CA1319768C - Channel redundancy in a digital loop carrier system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A channel redundancy system for use with a central office connected to a remote location. A central office terminal at the central office has a plurality of channel units including at least one spare channel unit. A remote terminal at the remote location also has a plurality of channel units including at least one spare channel unit.
The channel units in the remote terminal are correspondingly associated with the channel units in the central office terminal. From a repair service bureau located remote from both the central office and the remote location a defective channel unit can be identified find replaced by the spare channel unit.

Description

~ACKGROUND OF THE INVENTION
The present lnvention relates to ~n appsretus and method for use in channelizing telephone transmission equipment, and in particul~r, to providing channel redundancy to replace defective equlpment remotely thereby providing immedi~te restoral of service and delay in repair dispstch.
Sub~crlber loop pair g~ln systems sre well known in the prior art and the tes~ing of such systems is disclosed for example in U.S. patent No. 4,270,030 issued to Brolin et ~1. This pstent discloses A testing system for telephone subscrlbing loops which are in part derived by multiplex fscillties and systems known as pair g~in systems~ In this testing arrangement, the local drop wires from a remote terminsl of the palr gain system to the subscriber are separated from the carrler system ltsel$ and sre tested by connecting them to ~ separate met~llic psir extendlng from a central office to the remote terminal location.
Simult~neously, the carrier derived portion of the ~ubscriber loop is connected to automstic testing appar~tus which sequences through a plur~lity of ~utomatic tests for not only transmission ch~rscteristics of the , , :

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c~rrler derived chflnnel, but also for testing the ability of the derived chsnnel to transmit information such as ringing, coin control, on/off hook states and party identification information. The remote terminal of the psir g~in channel is selectively terminated.by ~ reflective or absorbltive terminatlon to sssist ln this testlng procedure. The testing system is designed so as to mAke carrier derived channels appesr to the centrsl office testing personnel 8S if they were identical to metallic 1 0 1 oops .
Rockwell Internation~l provides products to implement dlgltal loop carrier systems which include ~ppropriate software for affecting such tests QS described above. In a typical digital loop carrier system, a channel bank at a remote terminal or at the central office will cont~in a plurslity of chsnnel units. In the present technology, these channel units have no redundsncy or backup units for ~utomatlc repl~cement. In channelizing equipment ~ssoclated wlth such telephone equipment, indlvldu~l channel units or circuit modules ~ssociated with specific channels, make up the maJority of equipment prone to fsilure. Failures of this type must be repaired ~s soon 8S
possible in order to restore telephone service to .,.,..................... ~

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customer, usu~lly within ~ matter of hours. This equipment msy be loc~ted in ~ress that ~re not easily sccessible on 24-hour basis, ~nd disp~tchlng of repair personnel durlng "non business" hours may be extremely costly. Thus, there S is ~ need in the prior srt to provide B method and ~ppsrstus to repl~ce the defec~ive equipment remotely in order to provide immediate restoral of the service ~nd while delaying ~ rep~ir dispatch until schedules permit.
The present lnvention provides a solution to thls drswbsck ln ~he prlor ~rt.

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SUMMARY OF THE INVENTIO~
It is ~n ob~ect of the present invention to provide ~
procedure for the remote replacement of ch~nnel units which is easy to sctivate using familiar procedures, and which does not require any speclallzed equipment in existing telephone company o~fices.
The lnventlon is a procedure for temporsrily substitutlng a spare lndlvidufll channel in channellzlng transmis~lon equipment for one that has failed. Immediate appllcation of the lnventlon ls found ln dlgltal loop carrler equlpment ~s commonly used ln the "loop" portion of the telecommunications network, but lt ls not limlted to these appllcations. In a typical dlgltal loop carrier appllcatlon, channel banks are located ln a telephone compflny's central o~flce and at some remote slte whlch may be ln a structure, in a cablnet ln the outslde plant envlronment, or on a customer's premlses, snd referred to ~S 3 remote termlnal. The lnventlon is not llmited to dlgital loop carr~er spplications, but can flnd usefulness ln trunklng environments in other types of sltuations where multiple channel banks are connected together via analog or digital carrier facilltles.

~3~.~7~8 The equipment substitution c~n tske pl~ce 8t Any time in order to immedi~tely restore ~ ser~ice interruption th~t has occurred, without the necessity for ~ disp~tch by repair per-sonnel. Speci~l circuitry, rel~ys, and so~tware ~re present in ~11 channel units and system equipment, such as chflnnel b&nks, which allow customer service to be bypsssed onto ~ dedlcated 'Ispare" unit in the event of ~ failure in the channel unit that W8S currently c~rrying the service. The procedure used to sctlvate the substitution does not requ~re the presence of a person ~t the loc~tion of sny of the ch~nnelizing ~quipment.
Using existlng manual ~nd/or softw~re controlled ~utomfited "loop testing equipment" that is generally sv~ilable in a telephone company environment, the invention csn be ~ctiv~ed ~nd desctiv~ted using existing, generally ~ccepted procedures without the need for sny sdditionsl equipment. Once ectivated, the "sp~re" chsnnel units are plsced into service st both ends of the carrler fscillty.
At ~ lster time when repslr personnel replace the "f~iled"
clrcult modules, ~he invention is provisloned for performin~
msnu~l "go/no go" tests on the new channel unlts before deacti-va~ion of the invention ~nd restorsl of service onto the new ch nnel unit. These "go/no go" tests do not require ~ny specisl test equipment ~nd are activsted via simple procedures from telephones equipped with dual tone multlfrequency dialing.

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In accordance with an embodiment of the invention, a channel redundancy system for use with a central office connected to a remote location is comprised of a central office terminal at the central office having a plurality of S channel units including at least one spare channel unit; a remote terminal at the remote location having a plurality of channel units including at least one spare channel unit, the channel units in the remote terminal associated correspondingly with the channel units in the central office terminal; apparatus for providing transmission lines for connecting the channel units of the central office terminal to the channel units of the remote terminal, apparatus for identifying a defective one of the channel units in one of the remote terminal and in the central office terminal, apparatus for automatically exchanging the identified defective channel unit with the spare channel unit in one of the remote terminal and the central office terminal.
In accordance with another embodiment, the channel redundancy system for use in a terminal is comprised of first and second channel systems each having a plurality of channel units and at least first and second busses, at least a predetermined one of the channel units being a spare channel unit in each of the first and second channel systems; apparatus for providing a transmission line connected to each of the channel units; each of the channel . ~

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units having apparatus for connecting the channel unit to an associated telephone line and to the first and second busses, the spare channel units being connected to an associated termination; test controller interface having S apparatus for cross interconnecting the first and second busses between first and second channel banks; apparatus for controlling the apparatus for connecting in each of the channel units and the apparatus for cross-interconnecting in the test controller interface; when a selected one of the channel units in one of the first and second channel systems is identified as defective, the apparatus for controlling disconnecting the selected channel unit from its associated telephone line and connecting the selected channel unit and its associated telephone line to the first and second busses, respectively, the apparatus for controlling disconnecting the spare channel unit in the other of the first and second channel systems from its associated termination and connecting the spare channel unit and its associated termination to the first and second busses, respectively, and cross-interconnecting the first and second busses between the first and second channel banks.
In accordance with another embodiment, a method for providing channel redundancy in a system having a central office connected by transmission lines to a remote location, is comprised of the steps of providing at least - 6b -~.,., . .. :

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first and second channel systems having a plurality of channel units connected to telephone lines with at least one spare unit in each of a central office terminal at the central office and a remote terminal at the remote location;
S testing for a defective channel unit in the remote terminal and in the central office terminal; identifying the defective channel unit in one of the channel systems in one of the remote terminal and the central office terminal;
remotely disconnecting the defective channel unit in one of the channel systems in the one of the remote terminal and the central office terminal from a telephone line and connecting the telephone line to the spare channel unit in the other of the channel systems in the one of the remote terminal and the central office terminal; disconnecting a predetermined channel unit in one of the channel systems in the other of the remote terminal and the central office terminal, associated with the defective channel unit from a telephone line and connecting the telephone line to the : spare channel unit in the other of the channel systems in the other of the remote terminal and the central office terminal, the spare channel unit in the central office terminal being connected to the spare channel unit in the remote terminal.

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~ 3 ~ 8 BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which ~re believed to be novel, ~re set forth with particularity in the appended claims. The invention, together with further obJects ~nd Advsntages, may best be understood by reference to the following description tsken in con~unction with the accompsnying drawings, in the seversl Figures of which like reference numer~ls 1dentify like elements, ~nd in which:
FIG. 1 is ~ general block diagr~m depicting a digital csrrier loop system incorporatlng the present invention;
FIG. 2 ls a schematic representation of two systems in a channel bank ~t a remote terminal location;
FIG. 3 is a schematic di~grsm of channel bsnks a~ a central office ~nd a remote location for normal oper~tion;
~nd FIG. 4 is a schematic dia8ram of chsnnel banks a~ a central office snd a remote loc~tion in which ~ defective ch~nnel unit has been replsced wlth a spare channel unit.

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DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention h~s general appllcsbility but is most ~dvantageously utilized in a digital loop carrler system of the type shown in FIG. 1. The FIG. l general block diagram also depicts the lncorpor~tion of a psir gain test system 2S ls known in the prior art with the digital c~rrier loop system.
As shown in FIG. 1, a central office location 10 is connected to a remote locatlon 12 by transmission line system 14 and a bypass pair llne 16. The transmisslon line system 14 is to be understood as having digltal multipliers snd dlgital lines between the central office terminal 18 ~nd the remote terminal 34. The bypass pair line 16 is utllized for the palr galn test system. The central office 10 h~s a central office terminal 18 also referred to as ch~nnel bsnks. The ch~nnel banks 18 are composed of a plurallty o~ channel unlts in a blue channel system 22 snd a white channel system 24. Each of the channel systems 22 ~nd 24 contaln at least one spsre channel 26 and 28 respectively. The references to "white" ~nd "blue" ch~nnel systems are terminology sd~pted by Rockwell Internstional for its equipment.
The centr~l of~ice 10 slso has a central offlce .. .. .

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1319 ~8 switch 30 which is connected by leads 32 to the central office terminal 18. Central office switches which sre known in the prior art may be utilized for the central offlce switch 30 shown in FIG. 1. The central office termin~l 18 provides derived subscriber channels over outgoing digit~l lines 14 uslng well known analog or digital multiplexing techniques. A corresponding remote terminal 34 of the system sepQrates the signals on the diglt~l line 14 into a plurality of ~oice frequency analog si~n~ls on loc~l drop wlres 33 for delivery to 8 plUrBlity of subscriber st~tions 35.
The remote terminal 34 has a blue channel system 38 and ~ white chsnnel system 40 each hsving a plurallty of channel units and at least one spare ch~nnel 42 and 44, respectlvely.
The central office 10 also lncludes a repalr service bureau 46 for testing purposes. The repair service bureau 46 may be physically located at the centrsl offlce 10, but often ls located ~t ~ locstion remote from the central office 10. The rep~ir service bure~u 46 normally ~ncludes either manual local ~est facilities for manually testing loops or msy include automatic testing equipment for ~utom~tically testing the loops. The principal function of _g ~7CR033/CBP
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the rep~ir servlce bureau 46 is a testing of loops when a report of equipment failure ls received from 8 customer at a subscriber statlon 35. The repair service buresu 46 is connected to ~ pair gain test controller 48 8S iS well known in the prior srt. The psir 8ain test controller 48 ls connected to the bypsss pair line 15 and ~o the centr~l office switch 30. As is known in the prior art a repeir service bureau 46 wlll use the psir gain test controller 48 to perform ~ test on ~he system, thereby identlfying for example, a defective channel unit in the remote terminsl 34 for 8 par~lcul~r associsted subscriber station 35. The pair gain test controller 48 determines that a failure exists, but cannot determine if the failure occurs at the central office 10 ~r at the remote location 12.
As shown in FIG. 2, each of the channel banks 18 and 34 are divided lnto a white channel system 40 and a blue channel system 38 with reference to the remote termin~l 34. The central office termin~l 18 h~s 8 similsr structure of channel banks. Typlcally, each of these ch~nnel systems .20 38 and 40 wlll contain 48 channel units. One of these 48 chsnnel unlts in each of the systems 38 and 40 have a spare channel unit 42 and 44 respectively. It ls to be appreclsted that the spare channel unlt ls identical to the other chennel units contained in the channel unit bRnks.

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The spare channel uni~ i5 retsined only for redundancy purposes snd ls not any type of specialized equipment. The spare channel unit may have one or two channels on i~. If lt contains two channels, only one is a spare; the other can be used for norm 1 servlce. For the purpose of this discussion the spsre channel is referred to as ~ spare channel unit.
FIG~ 3 ls B more deta$1ed schematic diagram depicting the central office terminal 18 Mnd the remote terminal 34 operating under normal conditions. Shown in this schematic for clarity purposes ls only one channel unit in the white ch~nnel system and one channel unit in the blue channel system, specifically, channel units 50 and 52 at the central office terminal 18, and channel units 54 ~nd 56 at the remote terminal 34. In both the central office terminal 18 flnd the remote termlnal 34, a first bus 58 and 60, respectively, snd B second bus 62 snd 64, respectively, ~re provided on the bsck plsne of the terminals 18 and 34.
In additlon, each terminal 18 and 34 contains a test controller $nterfAce 66 ~nd 68, respectlvely. Each channel unit is provided with a reley 70 and the test controller interfsces 66 and 6~ sre also ~rovlded wlth cross lnterconnecting relays 76. The relays 70 and 76 ure utilized for connecting the channel units ~nd the test controller interfsces to the first ~nd second buses.

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As csn be seen in FIG. 3, ~ typic~l channel unit 50 in the white chennel system of the centrsl office terminal 18 is connected to receive a customer telephone number on line 78 via relay 70. The tr~nsmission line 80 connects the channel unit 50 to ~ channel unit 54 ln the whi~e channel system in the remote terminsl 34. In turn, the chsnnel unit 54 ls connected through its relay 70 to the subscriber station 82 ~ssociated with the ch~nnel unit 54. The channel unit 52 is the designsted "spare" channel uni~ ln the blue channel system of the centr~l off~ce terminal 18 and is connected to receive a test telephone number on llne 84. Transmlsslon line 86 connects the channel unit 52 ~o the channel unlt 56 ln the blue ch~nnel system of the remote terminal 34. The channPl unit 56 ls designated the "spare" channel unlt in the blue chsnnel system of the remote terminal 34 ~nd msy be approprlately termlnated as schematically shown BS box 88 ln FIG. 3.
A bank controller unlt 90 lmplemented ln firmware controls the operatlon of the ch~nnel units 54 snd 56 in the remote terminal 34, ~s well BS, the test controller interf~ce 68. The ~ank controller unit 90 receives commands from the bank controller unit 91 which in ~urn recelves commands from the central office 10 over ~n internfll dat~ link between the centrel office terminsl and the remote terminal.

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FIG. 4 shows the results of the ldentificatlon o~ a defective channel unit at the remote terminal 34. For the present example, it wlll be ~ssumed that the channel unit 54 at the remote terminal 34 h~s become defective, therefore, eliminating service to its sssociated subscriber station 82. It is to be understood that the defective channel unit could be at the central office terminal 18 rather than et the remote terminal 34. After the above described psir g~in test has been performed by the repair service bureau and a defective channel has bsen ldent~fied, ~n appropriate signal ls sent to the bank controller units 90 ~nd 91 from the central office 10 ~s described in the prior art. In response to this signal, relay 70 in the channel unlt 54 is activated which disconnects the channel unit 54 from the subscriber station 82 and also connects the channel unlt 54 to the first bus 60 and connects the ~ubscriber station 82 to the second bus 64. The activ~tion can be ~ccompllshed from a Repair Servlce Bureau or vla direct communication with the Bank Controller Unlts through a computer terminal. Simllarly, the relay 70 in the xpare channel unit 56 disconnects the spare channel unit 56 from its termination 88 and connects the channel unit 56 to the -- 1 3~.~7~

first bus 60 ~nd connects the sp~re terminatlon 88 to the second bus 64. Simult~neously, the bank controller unlt 90 causes the test controller interf~ce 68 to sctlv~te the cross interconnection relsy 76. This relsy 76 8S shown ln FIG. 4 causes the buses 60 and 64 to be in~erconnected, th~t is, the first bus from the channel unit 54 becomes the second bus ~t the channel unit 56 ~nd the second bus ~t the ch~nnel unit 54 becomes the f$rst bus at the chsnnel unlt 56.
Similsrly, the relsys 70 ~nd the channel units 50 and 52 ~t the centrsl of$ice termin~l 18 ~re activ~ted, as well ss, the cross interconnectlon relsy 76 ln the test controller interf~ce 66. This results in a similsr connection ss ths~ st the remote termlnal 34. By observing FIG. 4, it can be seen thflt st~rting with the subscriber st~tion 82 the connection psth now goes through the second bus 64 until the path reaches the test controller lnterf~ce 68, where it then follows flrst bus 60 to the spsre channel unit 56. It is then connected ~long trsnsmlss$on llne 86 to the spare channel unit 52 ~t the centrsl offlce termin~l 18 where it now proceeds slong the first bus 58 until it reaches the test controller interfsce 66 where ~t h~s been switched onto the second bus 62 which proceeds then to be ,- ~
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connected to the customer telephone number line 78. A
simil~r path now connects the test telephone num~er line 84 to the spare termination 88 es can be seen in FIG~ 4.
Thus, the defective channel unit 54 has been effectively And automstic~lly repl~ced from the centrsl~office terminal 18. While this now has the effect thst no further pair gsin test csn be performed upon the system, lt is generally Xnown th~t it ls very rsre thst a second channel unit will fsil before the defective unit can be replaced durlng normsl worklng hours.
Furthermore, once the defective ch~nnel unit hss been replaced with ~ new chsnnel unit, a go/no go test can be performed upon the system to ensure that the new channel unlt operates properly. The repair personnel at the remote terminsl or centr~l office terminsl then resets the rel~ys 70 ~nd 76 in the chsnnel units snd the test controller lnterface to return the system to operation as shown in FIG. 3. Thls restorisl can be done from the remote termin~l, from the centr~l office terminal or from a Repair Service Bureau.
The go/no go test is sctiv~ted vi~ Rny telephone which hss the abili~y to ~end DTMF signaling. The purpose of this test is to verlfy thst the suspec~ed bad channel unit `^` ~3~ ~7~

is n~w working since a new channel unit hss been ~nstalled in the channel unlt posltion. This is done by dl~ling the test telephone number. The centr~l office swltch equipment will terminate this call on the suspected bad centrfll office terminal channel unit, 50, via pair 78, relay 709 test bus 62, relay 76 and test bu~ 58 ~t the central office terminal. The call is transmitted to the suspected bad remote terminal channel unit, 54, v~a the dlgitsl facillties, 80, ~nd then routed over test trunk 60, relay 76, ~nd test trunk 64. Relay 70 in the suspected b~d RT
channel unlt connects the c211 to termination 88 which detects the rlnging signsl. Termination 88 presents an off-hook state. If ringin~ is successfully tripped, it lndlcates that slgnallng informatlon can be transmitted in both dlrections on the suspected bad channel unlt p~ir. In order to verify transmission in both directions, any DTMF
key in the middle row Df keys (2,5,8, or 0) should be depressed. The termlnation, 88, wlll detect th1s DTMF tone ~nd respond by sendlng back a 1 KHz tone through the same voice frequency path ell the way back to the telephone whlch lnitiated the test c~ll. If all o the sbove ls successful, then the pair of suspec~ed bad chsnnel unlts ~re operatlng ~nd the bad channel unit has been successfully exchanged for a good un~t.

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An ~ltern~tive test can be performed from the remote termin~l vi~ a System Access Unit ~SAU) module which is unique to the Rockwell system. When redundAncy is sctivsted, the SAU will dlsplay the number of the bad chsnnel unit. In ~ddition, lt wlll provide a monitor sccess to the tip ~nd rlng wires of the suspected bad - channel unit. During channel redundancy the SAU is locked in this mode, thus ~ny testing of the suspected bad ch~nnel unit c~n be done through the SA~. Typically, ~ suspect channel unit ~t the remote terminsl would be repl~ced, and Q csll would be sttempted over the new ch~nnel unit via the SAU ~ccess. If the csll c~n be placed successfully, then the bsd chsnnel unit has been successfully exchanged for 8 good unit.
When the suspected bad chsnnel unlt ls repl~ced by 8 known 800d one, the system will still remsin in the chsnnel redund~ncy mode. The two methods of testing ~bove csn be performed on either the originsl suspected bsd ch~nnel units or the units ~hst hsve been swspped lnto the ~ystem.
A more detailed descriptlon of the method of the present invention as ~mplemented in Rockwell Intern~t~onal's telephone system will now be set forth.

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1) A Palr Gflin Test Controller (PGTC) test is set up on ~ Ch~nnel Unit (CU). The B~nk Controller Units (BCUs) record the slot of the CU belng tested. The mess~ge ~low used is the norm~l PGTC message flow.

2) The BCUs send a poll data (GPOLLR) command to the Test Contro~ler Interf~ce c~rds (TCIs). In the TCI's response is the st~te of 8 redundancy selection switch.
The redundancy selection switch is provided ~s ~n option to disable this fe~ture and is not shown ln the drawlngs.

3) The BCUs check if the redundancy mode is selected. If the redundancy mode is not selected the BCUs exit the redundancy waiting routine. If the redundancy mode ls selected the BCUs begin ~ one minute timeout.
lS During this timeout the following could happen.
A) If ~ PGTC test were to be lnltisted on Q CU
which was not the sp~re CU, the BCUs would ~end the TCI ch~nnel seized (TCSEZ) commsnd to the TCIs wlth the test bus busy bit (bit l) set. This will cause the test controller interfRce in the centr~l office terminsl (TCI/C) to send the SEZBY sign~l to the PGTC
whlch in turn will csuse the PGTC test to be ~borted.
The BCUs will not record the slot of this CU nor will ~he BCUs reset the timeout.

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B~ A PGTC test could be initiated on the ssme channel unit that was previously tested. The BCU will ~llow a PGTC test to be performed once ~gain, but at the completion of the test, the one minute tlmeout would be reset. The BCU now once again waits for an action (A,B,C, or D) to occur.
C) The timeout could expire. The BCUs would exit the redundsncy wait routlne.
D) A PGTC test could be initlated on the spare CU. When the BCUs receive the interrupt d~ta (DINTD) command, the 8CUs note that the messag2 is from the redundant CU ~nd enter the redundancy mode.

4) The timeout ls needed to prevent a second CU from being tested while the redundant CU ls being selected for a PGTC test. If this happened, an unexpected CU would be switched onto the spare channel.

5) The BCUs send the test byte write (CUTESTW) command with the Test Mode blt set (bit 7) to the customer's CUs. Thls causes the customer's CUs and drops to be connected to the lnternal test busses.

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6) The BCUs send the CUTESTW command with the Test Mode b~t set to the spare CUs. Thls ~auses the spare CUs 2nd drops to be placed on the intern~l test busses. After the sp~re Cen~ral Offlce (CO) CU ls switched onto the internsl test busses, the PGTC test vo~tage wlll be swltched from the spare CO CU to the customer's CO CU.
Thls wlll csuse both CUs at both ~nds to change the status of thelr test bits (the bad CUs' blts will clear ~nd the spare CUs' blts wlll set). Thls can be used ~s feedbdck to the BCUs to lndic~te that the TICs have msde the switch.

7) The BCUs send the redundancy enable (TCUREN) command to the TCIs. Thls informs the TCIs that 8 redundancy swltch is active.

8) The TCIs check the status of sn associated pln J~ck. If a pln plug ls in its pln ~ack, lt wlll not send the redundancy disconnect (TCURDS) message until the pin plug is removed ~nd reinserted.

9) The TCIs set the M-Fleld to TSTALM. Slnce both ends ~re in CU redundancy, the TICs wlll suppress the TSTALM. If one end does not receive TSTALM wlth1n R given time perlod, that TCI will send redundancy error (TRURER) to the BCU. This ~nforms the BCS thst the other end has not entered the redund~ncy mode.

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3~ ~7~8 10) The BCUs send the System Access Units (SAU) the redundancy command ~SCURC), Th$s csuses the SAUs to bridge their bantam ~cks onto the internsl test buses which provides test ~ccess to the bsd CU. It also causes the SAUs to display the number of the CU which ~as been 8wl tched onto the spare CU.

11) The BCUs send the TCSEZ with the test bus busy blt set to the TCIs.

12) The TCI/C sends a SEZBY to the PGTC. This sends back a busy ~ignal to the person setting up CU redundancy.

13) The TCIs monitor their pin ~acks. If a pln plug is lnserted into one of the TCI's pin ~ack, that TCI will send the TCURDS message. This message lnforms the BCUs to remove the CU redundancy set up. The other TCI will detect the M-Field return to idle. This TCI wlll send the TCURER
mess~ge to the BCU. Thls will have this end remove the CU
redundancy setup.
If the CU which is in the redundsncy is replsced, the new CU must be instructed to connect itself to the intern~l test bus.
For ~n integrated system where only the remote end is ~ 3192 system, a second switch hRs been placed on the TCI/R. Th~s ~witch would have the test controller interf~ce in the remote terminRl (TCI/R) ignore the f~ct ~3~ ~7~

th~t the centr~l office end did not enter thP redund~ncy mode. The only way the remote end could be removed from the redundancy mode is to insert 8 pin ~ack in the TCI/Ro The switch would have to be changed to lnvoke the switch to S the centr~l off~ce end.
If the BCU cannot setup CU redundancy, the BUCs will not send TCRCV. The PFTC will tlmesut and tear down the test. The lsck of ~ busy signal to the person setting up CU redundancy will indic~te that CU redundancy was not setup.
The invention is not llmited to the p~rticular details of the ~pparatus depicted and other modlfications ~nd ~pplications are contemplated. Certaln other changes may be msde in the above described ~pparatus without dep~rting lS from the true spirit ~nd scope of the invention herein involved. It is intended, therefore, that the subJect mstter in the sbove depiction shall be lnterpreted ~s illustrative and not in a limiting sense.

Claims (18)

1. A channel redundancy system for use with a central office connected to a remote location comprising:
a central office terminal at the central office having plurality of channel units including at least one spare channel unit;
a remote terminal at the remote location having a plurality of channel units including at least one spare channel unit, said channel units in said remote terminal associated correspondingly with said channel units in said central office terminal;
means for providing transmission lines for connecting said channel units of said central office terminal to said channel units of said remote terminal;
means for identifying a defective one of said channel units in one of said remote terminal and in said central office terminal ;
means for automatically exchanging said identified defective channel unit with said spare channel unit in said one of said remote terminal and said central office terminal.

2. The channel redundancy system according to claim 1, wherein said means for automatically exchanging also exchanges in the other of said remote terminal and said central office terminal a channel unit corresponding to said defective channel unit in said one of said remote terminal and said central office terminal with said spare channel unit in said other of said remote terminal and said central office terminal.

3. The channel redundancy system according to claim 2, wherein said plurality of channel units in each of said central office terminal and said remote terminal are divided into at least first and second channel systems, each of said channel systems having a spare channel unit.

4. The channel redundancy system according to claim 3, wherein a defective channel unit in one of said channel systems is exchanged with a spare channel unit in the other of said channel systems.

5. The channel redundancy system according to claim 4, wherein said means for automatically exchanging comprises in each of said central office terminal and said remote terminal;
each of said channel units having means for connecting said channel unit to an associated telephone line and to first and second busses in said terminal, and said spare channel units connected to an associated termination, test controller interface having means for cross inter-connecting said first and second busses between said first and second channel banks, means for controlling said means for connecting and said means for cross interconnecting;
when a selected one of said channel units in one of said first and second channel systems is identified as defective, said means for controlling disconnecting said selected channel unit from its associated telephone line and connecting said selected channel unit and its associated telephone line to said first and second busses, respectively, said means for controlling disconnecting said spare channel unit in the other of said first and second channel systems from its associated termination and connecting said spare channel unit and its associated termination to said first and second busses, respectively, and cross-interconnecting said first and second busses between said first and second channel systems.

6. The channel redundancy system for use with a central office connected to a remote location according to claim 1, wherein said means for identifying is a pair gain test controller.

7. The channel redundancy system for use in terminal comprising:
first and second channel systems each having a plurality of channel units find at least first and second busses, at least a predetermined one of said channel units being a spare channel unit in each of said first and second channel systems;
means for providing a transmission line connected to each of said channel units;
each of said channel units having means for connecting said channel unit to an associated telephone line and to said first and second busses, said spare channel units being connected to an associated termination;
test controller interface having means for cross inter-connecting said first and second busses between first and second channel banks;

means for controlling said means for connecting in each of said channel units and said means for cross-interconnecting in said test controller interface;
when a selected one of said channel units in one of said first and second channel systems is identified as defective, said means for controlling disconnecting said selected channel unit from its associated telephone line and connecting said selected channel unit and its associated telephone line to said first and second busses, respertively, said means for controlling disconnecting said spare channel unit in the other of said first and second channel systems from its associated termination and connecting said spare channel unit and its associated termination to said first and second busses, respectively, and cross-interconnecting said first end second busses between said first and second channel banks.

8. The channel redundancy system described in claim 7 wherein the system further comprises a central office with a central office terminal and a remote terminal connected thereto by said transmission lines; each of said central office terminal and said remote terminal having said first and second channel systems, said test controller interface, and said means for controlling; a means for identifying a defective channel unit in one of said remote terminal and said central office terminal; and means responsive thereto for causing said defective channel unit and its associated channel unit in said other of said remote terminal and said central office terminal to be replaced with said spare channel units in said remote terminal and said central office terminal.

9. The channel redundancy system described in claim 7, wherein said means for identifying is a pair gain test controller.

10. The channel redundancy system described in claim 7, wherein said means for causing is a bank controller unit in said central office terminal and a bank controller unit in said remote terminal.

11. A method for providing channel redundancy in h system having a central office connected by transmission lines to a remote location, comprising the steps of:
(A) providing fit least first and second channel systems having a plurality of channel units connected to telephone lines with at least one spare unit in each of a central office terminal at the central office and a remote terminal at the remote location;
(B) testing for a defective channel unit in said remote terminal and in said the central office terminal;

(C) identifying said defective channel unit in one of said channel systems in one of said remote terminal and said central office terminal;
(D) remotely disconnecting the defective channel unit in one of said channel systems in said one of said remote terminal and said central office terminal from a telephone line and connecting said telephone line to said spare channel unit in the other of said channel systems in said one of said remote terminal and said central office terminal;
(E) disconnecting a predetermined channel unit in one of said channel systems in the other of said remote terminal end said central office terminal, associated with said defective channel unit from a telephone line and connecting said telephone line to said spare channel unit in the other of said channel systems in said other of said remote terminal and said central office terminal, said spare channel unit in said central office terminal being connected to said spare channel unit in said remote terminal.

12. The method described in claim 11 wherein said method further comprises the steps of:
(F) manually replacing said defective channel unit with new channel unit, and (G) resetting said system to connect said new channel unit to said telephone line and to disconnect said telephone line from said spare channel unit, and also to reconnect said associated channel unit and disconnect said spare channel unit.

13. The method described in claim 11, wherein said method further comprises in step (D):
connecting said defective channel unit to a first bus and connecting said telephone line to a second bus;
disconnecting said spare channel unit from an associated termination, connecting said spare channel unit to said first bus and connecting said associated termination to said second bus; and cross-interconnecting said first and second busses between said first and second channel systems.

14. The method described in claim 11, wherein said method further comprises in step (E):
connecting said associated channel unit to a first bus and connecting said telephone line to a second bus;
disconnecting said spare channel unit from an associated termination;
connecting said spare channel unit to said first bus and connecting said associated termination to said second bus; and cross-interconnecting said first and second busses between said first and second channel systems.

15. The channel redundancy system according to claim 1, wherein said plurality of channel units in each of said central office terminal and said remote terminal are different types of electronic units.

16. The channel redundancy system according to claim 15, wherein means for automatically exchanging replaces a defective channel unit with a spare channel unit of the same type of electronic unit.

17. The channel redundancy system according to claim 1, wherein said means for automatically exchanging and said means for identifying are controlled from a Repair Service Bureau.

18. The channel redundancy system according to claim 1, wherein said means for exchanging and said means for identifying are controlled from a computer terminal which communicates with bank controller units connected to said central office terminal and said remote terminal, respectively.