HỆ THỐNG CHUYỂN MẠCH

8/2/2019 H THNG CHUYN MCH

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21. vi nt v m hnh an ninh mng

21.1 Gii thiu

Vi vic s dng ngy cng ph bin h thng my tnh v mng, tin cy trthnh

mt yu cu quan trng. tin cy thng biu thdung sai hay hn ch cc li.Nguyn nhn ca li vc bn c th l do s ngu nhin, v dnh, trong trnghp b li phn cng hoc phn mm, hay c do mt s loi hnh vi nguy him.Nhng hnh ng c , c hi l ch ca bo mt. Mt ci nhn tng quan hn vquan h gia tin cy v bo mt c thc tm thy trong [31]. Song song vivic s dng cng ngh ngy cng c s dng rng ri, nhng sai st trong vic sdng chng cng tng ng k, i hi cn c nhng bin php khc phc.

Ni chung, vn bo mt c thc nhn thy t nhng quan im khc nhau. V

d, nhn tquan im ca mt th phm tn cng, ngi ta c thiu tra ng c tncng, cch thc tn cng, mc tiu tn cng... iu quan trng l c th bit v ccmi e da tim n, mc tiu bo mt cn phi c thc hin v cc bin php bomt c thc thc hin. Bng 21.1 lit k cc mc tiu bo mt quan trng v ccmi e da tng ng.

Ngay t ci nhn u tin, lin kt gia m phng v bo mt kh nhn thy. Bo mtlm vic ch yu bao gm kim tra, sa li v cp nht phn mm, nh gi on m,cc cch thc, lm cng h thng, gim st..Do , cu hi t ra l lm thno

m phng c th gip nghin cu v bo mt? Cu tr li cho cho cu hi ny ctrong cc ng c cn bn ti sao chng ta thng s dng m phng:

Mi khi n qu km, khng lp li c, qu nguy him hoc n gin l khng thlm nh vy trong thc t, m phng c th l mt thay th. Mt trng hp in hnhl mt h thng trin khai y bao gm rt nhiu trng hp tch cc m skh to ra mt th nghim ng tin cy. v d, hy xem xt mt mng qung co c bitkhng dy vi hng trm, hng nghn cc nt.

Mt trong ngng lnh vc ng dng cho m phng bo mt l lm thno c cci nhn su sc trong cc cuc tn cng nh hng n h thng tng th, chng hnnh l mt mng li phc tp [336]. iu ny c th bao gm s hiu bit chi titca cc cuc tn cng c tin hnh hoc phn tch vtc ng ca mt cuc tncng. V d, tc ng ca mt cuc tn cng t chi dch v trn mt h thng cnbng ti c thc m phng. iu ny c th gip cho vic c tnh khnng thithi cng nh khnng xy ra ca mt cuc tn cng. Nu kt qu ca m phng cho


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thy rng ch c vi trm l cn thit gim cn bng ti, tn cng c nhiu khnnghn so vi mt cuc tn cng vi s tham gia ca hng ngn my ch.

Mt cch s dng m phng th nghim trong vic thit k cc bin php bo mt.Th nht, hiu qu ca mt c ch bo mt chng li.

Mc tiu mi e da

Tnh x thc Hnh vi trm cp

Tnh vn ton siu khin

ring t, Bo mt Nghe ln

iu khin truy nhp xm phm

khng ph nhn trch nhim Mo nhn trch nhim

Bng 21.1 Mc tiu bo mt v cc mi e da

Mt cuc tn cng c thc kim tra, v hn na ngi ta c th nhn c cinhn su sc t vic n lc gii thiu b sung n.

21.2 Vai tr ca m phng trong m hnh an ninhtm kim

i ph vi an ninh l mt lnh vc rt rng ri v a dng trong cng vic. Mt trongvic u tin thng l mt ci nhn tng quan v h thng kim tra, nh gi cc mctiu v ri ro. iu nay cung cp mt ci nhn v cc yu t cn bo v. Trn c s,ngi ta thng xem xt thc t tt c cc b phn ca mt h thng vim mnh vim yu ca n. Sau , ngi ta p dng quan im ca mt i tng tn cng xydng trn cc mc tiu tim n v cc cuc tn cng tip theo trn h thng. Vi shiu bit , ngi ta c th bt u suy ngh v cc bin php lng ghp v h thnggip ngn chn cc cuc tn cng hay gim thiu tc ng ca cc cuc tn cng.

Tuy nhin, nhng i tng tn cng cng iu chnh hnh vi ca h thch nghivi nhng tin mi, v do , s vic li lp li.

Hnh 21.1 cho thy mt ci nhn tng quan v quy trnh m t, t mi ln m phng.Phn ny s cung cp mt s gii thiu, cc yu t no ca nghin cu bo mt c thc m phng v lm thno a nhng cch thc ph hp vo th gii mphng tng th. Mt kha cnh khc c lin quan l cc loi s liu khc nhau m cc


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Hnh 21.1 Tng quan v quy trnh, m hnh tham gia v cc s liu trong m phngca bo mt.

Mng c bit, ngi ta m hnh ha mi trng ( chng hn nh nhng trngi,lan truyn tn hiu) v nhng thnh vin ca mng (chuyn ng, truyn dn tnhiu vt l, phng tin truy cp. cc giao thc nh tuyn, cc ng dng v nhngvn tng t).

Nh m ttrong hnh 21.1, bc tip theo i vi m phng ca bo mt l giithiu cc cuc tn cng trn h thng. ngn chn cc cuc tn cng v tc ngca chng, cc bin php bo mt lun i theo cc cuc tn cng. Do , m phng vvn bo mt cho bit thm hai kha cnh ca m hnh h thng:

- M hnh ha cc cuc tn cng.- M hnh ha cc bin php bo mt.

Cc cuc tn cng thng thng c biu hin bi mt hnh ng thay i so vi hthng hot ng bnh thng. V d, mt k tn cng c th s dng mt giao thc lkhng tun theo c im k thut hoc chng c th to ra nhng iu kin c bitcho h thng chng hn nh lng truy cp tng ln. Tt ciu ny c thng tn vinca n trong m phng c bn nh l mt m hnh. V d, mt cuc tn cng trn mtgiao thc nh tuyn chung c thc gi email hoc tin nhn ngm cu kt vik tn cng (l nh tn cng [507]).

to ra cc ti lu lng truy cp cc m hnh c s dng m phng cch sdng ca h thng. Mt cuc tn cng lm tng ti lu lng ca h thng do linquan n m hnh lu lng. Ni chung m hnh ha mt cuc tn cng thng cngha l thay i hoc gia tng mt hoc nhiu m hnh m phng c bn.

Bc tip theo, sau khi phn tch cc cuc tn cng, l pht trin v nh gi c chbo mt. Trong khi mt sc ch bo mt l v ch m phng ( chng hn nh xcthc mt m), m hnh ha v m phng bng nhiu phng php c th cung cp ci

nhn su sc v tnh hiu qu ca n. M hnh c ch bo mt thng lin quan chtch bo v cc b phn ca h thng. V vy, cc m hnh ca bin php bo mtcng thng bao gm cc phn mrng ca m hnh m phng c bn.


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21.3 nh gi sliu

nh gi h thng tquan im bo mt c th l mt trong ba cch tip cn, gingnh s pht trin ca m hnh cho cc cuc tn cng v bin php i ph.

21.3.1 Hiu hnh thng thng

Bc u tin l m phng cc h thng m khng cn tn cng. Cc m hnh cah thng cung cp nhiu s liu m sau lm c s so snh. V d, ngi ta cthnh gi s chuyn pht nhanh,trung bnh, chm trthng thng qua mt mngqung co khng dy.

21.3.2 quy m tn cng h thng

M phng ca mt h thng b tn cng s dng c hai m hnh, v cc m

hnhthng xuyn tn cng mod-ified. T cc s liu thng thng ca h thng, cth rt ra kt lun vtc ng ca cuc tn cng trn ton b h thng l mt u raca 2 m phng, mt bnh thng v mt bao gm m hnh tn cng, cc s liu nyc thso snh v do nh hng ca cuc tn cng c thc tnh c. v d trnmng qung co mt cuc tn cng lm ri lon s chnh xc ca vic nh tuyn,ngi ta c th quan st thy chuyn pht gim i hoc lu hn .Hn na, s liu cth c th bit c l do ti sao mt cuc tn cng thnh cng hay khng v do cung cp ci nhn su sc hn v cc bin php bo mt tim nng.

21.3.3 cc bin php bo mt c kch hot khi h thng b tn cng

Sau khi phn tch mt cuc tn cng kt qu c thc s dng trong vic thitkcc c ch bo mt ngn chn cc cuc tn cng. C ch bo mt ch yu l sai hoc mrng cc m hnh h thng hin c bo m chng li h thng cccuc tn cng. ngi ta c th tin hnhm phng gm c ca m hnh tn cng cngnh cc m hnh h thng bo m thnh phn.

Ngi ta c th phn bit ngun gc cc s liu sau yqua ba bc:

- Hiu sut s liu thng xuyn ca h thng- C ch bo mt s liu r rng- v d, pht hin thnh cng cc cuc tn cng, sai tch cc ca mt h

thng pht hin xm nhp, s liu v mc t c ca s b mt / ngunhin


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- trn c ch bo mtv dnh x l ti trng b sung, b sung mng li ti

Ging nh trc y, s liu cung cp trong h thng ch dn trn c ch bomt c gii thiu. Trong mt trng hp tt, cuc tn cngkhng c tc ng trnh thng bt c khi c ch bo mt ang hot ng, tc l, h thng hotng bnh thng c thc duy tr. Ngoi ra, cc s liu chi tit c th cungcp thng tin vcc c ch an ninh chnh n. V d, nhiu c ch bo mt cng cnhng nhc im ca h, pht hin sai lm vcc cuc tn cng hoc cn thit khc. Nu h thng to ra mt "bo ngsai"(orfalse tch cc), hiu sut hoc kinh nghim ngi s dng c th bnhhng. Nu thng ip c m ha xc thc, n c thc yu cu tnhton, xuyn cng v xc minh ca mt tin nhn cn thit khng tnh ton cho cc hot

ng m ha bt i xng c thvt qu khnng ca cc thit b nh.

Tm li, cc s liu c cung cp bi s m phng c thc s dng ti uha bo mt ca h thng.

21.4 Tho lun

Trong khi nhiu cuc tn cng v cc bin php an ninh c thc mphngbng cch s dng cc m hnh sa i hoc mrng, c nhng vn khc cabo mt m hu nh khng th gii quyt bng cch m

phng hoc khng th m phng.

Cc m hnh m phng thng lin quan n thc tc th nomena -phe. Vd,khi ngi s dng h thng l mc tiuban u ca mt cuc tn cng, ging nhtrong cc cuc tn cng chng trnh khc, mt m hnh phc tp ca ngidngsc yu cu. Trong trng hp n gin, y l mt m hnh thcnghim,ningi dng b la bi mt cuc tn cng vi mt xcsut nht nh. Tuynhin, trn thc t, rt nhiu yu t thc tnh hng n hiuqu ca mt cuc tn cng nh vy m n l kh a ra mt slng thch

hp cho xc sut nhvy. Mt v d khc nh cc cuc tn cng trn th gii nh gicao thc t ph thuc khai thc ca l hng thc hin chng hn nh trn bm. Ns khng c ngha m hnh ha nh mt cuc tn cng chi tit, biv chn gin l c th ginh s thnh cng ca mt cuc tn cng nh vytrong mt t l nht nh.


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Ging nh vi cc cuc tn cng, mt s bin php an ninh cn phi c thc hinm bo mt h thng kh c thc m phng. V d, an ninh ca mt mych khng ch ph thuc vo phn mm m n ang chy, m cn vo s sn c camt v tr an ton. Nu my ch chn gin l c thc ngng hot ng do b

cp in hoc bng cch ph hy vt l, h thng tng th l khng anton. Tuy nhin, cc bin php an ninh nh vy tt nhin khng thc baogmtrong m phng.

Bn cnh nhng vn ny, thng l khng cn thit cho cc mhnh chnh xcca cc bin php se-curity. Chc nng m hang mt vai tr quantrng trongnhiu c ch bo mt, v dnh, m ha d liu hoc ngnhp d liu. htnh ton Chn-in l rt tn km, v d, hthng yu cu tnh tonphc tp.Simulat-ing tnh ton y cc hot ng m ha khng cn thit, tr

khi m phng chn gin l c th ginh mt php tnh chnh xc ca mt chcnng m ha.

Mt vn khccho cc m phngcabo mt l tnh chttun hon ca cc cuctn cng v ccbin php i phtng ng.Thng thng,cc bin php anninh l intro-duced t i ph vimt s cuc tn cngcth.Sau ,nhng ktn cng c th thch ngvihnh vi ca hv gn kt cc cuctncng tinh vihn.Da trncc cuc tn cng,bin php an ninh im-proved c kh nngc thmvo v nh vy.

cc m hnh tn cng vbin php i phiu tra chu k nythch ng.Mt cchtip cnnhvys i hi cc m hnh thng minh v t thch nghi cak tn cngv ccbin php an ninh, m hin nay ang khng kh thi vim phng.

Ngoi ra, m hnh bo mt cho cc vn thng gp ca m phng ni chung.Mttrong s l tin cy ca mt m hnh, c bit l v cc m hnh tn cng.Biv c rt nhiu cuc tn cng tim n v trnh t tn cng khc nhau, rt kh thitlp mt m hnh chnh xc ca k tn cng.

21.5 Tm tt:

M phng c th rt c li cho vic nh gi s pht trin ca bo mt. c bit ltrong cc h thng rt ln v phc tp. Cc phng php khc ( m hnh Markov,mng li petri) n mt gii hn no . M phng c th c s dng xcnh s lng tc ng ca cuc tn cng. T ci nhn su sc, cc gii php bo mtsolu-tions c th c th c xy dng v cng c th kim tra chng li m hnh tn


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cng. Thng thngmt cch tip cn ba bcrt hu ch l, so snh h thng hotng bnh thngvi hot ng ca h thng b tn cng, v vi kt qu khi cng dng cc bin php bo mt. Tuy nhin, m phng ca bo mt phi u tranhvi vn tng t . V vy, t kt qu ca vic m phng rt ra kt lun ng.

22.M hnh ha cu trc lin kt mng

22.1 Gii thiu

Cc cu trc lin kt mng l mt khi c xy dng ch yu cho truyn thng dliu.Chng m t cch cc thc th mng c kt ni trc tip vi nhau v do xcnh thng tin c thlu thng qua nh th no.L mt cu trc ca cc quan h node

c thc xy dng trn cc lp khc nhau dn n cc cu trc lin kt vt l haylogic.Vic u tin s l xy dng trong vic kt ni cc thit bqua mi trng vtl.Pha trn ca cu trc ny,vic trao i d liu c thc sp xp qua lp mng vlp ng dng to nn cu trc lin kt logic hay ph.

Truyn thng mng ph thuc vo cu trc pha di n.iu ny iu khin hiunng giao thc v tc ng n cc hnh vi, phc tp vic chn tuyn.Vic chnmt cu trc lin kt thch hp cho m phng,nghin cu phn tch hay th nghim lmt nhim v quan trng.Mt v dn gin, xem xt hnh 22.1(a) v 22.1(b).C hai

trng hp ny i din cho mt mng cc b kt ni cc thit b cui qua cc bnhtuyn n internet nhng khc nhau v tnh cht hnh hc.Vic nh gi giao thc vth c th dn n cc kt qu khc nhau hon ton.Cho v d,c ch chuyn i dphng ca mt giao thc nh tuyn khng thc quan st nh vic lp t ch ra hnh 22.1(a),cc ng i d tha khng sn sng hn gn cc kt ni hng.

Cu trc lin kt mng v cc c tnh ca n l nhng thnh phn quan trng chovic nh gi giao thc v h thng.Chng c la chn cc c tnh ca vn di squan st theo di.Do bc u tin trong vic la chn cu trc lin kt

thch hp l lm r cc trng hp trong ci giao thc s hot ng.Trong nhiutrng hp,cc tnh cht c tnh ca mng nm pha di cha bit hay chm h.Vl do ny c mt xu hng lm phong ph m hnh cu trc lin kt bng vic olng mng.Tuy nhin lm vic vi d liu thc c bit l ln,vic pht trin ccmng nh l mng internet gy ra nhng vn c bit.u tin l nhim v phctp khi phc d liu thc nh l mt cu trc.Th hai mi vic o lng i din chcho mt hin trng c th li thi nhanh chng.Hn na,bkch thc thc t ln c


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thkh khn x l vi b nhsn c hin thi v chu kCPU.Do thay v pdng bi ton i vi cu trc lin kt mng dnh ring,khng gian cu trc lin kttng ng sc tm hiu.

Trong chng ny,chng ta s gii thiu mt vi m hnh cu trc lin kt thngdng.Chng ta a ra nguyn tc tru tng ha c bn cho cc cu trc lin ktmng trong phn 22.2 v gii thch cc m hnh mng c biu thc im trongphn 22.3.Phn 22.4 m t cc m hnh cu trc lin kt c bn.Cui cng chng tatho lun phng php tip cn m hnh internet trong phn 22.5

Hnh 22.1:Cc cu trc lin kt mng khc nhau

22.2 Tru tng ha cc cu trc lin kt mng bng biu

Cc cu trc lin kt vt l v logic bao gm cc thc th trong mi quan h vinhau.Trong hu ht cc mng nhng thc thny i din cho cc loi khc nhau.Cutrc lin kt ca mng my tnh cho v d bao gm cc trm cui c ni ti cc b

switch(lp 2) v kt ni qua cc bnh tuyn(lp 3) hnh 22.2(a).Trong chng nychng ta ni n m hnh cc cu trc hiu qu.

Qa trnh m hnh ha bao gm mt vi mc tru tng ha.Mt m hnh cutrc lin kt mng hnh thnh cc thuc tnh cu trc ca mng.Nhng trng hpring ca thit b mng nh kiu loi khc nhau ca bnh tuyn b switch hay cc


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node h thng cui b b qua da vo s hp nht(hnh 22.2 a).Bc th 2 loi trtt c cc thc th r rng ti cc tng di cc thit b quan st.Trong th d cachng ta,chng ta tp trung vo cu trc tuyn cc b.Do cc b switch sc bqua v cc thit b cui c thc hp nht ti vng i din bi thc thn(hnh

22.2 b).Trong giai on ny mng ca chng ta bao gm cc b nh tuyn, vngngi s dng cui v mt kt ni internet.Bc cui cng l bin i mng c thtrong mt biu din biu tru tng(hnh 22.2 c).Cc node v lin kt bng cccnh v nh tng ng

Hnh 22.2:Qa trnh tru tng ha cu trc lin kt mng

Biu G t cc nh kt ni qua cc cnh.Vic t cc nh thng biu th bi

ch V v cc cnh bng ch E.Cc cnh c thnh hng hay khng nh hng vdo cho php cc m hnh n hng v hai hng.Hnh 22.2 c ch ra biu khng nh hng.Cc nh v cc cnh c thc mrng bi cc thuc tnh v dnh cnh c trng s biu din gi trng lin kt.Mi nh c mt c tnh cutrc vn c gi l cp c biu th l k.Cp ca mt node l s cc kt ni tin(bng vi s hng xm gn nht).Trong trng hp cnh c hng,cp c thcchia thnh cp trong v cp ngoi.


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c tnh cp cho php gin tip m hnh ha cc kiu node khc nhau.Xem xt vdhnh 22.2,vng ngi s dng cui c hp nht ti mt nh n.Cu trc bntrong ca cc vng ny khng t di sxem xt v chng c kt ni ti cc bnh tuyn n.Kt qu cc vng ny c thc xc nh vi cc nh c cp l 1.

Thng thng c tnh ca mt nh ring khng hu ch lm v khng phn nhton b biu (hay mng).Tip theo chng ta m tcc c tnh ca biu honchnh.

22.3M t biu

M hnh biu c th da trn hai phng php tip cn;ad-hoc v c s olng.M hnh ad-hoc c pht trin c lp vi o lng thc t.Ngc li vi iuny,m hnh c so lng c gng ti to li cc c tnh biu hay ti lp.Phng

php tip cn ad-hoc cng nh da trn c so lng yu cu s m tc im cabiu xc minh s gn ng ca mng thc

Trong phn ny chng ta tm tt mt sc tnh c bn ca biu .Da vo cc so biu ,chng ta c th m t v so snh cc mng.Vi mi kiu mng a ra mtcu trc khc nhau.Th d mt mng li bao gm nhiu mi lin kt ng khn sovi mt mng cc b.c tnh ny sc gi li trong m hnh cu trc lin kttng ng.Tuy nhin,thng mt mng khng th c m t bi mt s on,nhng so c thtng quan vi nhau.

Cc so c ngha ton cc hay cc bi vi biu

c tnh c bn ca mt biu l s cc cnh |E| v scc nh |V |.

Vi mt biu khng nh hng,theo sau l cp trung bnh canode=2|E|/|V |.Quan trng hn(thng s dng) l phn b cp P(k) c tnhton l xc sut la chn ngu nhin node c cp k.Chng ta biu din s cc node ccp k l n(k),khi :

iu ng ch l da vo phn b xc sut ny,gi tr trung bnh c th cc tnh.Trong trng hp ny:


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Phng trnh 22.1 tnh ton phn b cp cho trng hp chung ca mt mng.Cba phn b cp thng dng [122]:

Phn b Poisson:

Phn bhm m:

Phn b lut ly tha:

Mt ci nhn gn hn trong cc c tnh lin kt ca biu l a ra phn b cpchung.Lut tng quan ny nh ngha xc sut la chn ngu nhin mt cnh kt nin cc node c cp k1 v k2.t m(k1,k2) biu din s cc cnh trong ton b |E|cnh kt ni hai node c cp k1 v k2 trong biu khng nh hng.Sau chunha chnh xc,phn b cp chung c tnh ton:


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Hnh 22.3 Ba cu trc lin kt biu cui cng

Ch rng phn b cp ca node n P(k) khng theo trc tip t php ly tch phnnhng yu cu h s hiu chnh lch

Nhng ng dng nhy cm v tr hay cc giao thc nh tuyn bnh hng bislng cc node trung gian gia ngun v ch.Chng iu chnh bm hay quytnh ng chuyn tip da trn khong cch gia cc node.Khong cch gia hainode l di ca ng i ngn nht gia chng.Phn b khong cch d(x) o xcsut la chn ngu nhin hai node c kt ni qua khong cch x,thng thng ctnh ton bng cc hop. di ca ng i ngn nht tt nht i qua tt c cc cpnode m c gi l ng knh ca biu .Trong mt vi cng b,ng knh m tdi ng i ngn nht trung bnh.

di ng i ngn nht trung bnh(d) cho mt biu khng nh hng cnh gi nh sau: d(i,j) biu din khong cch ca ng i ngn nht gia hainode i v j.Khi di ng i trung bnh c chun ha cho bi:

Trong mt vi trng hp chuyn tip,cc node trung gian gia ngun v thu tc vai tr ring bit.Scc ng i ngn nht thng qua mt node m c nh


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lng bng thng sB(m).tnh ton,chng ta m tt ccc ng i ngn nhtgia bt k hai node i qua node m v phn ra s lng cc ng ngn nht ca tonb cc cp node khng bao gm node m.Do nu ton b s lng cc ng ingn nht gia hai node i v j l B(i,j) v scc ng i i qua m l B(i,m,j).Khi

h s trung tm ca m c nh ngha nh sau:

Bng 22.1Cc c tnh cu trc ca biu ch ra trong hnh 22.3

H s trung tm l thng s thng dng trong phm vi ca k thut lu lng haycc mng x hi.Vic o lng nh lng s quan trng ca mt node trong vic traoi thng tin v lng ti trn nh trung gian.Ga slu lng c phn bngu theo cc ng i ngn nht,lu lng i qua mt node trng vi thng s h strung tm ca n.So snh cc kiu mng khc nhau,cc mng c nh hng,h s

trung tm ca cc node v cc cnh c th c chun ha bi v.Ch rng i vi cc biu khng nh hng cn mt h s phn chia

b sung l 2.Vic tnh ton h s trung tm trong cc mng c ti v khng c ti cnv thi gian,tng ng vi tiu th b nh.

Bng 22.1 a ra cp node trung bnh,di ng trung bnh v thng s h strung tm cho cc node ca biu c ch ra trong hnh 22.3.V d vi cu trc linkt dng sao v chui c slng node nh nhau,cp node trung bnh ging nhau.Tuynhin c hai cu trc ny khc nhau ng k trong vic chng li cc cuc tncng(khong cch trung bnh) v trong lu lng c th chy qua mi node(h strung tm).Trong trng hp ca kiu mng li y ,thng s h s trung tm biuthkhng c nh no t c vai tr ring bit trong qu trnh chuyn tip.Theo mtcch khc thc th trung tm trong cu trc hnh sao c thc nhn bit d dng.

22.4 Cc m hnh cu trc lin kt thng dng


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Trong phn ny chng ta bn v nhng cu hi lm thno xy dng mt biu tha mn cc c tnh c th.

22.4.1 Biu ngu nhin

M hnh biu ngu nhin c bn v l thuyt tng ng bt ngun t Erdos vRenyi.Biu ngu nhin cng c gi l biu Erdos-Renyi c xy dng nhsau:

Hnh 22.4 Hnh nh ca cc cu trc lin kt pht sinh khc nhau

Cho mt s node cnh v mt xc sut p,sau vi mi cnh gia hai nh cxy dng c lp vi xc sut p.Ga m c a ra trong thut ton biu ngunhin

Thut ton biu ngu nhin n,pA biu din l ma trn lin k ca G vi n nh

p biu din xc sut hai nh bt kc kt ni

getRandom() trv phn bu qua[0,1]

Mt bin th khc ca biu Erdos-Renyi xem xt s cnh l cnh:cho b ttc cc biu c n nh v m cnh c la chn ng u.Cc m hnh to ramt lp biu vi cc c tnh cp thng k nh nhau.Cho n ln,biu ngu nhin


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a ra phn b cp Poisson.Tt c cc kt ni c phn b vi xc sut nh nhauqua cc cp node.V vy,biu ngu nhin c in khng lm m hnh c tnhnhm,n khng ph hp cho vic thc thi cc mng thc t.Tuy nhin c sng gptng qut ha biu ngu nhin hiu chnh nhng vn ny

iu ng lu l theo phng thc xy dng khng phn nh m hnh biu ngu nhin:xem xt tt c cc biu m c snh cnh.Chng khc nhau v slng v s kt hp cc cnh v t c cu trc lin kt khc nhau vc tnh cp.

22. M hnh ha cc cu trc lin kt mng

22.4.2 thhnh hc ngu nhin - M hnh WaxmanKt ni vt l gia cc nt ca mt mng my tnh khng c to raty tin nhng c th theo cc kha cnh chi ph ca chiu di cp. mt nng cao

Erds-Rnyi-m hnh th hnh hc ngu nhin. H chim khong cch gia haint v do gii thiu cc kha cnh sthch. cc thnh lp m hnh cho lp nyca th l Waxman c gi l th, c gii thiu so snh cc thutton cy Steiner [489].

Trong m hnh ny, cc nh c t ngu nhin trn mt li ta Descartes;P xc sut m mt cnh kt ni hai nt u, v ph thuc vo h Euclide khongcch d (u, v):

P (u, v) = e-d (u, v) /L,0


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C hai thng thng, cc m hnh cbn phn cp trong bi cnhmng my tnh: Transit-Stub [511] v tng lp [120] m hnh. ccqu cnh, thcn s khai h trhai tng, v nhn nt cha phn cp thng tin.Cc cnhc kt hp vitrnglng chnh sch.Ngc li, Tier m hnh h trmt

h thng phn cp cp ba. Tt c cc nt trongmt lnh vc duy nhtl connected bi mt thut ton cy bao trm tithiu. Kt ni lin min da trn m hnh Waxman.22.4.4 Lin kt u i- M hnh Barabsi-AlbertMt m hnh lin kt u i thc hin cc khi nim quan trng nh gi cao concc nh nected c khnng trthnh thm ch nhiu kt ni. M hnh u tin22,4 thng Topology M hnh479 kt hp s pht trin mng li v u i lin kt l Barabsi-Albert m hnh[49]. Thc y bi phn tch ca h v cu trc lin kt web, Barabsi v Albert quanst thy rng mng li phc tp pht trin lin tc ca cc Emergence nh b sung,v nh mi thch vic thnh lp lin kt vi cc nh c kt ni. Ki biu th mc ca nt i, sau l P xc sut m mt nh mi l:P (ki) =kij KJ

Cc thut ton xy dng c bn lm vic nh sau: Bt u vi M0 con cc nhnected, v k c xc nh trc mc cnh, thi gian mi bc mi l k nhc b sung v lin kt vi xc sut P (KL) j ngu nhin la chn, c cc nhkhc nhau. Mt phin bn mrng bao gm mt la chn i dy li c trnh by

trong [30].Tt c cc nt mi theo trng lng tng t trong tp tin nh km u i. DY-

namically iu chnh trng lng ca sthch, tuyn tnh tng qut thch ence Model(GLP) c gii thiu vi mt tham s trng lng [82]:P (ki) =ki - , Vi (- , 1) (KJ - ) j

M hnh ny gii quyt chiu di ng dn i din v phn nhm. C hai mhnh Barabsi-Albert v trin lm m hnh GLP mt mc quyn lc php lut phnphi.

22.4.5 Trung cp kt quDa trn cc m hnh trnh by cho n nay, chng ta c th to ra ngu nhin cutrc lin kt vi ra clustering, mng phn nh sthch a phng hoc ph bin, vphn cp cu trc. M hnh phn cp tha k ti sn t m hnh ph. th ngunhin, m hnh Waxman, v Transit Stub cng nh tng lp m hnh c thc tmtt nh qung co c bit m hnh, typi-Cally khng ph hp vi quy m ln, mng


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li pht trin. Barabsi-Albert m hnh l mt v d cho cch tip cn o lng iukhin c gng ti sn xuttheo kinh nghim quan st tnh cht ca cu trc th gii thc.

Hnh 22,4 hnh dung th (hnh hc) ngu nhin cng nh

Barabsi Albert m hnh. Minh ha ny s c gng cung cp cho mt s trc gicl chn sau cc m hnh ny. Tuy nhin, iu ng ch l cng mt v d ca mt th c thc rt ra kt qu khc nhau trong hnh nh kh khc nhau. Mt thkhng cn phi c xc nh da trn cu trc hnh nh ca n, nhng o lng can ti sn.

22.5 M hnh ha InternetTrong phn ny, chng ti tp trung vo cc m hnh cu trc lin kt Internet. CcInternet l mt mng li a tng, trong bao gm cc thnh phn giao tip cc ngdng mng, v thm ch c lp vt l. cp Internet cu trc lin kt c ngha lnhn vo cu trc chu trch nhim gi tin chuyn tip. Chng ti do loi tr cccu trc nh World Wide Web th [359, 150].22.5.1 Bi cnhCu trc lin kt Internet khng c tt quy nh. Internet bao gm ca cnh lnhvc (hoc truy cp mng) kt ni vi t nht mt router, c th phc v mt s ccmng IP.Nh mt bnh tuyn truy cp thng l mt phn ca mt ln hn min,cng c nhiu tin t IP. Router administrated bi mt ti li gle c quan c tnghp trong mt h thng t tr (AS). Bin gii thit bnh tuyn ca ASE ngang hngvi nhau. nh tuyn trong cc ASE c th khc nhau,

ent giao thc, nh tuyn gia cc ASE c da trn mt giao thc duy nht hinnay BGP [386].Ngc li trong min nh tuyn, nh tuyn lin min cn khngtheo la chn con ng ngn nht, nhng cc quy tc kinh t hoc chnh tr, cuphong ph. Nhn gia ASE c thl t nhn, hoc cng khai t ti InternetTrao i im (IXP). Mt AS ca mt nh cung cp dch vInternet (ISP) ng chp nhn v chuyn tip lu lng truy cp n cc nh cung cp dch v Internetkhc, nhng khng chy ring camng truy cp, c gi l mt min qu cnh.

M hnh ha cc cu trc lin kt Internet ng s la chn ca granularity, tc l,loi ca cc thc th gii quyt (AS cp, router cp hoc cp IP), hoc mt

combination. Sgia tng 1 AS cu trc vi cc mng truy cp (router cp mng)khng phi l tm thng nh cc h thng t trl khng ng nht v cc cu trcbn trong c th khc nhau. H thng tng c thc phn loi theodanh mc hnh chnh hoc cc mi quan hngang hng (x. [119] v lin quan ncng vic trong ).22.5.2 Topology suy lun v cc ngun dliuCc m hnh chnh xc v phn tch cu trc lin kt Internet yu cu quan st trng


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thi hin ti ca n. Thu thp cu trc Internet y l mt thch thc phc tp,khng thc hon ton thnh cng nh khng c xem trn tt c cc kt ni toncu, chng ti cng khng c mt phng php xc nhn cc tuyn ngv m bo tnh thng nht ton cu. Tuy nhin, mt so lng nghin cu ctheo ui trong thp kqua hiu c cu trc Internet v cung cp cho cc nhnghin cu vi mt topo Internet thc t. i vi chi tit 22,5 Modeling Internet 481tng quan v suy lun cu trc lin kt Internet v cc vn ca n, chng ti thamkho cc cc cuc iu tra [192], [121].

Suy lun cu trc lin kt c thc hin trn cp khc nhau ca Internet. IPng dn c thc pht hin bi traceroute. S dng c ch gii quyt b danh[121], IP a ch giao din c thc tm tt v nh x ti mt bnh tuyn duynht. C haibc, tuy nhin, khng phi l tm thng: cc ISP lc ICMP tin nhn c s dngbi traceroute gy ra cc b d liu khng y . Ngoi ra, mng ring o, nghm, hoc cc ng dn MPLS c thkhng c tit l bi k thut nh vy. Tphp IP khc nhau nhy mt bnh tuyn duy nht thng theo phng php tip cnkhm ph. Hn na, nh tuyn ng dn khng cn phi l i xng, v nh tuynngun c hu nh khp mi ni b cm.iu ny phc tp o lng traceroute v yu cu mt sim thun li khm phsa dng ca cc lp nh tuyn. C nhiu nghin cu xung quanh nh gi tnhchnh xc ca d liu da trn traceroute, v dnh, [40].

Mc IP c thc chuyn ln cp -AS da trn mt tin t IPn AS s mapping.4 Tuy nhin, mt tin t c thc cng b bi nhiu ASE,c bit n nh l ngun gc nhiu AS vn (MOAS) [516]. Suy lun cc AS cp

ng dn Internet t cc du vt cp bnh tuyn l mt vn ni ting, nhngvn cnmt vn cha c gii quyt.Ngc li o lng hot ng, chng ta c thsuy ra cc AS- mc cu trc lin kt bng vic s dng d liu cng b cngkhai. C hai ngun:ng k, Internet v cc BPG nh tuyn dch v. nh tuyn thng tin ng k cda trn d liu c cung cp bi cc nh cung cp dch v Internet v c th khngy hoc li thi. Thng thng, thng tin ny c s dng tng cng ccngun khc. ASthng tin cu trc lin kt cng c thc bt ngun t bng nh tuyn BGP bi v

cp nht, cc my ch tuyn ng, v tm kim knh. Mt my ch tuyn ng lthnh vin BGP nhn chm . N cung cp hn ch telnet truy cp truy vn nhtuyn BGPthng tin. Mt ly tm kim l c bn mt giao din web hot ng nh telnet bao bccho my ch tuyn ng. Mt phin bn offline ca cc bng BGP cung cp BGPbi. Cc d n chng hn nh RouteViews5 trn ton cu phn phi thu gom tuynng,


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nh klu trnh chp nhanh ca bng BGP. ti to li nh tuyn thay i, iuny c thc hin kt hp vi mt bi cha ca tt c cc cp nht BGP thu cgia nh chp hin ti v trc . Cp nht BGP cng c thc s dng baogm cc bin ng, v d, lin kt sao lu [514]. l gi trlu rng nhn chmch vi mt my ch tuyn ng l t nguyn. C mt s my ch tuyn ng, mc thc quan im khc nhau v cu trc lin kt BGP. Cc BGP bng ph thucvo vtr. Do , tp hp cc thng tin sc sp nhp.

C hai d n ph bin traceroute IP, CAIDA6, v Dimes [419].Trong Ngc li CAIDA, Dimes thit lp cc im thun li ti Danh cui systems,tng tnh SETI @ home, v do thu thp d liu t nhiu hn ng k Internetquan im (tc l, ASE). i vi mt so snh d liu c hai b chng ti li fer [481].

Trn thc t, CAIDA l mt t chc hot ng mt s dn o lng,e.g, Ark (trcy l chy mau). 482

22. M hnh ha cc cu trc lin kt mngNgun d liuDatCat

CAIDA

Dimes

RIPE RIS

RouteViews

UCLA

NEC

Granularity-

AS, IP (Router)

AS, IP, Router

AS

AS

AS

AS

URL

http://www.datcat.org

http://www.caida.org/projects/arkhttp://www.netdimes.org

http://www.ripe.net/ris

http://www.routeviews.org

http://irl.cs.ucla.edu/topology

http://topology.neclab.eu

22,2: La chn ngun cho cc d liu o lng nh k cp nht
http://www.datcat.org/http://www.caida.org/projects/arkhttp://www.netdimes.org/http://www.ripe.net/rishttp://www.routeviews.org/http://irl.cs.ucla.edu/topologyhttp://topology.neclab.eu/http://topology.neclab.eu/http://irl.cs.ucla.edu/topologyhttp://www.routeviews.org/http://www.ripe.net/rishttp://www.netdimes.org/http://www.caida.org/projects/arkhttp://www.datcat.org/


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traceroute. Dn RouteViews cng nh nh tuyn RIPE Thng tin du lch cp thngtin dch v (RIS), v d, cung cp cc bi bng BGP. Vic nh tuyn bi bng phic sau ch bin to ra AS mi quan h. Internet Topology Bsu tp ca UCLAkt hp cc ngun c hai, v qung co my ch tuyn ng ditional v tm knh cung cp mt d liu b sp nhp trn mt hng ngy c s. Cn c vo vic x l ccbn cp nht ca BGP, to ra AS thc bit nhn thc ca cc lin kt sao lu, mkhng nhn thy c trong cc bc nh chp bng nh tuyn BGP [514]. D n chgii th vi AS li lationships. Mt n gin AS th da trn RouteViews, RIPERIS, v UCLA d liu, c tnh ton trong d n ca NEC [498]. N th hin mtunweighted v trng tip theo hop ma trn, tnh ton ng i ngn nht (s dngchnh sch min ph v cc cnh c trng s), v phn loi cc ASE trong ba tng.

o lng Danh mc d liu Internet (DatCat) [418] ch s Internetcc php o trong mt bi cnh rng hn. N khng ch bao gm mng Internet cutrc lin kt, nhng cng DNS du vt, o lng P2P, vv N to iu kin tm kim-ing v chia s d liu gia cc nh nghin cu. DatCat l mt cch ton din c sdliu, truy cp min ph bi cng ng nghin cu trong bi cnh o lng Internet cho php cc d liu ti sn xut.

Tt c cc ngun d liu c tm tt trong bng 22,2.22.5.3 Trn Internet Topology tnhMc d cu trc Internet thc s l khng r trong vng mt hon ton lin net bn, c nhiu cng vic phn tch cc phn o.Mt trong cc ginh gy tranh ci nht ca cu trc lin kt Internet l nhn rngcc mi quan h ca mt s ti sn theo php lut ca quyn lc. Bn ca h nal cngvic, Faloutsos et al. [140] phn tch Internet AS cp cu trc lin kt RouteViews

bng BGP. H quan st thy rng ra mc ca mt nt, mc phn phi, vEigenvalue ca mt ma trn k ca th theo php lut quyn lc. Quyn lc phplut sm c lin quan n thc bn char- cteristics (v d, slng cc ntv cc cnh). Cc tc ginh vy, tm thy mt cch thanh lch m t cu trc linmin Internet pht trin. Mt s cc nh nghin cu xc nhn cng vic ny [424],[301], v c gng hiu c ngun gc

22,5 Modeling Internet 483ca php lut quyn lc [313]. Mt m hnh ph bin trong bi cnh ny l Barabsi-Albert m hnh (xem mc 22.4.4). Ly cm hng t cng vic ca Faloutsos et al, Bu

v Townsley [82] theo kinh nghim Internet o phn tch cu trc lin kt. H chothy cu trc lin kt AS cp l mt th th gii nh [488].Mc d cc quan st Faloutsos et al. c xc minh,

ch mu thun vi php lut quyn lc. Chen et al. [98] cho rng-detopology AS cp rived khng phi l i din cho cc kt ni Internet nh t nht l 20- 50% ca cc lin kt vt l c. S dng d liu mrng thit lp chng cho thymi quan h quyn lc nghim ngt lut php khng gi cho nt mc phn


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phi. Trong mt bi bo tip theo, Siganos, Faloutsos et al. [424] li phn tch cngvic ban u ca h [424] da trn mrng AS bn v i li quan st quyn lcphp lut bng cch s dng nh gi hi quy tuyn tnh. Mt ob-c bn servationlin quan n mi quan h quyn lc php lut ca phn phi bng nt v nhngthnh kin ly mu c trnh by bi Lakhina et al. [273]. Cc au-Thor xy dngmt th con ph m l da trn mt cu trc ln hn m khng cn bt kc imphp lut vnng lng (v d:, th ngu nhin). H cho thy rng th con phny xut hin c phn phi bng php lut v quyn lc. Do , mt mu khng ngu ca cu trc quyn lc php lut khng c th dn n ti sn ca php lut quynlc.

Cu trc bn trong ca mt AS min lin quan n tnh a dng ng dn IP c nghin cu bi Teixeira et al. [460]. Con ng a dng cc bin php s cctuyn ng sn c gia hai nt. Phn tch c da trn mng thc sthng tin ccung cp bi cc Sprint ISP, v suy ra cu trc lin kt. Teixeira etal. cho thy rngkhong 90% cc cp 17 ca Sprint im Presence- (Cc cht nhim hu c khphn hy) trong trin lm M t nht bn phn chia ng dn lin kt, v rng 40%cp c lin kt vi tm hoc nhiu tuyn ng.Ngc li, cc cu trc lin kt cngun gc tcc php o hot ng nh gi qu cao slng cc con ng phnchia.

Cc hnh vi nh tuyn gia hai my ch cui cng c phn tch ban uPaxson [356]. Daemon thm d s dng mng li phn phi trn 37 Trong ternetmy ch nm trong 34 mng cn s khai khc nhau, Paxson o khong 30% cc cptrang web qua t nht mt khc nhau AS trong tin ln pha trc hoc o ngc conng, v khong 50% truy cp t nht mt thnh ph khc nhau. i vi tip tc lm

vic v ch ny xem, v d, [198].nh tuyn trn cu trc AS cp ph thuc vo h thng t trmi quan h. Hxc nh xem nh tuyn chnh sch xut khu v la chn. Lin ktgia AS lnh vc c phn loi (1) nh cung cp-khch hng, (2) khch hng nhcung cp, (3) peer-to-peer, v (4) anh, ch, em rut, anh, ch, em rut mi quan h[173].

Khng c giao thng qu cnh c php cng peer-to-peer-lin kt, v nh cung cpdch vInternet thng trc fer cc tuyn ng ca khch hng trn cc lin ktngang hng hoc nh cung cp.Tip theo chnh sch c th, c rng buc vi ccloi lin quan, thc t la chn AS ng dn (o trong cc bc nhy router) di tri

ngc vi nh tuyn ng i ngn nht. B quami quan h gia cc ISP v s dng 1 n gin ngn nht AS m hnh chnh schng dn, Tangmunarunkit et al. [455] phn tch rng 20% cc ng dn Internetc thi phng hn 5 cp bnh tuyn hoa bia. Trong cng vic tip theo ca h,cc tc gimrng cc m hnh chnh sch, nhng quan st thy rng 96% cc ng dn vncn 484


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22. M hnh ha cc cu trc lin kt mngCp ASVng

Vng

Vng

KhngCp Router-

Khng

Khng

Vng

Vng

H thng cp bcVng

Khng

Vng

Vng

URL

http://www.cc.gatech.

edu / d n / gtitmhttp://topology.eecs.

umich.edu / inet

http://www.cs.bu.edu/~~V

Brite

http://www.info.ucl.

ac.be / ~ bqu / iGenMy pht inGT-ITM

Inet

Brite

IGen

Bng 22,3: Topology mng my pht in cng mt chiu di c lp ca m hnh sdng [454]. Da trn nh tuyn pol bng gi m hnh phn nh mi quan hthngmi, Cao et al. [174] ly ccon ng ko di trong AS bc nhy. Hn 45% ca tt ccc AS ng dn c

thi phng bi mt AS hop.22.5.4 Cu trc lin kt th hMt cu trc lin kt Internet tiu chun ha c thkhng c cung cp min lInternet cu trc khng hon ton hiu r. Mt ngi c th nhp khu thc solng d liu (xem mc 22.5.2) vo m phng cu trc lin kt c to ra vn cnkhng y (v d, lin kt cn thiu ang ng mc-AS [41], [199]). Ngoi ra,
http://www.cc.gatech/http://topology.eecs/http://www.cs.bu.edu/~~Vhttp://www.info.ucl/http://www.info.ucl/http://www.cs.bu.edu/~~Vhttp://topology.eecs/http://www.cc.gatech/


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ng minh, i vi hu ht cc m phng s suy lun ca cc nt v cc lin kt lqu ln.Krishnamurthy et al. [267], v d, gii thiu mt phng php ly mu gim kch thc th trn mt mt, v bo v php lut quyn lc s liu v dc mt khc. Cu trc c to ra l mt v hng biu cp AS. chophp nh tuyn lin min thc t, cnh cn c ch thch vi AS mi quan hnhtrong mt solng d liu [514], [498].

C mt smy pht in mng c sn to ra tng hp topoloGies (x. Bng 22,3). Mt trong nhng my pht in c thnh lp u tin l GT-ITM. N cung cp th phng ngu nhin, v mt m hnh vn chuyn cn s khaiphn cp phn nh cu trc AS. 3,0 inet cng l mt mc h thng t trMy pht in cu trc lin kt Internet. N to ra mt mng li ngu nhin v cgng li sn xut cc ti sn lin min da trn cc thng su vo: slng ccnt, v mt phn bng mt nt. Cc c im tng tnh quan st Internet tnm1997 v thng 2 nm 2002 [497].Cc tc gi cp n m hnh cng khng i din cho Interneti vi phe nhm v phn nhm ti sn. Mt my pht in cu trc m phn nhInternet AS cp v router cp Brite. Brite ph hpcho th c quy m ln quyn lc php lut. N s dng Waxman, hai Barabsi-Albert m hnh, v tt hn m hnh tng qut to phng AS, Router phng, v thbc cu trc lin kt. Brite cng thc hin nhp khu mt s

22.6 Kt lunCc n chuyn i th gia cc my pht in cu trc lin kt khc nhau v m

phng. Brite, v GT-ITM l my pht in da trn mc tinh khit.Gn y, ccmy pht in iGen c gii thiu nhng n lc to ra end-to-end ngdn. IGen sau mt cch tip cn th h mi, trong bao gm thit k mng li chnon v hn cha l.22,6 Kt lunCu trc lin kt mng li i din cho cc kt ni ca truyn thng en- tities. N mtcc ng dn thng tin c th chy, v c th phn ln nh hng n nh gica cc giao thc truyn thng. S hiu bit hin c structures, chng hn nhInternet, l mt iu kin tin quyt m hnh thc t cu trc lin kt. Ccc im k thut ca mt th ni chung c thc m t da trn mt tp hp

y ti sn, hoc xy dng bng cch s dng quy tc th h. Mt sng to xydng mt ln na c thc phn bit trong hai cch tip cn khc nhau: C bnthut ton con struction xc nh cc th tc to ra mt biu vi cc thuc tnhc thc lp trong nhng l do thc t, c ngun gc t mng.Ngc li, mt quanh nhn qu ly cm hng t m hnh xy dng s hiu bit ca th evo-lution ltng hp qu trnh xy dng c bn mng. l gi tr ch l hai c ch xy dngtheo quan im trc giao v c th dn n kt qu khng mong mun khi trn khng


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c chm sc.Trong chng ny, chng ti gii thiu c bn v m hnh cu trc lin kt, trong

chng ta tp trung trn cc mng cnh. Chng ti bt u vi m hnh u tinbc: tru tng ca cc mng thc s ca mt th, trong bao gm ccElimination ca chi tit khng cn thit. Sau , chng ti tho lun cc s liu cnthit m t mt th, v phn tch cu trc hin c. C trnh byamples cha hon chnh, nhng nn c xem nh im khi u. Cc la chn cas liu v s hiu bit ln nhau ca h vi chiu tra l mt phn quan trngtrong m hnh. Sau khi c trng th, chng ti gii thiu cc m hnh cu trc lin kt ph bin. Tt c trong s hkhng trc tip p dng i vi cu trc lin kt Internet, nh cc kt ni Internetkhng xy dng do ngu nhin, cng khng lm h theo tp tin nh km hnh hcn gin hoc u i quy tc. Chng ti tho lun v Internet m hnh cu trc linkt trong phn cui.

Cc m hnh ca Internet l mt nhim v phc tp. Trc ht, chng ti khng thnm bt c Internet y , v do hon ton khng c s hiu bit v cu trcca n. C nhng dn o. Ch bin sn lng ca h (v d, sp nhp cc ngunkhc nhau) c th l mt phn ca m hnh.Trnh by mt cu trc lin kt Internet m khng cp n mc granularity (Tcl, AS, router, hoc IP cp) l v ngha. Lun gn y, [193] t vn lm giu choth h cu trc lin kt bi mt s mc ngu nhin phn nh cc kha cnh khcnhau tin ha ca Internet.

22. M hnh ha cc cu trc lin kt mngBc tip theo c th bao gm cc m hnh ca lp mng (Chap-ter 16), lm tng kt ni bi s chm tr lin kt tng ng (Chng 19) v nh gica cc giao thc da trn m hnh giao thng thc t (Chapter 18) i vi mt iutr chuyn su ca mng li cu trc lin kt trong bi cnh mng li thng tin linlc, chng ti tham kho nhng cun sch tuyt vi [69], [122], v [471].

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