CA1116733A

CA1116733A - Interoffice callback arrangement

Info

Publication number: CA1116733A
Application number: CA000320940A
Authority: CA
Inventors: Daniel Sheinbein
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1978-02-17
Filing date: 1979-02-06
Publication date: 1982-01-19
Also published as: US4166929A

Abstract

D. Sheinbein 1 INTEROFFICE CALLBACK ARRANGEMENT

Abstract of the Disclosure A telephone switching system is disclosed with facili-ties for processing interoffice callback information over a common channel interoffice signaling system (4) between program controlled call processors (21, 34) in call originating and terminating offices (1,2) upon encountering a called station busy condition. The terminating office call processor (34) is equipped to examine the busy-idle status of the called station (5) by consulting its supervisory memory (46) and by directed called station line scanning and then to enable an automatic call retry only after it is determined that the called station has become idle. Each of the call processors (21, 34) includes an originating register-callback register (47) for storing callback information comprising the calling and called station identities originating office identity, a callback code dialed from a calling station (3), a mark to specify the callback mode of register operation, a line recheck time delay and a time limit on the callback service. Automatic callback is effected in one arrangement by transferring the callback information from the originating to terminating office, ascertaining when the called station becomes idle, and then making a terminating-to-originating office call in an attempt to complete call connections between the calling and called stations.
Another arrangement bypasses the terminating-to-originating office call and retransfers the callback information to the originating office for enabling it to initiate the call retry.

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Description

~ I
D. She~n~e~n 1 INTEROFFICE CALLBACK ARRANGEMENT
_ _ _ Techn~cal Field This lnvention Eelates to communication switching systems and particulaEly to equipment foE automatically EetEying customeE d~aled calls when they encounteE busy conditions when fl~st attempted.

BackgEound AEt . . . _ . _ Occasionally, telephone calls aEe not success-fully completed because the called station is eitheE busy or does not answeE. Less fEequently, calls aEe not completed because all available communication paths through the switch~ng netwoEk aEe busy. Upon encounteE~ng eitheE type of busy condition, a calleE
usually EeoE~ginates and ~edials the called numbeE in a EetEy attempt to complete the call.
Call Eetly seEvice has long been an available telephone service to el~minate the undesired calling paEty effort duEing the persistence of a busy condition.
In some switch~ng systems, the SeEViCe is manually pEovided by an opeEatoE at the calling pa~ty expense and on a ~ecall basis.
Sign~ficant advances have been made in Eecent yeaEs to the extent that switching systems aEe now capable of automatically retEying lnteEoffice calls without OpeEatoE assistance wheneveE they cannot initially be completed due to e~theE busy OE no answeE
conditions. One such system discloses the use of pEogEam contEolled electEonic facilities in a TEaffic SeEvice Position System fo~ automatically EetEying calls without Ope~atoE assistance and at a time specified by the calling pa~ty.

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D Sheinbein 1 1 In the foEegoing call EetEy aEEangements, a EetE~ed call often has not been successfully completed when Eeattempted because, for example, the called station Eemained busy OE the calling station became busy in the lnteE~mO To pEovide moEe assuEance that such a call EetEy is successful when attempted, the aEt has pEogEessed in Eecent yeaEs to the polnt wheEe automatic callback equipment is now commeEcially available foE
EetEying intEaoff~ce calls in such a manneE that the called station ~s checked to deteEmine that it is idle before any Eeattempt is made to complete call connections.
While such equipment is a valuable adjunct to switching systems its utility has p~oven to be limited to SeEving intEaoffice calls and especially those seEved, for example, wlthin a single pE~vate branch exchange. A
peEsistent pEoblem in the aEt has been that no facilit~es have heEetofore been available for p~oviding automat~c callback seEvice between one OE moEe switching off~ces in such a way that ~nteEoff~ce call EetEy attempts are init~ated only afte~ it has been asce~tained that the called station has become idle. Obviously, such a pEoblem is paEticulaEly aggEavated foE long distance calls involving many switching centeEs and miles of tEansmission facil~ties. The problem has also pEOven undesiEable fEom a telephone company standpoint because ~t consumes valuable SW7 tching time and eneEgy Eesources and, in many cases, without any Eevenue foE the noncompletable inteEoffice calls. In addition, the calling parties aEe inconvenienced by being Eeengaged ~n the futile Eetry pEocessing of interoffice calls.

Disclosure of the Invention In accordance w.ith an aspect of the invention there is provided an interoffice callback arrangement for use in a communication system having a first switching office for establishing call connections from a calling station, a second switching office for extending the connections from the first switching office to a called station, equipment for processing interoffice callback information between the first and second switching offices when the call con-nections from the calling station to the called stationcannot currently be completed due to a called station busy condition and the equipment including circuitry for storing called station busy-idle data and characterized in that the equipment comprises apparatus responsive to the pro-cessed callback information for examining the storing circuitry to determine that the called station is idle before automatically initiating a callback attempt to complete interoffice call connections between the calling station and the called station through the first and second 2Q switching offices, the equipment signal processes the interoffice callback information over a data link signaling system independent of the interoffice call connections between the first and second switching office, apparatus is responsive to a determination that the called station is idle for controlling a transmission of the callback information from the second switching office over said signaling system to the first switching office and the equipment further comprises circuitry in the first switching office responsive to a receipt of said callback 3a information from said signaling system for automatically retrying a completion of interoffice call connections from ,~
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the calliny station through the first and second switching offices to the called station.
The foregoing problem is solved and a technical advance is achieved with an automatic callback arrangement for use in a communication switching system to process interoffice callback information between first and second switching offices and to ascertain automatically that the called station is idle before an interoffice call is automatically retried.
When a eall cannot currently be completed due to a busy condition, this callback arrangement is designed so that a first call processor in the call originating office is responsive to callback service request signals from a calling station to effect a transmission of automatic eallbaek information to a seeond eall proeessor in the eall terminating office. All e~uipment in the originating offiee is then temporarily withdrawn from serving the eall and all intelligence for automatic eallback proeessing for the call resides in the faeilities of the terminating office. An advantage of such a mode of operation is that the equipment of the originating offiee is not tied up during the existence of a ealled station busy eondition.
Upon receipt of the callbaek information the seeond eall proeessor periodically controls an examination of the busy-idle status of the called station. When it is found to be idle, the second processor is selectively programmed to return automatic callback information to the first ! proeessor which, after cheeking that the calling station is idle, automatieally retries the eall from the originating to the terminating office. In another arrangement, when the ealled station is found to be idle, - 3a -~$ ~F~

D. Sheinbein 1 1 the second processor is pEogEammed fo~ immediately initiating a call fEom the te~minating to the oEiginating office in a Eet~y attempt to complete call connect~ons between the calling and called stat~ons. These aEEangements facilltate conform~ty with established call chaEging and b~lling equipment opeEations and Eapid call set-up.
The callback aEEangement advantageously functions with a CCIS ~Common Channel InteEoffice Signaling) system which inteEcOnneCtS the fiEst and second call processo~s for impEoved infoEmation signaling. This CCIS system is essentially a data link signaling system which ls separate f~om the t~unking facilities which carEy interoffice voice communlcation between the calling and called stations. It pEovides foE the communications of the aforementioned automatic callbac:k information between the first and second processoEs foE checking the called and calling station busy-idle states and foE
automatically reattempting a completior. of call connections between those stations afte~ they aEe found to be idle.
In accordance with the best mode for CaEEying out the invention, each of the fiEst and second call pEOcessO~S compEises an indiv~dual call stoEe for strong dynamic Eeal-t3me call processlng data. The call sto~e includes a superv~sory memo~y for stOEing busy-idle data foE all stations in the office with which it is associatedO It advantageously includes a EegisteE fo~
sto~ing callback infoEmation comprising a callback SeEviCe Eequesting code dialed by a calleE as a pEefix to the dialed called station numbeE OE a callback code D. Sheinbein 1 1 dialed following a ~eceipt of a busy indicating tone.
The EegisteE is equipped also to stoEe the calling and salled station identities, line-busy Eecheck time delay data, and data foE a tlme limit on the callback service.
The callback EegisteE is seEved by its pEOcesSOE at EecUEEent inteEvals and the latteE decEements the line busy Eecheck time delay data unt~l the delay peE~od expiEes. Upon that event, the pEOcesSOE examines the SUpeEvisoEy memOEy to asceEtain the busy-idle status of the called OE calling station which it is SeEving.
If it is busy, the pEocessoE EeenteES data into the callback register for anothe~ line busy Eecheck time delay peEiod. A maximum number of such EeentEies aEe effected undeE contEol of the time l~mit data. The processor peElodically decrements the latteE data to reduce the time Eemain~ng foE callback seEvice. ~hen ~he time limit expiEes, the pEocessoE el-ases all data ~om the callback registeE and the callback SeEViCe foE that call ~s terminated.
When the called station is found to be idle in the supervisoEy memoEy of the call teEminating office, the second call pEoceSsOE causes the called station line to be scanned to aSSuEe that it is not off-hook, or busy, on a newly oE~ginated call. If that line is busy~ the SUpe~v~SOEy memoEy foE that station is updated and the pEoceSSoE EeenteEs data into the callback reg~steE foE
anotheE line Eecheck time delay period pEovided that the time limit has not expiEed.
AfteE the called station is found to be idle and on~hook, the second pEOCeSSOE is aEEanged to retu~n callback infoEmation to the fiEst pEOceSSor oveE the CCIS

3~3 D. Sheinbein 1 1 facilities foE enabling it to ln~tiate a call EetEy fEom the originating office. Such an aErangement Eacilitates the use of oEiginating office call chaEging and billing foE that call to the calling paEty. FOE moEe rapid call set-up, th~s invention is also aEEanged so that the second pEocessoE bypasses the infoEmation EetuEn to the fiEst pEocessoE and immediately utillzes the callback information to initiate a call fEom the teEminating to OEiginating office in a Eeattempt to complete call connections between the calling and called stations. In the latteE aEEangement, chaEging and billing foE the teEmlnating office call to the calling station 3S
administeEed by the teEminating off~ce and accounting CenteE facilities. When the teEminating to oEiginating office call EetEy cannot be completed due to a busy condition, the second pEocessoE sends the callback infoEmat~on from its callback ~egisteE over the CCIS
system, to the fiEst p~ocessoE.
Upon EeCeipt of the callback info~mation, the f~Est processoE Eeads its SUpeEViSoEy memoEy to deteEmine the busy-idle status of the calling station and, if idle, causes its station l~ne to be scanned to deteEmine the pEesence theEeon of an off OE on-hook signal. If an off-hook is pEeSent, the calling station is busy and the callback connections aEe not then attempted. The fiEst pEocessoE pEoceeds to enteE line Eecheck time delay data and t~me limit data ~n the callback EegiSteE of the flPst office to allow time foE the call~ng l~ne to become idle.
AfteE the call~ng station ~s found to be idle and on-hook, the f~Est pEOcesSOE causes the calling station to be distinctively Eung to aleEt the calling paEty to D. Sheinbein 1 1 the callback seEviCe. The fiEst pEoCeSSo~ ~s selectively aEEanged to extEact the called numbe~ fEom its callback registe~ and to foEwa~d it to announcement equipment wh~ch cOnveEtS the numbeE into an audible announcement message fo~ tEansmission to the call~ng station following an answeE of the Einglng. The message EepOrtS that the call to the called stat$on is now being reattempted. The annvuncement featuEe is useful wheEe EetEy seEvice ls concu~Eently being fuEnished on a pluEality of calls fEom the same call~ng stat~on and enables each call EetEy to be uniquely identiEied. AfteE the message has been deliveEed, call connections aEe extended fEom the calling towaEd the called station. The latteE is then Eung and Eingback tone is supplied to the calling station. Upon called paEty anSweE~ call conveEsation connections aEe cut-thEough.
Brief DescE ption of the DEawlng In the drawing:

FIGo 1 shows, in block diagEam foEm, exemplaEy electEon~c sw~tching offices utilizing CCIS equ~pment;
and FIG~ 2 illustEates call pEoceSsoE equipment ~ncluding call StoEe stEuctuEe comprlsing an OEiginat~ng registeE~callback Eegister togetheE with centEal contEol StEUctUEe used foE automatic callback seEvlce.
The pEinclples o this ~nvention aEe disclosed by way of example in an electEonically pEogEam controlled telephone switching system. PEioE aEt may be consulted foE an unde~standing of the constEuction and opeEation of the SCanneES 8 and 12, pulse distEibutoE 28, digit ~eceiver 15 and tEansmittel 19, t~unk ci~cult 11 and centEal -7~

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D. She~nbein 1 1 pEOcesSOrS 21 and 34.
Best l~ode F'or CaEEying Out ~he Invention _ Swltching offices 1 and 2 of FIG. 1 foEm a communication swltching system and aEe illustratively both electEonic pEogEam contEolled switching offices and aEe designed to SeEve many types of telephone calls including inteEoffice calls. An inteEoffice call is originated fEom a local customeE stat~on, for example, station 3 of a call OEiginating of:Eice 1, and is 10 te~minated via anotheE telephone office, such as teEminating office 2 to a called customeE station, such as stat~on 5.
Station 3 is connected to the o~iginating o:Eflce 1 over telephone line 6 and is teEminated in both a line ScanneE 8 and a line link netwoEk 9O Scanner 8 is employed foE sens~ng "on-hook" and "off-hook" slgnals repEesenting calling EeqUeStS for seEvlce and supervisoEy idle-busy slgnals on line 6.
Office 1 is connected to offce 2 via tEunk 10 : 20 and a tEunk CiECUit 11 which aEe, in turn, connected to both the scanner 12 and the tEunk link netwoEk 13. The ScanneE 12 is employed foE senslng "on-hook" and "off-hook" signals ~epEesenting switching commands, supeEvisoEy busy-idle conditions, and calling Eequests for seEvice.
NetwoEk 9 compE3ses switching facilities foE
establishing, undeE pEOgEam contEol, communication connections fEom line 6 to a tEunk llnk netwoEk 13 v~a netwoEk wiEe junctoEs 14. SimilaEly, netwoEk 13 includes switching facil3ties for establishing progEam contEolled communication connections fEom the junctoEs 14 to d~glt '3~

D. Sheinbein 1 1 EeceiveEs and dial tone supplies, such as Eeceive~ 15 andsupply 16, as well as tEunk ClECUitS, such as ciECUit 11, which aEe used foE seEVing outgoing calls to office 2. In add~t~on, netwoEk 13 pEovldes connections from announcement equipment 17 to a calling telephone line via network 9. NetwoEk 13 also pEovides outpulsing connections fEom an outgoing tEunk CiECUit 11 via wiEe junctoEs 18 to the digit -tEanSmitteE l9. These connections aEe used EOE outpulsing dfgit information needed by an office 2 to complete inteEoffice call connections. NetwoEk 13 furnishes connections undeE
progEam contEol between any of the system tEunk CiECUitS, announcement equipment and data Eeceivers OE
tEansmitters.
The tEunk CiECUitS, digit EeceiveEs and announcement equ~pment aEe pEovided wlth a plu~ality of scan points, such as point 20 O:E tEunk CiECUit ll to which aEe appl~ed the appEopEiate on/off-hook and digit s~gnals. These scan points aEe connected to the scanneE
12, which senses the applied signals foE subsequent use by a centEal processor 21.
A vast majOE~ty O~E the logic, contEol, stoEage, SUpeEviSiOn and tEanslation functtons EequiEed for the opeEation of the tEunk clEcu~ts, digit EeceiveEs and otheE CiECU~tS of off~ces l and 2 aEe peEfoEmed by common contEol equipment compEis~ng the centEal pEOceSSOEs 21 and 34. Resultingly, a minimal amount of contEol CiECUitEy is needed in the individual tEunk CiECUitS and EeCeiveEs and only essential tEansm~sSion appaEatus and switching devices aEe included therein. The latteE
devices aEe connected to a signal dlstEibutoE 22. Th~s _g_ D. Sheinbein 1 1 distEibutor acts as a buffe~ between the high speed centEal pEocessoE 21 and the Eelatively slow speed swi~ching devices to pEov~de foE theiE opeEation wheEeby the c~cuits aEe switched into diffeEent functional stat~s EequiEed foE seEving calls. DistEibutoE 22 causes the operation and subsequent Eelease of the switch~ng devices upon Eeceipt of pEogEammed instEuctions fEom the cent~al pEocessoE 21.
Communications between the signal distributoE 22r scanneEs 8 and 12, and pEoCeSSOE 21 aEe by way of bus systems and multiconductoE cables which pEovide d~scEete communication paths between selected ones of the CiECUitS. These bus systems and cables aEe EepEesented heEein by the bus systems and cables 23.
PEocessoE 21 is a centralized data pEOcessing facility which is employed to imple~lent the varied telephone SeEvice, administEatlve and maintenance ~unctions of the switching system. It is divided funct~onally ~nto thEee units compEislng a call stoEe 24, pEOgEam StOEe 25 and a centEal contEol 26. The call StOEe 24 is a tempOEaEy OE eEasable memoEy facility which employs appaEatus for stoEing infoEmation peEta~ning to call SeEv~ces. Such infoEmat~on includes: ~1) the busy-idle status of stations and communication paths thEough the line and tEunk link netwoEks 9 and 13, ~2) the digits Eeceived fEom a digit EeCelVeE 15, ~3) the digits EequiEed to be outpulsed by a tEansmitteE 19 fo~
completing a call, ~4) intomation EequiEed to intePfacing with the CCIS equipment, and ~5) the chaEging infoEmation to be EecoEded by automatic message accounting equipment

2~ foE bill~ng puEpOseS.

D. Sheinbein 1 As shown in FIG. 2, an ~ndlvidual SupeEvisoEy memoEy 46 is included in each of the call stoEes 24 and 42 for storing the busy-idle status infoEmation for telephone stat30ns seEved by that call StoEe. Each of the call stoEes 24 and 42 ~s also equipped with an ind~vidual call oEiginating Eeg~steE for StOEing d~gits dialed by a calling station. Such d~gits illustEatively compEise a 7-digit called station diEectoEy number and a callback coder foE example a two dig~t code. Register 47 10 is also equipped to stoEe a EegiSteE busy-idle sta-te maEk, a calling station line identity, such as the line equipment numbe~, an address oE the digit EeceiveE, if any, with which it ~s associated on a call, a line Eecheck time delay peEiod count, and a time limit count for callback service.
The pEogEam StOEe 25 is a semipe~manent memoEy arEangement which is employed to store the less changing system ~nfoEmation including the system pEOgEamS and a ~' ~ vaE~ety of -tEanslation infoEmation, such as the diEectoEy 20 numbeE-to-line equipment location data. T~anslation facilities aEe also fuEnished in the pEogEam StOEe 25 fo~
deEiving SemipeEmanent infoEmation Eo~ Eouting via the CClS equipment as well as foE chaEging, Einging, and the like on telephone calls.
CentEal contEol 26 is a pEimaEy call pEOcesSing unit of the system. It peEfoEms call pEOCeSSing in coopeEation with the call st:oEe and pEOgEam StOEe and ls capable of executing one at a time many difEeEent types of basic instEuctions~ OE OEdeES, EeqUiEed fOE
30 controlling the line and tEunk link netwoEks, tEunk CiECU~tS, announcement equipment and digit receiveE

~f~ ~

D Sheinbein 1 l duEing calls. The5e ~nstEuctions aEe WEitten in the foEm of pEOgEams wh~ch are stoEed in the pEogEam StOEe 25.
The pEogEamming inStEuCtiOnS aEe the vocabulaEy of the machine and aEe used to infoEm the switching CiECUitS of the syustem how and when to peEfoEm thel E vaEious functions. The central contEol 26 Eequests an instEuc~ion from the pEogEam StOEe 25 every few micEoseconds and upon Eeceipt executes, OE commands, the appEopEiate CiECUit OE CiECU~ ts to caEEy out the 10 appEopEiate functions. AccoEdingly, the centEal contEol 26 is the hub of the system which oEiginates all addEesses and commands to other CiECUitS and receives back all answeEs from the controlled CiECUitS. It is impoEtant to note, however, that the central contEol 26 is capable only of execut~ng individual inStEuctions and that the mech~nlzed intelligence required to supply the instructions needed for the complex t:elephone functlons of the system ~esides entiEely in the stoEed progEam.
Cent~al pulse d~stEibutoE 28 is utilized to 20 provide the centEal contEol 26 with fast access to many contEol po~nts of the functional switchlng CiECUitS of the office. Upon receiving an o~deE f~om the centEal contEol, distEibutor 28 selects and applies pulses to one of seveEal hundEeds of contEol points. For example, the distEibutoE 28 is select~vely arranged to supply peEiodically EeCUEEing pulses OveE the lead 29 to the tEansmitteE l9 EOE outpuls~ng infoEmat~on via the trunk C~ECUit ll to the office 2 while call connections are being established foE a call.

The CCIS equipment ~ including terminal circuitEy 30 and 31 and data tEanSmiSSiOn units 32 and 33 D. Sheinbein 1 1 illustEatlvely interface the centEal pEOcesso~s 21 and 34 of the switching offices 1 and 2. It p~ovldes foE (1) data tEanSmiSSion and EeceptiOn oveE a voice fEequency link 35, (2) pEOcesSing and translation o:E telephone data pEepEocessed by the central pEOcessoES 21 and 34, and (3) inteEface signaling between pEOcesSOEs 21 and 34.
Office 2 basically COmpEiSeS the same elemental components as office 1. Consequently, only those paEts of office 2 which aEe necessary foE the undeEstanding of 10 the invention aEe shown in the dEawing and opeEationally descElbed in the following paEagEaphs.
Call OEigination ___ TuEning now to the manneE in which an interoffice call ~s pEocessed, it is assumed that a customer at station 3 originates an inteEoffice call to station 5.
When the calleE EemOveS the telephone handset f~om its cL-adle to oEiginate the call, an o:Ef-hook signal ~s sensed ~n the scanner 8~ Subsequently, the centEal contEol 26 in executing a line scanning OpeEation 20 inteEEogates the SCanneE 8 and then consults the busy-idle infoEmation stoEed in the call StOEe 24 to ~nSuEe that the off-hook condition has not been pEeviously obseEved. Upon aSceEtaining that the station

3 was pEeviously on-hook, the centEal contEol 26 concludes that a call oEigination has occuEEed and it updates the busy-idle infoEmation fo~ station 3 in call StOEe 24. The centEal contEol 26 knows the scanne~
addEess of line 3 and uses it to EefeE to a t~anslation aEea of the pEogEam stoEe 25 which p~ovides it with all of the seEvice infoEmation it needs COnceEning line 3.

Such infoEmation ~ncludes class-of-service data ~ 3~ ~ ~

D. ~heinbein 1 1 peEtain~ng to whetheE the line is entitled to automat~ccallback seEvice and whetheE the assoclated telephone tEansmitS dial pulses OE TOUCH-TONE signals.
The centEal contEol 26 then selects an idle digit EeceiveE 15 and the assocfated d~al tone supply 16 foE use on the call. Next, the contEol 26 asceEtalns the availability of an idle path fEom line 6 through the netwoEks 9 and 13 to the EeceiveE 15 by consulting the busy-idle infoEmation stoEed in the call stoEe 24 foE all paths thEough the l~nk netwoEks. Upon f~ndlng such a path, the contEol 26 sends oEdeEs to the netwo~ks 9 and 13 to establish the appropE~ate switching connections.
The~ea~teE, the ScanneE 8 ~s disconnected fEom line 6 when the netwoEk 9 opens the cut-off contacts 36 and theEeby avo~ds any t~ansm3ss~on degradation OveE line 6 due to the scanne~ CiECUit~y. The centEal contEol 26 then requests the signal distEibutor 22 to operate appa~atus ~n the EeceiveE 15 for caus~ng d~al tone to be sent to the call~ng line 6.
After dial tone has been extended to line 6, the centEal contEol 26 scans the EeceiveE 15 and hence line 6 eve~y few micEoseconds v$a scanneE 12.
This scannfng opeEation is perfoEmed to check both or the eaEly aban~onment of the call and for d~al OE
TOUCH-TONE pulses. An abandoned call is s~gnified by a pEolonged on~hook condition on line 6 and dial pulses aEe s~gnified by peEiodic on/off hook conditions theEeon.
These conditions are sensed by scanneE 12 and Eead-out by pEOcesSOE 21. Each tlme the central control scans the receiver 15 and the calling line, it compaEes the p~esent SCanneE reading with the immediately pEeceding one which D. Sheinbein 1 1 is EecoEded in the call stOEe 24. T.~heneveE a disagEeement is found by a compaEison and the calling telephone is found to be off-hook on the next scanning opeEatlon, the contEol 26 EecOgnizeS that a digit is being tEansmitted and adds one to the pulse count kept in an OEiginating EegisteE-callback EegiSteE 47 ~FIG. 2~ of the call stoEe 24 foE the call. ~ digit is deemed complete when the calling line is off-hook and no momentaEy on-hook changes have been detected foE a 10 pEedeteEmined lnteEdigital peE~od.
When the centEal contEol 26 Eecognlzes a Eeceipt of the fiEst digit pulse tEansmitted fEom station 3, it causes the dial tone tEansmission to that station to be inteEEupted.
Callback Request PEioE to Dial~ng Ca:Lled Numbe_ Offlce 1 is aEEanged to peEmit the callng paEty to EeqUeSt automatic callback SeEvice at the inception of the call befoEe the called station dlrectoEy numbeE is dialed and befoEe the busy-idle status of the called stat~on ls asceEtained. To do so, the calleE dials a distinctive callback seEv~ce code as a pEefix to the dialed called numbeE. TheEeafter, if busy tone is EetuEned to the calleE,the automatic callback SeEviCe is activated immediately in EespOnSe to a called station hang-up. The call Eet~y is automat~cally ~nit~ated afteE
a pEesclibed line Eecheck time delay peE~od following the calleE hang-up and undeE contEol of pEOcessoE 21.
~ s each digit of the pEefix callback code is Eeceived via the EeCeive~ 15 and scanner 12, the centEal contEol 26 effects its stoEage in a callback code memoEy 48 of EegisteE 47 ~FIG. 2) foE subsequent use, if needed, D. Sheinbein 1 1 on the call.Called_Office Code Translation After the called office code ~OEtiOn of the dialed called numbeE has been ~eceived, the centEal contEol 26 ef:Eects a tEanslation of that code with the COOpeEation of the call stoEe 24 and pEogEam store 25 in oEdeE to obtain call Eouting/ alteEnate Eouting and/oE
signaling info~mation needed to complete the call to station 5. In addition, the centEal contEol 26 obtains info~mation fEom the office code tEanslation which ~ndicates that a pEedeteEmined numbeE of called station digits aEe to be received. The EOuting infoEmation diEects the centEal contEol 26 to select an idle outgoing tEunk ciEcult ll for use on a call fEom station 3 to 5.
It also infoEms the centEal contEol 26 that a digit tEansmitteE 19 is needed fo~ outpulsing the digits -equiEed to complete the call connections thEough office 2 to station 5. TheEeafteE, the centEal control 26 consults w~th the call stoEe 24 to asceEta~n the busy-idle status of both tEansmitteE 19 and communication paths theEefEom to the tEunk CiECUit 11. If they are found to be idle, the centEal contEol 26 commands the network 13 to inteEconnect the tEanSmit-teE 19 and tEunk CiECUit ll. Next, the contEol 26 EeseEves an available communication channel thEough netwoEks 9 and 13 between the calling l~ne 6 and tEunk CiECUit ll. AfteEwaEds, a se~zuEe signal is sent over tEunk 10 to off~ce 2 and tEunk continu~ty between the two offices is checked at tEansmitteE 19 in a known manne~. Following the check, 30 office 2 sends a "wink" signal to office 1 as a signal to commence outpulsing.

D. Sheinbein 1 1 Afte the called station digits have been Eeceived and sto~ed in the OE~ginating register 47 tEanSmitter 1~ outpulses the EequiEed called station digits to office 2 foE stoEage in an ~ncoming EegisteE 49 ~FIG. 2) of the call stOEe 42. Connections between tEanSmitteE 19 and tEunk CiECUit 11 and the digit EeceiveE 15 aEe then Eeleased oE SeEVing otheE calls.
The reseEved connections fEom the calling line 6 th~ough networks 9 and 13 to tEunk CiECUit 11 aEe then 10 cut-thEough.
Upon completion of the outpulsing ofice 1 oEdinaEily Eeleases the oE~ginating r.egister 47 fEom the call. Accord~ng to the pEeSent invention it is Eetained on the call so that its stored contents can be used foF
callback seEvice in the event that the called station is busy. The decision to Eetain Eegist:er 47 on the call is made by the class-o:E-service of statlon 3 OE the centEal contEol 26 detecting the pEeSenCe oE the pEeE~x callback code stoEed in that EegisteE. If the called stat~on 5 is not busy the centEal control 26 Eeleases EegiSteE 47 following a Eeceipt o a called paEty answeE signal fEom of:Eice 2 in a known manneE.
The call to station 5 is pEocessed thEough of~ce 2 ~n a manneE known in the aEt. BElefly~ the digits outpulsed fEom ofice 1 oveE trunk 10 aEe assembled with otheE call inoEmation ~n an incom~ng EegiSteE 49 ~FIG.
2) of call stoEe 42 and aEe then used by the centEal contEol 40.to inteEEogate the supeEvisoEy memoEy 46 of call stoEe 42 to aSceEtain the busy-idle status of station 5. If the stat~on ls found to be idle the call pEocessoE 34 contEols the connection of E.lnging CiECUit D. Shein~ein 1 1 38 to call connections so that Eingback tone is supplied to station 3 and act~ve Einging is suppl~ed to the called station 5. Upon a called paEty answeE, Einging CiECUit 38 is eleased, the anSweE signal is EetuEned to office 1 and call connections between stations 3 and 5 aEe cut-thEough undeE contEol of processoE 34. PEocessoE 21 detects the Eeceived answeE signal to effect the Eelease of its call stoEe oEigfnating EegfsteE 47 and the activation of the AMA equipment 27 to commence chaEging 10 foE the call if Eequ~Eed.
Called Station Busy - PEefixed Callback Code On the other hand, when station 5 is found busy, the central contEol 40 connects a busy tone to clEcuit 3~ to tEunk 44 via netwoEk 43 foE EetuEning a busy tone to the calling party ~n a known manneE.
ConcurEently, the centEal contEol 40 tEanSm$tS a busy message conceEning the call on t~unk 10 to office 1 via the CCIS teEminal and data units 31, 33, 32 and 30. At office 1, this message ~s stored in the call stoEe 24 and is used to distin~uish a busy condition from a call-not-answeEed condit~on.
Upon heaEing the busy tone, the calleE causes the automat~c callback servfce to become effective by simply hanging-up the EeceiveE of station 3. PEocessoE 21 theEeupon Eeleases connections fEom station 3 th~ough netwoEks 9 and 13 and tEunk c~Ecufts 11 and 44 to effect the Eelease of off~ce 1 fEom the call and subsequently ~o enable office 2 to contEol the automatic call retEy pEOceSSing. Specifically, the centEal contEol 26 detects the hangup via ScanneE 12 and then consults the call StOEe 24 to check whethe~ it has stoEed the 6~3~
D. Sheinbein afoEementioned busy message and automatic callback info~mation including the callback code and the calling and called numbeE data in an OEiginating ÉegisteE-callback EegiSter 47 of StOEe 24. If it had not, the call is Eout~nely teEminated. If the check shows the presence of callback info~mation, contEol 26 ~n coopeEation w~th Eegister 47 fo~mats and sto{es ~n the CCIS te~minal 30 a CCIS callback message lncluding the identity of office 1, calling station data, the called station d~Eectory numbeE, callback code and maEk, a line Eecheck time delay count and a callback time limit count.
TheEeafter, teEminal 30 tEanSmits the stoEed message to CCIS terminal 31 of office 2 v~a data units 32 and 33 and the common ~nteEoffice signaling channel 35. The received message is tEansfeEEed by pEocesor 34 fEom teEminal 31 to an originating regfsteE-callback EegiSter 47 in call stOEe 42. The office identity is stoEed in StOEage circuitEy 53 and the callback mark in StOEage C~ECUitEy 54 of the callback EegisteE 47. The callback maEk identifies ~egistel~ 47 as opelrating in its callback mode. Control 26 thereafteE coopeEates with the pEOgEam StOEe 25 to eEase the callback infoEmation fEom the oE~ginating EegiSteE 47 of stOEe 24 and contEol oveE the automatic callback seEvice is tEansfeEEed to pEOcesSOE
34.
Callback Re~uest AfteE Called Station Found Busy If the pEeflx callback code had not been d~aled and station 3 desiEes automatic callback seEv~Ce afteE
heaEing the busy tone, the caller flashes the switchhook of phone 3. ContEol 26 detects the flash via scanneE 12 duEing a scan opeEation and then consults the call stoEe 73~

D Shelnbei~ 1 1 24 to check the stoEed class-of-service infoEmation for station 3. Upon deteEmining that stat~on 3 is entitled to callback se~vice and that the :Elash is valid, contEol 26 continues to Eetain the calling and called station identities in the orig~nating Eeg~steE-callback Eegister 47 of StOEe 24 and then pEoceeds to effect a Eelease of call connections fEom line 6 to tEunk C.iECUit 11. Next, contEol 26 with the aid of stoEes 24 and 25 locates an idle digit EeCeiVeE lS and connects it to line 6 via netwoEks 9 and 13. Dial tone ~s then sent to the calleE
via receiveE 15 and netwoEks 13 and 9 as a signal to dial the callback code and then hangup. ContEol 26 detects the dia.led code via scanneE 12 and effects its stOEage in the oEiginating EeglsteE 47 o:E StoEe 24 whlch ls stoEing the calling and called station identities. Next, the dialed code is tEanslated under cont~ol of the program StOEe 25. TheEeafter, control 26 foEmats a callback message including the call~ng station data, the called station diEectoEy numbeE, callback code, time limit and l~ne Eecheck time delay counts and then sends ~t via the CCIS fac~lities to pEocessor 34. All CiECUitS of office 1 aEe then Eeleased fEom the call and callback information in StOEe 24 is eEased. Automatic call EetEy is theEeafteE undeE contEol of processoE 34.
Terminating Office Callback ContEol Upon Eeceiving the callback message foE eitheE
the pEefix OE lateE dialed callback code, pEocessoE 34 effects its StOEage in an oEiglnating EegisteE-callback EegiSte~ 47 in call StOEe 42. The centEal contEol 40 theEeafteE tEeatS the callback EegiSter as an incoming call EegisteE. DuEing conventlonal SeEving of calls ln 3~
D. She~be~n 1 1 such EegisteEs, contEol 40 in executing a digit analysispEOgEam Eecognizes that the callback EegisteE has stored the complete called station diEectoEy numbeE. ContEol 40 detects the callback code in the EegiSteE and then pEoceeds to examine the line Eecheck time delay StOEage caEcuitEy 50 in the same EegisteE. If the count in C~ECUitEy 50 ls otheE than zeEo, contEol 40 appEopElately decEements the count undeE contEol of the system clock and defeEs a check of the called stataon line. The count decEementing OccuEs at EecUEEent time peEiods such that, foE example, a minute delay peEiod is allowed befoEe a recheck of the called line busy-idle condition. When the count ls decremented to zero, con~ol 40 p~oceeds undeE
contEol of a translatxon pEOgEam in store 41 to use the directo~y numbeE of station 5 to pEoduce a te~minating line equipment numbeE and then to e2~amine the teEminating line supeEvisoEy memory 46 (FIG. 2) of StOEe 42 to check if the called station S is busy. When station 5 xs found to be busy, contEol 40 EetainS the contents of the callback ~egiste}, jams a line recheck time delay count into that EeglSteE and proceeds to SeEve otheE calls.
Each time the centEal contEol 40 decrements the l~ne Eecheck count to zeEO undeE contEol of the system clock, it also dec~ements the time limit count in the StOEage c~EcuitEy 51 of callback EegiSteE 47 of StOEe 42.
IllustEatively, the time limit count is decEemented to zeEo afteE ~h~Ety minutes and it ind~cates that callback seEvice as to be teEminated ~f stat~on 5 is not found to be adle after the next Eeading of the supeEvisoEy memoEy 30 46 of StOEe 42. ~ontEol 40 then coope~ates with the pEogEam StOEe 41 to eEase the callback infoEmat~on from -21~

D. Sheinbein 1 1 the callback ~egisteE of s~o~e 42.
When the afoEementoned check finds that the called station 5 has become idle, control 40 pEoceeds to maEk the station busy ~n the supeEvisoEy memoEy 46 oE
StOEe 42 and then to extEact its line equipment locatlon identity in a known manneE. ContEol 40 next undeE
contEol of the pEOgEam stoEe 41 makes a diEected scan of line 45 to deteEmine whetheE station 5 is busy OE idle.
If it is busy, contEol ~0 EetainS the callback 10 information in the callback Eeg~SteE, jams a line Eecheck time delay count $nto that registeE and pEoceeds to SeEve otheE calls.
TeEminating to OEiginat~ng OfEice Callback _ _ When the diEected scan finds station 5 idle, the centEal contEol 40 in conjunction with a progam in progEam stoEe 41 is optionally aEranged to utilize the infoEmation in the callback EegisteE 47 of store 42 foE
lmmediately $n~tiating a call fEom office 2 to office 1 in an endeavoE to establish call connections between 20 stations 3 and 5. A high pEobability ex~sts that such a call will be successfully completed because telephone stations aEe geneEally idle moEe often than they aEe busy and, moEeoveE, station 3 is expecting the callback.
Advantageously, th~s callback pEoceduEe Eeduces call set~up time VeESuS tEansfeEEing the callback infoEmat~on fEom pEOceSSOE 34 to processoE 21 foE making a call retEy fEom the oEiginat~ng office 1 as lateE explained.
This call pEocedure, however, necessitates an o~iginating off~ce 1 COnveEsiOn of the calling line equipment numbeE to a call~ng directoEy number by pEogEam stoEe 25 and centEal contEol 26 befoEe it is withdEawn -2~

6'7~
~ Sheinbein fEom the callback EegisteE 47 of stOEe 24 and, CCIS
message EoEmatted, stoEed and transfeEEed to the callback EegisteE 47 oE StOEe 42 as pEiorly explainedO It also necessitates a conveEsion of the called station diEectory numbeE into a line equipment numbeE by pEogEam StoEe 41 and centEal contEol 40. Consequently, foE this type of call, the station 3 is tEeated as the "called station"
and station 5 as the "calling station". The manneE in which such a call is seEved is otheEwise essentially the 10 same as pEioEly descEibed foE the call fEom statlon 3 to station 5 fEom the point that call details, such as the completed called station diEectoEy numbeE, is stoEed in oEiginating Eegister 47 of stOEe 24. When both stations 3 and 5 aEe found idle, actlve ~!inging is supplied to line 6 via netwoEks 9 and 13 by Einging ciEcuit 52 and to line 45 via netwoEks 43 by ringing CiECUit 38. The centEal contEol 40 recognizes the need fOE active Einging EatheE than Eingback tone foE station 5 by the fact that it is SeEving a callback EegiSteE of StOEe 42. If 20 station 3 is busy, the call fEom office 2 to off~Lce 1 is not completed and the centEal contEol 40 ln conjunct~on with stoEes 41 and 42, afteE a pEescEibed peEfod, ~llustEatively abandons the call and EetuEns callback infoEmation to office 1.
Callback InfoEmation RetEansfeEEed to OEiginating Office InfoEmation in callbaclc EegisteE 47 of StOEe 42 is EetuEned by pEocessoE 34 via the CCIS facilities to processoE 21 undeE two ciEcumStances. The Ei~st is when the teEminating to oEiginating ofEfce call cannot be 30 completed due to a busy cond~tion of station 3. The second is when the pEocessOE 34 is pEogEammed not to ~ ~6~73~
D. Sheinbein 1 1 in~t~ate the latte~ call and instead the callback ar~angement is equ~pped to oEiginate callbacks fEom theoEiginating office 1.
The infoEmat~on EetuEn to office 1 ls initiated when the afoEementioned diEected scan of line 45 dete~mlnes that station 5 is on-hook and idle.
Resultingly, the centEal contEol 40 in conjunction with the StOEeS 41 and 42 oEmats a callback message and t~ansmits it via the CCIS facilit~es to pEOceSSOE 21 foE
ini-tiating anotheE attempt to complete the call between stations 3 and 5. The tEansmitted message includes the identity of oEiginating office 1, called station diEectoEy numbeE, calling station identity, and an indication of the calling station idle condition.
PEocessoE 21 StOEeS the received message in an oEiginating ~egister 47 of store 24 and pEoceeds, in the execution of a tEanslation progEam, to examine the SupeEvisoEy memOEy 46 of StOEe 24 to asceEtain the busy-~dle status of station 3. When it ls found to be idle, control 26 makes a diEected scan of line 6 via scanneE 8 to verffy the idle status of station 3. Next, the centEal cont~ol 26 in coopeEation w~th StOEeS 24 and 25 effects a connection of an available Einging ciEcu~t 52 to line 6 via netwo~ks ~ and 13 foE alerting the called station to anSweE. Distinctive Einging is fuEnished to station 3 EOE aleEting the anSweEing party to the callback attempt.
Following an answer by a paEty at station 3, Einging ~s tEipped and line 6 is disconnected fEom E~nging CiECUit 52 and is connected via netwoEks 9 and 13 to equ~pment 17 foE EeCeiving an announcement. Control ~3.~ 7~3~

D. Sheinbein 1 1 26 is select~vely aEEanged to extEact the called diEectoEy numbe~ f~om the oEiginating EegiSteE 47 of StOEe 24 and to forwaEd ~t via distEibutoE 28 to equipment 17 fo~ conveEslon ~nto the callback announcement message, such as "YOUE call to the numbeE
NNX-~XXX ~station 5) is now being attempted."
Upon completion of the announcement message OE
simply upon a calling station anSweE when the announcement feature is not pEovided, pEOcesSO~ 21 10 contEols netwoEks 9 and 13 to effect a Eelease of connections between station 5 and eitheE the announcement equipment 17 OE the Einging CiECUit 52 and to select an available inteEoffice tEunk CiECUit 11 and tEunk 10 to office 2. The Eema~ndeE of the pEOcesSing to complete call connections between stations 2 and 5 is essentially as desc~ibed he~einbefore. The trans,lat~on program places the information ~n a buffeE memoEy so that it can be passed to the lncom~ng ~egiste~ undeE control of the p~ogEam StOEe 41.
PEocessOE 21 next pEoceeds undeE contEol of p~ogram stoEe 25 and call StOEe 24 to establish call ~ .
connections fEom calling stat~on 3 through netwoEks 9 and 13, and the selected tEunk ci~cuit 11 and tEunk 10 to office 2. SeizuEe and supeEvislon a~e exchanged between tEunk CiECUitS in a conventional manneE. CentEal contEol 40 in conjunction with StoEeS 41 and 42 then pEoceed to effect a connection of Einging CiECUit 38 to called station S and trunk CiECU}t 44 via the line and trunk link netwoEks 43 foE aleEting the called station 5 30 to anSweE and the calling station 3 to the ringing.

AfteE a paEty at station 5 answeEs, the Einging D, Sheinbein 1 1 is t~ipped. CentEal contEol 40 detects the ~inging and then pEoceeds to disconnect tEunk CiECUit 44 and station 5 fEom the Einging CiECUit 38 of office 2 and to inteEconnect station 5 and CiECUit 44 via netwoEks 43.
PEocessoE 34 then switches tEunk CiECUit 44 into its talking state foE call conveLsat~on.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An interoffice callback arrangement for use in a communication system having a first switching office for establishing call connections from a calling station, a second switching office for extending the connections from the first switching office to a called station, equipment for processing interoffice callback information between the first and second switching offices when the call connections from the calling station to the called station cannot currently be completed due to a called station busy condition and the equipment including circuitry for storing called station busy-idle data and characterized in that the equipment comprises apparatus responsive to the processed callback information for examining the storing circuitry to determine that the called station is idle before automatically initiating a callback attempt to complete interoffice call connections between the calling station and the called station through the first and second switching offices, the equipment signal processes the interoffice callback information over a data link signaling system independent of the interoffice call connections between the first and second switching offices, apparatus is responsive to a determination that the called station is idle for controlling a transmission of the callback information from the second switching office over said signaling system to the first switching office and the equipment further comprises circuitry in the first switching office responsive to a receipt of said callback information from said signaling system for automatically retrying a completion of interoffice call connections from the calling station through the first and second switching offices to the called station.

2. An interoffice callback arrangement of claim 1 characterized in that equipment signal processes the interoffice callback information over a data link signaling system independent of the interoffice call connections between the first and second switching offices.

3. An interoffice callback arrangement for use in a communication system having a call originating office for establishing call connections from a calling station, a call terminating office for extending the connections from the originating office to a called station, equipment for processing interoffice callback information between the originating and terminating offices when the call connections from the calling station to the called station cannot currently be completed due to to a called station busy condition, and the equipment comprises a call processor in the originating office responsive to a receipt of a callback request for transferring the callback information from the originating office to the terminating office and a call processor in the terminating office responsive to a receipt of the transferred callback information for automatically determining that the callback station is idle before automatically initiating a callback attempt to complete interoffice call connections between the calling station and the called station through the originating and terminating offices, and characterized in that equipment signal processes the transfer of the callback information from the call processor of said originating office to the call processor of said terminating office over a data link signaling system independent of the interoffice call connections between the originating and terminating offices, the transferred callback information comprises a calling line equipment number and a called station directory number and the call processor of said terminating office comprises apparatus responsive to a determination that the called station is idle for controlling a retransfer of the calling line equipment number and the called station directory number from said terminating office over said data link signaling system to said originating office and the call processor of said originating office comprises circuitry responsive to a receipt of the retransferred line equipment number and directory number for auto-matically retrying a completion of interoffice call connections from the calling station through said originating and terminating office to the called station.

4. An interoffice callback arrangement of claim 3, characterized in that equipment signal processes the transfer of the callback information from the call processor to the call processor over a data link signaling system independent of the interoffice call connections between the originating and terminating offices.

5. An interoffice callback arrangement for use in a communication switching system having a first switching office for establishing call connections from a calling station, a second switching office for extending the call connections from the first switching office to a called station, call store apparatus including register circuitry for storing callback information including calling and called station data when the call connections from the calling station cannot currently be completed to the called station due to a busy condition and a memory for storing station busy-idle data, call processing equipment responsive to said information stored in the register circuitry for automatically reattempting the completion of said call connections between the calling and called stations and the call processing equipment comprising a first call processor in the first switching office and a second call processor in the second switching office, characterized in that the second call processor is responsive to the stored callback information for reading the memory to determine when the called station becomes idle and the first and second call processors are responsive to a determination that the called station is idle and to the stored callback information in the register circuitry for automatically reattempting the completion of call connections from the calling station through the first and second switching offices to the called station.

6. An interoffice callback arrangement of claim 5 characterized in that a common channel interoffice signaling system interconnects the first and second call processors, for callback information signaling independent of interoffice call connections used for communication between the calling and called stations and the first and second call processors communicate the callback information over the signaling system for automatically reattempting the completion of call connections between the calling and called stations in response to the determination that the called station is idle.

7. An interoffice callback arrangement of claim 6 characterized in that the first call processor cooperates with the common channel interoffice signaling system for sending to the second call processor the callback information including the calling and called station data and a callback code dialed from the calling station and the call store apparatus comprises in the second office a callback register for storing the calling and called station data and callback code received by the first call processor.

8. An interoffice callback arrangement of claim 7 characterized in that the callback register stores the callback code dialed as a prefix to a called station identifying number dialed from the calling station immediately following an origination of the call therefrom and communicated from the first to said second call processor over the common channel interoffice signaling system.

9. An interoffice callback arrangement of claim 7 in which the communication switching system comprises apparatus for transmitting to the calling station a signal indicating a called station busy condition, and characterized in that the callback register stores the callback code dialed from the calling station following the transmission of the busy condition indicating signal.

10. An interoffice callback arrangement of claim 7 characterized in that the second call processor stores data in the callback register indicating a time delay period for callback and alters the stored time delay period data at recurrent intervals until the time delay period expires and said second call processor is controlled by said callback register for interrogating the memory upon an expiration of the time delay period to determine when the called station becomes idle.

11. An interoffice callback arrangement of claim 10 characterized in that the second processor responsive to an expiration of the time delay period and a determination that the called station is busy for controlling a reentry storage of data in the callback register indicating the time delay period for callback.

12. An interoffice callback arrangement of claim 11 characterized in that the second processor controls a successive number of said reentry storages of the time delay period data in the callback register when the memory interrogating successively indicates that the called station remains busy and is responsive to a prescribed number of successive reentry storages of said time delay period data in the callback register for erasing the callback information from the callback register.

13. An interoffice callback arrangement of claim 10 characterized in that the second call processor effects a transmission of the callback information from the callback register over the common channel interoffice signaling system to the first call processor in response to data from the said memory indicating that the called station is idle, a supervisory memory in said switching office for storing busy-idle data for said calling station, and the first call processor is responsive to a receipt of said callback information from said common channel interoffice signaling means for examining the supervisory memory to determine the busy-idle status of the calling station.

14. An interoffice callback arrangement of claim 13 in which said first switching office comprises apparatus operable for scanning the calling station line to check the on/off-hook status of the calling station, and characterized in that the first call processor is responsive to the supervisory memory examining indicating that the calling station is idle for operating the scanning apparatus for ascertaining that the calling station is on-hook before reattempting the completion of the callback connections between the calling and called stations.

15. An interoffice callback arrangement of claim 14 in which the first switching office comprises a circuit operable for alerting the calling station, characterized in that the first call processor is responsive to the ascertaining that the calling station is on hook and idle for effecting an operation of the alerting circuit to alert the calling station to an automatic callback attempt to the called station.

16. An interoffice callback arrangement of claim 15 characterized in that the alerting circuit is operative under control of the first call processor for supplying a distinctive audible callback alerting signal to the calling station.

17. An interoffice callback arrangement of claim 15 characterized in that the alerting circuit comprises circuitry for ringing the calling station and equipment responsive to the calling station answering the ringing for supplying a callback announcement message to the calling station.

18. A callback arrangement for use in a communication switching system having a network for establishing call connections with a calling station, a register for storing callback information including calling and called station data when call connections cannot currently be completed to a called station due to a busy condition, and a call processor responsive to the information stored in the register for automatically cooperating with the network to reattempt the completion of the call connections, characterized in that equipment is effective following a receipt of called station busy signals from another communication switching system for cooperating with the call processor to transmit the callback information stored in the register to the other communication switching system, and said call processor is responsive to a return of callback information from the other communication switching system upon a determination that said called station is idle for automatically cooperating with said establishing means to reattempt said completion of said call connections.

19. A callback arrangement of claim 18 characterized in that said register comprises a callback register for storing the calling and called station data and a callback code dialed from the calling station.

20. A callback arrangement of claim 19 characterized in that the callback register comprises apparatus for storing the callback code dialed as a prefix to a called station identifying number dialed from the calling station immediately following an origination of the call therefrom.

21. A callback arrangement of claim 19 characterized in that the callback register includes apparatus for storing the callback code dialed from the calling station following a transmission of a called station busy signal to the calling station.

22. A callback arrangement for use in a communication switching system having a network for extending a call connection to a called station, a memory for storing busy-idle data for the called station, a register for storing callback information including calling and called station data when call connection cannot currently be completed to the called station due to a busy condition, and a call processor responsive to the information stored in the register for automatically reading the memory and reattempting the completion of the call connection, characterized in that the call processor reads the memory in response to the callback information stored in the register to determine when the called station is idle, and a common channel interoffice signaling system cooperates with the call processor and another communication switching system and is resposive to a determination that the called station is idle for communicating the callback information from the register and call processor to said other switching system.

23. A callback arrangement of claim 22 characterized in that the register comprises a callback register operable for storing the callback information, and the call processor is responsive to a receipt of said callback information including calling and called station data and a callback code from the common channel interoffice signaling system for operating te callback register to effect a storage of the received callback information therein.

24. A callback arrangement of claim 23 characterized in that the call processor controls a storage of data in said callback register indicating a time delay period for checking the busy-idle state the called station alters the stored time delay period data at recurrent intervals until the delay period expires and interrogates the memory upon an expiration of the time delay period to determine when the called station becomes idle.

25. A callback arrangement of claim 24 characterized in that the call processor is responsive to an expiration of the time delay period and a determination that the called station is busy for controlling a reentry storage of the time delay period data in the callback register.

26. A callback arrangement of claim 25 characterized in that the call processor controls a successive number of the reentry storages of the time delay period data in the callback register when the interrogating successively indicates that the called station remains busy and is responsive to a prescribed number of successive reentry storages of the time delay period data in said callback register for erasing the callback information from the callback register.