BSTJ 50: 2. February 1971: The Picturephone System: Transmission Plan. (Brown, H.E.)

24.2 MB·English

The Picturephone® System:

‘Transmission Plan

By HK, BROWN
(laste secned eta 3 0)

An énportant ep in preparing fo nation, ewitehd, ideo tephone
service Ge the formation of @ teamanseion plan [orth widen and audio
[portion of tha natoork, The trenamission plan dow inthis paper
Features dial trasamsanion for the loartaul portion ofthe network ond
‘onlag trawemiesio forthe feel portion, los fa the easton. Th p=
ormence ofeach ofthe eomponrats of te network dat i, wation opsip~
crt, lea! oops, srunky ot mace, fa discussed for the netcor ae #32
apace lobe conrad intaly and 8 ik mip evo trough the 1870s.

‘The sinnal standards ana performance objectives for the overetl
yee deus in previous pipers were srived cc chrough wrer‘ee
fof mbjective teal and system studs whieh inceated that the re-
lant pictore quality would br aveetable to the veor. Given the
fend-te-cul transnission objectives, The inter in formuletingw tree
tnision slan for the network ln etike a balance between the ooet
fd perforce of ceeh of the compenan:s: the staion eupment,
Tops lea evitching wud Ussing, and longa swing md nk
ing, Impairments erp allactel Ia ch of these components sue: that
te overall col ofthe service ie winimzed, taking iso account that
the loop connceing the ration equipnent o the local cantza fice is
hormolly dedicate! lo a single eastomer, whereas the switching exoi>-
nen and truoks are dazed by hovered or perhaps thousands of eu
‘omer.

‘An orderly deverintion of the trammision plan starts with the
itching hierarchy" hich will closely resemble thal of the tee
‘hone nelwonk. ‘The wlkimate number of switching lve inthe hier
{60 num nm, sre0me TROMteAL. FOCANAL, FERGCARY 1871

‘rehy wil depend on the relative eoxt of switching and transniasan
equipment and the number of subcribers connected tothe network, A
‘the network grows and the trafic betwoon various evitching nodes
{ncreses high usage or direct trunks Will be used Ia whet follows, the
hereby ie desribed aa itis capeatad to develop in the mid-ta-late
reventin Difterenor below tema the lwork in Ue initial yeary of
ervioe aro noted where appropriate,

‘A call may be viewed as eneauntering three major pieces of the
network: Ue digital portion and lwo Tees analog arese, one ab ech,
od of « connotion (Fig. 1). For the intial years, the digital portion
Will consist sulatly of troncmission feaitia, La, ewitehing of the
‘ideo or audio signal in digital form (hitsteam switohing) is not
‘cavisoned, Decoding and recoding to ewitch th video egnal in analog

hens 9 OE ELAS 2)

Su ante fess)

Crane sen (ass 9}

‘ig, _Aetrephone network,
mansion Fran 358

form ie not permitted singe the noice that would result from multiple
‘nealing and decadinge of the vgnal would exosed the nosoalloce-
ton diameze’ in Section 2, Bosse the noise irkrodoved hy multiple
cncodingas end devodings exceeds the amount allosted, a network plea.
Joes boom formlsted whieh unos bilstrsara vwitdhox rather then anal,
‘ila fr the Tong-hwul poron of the netwosk, The plan requires
that the video signal, once it has been encoded, be transnitied al
wile in digital farm until St reaaea @ pont where ican be de=
‘codod and delivered ta ite final destina on point over analog tactic,
Initially, the andio chennel, which contains the Voie, sigusling snd
‘supervision iniermation, wil be tranamitted ae soporte signal over
‘ny axe of 9 numberof Tnlltes steady expablo of transmitting these
sianala. In the mid-1070s, withthe advent of bitetragra enitehes, the
landio channel iy expected vo bs encoded and multiplexed with the
‘nooded video sigaal to predace a eompaste digital signal.

Digital tearwssion over analog snd digital facie is attractive
for long-hasl texramision of the video and audio signal for several
reason (9) Virwly all of the inpaivment in the transmission Tink
‘owns inthe terminal equipmeat es th eign ie converied from anslog
to digital and from digital to snslog Very little impairment is intro-
Awe in the tranarision path; enc, tho performsnes of the digital
portion of the network it teentially inlependest uf ditanee. (3)
Digital faction now boing develope are expected to compote cecuom-
ienlly with anwlng tele for woiee srvice and be sigfeantly
cluaper for Piclarenhone ervice singe tho video signal requires the
tquivalent eapacity of fewer voice channel on the digital facilis!

Although & bil rate of 6312 Mbjs will be uscd intially for
transatting the video information in dig form, the potential es
to reduce the bit rato hy & Saetor af fram uno to four. A reduction
of thie magnitude appotrs powible thraugh the use of redundency-
Femoval techniques diring eteesting which fake advantage of th sai-
lavity between sussesive nes ex irae of video information."

"The interface beoxren the anslog az dsital portions ofthe nebwork
i throush aa A/T) eonverter called rodee’ (for codor-docoder)*
‘Te inital servo eodoe supa the incoming analog video signal at
‘the Nyquist mite of uboat vo megeamples/s and encodes the ampli
tudes of the diflerences beteen matoenive samples into thre-bit
Dinery codes, The reeutant bit rato, ineuding mizeelianeoue bits for
framing end moaitenane, is 612 Mb/s This tate a the ame aa that
ofthe 12 digital ropentored line."

‘The T2 line, wiih wllae wine paisa equipped with zegsnerstive
86am mm svarex mocmnAs sound, YmNANT 107.

repeaters, Ia a digit) facility designed for ditanoes up to eaverul
Dbundred ‘miles. Tts mejor application in he Picturephons network
vill be na feodoe betwoun th bitcream snvches pleated to be Sutto-
Ae io fanuro years end the Jongh! aves, end as sbore-baut
trunks where tho distance exeeede thet permitted for anslog transmis~
Ty the initia years, two eysteme will bo evullable for transmitting
the digalized Plcturophone signal over long-haul fullities, The fist
uuise the TD-2 miecoweveralio relay ayatam. Termine] equpzent,
Gesignatod MR, scultiplense theeo 6:312-Mb/s coded Pleturephone
tiganle into a 202-M/sbeeaeam, Hach 20.2-MB/ebitetenm i r=
rite over & single madin channel. There is ans channel for exoh
Uioeton of tranemizton. The eetond eyatern will mako uso of the To
tosnial eabla eater system,” In this ayetane, L-Mawiargroup Digs
(LMD} terens} equipment riplexe two &812-Mb/s coded Pic-
frephone signala into a 1329-Mlb/e bistromm euitable for tnnsmni
sion over any one of the six mastergroups on a I-4 eoexial ual ia 9
‘able. Thu, one pair of cosxialn will be capable of tranemitiing 12
‘two-way Picturephone sgnala. In both systems, dita sogenors tion
vill be required--about every 400 miles along the zouto for the TD-2
yatom and cbout every 400 mile forthe Ld eyatam.

“Tas local analog <rea (LAA) is defined as that portion of cho ne!-
‘work which ia wholly interonneocable by snslog iacities (Fig. 1)
1 comprices the customer’ elatnn et, Joon, end alee, toll centr
short-haul trunks and eodeo, Figure 1 illuserates two ways in which
tho codeo may he used. Tn the LAA on the left of Fig. 1, the codee
is betwors he ral canter and the next higher level in tho hieratehy.
‘Tn the uwo LAAs on tbe right of Fi. 1, the code is between the end
fotos end the call center, In which ease the toll center would wile
' bileirein site, Other eleronves are porables for example, the
dee could be pact of w digital high-usage trunk group to sn office
Jina distant LAA, Figute 2 shows Mosiratve onal aren eonfigalins

Tn the enrly yeane of ecviee, 40 leop the est of the Toe) ams
cuipment low, mnxioam use of exiting plant will be made. This
‘voids the placement of expensive now eable plant for the exelasive
tse of Pisturephone verve. Furl, the use of existing plant evoide
‘he long lead time required to onder and install new enble plant nn
res the telephine compan the ably to respond rapidly tw no
service regutee, Por the loop ie? mil sho-ichoal Url, thie Emplice
busobene video transmission on peicod cabo, the same typo cable that

ure yea th oll enter could be a bistewam ald and would be
omar puto he lpr fle aero
mansion 2149) 356

soy

aemnege \
Grr core tease

Dreiser fa

ig, "tne Soa are cotgurains,

is used for providing ‘clephone servive, with equalizers placed st
regular izerene along the ea

Titaly, ie eulivers desighet for the ope will eso be us for
foes trunks, There equalizers can be usod on underground cable of
fy ange frown 16 2 26 gauge. Aerial eable it nol permisted with
‘his design for twa reasons Fnet, diumal chines inthe lempersbre
of veri! euble revll in escemire gain and phase deviations from
fist enim end linea phage vereua fseaueney. Severs, che signal love
fon the onble snot high enough to override intererenee from browteas,
racio tetione
356 num am SreFIDC THOLNGGAL JOURRAL, FERECARY 172

‘Tho ute of the loop equalizer for trunks in the initial years hes
ssveral advantages, Among. thom ie tho ability af the equeizer to
handle many gauzes which gives the engincer planning the Tal analog
fren the ability to pick from the available cabliche one that best
[es his needa, ‘This is of prime imporeance in the initial years when,
on underground cable, the Teck of temperatuce equalization wl limit
frank length to only few miles on 22-gaugr call the prevslent
sauge in tha trvak networe Tho ability to use T6-pauge eabie onthe
ther hand, permite teonk length several times thse possible with
22 guuge, Another advantage is Liab engineering, inwallcion, and
‘maintenance pasonnel eneounteroniy one basie desig of exble equa
ier. This equipment permita development of « modestly sized serving
ares of about sc mile in diameter”

“Extensive expansion af the cavioe ia planned and ie expeated tobe
‘ade possible by the avaiebiity of « seannd generation of lnop sal
trunk eaqaliere for Toal area Aramvmivion. ‘These equalisere will
‘ake advantege of antomatie tmparatue conpenantion and inoreaned
ynamie range, enabling. analog trensmision on aersl kad wnder
‘round cable over an a7e8 up fo ubout 48 miles in diameter?

This eeeard peneration of equelizere for Toop wil employ dfernt
Aevigae than thowe for trons Zor everal reawzra, One ie thatthe ele
Tocation of impairments tote loop is wo thee short loops will aot
reaqire autorasie tempertturo compensttion. This avoids tho coste
involved in providing and maintaining the more complex equipment
‘sociated with automstic tomperature compensation. Another is that
The onst of tho trunks ia chezed among mary wecres hence, more
fepbietieted cireity, capeble of a higher level o: performen
jurfied. Second. gereration cruake will employ equalirers epaced et
Intervels up to 0 kit, nth automatic emperstare ootapensetion in
forary equalizor,regorless of the legs of the trunk,

‘The provioan sestions brit autlined the enitshing hierarchy for
the Picorephove uetwarke an the role of the rxnsmiaion Falities
‘het will be usod to interconnect the switching machines. Planaing
‘a network and allocating impairments to ite indvidanl components
require thet the network be reviewed ae it might ultimataly be eon
figured Ths, ¢ description of «mature network hes been ineludet

pe il for mack ngp and fur ley of ssl
TRAC hee el lo and phon SS a alg nie.
suanenussion mL ar

in Section II, In the early yea, the network will have fewer eviteh~
ing loves, not all the eering acess wil be infereonnecte, loops and
trunks will be shor: and the eure for the mnst purty will be
‘conoentrated with feiny low denwity im the downtorm arese of mi
citien Tilly, only enalog satehing zascinet will be available. The
Alloowon of impairments claeasted tm cho ec'‘ons to follow is con-
Sele with the netwerk ae ik iv exgacted “o dovlop initely end se
tis expeoted to he nkimacely configured. 1: recognises that future
fgeneritons of eigen wi have exxaded capaliliy for trans
rising Pistsrphone sgnalh at. baseband or paired cable, Also, 5b
ecoguiros that coding of Plcturephone siganle bi rls less thea.
(312 Mb/s is probable inthe fstaee and should beve oonsiderahle
impact on the cost of longchau! transmission

"The allocation of impairments, se given hore, represents « nepabol
in azo of the best balance besnten the cast and performance of euch
‘of the components of the nelwork. ‘These allcetions are eontinnally
being reviewad se expecienee i ysiaed end advanots are mace in
techrology

"The end-to-end tretsmision cljewlives for the video porsion of
the Pickanphowe network ave ciseased in « eoxapanion ertile# These
objeetivee were allootad te the compoxente of the netnork in such
fb way 28 to ito that they wi. wifora be ezeeedee. fro re hac ne
Iaeert of the eannestions) even ot be lougeet caxnoction. ‘Tht it
fccomplished by fret stubs, tha confgurstin of the longest on=
nedion and then arortiniyg the endeto-esa cbjowive to wach
component

‘The inparinents of interest may be divided into two eatogrie:
howe astviated with the digital Portion uf the network: and those
smociated with the analog portion of the notworle (Fis. 1)

The digital portion of the netwovie wil bo considered Grst, ‘The
‘maximum length connection (his porlion is assumed ta consist of
4500 rniles of digital traamnsion Tueices snd Len passes through
Ditetresm evitehes, Thin permit eight bitetveam evitehes in tandem,
sth two passes Ciro lve of them for aperetor-honeled ells. Thus,
the netwose i congue in 9 hiere vier! rien wth n tonnes
‘vforintareiy servos when and wire rived to meek Ge demand

‘Diglal tranision com aot che cunkty of the vie signal by
Irzodacing evors ast tzsing jitter. Kivere sre introdveod mt rogeners-
tion points along, tar tranamisscn path where noi, inlerferanoe from
plser in achasek Line rata, snd coviations in the pulea poitins
tomb Yo eanse che regeierslre Lo Telly rescoduee the informe
358 mun anes, seeOmar mmomToAL FOMRNAL, FRENGARY ort

tion in pestioalar pulse alos. ‘Timing jitter octure whon the time
betmeen adjacent pulse positions is altered due ta imperfect timing
eonvery in the regenera

‘The plan for the digital portion of the network assumes the avsila-
Diliy of geal ehanne'shlwoon allo? Cie malor ete in the mid
Allee 197, Those ciglaleanee ae being deigna to tanzmit
‘number of difernt sigs in action to Picturephono signals: for
‘eammple, vole, date and tclevsin, Sine Pistrephone signals ene not
coniolizg inthe establishment of objectives fr Use digital hanes,
oom it [ef to llocata some of the overall impairment allowed for
‘Picturephona serve tothe bitsteam seitaher. The emer rate alloca
tion for the digital portion af the Picturaphowe netore is shown in
‘Table I. The eror rato is sllocetad to two clases of tranzmission
Jilin, chor- and long-bou!, and to the bittream switshing me-
shines, Ina companion paper? itis gfvan that en eror rate af 10

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