Manual / Guide · 1943
Step-by-Step Dial System, Pamphlet No. 37
WE installer's introduction to the step-by-step dial system.
Manual / Guide · 1943
WE installer's introduction to the step-by-step dial system.
7 - STEP BY STEP DIAL SYSTEM Pamphlet No. 37 . Wesfem Eiechr? Compmy I~CO~WIATCD NSTALUllON DEPARTMENT . Insued By GENERAL I ~ T A U T I O NENGINEER MBRCH, 1937 REPRINTED OCTOBER, 1943 37 e r ! c i j P R P F A C E Thir pamphlet is ieeued f o r t h e b e n e f i t of t h e W e r t e r n ~ E l e c t r i cI n s t a l l e r and d e s c r i b e s i n a gene r a l vny t h e fundamental p r i n c i p l e s and characteri r t i o a of t h e step-by-step d i a l syetem. The contents a r e taken from m a t e r i a l which has been prepared by Bell Telephone Labo-zlatories, Inc., f o r t r a i n i n 6 purpoeee. Although p a r t i c u l a r types of apparatus a r e d i s cursed, it ir not intendrd t h a t t h i s publication rhould be ured f o r o p e c t f i c descriptions. The pamp h l r t w i l l .not be kept up t o d a t e with c u r r e n t changer i n t h e equipment. The oontentr of t h i s pamphlet a r e of a purely d e r o r i p t i v e nature and a r e not designed t o p r e r c r i b e methodr o r i n r t r u o t i o n r f o r t h e i n s t a l l a t i o n of cent r a l o f f i o r equipment. - 4 DIAL SYSTEM ST=-BY-8Te Issued By O E N W INSTALLATIOIO g108IIQEEW b L Sa;cTSW 1 W A M B N T A L MBntODS OF OPERATION iw - t P" . 5 : I E I f '&W LC k "t" 3 L i -. the switchhook t h e o i r c u i t is completed through the switchhook contacts in %cries with a relay in the central office, a s shown i n Fig. 1. One h e subd i aof l wthe i t h funcblcnts t h e r e o e h eofr toff the scriber's witohhook is t o o en t h i s c i r c u i t a specified number of times aS by man8 of these open c i r c u i t s or mpulaesn t o give We aut9ssa.tic equipment the proper in$onnation. 'fhd d i a l is provided w i t h a s e r i e s of flnger holes, each is numberad, m e euBscriber placesof hwhich i 8 finger i n one of these holes and \ carries it to t h e back stop, a f t e r which the \ d i a l restores to normal under t b e influence ' of a overnor which r e g u l a b a it8 #peed. A s the d f a l restores t o 'normal it 0the c i w cthe u i t f ai nnumber ab t i m n e q m l t o the nmber ~ r e rhole which vrur saleil~tod)3Y t h on suesorrear. Ttrurr, dialing own$ tB. circ u i t twice; d i e l i n g *5* opens it i t v e ti^^.. I t should be notlaed am that aia-rr&g *seroW open8 the c i r c u i t ten times. The openiqg and c l o s i ~ of~ t h e c i r c u i t alternatef o p e . raks and releaaes a raluy whi* hM, ren al!uu& placed i n e e r i e r w i t h the 0itBsstiber~r1 % ~. . T I n only diifercmco betureh suto~orrticand A p u l ~ ew a l e war;$.bqf the tiaw romanual e uipmont a pafant k, t;bs suarcrcibe~ pmniirer. is the d b l ~t ir 1ocat.E f o ra tthis the i n rearon .tll~ that n t on autohis qutrac~ oir c u i tf oinr OW the .open eerierb b i .ocd iptt~r a cssone wat out closedas matie opstema a r e u n i v e r s a l 4 knova a8 * d i a l n the d i a l restores to ao 1 Tho o m cirly8t4r~.. Phe & R W ~ Q ofS ~the d i r l i8, of owit 18 a p p ~ ~ i l t&i~ w th. &I pulsillg time. . mist is ts tWuru tbo positive OOUPM, t o enab&e a u~bsgl'iber20 ~ 0 n t r o 1the auWmatic e uipment s o that a connection w i l l release of the pulsing -lay i n t h e automat& equipment a t the cmtral offLee. be complete8 to th. n u b e r tw is eallin&. Uhen the sub8uriBbl. rmaoves h i s receiver from m e r e are two nwtho&s of automatically corapletin telephone cral'ls in general use in the B I l l &tern l.Ma$ Of these two, the step-by-step s at.rrtma is t h e first, t o beuse& The term *.tap-&-step? descriptive of the manner i n which the c a l l progresses, each d i g i t dialeel by the subscriber causing a sapa r a t e nuchanlsm t o funation t o advance the calf -0 the various *step8* 'necessary f o r aoaeg;s ion. The skp- -step syakm is quite flexible i n that it nwg e aeed f a r croaa~uritiesreq u i r i r y 1ma than 100 l i n e s o r f o r c m t r p l oNl;en re#uiring 10,000 l i n e s o r more. In tbl. ~ a p e c t .the s t e p -*tep ys(em 18 the . DIE)= ecsoboralcal f o r rura t o m o r commnities ef *oe~ageairre and f o r larger m t r o p o l t t a n area# rhrr~ trunk problem is not too aoxaplex. ?he panel W8 , i r mop*. .dvsnta~ P i nU 16114e ~ ~ ~ t r o p o l k t f r areas a ~ Vhdre OOPB; p k i a a t d intcrraffice t n u r L i q is necessary, 7 "r *, P-" k k it C r i E , , L by-step switch w i l l be described i n g r e a t e r d e t a i l i n the s e c t i o n s t h a t follow. BANKS Rigurs 2, gives a schematic of a subs c r i b e r ' s s t a t i o n circu2.t containing a d i a l . Here the d i a l i a Sbwn i n its normal p o s i t i o n . The r e c e i v e r c i r c u i t is closed through the coirtacts shown ss a o f f normal c o n t a c t s n . AS soan a s t h e subscriber moves t h e d i a l *off normalD, tfr'e o f f normal c o n t a c t s change pos i t i o n so t h a t t h s C8i3sivt3r c i r c u i t is opened t o prevent t h e anwyance of a s e r i e s of sharp c l i c k s i n t h e s u b s c r i b r l s e a r and a s h o r t c i r c u i t is placed around the t r a n s m i t t e r t o remove its v a r i a b l e r e s i s t a n c e from t h e d i a l i n g c i r c u i t . Tke o f f normal c o n t a c t s remain i n t h i s condition from t h e time t h e . s u b s c r i b e r ' s d i a l f i r s t moves off normal u n t i l it has r e s t o r e d under t h e influence of a governor. Tha contgcte labeled n p u l s e cont a c t s " , however, open and c l o s e only while t h e d i a l is r e s t o r i n g t o normal a t a constant speed determined by the governor. QWITCHINO MECHANISM8 The 8WitcBing mechanism employed i n t h e atep-by-step system is i l l u s t r a t e d i o Figs. 3, '4,. and 5 and is arranged t o take t e n vert i c a l s t e p s and t e n h o r i z o n t a l s t e s, thus formin6 a switch having access t o PO0 s e t s o f terminals. Variations of t h i s . fundamental mechanism a r e ernployed f o r the d i f f e r e n t functions r e uired. One switch of % h i s type, known as a 'fine f i n d e r N , is used t o find the c a l l i n g s u b s g ~ i b e r ' s l i n e , thus performing t h e same functioRs f o r t h e automatic equipment t h a t t h e *Aw board operator does i n t h e manual sys'tem by i n s e r t i n g an answering cord i n t h e answering jack of the c a l l i n g subs c r i b e r ' s l i n e . One o r more of these wechan i s m known as U s e l e c t o r s n a r e r e u i r e d t o s e l e c t a trunk to -the d i s t a n t o f f h e Ano t h e r s e l e c t o r determines i n which 1600 l i n e s the c a l l e d l i n e appears. Another s e l e c t o r picks the p a r t i c u l a r 100 l i n e s i n which the c a l l is t o be cotnpleted, and f i n a l l y a s i m i l a r mechanism known as a % o m e c t o r is required t o coropleta the c a l l t o t h e number which has bean d i a l e d . Such. uses of the step- The banks t o which t h e switch has access, a r e shown i n Fig. 6. The step-by-stet system borrows the f a m i l i a r terms " t i p n and ring" t o r e f e r t o the conductors of t h e s u b s c r i b e r ' s l i n e o r t o the conductors of a trunk and the term "sleeve" t o r e f e r t o t h e supervisory lead r e u i r e d i n t h e c e n t r a l o f f i c e . The banks i q l u s t r a t e d a r e so a r r a n g d t h a t t h e switch has access t o 1 0 0 . t i p s and 100 r i n g s i n the lower bank and t o 100 s l e e v e s i n t h e upper bank, The s w f t c h . s h a f t has brushes mounted on its lower end which a r e so spaced as t o have access t o the banks. The lower brush mounted on the s e l e c t o r rod, therefore. makes c o n t a c t With two terminals and t h e upper with one terminal. Variations of t h i s a r e found at.tcixpes where a s e c ~ n 4c o n t a c t may be made i n t h e upper bank g i v i n g a t o t a l of four instead of t h r e e , and i n the case of t h e 200 p o i n t l i n n f i n d e r s where t.hrea hank^ a r e employes. The brusnes mounted on t h e rod a r e wired through f l e x i b l e cords t o t h e r e l a y equipment on the switch, access into the w i t c h being by means of a f l e x i b l e plug and jack arrangement a t t h e back o f t h e switch rend access o u t of t h e switch bding through t h e bank tei?ihals. SWITCHING ACTION An i n t e r g s l p a r t of the switch s h a f t is a s e r i e s of t e e t h , t e n f o r moving t h e s h a f t upward and t e n f o r r o t s t i n it. The vert i c a l t e e t h a r e arranged afong the s h a f t and a r e c o n t r o l l e d by means of a u v e r t i c a l pawl* and a v e r t i c a l magnet. The r o t a r y o r hori z o n t a l t e e t h a r e asranged around t h e s h a f t and, ape c o n t r o l l & by a " r o t a r y pawl* and a . r o t a r y magnet. The v e r t i c a l . a m of t h e *double dog", s l i d e s over t h e v e r t i c a l t e e t h as the switch r i s e s and prevents its f a l l i n g back t o normal. A s soop as the switch begins t o r o t a t e the " s t a t i o n a r y dog* enga e s one of t h e x e r t i c a l t e e t h and p r e v e n t s tr res t o r i n g t o normal while t h e r o t a r y arm of the "double dog" ' s l i d e s over t h e r o t a r y t e e t h and prevents its r e s t o r i n g i n a h o r i z o n t a l d i r e c t i o n u n t i l a f t e r t b e switch has been re. l e a s e d upon conclusion of the c a l l . The v e r t i c a l and r o t a r y stepping mechanism is i l l u s t r a t e d i n Figures 7 t o 10. The f i r s t s e r i e s of pulses which come t.hrou,~hfporn t h e s u b s c r i b e r ' s -dial causes t h e pulsine; r e l a y i n the swiscn t o operate and r e l e a s e i n synchronism with t h e pulses and i n t u r n operate and r e l e a s e the v e r t f c a l magnet. Under t h e influence of the v e r t i c a l pawl the switch r i s e s u n t i l the brushes a r e opposite t h e l e v e l determined by t h e number of pulses s e n t from t h e d i a l . I f t h e switch is a " s e l e c t o r n i t will now r o t a t e automatica l l y under t h e influence of the r o t a r y ma and pawl u n t i l a n i d l e trunk on t h a t l e v e r e t is rqached. I f it i a a"connectorn it w i l l w a i t f o r the s u b s c r i b e r t o d i a l another d i g i t , i n which case it w i l l r o t a t e under . t h e influence of t h e d i a l pulses u n t i l it recCc2ies the p a r t i c u l a r s e t of terminals determined by t h e l a s t d i g i t . f FIG. 3 STEP-BY-STEP SELECTOR SWITCH \t%-r FIG. 4 FIG. 5 STEP-BY-STZP CONNECTOR SWITCH REAR VIEW WITH COVER PLATE OPEN STEP-BY-STEP FIG. 6 STEP-EY-5Tkr CONNECTOR SWITCH : . I U L ~ I P L ZBAXKS VERTICAL MAGNETS -VERTICAL ARM. M R T . ARM. SPRING 1' SHAFT : 7- ,. 1 1 g r ' * P 8- ' k ' , * )', , ' e V E R T . RATCHET 6 STATIONARY DOG . M PAWL V - & r \-VERT. . PAWL GUIDE -- - -* i' I r'IG. 8 VERTICAL STEPPING MECHANISM NORMAL POSTDOUBLE DOG SPRING RELEASE MAGNET SPRING NORMAL PIN--.: ROTA RYDOG DOUBL DOG \ RELEASELl NK I I RELEASE ARM. PIN , ROTARY MAGNETS ROTARY ARMATURF SPRING I ' 7 A, > - . RELEASE LINK PIG. 11. 100 LINE STEP-BY-STEP t h e switch is now held i n its r o t a t e d p o s i t i o n by t h e double dog and held i n its v e r t i c a l p o s i t i o n by the fixed dog. Upon r e l e a s e o f the w i t c h 9 magnet is operated (known as t h e "release magnet*) which removes the double dog from engaging the r o t a r y t e e t h allowing the switch t o r e s t o r e horizontally under t h e a c t i o n of a coiled s p r i n g i n the s p r i n g cup. When the hori z o n t a l r e s t o r a t i o n is complete the fixed doe aisee s t h e v e r t i c a l t e e t h because oi the v e r t i c a f s l o t and t h e s h a f t restore's t o normal in a v e r t i c a l d i r e c t i o n by means of gravity . THB FUNliAMHTAL STEP-BY-STEP SYSTW A simple 100 l i n e step-by-step system Each suba c r i b e r t s l i n e terminates on t h e bank o r a oonnecuWr and is multipled t o t h e banks of a lib 'Ifodrr. The l i n e f i n d e r a c t s as an answsriag. cord i n t h a t i t maker connection t o t h e c a f l i n g l i n e and extends t h a t l i n e t o a connector. The s u b s c r i b e r rec-eives d i a l tone Irom t h e conrlector ana a l a l s tne c a l l e d number, %ha connector having aocess t o a l l t h e 100 l i n e s . ls i l l u s t r a t e d i n F i g w e 11, , . DIAL SYSTEM In order t o handle more than one c a l l a t a time, the system i l l w . t r a t e d might have t e n l i n e f i n d e r s and t e n connectors f o r a group of 100 l i n e s . In t h i s case esch l i n e f i n d e r is wired t o a connector. The %nks of a l l l i n e f i n d e r s a r e multipled together and t h e banks of a l l connectors a r e multipled. This means t h a t t e n paths a r e provided f o r the completion of c a l l s . I f t h e call% r a t e is very h i b more paths may be p r o v i d g . xn p r a c t i c e , s u f f i c i e n t l i n e finder* and connectors would be provided t o handle t h e normal t r a f f i c but not q u i t e enough f f i t a h s a t o handle t h e extreme peak load condition which would probably occur only during a s h o r t period of the bay. I t would. of course, be possi&le f o r a l l paths t o be ~ u e yand. i n t h a t case a c a l l i n g s u b s c r i b e r would not receiva d i a l tone u n t i l a f t e r a l i n e f i n d e r and its associated conneptor became i d l e . A s we s h a l l s e e l a t e r t h e systetn illu s t r a t e d i n Fig. 11 is the b a s i s f o r a l n o s t a l l s t e p b y - s t e p systems. By adding s ~ i t e h e s between t h e l i n e f i n d e r s and connectors s o t h a t each a a l l i e completed through a " t r a i n * of switches, t h e s i z e of t h e o f f i c e ma^ be extended t o 1090 o r t o 10,000 o r mope liws. ._ I I I 1 SECTION 2 LINE CIRCUITS AND LINE FINDERS I n t h e manual system, s u b s c r i b e r s ' l i n e s a r e answered by an *AU board o p e r a t o r who is r e s p o n s i b l e f,or a l l of t h e s u b s c r i b e r l i n e s appearing a s answering jacks i n h e r p o s i t i o n . In o r d e r t o e s t a b l i s h c o n t a c t w i t h r c a l l i n g s u b s c r i b e r who has removed t h e r e c e i v e r from t h e switchhook, an answering cord is placed i n t h e r e q u i r e d answering jack a s i n d i c a t e d by t h e l i g h t e d l i n e l a n ~ p . I n t h e step-bfs t e p system t h e answering cord of t h e "A board o p e r a t o r i n t h e manual system is replaced by a step-by-step s w i t c h known a s a l i n e f i n d e r . The f u n c t i o n of. t h e * l i n e finde r is t o make c o n t a c t w i t h any c a l l i n g l i n e i n a p a r t i c u l a r group and extend t h a t . l i n e t o a f i r s t s e l e c t o r ( t o a connector i n t h e 100 l i n e system p r e v i o u s l y d e s c r i b e d ) , t h e f i r s t s e l e c t o r giving the subscriber d i a l tone and r e c e i v i n g t h e f i r s t d i g i t d i a l e d by t h e s u b s c r i b e r . I n t h e manual system, t h e number of . answering jacKs appearing i n each "An board p o s i t i o n is dependent upon t h e c a l l i n g r a t e of t h e l i n e s involved and t h e load which t h e # A n board o p e r a t o r is a b l e t o c a r r y . In t h e step-by-step system, l i n e s a r e i n most c a s e s arranged i n groups of 200, t h e number o f l i n e f i n d e r s having a c c e s s t o t h i s group of l i n e s varying w i t h t h e c a l l i n g r a t e . POINT LINE FINDER A l i n e f i n d e r arranged t o s e r v e a 200 l i n e group is i l l u s t r a t e d i n Fig. 13, and is known a s a "200 p o i n t U l i n e f i n d e r . Each l i n e f i n d e r has a c c e s s t o 3 banks of 200 t e r m i n a l s each. The lowest bank c o n t a i n s t h e t i p s and r i n g s of 100 l i n e s numbered 11, 12, 13, 14, .19, 10 on t h e bottom l e v e l and 01 t o 00 on t h e t o p l e v e l ( s e e . Fig. 1 2 ) . I t should be n o t i c e d t h a t t h e t e n t h t e r m i n a l on t h e t o p ' l e v e l is numbered "00" because t h e s w i t c h s t e p s v e r t i c a l l y t e n times and h o r i z o n t a l l y t e n times t o r e a c h it. The middle bank c a r r i e s a second 100 l i n e s t h e t e r m i n a l s o f which a r e numbered 111 t o 110 on t h e bottom l e v e l and 101 t o 100 on t h e t o p l e v e l . The t o p bank c a r r i e s t h e s l e e v e t e r m i n a l s o f t h e e n t i r e group of 200 l i n e s , t h e s l e e v e s 11 t o 10 and 101 t o . 110 being arranged on t h e bottom l e v e l and 0 1 t o 00 and 101 t o 100 on t h e t o p l e v e l . The purpose o f t h e s l e e v e bank is t o permit t h e l i n e r e l a y of a c a l l i n g l i n e t o put b a t t e r y on its corresponding s l e e v e t e r m i n a l t o s t o p t h e l i n e f i n d e r a s i t sweeps a c r o s s t h e row of t e r m i n a l s . The l i n e f i n d e r s h a f t c a r r i e s t h r e e s e t s of b r u s h e s , one t o make. c o n t a c t i n each bank. A v e r t i c a l commutator c o n s i s t i n g of 10 segments is arranged a t t h e s i d e of t h e l i n e finder s h a f t sq t h a t a s the s h a f t r i s e s a comr~~utator brush makes c o n t a c t with t h e f i r s t segment when t h e l i n f i n d e r b r a s h e s a r e o p p o s i t e t h e f i r s t l i v e 1 of t h e banks, t h e second segment when they a r e o p p o s i t e t h e second l e v e l , e t c . The l i n e f i n d e r c i r c u i t is s o arrsnged t h a t , a s soon a s any l i n e r e l a y i n t h e group of 200 l i n e s is operated. 3ne o f t h e i i n e f i n d e g s s e r v i n g t h e group w i l l comence t o s t e p up and w i l l continue s t e p p i n g up u n t i l i t meets a commutator segment t h a t is grounded. There a r e 20 l i n e s on each l e v e l and each "sub-group" o f 20 l i n e s h a s a c c e s s t o a common sub-group r e l a y which may be operated by any l i n e r e l a y i n t h e subgroup. The o p e r a t i o n of t h i s sub-group r e l a y grounds t h e commutator segment corresponding t o t h e l e v e l on which t h e s e 20 l i n e s appear. T h i s w i l l cause t h e l i n e f i n d e r t o s t o p its v e r t i c a l motion a t t h e l e v e l on which t h e c a l l i n g l i n e appears. A f t e r t h e l i n e f i n d e r has stepped up t o t h e proper l e v e l i t w i l l , of i t s own accord, begin t o s t e p o v e r t h e t e r m i n a l s o f t h a t l e v e l , t e s t i n g t h e sleeve terminals i n the t o p bank, two a t a time, a s it goes along. A s soon asRn-ds a s l e e v e t e r m i n a l w i t h b a t t e r y on i t from t h e operated l i n e r e l a y it w i l l s t o p w i t h its t i p and r i n g brushes on t h e t i p and r i n g of t h a t l i n e i n o r d e r t o extend t h a t l i n e t o a f i r s t s e l e c t o r . Thus i f l i n e 12 is c a l l i n g commutator s e g m e n t ' l w i l l be grounded and t h e l i n e f i n d e r w i l l s t e p up t o t h e f i r s t l e v e l and i n on t h a t l e v e l t o t h e second t e r m i n a l . A f t e r the l i n e f i n d e r has stopped on a given s e t of t e r m i n a l s i t connects t h e brushes i n t h e bottom bank o r i n t h e middle bank t o a f i r s t s e l e c t o r , i n accordance w i t h which of t h e two s l e e v e s i n t h e upper bank h a s t h e b a t t e r y condition. SLIP WIRING OF LINE FINDER BANKS AND s;omum Obviously i t t a k e s a c e r t a i n amount of time f o r a l i n e f i n d e r t o r i s e t o t h e h i g h e r l e v e l s of i t s banks and c u t i n t ~t h o s e l e v e l s u n t i l it f i n d s t h e t e r m i n a l s of t h e c a l l i n g l i n e . The i d e a l c o n d i t i o n would b e t o have t h e c a l l i n g l i n e on t h e f i r s t l e v e l of t h e l i n e f i n d e r bank i n every c a s e , s o t h a t t h e Line f i n d e r would have t o s t e p up only one l e v e l and then c u t i n t o t h a t l e v e l t o f i n d t h e c a l l i n g l i n e . This would mean t h a t t h e s u b s c r i b e r would r e c e i v e d i a l tone from t h e f i r s t s e l e c t o r w i t h a minimum amount of waiting. I t is n o t p o s s i b l e t o a c h i e v e t h i s i d e a l c o n d i t i o n f o r every c a l l , b u t t h e hunti n g time f o r l i n e f i n d e r s is c o n s i d e r a b l y aec r e a s e d by n s l i p p i n g " t h e l i n e f i n d e r multip l e a s s h o w on F i g . 12. Suppose t h a t a group o f 200 l i n e s is served by 2 0 l i n e f i n d e r s . I n t h i s c a s e l i n e r 11 t o 10 appear on t h e f i r s t l e v e l o f t h e lower bank o f t h e f i r s t l i n e f i n d e r of subgroup 1, and l i n e s 111 t o 110 on t h e bottom l e v e l o f t h e middle bank o f t h i s l i n e f i n d e r . However, t h e s e l i n e s a r e wired t o t h e t o p ( o r t e n t h ) i e v e l s o f t h e banks on t h e f i r s t l i n e f i n d e r of sub-group 2 and t o t h e n i n t h l e v e l s o f t h e f i r s t l i n e f i n d e r o f sub-group 3, t h e e i g h t h l e v e l s of t h e f i r s t l i n e f i n d e r of sub-group U, e t c . , and appear a g a i n on t h e f i r s t l e v e l s o f t h e second l i n e f i n d e r of sub-group 1. T h i s means t h a t t h e f i r s t and second l i n e f i n d e r s of sub-group 1, a r e "first c h o i c e V o r t h e u s e o f l i n e s 11 t o 10 and 111 t o 110 s i n c e t h e s e two l i n e r f i n d e r s h a r e t h i s group of 20 l i n e s on t h Q i r f i r s t l e v e l s . Likewise the f i r s t and second l i n e f i n d e r s of sub-group 2 a r e f i r s t choice t o l i n e s 21 t o 20 and 121 t o 120, and the f i r s t and second l i n e f i n d e r s of sub-group 3 f o r l i n e s 31 to 30 and 131 t o 130. The wiring t o t h e corresponCing com~rutatorsegments is slLpped i n a corresponding manner. ALLOTMENT OF LINE FINDERS Fig. l2 i l l u s t r a t e s the method of a l l o t i n g l i n e finder8. The operation of the sub-group r e l a y of a sub-group of 20 l i n e s does two things. F i r s t , it placea a ground on t h e commutator segment corresponding t o the l e v e l i n which the group of 26 l i n e s appears on the l i n e f i n d e r banks. Second, it grounds a s t a r t l e a d which o p e r a t e s a " s t a r t n r e l a y i n the l i n e f i n d e r t h a t is t o be used f o r the c a l l , causing it t o s t e p up and hunt f o r the grounded commutator segment. Tracing t h e start l a a d from t h e subgroup r e l a y i n sub-group No. 1, tte ' a r r i v e a t t h e back Contacts of the (D) r e l a y i n t h e f i r s t l i n e f i n d e r s of t h e 8ub-group (which has t h e l i n e s i n sub-group Ao. 1 on its f i r s t l e v e l ) aad thence on t o t h e winding of t h e a s t a r t * r e l a y (A). If, however, t h i s l i n e f i n d e r is b w y on a e a l l t h e (D) r e l a y w i l l be operated and t h e start lead w i l l be extended t o t h e back.contacts of the (Dl r e l a y of the second l i n e f i n d e r of t h e subgroup. I f t h i s l i n e f i n d e r is a l s o busy t h e (Dl r e l a y w i l l be operated and t h e start lead w i l l be extended t o t h e o t h e r l i n e Cinders i n sub-group No. 1. I f a l l f i n d e r s i n t h e sub-group a r e busy t h e a t a r t lead is extended t o the f i r s t l i n e f i n d e r i n subgroup No. 10 s i n c e t h e l i n e f i n d e r s of t h i s group have l i n e s 11 t o 10 and 111 t o 110 on t h e i r second l e v e l a . The process of allotment thereupon continues a s necessary through t h e l i n e f i n d e r s i n sub-group No. 10 sub-group No. 9, etc., the l a s t choice l i n e f i n d e r s f o r t h e No: 1 sub-group of l i n e s being the l i n e f i n d e r i n sub-group No. 2, s i n c e these l i n e f i n d e r s have sub-group No.1 l i n e s on h e i r top l e v e l s . By meano of t h i s bank-to-bank s l i p o n l i n e f i n d e r multiples', each group of 20 l i n e s is given equal preference i n ' b e i n g chosen by l i n e f i n d e r s . I f 20 l i n e f i n d e r s a r e provided t o s e r v e a group af 200 l i n e s t h e r e a r e two f i r s t choice l i n d f i n d e r s per sub-group. I f 30 l i n e f i n d e r s serve the group of 200 l i n e s t h e r e a r e t h r e e f i r s t choice l i n e f i n d e r s per sub-group, t h r e e second choice, t h r e e t h i r d choice, e t c . This i n s u r e s that; t h e waitin.g time f o r d i a l tone w i l l be kept down t o a minimum. I f i t should so happen t h a t a l l l i n e f i n d e r s a r e busy a t t h e time' s subscriber removes h i s r e c e i v e r from the switchhook, of course he w i l l n o t be conniGcted t o a f i r s t s e l e c t o r , w i l l not r e c e i v e d i a l tone and w i l l not be a b l e t o make h i s c a l l u n t i l s o m e l i n s f i n d e r becomes i d l e . This is comparable t o the custom i n manual o f f i c e s of providing only t h a t number of cord c i r c u i t s i n an "Ae board p o s i t i o n which is required t o handle j u s t a l i t t l e l e s s than t h e rush hour load, The l i n e and l i n e f i n d e r e uipment required t o serve a group of 208 l i n e s is mounted together i n one equipment u n i t , a s i l l u s t r a t e d i n Fig. 14, c o n s i s t i n g of the required number of l i n e f i n d e r s with t h e i r banks, commutators and jack wiring, the l i n e c i r c u i t s with t h e i r associated wiring, the sub-group c i r c u i t s required f o r eaoh group of 20 l i n e s and t h e r e l a y s required f o r the common group of 200 l i n e s . This equipment u n i t is shop-wired and may be shipped from t h e f a c t o r y ready t o be mounted upon a l i n e f i n d e r frame. * SECTION 3 SELECTORS AND CONNECTORS In S e c t i o n 1 a step-by-step system employing only 100 p o i n t l i n e f i n d e r s and connectors was de,scribed and i t was shown t h a t t h i s was a b a s i c step-by-step system. Such a systern, modified by t h e use of " s e l e c t o r connectors" capable of picking an i d l e trunk on one o r more l e v e l s and l i n e s on the remaining l e v e l s i n s t e a d of t h e conn e c t o r s d e s c r i b e d , is a c t u a l l y i n use f o r srnall d i a l o f f i c e s i n r u r a l comnunities. In t h i s s e c t i o n t h e method of i n c r e a s i n g t h e s i z e of s step-by-'step o f f i c e beyond 100 l i n e s w i l l be d e s c r i b e d . This is done by i n s e r t i n g s e l e c t o r s i n t h e ' t r a i n u of switches r e q u i r e d t o complete a given c a l l . Figure 15 shows a method whereby t h e 100 l i n e scheme previously described may be expanded- t o 200 l i n e s by t h e use of sel e c t o r s . The 100 p a i n t l i n e f i n d e r s of t h e previous system a r e cow replaced by a group of 200 p o i n t l i n e f i n d e r s each l i n e f i n d e r belng capable of s e l e c t i n g any c a l l i n g l i n e i n a group of 200. Bach l i n e f i n d e r is now wired t o a " s e l e c t o r n . The c h i e f d i f f e r e n c e between a s e l e c t o r an4 a connector is t h a t the s e l e c t o r w i l l move up t o the s p e c i f i e d l e v e l under the influence of t h e customer's d i a l and w i l l then proceed t o f i n d a n i d l e trunK on t h a t l e v e l o f its own accord. The connector, s t e p s up t o ' t t i 6 c o r r e c t l e v e l under t h e . i n f l u e n c e of t h e custoroer's d i a l and f i n d s t h e proper terminal i n t h i s l e v e l i n accordance w i t h a second s e t of I n a 201 l i n e p u l s e s from t h e d i a l . system two groups of connectors would be r e q u i r e d , each having a c c e s s t o 100 l i n e s . Since it w i l l be necessary f o r t h e custonier t o d i a l two d i g i t s i n o r d e r t o cont r o l whatever connector is used on the c a l l , an a d d i t i o n a l d i g i t must now be d i a l e d t o aeterrnine i n which group of connectors t h e c a l l w i l l be completed. The d i g i t w i l l be d i a l e d i n t o t h e s e l e c t o r t h a t has been introduced i n t o t h e t r a i n . In order t o cause t h e s e l e c t o r t o choose t h e r i g h t group of connectors, ' t h e connectors having a c c e s s t o one group of 100 l i n e s g i l l be wired t o one l e v e l of t h e s e l e c t o r , say t h e f o u r t h . and t h e o t h e r group of connectors t o a n o t h e r l e v e l of t h e s e l e c t o r , s t h e e i g h t h . Thus, first digit o i f t h e customer d i a J s as% f o u r , t h e s e l e c t o r w i l l s t e p up t o its f o u r t h l e v e l and w i l l hunt a l o n g .that' l e v e l f o r a n i d l e connector having aocaos t o t h e l i n e s 400 t o 499. I f h i s f i r s t d i g i t is an e i g h t , t h e s e l e c t o r w i l l s t e p up t o t h e e i g h t h l e v e l and w i l l choose an i d l e connector having a c c e s s t o t h e numbers 800 t o €399. In a d d i t i g n , t r u n k s may be provided on t h e t e n t h l e v e l of t h e s e l e c t o r t o an a s s i s t a n c e operator i f required. The presence o f t h e one s e l e c t o ~i n the t r a i n of,switches presents the p o s s i b i l i t y of i n c r e a s i n g t h e s i z e of t h i s step-by-step o f f i c e ' t o 1000 l i n e s , providing a s e p a r a t e group of connectors is wired 'to .each l e v e l of t h e s e l e c t o r . The number of s e l e c t o r s r e q u i r e d w i t h t h e i r banks i n m u l t i p l e w i l l be determined by t h e number of l i n e f i n d e r s r e q u i r e d t o handle t h e c a l l i n g r a t e from each group of 200 l i n e s . For a 1000 l i n e o f f i c e t h e c a l l i n g l i n e s w i l l be divided a s b e f o r e i n t o groups of 200 l i n e s , each group of l i n e s being served by its own l i n e f i n d e r s . The l i n e f i n d e r s of a l l groups w i l l , however, be wired t o s e l e c t o r s having t h e i r banks i n m u l t i p l e s o t h a t a s u b s c r i b e r i n one group of l i n e s , having gained a c c e s s t o a s e l e c t o r by means of l i n e f i n d e r a c t i o n , w i l l have . a c c e s s t o a c t u a l l y t h e same connectors as a c a l l i n g ' s u b s c r i b e n i n any o t h e r group, In t h e event t h a t any l e v e l of t h e s e l e c t o r is r e q u i r e d f o r t r u n k s t o o t h e r t h a n connectors, t h e t o t a l number of l i n e s which it w i l l be p o s s i b l e t o s e r v e w i l l be reduced by 100 f o r each l e v e l r e q u i r e d f o r t r u n k s t o o t h e r t h a n connectors. FIG. 16 STEP-BY-STEP 4 DIGIT OFFICE 7080 LPBJES EQUIPPED The a d d i t i o n of a second s e l e c t o r i n t h e t r a i n of s w i t ~ h e srequired f o r the completion of each c a l l errnits the s i z e of the o f f i c e t o .row beyon! 1000 l i n e s . Figure 16 i l l u s t r a t e s the switches required t o eerve a four-digit o f f i c e with 7000 t a r minalr equipped. This system makes use of 200 point l i n e f i n d e r s a s before, f i r s t s e l e c t o r s t o choose t h e p a r t i c u l a r 1000 l i n e s i n which the c a l l is t o be completed, and second s e l e c t o r s t o choose t h e particular 100 l i n e s ( o r r a t h e r t h e p a r t i c u l a r group of connectors) i n which t h e c a l l is t o be completed. Referring t o Fi ure 16 assume t h a t the number t o which a c a l f is t o be completed is 8195. The method of completing the c a l l w i l l be a s follows: The f i r s t s e l e c t o r hunts f o r an i trunk t o t h e 8000 group of second s e l e c of which t h e r e a r e ten on its eighth l e The customer d i a l s a 1 a s h i s s e ~ digi't and t h e second s e l e c t o r s t e p s up its f i r s t l e v e l , The second s e l e c t o r hunts f o r connector i n the 8100 group by t e s t i terminals on its f i r s t level. The customer d i a l s a 9 a s h i s d i g i t and a n i d l e cormnector s t e p s up n i n t h l e v e l under t h e influence of pulses. The fourth and l a s t d i g i t d i a l e d t h e customer is a 5 which causes t h e co nector t o s t e p t o t h e f i f t h terminal on n i n t h l e v e l which r e p r e s e n t s t h e t e m i a a of t h e l i n e 8195. When the customer removes h i s r e c e i v e r from t h e switchhook, aa i d l e l i n e f i n d e r i n the group s e r v i n g t h e p a r t i c u l a r l i n e w i l l a t t a c h i t s e l f t o the c a l l i n g l i n e and exter~d The c a l l e d p a r t y ' s b e l l is rung it t o the f i r s t s e l e c t o r . connector u n t i l t h e m l l o d papty answ The customer r e c e i v e s d i a l tone from the f i r s t s e l e c t o r . Tbe l i n e f i n d e r , first s e l e c t o r , secbnd s e l e c t o r and connector chosen f o r c a l l remain operated u n t i l $he conclusto T h e custorner d i a l s 8 a s h i s f i r s t d i g i t , the conversation. and t h e f i r s t s e l e c t o r s t e p s up to the eighth level. I n ;he e v e n t t h a t a c u s t o m e r r e q u i r e s s p e c i a l a s i s t a n c e w i t h h i s c a l l , he 1s i n s t r u c t e d t o d i a l " 0 " . I f t h i s ''0" is d i a l e d as h i s f i r s t d i g i t i t w i l l c a u s e t h e f i r s t s e l e c t o r t o s t e p up t o i t s t e n t h l e v e l a n d h u n t a n i d l e t r u n k on t h i s l e v e l o v e r w h i c h he w i l l b e a b l e t o r e a c h a s p e c i a l service operator. s t e p p e d up t o i t s f i r s t l e v e l c o n n e c t i n g t h e customer's l i n e through t o a n a u x i l i a r y f i r s t s e l e c t o r . I f t h e c u s t o m e r now p r o c e e d s t o d i a l t h e f i r s t d i n i t o f h i s number t h e a u x i l i a r y f i r s t s e l e c t o r w i l l s t e p up t o t h e d e s i g n a t e d l e v e l and a n i d l e t r u n k w i l l b e s e l e c t e d on t h a t l e v e l j u s t a s though t h e d i g i t had b e e n d i a l e d i n t o t h e f i r s t s e l e c t o r i n t h e p r o p e r manner. T h i s i s t r u e r e g a r d l e s s of whether t h e customer d i a l s t h e f i r s t d i g i t o f a l i n e number o r w h e t h e r h e d i a l s "0" i n o r d e r t o g a i n a c c e s s t o a s?ecial service operator. The f i r s t l e v e l o f t h e f i r s t s e l e c t o r b a n k s i s r e s e r v e d , however, f o r a c c e s s t o "auxiliary f i r s t " selectors. A l l levels of the auxiliary f i r s t s e l e c t o r s a r e multipled t o t h e banks o f t h e f i r s t s e l e c t o r s except t h e f i r s t l e v e l . The f i r s t l e v e l o f t h e a u x i l i a r y f i r s t s e l e c t o r goes t o "service code1# s w i t c h e s . One p u r p o s e o f t h e a u x i l i a r y f i r s t s e l e c t o r s is t o n u l l i f y t h e e f f e c t of "preliminary impulsesn from the customerts d i a l . I f the s u b s c r i b e r a c c i d e n t a l l y opens t h e c i r c u i t o n c e b) t o u c h i n g h i s , s w i t c h h o o k a f t e r t h e l i n e f i n d e r h a s found h i s l i n e t h i s w i l l h a v e t h e same e f f e c t a s d i a l i n g t h e d i g i t "1" a n d t h e f i r s t s e l e c t o r w i l l b e The p u r p o s e o f t h e s e r v i c e c o d e s w i t c h is t o e n a b l e t h e c u s t o m e r t o ' g a i n a c c e s s t o long distance, repair servj ce, i n f o r m t i o n , e t c . , w h i c h a r e t o b e o b t a i n e d by d i a l i n g one o f s e v e r a l s p e c i a l s e r v i c e c o d e s . Long d i s t a n c e , f o r i n s t a n c e , i s o b t a i n e d by d i a l i n g 110, t h e f i r s t d i g i t b e i n g recorded by t h e f i r s t s e l e c t o r , t h e second d i g i t by t h e a u x i l i a r y f i r s t s e l e c t o r and the l a s t d i g i t by t h e s e r v i c e c o d e s w i t c h . I f t h e s u b s c r i b e r inadvertently causes a preliminary impulse, t h e c a l l w i l l be completed t o one o f t h e s e r v i c e c o d e s w i t c h whose b a n k s a r e m u l t i p l ed w i t h t h o s e o f t h e r e g u l a r s e r v i c e s w i t c h e s . restor When b o t h p a r t i e s h a n g u p a l l s w i t c h e s t o normal. % SPECIAL SERVICE SWITCHES FIG. 1 7 TYPICAL CON:4PCTOR FRAME 13 of 100 l i n e s . The connector frhme i l l u s t r @ t ed is equipped with e i g h t connectors f o r each 109 l i n e s . The f i r s t is wired 88 a t e s t ConFigures 4 and 5 i l l u s t r a t e a t y p i c a l connector switch. There is l i t t l e t o n e c t o r and is used by t h e maintenance f o r c e s d i s t i n g u i s h t h i s switch i n appearance from f o r t e s t i n g l i n e s . The remaining seven conf - o t h e r step-by-step switches. I t has a l a r g e r n e c t o r s a r e used f o r completing c s l l s by number of r e l a y s a s s o c t a t e d w i t h i t than does s u b s c r i b e r s , and on t h e frame i l l u s t r a t e d a s e l e c t o r because i t has more d u t i e s t o seven such c a l l s can be corn l e t e d skraultanep e r f o m oh a given all. F i r s t of a l l , t h e o u s l y i n each group of 100 i n e s . UndeP connector is required t o s t e p both v e r t i c a l l y h e a v i e r t r a f f i c c o n d i t i o n s more connectors and h o r i z o n t a l l y under t h e influence of t h e would be provided. The t~ximurnnumber of subscriber's d i a l i n o r d e r t o a e l e c t a connectors per s h e l f is eleven including t h e p a r t i c u l a r t e r m i n a l r e p r e s e n t i n g . the l i n e t e s t connector. Where mqre than t e n % r e rebeing c a l l e d . In a d d i t i o n , i t must r i n g t h e quired f o r s u b s c r i b e r t r a f f i c t o a group d t c a l l e d s u b s c r i b e r ' s b e l l , maintain s u p e r v i s i o n 100 l i n e s , two o r Inore s h e l v e s [nay be over t h e c a l l i n o r d e r t o s i g n a l t h e o t h e r multipled t o g e t h e r , providing an a d d i t j a n a l s w i t c h e s i n t h e t r a i n when both s u b s c r i b e r d 5 o r 10 connectors per 100 l i n e s . have hung up and, on a l o c a l c a l l , supply Figure 18 i l l u s t r a t e s how t h e vkaiauar t a l k i n g b a t t e r y t o both s u b s c r i b e r s . frames a r e cabled together. The s u b s c r i b s r * f , In the event t h a t a connector' f i n d s l i n e s a r e wired $0 t h e banks of both l i n e f i n d e r s and connecgors. The jacks of l i n e t h e c a l l e d l i n e busy, t h e r e w i l l be a ground on t h e s l e e v e t e r w i n a l . This w i l l s e t up a f i n d e r s a r e wired t o - t h e jacks of f i r s t i sec i r c u i t c o n d i t i o n which w i l i cause a busy l e c t o r s , t h e connections, however, going tone t o be r e t u r n e d t o t h e c a l l i n g s u b s c r i b e r . through t h e I.D.F. providing f l e x i b i l i t y foe t h e changing of t h e p a r t i c u l a r f i r s t selec?t&r Figure 1 7 shows 8 t y p i c a l connector wired t o a given l i n e f i n d e r , The banks o f f i r s t s e l e c t o r s a r e wired t o t h e jacks o f frame: Each " s h e l f " of connectors on t h e frame is arranged t o s e r v e a separatie group second s e l e c t o r s , and t h e banks of second s e l e c t o r s a r e wired t o t h e jacks of connectors CONNECTOM ! -- 18 CABLING 3CXEPlATIC OF REGULAR SWITCH TRAIN F 14 SECTION 4 TRUNKIlYG PROBLEMS IN STEP-BY-STEP OFFICZS The discussion i n Section 3 i n connection with t h e 4 d i g i t o f f i c e with 7000 terminals equipped assumed t h a t no o t h e r o f f i c e s were required i n the a r e a , In cert a i n a r e a s where more than one c e n t r a l o f f i c e is required, t