BSTJ 50: 1. January 1971: Inherent Load-Balancing in Step-by-Step Switching Systems. (Buchner, M.M. Jr.; Neal, S.R.)

14.7 MB·English

Inherent Load-Balancing in Step-By-Step
Switching Systems

By MM. BUCHNER, Jit, sad 8. NEAT

anit ro fH

veatins hae a raid or Ge yacs regarding th ea
waficenineeriug tos vied by te Tl Stem and ater jer te grade:
srl runes ihn the teptyat etehing ato, Te ee
bows that che mp of a graded wnliple 4 toroued thew we
Frbeed in tx aeptgonep nyt, the tareae looming lager
Dumbr of eile rreid tose pred maint donne. The sere
Fr copeciy nuppruntly sate bora of tsrures fect”

To this ran, nn ftigate i data the oe of ago Urey he
step lg slop nua t dtc teva ofthe fal, By w nas
of saul and anaes, ce sow tha the inerenne Sv cnpety arses
‘ot fram a fasnruns efi Dud fom. a avheentlaestatoncig that
‘ele fect ter ater hich he see al Iran noe ter
Puneet TP one that, he od fer eer tte yao of
ox in dy wore, the tabla ave adenunte when the gradings aro weed

Tih tio lngs eae gros, or She wanna shir of ate, th
lubes vate fairy essary th cay te Umpe radnge,aigiy
teneatinat te expasty jor the madevmeied gradings, acd ceresinale
the eapaity of smo Hs amie prainge By aBout 20 prcer

‘The geeded-raitiple crunk erp saab unl le oneion sited
ing stages of tee etep-by-atop svitohing nyesem® are cammconly exgi-
ran asconding to 4st of Labs fursabe? by: Aweriean Thlesbone
Dad Telegtanh Canepa Dense (ie tle, whieh weve porpsend
fone prara ago, ato bazad upon 2iaia amprosimacions and a gBoe
fal of enginesng joviguest wel tease cles eygameate 8a 10

LE rnc te ur Sia le pan ae Rr
1G me amy gverme roommcese sovasnL, saxuen IL

inshify the tahlne ane net eonvieing, their walldiy oe bern qure=
Tiare

prolly, ke lale itinee thes the tafe capacity of « graded
nlp ie ineenaed whem ie in ibadied in the ekp-by sie yale
tne tial the snore borne more significest ar the umber of
fritebee eannotted to he grating venesere Tho commen “explaza-
‘Boas foe the inerenae in expasi'y Saually erate it some ime
mares to iveaoance effet.”

ever commen incorrect «spurts © Ua ele fo bw eapacity
of the arn multiples in the strvcty-sep aye ane ecomaraes
AppersveC. thi iui uy lie oe wane of Dene areumanes
in ovde- Co nupresiae It wine-ainty Feat hes posited eoneering 2h
ality of the toes avd tn view the preent stucy in the proper

perepeeive

‘To lacy the ismice iavulyol, we examine in del the Foot
teste through the oteyeylep sywiem. We demooscrare Yast the
cepaccy of grab willis invest when ei anbedded in the
seep-byestep sven ne Ue inoence beonmaa larger ache mam
ter of rentrhes consent to The geading desreoes, We edow that the
iurecee iu enpuey rests fone en “inert lod-blaneing™* eased
5 tlc way iy wh listen and trunk ape interecraseted 2ct308
than from a frittnmor effet. By a sombinction of sulstion und
futjas, we con Tule tha the ansneaey of the tables depends spon
he sizeof th ering Uw nba sales

Iu ix sting, ee abowr quatatively why the expusity of w geno!
vehiy' neveaee ea trade ollred co uhe gee nlp sod
$e Tie Aversa selectors

Tron fuy enipged ne-nder soups und (oar fisiceeector ball
glee wre pitaned ia 15g. 2. Var elaity, the lie-finder te fret
feleetos santectiona are abowa only for ane lce-inckx grows. ‘The
traded nlite in Pig 1 Hs amazed to « pardeala level ofthe fem
Selector ‘ye oo the vol an ut Teel. Te araded mip
i ral Ig elle dineced vo oor lew alls is clher lavule aad, th,
(lo her cetinaions azo tone roa lars vi eho,

$i enti tpt of he petty eo a
ote i efron or tui wriis eno th Foro Ge
po glee tte Toy FoR Sella, Trnvvierm ‘Trleghere and ‘Teegrn
unven-ora swanCuTMe erEUS wr

Ascume thal the Sve cells indented by dashed line in Fig, 1 sre
in progress. Now, sapere that sulseviber carved by the cop Tine
finder aroup originates a ell. OF Uhe 16 ile line finders only one
can dirce: the eal ule the top asaior belt-abel, ie, the wlalively
foxgested part 0! the syetem, However, there 296 15 line faders
that wil drec te eel into one ofthe lover vlatar has-shelve, ie
te relatively unconnesed pas of the system. The isporant point
that the call is much one gly to be rote! thenugh the zlaively

ig, Ie oti
4188 om nm 6yOMME THERCAL JOURNAL, JANUARY LT

{roo part of the eystem than through she relatively bury part. The bias
foward the les oceupied selelar ballshelves inereaeer wx the ime
Daiunee in eesnpuncy increases. Therefore, we hee the desirable itus-
tion sherein new amivaa tend to be ofered to the lee oveuied Ri
‘oie wabgroape, aie reelte ing more unten ling of the grading
td a corespanding reduction in the chance thet a call is blosked ut
tno first-choice subgroup of the greding when there are ile trunks in
Sexe other eubgroup. That is, che capacity of the grading is imcrenet
‘The term “inhesentload-baleacing" is used tater to this offer,

We wish to mrasuze quantitatively Ue incense in grading eupucity
‘that seelte from the inberon lond-beleneing and to determine the
validity ofthe cals,

1 Compe Ma

‘For the complete model, the etep-by-rap eyeiem is considered in
etal, Trafic is efferd to the graed multiple through the complex
{terootiona of the lite fndsrs and fret seesions. Inehled in te
rrodel are ell physical shararcrides of che switching system deroed
Devine to fe determination of the eapacty of the grad’ng, (These
ucecteristig mre specie in Appendix A.) Tae ‘allowing assun>-
Hone are made rancoring fhe ta

(0) Bech ne rder goo ie aly equipped (contain 20enitchet)
teed erro 20 wabnbes* Requests for sori srom eu gr
1-200 satertert are nywoxinated by » Polen proves. The
feparan poe ree eer roupt ae aato! t be Ende.
pendent with she arn man,

{G9 Th 200 rabecribe sere by a Hnefnder grap ate divide
Jato 10 bgreupe of 29 raborbar each. For the fh mobgroup
Cf tbe fh Boefinder group, let by denote the numberof by
tubocibers. liven fat the teva ocers it the jh ne.
Sider grou. che proablity tv the not seal oes fn the
ho

w=,
200 — Yd.

atin he rae of woking hg oot sar en 18, Hore
spotty es bu besos ta aig coe ouvir a ben
Lyi-ormy smmestse AxenEs5 130

“Th ine findess operave sm dora in Sestion A, Calls Bove

she ie dene are delayed, An Haportart gpeet ofthe complete

tol in thet the wetual ive-fndor to fest-seloto wcing palleros

‘ie used. ‘Therefor, (ae is dseionted ovar the fost eclcetore

‘exactly asin tho physical aystem.

ie) Arve go fo our hovel with probability ps, Le, ps isthe propor.
tion of the evils weriving at the fee slotors eat require a trun
in our graded mattiple

(0) Holding simot aro independent and ioniolly distributed ae-
cording lo © neyativeesponentin! distribution,

(oi) Calle biked at tha goded utp louvre tho systm immodincely
fondo not return. Cala rectal ta olher levels ave never Booked

fond real In fhe ptm for one holdin Une

2 Anpreaiate Model

‘The eompleiiy of the complete mace arises borh frou the inor=
actions oesuig in the subscriber co lne-tvvler nolwork and from
ie intercouncsions btwn Tine Anders end Gest sletor, Te reduce
complexity (and sialon ewepating time, an appresiuale zoe]
ties been develope. In the model, the Hae Snders end she line-finder
tp Sitaeieecer ntereonresiors we wodeled by ascuming that an
{atval sees tarleeor nl vans uau Une group of ile Set solectors

"Th inal i llutrlo’ ia Fig. 2 Suppowe val The Tee call indie
fated by dashed lives are googreas when 4 new call acces. The
rohibility tab the eal fered ya sccenar in the top ball-eel
5/95 whereas the peebobiity fat the eal. iv ecrved Syn elector Ha,
fap, the totond hallshe'T 10/86, Deewuae the wrivel Seve to be
{Teele the relatively wicongrated pare of the system, Ue model
Droviles gn eharneteriation of #22 iron: leal-balancing

‘he following seturpiions giv reeds eoneerning the trie in the
suprosvate model

(i) All sabseibers wo ei originate eala to our grading are con
Sidrot ns ne lenge group. Heres for serie from The arouD
‘of subveribem ane appresimated by m Peirann pane

Ge) Se orival ban fol acces to the firs aostors and oxi «
elector at rndonn froma the group of ile fst areas

(it Assumptions Gand @) fom he eummplete model are alsa
‘ted hor

(in) Cals Bleeked wt tye selertow of atthe graded multiple lve
‘he aystem izumelistly nad do ane retar, Calle dirsted to
Mari rim sesame Tmorsceat oR, ASMANY Tt

ig 2 Areata mod

‘othor level are nevor blacked endl romain in tho aystem for
‘ne holding tire

93 fooated Sel
‘We wish to mousre the irons ia exputy tat results froma ibe
ding a graded multiple inthe step-by-step systom. Thus itis mecesary
to determine the expat of do gruded multiple when al trai elects
hat arise because of the Ear Gndors and Szsteclectors ezo ignored,
‘This ie called the iolted model, Tha load-oee relations fr the ieolated
model ex be eumpultd by mieuns ofthe equirdens-uadom method."
The folowing metmobins nce mde eoneernive the trl
(© Calls crtive at the greding avoording. to a Poisson prooet
(3) Arivale ere unilomly distetbated over the frstahoice sub

soups
srmmeniseney VIER ENDS ua

Calla blocked ct tho grids] multiple Jove the system me

tmadinily tad aot ee

(Ge) Ifedine. Vines axe, indesendent snd identically. distributed
eeong eo 9 nope exponenta Tistibaton,

ks difeul to molyan a ended maipieeven without complesty
of tio step byatey sper The eoprosivations mot olen employed
(tuk othe equiralent-rudons method"? are not diestly applicable
frbon te inberont Toa balaner fla the expevity 0 the ending
"Thug, to randomwalke sink aioe wero constrict, one wing the
cenplete model al wae tang the appzos mate model,

“Considers effort was devtalto datarminiag the numer of calls
‘at should be procewai-ut various Towle to achieve a renapnably
Somogeasuin tofivcent of variation fr the Blocking pribabity. By
eae! staid sonlysis of che silat result, ik was shown
that, fora ll the desnal homogeusity ‘3 obtoned yy proceeing
1500/{pea] ale where Ba) i he ody probobility The resulting
onilelent of voriation fell in the Tange of four to Sve peront, Since
fe umber of eala proce (on, ch, the oampusing cme) inert
Fapialy vn beromes sil, ou reels re for Ps 2 1

Becnuse fhe oor putine Ue is setaye tp ib would be deze
to show thal meaning’ swalte em be abtained show the nellvel
[tpoot of the selectors ams ignore, ny = Tn peter it would
be vor eal if eatisfortry estimater of blocking could be obtalnest
from Uw anpesimate adel with r, ~ 1. This idea wer trad meoess-
fall the dati gee: in Boron 4.

‘One parporo of this study is lo cater the elfce of the mumber
ot vloctos tonnecied co © grtded multiple. Thus, eo extreme sta
ona ave considered: the maisnun and mina number of weleetors
Soed with each gracing, ‘The maximum is alvays 520 mestors. The
‘Binion ie determina the rguviment tat there be at Least sen
‘recone Zar atch firtoieosubgzonn.

‘Wor ile graced mulipee consideral belo, Ue tables in Ref, 1 were
orld to cbtsin the eas, vations prawently in use. he loa
Time relations for the iglated model sere obtained drom the recut
i Ret. 6

1 Gormoarsan ef tie Complete oat Apurorimate Soviet

"The models re compared for bot n-omall alae graded mtn
Tov Piga and 4 rolls ve presented Zor » 25-tmmie and 45-tnmnk
sraded multiple. Let us begin by doseibing how the four curves for 40
‘scloctors in Tig. (indicetod by deshed linea) were obtained trom tho
bomplote and approximate models: eubeequentiy we shall comment
‘on the signifiennoe of the curva. The top two curves, Inbeled 2, = 1,
wwe generated by Jetting pr ~ 1 in bath the complete model und the
pprosimate model. The nox dashed curve wis ubtained Iya the
complete model whan tie loud elered to the sntehing system ae
Ind constant xt 989. CCS (27. erlang) end dhe Tou fferod to the
ding wt varied by charging 9? Gx vo seven peroent of the clit
‘wero delayed a6 the line finde). A since cnree was obtained using

~Ssnets rhy-eytd ed
renee eraser masa
soererran aminenne eviews 43

the wpproxiusis mode! bt, because the eurve fall ever so slightly
Te rn of the py = 1 ve, iis not shown,

"The bottom curve wav alto obtsined BY holding th lol offers to
te eystem constant at 982 CC, Howsor, ia tbls cao the complete
Inodel vas muliied on that the Tine lets eperated en w blocked
Callseloced busin, i all ne finders im a ino-inder grap are busy
then seal ariv a ch group, che hind cals immedntlyelsned
{obout two perent of tho etlly wore blood atthe ine fader). The
‘over slut would operate between tho Hier tn eurres because,
Although Bloke eas wr delayed, defections ean vorur.

‘Consider the cause of the diqatity in ho eurvas. Beeaus there 16
fea slotars par Brs-cholee subgroup, 0 eal sn be blocked ab the
line fndeve when py = 1. Therefore, the ony diferencia the mode's

/ / a tne

cy

{ig 4 Towle mea Aone ered me
144 rw ny Nera rronINsL somal, SAREARY 19

fs the ropnsentation of the inberont lotcalaneing, i, in eomapate
‘etal versus our aponaximaton. The eat paeitet hy he appecsi=
mato model's about 2. percent Ise than che eapucity obtained from
the complete model We eonalude that, in this cus, the spproximate
Inne in goin cvaactariaaion of the inkorent load-balancing’ and
provides 4 utful apse bound for the load-oss reletion

tral hat, in the approximate model, arivals have full uccess to
the saloetors. nthe completa model, resuoste for service aro directo
toon of the fo linedinder groupes herby providing only yard)
nooo, Th flue Und, when py <1, dhe tale offered to the goaling
is somerhet smoother in tie eomplete mods than ia the wpprosimute
‘ol. The dfermne in emoothing appears to be the reason te eompete
terol devistr oom the py = Letve wien ps © Ushers the anon
‘ale model is mativelyineensiive to changes in pe

Durtheriote, the eo ourvee for eonstent input load differ beenuee
blocked eclls recive diferent tratrint in tke blockedsale-cleered
‘hamnoterintion of the line Anders then in tho block delayed
‘iseation. However, in bot ett of oontant iaputiond, the Blocking
fa the five Bidens ror Higher tan Bell Syste dose ad the
‘Gevintion fin the py ~ 1 eure i, therefore, emetbet exagzersed

For 800 arestor, abcerve thet she enmplete snd approximate mod
ve almost enticalrelte thr py = 1. Ten expensive én evaluate
fompletaly the eflosts af emosting becase, in ender fo achieve iit-
fant soning at the lie Andra, pe must be smal, One test ue ran
veth an ip lad to tae evstehing system of 5500 CCS and pe ~ 0.12
(only 0.8 pereane ofthe exile wore ley al th Hie ale). To this
vet, te smoothing didnot shangs the backing probity fom the
P= 1 nee,

“In Fig the madole ave compared fr 80 and 329 calactas eounertod
toadtronie grading, Ae above, the approximate model understate
the espeity By about 2. peoeat for SD electors bus, for 320 seloaors,
‘the exo medele eno in good agnecmsat

‘We sonelude that the approximsto model provides u good chamse-
tesisstion of the interant losd-bulancing, For he minim aio
af elestrs, the soprinmte male anleretiwsten Ue slogle-hne
cvpatity by abuut 25 porwunt but, fo eyes suber of selector, it
Jin almoet exact agreement with the complete model When the
bFg?nating ralieiaarmothed anmerhat by tho lise der, the epprex
tale tiode! preiete blocking probeblition thee are nightly higher
‘han those abtsined with the complete model. Thus, for the range of
blocking at fhe fine Tides exoountened in all Sytem designs, the