CA1041201A - Intra link calling within a subscriber digital system - Google Patents

Abstract

INTRA LINK CALLING WITHIN A SUBSCRIBER DIGITAL MULTIPLEXING
SYSTEM

ABSTRACT OF THE DISCLOSURE:
Disclosed is a feature for use in a subscriber digital multiplexer interfacing between a central telecommunications office (CO) and a plurality of remote terminals, each remote terminal serving a number of subscribers. Calls from and to lines at the same remote terminal are identified over a special network at the central office for the purpose of by-passing the speech channels to the central office and thereby freeing the central office equipment and two channels for use in processing the other calls. The special net-work or intra link network is activated after the called station has re-responded to a call. First, a check is made to see whether a station at the same remote terminal has originated a call. A tone is then sent out over the line to determine whether the call originated and ter-minated at the same remote terminal. If both lines are from the same remote terminal, the call is transferred from the speech channels to intra link channels as controlled at the central office over sig-nalling channels.

Description

W. Wurst - 3 RELATED APPLICATIONS
A companion application was filed previously by me on 12/9/74 under Can. - S.N. 215,477 entitled "Subscriber Digital Multiplexing System with Concentration" showing a basic system for providing a subscriber line multiplexing system. This pres-ent invention is a feature which may be inserted into that sys-tem. Reference may be had to that application for more detailed showing of various portions of the multiplexer system.
BACKGROUND OF THE INVENTION
The present invention provides an intra link or intra terminal call completion apparatus for a subscriber digital mul-tiplexing system. Subscriber digital multiplexer systems are known generally. Such systems provicle a carrier span line or the like to provide plural channels between a CO and one or more remote terminals, each remote terminal having a plurality of sta-tion lines connected to it. Intra link calling or local link calling is completed at a remote terminal for calls between sta-tions connected to the same remote terminal. In this way, two span line channels are freed for further use by completion of the call locally. In such systems, the intra link capability is generally low, on the order of four links for 24 channels avail-able. In such systems which generally employ space division switching, a latch may be set for an off-hook line and a tone is sent to that line. When the tone is detected, the latched line and a line detect~d as having the tone 7 are marked and the calling trunk is freed when a local link has been designated to handle the call.
SUMMARY OF THE INVENTION
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Intra link processing comes into operation in the pres-ent digital multiplexer system when a call is completed through the central office switching apparatus and over the span line through the remote terminal to a line unit and after ringing has been started. ~
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A check is originated from the channel memory associated with the terminating line of the time division switch of the multiplexer to see if any calls are originating from the same remote group as the terminating line. All lines accessible from one shelf scanner will have their addresses identical as to the three most significant bits, and c~n be identified in this way. Means are provided to enable shelves to be assigned to a group in any sa-quence. If a line in the ~ame group is in the call-originating condition, then a t~ne is generated at the CO multiplex terminal and sent out on the line from the terminating line through the central office switching apparatus toward the originating line. If an originating line in ~e associated group shelves receives the tone during the proper channsl period, then a call tran~fer is activated to emit a signal~ to the remote terminal unit of the or~ginating and terminating parties, indi-cating an IL channel is available,bytthe channel organ-izer.
Swit~ching is effected within the remote term-inal by transferring the call from the normal call pro-cessi~g portion of ~wo channels to the intra link portion of two adjacent channels. The call is completed within the remote terminal or group during the intra link channel periods. R channel is divided into halves, one hal~
being the no~mal call processing portion and the other the intra link p~r~ion. On the completion of the switching at the remote terminal, the channel memory unit for normal speech channel control drop~ the call from its memory, and the channel is available for other calls.

A separate~-imemory stores the address of the originating and terminating line in its own memorv for control of the call at the CO by the use of supervisory channel~.
: Control information concerning the call passes over the span line during the pendency of the intra link call but the call speech path is comp~eted only throu the remote t~rmi~al.

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Supervision of the call is effected during one con-trol channel which is employed for IL control. As noted in the companion case, the exemplary system employs thir~y-five channels, thirty-two for speech or information trana-mission and reception and three for control functions.
One of these three is allocated for intra link and time division switch supervisory control.
For the completion of a call between the different channel portions, a latch in the remote timing unit sam-ples the condition of a channel inthe middle of the pulse, and the latch holds for one f`ull channel period. An out-put gate from the latch provides the one-half channel in--terval.
By the use of this approach of employing -two local channels for an intra link call, the number of intra link calls which may be in process (16) total one-half the num-ber of` normal speech channels (32) in the system. Thus, by use of the intra link apparatus, a to~al of forty-eight calls may be in process in the system at one time.
It is therefore an obj$ct of the invention to pro-vide an improved, high capacity intra link calling ap-paratus for use ln a subscriber digital multiplexer systm.
~ It is further object ~-the invention to provide an ; intra link aalling capabilïty Nil:i ch allots one-half of`
eac~h channel calling period for intra link calling and associates one calling line unit with one called line unit during half cycles representing adjacent channels.
,It isi'further ob,ject o~ the invention to provide an intra link calling apparatus for a digital multiplexing system in which the intra link channel capability ~ _ 4 _ o~

is one~half of the number of normal speech channels for the system.
It is further object of the invention to provide a time division ~ultiplex communication system between a central office terminal and at leat one remote terminal in whic there is an intra link apara-~`
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, W. Wurst - 3 tus for effecting speech communication between two lines at the same remote terminal independently of the central office ter-minal.
Other objects, features and advantages of the invention will become apparent from the following detailed description viewed in conjunction with the drawings described briefly here-after.
E~RIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a chart showing how lA and 1~ are positioned to comprise a schematic block diagram of the system;
FigO 2 is a schematic block diagram of an intra link control circuit of Fig. l;
Fig. 3 is a schematic block diagram of an intra link memory circuit of Fig. 1;
Fig. 4 is a schematic block diagram of an intra link detector circuit of Fig. 1;
Fig. 5 is a circuit diagram in greater detail of the control unit of Fig. 2;
Flg. 6 is a circuit diagram in greater detail of the memory circuit of Fig. 3; ?
Fig. 7 is a circuit diagram in greater detail of the detector circuit of Fig. 4;
Fig. 8 is a schematic block diagram of the system show-ing the memories used in the intra link calling feature;
; Fiy. 9 is a chart showing the relative positioning of channel sections used for intra link calling.

Briefly stated, the call sequence for an intra link call or local call in the system follows the principle of allow-ing a call to progress normally as set out in my co-pending appli-cation, Can. - S,N. 215,477, filed 12/9/74, and by waiting until the called line answers dQ 3~

at which time a memory location individual to the trunk channel used by the called line is marked. The location operates circuitry common to all trunk channels which, -`
in turn, causes a digitally synthesized tone to be sent out to the called trunk channel. The calling trunk channel which receives the tone is connected to a tone detector circuit which, in turn, detects the tone received during the proper channel and as a result sends a signal back to the intra link memory.
As a further test, when the tone has been successfully received, the frequency of the tone is shifted and a check is made to see if a corresponding change occurs to the fre-quency of the incoming tone. When all conditions are sa~is-fied, instructions are sent through the remote terminal to transfer the two parties to the local link called here-in the intra link. A signal is sent to the control cir-cuit at the CO terminal to release the two trunk channels which had originally comple-ted the call. This last-mentioned signal cancels any information contained in the CO memory locations indi~idual to the two lines being joined in the intral link call and frees the two channels for o-~her calls.
The call transfer occurs by switching the call at the remote terminal of both calling and called station to two unused portions of adjacent channeIs, the channel periods having been subdivided into normal call portions and nor-mally unused or intra link portions.
SYSTEM BLOCK DIAGRAM

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- In figs. lA and lB, I show in block form a multiplexer to which my intra link calling function has been applied The basic system shown is generally similar to that shown in my copending application noted previously. The system ~ .
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shown has the capability o-f serving 128 lines over 32 duplex channels in which two unidirectional~leads are directed to each line unit. Since there are more lines than. channels, a concentrator or switching stage is employed. In the system shown, this stage employs time division switching in which mem~ry position is ' ~:

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~ - 6a -maintained permanently for each channel. In each memory position, the address of a line using that channel is stored.
The system disclosed in the drawings includes a central office ~CO) terminal 10 (Fig. lA) and a plurality of remote terminals, two such termianl - 12A and 12B
~Fig. lB) shown. As many as eight remote terminals may be coupled to the CO by a suitable digital repeatered line such as the tvpe known as the Tl carrier system.
The number of line units per terminal is limited by the maximum capacit~ of 128 lines. With two remote term-inals, as shown herein, each may have up to 64 lines in multiples of sixteen lines, sixteen lines constituting a line group. Connection of the indivdual station lines to the remote terminal is usually by way of solid conductors.
Within the CO terminal 10, the input~ to the CO line units shown, such as 20,22,24 and 26 shown are connected to the final switching stage of the CO net-work on a line-to-line ~asis in the conventional manner.
The line unit outputs are commoned to respective shelf scanners 30 and 31, each having access to a plurality of line units to provide partia~- address decoding between the respective line units and the time division stagc (TDS). The TDS within the CO includes a tim~ division interface circuit 32, a time division memory 34, and a time division control 36~
The inte-ace unit 32 provides one stage of address decoding in directing line unit selection data to the proper shelf scanner unit for one direction of information travel and from the scanner unit for the reverse direct~on of information travel.

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The control unit 36 provides the time division decision-making or switching con~rol for recording the line status and channel assignment in the TDS (t~me di-vision msystem) memory 34 for call completion and super-vision. The control also acts to distrib~te the assign-ment of channels evenly to the 32 channels of the system ~y rotation. Within the TDS memoxy unit 34, each channel is accorded a - 7a -"' .

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permanent position to record line addresses to provide coordination between the channel and the lines which may be assigned to that channel. Information on the assignments is forwarded from the memory to the memory in the remote terminal for coordination at the remote terminal involved.
In addition, the CO terminal provides timing con-trol for both the transmit and receive;directions through timing control 40 which is the master timer of the system. Timing signals are initiatad in the transmit timing circuit 40, sent to the remote timing circuit 62 and returned to the receive timing circuit 42 for comparison and for alarm control through alarm circuitry 44.
Control and digital data are sent from the trans-mit timing control 40 through a conventional span line swithh (not shown) and ovar the span, which as men-tioned, may be a Tl line or the like, to a span line switch at a remote tèrminal. Within the remote term-inal of Figure lB, received information is channeled hrough the remote terminal timing circuit 62. The remote terminal timing circuit 62 (a slave of the CO
transmit timing) forwards received data to the re-mote TDS ci~cuit 64 for directing shelf unit selection to the shelf scanners 66 which perform a further de-coding of information to select a desired line unit 70. The timing circuit sends control information to framing circuit 72 to provide a pattern match of timing and synchronization control signals to actuate alarm circul~ 74 when in~i`c`ated. In~-a~remot~ term-inal,z~he}-only additiisn~l clrcuitslovër~`and ~ ové --those used for the multiplexer with concentration are the originating and terminating memories within the remote TDS. The function ~ -8-1~4~ J

of the memories within the intra link (IL) call pro-cessing will be explained later herein.
The system as shown herein uses 35 channels per frame in a full duplex system, the first three channels A, B and C being used for control and sychronization purposes. The final thirty-two channe~s are . ~

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used to carry message information and messages betwe~n a CO line unit at a central office and remote line unit separated from ~he CO by a distance with a span line between the CO and each remote unit. The span line as is known, is comprised of two unidirectional lines. Within this framework, the system provides facilities for time division multiplexing the 32 channels and time sharing o those 32 channels by up to 128 lines. The system is compatiblb with Tl-type span lines and may use Tl-type repeaters, as are well-known in the artO The system as described to -this point is shown in detail in the cited copending application.
The intra link feature provides a method of by-passing the span line for speech tra~smission so that calls from a remote terminal line unit destined for a line unit at the same terminal may continue without use of the span lîne speech channels. All calls are first completed using the ~pan line. A check is made to determine whether the call is a local one eligible for use of an intra link channel. A call found to be originated locally and terminated locally may be transferred to intra link control if an intra link channel is available.
The intra link ~IL) feature uses, in additivn to certain circui~s of the CO and remote terminal, the services of an intra link ~IL) detector 80, an IL
memory 82 and an IL logic circuit control 84, all located in the CO. The detector R4 i9 apprised of the need for generating the transmission of a tone signal over the completed call path, generates that tone and ~ _ g _ and detects the return of that tone to signify that intra link transfer should be effected and signals the IL control accordingly. The IL control ~hen signals the IL memory to transfer the call to the IL mode to switch line addresses into the IL memory a~d to cause removal bf these addresses from the normal call channel memory.
In the remote terminal of Fig. lB, ~emories within the remote TDS 64 also act to provide intra link call control in agreement with in-' ~`
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formation stored at the CO terminal.
An intra link call is a subscriber originated ~all at a remote terminal intended for another subscriber at the same remote terminal. The intra link feature permits a total of 64 lines to be in use at a given time - up to thirty-two in normal calls and up to thirty-two in intra link calls. Any eight lines at each of four terminals can use the intra link facili-ties while an additional thirty-two line~ at that or the other remote terminal are engaged in trunk calls.
The intra link facili~y permits the IL calls to be made without tying up any of the normal speech channels except during the signalling period and be-ginning portion of a completed call. Local calls within the system can only be made if two ro more normal speèch channels are idle when the call is ini-tiated since a call between the two stations of the s~stem are initially processed through4 the two normal speech channels, and since each connection of a station to the CO requires the use of a ~peech channel.
The intra link control 84 determines the status of all 32 channels and determines when the correct conditions for intra link call occurs. On ~he occur-rence of these conditions, the control signals the de-tector to generate a called party identifier tone and initiates time out circuitry to make a call ineligible if it is not transferred to intra link wi~hin one minute. The intra link detector 80 ini~lates the iden-tification of ~he location of the originating subscriber while checking for inta link eligibility and acts to generate an identifier tone signal. The intra link memory 82 stores the address of both the calling and called parties, transfers this information to the TDS
memory at the CO channel for transmission to the remote terminal, causes the release of bo~h normal channels when the intra link call is established and de~ermines eligibility for intra link calling. If both parties are not from~the~-;same remote terminal, they are consi-dred~'ineligi-. .
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ble and the call is maintained in the normal nammer using two channels.
The system of Figs. lA and lB operates generally as follows: ~hen a remote subscriber initiates a call, it is processed in the normal manner~ Even if the call is to another subscriber on thesame remote terminal or line group system, the CO equipment seizes the appropriate line unit and proceeds notmally. The incoming call from the CO and the call from the remote terminal are both identified in the intra link memory unit 82. If the two parties are from separate remotes, the call proceeds normaly; if, however, the two parties are drops from the same remote, the intra link memory unit 82 passes both their addresses to the TDS memory unit 34j which in tur~ipas3es them via the CO timing unit 4b and span line to the remote terminal.
At the remote terminal, the addresses of both ~arties are pas~ed into the remote TDS 64 which then sets up the intra link circuitry throygh the originating and terminating call memo~y.
~ he de~ision as to whether the inta link function is to be used is made at the central office and is transmitted to the remote terminal in -the third or four~h bit of channel B, the second of the three con-: .
trol signaI channels. The third bit is for intra linkand the fourthefor normal calls. Normal and IL channel assignments are transmittad on other positions of chan-nel B. A total of 64 lines addresses are transmitted to the remote terminal in one ehannel B cycle.
Within the remote TDS interface 64, the addresses of ~he lines in an intra link path are written into the intra link memory, thereby causing the line unit addresses of the calling and called stations to be ~- 11 -~ u~
selected during the chà~nel scanning period, Control information is rec~iv2d from the CO which causes the normal channel memory positions assigned to the two line~ during call initiation to stop selecting the lines during the channel scanning period. This op-eration frees the channels for use by other lines.

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- lla -After the call i5 finished, the on-hook status is sent to the Co in the normal manner and the intra link connection path is released. The two line units may then be scanned in normal sequence.

The intra link control circuit shown in block form in Fig. 2 receives signals from the CO TDS control 36 to originate an intra link eligibility check and for this pu~pose, it holds the status of all 32 system chan-nels in the IL control channel status memory 110. This status memory of 32 positions ~ one per speech channel ) has four bits per position and is used to examine the intra link status to determine when correct conditions for intra link calling occur. Of the four bits p~r channel, bit #l is marked if a ring signal from the CO is received for this channel. The next bit is marked when a station goes off-hook. The condition of bit #l is held when bit #2 is marked to maintain the direction of the call using that channel until the channel is released. Bit #3 is marked when a condition is reached that intra link calling is not now possible but may be possible subsequently. ~it ~4 is marked when the call is found ~o ba~ineligible for intra link calling i.e. r both lines ~ot from the same remote terminal.
This status memory 110 provides an in~ication whether a call in a channel is an ori~ina~i~g or terminating call at a remote terminal and whether a channel is in use or not.
When an originating call at the CO is indicated, the channel demand lead fromtthe status memory 110 i~ 2 rung and gone off-hook and time-out unit 118 has not completed its time out period, an intra link check is instituted through the terminating call marker 114 3:
which stores the address of the assigned channel until intra link tests for that line are completed. The ter-minating call control 112 directs the operation of the marker 114 and enables the detector unit 80 at the ap-propriate time over the detector enable lead ZDE.
The terminating call control also limits the time dur-ation of identifier tone to minimize effect to subscriber of the tone.
If all tests prove that an intra link transfer sh~ula~-~be instituted and that intra link channels are available, call transfer unit 120 provides a demand for an idle intra link channel to handle a call at the remote terminal of the originating and terminating line.

The intra link memory shown .Ln block form in Fig. 3 provides termporary memory in respective latch registers la0iand~el32 for holding the addresses of the originating and terminating lines involved in a possible intra li~k call while eligibility~for IL transfer takes place.
These addresses are then ~ed to the more permanent originate and terminate 8x16 memories 134 and 136 when an intra link transfer is call for. Output gate3 156 are used to provide information to the TDS memory of the line ~tatus from the IL memories, and sends data TDS`-memo~ or transmission to the remote terminals.
The IL memory causes the release of normal channels by way of call release 140, and IL demand status 150.

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~s activated. The memory first is checked to deter-mine whether any lines are off-hook and have not been rung indicating a call or~ginating at a remote terminal in the system. If the answer is yes, op-exatlon of the originating call time-out unit 118 is started to time-out calls not tran~ferred to intra link duxing the tining period. The memory is then continuously checked to determine when a terminating call occurs. When a line has been ;. ' .
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- 12a -Transfer to an IL channel i~ demanded by demand unit ~:
150 and transferred by channel organizer 152 once an intra link connection is established, and cause the release of the intra link section when the call is completed. The IL memory stores originating station and terminating station addresses in latch registers 130 and , .:

- 13a -132 while eligibility is determined and is opera~ive to determine intra link eligibility through link assign-ment switches 144 and call cla sifier 146.

_ The intra link detector shown in block form in Fig. 4 identifies the location of originating channels through identifier control 160 while eligibility for intra link calling is being established. This detector originates and transfers an identifier tone from the transmit timing phasing to receive timing phasing and detects the receipt of the tone for validation of the call as eligible for intra link processing.

The detector enable input lead ZDE which may be followed to identifier control circuit 160 is activated from the IL control and memory when a tone is to be sent out on the line. The originating call marker 166 stores the address of the assigned channel until intra link tests for that line are completed.
The identifier control circuit 160 activates the tone generator 162 to send the tone from the CO over the received timing circuit. When tones are returned from the CO timing, the~ are detected in detector 164 and validated through validator 168.
The timing interface 163 provides gating for c channel control timing between the transmit timing and receive timing.
Thus, stated in another way, the IL detector generates ident~fier tones which are used to identify the location of the originating and termi~ating channels during call set-up. On receipt of an enabling signal from the channel status memory and/or the terminator o~

call con~:rol circuit~ in the IL control, the identifier control circuit activates the identifier tone generator which sends th~ tonPs to the CO receive timing unit.
Similarly, the identii~ier tone cletector - 14a -~L(34~1Lf~
circuit receives tones from the CO transmit timing unit and, after identification, passes the tones to the call validator circuit which then informs a call transfer circuit in the IL control unit whether the call is valid.
In Figure 5, we show in greater detail the IL
control aircuit 84 of Fig. 2 In figure 5, the originate time out circuit 118 is a settable maximum two-minute timing circuit whose cycle is initiated on the start of an IL eligibility check. The circuit is capable of timing out 32 channels simultaneously under co~di-tions where the ime out for each channel does not begin at the same time. This is achieved by breaking down the time out period into eight intervals arAd~
storing the intermediate counts inli!memories 512 and 514.
The time out clock 510 increments counter 520 eight times to advance one time out cyclls. When a time-out commences for any channel, the condition of the counter 520 is stored in a memory position in 512 or 514,~--unique to that channel. When the counter advances eight counts, gating circuit 5~2 determines ~hat the time out is com~lete. Gating circuit 524 and latching cir-cuit 516 control the routing or signals to and from memories 512 and 514. If no ~dentification of a call as an Ih call and no IL transfer occurs within the se`t period, the IL check is terminated and the call continues as a normal call.
The channel status memory 110 as shown in Fig. S
comprises a plurality of gates 530 fed from a four-bit latch register 524 to input the 4x32 memory 534.
Ther terminating call control 112 compriese a ~ating and flip flop network 536 for receiving input .: . . : .

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from-.the IL detector and includes an enabling flip flop to enable the tone detection on lead ZDE. This section also includes two time delays, timer 542 delaying the start of tone transmission allowing the call to enter a stab~e pattern before the tone signal is ini-tiated, and the other, timer 544 for timing , - 15a -o~
out the identifier. This unit responds to the term-inating call marker 114 which com~rises a five flip flop latch register 550 and timing gates comprised of exclusive OR gates 552 feeding a six input NAND gate 553 to mark the terminating call channel.
The call transfer unit 117 acts as a pulse aligner an~ is compri~ed of two f1ip flops 554 and 556 and a NAND gate 557 responding to input fr~m the IL detector.
The IL memory 82 is shown in detail in Fig. ~
and includes as its basic elements the two 8x16 memories, memory 134 for the address of a line associated with an origianting channel and a second memory 136 ~f like size for terminating lines. Associated with each of these memories and providing temporary memory for input to the memories are respective latch registers 130 and 132.
The output from memories 134 and 136 to the TDS
memory is over the resp~ctive multiple NAND gates iden-tified in Fig. 3 as output gates 156. The call release circui~ 140 and the IL damand status are shown in Fig. 3 as separate boxes and are, in fact, p~rt of the same gating and flip flop chain. The demand status section 150 is comprosed of exclusive OR gates 610 receptive of signals from the memories 134 and 136 to feed through multiple NAND gates 612 and 614 to output to the demand status flip flops 620, 622 and 624 for the purpose of signalling the release of an IL channel and to block the demand for a normal channel when an ou~put pulse f rom the flip f lops appe ars on le ad ZLBS as a can-cellation of channel demand signal for the TDS control unit.
* - 16 -The channel organizer 152 is comprised of gates anda flip flop 560 which receives as it5 input a signal on lead ZTRC to provide a proceed signal for writing in the memories 134 and 136~
The link group assignment switches 144 comprise switches for assigning shelves to link groups. In the apparatus shown, a link group is a group of four intra link channels. Each link group is .~

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c~pabl~ of h~ ciLls bst-~een ~i~ht subscribers a~ th~ ranote tsrm~nal to tih~ch it ha3 been assigped. A lirLlc grou~ calnot bo ~p~it bet~san t~ tarcdnal~. A total o~ ~ur link grcu.ps are avail-a~le for assignment to up to rour remota te~nals o;' a full mul~i-pl~ sgst~m.
~ .~en establishi~ 0Up5, each CO l~a ~t sh~lr is dedi-catod to ~ovida intra ~irik sarvices fc~ remote lin~ ~its ~n ~e .
corre3pond~g ~e urli~ she~ at a remote ~erminal. Ig the services o~ a part~cular CO ~i~e unit 3hel~ are sp~:it bet~;een t~ emots termî-g ~e 1~ um.ts 3~ ~a line unit shel~es at the ra~t)ts t~n~als ~a~no~ u~e ~hs irl~d li~k ~acil;ty. Plult~ple ~ine urit shalves lo~
~:atsd at a reD~ote ter.~inal ma;sr be assigl~ed li~c ~ro~s ~ such a ~ann~r t~hat ~ntra ~ ca~s ma;r be set up ~ oetw~en shel~s alt t~e re~o~e t~n~l, independsnt o~ shelv~ a3~g~ed to ot~r r~ote tsrminals.
arr~g3me~t p~ ; intra l~c ca:Lls betwa~ subscrLber~
~:t a g;;veD, tç}rn~dnal to all other sub~cri.bsrs at ~e same re~ e t~ni-~al.
~ tches ~41s 1~ t~8 ~tra ~ ~o~r unit pro~id~ ea3~3 o~ ectiDg i~tra li~c ~acili~ies to ba as~gned ~o syst~
~andam grow~ er~s. The s~3itc~ positicns provid~ ~ groups *or a~sr presen~ de~d patternO
Ths o~ll cl2~:~ier 11~6 i~ as~ociated witi;h ~he s~itche~ to oode a~d decode infc~ma1i~on to and from the s~itchas a~d t~eir out~put gat.-~g 6l~o a~d l~t~ 6~2.
q~he II~ detectar 80 o~ Fig. 7 is essenti~Lly co20r~sed o~ t;he .
tone ge~ra~ors zrld detectors and control ga~n~, or tl~.e tc~es. A
~:lip ~lop 710 is clocksd ovar t~e ZBB'r to feed incom~ng code and star~. ~ dstact;lon ~oceas~ l~e tone genarator ~62 ~e a ~ to~e syr~th~sizer ~osa ~requenc~ is sattable ~ ~he settir.,> Q.e th9 manual 8~L.~ 701. T~s s~ch al50 controls th~l s9ttu~g t~ th~ twO~be~ld ~7 - - . . .. .... ...... .. :.. . . . .

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pass ~ilter detector circults 702 and 7C~ and th~ir r~speGtive amplifier3 712 and 71~ ~nd ou~put datac~ora 722 a~d 72~.
The de~ac~or anable input lead ZDE ~eeds t~ orig~a~ing cal:l ~arksr 163 and ID control 160 b~ activating ga~e 719. This circu_t also inc~uda9 a ~rsquency s'ni~t ne~worX 731.
Ths call ~l;dator 16~ o~ the detector provides ou~put on ~s lead ZVC a~ an output o~ its ~lip flops and ga~es ~han tonss o~
both prop~r ~requ~ncies h~ve been recei~ed. On the first tone, t~s freq~ncg shi~t flip flop 7~0 is operated ~o ~hi~ t~ t~t f~equ~Qc~ ., .
~r~m the ~r~t to ~e ~eco;nd test ~requency, The second correct fre~
qus~cy ig sig~ ed b~ the v~l;dator to pro~uce an output indicating on ~cad ZVG t~a~ an intra li~ el be allotted to t~e c~l i~
oated. T}~i9 9ig~a~L on lead æ~c pa09e9 t~ t}le IL co~trol ~Figs. 2 and 5) and il;9 pulse ali~er ~ p fl~p 551~ ~o prc~lùce an ~utput. cn lead 2TRC to ~he ~emories to execute the IL ~ran~fer~
:~n Figure ~, ~e sho~ l~h0 memories ur~sd to process a call~ check ~or in~ra ~ k ~n¢tioning and ~or trans~erring ~* control~Da a call intra l~c mod~ show in the ICO a TDS monory :~or ~ g ei~ bit addra~se~ of lin~a ~ g the thirt~-t~ cha~nels. ln t~l8 CS~ also are t:he ~ha~el ~tat~s memory ~ith a *our-b~t storags ~or ea~h cha~l, the bit~ 8iga~g ~1) t~ char~ne~ line hav~g be~n ra~g ~r ~ot tG 8i~nig~ a~ a te~rhna ~ g ~ina or non-tlsr~ na~i~g (oiigi~
za~i~g ll~e~; (2) o~f-hQoX or o~-ho~k; (3) marked as t~mporari~
elig~ble for IL ~rans~er, and ~) mar~ed a~ ~nsli~ible for IL trans~
fer"
~ hen a call i~ tran~erred t~ IL mode, the addrea~es of the lin~9 involved ar~ storsd in the IL memor~, on an I~ channel ba~i~
~or the sixte~n IL c~an~el~.
In the r~moto t~rminal, a normal memory stores addre~ses o~
lines associated with cha~nels in~olv~d in a caIl and two memories '~

~ ~ - - .
, lQg~
for storage of addresses of lines associated with intra link channels, both originating and terminating.
By refarring to these memories, addresses may be transferred under the control o~he status infor-mation ~found and stored in the IL control memory.
An originating call marker comprised of a five flip flop latch register 760 feeding exclusinve ~R
gates 762 and a six input NAND gaté 764 is provided in the detector circuit 80, the register being marked on an originating call to provide the one-at-a-time check of lines originating calls.
PROCESSING OF AN IL CAL~
A call originating in the system is started in the usual manner by a station going off-hook. The call is processed throughtha remote terminal to which the calling station i9 connected and an indication of this call ià noted by the central offic:e during the signalling channel periods.
A channel is then assigned ~o the call and the statu~ of the call is stored in two lications~ The irst locaiton is an 8x32 bit memory 834 in the time division switch memory 34~Fig 8,) which monitors the use of the channel assigned to handle the call. The second storage location is within a 4x32 channel status memory 110 in the intra link control unit in the CO. One bit of the memory 110 for a channel is marked when an off-hook station is found and assigned to have the call processed through a specific channel.
This action begins a timing cycle of one to two min-ute~ duration during which an intra link transfer must take place. If no intra link transfer occurs within ~ - 19 -the timing interval, it is assumed that intra link cPases for that channel and bit #4 of the channel status memo~y is so marked.
The call is process-d in the normal manner as set forther in the copending applica.tio~ noted, by the CO , :
with tha originating station dialing the called or term~
inating station and the call being completed :

~, - l9a -to the called station. It will be assumed that the called station is at the same remote terminal and is therefore eligible to be con-nected to the originating station over the intra link network.
The terminating statlon receives ring signals from the C0 over a second channel of the available speech channels. Nhen the terminating station responds by going on hook, two channels are in use forrthe call. Where both stations at the same remote terminal are involved, it of course would be advantageous to eliminate the use of speech channels to the C0 and transfer the call to a local path requiring only signalling channels to the C0 for control purposes.
The ~act that the first local station is an originating station has been stored o~ the channel status memory 110 for its channel and the fact that the second local station is 8 terminating one is sensed and marked in tbe channel status memory for its channel as mentioned previouslyO The off-hook condition coupled with called direction of the call on the second channel is received by the IL control logic terminating call control 112 (Fig. 2~.
Within the IL memory 82, latch register 132 is sctivated ~o mark the terminating station address. The terminating call marker 114 . . ~ .
is activated to mark the terminating station channel. This register 114 sends a co~mand to the IL detector (Fig. 4) to enable circuits of the timing interface 163 to mark a channel on the receive timing cir-cuit 42 at the C0. This channel marking also activates ID tone genera-tor 162 to produce a digitally generated ID code to be inserted into the terminating channel at the channel at the CO receive timing cir-cuit 42 (Fig. lA). The digital code signal is routed to the line as~
sociated with the terminating channel. The code signal digits are decoded at the line demodulator to become a tone of approximately 3 KH~ which is sent to the called line.
The tone passes through the CO switching equipment ànd passes W. ~Jur~t - 3 ~4~

throu~h to the line unit of the orig~atirlg station w~ere the tons i~ digitized to pas~ throug~a th9 tran~nit timing c~rcuit ~ di~Ltal forw to t~3s IL detactor 80. It should b~ n~ted t}~at ~en ~e t~
na~ st~ation goee off-hooX, an ID tone dslay (of up to one second ~ra~on~ wit~ ~he t3rminating call control 1-2 is acti~atad. T~is dalay pro~ents tra~ ssion of ID tone for a p6riod long enou~h to~.
~lo~ 1~e CO 9Wl.tChing equiE~ment to complate its ;fl~nctior~ and pro-~uce a s~able speech pa~. The end of t~s d0aay i~itiates t~e tra~
mis~ion o~ ~ ID tone.
I~ a n~ber of stations a~ a te~ nal have orig;~atad calls, ~3ac~ must be examined ~n turn uutil the originating call ~md ter~-nab;~g caLl. are mato~sd ~th the code signal ~nt out on t~e line~.
ig checX i~ ma~e at t~e orig}nati~g ca~l marker l6~ hin t~e II.
de~ector in ~ich each e~gible orig;L~ating ~tation ch~n~ marXed at a tim~. An eliglble c~iginat~ 9ta~0n i~ de~ned as orle ~dicated ~ tha bhan~:Lel BtatU9 men~.o~y :llO aB ha~ing originated a call ~lbit ,~ arked i~dicating tha~ the station wa3 2~0t rung, bit ~2 a~ ed .a~ of~-hooXj a~d bit #4 ~mar}ced aB sig~i~ng that the chaDnel d has ~o~ basll declOEed i~eligi~le ~ tL ca~ ,, Eac~ arig:~a-tat;io~ et~g t~e criteria a~d having t~ho remote ter;~al a~e3~ id~ e digLt~ ~n ie9 addre~ code a~ dete~ed b~r l~c ~rs)up a9~ nant s~tc~ s~ l checked i~ sc~ence.
roces~ o~ exa~ni~g lthc channel~ ~cr a tone i~ perfon~d }D tone datector 80 ~ cou~led to rece~;ve 9igllal~1 from ~he trans~t t~in~g circuit. Th9 detect;ion o~ t~e code ~ ena~}ed o~r a pa~ to t~e ID tone det~ctor from ~he term~atin~ sta~o3~
oall control 112 over lead detactor enable (ZDE~ rou~h ID control 160 to ~h~ ID detector 164. The detec~or include3 two co~utating ~ilters connected in para31el, each b~ing tunsd to anot~her frequency, These i~ilters checX secIuentiall~ durin~ roper c~annel tims period ~3 cloclted ~ ~lip Mop ~lO ~ Fig. 7, the ~p ~lop having recei~fld ' ;2,1 '' ,"' ,''. ' ' "' ' ', " ' ' '',- " .

~ brst - 3 , ~t~ timing on lead Z~BT~ Tha filter3 checX for the presence of one specific frsquenc~ and for th3 absance of the oth3r frequ3nc7.
Each 3u~h filter has at its OUtp`lt an amplifier and a detactor circuit~
An exami~ation sequence ~hich success~ully det3r~ina~ eli~
bility of both stations ~or intra link call completion includes ~he r~l~Owi~g four ~teps: (1) Sending of a first frequency; (2~ Detac-t~ng ~he ~ir5t grequency and ~he a~sence of 2 second frequenc~;
(3~ Sending a second ~requancy~ and (O ~etec~lng t~e seco~d ~requenc~
: an~ tba a~sance o* the ~ir~t ~requanc~
In the c~rcuit of Fig~ 7~ there i9 9~0~n a ma~ually sstta~le ~itch 701 ~l~h thr~e po~Ltion3. ~ach po~itiDn provldes a diffarent co~bination of fir~t and second frequencias. For e~ample, one ~et of combinatlo~ ound accep~abla ~ a~ .~ollow~: For position ~1 o~
the 9Nit~h 701, Fl is 2757 Hz and F~ is 3153 Hz; ~or posi~ion #2~
Fl ~ 2~41 ~z and F2 ~9 3153 Hz; and foi~lp~sl~lon ~3~ F1 ~9 29~1 ~z and F2 is 2757 Hz~ Of course~ other oombination~ ma~ be used in place of t~e~e exsmpl2ry ones, tha prasent to~e~ havîng bee~ cho3en b~c~use o~ con~eniflnca and ~o ~ æe ~nter~ct~o~ be~esn s~g~alling ~one~ u~ ~ for o~her purpOse~. .
: The ~our ~tepa noted abov~ for 8~nding ~d reoeiYing the twv ~req~n$ie~ aro se~ed ffl ~all ~al~dator 16~ o~ t~e detector. Th~
dNrat~on ~ ~he examl~atîon p~riod ~br caGh to~e ~9 d~term~n~d by a ~rsgus~cy shi~t potentiomster 79~ hin ~ha ti~ing circuit containsd i~ the ID control 160 and shown i~ Fig. 7.
On comp1etion o~ a succe~sfu1 eXamQnatiOn se~en~e9 tSe verify-i~g circu~t or call ~alida~or 165 provides a transfer command t~ tha cal1 tran~f~r circuit 117 of the IL contro1. This command is passed t~ough channe1 organizor 152 to m~mories 134 and 136 to cau~e a trans-~er in msmory bit #~ tchanne1 ~tatu9 m6~0ri~) of the originating and , .. , ' , . ,~ . . .

1~431~0~L w. Wurst - 3 ..

inatlng channals, sincs the call ha3 been dispos0d of for ~ntra linls purposes by this act an.
The li~a addressas from locations in the I~ memor~es 13t~ and ira sent th~ough the output gate~ 156 to the TDS memory 3~s ~Fi~.
1~.
l~e~e m~or:~3 131~ and 136 conta~r~ 8~d6 ~its tan e~ght bit ~dd~ess ~or each avs~lable ~ntra lin}~ channal). The trarls~er ccmmahd pro~uces a ~r~te slg~al :in ea~h o~ tha IL mamories 131~ and 136 for ~he ~ir~ a~a;lable channsl~ t~e addre3seq having ba~ recai~ed ~rom ~he TDS ~morie~ and s~ored in latch re~sters 130 and 13~ no IL channsl is av~lable a~ eYidenced by all ~ixteen memory locations ln ~he 8x16 IL memories 13~ and 130 having an IL control bit sarking the c~annel as aotivs or as~ig~sd, the IL damand status unit 1~0 ^~
the I~ memor~ will ~t notify the TDS control 3b via lead ZLBS to cgncel the dsmand for normal cha~els ~hat were assigned to t~e calls.
No caIl trans~er can occur, and the call i~ ~aintained in the ~ormal a2merO
re an IL chann~l is availabl~, ~ha wYite command plac~d b~
~he chan~sl organizer 1~2~ ~auae~ ~ e o~t6nt9 0~ ~he originat~ng IL
1Qt~h regi~*~x 130 and the terminating la~oh r~gister 132 to be loaded i~ the ~elect~d ~L channel ~n ra9p3ctive m~morie~ 13~ and 136~ The3e ~a~ch rsgi~-~ers had been load~d ~rom the output~ of t~a 8x32 chan~81 a~dress ~mory loca~ed withi~ the TDS mamory 3~, at the same ~ime as ~h~ originating and terminating ~arkers 166 and 114 of tho control cir-~u~t~, thus the r~g~sterl.oDntain ~he addresse~ placed in the marked channsls.
Tha outputs of the originating and ~erminat~ng address msmo~ies ~3b a~d 136 are gat9d through output gate~ 156 and are forwarded through the parallel to a series shi~t re~ister located withi~ ~he TDS memor~ circuit 3~. ~his shift re~i~ter tran.s~its commands to ~he ~ ~ .

s-il~412~1 w~ Wurst- 3 r~mote t~n~nals causing ~he routing o~ calls from the nor;nal to in~ra lir~c mode wit~i~ t~ r~ote TDS circuit of ~ig. 8, Th~ II, cDntro~ bit ~discussed preYiou~ly as provi~ng an II. cha~l busy indication) i3 also used by ths IL demand ~tatus circui~ 1~0, to ge2~ra~e ~ signal cau~ng tha TDS con~rol to cancel chan~sl ~nand caused by t~ o~-hook co~tion of 7;l~e~ i~ ths ~n~a link ~node. Ey cancelling the chann~L delllands, ~e normal speech cha~sls o~ na;Ll~r uesd bg the stations ~L estab~ishln~ the I~ call may be r~leasad. Xt should be notad that t~is ~Ef-hook ~ig- -n~ n~ had besn transmitted over a sigr~alling ch~nèl ~ro~ the re-ote t0ri3~al a~d did no~ US8 a speech c}la~l.
l~hs ;in~ra lin~c ca~l once trans~rred U:3e9 ~tra lin~c inte~als Wit~il~ ~e channel ~iming, as ~ho~ by Fig. 9. Vie~Lng Fi~.. 9., it ca4 be see~ t~at ca~ih cha~al ti~ns intsrval ha~ a tran~:it sub-~ntarval and a r~cei~ hP~ intsrval. Since traxlsmit and r3csive ~ach use separ-ate line3~ alternate sub-inter~rals are alvailabls on each li~e. These are used il~ t~e marmer sho~ ~n Fig. S~ The9e in~ra li~c channel in-tervals ars li~csd at the re~no~e terndn3l1 ldthin ~e l~x8 originate and t~r~ats ca~ smo~i~s at t~9 remote teinal ~ile control o~ ~hs call i9 m~tai~d in t~he CO by ths IL m~mory.
lr~ a ~tation invol~ed ~n an int;ra lillX call goe~ on hooX, a~ on~t~on chan~ is reported to t~3 Tl)S colltrol l~ro~ th~ ~i~a~ing channel9. 1~9 ~onDation is fed on Yhe call 8~atu~ leadl to ca~l ralease c~rc~t ~l~o. T~3 data alon~ II. de-Dl~d status ~onnation causes a writa pulse to be gs~eratsd far the haru2el in t~e msrnories 131~ ~nd 136. The contrsl bit ~or that IL
chann~il rev9rt9 to it3 ur~nar~ced state. Th~ chan~9 of control bit is ;~
~ad througll ou~ut g~te~ l~;t; and i~ fed to th9 r6mote TDS memo~ caus-ing ~le intra l~r~c connaction to be released.
~ ha ~ncellation vf t~9 channs~ dem~nd wi~in ~e TDS contro~

~Y. Wurst- 3 is removed cau3ing t,hs line still ofr-hooX to d3mar.d and be assi~ned a normal ~F chanr.31 until the lia3 goes on hooX.
Tns link roup assignm~nt swi~ches 1~4 In Fig. 3 are sho~n ~ig. 6 as comprising four groupings o~ aigpt switches ~o program a lisk group o~ four links to a maximum o~ ~our r~ote terminals.
The lin99 th~mselves are a~signed tD remo~a te~inals i~ groups o~
s~xteen, eac~ group co~prisin~ one shelf. The shbLV9S may be as-signed to terminals in an~ dssired order, as detar~insd by t~e illter-cor~ec~on bstween shel~s and a rai~ote TDS c~cu:Lt at a relr.ote te3~-n~ Ths l ~ c ~ro~p assig~nent s~t~es allows thQ shslve~ to be a-q-~i~ned to li~c ~Oroups in an3~ sffq~snce. Ea~ li~c group has a7t IE;D
in~cata if a~l li~s in tha grou~ have besn assigned.
The ca~l classi:eier 11~6 of Flg. 3 comp:rises a gating and latch n~t~ork to interconn0ct the ~our li~c groups with the lis~c grou~ a~sign-rrlent switch out~uts. B~ t}~i~ gatin~ net~ork, t~e classi~ier 9xam~es t~e association bst~een t~e ordar o~ t~e s~tches, as E~rngra~n~d~ and ~e ~ra~c conditioDs. When a term:LI~a~ng ca~l occurs, the she~ ad-s ~1-8) i~ noted and comparsd with the switch setti~s to see ii~
that sillel~ is assignQd to a speci~ic 1~ gr~up. I~ t~ere is no 9u~h as~ig~nent, bit ~J o~ the l~x32 cha~el stat~ manor~ i~ ~arlc~d ~a7~g ~at cha~nel o~ th~ ~rminating call inel~ible ~or intra li~c ~sage.
Bit ~ or a channel i~ aLso marXed bus~ shel~ is as~gned to a lin~c group in ~c~ ink9 are busy.
e t~ nating call i~ made to a shel~ ~le a previously occurr~ng ter~tlng call i~ being examined, bit ~3 of t~e 1~x32 charmel status memor~ be marksd busy for the l~tter call. Tnis condition ~7ill place t;;he call on stand~y until t~e previous call has b~en ~x~ d. At this ~ , ths status ~ bit " 3 will rever~ to its rnarXed state allo~n~ t~e call to be examined.
lt ~houl~ also be noted ~at ~en an e~igibl9 terminatiIlg call - , ~.

, _ , . .
' ~ L~ Z~1 W. Wllrst - 3 oted, and no local ori~nating caUs are pre9ent, the abs~ncs o~ loc~l originat;ing calls is in~icatad to marlc bit ~4 of`~e t~x32 channsl status mamor~ to p~evant intra ~i~l; chectcing from occu~ ring.
In this wa~, a system having a ~rge number o~ a~ail~ble intra li~c c'nan~sls may be providsd, to e~ance t~ call-carryir g capabil;~r o~ t~e systam.

~IC :~s .
~eb . ~ 75 ~ ' ` ' ' ' ~ ' .

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Claims (6)

I CLAIM:

1. A telephone subscriber multiplexing network for coupling a plurality of subscriber lines to a central office by way of a remote terminal coupled to said lines with the coupling from said remote terminal to said office being completed via a plurality of channels, a plurality of lines coupled to said cen-tral office externally of said remote terminals, memory means at said central office for storing the calling and called condition of each of the lines, storage means for storing the condition of a line using a channel for initiating a transfer determination, means responsive to the storage of said condition of one of said lines in said storage means for initiating the transmission of digitized tones over any channel coupled to said one line, during a time interval unique to the remote terminal, means responsive to the failure of receipt of said tones by any line using said channels for storing an indication of said failure for said one line in said memory means and for erasing the storage of said condition of said one line from said storage means.

2. A network as claimed in Claim 1, wherein there is timing means initiated coincidentally with the initiation of the transmission of tones, said timing means operative to time a period for the receipt of one of said tones, and means for indi-cating a failure of receipt of said one tone by the end of said period for marking said failure in said condition storing means.

3. A network as claimed in Claim 1, wherein there are means for sequentially transmitting tones over channels to other lines indicated by said condition storage means as being in an off-hook condition.

4. A telephone subscriber multiplexing system as claimed in Claim 1, further comprising: a plurality of remote terminals coupled to said office via said multiple channels with a plurality of subscriber lines connected to each terminal; the channels of said network being divided into signalling channels, digital data channels and intra link channels, means for signal-ling calls over said signalling channels to enable digital data channels for the completion of a call from a calling line to a called line via remote terminals, and means employing said digi-tal data channels for testing for the transfer of a call between a called line at one of said remote terminals and a calling line from the enabled data channels to intra link channels for contin-uation of said call over said last mentioned intra link channels internally at said one remote terminal as an intra link call.

5. A system as claimed in Claim 4, wherein said chan-nels are positioned within recurring time frames with said sig-nalling channels at an end of each frame, and said data and intra link channels interspersed throughout each frame with supervisory control of a call continued using said intra link channels main-tained over said signalling channels.

6. A system as claimed in Claim 4, wherein said memory means at central office includes first memory for calls using digital data channels and a second memory for calls using intra link channel.