh hiu ghi v chuyn tn hiu n tt c cc b nh m khc. Nu cc b nh m ny c ni dung ging nh trong b nh, chng c th chi b bn sao v cho php b iu khin ghi cht khi b nhmtrongbnhdngchungtrckhithayinh.Mtsbnhm ang thay i, n phi ghi li ni dung nh vo b nh dng chung trc khi yu cu ghi c th tip tc thc hin hoc chuyn trc tip gi tr n b iu khin ghi qua knh truyn. Hnh 1.4-c minh ha mt kin trc khc, CPU khng ch c b nh m m cn c b nh cc b ring c truy nhp bng knh ring. s dng cu hnh ny mt cch ti u, trnh bin dch s t tt c chng trnhm cc hng s, d liu ch c v cc bin s trong b nh ring. B nh dng chung khi s c dng cho cc bin dng chung. Ni chung, kin trc ny gim ng k lu lng trn knh chung nhng n i hi trnh bin dch phi c s phi hp rt cht ch. Kin trc UMA ch ph hp vi cc h thng c t CPU, khi s lng CPU tng ln s phi chi ph ln cho vn x l chuyn mch. Mt kin trc khc c xut l kin trc truy nhp b nh khng ng nht. Ging nh a x l i xng, l cng nghmrngtnhkhbincamychbngcchbsungthmbxl.Chai cng ngh ny u cho php ngi dng khi u vi nhng my ch tng i nh v sau b sung b x l nu ng dng pht trin thm. i vi hu ht my ch i xng,vicbsungthmsaukhic8bxlrtttinmhiusuttc khng cao nhng NUMA th cho php m rng hn th nhiu - n 256 b x l, lin kt vi nhau trong mt my.TngththngUMA,NUMAchophpkhaithcscmnhkthpca nhiu b x l m mi b x l truy cp mt cm b nh chung. Tuy nhin, cc b x H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 14 l c phn thnh nhng nhm nh hay nt, trong tt c cc b x l u lin kt vi nhau. Chng hn, mt my ch 16 b x l c th sp xp thnh bn nt, mi nt c bn b x l v c b nh ring. NUMA lm gim tnh trng tc nghn bus ca kin trc i xng bng cch cho cc b x l trong mt nt giao tip vi nhau v vi b nh cc b ca chng qua nhng bus ring, nh hn. Cc b x l cng c th truy cp nhng vng nh ca tng nt khc, tuy rng thi gian truy cp ny thay i ty theo khong cch gia cc nt. V th c ch c tn l truy cp b nh khng ng nht NUMA. Trong h thng nhiu b vi x l thun nht, mi n v x l trung tm truy xut vo b nh cc b, vn cn li l vic trao i thng tin gia cc b vi x l vi nhau. Trong h thng nhiu b vi x l khng thun nht cc my tnh c xy dng trn nn tng ca cc b vi x l khc nhau. Phn cng ng vai tr quan trng trong h thng phn tn, nhng s hot ng ca h thng ny li do h iu hnh quyt nh. H iu hnh cung cp cc tnh nng qun l ti nguyn phn cng, cho php nhiu ngi dng v nhiu ng dng chia s phn cng nh: CPU, b nh, thit b ngoi vi, mng v tt c cc loi d liu. H iu hnh cng n gin ha s phc tp v a dng ca phn cng bng cch to ra my o,nhvyccngdngcththchinddnghn.Hiuhnhchoccmy tnh gm hai loi: H iu hnh phn tn (DOS) v h iu hnh mng (NOS). H iu hnh phn tn qun l tng th tt c cc my tnh thun nht trong h thng phn tn, h iu hnh mng thng dng cho cc h thng khng ng nht, mi my tnh to ra cc dch v cung cp cho cc my tnh khc. T cui nhng nm 1990, mt s cc dchvdohiuhnhcungcpccitinvgilphnmmtrunggian (Middleware).Bng 1.1 H iu hnh phn tn, h iu hnh mng v phn mm trung gian. H thngM tMc tiu DOSH iu hnh lin kt cht dng cho cc h thng my tnh thun nht Che giu v qun l cc ti nguyn phn cng NOSH iu hnh lin kt lng, dng cho cc my tnh khng thun nht (mng LAN v mng WAN) Cung cp cc dch v cc b cho cc my tnh khc truy nhp t xa. MiddlewareLp pha trn ca h iu hnh mng, ci t cc dch v mc ch chung. Cung cp tnh trong sut cho h thng phn tn C hai loi h iu hnh phn tn: H iu hnh phn tn cho h thng nhiu b vi x l v h iu hnh phn tn cho cc my tnh cng chng loi. Ngoi kh nng qunlnhiubvixl,cctnhnngkhccacchiuhnhphntncng ging nh h iu hnh dnh cho cc h thng chy trn mt b vi x l. H iu hnh chy trn mt b vi x l Mctiuchnhcaloihiuhnhnylchophpngisdngvcc phn mm ng dng truy nhp d dng n cc ti nguyn dng chung nh CPU, b nhchnh,avccthitbngoivi.Ccphnmmngdngdngchungti nguyn ca h thng nhng vn m bo tnh c lp cho tng ng dng, nh vy h iu hnh cn phi c chnh sch chia s cc ti nguyn dng chung , iu ny ch H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 15 c th thc hin bng cch thit lp c ch my o, cung cp kh nng x l a nhim choccngdng.Vd,giiquytvntngtranhtronghthng,ccphn mmngdngkhngcphptruynhptrctipncctinguynmng,vic truy nhp phi c thc hin thng qua cc hm nguyn thy do h iu hnh cung cp. H iu hnh cn phi nm ton b quyn kim sot vic s dng v chia s ti nguyn phn cng, do hu ht cc b vi x l h tr t nht hai ch : -Ch li: Tt c cc ch th c php thc hin v c th truy nhp ton b b nh v cc thanh ghi trong thi gian thc hin. -Ch ca ngi s dng: Hn ch vic truy nhp thanh ghi v b nh (v d chcphptruynhpvovngnhdohiuhnhquinh,khngtruy nhp trc tip vo cc thanh ghi) H iu hnh cho nhiu b vi x l L cc h iu hnh dng iu khin s hot ng ca cc h thng my tnh c nhiu b vi x l. Cc h iu hnh cho nhiu b vi x l gm c 2 loi: -a x l i xng: Trong h thng ny vi x l no cng c th chy mt loi tiutrnhbtk,ccvixlgiaotipvinhauthngquamtbnhdng chung. H i xng cung cp mt c ch chu li v kh nng cn bng ti ti uhn,vcctiutrnhcahiuhnhcthchytrnbtkbvixl nonnnguycxyratnhtrngtcnghnCPUgimingk.Vn ngbgiaccbvixlct ln hngukhithitk hiuhnh cho h thng i xng. -a x l bt i xng: Trong h thng ny h iu hnh dnh ra mt hoc hai vi x l s dng ring, cc vi x l cn li dng iu khin cc chng trnhcangisdng.Hbtixngnginhnnhiusovihi xng, nhng trong h ny nu c mt b vi x l trong cc vi x l dnh ring cho h iu hnh b hng th h thng c th ngng hot ng. H iu hnh mng l cc h iu hnh dng iu khin s hot ng ca mng my tnh. Ngoi cc chc nng c bn ca mt h iu hnh, cc h iu hnh mng cn phi thc hin vic chia s v bo v ti nguyn ca mng.1.4.2Phn loi kin trc h thng phn tn H thng phn tn c th c xy dng theo kin trc phn tn dc, phn tn nganghoclaighphailoitrn.Trongkintrcphntndc,cccngvicxl c thc hin bng cch t cc my tnh ln theo cu trc lp. Cc tin trnh x l c phn cho cc lp thp hn tng ng vi cu trc t chc v loi nhim v. Kin trc phn tn ngang bao gm nhiu my tnh c kt ni ngang hng vo mng x l cng vic, c th thm my tnhnhm nng cao linh hot v nng cp h thng. Cc cng vic trc kia c tp trung trn mt my tnh th c th chia tnh ton vi cc my tnh khc. C th s dng cc th vin c cung cp t cc my tnh khc, iunymbocsphntnchcnngvsdngchungccngunti nguyn.Mhnhhthngphntnlphngthctchcphnmmbntrongh thng, hin nay c bn m hnh ang c p dng ph bin bao gm: M hnh phn tng,mhnhdatrnitng,mhnhdatrnskinvmhnhdliutp trung. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 16 Cc thnh phn trong m hnh phn tng c t chc thnh tng lp c s rng buc cht ch, lp trn gi cc thnh phn lp di lin k. Bn yu cu gi thng tin yu cu c lu chuyn t lp trn xung lp di, kt qu tr v c chuyn t lp di ln lp trn. Bn thc hin yu cu tip nhn thng tin yu cu c lu chuyn t lp di ln lp trn, kt qu tr v c chuyn t lp trn xung lp di. Nh vy, s lng tng cng ln th h thng s cng c m un ha cao v hiu nng ph thuc vo s lng tng. Hnh 1.5 M hnh phn tng Mhnhitngphntnrngbuclnghnmhnhphntng,mii tng c coi l mt thnh phn v c gi bng c ch gi th tc t xa. Cc i tng trong m hnh ny hot ng tng i c lp, d dng thay i v nng cp, y l m hnh rt ph hp vi m hnh khch/ch. Hnh 1.6 M hnh i tng phn tn M hnh Khch/Chang c p dng ph bin trong cc h thng phn tn, hin nay m hnh Khch/Ch pht trin theo hng s dng cc i tng phn tn. M hnh Khch/Ch c hiu l hnh thc trao i thng tin gia cc tin trnh cung cp dch v (My ch) v tin trnh s dng dch v (My khch). Trong m hnh ny, my khch yu cu cc dch v c ci t trn My ch, My ch x l yu cu H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 17 vtrvktquchoMykhch.Cchtruyntinsdngtruyntinbogiacc tin trnh (IPC), n cho php ci t cc tin trnh my khch v my ch trn cc my tnh khcnhau. M hnh Khch/Chng vai tr quan trng trong cc h thng phn tn, n c cc c trng sau: -My khch v my ch l cc m un chc nng vi cc giao din xc nh: Cc chcnngthchincamykhchhocmychcthgmnhiuchcnng con, vic ci t cc ng dng my khch hoc my ch khng nht thit phi trn my ch m c th ci t ti bt c my no trn mng. -Quan h khch/ch c thit lp gia hai m un khi my khch a ra yu cu dch v v c My ch p li: Khi nim my khch v my ch ch l tng i, mt m un c th ng vai tr my ch i vi m un ny nhng li ng vai tr my khch i vi m un khc. -Trao i thng tin gia cc m un c thc hin thng qua c ch truyn tin bo: tt c cc yu cu ca my khchc tp hp thnh tin bo chuyn n my ch v ngc li cc kt qu tr v cng c t trong cc tin bo chuyn n my khch. -Traoitinbogiamykhchvmychthngcthchintheocch hi p. -my khch v my ch c ci t trn cc my tnh khc nhau v c ni vi nhau trn mng: V mt l thuyt, trn cng mt my c th ci t ng thi m unMykhchvmunMych,tuynhintrongthctthngccm-un ny c ci t trn cc my khc nhau. Vi cc c im trn, m hnh Khch/Ch c th ci t theo hai mc: -Mcdchvnn:tocsphttrin,htrvqunlccngdng Khch/Ch. -Mc ng dng: l cc phn mm cung cp cc chc nng nghip v theo m hnh Khch/Ch. MhnhKhch/Chcungcpccphngtintchhpccngdngringvi cc nhu cu x l nghip v chung m bo thng nht vic x l thng tin trong ton b h thng. M hnh ny c cc u im sau: Chiasdliu:trongmhnhKhch/Ch,dliuclutrnMychsn sng cung cp cho tt c nhng ngi s dng c quyn truy nhp. Vic s dng ngn ng SQL thng nht cc thao tc truy xut d liu h tr cho ngi s dng d dng truy nhp d liu.Ccdchvtchhp:Ngisdngcquyntruynhpucthnhnc thng tin cn thit t cc my trm v c th x l cc thng tin ny theo nhu cu s dng. Theo quyn truy nhp, My khch s dng chung cc dch v do My ch cung cp. Chia s ti nguyn gia cc h thng khc nhau: C th to cc ng dng c lp vi h iu hnh v thit b phn cng, do cc ng dng My khch u c th s dng cc ti nguyn chung trn mng: d liu, dch v.... Khnngtraoivtngthchdliu:Huhtcccngcsdngpht trin cc sn phm theo m hnh Khch/Ch u da trn tiu chun ca ngn ng H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 18 SQL, do m boc tnh tng thch v kh nng trao i d liu gia cc tin trnh My khch v My ch. Khng ph thuc thit b lu tr d liu: Trn My ch, d liu c th c lu tr trong cc thit b khc nhau nh a t hoc bng t, ngi s dng vn dng tp cc lnh chung truy xut d liu m khng ph thuc vo phng tin lu tr. c lp vi v tr x l d liu:Vic truy xut d liu khng ph thuc vo thit b phn cng, h iu hnh v v tr lu tr d liu. Qunltptrung:Vicqunltptrungcthchinbngcchsdngcc cng c gim st v h tr t trung tm Tin trnh My khch Tin trnh My ch Phn mm trung gian My khch (MiddleWare) Phn mm trung gian My ch (MiddleWare) Dch v cc b Dch v mng Dch v mng Dch v cc b H iu hnh v thit b phn cng Giao thc trao i lp trn H iu hnh v thit b phn cng Trao i thng tin lp vt l Hnh 1.7 Cc thnh phn c bn trong m hnh Khch/Ch Hnh 1.7 th hin cc thnh phn c bn trong m hnh Khch/Ch, baogm cc thnh phn: tin trnh my khch, my ch, phn mm trung gian (MiddleWare), dch v mng,dch v cc b (v d: qun l d liu v qun l tin trnh), h iu hnh v thit b phn cng. Tin trnh my khch bao gm cc chc nng ca lp ng dng, n thc hin giao tip vi ngi s dng v cc chc nng ng dng cn thit nh hin ththngtin,tnhtonccbngtnh...Tintrnhmykhchgiaotipviccphn mmtrunggianquagiaodinlptrnhngdng(API)giccyucunmy ch v nhn kt qu tnh ton. Tin trnh my ch thc hin cc chc nng lp ng dng, n cung cp cc dch v cho my khch vi vic che du cc thng tin ring, m bo cung cp cc dch v x llivcththchinchcnnggimst/iuphi.Phnmmtrunggian (MiddleWare)cungcpnhiutnhnngkhcnhaunhthitlpphin lmvic gia cctintrnh,bomtdliu,nn/giinndliu,xlli.MiddleWarelmi trng trung gian kt ni tin trnh my khch vi tin trnh my ch, n giao tip vi cc tin trnh qua giao din API. Phn mm trung gian trn my khch thc hin cc chc nng cung cp giao din API, thit lp lin kt vi tin trnh trn my ch bng cch gi cc lnh thng qua giao din mng v phn mm trung gian (ca my ch). Phn mm trung gian trn my ch gim st cc yu cu t pha my khch v gi cctintrnhmychtngng,nthchinccchcnng:Nhnccyucut pha my khch v chuyn cc yu cu cho tin trnh my ch, kim tra bo mt h thng,xltngtranhkhingthinhncnhiuyucutphamykhch, H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 19 nhn kt qu x l ca tin trnh My ch v chuyn n my khch, gim st v x l li. Hnh 1.8 M hnh da trn s kin Mhnhdatrnskinlmhnhmcctintrnhtraoithngtinda trn vic pht tn s kin, cc s kin thng c gn vi cc lut phn pht s kin. Cctintrnhphttnskinsaukhicphnmmtrunggianmboch nhng tin trnh ng k mi nhn c s kin. Mc rng buc gia cc tin trnh ca m hnh ny tng i thp. Hnh 2.9 M hnh d liu tp trung M hnh d liu tp trung l m hnh trong cc tin trnh trao i thng tin vi nhau qua kho d liu chung ( ch ng hoc th ng). M hnh ny m bo tnh c lpgia cc thnh phntrongh thngvngthi tin lichovicchiasd liu ln. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 20 CHNG 2:VN V GII PHP TRONG H THNG PHN TN 2.1Truyn thng Trao i thng tin gia cc tin trnh l trng tm ca tt c cc h thng phn tn, do cn phi nghin cu k lng cch thc cc tin trnh trao i thng tin vi nhau.Thcchttraoithngtintronghthngphntnlchuynthngipdomngmytnhmnhim,qutrnhphctphnrtnhiusovivictraoi thngtintrnmtmytnh.Cch thng phn tn hin ibaogmhngtriu tin trnh trao i thng tin vi nhau qua mng Internet khng tin cy, nu khng thay i cc phng thc truyn thng nguyn thy th s rt kh pht trin cc ng dng phn tn.Vbncht,traoithngtingiacctintrnhvnsdngccgiaothc truyn tin truyn thng qui nh trong tng lp mng. Cc giao thc ny c ng dngxydngccmhnhtruyntinkhcnhGi thtc txa(RPC),gii tng t xa (RMI),phn mm trung gian hng thng ip (MOM). M hnh truyn tin u tin trong h thng phn tn l RPC, bn cht ca n l n nhng th tc phc tp trong vic truyn thng ip v l cch l tng trong cc ng dng khch/ch. V sau, m hnh ny c ci tin da trn vic ci t cc i tng phn tn. Mtsngdngphntnsdngphngthctruynthngip,tnhtrong sut ca phng thc ny kh thp, do nn chuyn sang m hnh hng i (tng t nh th in t) hoc s dng lp phn mm trung gian hng thng ip (MOM) bo m vic phn loi cc thng ip. Cc d liu a phng tin nh m thanh, hnh nh ... i hi vic truyn tin cn phi p ng yu t thi gian v tnh lin tc, do m hnh truyn thng ip dng nh cha p ng c yu cu, khi phi s dng phng php truyn theo lung (stream). Vn cui cng cn nghin cu l vic s dng phng thc truyn tin im vi im-im hay im-nhm (multicast), ngha l cng mt ni dung s gi mt hay nhiu tin trnh khc. 2.1.1C s truyn thng Trckhitholunvtruynthngtrongcchthngphntnchngtas nhc li mt s kin thc c bn v cc giao thc mng v sau s cp n mt s cchtipcnpdngchnggiiquytvntruynthngtrongcchthng phn tn. 2.1.1.1Giao thc mng Cc tin trnh trong h thng phn tn khng s dng chung b nh, do vic traoithngtinphidahontonbngphngthctruynthngip.Khimt tin trnh A mun trao i thng tin vi tin trnh B, n to mt thng ip trong vng nhringcamnhvthchinligihthng,khihiuhnhsthchin chc nng chuyn thng ip n tin trnh B qua mng. V nguyn l th n gin nh vy, trong thc t qu trnh ny kh phc tp bi trong h thng phn tn c th c cc my tnh thuc cc nh sn xut khc nhau v s dng tiu chun m ha thng tin khc nhau. khc phc vn ny, t chc chun ha Quc t ISO a ra m hnh lin kt h thng m (OSI). Mc d cc giao thc trong m hnh OSI t c s dng, tuy nhin l m hnh kh tt hiu v mng my tnh. M hnh OSI c phn thnh 7 lp (xem hnh 2.1), mi lp l mt tp cc giao thc qui nh khun dng d liu v cc th tc x l (cch gi/nhn, cch x l li). C hai loi giao thc: H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 21 -Giaothcclinkt:Cnphithitlplinkttrckhitruynsliu,sau khi truyn xong th phi hy b lin kt. -Giao thc khng lin kt: Khng cn phi thit lp lin kt khi truyn s liu Hnh2.1 M hnh lin kt h thng m (OSI) Hnh 2.2: ng gi d liu ti cc tng m hnh OSI Mi lp trong m hnh OSI thc hin mt s chc nng nht nh: -Lpngdng:Cungcpgiaodinphcvchongisdngvccngdng khc -Lp trnh din: Thc hin m ha/gii m, nn/gii nn v bo mt d liu. -Lp phin: To ra cc phin lm vic. -Lp giao vn: To lin kt gia u cui vi u cui, iu khin tc truyn d liu, x l li truyn tin. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 22 -Lp mng: Qun l a ch logic ca cc i tng tham gia vo mng, tm ng i tt nht cho mi gi tin. -Lp lin kt: Thit lp lin kt gia hai thit b vt l k cnh nhau -Lpvtl:Biniccbitdliuthnhcctnhiuphhpvimitrng truyn dn v thc hin thu pht cc tn hiu . Khi mt tin trnh A trn my tnh th nht mun gi thng tin cho tin trnh B trn my tnh th hai, n thm to d liu ti lp ng dng v ln lt chuyn n cc lp di trn my tnh . Khi i qua mi lp, thng tin iu khin c thm vo d liu, qu trnh gi l bao ng d liu (hnh 2.2).Cc giao thc mc thp Cc giao thc mc thp hm ch cc giao thc ti lp vt l, lin kt d liu vlpmng.Lpvtllinquantivicchuynccbtdliu,quinhcctiu chun v in, c v cc giao din kt ni mng, phng php truyn cc bit. Lp lin kt d liu tp hp cc bit thnh tng nhm (gi l khung d liu) ,pht hin v sa li khi truyn cc khung d liu . Trong mng din rng, vic trao i thng tin gia cc my tnh phi chuyn qua nhiu thit b nh tuyn. Nhim v chnh ca cc thit bnylduytrbngnhtuynvtmngitt nht chomi gi tin. Hinnay giao thc mng ang c p dng ph bin nht l giao thc IP. Cc giao thc lp giao vn Hnh 2.3 Qui trnh truyn s liu c lin kt Lp giao vn l lp cui cng trong ngn xp giao thc c s (ngi pht trin phn mm s dng tp cc giao thc ny pht trin cc ng dng mng). Chc nng c bn ca lp giao vn l qun l vic trao i thng tin gia hai thit b u cui ca ngi s dng. K thut truyn s liu c hai loi: truyn s liu c lin kt v khng H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 23 lin kt. i vi truyn s liu c lin kt, lp giao vn thc hin thm cc chc nng pht hin, sa li v iu khin tc truyn d liu gia cc thit b u cui ca ngi s dng. Trong phng php truyn d liu c lin kt, trm pht v trm nhn cn phi thit lp lin kt trc khi truyn s liu, sau khi truyn xong th phi hy b lin kt. Cc giao thc mc cao Ccgiaothcmccaonmtrnlpgiaovn,OSIkhuynngh3lp:Lp phin, lp trnh din v lp ng dng. Ngoi ra, ty theo yu cu pht trin h thng ngi ta c th thm mt s cc giao thc khc nhm n gin ha qu trnh pht trin cc sn phm phn mm mng, cc giao thc c gp chung vo nhm phn mm trunggian(Middleware).Lpphinqunlcuchithoigiaccmytnhtrn mng. Ti lp ny ngi ta thit kt cc im kim tra nhm hn ch vic phi truyn li ton b d liu khi xy ra s c mt d liu trn mng. Lp trnh din thc hin cc nhim v m ha/gii m d liu nhm thng nht cch th hin cc loi d liu khc nhau ca ngi s dng (dng bng m ASCII), nn/gii nn d liu m ha/gii m bo mt d liu. Lp ng dng bao gm cc giao thc phc v trc tip cho cc dch v ca ngi s dng nh: th in t, truyn file, truy nhp trang thng tin in t. Phn mm trung gian Vmtlogic,phnmmtrunggianthngnmtilpngdng,ncha nhiugiaothcanngbotnhclpviccngdngring,chngthng c th hin di dng cc dch v. Tu theo yu cu s dng v kh nng pht trin, cthxydnghthngphntntheocacmc:truyntptin,xlkhch/ch thun tu (My trm/My ch), xl hnh ngang hng (Peer-To-Peer). Phng php truyn tp tin l mc n gin nht trong cc h thng phn tn, thng tin cn trao i gia cc i tng trong h thng c lu di dng tp tin, cc my tnh phi cng s dng mt giaothc truyn tp tin.Phnmmtrunggiannginhosphctptrongvictruyndliutrong mng, nh c phn mm ny m vic gi cc th tc t xa s c th hin tng t nhgiccthtctrnmyccb.ichiuvimhnh7lpOSI,phnmm trung gian th hin cc tnh nng ca n trong lp trnh din v lp phin. Hin nay c nhiu kin trc khc nhau dng th hin phn mm trung gian nh: Gi th tc t xa(RPC),kintrcmitrngyucuitngchung(CORBA),mhnhi tng thnh phn phn tn (DCOM) v gi thao tc t xa ng dng trong Java (RMI). Gii php RMI p dng ring cho ngn ng lp trnh Java, n s dng nhiu c tnh ca phng php gi th tc t xa RPC v kin trc CORBA. Tuy nhin khi kin trc CORBAcavolicangnngJavathkintrcnysdnthayth RMI. MhnhDCOMchcngdngtrongcchthngcithiuhnhca Microsoftvchiuhnchtrongvicthitkhthng.Mcxlnganghngl mccaohntrongmhnhkhch/ch,cctintrnhtngtccthlmy khch, my ch hoc ng thi l my khch v my ch. 2.1.1.2Phn loi truyn thng hiu v cc loi truyn thng m lp trung gian cung cp cho cc ng dng, chng ta coi n nh mt dch v ph tr trong m hnh tnh ton khch/ch.V d h thng th in t, v nguyn tc th li ca h thng ny l dch v truyn thng trung gian, trn mi my ca ngi dng ci t phn mm cho php bin son, gi v nhn H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 24 th in t. Ngi dng bin son th, gi ln h thng phn pht th in t v ch i kt qu phn pht th n ngi nhn. Tng t nh vy, ngi nhn kt ni n h thng th in t, kim tra xem c th ca mnh hay khng, nu c th h thng th in t s chuyn cc bc th ti my ca ngi dng. H thng th in t l mt v d in hnh v phng php truyn thng bn b (persistent),ccthngipcangidngclutrtronghthngchonkhi chuyn thnh cng n ngi nhn, bn gi v bn nhn hot ng hon ton c lp vi nhau. Ngc li, phng php truyn thng nht thi (transient) ch lu gi thng ip trong thi gian gi v nhn, ngha l bn gi v bn nhn ph thuc ln nhau, nu bn nhn khng hot ng th cc thng ip s b hy b. Truynthngcngcthcthchindihnhthcngbhockhng ngb.Trongphngthctruynthngngb,bngisbphongtachon khi bit chc chn yu cu ca mnh c bn nhn x l. Phng php ny nh dubathiim:Thiimthnhtbngisbphongtachonkhihthng trung gian tip nhn xong yu cu, thi im th hai h thng trung gian thng bo chuynyucuchobnnhnvthiimthbanbngis tipnhnkt qu bn nhnxl.Ngcli,truynthngkhngngbchophpbngitiptcthc hin cng vic ca mnh sau khi gi thng ip n h thng trung gian. Hnh 2.4 Nguyn l truyn thng s dng thnh phn trung gian Trongthctngitathngkthphailoitruynthngtrntraoi thngtingiacctintrnh,phngphptruynbnbvngbthngcp dng trong cc h thng truyn thng ip trong khi phng php ngn v ng b li c p dng rng ri thc hin gi th tc t xa. Bn cnh tnh bn b v tnh ngbngitacnphnbittnhrirchaylintccatruynthng,nhngh thng m mi thng ip c truyn i l nhng n v d liu c lp s c xp H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 25 vonhmrirc,nuccthngipctruynlnltvlintcgilphng php truyn tin theo lung.2.1.2Gi th tc xa Nhiu h thng phn tn s dng phng php trao i trc tip cc thng ip gia cc tin trnh, qu trnh ny c thc hin tng minh do khng p ng yu cutnhtrongsuttruyntin,ccthtcgivnhndliuhontonkhngquan tm n qu trnh trao i thng tin. Cc khuyn ngh v phng php gi th tc t xa (RPC) c a ra t nm 1975, nhng mi ti nm 1984Birrell v Nelson mi xut gii php hon ton mi thc hin trao i thng tin bng phng php ny. tng ca phng php vn da vo qui trnh gi th tc, tuy nhin im khc bit nmchthtcccittrnmtmytnhkhc,ngilptrnhchcn chuyn cc gi tr vo cc tham s ca th tc. V nguyn tc, phng php ny kh n gin cho vic ci t, tuy nhin trong thc t ny sinh kh nhiu vn nh:thc thi m lnh c thc hin trn cc vng nh khc nhau hoc nu mt trong hai my tnh b li trong qu trnh thc thi m lnh cng ny sinh nhiu vn phc tp. Mc d vy, phng php gi th tc t xa vn l phng php c p dng ph bin nht trong cc h thng phn tn. 2.1.2.1C ch hot ng ca phng php gi th tc t xa Phngphpgith tc txachophpci t cch thng phn tn theom hnh khch/ch: Cc ng dng khch kt ni vi my ch v s dng cc dch v do mymychcungcp.Ccbcgithtctrnmychcthchintngt nh gi th tc trn my cc b, my khc chuyn cc tham s u vo khi gi th tc vdchvtrnmychskimtratrnhhplcaccthams,thchintnh tonvtrvccgitrtheoyucucangdngmytrm.hiuvphng php gi th tc t xa, trc ht chng ta cn phi nhc li qui trnh thc hin khi gi mt th tc truyn thng trn mt my tnh. Gi s c mt th tc c tp tin n gin sau:count = read(fd, buff, nbytes); trong fd l con tr tp tin, buffl vng m, nbytes l s lng byte cn c. Hnh 2.5 Gi th tc t xa theo phng php truyn thng H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 26 Khi chng trnh gi th tc, n to ra mt ngn xp dnh cho th tc . thcthiligithtc,ntruynccthamscathtcvongnxptheotht ngc(thamsutinscchuyn cuicng).Saukhithc hinxongthtc, gi tr tr v s c chuyn ti cc thanh ghi, gii phng vng nh v chuyn quyn iu khin cho chng trnh gi, chng trnh gi s loi b tham s ra khi ngn xp, tr ngn xp v trng thi nh trc khi gi th tc. Vic truyn tham s c th c thc hin bng mt trong ba phng php: Truyn gi tr, truyn con tr (pointer) v truyn tham chiu (reference) . Con tr n gin l a ch ca mt i tng trong b nh. Thng thng, cc i tng c th c truy xut trong hai cch: trc tip bi tn i din hoc gin tip thng qua con tr. Cc bin con tr c nh ngha tr ti cc i tng ca mt kiu c th sao cho khi con tr hy th vng nh m i tng chim gi c thu hi. Cc con tr thng c dng cho vic to ra cc i tng ng trong thi gian thc thi chng trnh. Khng ging nh cc i tng bnh thng (ton cc v cc b) c cpphtlutrtrnngnxptrongthigianchy(runtimestack),mtitng ng c cp pht vng nh t vng lu tr khc c gi l heap.Tham chiu cung cp mt tn tng trng khc gi l bit hiu (alias) cho mt i tng, truy xut mt i tngthngquamt tham chiu ging nh l truy xut thng qua tn gc ca n. Tham chiu nng cao tnh hu dng ca cc con tr v s tin li ca vic truy xut trc tip cc i tng, chng c s dng h tr cc kiugithngquathamchiucaccthamshmcbitkhiccitngln c truyn ti hm. Hnh 2.6 Nguyn l gi th tc t xa tng phng php gi th tc t xa l che giu qu trnh thc hin th tc trn my tnh khc (m bo tnh trong sut). iu ny c thc hin bng cch che giuqutrnhtraoithngtingiaccmytnh.Khithchingithtctxa, mt thnh phn trn my khch (gi l Stub) s ng gi cc tham s vo thng ip vyucuthngipphicchuynnmych.Timych,mtthnh H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 27 phn tng ng vi Stub (gi l Skeleton) s gii m thng ip nhn c v thc thi cc m lnh nh phng php gi th tc truyn thng, sau tr vli c ng gi thnh thng ip v tr v cho Stub. Stub trn my khch s gii m thng ip v tr v cho chng trnh gi cc gi tr hoc cc tham s theo yu cu. Qu trnh x l gia Stub v Skeleton hon ton trong sut i vi li gi th tc. s dng tnh nng gi th tc t xa, mt chng trnh trn my ch phi cung cp cc dch v m t trong ngn ng RPC. Mi my ch c gn tn v s chng trnh, tt c cc dch v c khai bo trong danh sch vi y cc tham s th hin dch v. Vi nguyn tc ny, ngn ng RPC cho php thc hin cc kiu d liu n gin cngnhccdliu phc tpnh: struct, enum... Qui trnh thchinbaogm cc bc sau: -My khch s dng tnh nng gi th tc cc b trong Stub. Stub trn my khch gi cc tham s n my ch bng cch gi yu cu RPC. -Yu cu ca Stub c Skeleton trn my ch phn tch. -Thc hin th tc c phn tch trn my ch. -My ch tr v kt qu thc hin cho my khch Hnh 2.7 Cc bc thc hin trong gi th tc t xa Phng php gi th tc t xa th hin quan im tch bit gia giao din v phn ci t, xut pht t vic khai bo giao din, phn mm trung gian to cc m lnh h trchovicxlphntnbngcchthhinccngdngdidngngngha truynthngtrnmyccb,tuynhinnphimbonhiunhimvphctp nh: truyn d liu, ng b tin trnh. Qu trnh thc hin gi th tc t xa c thc hin qua mi bc sau: 1.Th tc trn my khch gi stub nh phng php gi th tc truyn thng. 2.Stub to thng ip v chuyn n h iu hnh ca my khch . 3.H iu hnh ca my khch gi thng ip n h iu hnh ca my ch. 4.H iu hnh ca my ch chuyn thng ip n Skeleton . 5.Skeleton gii m thng ip thnh cc tham s v gi th tc x l tng ng. 6.My ch thc hin li gi th tc v tr v gi tr cho Skeleton. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 28 7.Skeleton ng gi tham s gi tr tr v thnh thng ip v chuyn n h iu hnh ca my ch. 8.H iu hnh ca my ch chuyn thng ip n h iu hnh ca my khch. 9.H iu hnh ca my khchnhn thng ip v chuyn cho Stub. 10. Stub gii m kt qu v tr v cc tham s theo yu cu ca th tc gi. 2.1.2.2Vn truyn tham s Gi th tc truyn thng c ba cch truyn tham s: truyn gi tr, truyn tham chiuvtruyncontr.ivivicgithtctxa,khngthpdngphng phptruyncontrdochcththchinbngcchtruyngitrhoctruyn tham chiu. Truyn gi tr tr nn phc tp i vi h thng phn tn khng ng nht (c hai cch nh dng d liu, cc b vi x l ca Intel theo nh dng little endian, trong khi cc b vi x l ca Sun theo nh dngbig endian). Hnh 2.8 Vn truyn tham s trong cc h thng khng ng nht Hnh 2.8 minh ha v d th tc t xa gm 2 thm s (5, JILL), cc byte (thc cht l cc bit) d liu ln lt c chuyn t my tnh ca hng Intel sang my tnh ca hng Sun, khi n my Sun gi tr ca cc tham s theo th t ngc v my Sun s hiu s 5 l5 x 224, nh vy ch cn o ngc th t l s nhn c kt qu ban u. Tuy nhin, kiu s nguyn mi cn o v tr cc byte nhng d liu kiu xu k t li khng cn thit, do phi b xung thm thng tin v kiu d liu ca tham s. Con tr l kiu d liu c bit, n lu tr a ch ca mt bin s m a ch ch c ngha bn trong mt my tnh, nh vy khng th p dng phng php ny truyn tham s trong gi th tc t xa. Tuy nhin, gii php truyn tham chiu c ththchinbngcchtomtbinthamchiutngngtrnSkeletonvthtc trn my ch s s dng a ch ca bin ny nh phng php truyn tham chiu ca mt th tc thng thng. Hnh 2.9 Chuyn th tc thnh thng ip trn Stub H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 29 Phng php gi th tc t xa che giu qu trnh trao i thng tin trn mng, qu trnh ny c thc hin bng vic chuyn i tham s sang thng ip trong cc stub. thc hin cng vic ny, c pha my khch v my ch u phi tun th quy nh v nh dng tham s, l giao thc gi th tc t xa. n gin ha qu trnh to Stub cho my trm v my ch, mt ngn ng mi c s dng gi l ngn ng nhnghagiaodin(IDL).Lptrnhvinchvicvitcchmvccthtctheo qui nh ca ngn ng, sau dng chng trnh dch IDL chuyn thnh ngn ng lp trnh tng ng. 2.1.2.3Gi th tc t xa bng phng php khng ng b Gingnhphngphpgithtcthngthng,khigithtctxatin trnh trn my khch s b phong ta cho n khi nhn c kt qu tr v, vic ch i ny l khng cn thit. Hnh 2.10 Gi th thc t xa bng phng php ng b (a)v khng ng b (b) Hnh 2.11 Tng tc gi th tc t xa bng phng php khng ng b Phng php gi khng ng b cho php tin trnh gi trn my khch gi yu cu n my ch, sau khi my ch xc nhn nhn c yu cu, tin trnh trn my khchcthtiptcxlcc tcvkhcmkhngcnchiktquxlca my ch, nh vy s rt ngn thi gian phong ta h thng. 2.1.2.4M hnh i tng phn tn Hin nay vic xy dng ng dng mng da trn hai quan im: Hng i tng v h thng phn tn. Mi ng dng phn tn l tp cc i tng (giao din ngi s dng, c s d liu, cc m un ca ng dng...), mi i tng c cc thuc tnh v H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 30 cc hm ring, tng tc gia cc i tng c thc hin thng qua vic trao i tin bo gi cc hm thch hp. Kthutlptrnhhngitngchngtctnhuvitkhiphttrin cc ng dng phn mm chy trn mt my tnh. c tnh c bn ca lp trnh hng i tng l vic che giu x l bn trong, do nhng thay i bn trong i tng s khng nh hng n cc i tng khc s dng. T u im ca k tht lp trnh hng i tng, trong cc h thng phn tn ngi ta pht trin phng php gith tc t xa thnh phng php gi i tng t xa.Tiu biu trong k thut ny c thknJavaRMI,MicrosoftDCOM,CORBA.Mhnhccitngphntn c th hin trn hnh 2.12, trong : -i tng: l d liu c ng gi trong chng trnh, n c y cc tnh cht ca mt i tng theo quan im lp trnh hng i tng nh: tnh tha k, tnh a hnh.... Cc i tng c th ng vai tr My trm, My ch hoc c hai. -Mi trng yu cu i tng (ORB): l mi trng cho php cc i tngtm thynhautheophngphp ng v giao tip vi nhau qua mng,yl xng sng ca cc h thng hng i tng phn tn. -Cc dch v i tng: l cc dch v cho php ngi s dng thao tc v x l cc i tng. Hnh 2.12 M hnh cc i tng phn tn Phn mm trung gian ng vai tr cung cp cc cng c h tr vic xc nh cc i tng t xa v to mi trng thun tin i tng giao tip vi nhau. Xu th chun ha phn mm trung gian Victhitlpcctiuchunchophnmmtrunggiannhmmcchcungcp kh nng tng thch v tnh mm do ca cc ng dng My trm/My ch, trong tp trung vo vic: Chun ho giao din lp trnh API v chun ho giao thc trao i thng tin. Theo hai tiu ch trn, phn mm trung gian c chia thnh bn loi sau: i tng Client (Client object) i tng Server (Server Object) Mi trng yu cu i tng (Object Request Broker) Cc dch v i tng (Object services) H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 31 -Phn mm trung gian m hon ton: s dng giao din API chung v giao thc trao i chung gia My trm v My ch, ni chung cc sn phm loi ny phi m bo kh nng giao tip gia My trm v My ch m khng ph thuc giao thc trao i thng tin ga cc cng mng. Sn phm loi ny bao gm DCE RPC (gi th tc t xa trong mi trng tnh ton phn tn), CORBA, OpenDoc. -Phn mm trung gian vi giao din API m: Cho php My trm giao tip vi My ch s dng sn phm ca cc hng khc nhau vi iu kin giao thc s dng trao i thng tin ging nhau, v d sn phm ODBC ca Microsoft. -Phnmmtrunggian vi giao thc trao i thng tin m: s dng giao thc trao i thng tin chung, tuy nhin c chuyn i giao din API khi My trm v My ch s dng phn mm trung gian ca cc nh cung cp khc nhau (v d kin trc c s d liu quan h phn tn DRDA ca IMB) . -Phnmmtrunggianring:ccngdngMytrm,Mychchgiaotipvi nhau khi s dng phn mm trung gian ca cng hng (v d ActiveX/OLE). i tng phn tn Mtctnhquantrngcaitngltnhbaongccthuctnh(hng, bin s) v cc thao tc x l cc thuc tnh , vic thao tc vi thuc tnh trong mi i tng u phi c thc hin thng qua cc hm giao din. Trong cc h thng phn tn, i tng khng n thun nm trn mt my tnh, a phn chng c ci t trn cc my tnh khcnhau. Khi my trm nhng vo mt i tng phn tn, mt thnh phn giao din ca i tng (cn gi l proxy)s c np vo khng gian a ch ca my trm. Proxy thc hin chc nng tng t nh my trm stub trong phng php gi th tc t xa, n m nhim chc nng chuyn i li gi cc hm giao din thnh dng thng ip h iu hnh chuyn n my ch v ngc li chuyn i thng ip t my ch thnhktqutrvcahmgiaodin.itngthcnmphamych,nc giaodingingnhtrnmytrmvngthimtthnhphngilskeletonc nhimvchuynithngiptphamytrmthnhligihmtngngvi yu cu ca my trm v ngc li chuyn kt qu thc hin ca hm thnh thng ip h iu hnh chuyn ti my trm. Cc thuc tnh trong i tng phn tn c th c t chc trn cc my tnh khc nhau, tuy nhin trong hu ht cc h thng phn tn, cc thuc tnh ca i tng phn tn thng c t trn mt my tnh, l i tng t xa. Bin dch i vi cc i tng phn tn Ccitngtronghthngphntnxuthindinhiuhnhthc,mt trong nhng hnh thc ph bin nht l lin quan trc tip ti cc i tng trong cc ngn ng lp trnh hng i tng nh Java, C++, l cc ngn ng bin dch, vic sdngccngnnglptrnhnystoiukinddngchovicphttrincc ngdng phn tn. Nhc im c bn ca cc i tng bin dch l s ph thuc vo ngn ng lp trnh, khc phc nhc im ny cn phi xy dng cc i tng phntnmtcchtngminh,khicthxydngccngdngphnmmt nhiu ngn ng lp trnh khc nhau. Viccitbntrongccitngphntncmchocclptrnh vin,iuquantrngcnphimbocctnhthngnhtvmtgiaodincc mytnhkhccthgiitng.Giiphpchovnnylxydngmt H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 32 thnhphnthchnghiitng,vaitrquantrngcanlvicthhincci tng phn tn trn mi trng mng. Nhng My trm vo i tng Vic gi cc i tng phn tn tng t nh gi i tng trn mt my tnh, im khc bit c bn l trc khi gi hm ca i tng phn tn cn phi nhng i tngccbvoitngphntn.Chaicchthchin:tngminhvkhng tngminh.iviphngphptngminh,cnphikhaibobincontrtrn my tnh my trm v sau gi hm bind nhng i tng phn tn vo bin con tr cc b . Distr_object* obj_ref; // Khai bo i tng tham chiu ton h thng obj_ref = ...; //Khi to bin tham chiu cho i tng phn tn obj_ref->do_something( );//Nhng khng tng minh, gi hm Distr_object* obj_ref;// Khai bo i tng tham chiu ton h thng Localobject* obj_ptr;// Khai bo bin con tr cho i tng cc bobj_ref =...;// Khi to bin tham chiu cho i tng phn tn obj_ptr = bind(obj_ref);// Nhng i tng bng phng php tng minh obj_ptr->do_something( );// Gi hm2.1.3Truyn thng hng thng ip Phng php gi th tc t xa hay phng php gi i tng t xa c u im lchegiuqutrnhtraoithngtintronghthngphntn,gpphnnngcao tnh trong sut ca h thng. Tuy nhin iu ny khng phi lc no cng ph hp vi cc ng dng phn tn. Ging nh qu trnh gi th tc trn mt my tnh, my trm phitrngthichtrongthigianitngphntntrnmychthchincc thao tc x l.2.1.3.1Tnh bn b v tnh ng b trong trao i thng tin Ccutchctraoithngipgiaccmytnhtrongmngcthc hin theo qui trnh sau: mi my tnh cung cp giao din trao i thng ip. Khi cn chuynthngipnmtmytnhkhc,ccngdngchcnchuynccthng ipngiaodin,cngvictiptheosdohiuhnhmnhim.Truyn thng ip trong h thng phn tn chia lm cc loi sau: -Truyntinbnb:Thngipclutibm,nukhngtmthychth khngbxa.Chuynthngipbnbtngtnhtchcmnglibu chnh,buphmcchuynnccbuccvngiathcnhimv chuynccbuphmnnginhn,qutrnhnycthphicchuyn qua mt hoc nhiu bu cc. -Truyntinchuyntipnhanh:Thngipchclutrongthigianthchin chuyn thng tin, nu khng tm thy ch th thng ip s b chi b. -Truyn ng b: Bn gi s tm ngng tin trnh cho n khi thng ip c lu trong vng m ca bn nhn. -Truynkhngngb:Bngichbtmngngtrongthigianchuynthng ip n vng m ca bn gi (cha cn chuyn sang bn nhn). Trong thc t, k thut truyn tin c th c thc hin da trn t hp ca cc c tnh trn: Truyn tin khng ng b, bn bH thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 33 Truyn tin ng b, bn bTruyn tin khng ng b, chuyn nhanhTruyn tin khng ng b, chuyn nhanh da trn bn nhn Truyn tin khng ng b, chuyn nhanh da trn bn gi Truyn tin khng ng b, chuyn nhanh da trn phn hi Gn y, hu ht cc h thng phn tn la chn phng php truyn tin khng ng b chuyn nhanh da trn phn hi p dng cho vic gi th tc t xa v i tng t xa. 2.1.3.2Truyn tin nhanh hng thng ip Nhiungdngtrncchthngphntncxydngdatrnmhnh hng thng ip do lp giao vn cung cp.Theo m hnh mng TCP/IP, mng my tnhcphnlm4lp,mbotnhduynhtcamithngiptrnmng, mithngdipc gnvi cng va ch logic camytnh,thpcngv a ch gi l socket. to iu kin thun li cho vic pht trin phn mm trn h thngphntn,mhnhmngTCP/IPquinhmtshmchun(hmnguyn thy), qu trnh truyn tin s dng k thut ny c tm tt trong bng sau: Hm ngha SocketTo Socket BindGn a ch cc b vo socket ListenThng bo sn sng nhn thng tin AcceptTip nhn yu cu lin kt ConnectThit lp lin kt SendGi d liu ReceiveNhn d liu CloseHy b lin kt Giao din chuyn thng ip Ht nhn ca giao din chuyn thng ip l cc hm nguyn thy bao gm: Hm ngha MPLbsendThm thng p vo vng m gi MPI-sendGi thng ip v ch cho n khi ton b thng ip c chuyn n vng m ca bn nhn MPLssendGi thng ip v ch cho n khi bn nhn bt u thc hin vic nhn thng ip MPLsendrecvChuyn thng ip v ch cho n khi c xc nhn ca bn nhn MPUsendTham chiu n thng ang ch gi MPLissendTham chiu n thng ang ch gi v ch cho n khi bn H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 34 nhn bt u MPLrecvNhn thng ip, phong ta nu khng c thng ip MPLirecvNhn thng ip, khng phong ta nu khng c thng ip 2.1.4Truyn thng hng lung Nhng k thut truyn tin cp trn y mi ch ch trng n vic trao i thng tin m cha ni n thi gian thc hin qu trnh chuyn tin . Trong thc t c nhiu d liu cn chuyn theo thi gian thc (v d m thanh, video.). Mt s d liu cn phi p ng yu cu v mt thi gian cng nh tnh lin tc ca d liu cn phi chuyn, khi cn phi k thut truyn dng lung. Nh vy, y cn phi thc hin theo ch chuyn tip nhn v khng ng b. i vi vic truyn tin ph thuc thi gian, yu cu quan trng l phi p ng tiu chun v cht lng truyn tin, l cc thng s m h thng phn tn cn phi p ng mbocht lngdchv.Ccdchvaphng tinbaogmnhiu lungdliukhcnhaunhvnbn,mthanh,hnhnhcnphicngb gia cc lung d liu , cn phi duy tr mi tng quan gia cc lung d liu (d liu c th xut hin di dng lin tc hoc khng lin tc). Vic duy tr ng b cn phi c thc hin ti cc u cui cng nh trong mi trng mng. 2.1.5Truyn thng theo nhm Truynthngtheonhm(multicalst)lphngphptruyndliutmt thnh vin n nhiu thnh vin khc trong cng mt nhm ch vi mt ln thc hin.Truyn thng theo nhm c s dng trong rt nhiu lnh vc ca ng dng phn tn nh: dch v truyn hnh, hi tho, trnh din bo co, truyn pht thng tin Truyn thng theo nhm c th c ci t trn ti tng lin kt d liu hoc tng mng hoc tng ng dng ca m hnh OSI.2.2t tn Vic t tn ng vai tr quan trng trong tt c cc h thng my tnh, chng dng xcnhduynht thc thkhi chia s ti nguyn trong hthng.Trongh thng phn tn, qui tc t tn c tri rng trn cc my tnh khc nhau. 2.2.1Tn, nh danh v a ch Trong h thng phn tn, tn l mt xu cc bit hoc c k t dng tham chiu m mt thc th, thc th c th l my tnh, a hoc cc tp tin. Mt thc th c th c nhiu tn. Tn (name) l xu cc bit hoc k t dng tham chiu n mt thc th trong h phn tn. a ch (address) l im truy nhp (access point) n thc th. Cc im truy nhp ny cng phi c t tn v tn chnh l a ch ca n. Nh vy a ch ca thc th chnh l tn ca im truy cp thc th tng ng. nh danh (Identifiers) l mt kiu tn c bit, mi thc th ch c tham chiu bi duy nhtmtnhdanhvminhdanhthamchiuduynhttimtthcth.Khng gian tn (Name space) dng biu din tt c cc tn, xt v mt hnh hc th y l mt th c hng, gm cc nt v cc cung, gi l th tn (naming graph). th c cu trc l th m mi nt l miu t mt mt thc th. Mi nt th mc gn vi nhiu nt khc v c lu tr trong bng th mc bao gm tp cc cp nhn v nh danh.Tnthnthin(Human-friendlyname)lcctnctmtcchdhiu, H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 35 thn thuc vi con ngi. truy nhp n mt thc th cn phi bit im truy nhp hay cn gi l a ch ca thc th . a ch l mt loi tn c bit: -Mt tn c th c nhiu a ch-Thc th c th thay i a ch trong qu trnh tn ti-Mt a ch c th tr n cc thc th khc nhau trong cc thi im khc nhau-m bo c th tham chiu ti cc ti nguyn bng tn-nh danh l mt loi tn c bit, n cn phi p ng ba yu cu sau: -nh danh ch tham chiu n nhiu nht 1 thc th -Mi thc th ch c mt nh danh -Khng c ti s dng nh danh. Vi vic s dng nh danh s trnh c nhng tnh hung nhp nhng trong vic truy nhp thc th. Trong h thng phn tn, vic truy nhp n mt thc th cn phi tham chiu n nhiu tn (ng dn ti thc th). 2.2.2t tn phng ttnphng thuc loi ttnphicutrc,nnthun ch gmchuicc bit ngu nhin khng cha bt k thng tin no nh v im truy nhp lin quan ti thcth.xcnhimtruynhpticcthcthcanhdanh,ngitas dng bn gii php: Gii php n gin, da trn ngun gc (home based), hm bm phna tn v hnh thc phn cp. 2.2.2.1Cc gii php n gin Giiphpngingmhaiphngphp:sdngqungb(broadcast)hoc nhm (multicast) hoc s dng con tr chuyn tip (forwarding pointer). Phng php qungbhocnhmcthchinbngcchginhdanhcntmtittccc my, my no c thc th trng khp vi nh danh cn tm th gi li mt thng bo chaachcaimtruynhp.Phngphpnyihittccctintrnhu lng nghe v tip nhn yu cu gi n, n ch ph hp vi qui m nh, do thng chcpdngtrongccmngnib.Phngphpdngcontrtipdatrn nguyntcmtthc th ding rikhiv tr A cannvtrB thns li mt tham chiu ti v tr mi ca n. Nh , khi nh v c thc th, my khch c th xc nh ngay c a ch hin ti ca thc th ny nh vt a ch . 2.2.2.2Cch tip cn da trn ngun gc Cch tip cn da trn ngun gc (Home-based): cp pht cho mi thc th mt v tr gc, phng php ny s to ra mt v tr gc lu gi a ch hin ti ca cc thc th (thng l ni thc th c to ra ). a ch ca gc c ng k ti dch v t tn. Gc ng k a ch ngoi ca cc thc th my khch lun n gc trc tin, v sau tip tc vi cc v tr bn ngoi.2.2.2.3Bng bm phn tn Bng bm phn tn (DHT) c t chc tng t nh bng bm thng thng dng cung cp chc nng tm kim trong h thng phn tn. Mt cp kha v gi tr c lu trong DHT v bt c nt no tham gia vo h thng cng c th ly c gi tr ng vi mt kha xc nh. Vic duy tr bng nh x gia kha v cc gi tr c lu phn tn trn cc nt, do vic thay i ca mt s nt tham gia vo h thng s ch nh hng n mt s nh cc kha lin quan. iu ny gip cho DHT c th d H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 36 dngmrngvi slng lnntthamgia,vcungcp khnng duy tr hthng khi c nt tham gia, ri khi mng, hay b li. u im ca phng php s dng hm bm phn tn l n khng s dng bt k mt my trung tm no qun l, d dng thch nghi m rng h thng. DHT cha khnggiankhao(vdnhchuicdi160bit),chngcphnvngcho tng nt trong h thng. Mt mng ph kt ni cc nt vi nhau, gip cc nt ny tm c nt ang gi thng tin v mt kha trong khng gian kha. lu mt tp tin vi tn v d liu ca n trong DHT, thut ton SHA-1 c s dng to m bm ca tn tp tin l kha k c di 160 bit. Tip mt thng bo put(k,data) c gi n cc nt trong mng DHT. Thng ip ny c chuyn tip qua cc nt qua mng ph cho n khi ti c nt gi trch nhim lu gi kha k c quy nh bi cch phn b khng gian kha. Nt s thc hin lu gi kha vdliu.Ccntkhccthlythngtincafilebngcchthchinhmbm trntnfile lyckhak,sau truy vnbtkntnotrongmngDHT tmkimdliungvikhakbngthngipget(k).Thngipnytngt c truyn trn mng ph thng qua cc nt cho n khi ti nt lu gi thng tin v kha k, nt ny s tr li thng tin v d liu ng vi kha.PhnlncchthngDHTsdngphngphpbmnhtqunnhx kha vo cc nt. K thut ny cung cp mt hm (k1,k2) tnh khong cch gia hai kha k1 v k2. Mi nt c gn cho mt kha nh danh ID. Mt nt vi ID l ix s c trch nhim lu tr vi tt c cc kha km nu nh ix l nh danh nt gn nht vi cc kha , tnh ton bng hm (k1,k2). Khi c s thm bt mt nt trong mng chi c nhngkhathucntmicnchuynsangccntlncn,trongkhikhngtc ng gnccntkhc.imnyhontonkhcbitviphngphpbngbm thngthng,khithayimtphnskhinchognnhtonbkhnggiankha phitnhtonli.Dovicchuynikhatntnysangntkhcyuculng bngthngtrongvicchuyniccdliu,dopngiukinmngc nhiu bin ng (nt ra vo vi tn sut cao) th vic c t thay i ln cu trc mi khi c thay i l yu cu cp thit. Mintduytrmttpccngdnnccntkhc(ccntlngging) haycngilbngnhtuyn.Tpccngdnnytolnmngph.Mtnt chn cc nt lng ging da theo mt cu trc nht nh gi l topology ca mng. Tt c cc hnh trng ca DHT u cha cc c im nht nh nh: vi kha k bt k, mi nt hoc s c l nt lu tr kha k hoc c ng dn ti nt c nh danh gn vikhakhn,theonghavkhongcchgiacckhanutrn.Ngoivic m bo nh tuyn mt cch chnh xc, mt hnh trng cn phi m bo hai yu t quan trng l m bo s lng ti a cc nt phi i qua tr li mt truy vn phi nh m bo p ng nhanh truy vn v s lng lng ging ca mt nt (bc ca nt) phi nh m bo khng lm gy kh khn trong vic duy tr h thng.Chordlmttrongnhnggiaothcphbinnhtcsdngtrongbng bmphntn.MngChordhtrkhnnggntngngmtkhachotrcvi mtntmng.TythucvongdngsdngChord,ntcthmnhim nhimvlutrdliucgnvikha.Chordsdngphngphp consistent hashing, gin tip thc hin vic cn bng ti gia cc nt do mi nt c gn vi mt s lngkeytng ngnhau.Victhamgiavrikhimng sch khin cho mt s nh cc key chuyn t nt ny sang nt khc. c im khin Chord H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 37 trnnthngdngchnhlkhnngmrngmng.Trongkhiviccthutton trc mt nt cn phi duy tr thng tin v nhiu nt khc trong mng th Chord ch cn mt s lng c nh. Chnh iu ny gip cho Chord c th hot ng hiu qu trong mng c s lng cc nt ln. Cc nt trong mng Chord to ln mt mng logic dng vng trn c cc v tr nt t 0 n 2m-1. Kha k c gn cho nt u tin c nh danh bng hoc ln hn nh danh ca k. Nt c gi l nt successor ca kha k hay successor(k). Trong vngnhdanhcaChordsuccessorcamtkhachnhlntgnnhttheochiu kim ng h tnh t kha k. Hnh 2.13: M hnh vng Chord vi kha c chiu di 6 bit Hnh 2.13 minh ha m hnh vng Chord vi m=6. Vng Chord c cha 10 nt v5kha.Successorca nhdanh10lnt14do key 10 s ct nt14. Tng t kha 24 v 30 s c t nt 32, kha 38 ti nt 38 v kha 54 ti nt 56. K thut bm nht qun c thit k vic cc nt tham gia hay ri khi mng s to ra t nh hng nht. duy tr bng mapping khi mt nt n tham gia vo mng, mt s kha trc y c t ti successcor ca n s chuyn sang cho nt n. Trong v d trn, nu c mt nt vi nh danh 26 tham gia vo mng, n s nhn c kha 24chuyntnt32.SuccessorcamtntlnttipsaunttrnvngChord, predecessor l nt lin trc trn vng Chord. TmkimnginlthuttontmkimnginnhttrongChord.Thut tonnychyucuccntbitcsuccessorcamnh.Truyvnchomtnh danh c chuyn xung quanh vng Chord qua cc nt successor cho n khi gp nt cchakhavinhdanhcntm.Hnh2.14lvdkhint8thc hin truy vn cho kha c nh danh 54. Nt 8 gi hm find_successor cho kha 54, kt qu tr v l nt 56 successor ca kha 54 ny. Truy vn c chuyn ln lt qua tt c cc nt trnvngnmgiant8v56.Thuttontmkimtrnsdngmtslng thng bo tng ng tuyn tnh vi s nt c trong mng. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 38 Hnh 2.14: Qu trnh tm kim n gin trn Chord tngtcqutrnhtmkimChordsdngthmmtsthngtinnh tuyn. Tng t nh trn, v d nh danh ca mi nt v kha c di m bit. Mi ntnduytrmtbngnhtuynchammc,cgilbngfinger.Mcthi trong bng ca nt n cha nh danh ca nt s sao cho s l nt u tin trn vng tip sau kha n+2i-1 s=successor(n+2i-1), vi 1 i m (ly s d vi modun 2m). Ta gi s l finger th i ca nt n. Finger u tin ca mt nt cng chnh l successor ca nt . Hnh 2.15: Bng finger ca nt 8 Hnh2.15 th hin bng finger ca nt . Finger u tin c tr n nt 14 d 14 l nt lin sau (8+20)mod 26 = 9. Tng t finger cui cng ca nt 8 tr n nt 42 do 42 l nt lin sau (8+25) mod 26 = 40. C th d nhn xt thy vi cc thit lp nh vy: mt nt ch lu thng tin v mt s gii hn cc nt c trong mng, mt nt cng ch bit n mt s nt nm gn vi n. Mt nt cng khng lu tr thng tin c th ngay lp tc tm c successor ca mt kha k. H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 39 Hnh 2.16 Gi m ca phng php tm kim ci tin Hnh 2.16 th hin on gi m ng vi vic thc hin tm kim successor ca key id c s dng bng finger. Nu id nm gia n v successor ca n, find_successor strlisuccessorcan.Nukhngntmkimtrongbngfingerchontnc nh danh ngay sau id cn tm kim v thc hin hm find_successor trn nt n. Hnh 2.17 : Qu trnh tm kim kha 54 trn nt 8 Nhhnh2.17trnnt8tmkimsuccessorcakha54.Quabngfinger ca nt 8 ta thy nt 42 l nt gn kha cn tm kim nht, nn nt 8 s thng qua nt 42,tngtqueryschuynquant51vnchlnt56.Cthchngminh c nh l c ni dung nh sau: Vi xc sut cao s nt cn thng qua tm kim successor trong mt mng N nt l O(log N). Trn thc t, mng Chord cn phi gii quyt cc vn nh vic mt nt mi tham gia vo mng, ri khi mng v t ngt ri khi mng. tham gia vo mng H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 40 mt nt n thc hin truy vn tm kim cho chnh id ca n thng qua mt s nt ban u tham gia vo mng v t a n vo vng Chord, v tr nm gia successor s v predecessor ca s thng qua qu trnh n nh mng. Bng finger ca n c khi tobngcchsaochpbngfingercacashocslnlttmkimccfinger cho n. Cc nt cn thay i bng finger khi c s tham gia ca n s ln lt thc hin vicnythngquaqutrnhnnhmngchynhk.Cuicngcckhaang c gi bi s, c id nh hn hoc bng n s c chuyn qua n. Khimtnttnguyndikhimng,ttcckha(ccitemlinquann kha)cchuynchosuccessor,sauthngbochosuccessorvpredecessor. Bng finger trn cc nt khc s dn dn c iu chnh thng qua qu trnh n nh mng nh k. Khi mt nt t ngt ri khi mng s gy ra cc hu qu nh sau: u tin vic ny c th gy mt cc kha (cc item lin quan n kha). Th hai: mt b phn cc nt s khng truy vn c mt s kha nht nh. Chord gii quyt vn ny bng cch lu trn mi nt mt danh sch cc nt nm sau n trong vng Chord. Nu mt nt t ngt khng lin lc c vi successor th n s s dng cc nt lin sau trong danh sch. Tip na cc kha (cc item lin quan ti kha) s c sao chp trn cc nt c trong danh sch . Do mt kha (item lin quan n kha) s ch b mt khi c log2(N)+1 cc nt trong danh sch phi ng thi ri khi mng. 2.2.2.4Cch tip cn phn cp Xy dng mt cy tm kim phn cp v thc hin phn min cc mc khc nhau. Mi min hnh dung nh mt nt th mc ring bit. Nt gc bit tt c cc thc th. Mi thc th trong mt min tng ng vi mt bn ghi trong nt th mc, n l a ch hin ti ca thc th hoc mt con tr. a ch ca mt thc th c lu trong mt nt l, hoc mt nt trung gian. Nt trung gian cha mt con tr n mt nt con nu v ch nu cy con nm ti nt con lu tr mt a ch ca thc th. Mt thc th c th c nhiu a ch (v d trong trng hp to bn sao). Nguyn l c bn bt u tm kim cc nt l cc b, nu nt bit thc th, tip theo s i xung pha di theo con tr, ngc li i ln trn. 2.2.3t tn c cu trc t tn phng ph hp cc my tnh nhng n hon ton khng thn thin vi con ngi, con ngi cn nhng tn n gin v d c, cho d l tn ca my tnh hay tn ca cc tp tin. 2.2.3.1Khng gian tn Hnh 2.18 th tn H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 41 Cctnthngctchcthnhkhnggiantn,chngcthhinbng cc nhn hoc th c hng vi hai loi nt: nt l v nt th mc. Nt l th hin thc th c t tn v khng cn nhnh no i ra nt na, n cha thng tin th hin thc th v d nh a ch, trng thi Mi nt th mc c gn nhn v c cc nhnh i ra, n cha bng th mc th hin thng tin ca cc nhnh i ra t nt . 2.2.3.2Phn gii tn Phngiitnlchcnngcnthitchovictraoithngtingiacctin trnh. l qu trnh chuyn i tn thnh a ch v c th c thc hin tp trung hoc phn tn. Khng gian tn a ra k thut lu tr v tm kim cc tn trn n mt cch d dng. Mt trong nhng phng php hay dng l s dng ng dn tn (path name).Qutrnhtmkimtntrongkhnggiantncgilphngiitn(name resolution). Qu trnh phn gii tn tr v nh danh mt nt, bao gm: -K thut gn (Closure): l k thut cho ta bit qu trnh tm kim tn c bt u nh th no v bt u u. -K thut lin kt (Linking): k thut ny s dng b danh (alias) - tn ging vi tn ca thc th. Vi k thut ny cho php nhiu ng dn cng tham chiu n cng mtnttrn thtn.Mtcchtip cn khc l dngmtntlkhngphi lutrachhaytrngthicathcthmlutrngdntuytiti thc th . -Kthutgnkt(Mounting):lkthutcthchinkhitmkimtrnhai khng gian tn. Mt nt th mc c gi l mt im gn kt lu gi nh danh hoc cc thng tin cn thit cho vic xc nh v truy nhp, mt nt th mc bn pha khng gian tn cn gn kt c gi l im gn kt. Thng thng, nu hai khng gian tn NS1, NS2 - gn kt mt thc th bn ngoi trong h phn tn, chng ta cn ti thiu nhng thng tin sau: Tn ca giao thc truy nhp ( c xc nh thc hin giao thc truyn thng), tn ca my ch (xc nh a ch my ch) v tn ca im truy nhp (xc nh nh danh ca nt trong khng gian tn bn ngoi). Phn gii tn tng tc (interactive name sesolution): vic phn gii tn thc hin bng cch truyn v nhn qua li gia my khch v cc name my ch cc mc khc nhau. Theo cch ny th cc my ch khng trao i trc tip vi nhau, mi my ch ch phn gii nhn tng ng vi lp xc nh a ch ca my ch tip theo, kt qu tr li cho my khch l a ch ca name my ch tip theo, v vic lin kt vi my ch tip theo l do my khch m nhim.Phn gii tn quy (recursive name resolution): theo cch ny th mi my ch qunltnsgiktqunmychqunltntiptheomntmthy.Vc nh vy cho n khi hon thnh phn gii ton b ng dn.Mi thc th u c tn v a ch tng ng, vic nh x t tn n a ch ca thc th c thc hin theo hai phng php: theo m hnh mt lp v theo m hnh hai lp: -Mhnhmtlp:chcmtmcnhxgiatnvthcth.Milnthcth thay i v tr, nh x cn phi c thay i theo. -Mhnhhailp:phnbittnvachnhnhdanhthcth.Gmhaiqu trnh:qutrnhtmnhdanhthcthtngngttncathcthcthc H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 42 hin bng dch v tn (naming service) v qu trnh xc nh v tr ca thc th t nh danh c thc hin bi dch v nh v (Location service). 2.2.3.3Ci t khng gian tn Qun l tn trong h phn tn thc hin bng cch phn mc qun l: -Mc ton cu(Global): Cha nhng nt th mc mc cao ( gc v con ca n). Trong lp ny cc nt th mc t thay i. Kh nng sn sng lp ton cu c yu cu cao hn so vi cc lp cn li. Nu my ch phn gii tn ca lp ny b li th vic phn gii tn khng th thc hin. -Mc qun tr (Administrational): Cha nhng nt th mc mc trung gian, n c th c nhm thnh cc nhm, v mi nhm c th c chia cho nhng khu vc qun tr khc nhau. Cc nt trong nhm ny cng t khi thay i. Kh nng sn sngcanamemychtronglpadministrationallrtquantrngivicc my khch do name my ch qun l. V nu my ch ny li th c rt nhiu cc ti nguyn khng th truy cp. -Mc n v (Managerial): Cha nhng nt th mc mc thp, cc nt trong mc ny thay i kh thng xuyn (V d nh cc my trong mt mng ni b). Yu cu i vi tnh sn sng ca my ch qun l tn ca lp ny t kht khe hn so vi hai lp trn. Tuy nhin, hiu sut hot ng yu cu i vi lp ny cao hn do phi thng xuyn cp nht cc thay i. Khng gian tn l tri tim ca dch v t tn, n cho php ngi x dng v cc tin trnh thm, loi b v tm kim tn. Dch v t tn c ci t trn cc my ch. Victmtncthcthchinquamthocnhiumych.ivimng Internet ton cu, vic t tn thng c t chc thnh chui k t gi nh nh vit tt tn nc hoc loi tn (doanh nghip, t chc phi chnh ph, t chc o to). 2.2.3.4V d v h thng tn min Mttrongnhng dch v t tn phn tn ln nht hin nay l h thng tn min DNS(DomainNameSystem)camngInternet.Hthngnycphtminhvo nm 1984 cho php thit lp tng ng gia a ch IP v tn min. H thng tn minl mt h thng t tn theo th t cho my tnh, dch v, hoc bt k ngun lc no tham gia vo mng Internet. DNS lin kt nhiu thng tin a dng vi tn min c gn cho nhng thnh phn tham gia v chuyn tn min thn thin vi con ngi vo nh danh ca tn . V d tn min www.ptit.edu.vn d nh i vi con ngi nhng li khng p dng c cho vic nh tuyn, trc khi tham gia nh tuyn, tn min ny sc chuyn thnh a ch 113.171.248.52.Tn min nn c t n gin v c tnh cht gi nh vi mc ich v phm vi hot ng ca t chc s hu tn min. Mi tn min c c ti a 63 k t bao gm c du .. Tn min c t bng cc k t (a-z A-Z 0-9) v k t -. Mt tn min y c chiu di khng vt qu 255 k t. H thng tn min s phn chia trch nhimgntnminvlpbnnhngtntiachIPbngcchnhrnhng my ch c thm quyn cho mi loi tn min. Nhng my ch c thm quyn c phn cng chu trch nhim i vi tn min ring ca h v ln lt c th ch nh tn my ch khc cho cc tn min ph.Banu,ttccctnminvachIPtngngclugitrongtptin hosts.txt ti trung tm thng tin mng NIC (Network Information Center) ca M. Tuy H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 43 nhin khi h thng Internet pht trin, vic lu gi thng tin trong mt tp khng th p ng nhu cu phn phi v cp nht. Do , h thng tn min DNS pht trin di dng cc c s d liu phn tn, mi c s d liu ny s qun l mt phn trong h thng tn min. Hin nay h thng tn min trn th gii c phn b theo cu trc hnh cy. tn min cp cao nht l tn min gc (ROOT) c th hin bng du ".". Di tn min gc c hai loi tn min l: tn min cp cao dng chung- gTLDs (generic Top Level Domains) v tn min cp cao quc gia ccTLD (country code Top Level Domains) nh .vn, .jp, .kr, . Cc tn min iTLD v usTLD thc cht thuc nhm gTLD (vic phntchrachcnghalchs).Tnmincpcaodngchunghinnaydot chc ICANN (Internet Coroperation for Assigned Names and Numbers) qun l, tham kho ti a ch https://www.icann.org/resources/pages/listing-2012-02-25-en.Tn min cng c th c phn theo lnh vc hot ng gm cc loi sau: -COM, BIZ: cc t chc, c nhn hot ng thng mi. -EDU:cc t chc, c nhn hot ng trong lnh vc gio dc, o to. -GOV: cc c quan, t chc nh nc trung ng v a phng. -NET: cc t chc, c nhn hot ng trong lnh vc thit lp v cung cp dch v mng. -ORG:cc t chc hot ng trong lnh vc chnh tr, vn ho, x hi. -INT: cc t chc quc t. -AC: cc t chc, c nhn hot ng trong lnh vc nghin cu. -PRO: cc t chc, c nhn hot ng trong lnh vc chuyn ngnh cao. -INFO: cc t chc, c nhn hot ng trong lnh vc cung cp thng tin. -HEALTH: cc t chc, c nhn hot ng trong lnh vc dc, y t. -NAME: tn ring ca c nhn tham gia hot ng Internet. Hnh 2.19 T chc h thng tn min trn mng Internet H thng phn tn Nguyn Xun Anh Khoa Cng Ngh thng tin 1 44 H thng tn min c sp xp theo cu trc phn cp. Mc trn cng c gi l ROOTvkhiul.,TchcqunlhthngtnmintrnthgiilThe Internet Coroperation for Assigned Names and Numbers (ICANN). T chc ny qun l mc cao nht ca h thng tn min (mc ROOT) do n c quyn cp pht cc tnmindimccaonhtny.Gisctnminwww.ptit.edu.vnscnhn dng t phi qua tri. Mc u tin ca tn min ny l vn ngha l thuc v Vit Nam, tiptheoedunghalnvgiodc,ptitltnnvvwwwnghaltrang web. Theo cu trc v cch phn chia trong khng gian tn min trnh by trn, ngi dng khi gp mt tn min hon ton c th bit t chc qun l tn min ny thuc lnh vc g, hay tn min ny do quc gia no qun l... Tn min tn cng bng .VN do tn min ny thuc domain .VN, iu ny c ngha n do t chc qun l tnmincancVitNamTrungtmInternetVitNam(VNNIC)qunl,tip sau l tn min cp 2 edu, do tn min ny c phn cho t chc hot ng trong lnh vc gio dc.Mychtnmin(nameserver)lmychchacsdliudngchovic chuynigiatnminvachIP.Nhcchphncpcahthngtnmin, tng ng vi mi cp v mi loi tn min c my ch tn min phc v tn min cpvloitnmin.MychtnminmcROOTschacsdliu qunltnminmctop-level-domain.mcqucgiascmychtnmin qun l domain mc quc gia. HthngDNSnhnghahaikiumychtnminlmychtnminchnh (primary name server) v my ch tn min ph (secondary name server). My ch tn min chnh l my ch tn min ly d liu cho cc zone ca n t cc file c sn trn my. My ch tn min ph l my ch tn min ly d liu cho cc khu vc ca n t mt my ch tn min chnh khc. Khi my ch ph khi ng n s kt ni n my ch chnh ly d liu t my ny v cho cc khu vc m n qun l. Qu trnh ly d liu t my chnh v my ph c gi l chuyn vng. My ch tn min mc cao nht (ROOT name server) l my ch tn min cha cc thng tin tm kim cc my ch tn min lu tr (authority) cho cc tn min thuc mc cao nht (top-level-domain). My ch ROOT c th a ra cc truy vn tm kim ti thiu l cc thng tin v a ch ca cc my ch tn min y quyn thuc lptop-level-domainchatnminmuntm.Sau,ccmychtnmin mc top-level-domain c th cung cp cc thng tin v a ch ca my ch authority cho tn min mc second-level-domain cha tn min mun tm. Qu trnh tm kim tip tc cho n khi ch ra c my ch tn min authority cho tn min mun tm. Theocchhotngtrnmychtnminngvaitrquantrngtrongvic tm kim mt tn min bt k trn khng gian tn min. Qu trnh tm kim tn min luncbtubngcctruyvngichomychROOT,nunhccmych tn min mc ROOT khng hot ng, qu trnh tm kim tn min s khng c thc hin. trnh iu ny khng xy ra, trn mng Internet hin ti c 13 h thng my ch tn min mc ROOT, cc my ch tn min ny ni chung v ngay trong cng mt h thng cng c t ti nhiu v tr khc nhau trn mng Internet. Gisngisdngmuntruycpvotrangwebcachlwww.vn