lt tDrtrcnr or Eleiro.ics, Td@6o!!iolio, & ttior.di.rl E.linerttrg
lt tDrtrcnr or Eleiro.ics, Td@6o!!iolio, & ttior.di.rl E.linerttrg
lt tDrtrcnr or Eleiro.ics, Td@6o!!iolio, & ttior.di.rl E.linerttrg
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Th. bse co6r l<strong>or</strong> lmck sgn.nc is t.0, i.pur pins 0,95. ad ouDut p,.s I O. rhe<br />
pIMt ongettion p.nahy dd lh. hisr<strong>or</strong>ical co4.srion p.n.<strong>lt</strong>y !c stculaled as<br />
in Sccrion 2.4.4, Ako.haptcr<br />
'i.s$ib€d<br />
iivc covcE congcnion €on exctusivety.<br />
The ten &pe.tedcoe(nj) in Equ<strong>or</strong>ion (1. | ) is d m.rslr of lhe crp..k/ <strong>di</strong>rzre<br />
ehaini|jg I-ronr nodc,r ro rc.ch thc rargcr sink i. lhc Exp€ctedcosl rem rbs ihe<br />
brsic alg<strong>or</strong>nhn inb a <strong>di</strong>rechd scarch lflwo routinS resource nodes have ihe same<br />
Pathcosr, bur one node is funho aw6y fiom the rargct sink th.n rhe <strong>or</strong>her node, the<br />
cllM nodc will have a lows Expecrcdcosl 6nd hcn€ a t<strong>or</strong>.r Tohlcosr.<br />
Tne €xpeted <strong>di</strong>stlncc is dcrcmin.d by munling rhe nininuft numb€r of rack<br />
sene.b <strong>or</strong>lhc smc ldgth a nodc,, rcquiEd o r.rch rh. r.rg.t sin*r'. we Bunc<br />
rhar th. @e ryp. oflEck sCmcn$ willbc os.d to Mch $. b4e( sink and rhd rhe<br />
rtrk esndc ato.g tnc shon.n p6rh arc rdually availablc. This is e<br />
appoximtion, b6.us in Ihc 4OOoX]it Nhn.cturc n is posibl. ro s*itcl b.lws<br />
<strong>di</strong>tlcE lengrh b&k egmcnls. our. an m.ny ca5c5. if rh. ourer sans on n c<strong>di</strong>n<br />
l.n8th hck 3gmc.t it *ill us moc oflh. $n. ryp. of nack sesm.nr ro Mch rh.<br />
$uce lfthere is rcutin8 congBtion. th.i th. rout.r msy b€ a<strong>or</strong>c.d ro seirch !o a<br />
<strong>di</strong>tterent length tmck Fgm.nr<br />
Fisure 1.4 illuslrrtcs 0 siNplc cxrmplc ol $c llxpLctd Cosi! wh.ru rhc nuhbrr <strong>or</strong><br />
mch tnck e8ncnr h tlB ErNclc! Con lo rcoch thc sihk Srartirg llm rhe sourcc,<br />
the sink sin b. rcachcd by using cirher a singl.-l.ngth segment <strong>or</strong> one oftwo double<br />
lengft ssments. ilsing lh. singlencngth leshent would rcqun€ thR m<strong>or</strong>c single-<br />
leng$ *lmenls !o Mch rh. sinl, Thc doubtn.nrdr scgme.t shown in black, would<br />
require j6l onc m<strong>or</strong>c sSn<strong>or</strong> !o @h rhc sin[. Th€ olher doubrc-lcn8th s86e.r.<br />
49
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