BSTJ 50: 2. February 1971: The Picturephone System: Central Office Switching. (Burgess, P.N.; Stickel, J.E.)

10.1 MB·English

‘The Picturephone” System:

Central Office Switching

By P..N. BURGESS and J. E, STICKEL
(Semneit msnval Scene 28, 10)

Cental ofre etching of Patarophone wells sequived te design of aa
eviomated neem’ expat of iting Largs number of widebont signals
Gn em analog Bois, We desert in thx pap the dvetopment of smiling
Blan tha ells arth infarction of ary enafomers f assy rants
Gnd ofthe wom ne tayesithinacorplaieteaumsion limite. We aso
die on ezplanatin of the ranaminioneonuratce onthe physical design
Of the coil afin nator

Allzough devin have Boer developed to switeh engl: band
swicth sents they have bee lini tna amall umber of inputs and
Dutpute Also, the hpial conteels for thie ceviees have been realively
imple. ‘ive ‘evelopment cseerbed in this etale ie the fist auto-
inated, rmo-sealesostening syst digned to swteh nngp numbers
of wideband rgoals on an entlog hivis We dinars the networt and
foxtols aided Wo the No.6 erossba> sntching eystem that entble a
fitting evitchingeystem to proves nls from Pitwrophone tations
5 well ne Lelepnes

1a Design Plotophy

ioturophane sevice i inten} to be 21 extension of basic tele-
pone serve sacher than x rears tr communication pclae. ‘is
feck ino inpertack capietions in all f tke Bell System, pectcalaly
in the design of exihing systems. As gush, the wideband switching
tystem developed for Pictureplone acevie wlzes the existing tele-
hone plant ae such a4 posible. Clessly this design method is
Teatonable ov an cearorsie stendpsint since x largo cumbor of
visting telephone swching funetions—registzation of dial digits,
‘horging all supervision, sgnsling—sre also ueoded for Pietwephone
584 ry mney, svarme racriC JOURRRE, FeMEUARY eT

fitehing, Thie philowophy ssn implice a tural exaneion of the
fandant aumbering plan; Uisreore, © Pictanphone customer can
receive both Picturephane wn telephone eas on the same number.
‘The only difference Sateen dialing © Picturephone wall and. telo-
hone eall is thot the dialed digile for a Pictasphona call will be
wetted with the 12th Pouel-Ton stton designated (E)-+

"The No. § croesbar eye was chosen tho svitahing machine to
provide initial earrioe dor Piclarephone customers. That system is
Widely available throughow. wos ofthe major metrpolian areas i
the Calted States, It ie argue on common coatrol busis ad,
toca af i inborent Geils, can add nee servies sich of Picture
phone calling, Foturo develaymente wil provide thin exit in
eetranie seiching sys,

1 Application

‘The eyeiom to be deserted it eapabe of serving ns Joo wishing
rystem by handling Pictrephone call to and from (¥) individual
Lines, (8) oontrox Ties, (6) PEX evitebing eystams maxi for
Pleticephone ervice, seule) Bell System operntor. The oen-
tv ines, ithe termingted dzectiy ia tho conta ofes (eorex CO)
fof on an amoeisted PBX {orntrex CU), willbe able to roosive deol
iratialet (DID) eal, to oruinate aromatics y-idencided-oubwacd
dined {AIOD) celle, and 4o ley four- of Hve-digt intercom calls,
"Tranafer features for snltex CO customers wl be provided ‘ma Iter
development.

‘in addition, the eetem will trve 68 6 toll and tandem machine
boy awitahing cull betwen Pictwrephone interofice trunks on an
analog basi

vr ewirema PuaN TOR No, 5 enoEsmAR

21 Central Ofer Switching Network

"The evitebing plan ia infoenced by tho eeesien) interface with
tie Picturophone it, Tha interface tx preseatod over thee pine
of wires; one for the biedimetional wutio signals, aod che hor
fro for the video truneinit wml rrvive signals. The sudo. pair
pitched by the existing No, 5 exomhar two-lce nelwork, while the
‘video pairs are switened by a now four-wire network, cacetialy ia
parallel with the audio netmore (see ig. 1). For eotral purpoees, this
‘how ewitohing network, ene the widehand Tink (WBE), is asocinted
with the tmaswire network jn» deinive manner. On the He wide of the
omer, often sw irene sas

= {BE atta

ns | _ |S wa

ti Sting, = wise ete ih; WIRES ~ ite

network, the Piturophone sttion’s adie appeerenee onthe twe-wire
eto in assoeeted diet on a one-for-one basis with the video
fppearunce or the WAL. Whenever the Pisturephone stetion ie ine
valved in a Pitwrephone eal, one peth 'sevitebes throws cho audio
network he aucio apgeazacse, and ancther ie aitaed through the
WE ve the aseicted video appetremee. Ifa Pleturephona steton
Js invalved in a ‘elephone call, cnly ie audia porion ie awitched
rough the ace.
505 urn ma, everest neLaAuUAG JOURNAL, seMRUARY Jt

(On the frank sie of th wetwork, the seme essoeiaton prineiple
olds se that every andi trmle with appearance onthe 2vo-wire
etwore har 1 atmeialed video trunk: With en appearance on the
WEL, Intevofioe Pictwreptone ells to thod wie video wreaks an!
their sere eouaterper. Tho contol 's ranged so that theee aul
‘nunks are never ured for telepkene eas

‘With thie eniceking plum, tav probably of a Plturephene eal
Ini lew i neater than or egal w ti of teleshona call snes
1 Picturophone cn! ie routed reugh two siting networks rier
than one. Although The tun netwineea are not stohistionly indepen
hn, the sepontence is aiallbosause the sitehed ehansala are
‘elected inlepesntely. Tn yartiouge, # Pend Py ore the probabil
‘tet of @ particular input Being blocked in the wntio ant video net~
Work, respectively, and Pie the probably thas « Pikarephone call
Jy bloc through thie af, then

Peo 1= (= Pa = Poy
A 1d Pe Pe hPa

= Pe Poll = PO.

Sines
Peel Pee Pat ly

‘The probehifly of « Péetwaptone opll boing blocked shoulé not be
sSgnifeantly above te blocking probably of « selene cal Heres,
Pe should be signideantly amelie thea Pa, and the WBI shoald be
‘early nonblocking

"Lae above sequiremente have baon eetisied by using 4 Uheewstage
aecorle hick bas nearly wll Uno expested. locking ix the Ses eepe.
Since the sceond and thind sages approximate a Clos nonbloccing
rework, the blocking is navel gro thvougk these stage. By allowing
fcencentreion im the art soy of up (0 8:1, the tlephose company
hus the flexibility of wong Wie Blocking in the nctwork by line
reansigmment, The netwack oun be provided with a minimum of 100
‘trunk terminations and bs uxparble, in 100-tank termination ino
‘ments oto 490-trmin oa ie, Mork! stlies have indicate thet,
fa the early years of service, a notwork with 400 turk terminsle it
ceguate, Foe ear nf the fous snes, a 4:1 ur 8:1 Tine cononiraion
tis is availie, ‘The reewnek topology ie eiown ia Tig. 2, end
verb’ Uelow whine N= T,2,5, wr

"The ft alaye consi of TA widchaxd “ino Links, eee line link
having tex cnipute and ay 9° 8) inputa for a maximum of 3209 Hines
eaermi ore evry aot

Fig 2 Widlund aout tebe

‘The second stage, the milabard junetor Tink stage, omnes of 10
jevurvwitea groupe, each group having JW tate gl UM onto
‘The did stage, the ‘wideband crunk link etazo, eouisiy ui 108
rope, cash baring tau ixpute aus em outta, Ths packaging of ein
‘guipmeat and its impact ox the canal aie oor plan as it ube
‘he fruaemienion eharavririess explain: in Sertion WL

“rhe cen outputs horizons of «Tne Tn are ven over the
leat juaelar wwe! grup he ius Maarzorils) fon seo
seit group are apron needy our she walebannd (our G03
“The networeeonfiineson pravies tom path oleten any inp a8
ny auvput

22 Ramcte Suitbicg Neteork

A prime earbilas lur ely Bisurephone sarsion ie the cntzes
boasiness eatin, EW he ill ercly foe ray, maz eal te
ner eraamene un Khe national Plctsophena acto grows, ae will
Tniit'y we votso Tate Deovertage a calle within che eosananty
ff alee on He a ens prea, IT the WEL were Lae enls
trtehing satwotc provide in th ewicehing plan, every cll beimeeD
{ao siecios within he eastener grep Ee, ‘ntereom alls) would
Svulvt fn arlsof krssiivian Fae ties batman the evoiner and
‘he eancral efi, By pucwiding switching netnoe atthe eumamar's
restive, ln idle tien a inlervin eal ean be eile
Entirely wh tie connate oni, ue grin Cie Uencmaision
facilities net Inthe etetones ar this of cll. The widsband
reanuce switely {WRRA) wae dane ona i we Te arrange
585 cue ay sree veewraat sormaL, maumeaRY 10r

to oviteh just the video signala, ene moto Ube oontrol” of the WORS
is in che centre! fee, The audio for cult etalon We ell apiccbed at
the conta of spying thet no modifestions are uacoxry fort
‘wleting wndio ‘aslves slzeudy provid Uy eentex CO arrangements,
As e consequence of pooriding the WERS ner he atsoroere, © re
‘inced maetinr of trnemierion links ate srorided Between the cara]
fies and the eng of the WEES. Taetefore, dhe WRRS ean also
fuveion een sailing, eyremuraine ior Plsturephone wer

“The WHIRS is erranged aa ine stage enecshar network wit 80
ingle aed a) wtp ‘The mys acces the ideo trans, wl
avive pits fm ue Péctavune sation aad the outous cither
tonnest direst 20 the WL 90 ce to pride video so Past
1 the Pietrvphone network e emer en intoa-reote ete ‘ce.
“These (rks curser Ue ewe video camnnstion an P¥etureptone
insereom eal

ie problems of ore, imptee nit, inention lone, and eres
in q lange ale TMs batch svitel ng nesmenk presented an
singran” challenge to ce withing ayumi designers. 1n addition to
providing « saisfaslory transmission path, 32 mecrork bad to be
Praciest from a mantfatorig, installation ane manigeaunce steil-
hak. hie selon in slevale! to dirtnsion of haw thet conatrainsa
Inirneod he teeing phpeiral sonfgarstion 0: the ache.

‘Figure 8 ayes The wileband ne-work in tema of the ectaal appa
twee alae in rvtahing the Picursokora ral, Flach line link ean
Stn of ten or fone MO-ortial, Wns lee", sR-Riee ooesbar eRihes,
tech S4y F398 ie, Te june swite groupe each have up 2 eh
trons rvs, Wie dew ine ie Ua, aed eae trunk aah
fron hes ona tan-verial, tan-erel, ax-wise exonbar enite, 20) in
% Oy in, Reyardlne othe method of equzncent peckaging, the dis
le Uvugh Ube wide veloc He an angneciate art of the
Piceienpone signet wavelenath and the trenemzeion characteristics
a tho twitching network tus be nonsidered. To eontzel fhe tran
asian curators, the widened neowune we deve within Ube
feoeseints impose? by an overillsrenemiason fvel plan for analog
fselites,

"chit ad he Pra ans: ghee ton oad Ate
i alten ef lotantin ne tz esa nail ee eon
cxcuane wuniaw see it

a Fond Phew

"The overal level pla alates thaw eatpue af any eable eine
ssh Inet the seme trensriesion “reel. ‘Tie roerrsee point Zero
Pistasnnhese Trateasion Level Poi {0 PTLP} is detood ws the
tj of the centzal oboe -ogp cysalizor inthe erection of :ransmise
on faa tae station out te the wna lie. Begining atthe cteiun
fet equalizer, shows in the overcT.evel plan, Fig 4 sec subscunt
foqalier eespensives (ors y-imeingtrapsinission pack and ile eu
fn ie editor ta beat 0 PTLD. As Tong as cho wena degzedation in
thie proeeding path ie reagonably sone:zat end predictable, zhe ql

fers nec nw wily Ted gain ané phase ebaracteistics (xed
eqzetiser.
"The Pictrephone eviteing network ‘evel pn er No, 5 ewshar,

shown in Fig. 6 nur satin’y the eamae ranemision roquements
‘he oeral level ln This plan was pa=ieululy ciel to isplement
Wrthin tao cour oes since any of he wc $200 Por ana
Tinee cout’ rowiner 29 a5y of the 400 wicebwad Unuaks, This scant
‘hee tho vacialiow in trazamisooa degradation emong the pach
(yom moka sve TACHA JOUNKALy HHHRUART 107

through the wideband network hed to he within the tolerance allowed
in 0 PLP. To scoomplich this, aaitional tvevominion constraints
‘were impoosd invemal bo the centalofiee, Lhewecoerain sil allow
‘xed uatizem (eater than dymaric aquelizers) ta be wise Th
Udit, walle baling ul both Plctcephone Lace nn Ammen ie
Sreuivod. The lor plan and patie be'ancing requiremenss ace wise
Ged by the wee of a widebend uileibting *aree (NHL loeated ©
fied elotriend dienes between the ecble equaliaae and Lae eeehing
capspmont, ‘by line eae semsianmenb wi:out equslices readjust
nea, th irpul (BY an wuloi. (88) levels atthe WEDW axe seed

1 Transmission Cable Length Redietions on Wideband Networt
Suarting at any of th enble oqunliucrs shown in Fig. 8 tho ctive
Aistunoe fo tke WISDY ie fves o0 Put he trasmiccion Lae is eenrtant
fd ena to th oes of 190 feet of alle, Tie uistvaen, choeen because
of th anticipated sizeof eablo equalizers end expected eratral office
pace valley, reprecnts the longest hin rom from an oqunl oe
to the WEDIC For equlinem elser lp the WHDR, the 350-0 path
say be » combination of elie uitloula CHO} sud neta ewble ‘The
Tevel of 51 ie thorefiee equal to 0 PTEP mina the cranemison fo
(0f $90 fet uf exe, The datace fom the WBDF through the itching
eto nd bunk Wo the WED ie 320 fest with an allowable vatatinn
Of 50 ‘owt. This nonin distanos and wariation mae ebocen aftr a
‘uly of Unvleot was mace, consdaring the followings
(2) Cost aud practica! init of grin snd phaco compensation in the
fixed ecules.
(i) Central afc space ovailebilty for the wideband actwore
(6). tim enbleditaner paable chro netwne hha 2
aime of BAD eosebar suites.

sdbornir

POLE pe en ye D> mean ONZE

Big 4 Oren tea

vio lee ya.
cess, opsien swmeAINE on

eae

BORE BP ER Eos

Fig, 6_Pitrophone airing mesma vel

“This total stance was spit inl to Woot sctions, ome with
4ovfect varioton, and the othor with & £1000! variation. The level
[BB atthe wideband trunk 1 riot 100 fot of central fice eal
"The () shows is Fig. 6 ts wr co icentifs the addtional shaped los
contribution by the evishing netwars over tht of euhle alone, The
Shaping ie equal to the digeenoe hetwoon 1020 feet of cable end <
inal path throwgh the wideband wwvehisg wetvork. Tae shaping
ie rimenlly consiouted by te lof the altel cables (bridge ape)
fn the ridebas junctor lis, TT wewmpenaated, the caping wold
renult in vido eee (gheete) on the Piauraphone secon, ‘The mid
ted to make these eabes ss srt-and oniform as possibie is expins?
fn Beotion 82.
2 an mri, svetmse mocmoan sovRNat, FEBRUARY 18

Since the network must switch intrenice and operstor eal the
‘ranks must be at the eausuision midpoint, lovel 82, to sci tho
level plan. Figure enmmarizes the loses in tnma of oat loss of
‘tn offs eable fom 0 PETP.

‘Tao wideband lie ak (WBLL) appearance of ewo-way and operator
trunks pases through tae WDE and a tandem cable equalize to
reeetablt O PILP before i extere the wideband networc, These
sppecrances tominate dicetiy on the WLDI' to take advantage of
the era asigament lexbiity ered,

‘1a Tronamiaton Reststons Due to Vidco Empaioments
In addition to tho distance restrictions imposed on the central fice
equipment to satis the level lan, « Emit on the magnitude of the
video ipairments—sebo, ryndema roi, impulsn noite, eroeiale and
power hus—is required 20 stay within the allowable overall loc al=
Tosttions® Buch of these impuinzents hus e perticees effet ox the
physical design of the wideband meter
2 nstenee, « exblo equalizer compunsstes ‘or some average (ro-
‘quency saeperse ad the cchavatnz ispuiement ef ary other path will
Aspen on ow ie devitee com tka verge serperse. Eckowe in the
ilaing fe, £5 exs:sined easier, exe caused primarily by them
Din of rabies necegeny lo iniaionest the vaviaws juretor sith
sroupe. Figure & shows cela sate? ge faretion of tke mum ara
lengtv brid tape. "Tho shaded rgien ofthis igure shewa the aiow-
blo ocho tating af the enitching efce wea function of only uzeqal-
ined bridge tape, and essumcs perfet oqualization of beth central
tiGee onble an svitshes, Sino dh allgewion of echo i based ox
tn sverege pot, it ie necessary to Keep the number of bridge tana
slong the path conetant, as rhort ae possible, and at fixed distance
‘tom the eable equalizer,

"Noi impuictnents rvul rom energy in the paths that, control
relays aod eros willie being fred Hevo the wile pains, wad
for: wide clocriol current fuctuavions in the Datlery and ground
Feedere coupling Unrough Lie feunwvonk sto the video pe. To
slny within the note alfestina, all wiley enblee are epaated by a
lnuet tre inchos fom congo) cates wun they mun paralcl ta each
theron s framne nc ane sun st cp euch etter where the 2” rie
mom apaeing eannet be mcistained. Als, eantact protection deviers
leeriee RC stents) exe ennneelad elween grou and the video
vtch consoles in once to reduce the offer of Fgh neray trane=
fens, Ballery snd round Teedere for dhe wideband netwack are