Home

Dual-processor line concentrator switching system

1. United States Patent Hutcheson et al 11 4 197 427 45 8 1980 54 DUAL PROCESSOR LINE CONCENTRATOR SWITCHING SYSTEM Alan G Hutcheson Sparks William Bonham Calvin H DeCoursey both of Reno all of Nev James H Glaser Bonham Tex Richard D Ross Reno Nev Wook R Shim Rohnert Park Calif Lynch Communication Systems Inc 75 Inventors 73 Assignee Reno Nev 21 Appl No 850 592 22 Filed Nov 11 1977 150 040 3 60 1524176 Clk acca 179 18 FC 158 Field of Search 179 18 FC 56 References Cited U S PATENT DOCUMENTS 3 592 970 7 1971 Capettiet 179 18 FC Primary Examiner William Cooper Attorney Agent or Firm Phillips Moore Weissenberger Lempio amp Majestic 57 ABSTRACT A switching system is disclosed for the concentration of a plurality of telephone lines onto a lesser plurality of intermediate trunks wherein an independent processor is included at both ends of the concentrator system These processors communicate with each other over a randomly chosen idle trunk thereby negating the need for a dedicated communication link between the proces sors Each processor controls the switching functions at its end of the concentrator independently monitors and retains trunk status subscriber line status and system operational status and provides syste
2. 4 197 427 13 cepted indicates that the system is presently busy with call processing indicates that the command has been successfully completed An E indicates that a keyboard 110 data entry is expected Finally an F indicates that the system is in a freeze mode In the freeze mode the system will not process new calls but will continue calls in progress In this mode certain system modules may be replaced without requiring system power shut down A teletype interface 108 enables communication to and from the PCC 12 22 to be performed using a stan dard teletype unit with attached paper tape reader This teletype interface 108 is relatively standard comprising mainly a teletype clock and a universal asynchronous transmitter and receiver a UART e g a TMS 6011 as made by Texas Instruments for input output to and from the teletype and control thereof A teletype con nector is provided at each concentrator 8 terminal to simplify connection of a teletype thereto A person reasonably skilled in the art should be able to construct such a unit without difficulty One advantage of having teletype capability in a concentrator 8 system is that it is easy to remotely hook up such a teletype unit That is it allows the teletype to Operate at a distance from the concentrator 8 system with connection to the concentrator 8 for example establishable over an independent telephone line using a modem T
3. state occurs when both terminals are in need of table refresh This state is entered by both terminals to cause all switching connections in the terminal to be released which had been previously preserved need for table refresh is indicated by a terminal in the following way Upon receiving a null message during the above data link communication recovery the COT 10 sends one of two messages to the RT 20 depending on its situation i e I have recovered or 1 need table refresh When the RT 20 receives either of these two messages it knows that data has been success fully transmitted in both directions over the data link The RT 20 then sends a similar message to the COT 10 If the COT 10 needs data the RT 20 if recovered will reply with here comes data followed by a block of status table data A similar procedure is performed if the COT 10 has data which the RT 20 needs If both the COT 10 and the RT 20 need table refresh the recovery state memory location in both terminals is set to 6 to initiate the system relay clearing process To perform the table refresh process a special block data transmission process is utilized to transmit the ap propriate tables to the requesting terminal A total of 16 bytes of data are transmitted at a time This minimizes the effect of data transmission errors without making the table transmission time excessive If a UART check byte error is detected during block data t
4. 25 30 35 40 45 50 55 60 65 6 takes 40 milliseconds ms to complete Further details on the operation of the XMTR RCVR 40 50 is pro vided in the Data Link section of the specification here inbelow As illustrated in FIG 2 interaction by maintenance personnel with the line concentrator system is via a 4 digit hexadecimal display 106 a front panel keyboard 110 a teletype interface 108 and various alarm circuits in an alarm and power unit 104 which exist both at the COT 10 and at the RT 20 Maintenance of the concen trator system is made easy by diagnostic routining via programs stored in the ROM 74 and by system mainte nance monitoring via the maintenance monitor 100 both of which are periodically automatically performed by each PCC and which may also be requested to be performed by maintenance personnel Any errors dis covered as a result of this process are analyzed and diagnosed by the PCC such that maintenance personnel will be directed to predetermined corrective proce dures The errors detected including PCC s diagno sis of the errors is stored in trouble number codes to await readout by maintenance personnel Operational errors detected by the PCC 12 22 independently of the above routines are also stored in trouble number format Note that these maintenance routines are designed to operate so that they do not interfere with normal con centrator 8 system operation Initialization of s
5. tion and all changes which come within the meaning and range of equivalency of the claims therefore are intended to be embraced therein We claim 1 A line concentrator system for the interconnection of a plurality of lines over a lesser plurality of trunks including a terminal at each end of the concentrator system said system comprising means in each terminal for the detection of a system service request initiated by a line connected to that terminal switching means in each terminal for enabling the switching of a plurality of lines individually to a corresponding number of trunks processor means in each terminal including means for determining which trunks are idle means for determining and selecting an idle switch path through said switching means from said service requesting line to a selected said idle trunk and means for controlling the state of said switching means such that said selected switch path is gener ated thereby said processor means having a a data processor b control program means for controlling the na ture and sequence of the operation of said data processor c a memory including a plurality of storage loca tions accessible by said data processor for tem porary storage of data needed by said data pro cessor and control program and d means for inputting or outputting data from said processor means under the control of said data processor and control program and means for communic
6. 10 enables relay L50 selec tion via AND gate L70 and F1 enables line status output from the multiplexer 64 via AND gate L72 Finally when a subscriber line goes idle after call completion or due to reorder the resultant subscriber C lead state change back to 50 volts is also detected by the C lead detector L54 associated with that particu lar line If the call was a reorder the output of this L54 causes the reorder relay L50 corresponding to this line to release thus providing an automatic discussion of the reorder signal C The Switching Matrix and Matrix Decode FIG 8 illustrates a typical configuration of 168 switch matrices 510 comprising one end of a line con centrator 8 system For example the first stage would switch 64 lines into 32 lines and a second stage would switch 32 lines into 16 lines for a total concentration of 64 lines into 16 lines 64x16 Two stage switching networks of 128 x 32 and one stage switching networks of 32 x 8 among others are also standard sizes Both the COT 10 and RT 20 contain identical switching matrices 14 24 and decode circuitry 42 52 FIG 9 shows the typical switch organization for a 16 8 switch matrix 510 with switch decode and pulser means 42 52 Each 168 switch matrix 510 contains 128 separate relays each one represented by a cross point as shown in FIG 9 The relays are magnetically latching two pole reed relays The contacts of these relays are sealed in glass t
7. 100 on lines E via one of the output ports 66 With regard to the other control and data lines which are either coupled from external systems to the PCC 12 22 input ports 62 or outputted from ports 66 70 these signal lines will be discussed as each corresponding system is discussed hereinbelow B The Line Interface 1 Remote Terminal Line Interface The remote terminal 20 line interface 28 provides one function that of off hook detection Off hook is defined as a subscriber loop closure request for service indi cated as a resultant current flow of at least 10 ma Cur rent detected in the range less than 10 ma is defined as 20 25 30 35 55 65 14 indicating on hook state It may be easier to under stand these terms if one pictures a subscribers request for service as his act of taking his phone off of its cradle or hook in order to make a phone call and the replacing of the phone back on the hook when the call is finished There is therefore one off hook detector for every subscriber line serviced by the line concentrator 8 re mote terminal 20 FIG 10 illustrates a typical embodiment of an off hook detection scheme at a remote terminal 20 In the present embodiment there are sixteen lines ser viced by each line interface 28 board so that a system with 64 subscriber lines would contain four such boards The use of 16 circuits per line interface board allows for flexibility in concentrat
8. Apr 8 1980 9 94 1 1 31 30 14 21 ve 50193134 5 IN3YuND MS 9001 WOUS OL 4 x ae SAV134u OL 021 40193134 ANAND 1 0 001 86 sna OL vob 1 1 4361 AV134 OS Ob NNIT Viva 01 991 SANNYL woud OL 4 197 427 Sheet 8 of 12 U S Patent Apr 8 1980 21 14 53 1 1 3 _ 4 0 1631 22 21 2 8 224 saad 99 40 04 NIT 9 9 ae 1404 gt 91 22 21 YNNYL 294 OL 10 OL eee U S Patent Apr 8 1980 Sheet 9 of 12 4 197 427 TO FROM Ist STAGE 1 OR C O ORIGINATING CALLS L I i 4 1 2 L 16 TO FROM TRUNK INTERFACE 6 26 L 17 8 T 8 6 8 PU
9. MS INIT OL 4 197 427 Sheet 12 of 12 U S Patent Apr 8 1980 _ _ 391440 92 61 ino SNLVLS oud 96 2 11 1 9 snivis E Ms X INIT 109 OL 13 4 2 9 123136 MS LOO OL 4 197 427 1 DUAL PROCESSOR LINE CONCENTRATOR SWITCHING SYSTEM BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates generally to telephone line concentrator switching systems and more particu larly to a concentrator system that includes a processor at each end of the concentrator for independent control at both ends of the concentrator of switching functions error checking and other functions 2 Description of the Prior Art Since not all subscribers require service at any one time there is no need to have an equal number of con nections between a group of subscribers and a telephone central office Line concentrators were therefore devel oped to concentrate the number of subscriber lines into a lesser number of trunks which would then be ex tended to the central office Such an
10. OE and signals control the input data multiplexer 88 whose function is to input data to the microprocessor 60 either from one of the eight input ports 62 or from the ROM 74 or RAM 76 The IN signal is also used to strobe the input port select 64 to enable data from the desired port to connect through to the input data multiplexer 88 input line The OUT 1 and OUT 2 signals control whether the latching output ports or the non latching output ports obtain and output contro data from the 4 197 427 9 microprocessor 60 OUT 1 strobes information into eight latching output ports having a plurality of output lines per port and OUT 2 strobes information into the eight non latching ports with each port having only one line The final signal is the WRITE ENABLE WE signal This signal tells the RAM 76 whether the micro processor wishes to read data out of or load data into the RAM 76 A detailed understanding of how the above described signals are produced by the state de coder 212 is not necessary to appreciate the present invention Reference to the INTEL 8008 User s Manual is suggested if further information on the specific con trol circuitry necessary to provide the described signal operations is desired 2 The RAM Subsystem A typical random access memory RAM and mem ory addressing scheme is shown in the system block diagram of FIG 2 In the present embodiment the RAM 76 has a storage capacity of 2048 eight bit words Me
11. The transformer DL 60 is merely an isolation transformer to aid in the protection of the XMTR RCVR 40 50 circuits Reception of a data link signal by the XMTR RCVR 40 50 comprises basically the reverse of the transmis sion process The input FSK signal is first coupled through the isolation transformer DL 60 and the inter nal data link bus 90 to an FSK decoder DL 14 which decodes the data link signal into a serial bit string com patible for inputting to the UART DL 10 The FSK signal upon entering the FSK decoder DL 14 is first passed through a band pass filter DL 20 to filter out any high and low frequency transients The FSK signal is then coupled to a limiter DL 22 which squares up the signal The output of the DL 22 is coupled to an edge generator DL 24 for insuring that a one shot DL 26 is activated at the proper time The square wave output of the DL 26 is passed through a low pass filter DL 28 to format this signal property for a comparator DL 30 which if the output of the low pass filter DL 28 is at 1000 cps generates a logic 0 and if the output of the low pass filter DL 28 is at 2000 cps generates a logic 1 This comparator output signal then goes into the circuitry that detects when a leader pulse has occurred A leader pulse is detected by first passing the signal outputted by the comparator DL 30 through a high pass filter DL 32 which only passes pulses that are longer than 2 ms The only pulses therefore tha
12. arrangement how ever was found to be cost competitive compared to in place cable only for relatively simple line concentra tor switching systems In the past line concentrators tended to be large electromechanical devices requiring a high degree of maintenance or devices that could operate only using a subscriber carrier or only if a system were connected to a certain type of telephone switching system Also maintenance could not be easily performed at the remote end of the concentrator except on the most expensive of systems because there was little or no way of checking whether an error correction made by main tenance personnel at the remote unit was effective in eliminating the problem This is because system fault or malfunction indicators were minimal or nonexistent at the remote unit In addition except for the most basic of maintenance routines any check out of a line concen trator required the interaction of maintenance personnel to enable the detection of errors and error diagnosis Often a system had to be taken out of service before such error correction tests could be performed Only recently have separate monitoring systems been devel oped to aid in the maintenance of such switching sys tems Even these systems however have not hereto fore been inexpensively incorporated as an integral part of a line concentrator system The present invention takes advantage of state of the art microcircuits to create a flexible
13. boards would be required to cover the servicing of 64 incoming lines In the more common three wire system the COT 10 line interface 18 performs detection of incoming calls from the 2 off hook detection by sensing changes in the C or sleeve lead status Subscriber off hook is defined in this case as being a C lead volt age that is at least seven volts more positive than the 2 battery voltage which is nominally 50 volts In the present embodiment a conventional voltage level detector comprises the C lead detect L54 When an incoming call is detected thereby the detector L54 outputs a status signal to a line status multiplexer L64 This multiplexer 1 64 selectively takes one of the sixteen separate C lead status signals and outputs it on an LS Y line for PCC 12 input via an input port 62 Since there are four line interface 18 boards for example in a 64 line concentrator 8 system the PCC 12 would input four status signals LS 1 LS 4 one from each board The PCC 12 controls which of the sixteen status lines is outputted by the L64 by varying the state of the four output data bus 98 lines bits 0 3 that access this multi plexer L64 Note that instead of a C lead detection as herein described a two wire line interface could be used for those C O s that do not use threewire control Such an interface would be similar to the RT 20 line interface 28 described above A relay L50 switches in the reorde
14. data enabling checking by said data link means and processor means of proper recep tion of said data word said start and stop bits enabling the differentiation between adjacent bytes 24 The line concentrator system of claim 20 wherein said data link means further comprises means for en abling the monitoring of said data link communications from a location remote from either terminal in said system 25 The line concentrator system of claim 20 further comprising system initialization means comprising means for initially surveying the present equipment status of said terminal and storing this status data in said memory including status data as to the present number of lines connected to the system and the number of trunks available means for initially resetting said switching means to a cleared state and 4 197 427 43 means combination with said data link means for establishing communication with said opposite terminal 26 The line concentrator system of claim 25 wherein said means for establishing communication with said opposite terminal comprises means at a selected one of said terminals under the control of said processor means for generating a leader pulse on a randomly chosen trunk means at the terminal opposite said selected terminal for randomly monitoring each said trunk for detec tion of said leader pulse and for replying to said selected terminal via said trunk when said leader pulse is detect
15. gram will be discussed in the System Operation section below In the present embodiment the ROM 74 has a capacity of over 14 000 words It is further designed to enable expansion of memory capacity when needed Stored in the ROM 74 is the concentrator 8 system control program for use by and control of the micro processor 60 The advantages of ROM controlled sys tems is that once data or instructions are stored in the ROM the information cannot be affected by system power failure or processor re programming whereas information in a RAM is alterable in these ways Note that can be initially programmed only by special devices at the factory and although some ROM s have the capability of being re programmed this also can only be accomplished by special devices which are not a part of the present invention The 74 if addressed by the microprocessor 60 outputs data onto the same memory bus 92 as does the RAM 76 This data is coupled to the processor 60 via the input data multiplexer 88 and processor bus 90 The addressing scheme for the ROM 74 is slightly different from that of the RAM 76 in that the address register 80 only feeds the first eight bits of address directly to the ROM 76 for word selection while four additional ad dress bits e g 8 11 are coupled to the ROM chip select register 78 In the present embodiment the regis ter 78 comprises a plurality of chip select registers one each on each memory board con
16. in the RT 20 and in an identical switching matrix 14 in the COT 10 Lastly battery means 30 are also included at the RT 20 to provide auxillary power automatically switched in during power failure Such failures are more likely at a remote terminal since they tend to be located in rural and developing areas Battery means 30 is rated to pro vide eight hours to emergency power FIG 2 illustrates in block diagram form the proces sor common control unit of both terminals i e PCC 12 and 22 The processor common control comprises a microprocessor unit 60 controlled by a control cycle program stored in a read only memory ROM 74 A ROM is used because the control program is the perma nent system controller of the terminal No change in the control program is desired or normally possible once the ROM has been modified to reflect the steps of the control program therein The PCC also includes a ran dom access memory RAM 76 which is used to store the current status of lines and trunks in the concentrator 8 system and to store other subscriber service data The RAM 76 is also used for the storage of any system oper ating errors detected and for the storage of trunk ser vice requests if more than one request is pending at a given time Access to the ROM 74 and the RAM 76 is via a bidirectional processor bus 90 for the outputting of data to the RAM memory and via an input data multi plexer 88 for the inputting of data to the microprocessor 6
17. indicate the numeral or letter desired and the next three bits A4 A6 selects which of the four digits will obtain the new data A control signal from the output port 70 enables the display 106 to accept this data The display 106 is used to confirm receipt of commands manually inputted to the concentrator terminal The micro processor can also output system status and other data or request the user to input additional data via the dis play 106 The display unit 106 is further used to display error information discovered by the PCC 12 22 This infor mation is in the form of trouble numbers The trouble number is coded by the microprocessor 60 to allow maintenance personnel to look up the number in a trou ble number dictionary for an explanation of what type of error has been detected and what the suggested re pair procedure is The microprocessor 60 and control program perform the system error analysis that makes this possible see the System Operation section below The first trouble number of a detected error automati cally appears on the display 106 Subsequent trouble numbers are stored in the RAM 76 for later readout by maintenance personnel As mentioned above the display 106 also is capable of displaying other data Such data includes subscriber line traffic information or the contents of specific mem ory words in the RAM 76 Maintenance personnel can even enable the display to continuously read out a word from memory to enabl
18. is the start bit then the eight data bits are transmitted A parity bit for the eight data bits is then sent Finally a stop bit is sent to indicate the end of the byte To generate a complete data link message as de scribed above first a leader pulse is generated by the leader generator flip flop DL 42 as seen in FIG 7 This pulse indicates to the terminal intending to receive the data link message that the message is beginning Prior to loading of the first eight bit UART DL 10 word for parallel to serial conversion the PCC 12 22 presets the generator flip flop DL 42 to begin the leader pulse This first pulse is coupled to the FSK generator by the OR gate DL 44 At the end of this leader pulse time the TBRL line is brought high by the PCC 12 22 which enables the UART DL 10 to generate a start pulse and begin outputting the first parallel data word as a serial bit string The UART DL 10 automatically outputs a logic 0 start pulse as shown in FIG 12A on the TRO line which also resets the leader generator flip flop The start pulse lasts one clock time after which the UART DL 10 begins its data transmission The UART DL 10 serial bit string is then coupled through AND gate DL 40 and the OR gate DL 44 to the FSK generator called the FSK encode DL 12 in the same fashion as the leader pulse The TRE line locks AND gate DL 40 off when no word message is being trans mitted by the UART After all eight data bits have been outp
19. performs traffic studies of individual lines within a line group to identify a heavy user therein and it performs 10 20 25 w 36 real time studies of traffic usage over extended periods of time Periods of up to one week may be tested to determine busy hour activity When a heavy user is identified within a given line group the traffic engineer can decide to either move the user to another line group that does not have such heavy usage to thereby lower the incidence of link blockage or he may want to take the heavy user com pletely out of the concentrator 8 system It also pro vides the engineer with needed data as to the overall system performance and provides an indicator for fu ture system upgrading needs based on present system usage TRAFFIC COMMANDS The traffic commands are as follows 31 Total calls 32 Total blocked calls 33 Display busy hour traffic i e CCS 34 Set busy hour 35 Display near terminal trunk blocking 36 Display far terminal trunk blocking 37 Display near terminal link blocking 38 Display far terminal link blocking TABLE The traffic commands listed in table III provide the ability to display the total number of calls the total of blocked calls the busy hour traffic in a selected busy hour and the occurrence of trunk blocking Note that commands 31 34 36 and 38 are commands only avail able in the COT 10 Commands 35 and 37 are available in both t
20. providing an erroneous subscriber 5 service request on a continuous basis This happens for example in severe weather conditions when lines may be shorted together The administrative lockout com mand is provided to enable the restricting of a sub scriber who for one reason or another is to have his service discontinued for a contemplated short period of time e g for billing purposes Note that maintenance lockout of a line is automatically removed when the off hook detector goes off Maintenance lockout may also be removed manually Further administrative line lockout of a line only prevents outgoing calls originat ing from that subscriber That line can still receive in coming calls This line status remains in effect until it is removed manually The information retained in the RAM 76 status table for each trunk and line should also be mentioned at this point The overall organization of the RAM 76 in each terminal 10 20 was described above and is illustrated in FIG 4 The line status tables include a storage bit repre senting the present state of each of the following condi tions for each line 1 Line is idle 2 Line is busy loop current detected Line is ringing before loop current Line is reordering Line is stuck off hook detector always on Line placed out of service by system Line placed out of service manually Line not equipped Also retained is the identity of the link path and trunk 35 wh
21. that is has resumed operation and that it is in need of system status updating With the other terminal storing a duplication system status knowledge of the position of each switch in the switch matrix 14 24 in both termi nals is retained Thus the terminal that has not lost its power has the ability to transmit this system status data over the data link to the requesting terminal to thereby automatically bring this terminal back into an opera tional state If both terminals lose power system status is irre trievably lost 1 neither terminal knows which sub scriber line is switched onto a given trunk Therefore both terminals will clear down their line and trunk relays to insure starting at a known state 4 197 427 7 The concentrator 8 system further provides for sub scriber line or system trunk lockout If the PCC 12 22 cannot establish data link communication on a given trunk or if maintenance personnel have manually input ted to the PCC 12 22 that a trunk be taken out of ser vice then the trunk is locked out from being used again by storing these occurrences in the trunk status RAM 76 memory location corresponding to that trunk If the PCC 12 22 cannot establish or maintain data link com munication on a given trunk then that trunk status word is marked system maintenance out of service MOS Attempts to use this trunk for communication will be automatically made when all other trunks are busy Line lockout can how
22. to a specific one of said I O means switching means or means for communicating with said opposite termi nal a plurality of input ports each said port connected to a specific one of said I O means switching means or means for communicating with said opposite terminal output port select means and input port select means said output port select means under the control of said data processor and control program acting to select a specific output port for enabling data from said microprocessor to be outputted therethrough said input port select means under the control of said data processor and control program acting to select a given input port for the enabling of data from a specific input port to be coupled to said data processor 5 The line concentrator system of claim 1 further comprising a watchdog timer said data processor and control program including means for the periodic reset ting of said watchdog timer said watchdog timer fur ther including means when not reset by said data pro cessor and control program for timing out and causing an interrupt of said data processor said data processor being caused thereby to access the start of said control program 6 The line concentrator system of claim 5 wherein said data processor and control program further com prises means for periodically monitoring the state of said watchdog timer enabling said data processor to reset said watchdog timer before the occurrenc
23. unit These timing pulses are used as a micro processor 60 programming aid The longest time counted by the WDT 82 is 472 ms This time interval is used as the WDTO signal that generates a microproces sor 60 INTERRUPT to thus initialize or reinitialize the microprocessor 60 and restart the control program The WDT 82 is normally periodically reset by the micro processor 60 so that it never counts up to the 472 ms time interval and thus never generates an INTER RUPT Only when the microprocessor 60 gets stuck for example performing an erroneous program task or if it has halted will an INTERRUPT occur This fea ture therefore automatically frees the system at least temporarily from microprocessor 60 or control pro gram malfunctions Also on power start up since the microprocessor 60 has not begun operating the WDT 82 is never reset but is allowed to count until the 472 ms has elapsed creating a WDTO signal and a resultant microprocessor 60 INTERRUPT thereby automati cally starting up the system without the need for any maintenance personnel interaction More about the operation of this circuitry is given below in the System Initialization section of this specification As shown in FIGS 2 and 3 the state decoder 212 takes the 50 51 52 and SYNC outputs of the INTEL 8008 along with three lines A12 A15 from the address register 80 illustrated in FIG 2 and the 2 line to generate the above listed output signals The
24. 0 from the RAM and ROM memory units An address register 80 loaded by the microprocessor 60 via the processor bus 90 defines what storage location in mem ory 74 76 is accessed by the microprocessor 60 The PCC 12 22 also contains various input and out put ports 62 66 and 70 and associated port selection registers 64 68 and 72 for the outputting of data and control signals and for the inputting of data and the monitoring of control signals as will be described in more detail herein Referring again to FIG 1 before data from a PCC can be put out on a trunk for transmission to the other terminal s PCC or received from that other terminal it must pass through the data link transmitter receiver XMTR RCVR 40 in the COT 10 and the data link transmitter receiver 50 in the RT 20 These units are needed to slow down the data because the trunks are not designed with the ability to transmit information at the speed that the PCC operates at Only voice grade signals can be transmitted thereon The data link data is formatted as a serial bit string which is transmitted via an FSK frequency shift keying coding system The XMTR RCVR 40 50 accepts a plurality of parallel digital 8 bit words from the PCC 12 22 and converts these words into a serial data bit string The XMTR RCVR 40 50 further performs the opposite function for messages received by it from the other terminal In the present embodiment each message 5 20
25. 5 10 ms LEADER FIG _ 12A SERIAL DATA LINK MESSAGE 12B 40 U S Patent Apr 8 1980 Sheet 5 of 12 4 197 427 START FIG_ 5 SYSTEM INITIALIZATION OR RECOVERY PERFORM SCAN LINE DETECTORS FOR SUBSCRIBER SERVICE REQUEST AND QUEUE DETECTED REQUESTS PERFORM PTASK SCAN TRUNK LOOP CURRENT DETECTORS AND QUEUE DISCONNECTION REQUESTS PERFORM PTASK SCAN_RINGING DETECTORS AT REMOTE ONLY PERFORM PTASK SCAN KEYBOAD AND TTY ANO PROCESS DETECTED COMMANDS ENTER FREEZE MODE COMMAND INPUTTED FREEZE MODE COMMAND RESCINDED YES PERFORM PTASK PERFORM ALARM PROCESSING OR ON LINE DIAGNOSTICS U S Patent Apr 8 1980 Sheet 6 of 12 4 197 427 START FIG 56 5 WATCHDOG YES TIMER OVERFLOW BIT ON RESET WATCHDOG TIMER NO SET FLAG TO RECEIVE UART DATA AND SCHEDULE RECEIVE TIMEOUT No IN NEED OF MESSAGE PROCESSING PROCESS MESSAGE FROM FAR END MESSAGE RECEIVED MESSAGE REPLY REQUIRED FORMAT REQUIRED REPLY START LEADER AND SET TIMEOUT TIME SELECT A MESSAGE TO SEND ACCORDING TO PRIORITY OF REQUESTS START LEADER AND SET TIMEOUT TIME PERFORM REQD PRIMARY TASK PERFORM REQ D SECONDARY TASK OCCURRED HAS A SECONDARY TASK TIMEOUT OCCURRED NO TIMEOUTS RETURN 4 197 427 Sheet 7 of 12 U S Patent
26. 51404 501915 v6 SNE LYOd LNANI 11 SS O Res 4 197 427 Sheet 3 of 12 U S Patent Apr 8 1980 913 96 sna 1100 OL 1304 1141 0 NOYA LOM 13834 28 300934 31 165 95 802 10 4 2 812 300930 44 NI 8 135 5 __ _ 4 sng 29 LYOd LNdNI OL 1 535709 ONIWIL on _ 34 09 nv 543151935 9 18 21901 33151933 3 INIL ALINHLIYY 406 8008 09 gt COCO eee ee eee U S Patent Apr 8 1980 Sheet 4 of RAM MEMORY MAP START BIT TRUNK STATUS LINE STATUS MISC OTHER SYSTEM STATUS BITS DISCONNECT QUEUE SERVICE REQUEST QUEUE SWITCHING MATRIX STATUS SCRATCH PAD AND POINTER STORAGE 8 DATA BITS at 000 BAUD 12 4 197 427 2048 WORDS OF 8 BITS EACH FIG_4 PARITY STOP BIT cc orn 5 6 St aS Seer 48215141516 TYPICAL DATA WORD BYTE FIG
27. C are de coded in the state decoder 212 to create in a conven tional manner many of the microprocessor 60 control signals These include the control signals defined as the IN OUT 1 OUT 2 and WRITE EN ABLE WE signals The various registers in the INTEL 8008 include the input output register 202 the arithmetic and logic unit 204 which implements the addition subtraction and logic operations called for by the instruction set and the accumulator memory and program counter registers 206 which among other functions provides temporary storage for data being operated on and temporary stor age for program and subroutine addresses The instruction decode and control unit 208 provides the logic for manipulating the registers 202 206 and the arithmetic unit 204 based on the type of instructions read in and decoded by the INTEL 8008 The timing is regulated by a clock generator 210 that operates from an external two phase clock 86 see FIG 2 It should be noted that in the present embodiment the two phase clock 86 comprises two crystal oscilla tors wherein one is the backup of the other Therefore if one oscillator has a frequency variation that is more than minor circuitry in the two phase clock 86 unit automatically switches in the other oscillator The Watchdog Timer WDT 82 is a counter that generates timing pulses by counting increments of time defined by an input clock pulse from the two phase clock 86
28. EAR ALL FAR END TROUBLE NUMBERS 057 CLEAR ALL ALARMS 1 XXX CONNECTION REQUEST 2XX XXX DISCONNECTION REQUEST The connection and disconnection request messages are formatted slightly differently A larger amount of data needs to be transmitted during such messages since the connection request requires not only the identity of the line requesting service and the trunk intended for coupling the line to the opposite terminal but also the switch path chosen by the originating terminal for cou pling the line to the trunk As described above a two stage switching network is used so that both a line link switch path first stage and a trunk link switch path second stage must be identified In a disconnection request only the line number and trunk number need be transmitted since at this point both terminals would have retained the line link and trunk link switch path data corresponding to the given line number and trunk number Table lists the various commands available to main tenance personnel or other operators of the system SYSTEM OPERATION COMMANDS 0 Abort 1 Single display of memory location contents 20 25 These commands are divided up into 4 classes the sys tem operation commands line commands trunk com mands and traffic commands The traffic commands will be described below in the next section Commands are entered into a terminal via numerical keys on the keyboard 110 In the present embodimen
29. LSER 8 SW DECODE MATRIX 42 52 L 32 PULSER amp SW DECODE 42 52 1 16 l T 9 6 8 LINES 1 sw IN AS MATRIX ABOVE 16 26 8 T 16 le L 48 16 PULSER SW DECODE 42 52 L 49 i 6 8 2 MATRIX i 8 L 64 6 PULSER 6 OUTPUT DATA BUS 98 AND SW DECODE SW MATRIX SELECT LINES 42 52 ____ IN FROM PCC 12 22 4 197 427 Sheet 10 of 12 U S Patent Apr 8 1980 mn 201193136 MS 594 40545 1 9 86 viva 1 01 SIXv A 123136 5 03 SLINOUIO 2 1 211 301 vivo 19101 8 108170 IA IX X 0 ANIOd 01 LAO eee Sheet 11 of 12 4 197 427 Apr 8 1980 U S Patent 63 Ol 9d 82 32 3 31 1 3 LOWSY 341426865 094 SLINOUIO 3 3734 MS X 1 WO 4 INIT OL S LINDMIO CEE 9 SUNIY 43614258015 40193130 woud WL NNOD
30. Office Terminal Line Interface The central office terminal 10 line interface 18 is similar in function to the RT 20 line interface 28 in that it detects subscriber requests for service incoming from the C O 2 in this case and enables this information to be accessed by the PCC 12 The type of detection used and the resultant switching performed may not be the same however Although a two wire detection line interface similar to that in the RT 20 may be used depending on the needs of 2 normally a three wire system including a lead is used In such a three wire sys tem detection is different in that the detector for the COT 10 line interface 18 is not switched in and out of the line path but remains continuously attached Also the concentrator 8 system by means of a reorder signal in the line interface 18 is enabled to indicate to subscrib ers having calls incoming via the C O 2 that all paths through the concentrator 8 are in use This signal is also designated as the All Trunks Busy signal ATB It therefore indicates to the subscriber that he should hang up and try again later FIG 11 illustrates an embodiment of one of the three wire line interface 18 P C boards As shown in FIG 11 a plurality of subscriber lines A X are sensed for service requests In the present embodiment sixteen lines are serviced on each line interface 18 board with two or three wires on each line Consequently for ex ample four
31. Reinitialize near terminal 52 Display far terminal s trunk 19 Reinitialize far terminal status 21 Enter freeze mode 53 Display trunk s line number 22 Remove freeze mode 54 Place trunk in service 23 Disable communication trunk 55 Release 1 path switching 56 Place trunk maintenance out of 24 Enable communication trunk service switching 57 Remove trunk maintenance out of 25 Select line for forced path service 26 Select trunk for forced path 27 Select link for forced path 28 Clear forced path selection 61 Select memory bank at far terminal which will be addressed in the next command 62 4 197 427 33 TABLE Select the address 0 3778 in memory bank The address contents will be sent from far terminal to be displayed at near terminal Redisplay contents of the last address that was displayed in command 62 Display trunk number that is currently in use for data communications been detected by the terminal wherein that display 106 is located Trouble numbers generated at the far termi nal are not automatically shown before inputting of commands is enabled The trouble number displayed on display 106 and all other trouble numbers which may have been queued in the near terminal s RAM 76 mem ory must be read out via this display unit or via the TTY interface 108 When a given terminal is ready to accept a command from the key
32. al status of all trunks in said system to be periodically checked 22 The line concentrator system of claim 20 wherein said data link means further comprises frequency shift keying transmission and reception means said transmission means comprising 1 means for the parallel to serial conversion of a digital data word inputted from said processor means into a serial bit string 2 means for slowing down the data rate of said inputted data word to enable transmission of said data over a voice grade trunk 3 means for generating a leader pulse and 4 means for converting said leader pulse and said data word into said frequency shift keying for mat said receiver means comprising 1 leader recognition means 2 means responsive the recognition of receipt of a leader pulse by said leader recognition means for converting a subsequently received data word in frequency shift keying form into a digital serial bit string and 3 means for serial to parallel conversion of said bit string such that the resultant data word can be outputted to and read by said processor means 23 The line concentrator system of claim 22 wherein said data word comprises three bytes of data each byte having a plurality of information bits therein said first and second bytes each including a start bit a stop bit and a parity bit said third byte comprising a checksum of the data contained in said first and second bytes said parity and checksum
33. and powerful line concentrator system that is cost competitive in compari son with the alternative of adding further trunk paths while allowing substantial improvements in operation over prior concentrator devices to be made The pres ent invention allows full system check out to be made at either the central office unit or the remote unit of any system faults or errors which have been automatically discovered by the unit Full control over system opera tion and access to trouble codes and systems status is available to maintenance personnel at both the central office terminal and at the remote terminal The inven tion also provides other unique features in the areas of real time maintenance of trunks and lines intercommu nication between the central office terminal and remote terminal over idle trunks and other advantages as de scribed herein Patents of general interest include U S Pat No 3 980 839 issued Sept 14 1976 a maintenance monitor for telephone switching systems and U S Pat 5 20 25 35 55 60 65 2 No 3 917 908 issued Nov 4 1975 a call concentrator control system SUMMARY OF THE INVENTION The present invention consists of two units or termi nals a central office terminal and a remote terminal interconnected by up to 32 trunks Both terminals con tain circuitry that function almost identically The pres ent invention is designed to switch up to 128 lines onto a maximum of 32 trunks Eit
34. ating the identity of said selected switch path and said idle trunk to the terminal opposite the terminal having said service request ing line the processor means in said opposite terminal enabled thereby to generate a switch path corresponding to said selected idle switch path such that the opposite end of said selected idle trunk is connected to a line in said opposite terminal corresponding to said service requesting line 2 The line concentrator system of claim 1 wherein said data processor comprises a microprocessor 3 The line concentrator system of claim 1 wherein said data input output means in each said terminal com prises I O means for maintenance personnel interaction said means comprising a keyboard for the manual inputting of data and com mands to said processor means means for displaying data from said processor means for external readout means for interfacing a teletype to said processor means for inputting of data and commands thereto and for printing out data on said teletype and 4 197 427 39 means for visually and audibly indicating system alarm conditions 4 The line concentrator system of claim 3 wherein said data input output means in each said terminal com prises means for selectively enabling data transfer with said I O means and with said switching means and means for communicating with said opposite terminal said means comprising a plurality of output ports each port connected
35. be used at so high a switching frequency The communication scanning process at the COT 10 consists of cycling through each available trunk looking for the leader generated by the RT 20 To monitor a 20 25 30 35 45 55 60 65 24 specific trunk the PCC 12 in the COT 10 causes the relay T30 in trunk interface 16 corresponding to the chosen trunk to be pulled in This enables any communi cation on that trunk to be coupled to the XMTR RCVR 40 in the COT 10 and thereby to the PCC 12 The PCC 12 allows 30 milliseconds in which to detect the leader pulse generated by the RMT 20 on the chosen trunk If leader is not detected during this 30 millisecond time period the chosen relay T30 is re leased by the PCC 12 and the next trunk in sequence is tested by the PCC 12 in the same way As can be seen if there are 32 trunks in operation between the RT 20 and the COT 10 approximately 0 9 seconds are re quired for the COT 10 to cycle through all trunks look ing for leader When leader is detected by the COT 10 the COT 10 waits up to 3 seconds for the expected null message If the null message is received by the COT 10 a received message is sent to the RT 20 over the same trunk The COT 10 then waits 128 milliseconds for a further response from the RT 20 However if a timeout or a message error is detected the COT 10 will resume scanning for a leader on the remaining trunks Should a null message f
36. board 110 or from a teletype unit con nected to the terminal that terminal can be instructed to perform as desired any of the operational traffic line or trunk commands All commands inputted to the terminal must be followed by an asterisk before the terminal will respond to the command Almost immediately after the command is inputted to a terminal an acknowledgement of the command is provided by the terminal in the form of one of five letters A F which are displayed on the display 106 An A indicates that all commands are cancelled This letter disappears from the display 106 after 2 or 3 seconds A B indicates that the system is busy with call processing Commands will be processed when the system has fin ished this higher priority processing Command pro cessing is signified by the display changing to a C indi cating that the command has been completed success fully or an A indicating that the terminal cannot pro cess the command An E indicates that the terminal expects a data entry on the keyboard 110 to follow the command entry For example a command requesting line status data must be followed by the line number An F is displayed to indicate that this terminal is in a freeze mode Only after the freeze mode is released will the display go blank During a freeze mode no commands are processed by the PCC except the remove freeze mode command Referring to Table II one can see that many of the commands listed are sel
37. by the receiving PCC 12 22 using the data received from the first two bytes If there is no match again the PCC 12 22 will request a retransmis sion of the message A request for retransmission is initiated by the PCC 12 22 whenever a message has been incorrectly re ceived If a given trunk continues to create data link 20 25 30 40 45 50 55 60 65 22 transmission errors e g after 32 erroneous messages have been received in a span of 256 messages the trunk is defined to be out of service by the PCC 12 22 There after only if all other trunks are busy will the PCC 12 22 attempt to use this trunk again at least until mainte nance personnel checkout of the trunk has been per formed Note also that if all trunks are busy no data link is needed since no new switched path is available for a line requesting services Only after a trunk goes idle due to a call disconnection will data link communication be reestablished The XMTR RCVR 40 50 may also contain a special test trunk which has access to the internal data link bus DL 90 via a second isolation transformer DL 70 for remote monitoring of the data link communication This system access is totally separate from the keyboard 110 or the teletype interface 108 of the PCC 12 22 This test input however does not give any ability to interact with the system only monitoring is allowed Remote traffic monitoring or the remote checking that the sys tem is s
38. ce personnel said subsequent trouble numbers means for maintenance personnel interaction with said terminal including means for selection and execution of further maintenance routines and including means for enabling the display of trouble numbers generated at said opposite terminal and means for enabling said maintenance personnel to freeze the operation of said system to enable re placement of faulty system components without damage to said system resulting therefrom 18 The line concentrator system of claim 1 further comprising means in combination with said micro processor and control program for system operators to lockout a selected line or trunk such that service re quests from a said locked out line is not processed by said system and such that said locked out trunk is not used as an idle trunk for switching a subscriber service request thereon 19 The line concentrator system of claim 1 further comprising traffic analysis means said means including first counter means for maintaining the current count of incidences of trunk blocking and second counter means for maintaining the current count of incidences of link blocking 20 A line concentrator system for the interconnec tion of a plurality of lines over a lesser plurality of trunks including a terminal at each end of the concen trator system said system comprising means in each terminal for the detection of a system service request initiated by a line con
39. ch decoder 42 52 Each 168 matrix 510 has its own pulser and switch decode 42 52 A switch matrix select pulse originating from the PCC 12 22 switch matrix select unit 102 is used to select the desired one of the units 42 52 Thus only one matrix 10 is selected at a given time for relay switching With six switch matrices needed to concentrate 64 lines into 16 trunks as illus trated in FIG 8 six separate select pulses are generated by the switch matrix select unit 102 of the PCC 12 22 Referring again to FIG 9 in each switch decoder 42 52 there is an X axis select decode 530 and Y axis select decode 532 These units decode data inputted on the output data bus from the PCC 12 22 on bits 2 for the X axis and bits 3 6 for the Y axis Decoder 530 has eight output lines and decoder S32 has sixteen They control which one of the eight X axes X1 X8 and which of the 16 Y axes Y1 Y16 is selected The eight outputs of decoder S30 are fed to their respective X axis lines via eight SCR switch select circuits SCR X1 SCR X8 will be explained below the de coder 830 output line selected by output data bus 98 bits 2 causes only the one corresponding X axis line to be actuated Similarly the output line of decoder 32 se lected by bits 3 6 determine via a respective SCR Y1 SCR 16 line only the one corresponding Y axis line to be actuated in the matrix 10 Thus each matrix X Y cross point is separately accessibl
40. cuits Thus only after this 100 milli second time out has occurred will a matrix 510 relay switch path be changed When a secondary task has been completed the con trol in the PTASK is again transferred back to a point in the PTASK prior to where a communication service test is made If no time outs have been detected in a pass through the PTASK program control is returned to the main control cycle at the point where the cycle left off C System Commands and Interterminal Messages Table I lists the various messages which are possible between the two terminals in the concentrator 8 system As can be seen from table I each message is composed of two bytes of message identifying data with a third byte used as a check byte for insuring that the message has been properly transmitted The format of a message was discussed above in the data link section of this specification and is illustrated in FIG 12 Many of the messages listed in the table have already been discussed Most of the others are self explanatory Note that the second byte in many cases is used for identifying a par ticular address line number trunk number or other specific identifying number needed to complete under standing of the message by the terminal receiving the message For example if one terminal finds a line out of service it will send a message to the far terminal to place line out of service by sending 051 in byte and by sending the identity of t
41. d forth until all previously busy switching relays have been cleared Thereafter table refresh from the COT 10 is performed on the RT 20 to insure that both terminals have the 15 20 25 30 40 45 50 60 65 4 197 427 26 same status information with regard to the equipment available and operational at each end of the concentra tor 8 system B Control Cycle Operation The control cycle program of each terminal 10 20 of the concentrator 8 system is illustrated in flow diagram form in FIG 5 Preferred means for implementing this control cycle program is by means of a ROM 74 in each terminal The ROM 74 is programmed to give a prede termined output either a logic 1 or a logic 0 on a plural ity of data lines as a function of the address applied to the ROM 74 on its address lines These data line states are what instruct and supervise the microprocessor 60 in its manipulation of the various elements in its PCC and thus in the terminal An essentially identical pro gram is stored in each terminal 10 20 The control cycle program is the system controller of each of the termi nals 10 20 in the concentrator 8 system As described above the first function that is per formed by the control cycle program after it is accessed by the microprocessor 60 in an interrupt mode is the performance of its system initialization or recovery routine Once this routine has been completed the main portion of the control pr
42. diagnosis thereof Based on the fault detected and diagnosed by such routines a trouble number is formatted and placed in a storage queue in the RAM 76 for subsequent display 4 197 427 37 the display 106 in response to a maintenance person nel command Some diagnostic routines also include fault recovery means wherein the terminal is caused to be reconfigured and to recover from the detected fault if possible The terminal restores normal operating functions by rerout ing around any detected existing fault condition Fur ther the terminal s PCC 12 22 transmits the fault de tected to the far terminal to enable that terminal to also reroute its functioning around the fault e g to also place the defective line or trunk out of service One example of fault recovery is when a trunk has been automatically placed out of service due to too many data link transmission errors When all other trunks are in use the control program will cause the PCC to re attempt a data link communication over this out of service trunk If the problem has corrected itself the trunk will be put back into service The trouble numbers are formatted to aid in the trou ble shooting by maintenance personnel of faults de tected by the system Written maintenance procedures are provided which correspond to the trouble numbers indicated by the terminal and are written primarily to minimize the need for maintenance personnel to have extensive trainin
43. e as illustrated in FIGS 2 and 3 When information is to be read from the RAM 76 to the microprocessor 60 only the address need be given the WE line is not strobed Writing information into the RAM 76 how ever does require that the WE line be strobed As shown in FIG 4 the RAM 76 is organized into different sub blocks including blocks of storage space for trunk and switching matrix status a scratch pad for temporary storage of numbers being operated on a queue for the storage of detected service requests that have not yet been switched through and various pro gram pointers for enabling the microprocessor 60 to return to routines that have been temporarily stopped in order to perform routines of higher priority 3 The ROM Subsystem typical non destructive read only memory ROM 74 and memory addressing scheme is also shown in the system block diagram of FIG 2 The ROM 74 is addressed in the same way that the RAM 76 5 10 15 20 25 30 35 40 45 50 55 60 65 10 is addressed except instead of using just the address register 80 the ROM 74 additionally uses a ROM chip select register 78 The addressing scheme for both the ROM 74 and RAM 76 memories is set up so that every memory location whether it be in the ROM 74 or the RAM 76 is uniquely addressable by the microprocessor 60 The ROM 74 contains all the stored programs for the line concentrator 8 Details of this control cycle pro
44. e microprocessor The microprocessor is capable of performing arithmetic and logical operations as well as control and sensing functions The input out put functions of the processor common control are performed via a plurality of input and output ports and their related control circuitry under the overall control of the microprocessor and control program Finally maintenance personnel interaction with a terminal is via the terminal input output means of the common control unit This means includes a keyboard for inputting of commands or data requests a four digit hexadecimal display for displaying data and trouble codes a teletype interface and various alarm indicators Monitoring of the interterminal communications via the data link is also possible at a distance from the concentrator system as will be described herein The line and trunk interface units provide detection of subscriber service requests trunk idle status data link switching from one idle trunk to the next etc A trans mitter receiver in each terminal allows the processor common control units to converse with each other via data link path on an idle trunk The data is transmitted as a serial bit string and at a slow enough bit rate such that no special high speed transmission characteristics are needed for the host trunk Accordingly it is a principal object of the present invention to provide a line concentrator system that takes advantage of the inherent flexibili
45. e of said watchdog timer time out 7 The line concentrator system of claim 1 wherein said control program means comprises a non eraseable read only memory means including a plurality of mem ory locations having defined therein a list of control instructions for manipulation and control of the state of said data processor 8 The fine concentrator system of claim 1 wherein said means in each terminal for the detection of a system service request initiated by a line connected to that terminal comprises line interface means including a plurality of off hook detectors for detecting and output ting a detection signal when the line operatively con nected thereto is requesting service each said detector operating to detect a voltage or current change on its associated line said line interface means further including a line sta tus multiplexer said multiplexer selectively en abling said processor means to readout the detec tion signal from each one of said off hook detec tors 9 The line concentrator system of claim 8 wherein said line interface means further comprises reorder generator means including means for gener ating an all trunks busy signal telay means including a plurality of relays and 10 20 25 30 35 40 45 55 65 40 means for selectively actuating one of said plurality of relays under the control of said processor means said selected relay acting to switch onto a line requesting service
46. e the monitoring of data stored at that memory location as it changes Maintenance per sonnel can control what is displayed by means of the keyboard 110 or the teletype 108 as further described below The keyboard 110 is the main means of maintenance personnel input to and control of the line concentrator 8 system Using the keyboard 110 maintenance person nel can request that system diagnostics be performed request that other special command routines be per formed by the microprocessor 60 e g request a traffic analysis routine request system status information tell the PCC 12 22 to lockout a line if it is malfunctioning force the switching of a particular line to trunk path and other functions The keyboard 110 is a standard telephone push but tom unit whose outputs are digitized and coupled to one of the input ports 62 Each time a push button is pressed the number is displayed on the display 106 to verify that the PCC 12 22 has correctly received that input Access to the PCC 12 22 via the keyboard does not interrupt system operation The microprocessor 60 fits in any keyboard request within normal system cycle periods The microprocessor 60 only acknowledges maintenance personnel requests when it is finished with higher priority subscriber service operations In the present embodiment once a command has been entered the keyboard 110 if an appears on display 106 it indicates that the command is not ac
47. e via the decod ers 30 S32 based on which of the X and Y axis lines are selected The means for driving the specific SCR s and corre sponding axes as selected by the decoders 530 and 32 is performed by a DC current pulse generated by a pulser 534 This pulse is fed to all of the SCR s of which there are a total of 24 in each switch decoder 42 52 Only the X and Y SCR s selected by the decoders 530 and 532 allow the pulse to be fed through to the switch matrix 10 Since only one cross point corresponds to each combination of selected X and Y axes only the one relay situated at this cross point will be actuated when a DC current pulse is coupled onto these axes No other relay will be actuated As mentioned before each set of X axis decoders and their corresponding 16 8 switch matrix 510 is uniquely enabled by a switch ma trix select signal generated in the PCC 12 22 This select signal activates the desired pulser S34 and thereby a selected relay cross point One feature of the present embodiment is that when a DC current pulse is applied to the selected X and a Y axis switch rows by the pulser S34 this pulse causes any relays on that particular axis other than the selected cross point relay which were in an actuated state to switched into a non conducting or released state This scheme thus provides for automatic disconnection of any erroneous switch paths that may have been set up in the past in the s
48. ed means at the selected terminal for randomly selecting another said trunk for generation of a leader pulse thereon when after a specified period of time no reply is received from said other terminal and for 10 20 25 35 45 55 65 44 randomly selecting further trunks until said reply by said opposite terminal has been detected 27 The line concentrator system of claim 20 further comprising recovery means for enabling a terminal that has lost system power and thereby system status data to regain said data from the opposite terminal when said data has been retained therein said means comprising means in combination with said data link means in said terminal not experiencing a power failure for transmitting its system status data including the status of its switching means and equipment status to the opposite terminal said opposite terminal including means for inputting said data into corre sponding storage locations in said memory such that the system status stored in each terminal s said memory becomes identical to enable thereby the re establishment of system subscriber servicing operation
49. en a line is being coupled through the concentrator 8 system Note that a plurality of bits of storage are re quired for this latter data for each line Trunk status tables include a storage bit representing the present state of each of the following conditions for 40 each trunk 1 Trunk is idle 2 Trunk is busy loop current detected 3 Trunk is ringing before loop current on term call 4 Trunk is pending loop before loop on orig call 45 5 Trunk is pending disconnection 6 Trunk placed out of service by system 7 Trunk placed out of service manually 8 Trunk not equipped Also retained is the identity of the line presently 50 being coupled through to the given trunk Again this requires a plurality of bits of storage for each trunk D Traffic Analysis Table III lists the various traffic commands available 55 in the apparatus of the present invention The control cycle program performs the data acquisition needed for traffic analysis as part of its on line diagnostics routine The information desired is stored in allocated memory locations in the RAM 76 Basically traffic analysis ena 60 bles a traffic engineer to determine system usage quickly For example this routine enables a determina tion of which line groups with a particular switch ma trix are experiencing heavy link blockage due to heavy use by subscribers attached to that switch matrix There 65 are eight line groups in a 64 line system The routine
50. en time in each terminal An example of a trouble number displayed on the 4 digit display 106 would be C001 The trouble number would indicate that there is no loop current detected on an originating call from subscriber line No 1 Another example would be D210 This trouble number indicates that the remote terminal 20 detects loop current on idle trunk No 10 Finally the concentrator 8 system is designed to facilitate maintenance checkout and fault correction without affecting the otherwise normal operation of the system On line diagnostics can be performed mainte nance personnel communication with both terminals either from the RT 20 the COT 10 or remote from both terminals via a TYY unit conventionally tied to either unit by a separate telephone line can be per formed This interaction can even take the form of forc 20 25 35 40 45 55 60 65 38 ing a selected line to trunk path The TYY can also have any data appearing on the display 106 printed on the terminal thereby enabling remote readout of trouble numbers traffic data etc Lastly the freeze mode is provided to enable certain plug in units to be replaced without causing subscribers using the system to have their service interrupted The present embodiment of this invention is to be considered in all respects as illustrative and not restric tive the scope of the invention being indicated by the appended claims rather than by the foregoing descrip
51. erminals Also display 106 displays the con tents of electronic peg count registers when a traffic command is made In the present invention these regis ters count consecutively from 0 to 9999 and then auto matically reset to 0 These registers cannot be reset by external command E System Maintenance and Fault Diagnosis On line diagnostic routines are periodically accessed by each terminal 10 20 These routines automatically check conditions such as 1 ROM memory checksums for each 2000 bit mem ory chip a checksum is kept to detect if any bits of data in that chip have somehow been lost 2 RAM 76 operation checks a set bit pattern is loaded into each memory location periodically and then read out again A mismatch in the read out pattern indicates a malfunction of that memory location 3 Maintenance Monitor 100 tests signals outputted from output ports 66 and 70 in the PCC 12 or 22 are wrapped around and fed back to the micro processor 60 via this monitor 100 to check for data mismatches One chunk of diagnostic routine is performed during each accessing of the routine by the control cycle pro gram If a fault is detected a trouble number is gener ated based on a diagnosis of where the error is and what plug in subsystem should be replaced to rectify the problem Other on line diagnostics may be called by mainte nance personnel or automatically by the control cycle program in response to a detected fault for
52. esponse to the subscriber service request PTASK test sequence is shown FIG 5B If the PTASK determines that UART DL 10 message processing is enabled it next tests to see if a message byte is to be sent to the opposite terminal or if a mes sage is to be received from the opposite terminal Each terminal is enabled alternately to have the opportunity to transmit a message Consequently if a message recep tion has just been completed the terminal receiving the message is enabled to control its UART to transmit a next message the contents of the message depending on the priority of messages waiting to be serviced in that terminal If a message is to be sent to the far terminal the PCC 12 22 loads a byte of data into the UART The UART DL 10 then automatically is enabled to complete the message transmission The PTASK then tests to see if this is the last byte to be transmitted in a given message Recall that three bytes of data as seen in FIG 12B comprise a complete data link message If there are one or more additional bytes to be sent these bytes are sent after a time out time has been sensed during 4 subse quent pass through PTASK If it is found that the pres ent byte being sent is the last byte in the message the PTASK sets a flag to indicate that the PCC 12 22 asso ciated therewith is to receive data from the opposite terminal at the next time out time which is set in con junction therewith Again as see
53. ests and switch disconnection requests The PCC 12 22 decides what information is to be trans mitted to the other terminal and relays this information in eight bit data word bytes to the data link transmit ter receiver 40 50 the XMTR RCVR 40 50 parallel to serial conversion of this eight bit word and FSK frequency shift keying translation is performed The XMTR RCVR 40 50 generates a leader pulse for each message It further generates a start pulse a stop pulse and a data parity check bit for each byte of data in the message to insure that the data word is accurately transmitted Each XMTR RCVR 40 50 also has the ability to receive FSK information and translate that into a parallel word for reception by the PCC 12 22 Also included in the receiving circuitry are the circuits that check to make sure that the various flags and parity bits have been received in their proper form In the present embodiment a data link message is formatted as a series of three bytes of data with a leader header pulse at the beginning of the message To elimi nate the need for a response from the terminal receiving the message as a verification of correct receipt of the message the third byte is composed of an algebraic check sum of the data bits transmitted in the first two bytes of the message This check is in addition to the parity check generated for each byte of data FIG 12B illustrates a typical data link message wit
54. ever only be done manually by maintenance personnel Note that no E coils need to be pulled as was required in older electromechanical sys tems To manually lockout either a line or a trunk one need only load in the number of the desired line or trunk to be locked out into the PCC 12 22 via keyboard 110 along with the lockout command This lockout ability is needed especially during bad weather conditions when lines shorting together look to the concentrator 8 sys tem like a service request that never goes away thus tying up the system as a result In addition with the PCC 12 22 the concentrator 8 can automatically bring the malfunctioning line back into service if it detects that the short has gone away This function is entirely control program initiated Reference is suggested to the System Operation section of this specification for fur ther details regarding the above and regarding the vari ous other command functions available for externally controlling concentrator 8 operation A The Processor Common Control As impliedly stated above the processor common control both in the COT 10 and in the RT 20 normally controls virtually every aspect of concentrator 8 system operation Relay switching commands trunk status storage operations subscriber line scanning in general almost all functions are controlled in the present inven tion by these PCC units 12 and 22 Since this aspect of the concentrator 8 is the most pervasive t
55. ext message time curs When a service request is detected by the PCC 22 as described above it sends to the other terminal this fact and including the selected switch path and trunk chosen by the PCC 22 to complete the requested call path This is assuming a data link already has been established If the other terminal has not received an error free mes sage a request that the message be retransmitted is sent back If the message is error free both of the 5 switch off of the trunk used as the data link and enable the line requesting service to be switched onto this trunk or onto another chosen trunk depending on traffic load parameters Both terminals then switch to the next idle trunk to attempt the reestablishment of the data link 4 197 427 5 on this new trunk Stored trunk status tables in each PCC 12 22 are what the terminals use to find which trunks are idle and which are presently in use If more than one idle trunk exists an algorithm is performed by each terminal to choose which of the available trunks will be used to reestablish the data link The data link switching circuits described above and trunk status indicators comprise the trunk interface 26 in the RT 20 and the trunk interface 16 in the COT 10 Ringing detectors 34 are also provided at the RT 20 to verify a ringing signal from the COT 10 The switching of a line requesting service to an available trunk is per formed in a two stage switching matrix 24
56. f explanatory The abort command clears the inputs and stops execution of any command in progress An A is displayed on the display 106 in response to this command for a period of about 2 seconds If a 1 3 or 4 command is inputted a specific memory location may be accessed after entry of such a command the memory address desired must also be inputted If continuous display of a memory location is desired the display 106 shows the contents of the speci fied memory location as it changes state in real time To enable maintenance personnel acting at one termi nal to find out the present operating state of the terminal at the other end of the concentrator 8 system a 5 com mand enables the system operator to display at the near terminal any trouble numbers which may presently exist at the far terminal As can be seen a memory location at a far terminal may also be displayed on the near termi nal s display 106 via commands 61 63 Three important memory locations in each terminal that are accessable via the above commands are the locations which store the terminals major alarm status 62 63 65 15 20 25 30 35 40 45 55 65 minor alarm status and hardware alarm status The alarm and power unit 104 in each of the PCC s 12 22 keeps track of many of the concentrator 8 system condi tions If one of these conditions is found to be faulty in the alarm processing section of the control program thi
57. for the XMTR RCVR 40 50 which needs only six the tele type interface 108 which only needs three and the maintenance monitor 100 which also only needs three The various units that are accessed and controlled by the output ports 70 include the display 106 one line the WDT 82 reset one line the teletype interface 108 two lines and the XMTR RCVR 40 50 four lines The PCC 12 22 also contains eight input ports 62 of eight bits each These input ports 62 receive information from both internal PCC 12 22 subsystems and from subsystems external to it The output bus of the input port 62 is the input port data bus 94 which couples selected inputted information to the input data multi plexer 88 and thereby to the microprocessor 60 The means for selecting which input port receives and passes information to the input port data bus 94 com prises an input port select 64 This unit operates simi larly to the output port select 68 in that it decodes three input lines A9 A11 from the address data bus 96 into eight output lines for individual input port selection The various units that input data via the input ports 62 include the keyboard 110 the maintenance monitor 100 and the teletype interface 108 which again are internal to the PCC 12 22 and trunk interface 16 26 status line interface 18 28 status an input data bus an output data bus fed back from an output port 66 and XMTR RCVR 40 50 status and data all of which orig
58. g or experience in the repair of the concentrator 8 system All trouble shooting procedures are designed to detect and replace defective plug in units Consequently once a fault has been localized to this extent maintenance personnel need only replace the faulty unit to return the concentrator 8 system to its full operating status To further make repairs easier the concentrator 8 system is designed to maximize the inter changeability of plug in modules All modules are iden tical between the COT 10 and RT 20 except for those relating to the line interface ringing detectors and auxiliary power functions Multiple problems can occur in more than one plug _ in unit and can cause the above described replacement practice to be ineffective If multiple problems are sus pected it may be necessary to replace all plug in units listed in the repair procedure for the specific trouble code As mentioned above to further facilitate fault diagnosis certain on line diagnostics are also provided which are enabled to be performed only at the request of the maintenance personnel Note that both major alarms e g power failure or loss of communication and minor alarms e g single line or trunk faults detected by the maintenance pro gram and placed out of service are examples of prob lems that also generate a coded trouble number Storage locations in the trouble number queue provide for a maximum of 10 trouble numbers to be stored at any giv
59. g the various trunks available in the concentrator 8 system Normally after each subscriber service re quest is processed and a call is switched through the concentrator 8 system the data link path is switched from the present trunk being used to a new trunk if a trunk is available This is to provide a means for check ing on a periodic basis the functioning of all trunks available in the concentrator 8 system Maintenance personnel may wish to prevent this random switching of the data link between available trunks during certain diagnostic testing or other maintenance testing of the concentrator 8 system Also available for maintenance personnel check out of the concentrator 8 system is the ability to command a specific path to be forceably switched through both terminals in the concentrator 8 system This function is performed via the commands 25 28 which enable a line a trunk and switch links to be selected for the forced path The line and trunk commands listed are provided for two purposes First they enable the present status of a given line or trunk to be displayed for maintenance personnel evaluation Secondly these are maintenance lockout and administrative lockout commands available 4 197 427 35 to lockout any line and maintenance out of service commands to lockout any trunks Maintenance lockout is necessary to prevent the PCC in a given terminal from recognizing an input from a line which may be malfunctioning and
60. h a leader pulse of 5 10 ms A complete 3 byte message is transmitted in approximately 40 ms at 1000 baud The key device in the XMTR RCVR 49 50 for the performance of XMTR RCVR 40 50 functions is the UART DL 10 universal asynchronous data interface circuit For further information on this device consult 20 25 35 40 45 50 60 65 20 the Texas Instruments data sheet for the TMS 6011 UART published on Mar 15 1973 This UART DL 10 provides serial to parallel and parallel to serial conver sion the ability to operate at a variable baud rate the ability to operate with different word lengths of up to eight bits per word the ability to generate a stop bit and a parity bit along with other diagnostic flags and other functions An embodiment of X MTR RCVR 40 40 is shown in FIG 7 When a PCC 12 22 wishes to transmit data on the data link it loads an eight bit data word from the lines into the UART DL 10 buffer register It then loads this information out to the UART DL 10 parallel to serial converter by strobing the TBRL line via the PCC 12 22 strobe output port 70 The UART DL 10 then automatically begins the parallel to serial conversion of this eight bit word Timing is controlled by an input clock pulse A typical data word byte as outputted by the UART DL 10 is illustrated in FIG 12A There are eight bits of data in each byte and three UART control bits for a total of eleven The first bit
61. he COT 10 and RT 20 as shown in FIG 1 The trunk interface 16 26 provides two functions As illustrated in FIG 6 it includes non latching relays T30 These relays func tion to switch data link signals onto the relay s respec tive associated trunk when a given relay T30 is actu ated The data link signal originates from one of the PCC 12 22 s and is received by the other via corre sponding relays T 30 in each trunk interface 16 26 In their normally closed state the relays T30 create a conductive path between each given trunk and the switching matrix 14 24 The normally open poles of these relays T 30 are tied in common with the data link signal path to the XMTR RCVR 40 50 Thus to tect the concentrator 8 from having crosstalk between trunks via the trunk interface 16 26 relays T30 the interface only allows one relay T30 to be actuated switched to its normally open pole state at any given time The trunk interface 16 26 also contains loop current detectors T20 which function to detect whether a par ticular trunk is presently in use or idle The main use of this loop current detection ability is to provide the PCC 12 22 with a means of checking the trunk operational status i e each detector can detect whether a subscriber line path switched through the concentrator 8 system is active and not malfunctioning As seen in FIG 6 the PCC 12 22 controls which of the relays T30 and loop detectors T20 are ch
62. he identity of the trunks which are currently operational and the identity of the switch paths which are currently opera tional 12 The line concentrator system of claim 1 wherein said switching means in each terminal comprises a two stage switching network including a first and second stage each stage including a plurality of switch matri ces wherein each said switch matrix including a plural ity of magnetically latching switches wherein each said subscriber service line is attached to a switch matrix in said first stage and wherein each said trunk is attached to a switch matrix in said second stage 13 The line concentrator system of claim 12 wherein said means for controlling the state of said switching means comprises an X axis select decoder in each said switch matrix a Y axis select decoder in each said switch matrix and means for selecting one of said switch matrices for switch actuation therein said X axis select decoder under the control of said data processor and control program acting to se lect one of said X axes in said switch matrix each said X axis having a plurality of switches opera tively connected thereto said Y axis select de coder under the control of said data processor and control program acting to select one of said Y axes in said switch matrix each said Y axis having a plurality of switches operatively connected thereto each said selected X axis and Y axis combi nation having a single cr
63. he main sub systems of the PCC 12 22 will be discussed separately below 1 The Microprocessor and Watchdog Timer As shown in FIG 2 the microprocessor 60 is the main manipulator of data and normally the controller or supervisor of all aspects of the processor common con trol 12 22 All input data passes through the micro processor 60 and all output data control and memory address information is generated through this unit A typical type of microprocessor includes the INTEL 8008 8 bit parallel word microprocessor unit as de scribed in the INTEL 8008 User s Manual Rev 4 November 1973 with some additional control circuitry as described below Referring to FIG 3 the microprocessor 60 communi cates over 8 bidirectional lines on the processor bus 90 Time multiplexing of the processor bus 90 allows con trol information addresses and data to be transmitted between the processor and external subsystems on this bus The microprocessor 60 is controlled internally by an instruction set of 48 instructions including data ma nipulation binary arithmetic and jump to subroutine instructions Microprocessor 60 control is also obtained via the Watchdog Timer Output WDTO line dis cussed below Other devices may be controlled by the _ 0 20 35 40 45 55 60 65 8 processor with the use of the 50 51 52 and SYNC output control lines generated by the INTEL 8008 In the present embodiment 50 51 52 and SYN
64. he subject line as byte 2 TABLE 1 BYTE 1 2 MEANING 000 000 FAR END MESSAGE 001 AAA STATUS ADDRESS FOR COMPARISON NO OTHER MESSAGE REQUESTS 002 CCC STATUS CONTENTS FOR COMPARISON NO OTHER MESSAGE REQUESTS 003 NULL MESSAGE 004 SWITCHING REQUEST DENIED 005 FROZEN 006 I HAVE RECOVERED 007 I NEED TABLE REFRESH 010 COMES DATA BLOCK BLOCK ADDRESS LSB 01 I STILL HAVE DISCONNECTIONS TO MAKE 012 BLOCK DATA TRANSMISSION GOOD 013 BLOCK DATA TRANSMISSION BAD 014 RESTART THE RECOVERY PROCESS 015 UUU MAKE UNIT UNAVAILABLE 016 FAR END KEY COMMAND BUSY 017 FAR END KEY COMMAND DONE 020 FAR END TROUBLE NUMBER PART 021 TIT FAR END TROUBLE NUMBER PART 2 022 CLEAR KEYBOARD COMMANDS 4 197 427 32 31 TABLE 1 continued BYTE 1 BYTE2 MEANING 023 SSS MINOR ALARM STATUS UPDATE 024 SSS MAJOR ALARM STATUS UPDATE 041 LLL LINE ADMINISTRATIVE LOCKOUT 042 LLL ADMINISTRATIVE LOCKOUT REMOVAL 043 OTT TRUNK MAINTENANCE LOCKOUT 044 OTT TRUNK MAINTENANCE LOCKOUT REMOVAL 045 LLL LINE MAINTENANCE LOCKOUT 046 LLL LINE MAINTENANCE LOCKOUT REMOVAL 047 LLL CLEAR DOWN LINE 050 OTT CLEAR DOWN TRUNK 051 LLL PLACE LINE OUT OF SERVICE 052 OTT PLACE TRUNK OUT OF SERVICE 053 LLL PLACE LINE IN SERVICE 054 OTT PLACE TRUNK IN SERVICE 055 REQUEST FAR END TROUBLE NUMBER 056 CL
65. her terminal can accept incoming requests for service from one of its respective lines and can create a subscriber signal path through its own switching network through an idle trunk and finally through the other switching network The two terminals continuously communicate with each other over a data link maintained on an idle trunk for the exchanging of the requisite switching status information and other data The present invention can be used on a trunk facility that is made up of physical cable pairs carrier trunks or any other types of trans mission facility and is electronically transparent to the subscriber line introducing no loss or gain Also no alterations or modifications to the associated central office subscriber lines is necessary to install the present invention Each terminal contains five main sections 1 a pro cessor common control 2 data link generation and reception means 3 a line interface 4 a trunk inter face and 5 a two wire stage switching matrix net work The processor common control consists of a micro processor controlled by a control program stored in a non destructive read only memory ROM a random access memory RAM and terminal input output means The RAM is used to store the current status of lines and trunks for scratch pad use by the micro processor for storage of system errors discovered and for storage of certain other indicators periodically needed by th
66. his would enable not only the remote moni toring of the concentrator 8 system but remote control as well For example multiple concentrator 8 systems could be monitored at a common location for traffic studies etc or be used to disable a particular subscrib er s access to the concentrator 8 system due to that subscriber s failure to pay his bill while yet still allowing such a subscriber to receive calls through the concen trator system It should be noted that since the micro processor 60 and control program assert virtually total control over the PCC 12 22 the possibilities herein exemplified should not be limiting except to the extent that program size is limited in the absolute Finally the concentrator 8 input output subsystem includes a maintenance monitor 100 The maintenance monitor 100 performs the function of wrapping around the data from all output ports except for the output data bus 98 which has its own input port 62 and connects this information to one of the input ports 62 for separate microprocessor 60 checking of all output port 66 states The monitor 100 function is performed by means of a multiplexer within the maintenance monitor 100 having six eight line input channels and one eight line output Note that the lines marked A through D indicate the various port wrap arounds that exist The monitor 100 multiplexer is controlled by three lines originating in the microprocessor 60 and fed to the maintenance monitor
67. ice request origi nating either from the central office CO 2 or from a remote subscriber 4 is processed in virtually the same way by either terminal except for minor variations to be described herein Therefore referring to the remote terminal s operation as an example the processor com mon control PCC 22 regularly scans the subscriber lines S 1 S N connected to RT 20 for detection of the next concentrator 8 system service request Circuitry in a line interface 28 accessed and controlled by the PCC 22 enables this process During the scanning process a data link between the remote terminal PCC 22 and the central office terminal PCC 12 is maintained if an idle trunk exists If no idle trunks are available the PCC s must wait until a trunk goes idle before interterminal communication over a data link can be reestablished Note that a data link path is not needed by the concentrator 8 if all trunks are busy since no new switching can occur until a trunk goes idle The content of data link communication if no re quests for service are detected consists usually of just the comparing by each terminal of the other terminal s status Note that the time interval between the sending of a message and the reception back of a reply and the times available between segments of messages are when the terminal does its scanning for new service requests and any other routines needing to be performed so that it is ready to respond when the n
68. ice requests test is performed after completion of the primary task so that further UART message processing may be performed if needed If no primary task is required the PTASK checks to determine if a secondary task time out has occurred Secondary tasks include such functions as disconnec tion tests etc In the disconnect example the micro processor 60 is directed via the hang up queue to con 0 5 20 25 30 35 40 45 30 firm that a customer has disconnected The procedure is that after hand up is detected the PCC waits 800 milli seconds before it checks the condition of the trunk again This is to prevent erroneous disconnections of a call in progress caused by transients on the line After the disconnection is verified the trunk number involved is placed in a separate queue to await actual disconnec tion of that trunk from the subscriber line switched thereto The terminal detecting subscriber call discon nection then sends a disconnection request message to the far terminal Both terminals 10 20 then perform the actual disconnection of the associated switch 14 24 relays Note that disconnection requests have a lesser priority than subscriber connection requests Another secondary task time out example is that the relays in a given switch matrix 10 can only be actuated or released after a minimum wait time of 100 millisec onds This is a result of capacitive effects which are present in these cir
69. inate from sources external to the PCC 12 22 Turning now to the operation of the various input output subsystems mentioned as being internal to the PCC 12 22 reference is first made to the switching matrix select 102 This unit merely takes the eight out put port lines selectively inputted to it under the con trol of the output port select 68 and decodes these into 32 lines for switching matrix 14 24 selection as will be further described in the Switching Matrix and Matrix Decode section of this specification The alarm and power unit 104 turns on audible and visual alarm indicators including a front panel alarm light to indicate to maintenance personnel that the PCC 12 22 has detected a system malfunction such as a power failure The fact that an alarm has occurred is then fed back to the microprocessor 60 via an input port 20 30 35 40 45 55 65 12 62 Note that as seen in FIG 1 backup power be provided by means of battery 30 The power unit 104 would automatically switch in this backup power if power normally available at the remote terminal was interrupted The battery 30 is large enough to provide power for up to 8 hours The display 106 is a four digit hexadecimal read out with associated drive circuitry Information to be dis played is transmitted from the microprocessor 60 di rectly to the display 106 via the address data bus 96 on lines through The low order four bits
70. ld be no way for either terminal to know which lines were switched to which trunks Such a situation does occur when both terminals lose power at the same time since neither terminal would then know which switch paths are presently in use Recall that since the relays in the switching matrices 14 24 are latching relays this enables the presently hooked up subscriber paths to continue to exist during a power failure Consequently only through manual in tervention by maintenance personnel or by waiting for all subscribers to disconnect would the two terminals be able to clear all of their relay paths without causing any conversations to be cut off Only when this has been completed would each terminal be able to reinitialize their RAM 76 status tables In the present embodiment however after a power failure at both terminals 10 20 25 all relays are immediately reset upon system power up with no ability to save calls still in progress The two terminals 10 20 keep track of the present state of the above status table recovery process by means of a recovery state number stored in the RAM 76 in each terminal A 1 state exists between the time that recovery is initiated and the time that communica tions are reestablished between the terminals A 2 state is entered by the terminal transmitting table refresh data to the terminal that has lost this data A 3 state 15 entered by the terminal being refreshed A 6
71. le the PTASK keeps track of when a mes sage is supposed to be received by the terminal and the 20 25 30 35 40 45 50 55 60 65 28 timing of the responsive message The PTASK also updates traffic statistic registers performs hangup and disconnection requests resets the watchdog timer and other time out scheduled tasks The PTASK is accessed a plurality of times during the control cycle to ensure that this routine is accessed at least once every 10 milli seconds As can be seen in the flow chart of FIG 5B the first test performed by the periodic task routine is to deter mine whether or not the watchdog timer overflow bit is on This overflow bit goes on during the last timing period of the watchdog timer If the bit is found to be on the PTASK causes the watchdog timer to be reset After testing the state of the watchdog timer the PTASK tests to see if the UART DL 10 in the XMTR RCVR 40 50 is in need of message processing In the present embodiment the PTASK determines first if the UART DL 10 is available for either a transmission or reception of a data link message If it finds a transmis sion to be enabled only then does the PTASK enable a queued subscriber service request to be analyzed i e a switch path is chosen to connect the requesting sub scribers line to an idle trunk and a message is formatted such that both terminals can thereby generate a new path through the concentrator 8 system in r
72. m fault detection diagnosis and recovery including communication to maintenance personnel of trouble codes based on the detected fault and its diagnosis Manual interaction with the system is also enabled at either end of the concentra tor system via display and input output units or remote from both ends 27 Claims 14 Drawing Figures LINE CONCENTRATOR 8 REMOTE TERMINAL OATA LINK RANSMITTER amp RECEIVER 50 34 24 PROCESSOR COMMON CONTROL 22 PULSER SW DECODE 52 4 197 427 Sheet 1 of 12 U S Patent Apr 8 1980 ee ee 25 3009340 MS 357179 1 2 NOWWOD 5405539059 08 8 vz 1 11 5 ANIT 0 1 02 NONWO 055320 331139535 8 YSLLINSNVYL ANIT 8 YOLVYLN3SINOD ol 351340 19 81 392 4 197 427 Sheet 2 of 12 U S Patent Apr 8 1980 MS 01 1 JJVAY JLNI ININ 22 21 224 96 508 86 SNE 1 2 vol LINN 39 2 1006 123136 140d YAU 02 2 01 61 14610 123135 119170 1404 ONIGOULS 3 0 gt ool YOLINOW
73. mory addresses from the microprocessor 60 are cou pled by the processor bus 90 to a sixteen bit_address register 80 Control signals CLR and EN2 from the microprocessor 60 strobe an address into the ad dress register 80 as two eight bit bytes to create the sixteen bit address word In the present embodiment only 12 of these sixteen address bits are used in address ing the RAM 76 The address register 80 is required to retain the address desired since the processor bus 90 is also used in a later part of the microprocessor 60 mem ory cycle as a data bus wherein data is either received by the microprocessor 60 or sent out from it to be stored in the RAM 76 During a read cycle the RAM 76 outputs data to the microprocessor 60 on the memory data bus 92 During such a read cycle the data is coupled to the micro processor 60 from the memory data bus 92 through an input multiplexer 88 which is used to give the micro processor 60 the choice of inputting either RAM 76 or ROM 74 memory information or data from one of the input ports 62 The output from the input multiplexer 88 is coupled to the microprocessor 60 by the bidirectional processor bus 90 Data is inputted to the RAM 76 for storage directly from the microprocessor 60 by means of the processor bus 90 As mentioned above the RAM 76 is told whether or not the microprocessor 60 wishes to write data into the RAM 76 or read data from the RAM 76 by means of the WRITE ENABLE WE lin
74. n the associated line interface 18 or 28 in the terminal to determine whether or not a subscriber service request has occurred In the RT 20 line interface 28 these are the off hook current detectors L2 X and in the COT 10 line interface 18 these are the C lead detectors 1 54 If such a service request is detected this fact is stored in a queue in the respective terminal 10 or 20 to await call processing Note that it is within the contem plation of the present invention to perform the line detector scanning described above in various ways 8 lines at a time or by first detecting that a change has occurred in a group of line detectors and only if a change is detected finding out the identity of the line requiring service In such ways a significant amount of time is not taken up in the scanning process between times that the control cycle is caused to access the 4 197 427 27 PTASK Once line detectors have been scanned again the PTASK is accessed for testing of task time outs to see if a task has to be performed After the PTASK has been accessed the control cycle next causes the microprocessor 60 to scan the trunk loop current detectors T20 X in the associated trunk interface 16 or 26 to determine which of the trunks are presently in use Trunks found to be no longer in use are identified and stored in a hang up queue for subsequent disconnection by the micro processor 60 of the switched lines connected theret
75. n in FIG 5B the PTASK then transfers out of the UART processing section If a message is to be received the PCC 12 22 is di rected to process this message including checking of all parity and check sums therein The PTASK then checks to determine if a reply is required for the given message received from the opposite terminal If it is the required reply is formatted and transmission of the message begun in response thereto The PTASK ena bles a leader to start and a message time out time is set Again after this step the PTASK transfers out of the UART processing section Finally if a message reply is not required after a message is received from the opposite terminal the PTASK enables the PCC 12 22 to select a message to 4 197 427 29 be sent to opposite terminal according to ity of current message requests that are queued in the PCC 12 22 One of the highest priority tasks would be if a message is to be formatted to enable a subscriber service request to be serviced When such a service request is queued the PTASK proceeds to scan for idle trunks and available switching paths through the termi nal switch matrix The routine then decides upon an appropriate line link and trunk for service Lastly the routine then formats a message to the far terminal indi cating that a connection request is being made for that particular switch path and trunk This message includes an indication of
76. nal that has retained the status data Otherwise both terminals must ex change data as to the current equipment status at their end of the system e g how many lines are functional how many switching matricies are operational etc System initialization is performed automatically upon the start up of the concentrator 8 system via the timeout of a watchdog timer 82 in each terminal 10 20 The operation of this timer was described hereinabove Basi cally when each terminal s watchdog timer times out it causes the associated microprocessor 60 in that terminal to be interrupted to thereby cause it to automatically access a specific location in its associated ROM 74 As seen in FIG 3 the watchdog timer 82 essentially comprises a frequency divider 218 fed by a clock signal CLK This frequency divider provides an output on the watchdog timer out line after 472 millisec onds have elapsed without the timer 82 having been 4 197 427 23 cleared This pulse sets a flip flop 213 which enables the interrupt INTR flip flop 211 to change state at the correct clock time needed by the micro processor 60 as controlled by AND gate 214 This flip flop output in turn is coupled to the microprocessor 60 as an INTERRUPT signal Although the microproces sor 60 automatically clears all of its internal registers upon sensing that power has been turned on when a restart has been generated the INTERRUPT signal also causes the i
77. nected to that terminal switching means in each terminal for enabling the switching of a plurality of lines individually to a corresponding number of trunks processor means in each terminal including means for storing systems status data said storing means hav ing a memory including a plurality of storage loca tions means for determining which trunks are idle means for determining and selecting an idle switch path through said switching means from said ser vice requesting line to a selected said idle trunk and means for controlling the state of said switch 5 20 25 45 50 65 42 ing means such that said selected switch path is generated thereby and data link means for communicating the identity of said selected switch path and said idle trunk to the terminal opposite the terminal having said servic ing requesting line and for communicating to said opposite terminal any said stored system status data and other data generated by said processor means 21 The line concentrator system of claim 20 wherein said data link means further comprises means for selec tively switching said data link onto an idle trunk ran domly selected by said processor means and means in each said termiual for independently determining that said selected idle trunk is operational prior to the trans mission between each said terminal of said data or com mands said random selection of said idle trunk enabling the current operation
78. nternal registers to be cleared It further allows subsequent initialization steps to be performed depending on the sophistication of the system using the microprocessor In the present embodiment the IN TERRUPT signal causes the microprocessor 60 to ad dress location 0000 in the ROM 74 which in turn points the microprocessor to the starting address of the control cycle program to be described below Once the microprocessor 60 enters the interrupt state this state is decoded in the start decoder 212 in response thereto state decoder 212 sends INTR RESET pulse to reset flip flop 213 At the next clock time this causes flip flop 211 to be reset thereby allowing the micro processor 60 to begin processing Initially the control program stored in each ROM 74 causes the associated PCC 12 22 to determine how many line interface and trunk interface cards are pro vided in the terminal the number of switch matrices 510 the operative state of the lines etc and to store this equipment status in corresponding trunk and line status tables in the RAM 76 Once these initialization procedures have been completed each terminal at tempts to initiate data link communications with the other terminal over the first available trunk This at tempt at setting up a data link continues through the accessing of each trunk periodically until a communica tion is successfully established To avoid confusion the remote terminal 10 is caused to
79. o After again accessing the PTASK the control cycle in the RT 20 causes the PCC 22 to scan the ringing detectors 34 which are also tied to the trunks A ringing detector is used to varify that a ringing signal is on the trunk pairs when a call is being coupled through the concentrator 8 system via the COT 10 The ringing detectors 34 thus verify that the subscriber call is prop erly being terminated at the RT 20 After again accessing the PTASK the control cycle scans its keyboard 110 and TTY interface 108 inputs to determine whether a command has been entered to the terminal If a command has been entered this command is processed Further information on the operational procedure involved in concentrator 8 system com mands is given in the next section of the specification The control cycle then tests to determine whether or not an enter freeze mode command has been inputted A freeze mode is implemented by maintenance person nel to allow switching units and certain other units in the terminal to be changed without incurring the risk of shorting out these boards while they are being pulled in and out All scanning and switching operations are stopped while in the freeze mode The frozen terminal replies to all messages I am frozen In response thereto the far end terminal will not try to originate any new switching requests Prior to entering the freeze mode the terminal will enable all currently pending switching requests
80. of two boards are needed in a sixteen trunk system Therefore two separate trunk status lines TS 1 and TS 2 are outputted to the PCC 12 22 in a sixteen trunk concen trator 8 system and the trunk relay operate enable strobe signal comprises two strobes 1 and 2 for selecting a given trunk interface board Also there are 8 relays T30 1 8 and 8 loop current detec tors T20 1 8 per board Note that a light emitting diode T22 may be connected to each loop current de tector T20 to provide a means for indicating to mainte nance personnel the present status of each correspond ing trunk It should also be noted that since the trunk lines are bidirectional in that they both transmit and receive information the loop detectors T20 are de signed to sense current flowing in either direction One drawback of any line concentrator system is that trunk blocking will occur if all trunks are in use and a larger number of subscriber call requests have been received Therefore as discussed elsewhere in this spec ification traffic studies to determine who the heavy users are provide again a valid means for determining if such users should be eliminated from the system E The Data Link The data link is the serial bit string means by which the central office terminal 10 and the remote terminal 20 intercommunicate There are generally three types of messages transferred general purpose messages switch connection requ
81. ogram is accessed to enable concentrator 8 system subscriber call request analysis and other concentrator 8 system functions to begin As seen in FIG 5A the first function of the control cycle is to perform a PTASK PTASK is short for Periodic Task Routine FIG 5B illustrates a flow chart of this routine The PTASK is periodically accessed during the control cycle to take care of various func tions which must be performed by each PCC 12 22 within a specific time The PIASK routine will be cov ered in detail hereinbelow However initially some aspects of the routine should be known to enable a clearer understanding of the rest of the control cycle One major aspect of the PTASK comprises a plural ity of timing tests for determining if one of a plurality of tasks is in need of being performed These tasks are divided into two groups primary tasks which have the most critical time dependance and secondary tasks having less critical timing requirements If a task timing test indicates that a time out is to occur for a given task the other major aspect of the PTASK is to cause the PCC 12 22 to perform the required task Once the task is completed the PTASK again makes a check of task time outs and if none have occurred it transfers system control back to the main control cycle Referring again to FIG 5A after the first PTASK accessing has been completed the control cycle causes the microprocessor 60 to scan all the line detectors i
82. or 8 system subscriber servicing size Note that each subscriber line really is two lines the tip and ring lines required for telephone operation in the present embodiment The signal that controls which line interface board 28 is enabled is the OE Y signal wherein Y equals the number of interface boards in the system This signal is coupled from the PCC 22 to the line interface 28 boards via an output port 66 Four line interface 28 boards therefore require four signals 1 for individual selection of each board The microprocessor 60 selects a given OE Y signal by load ing a single bit from address bus 96 into the output port 66 selectively enabled by the port select unit 68 As mentioned above one output port is used only for en abling commands to selected line interface boards Referring again to FIG 10 a relay L4 keeps the subscriber line hooked up to an off hook current detec tor L2 whenever the associated subscriber line is idle After an off hook condition has been detected relay L4 enables the current detector L2 to be switched out of the subscriber s loop by the PCC 22 Note that the subscriber line path is not switched by the line interface 28 i e the continuity of this path stays the same The relay L4 only allows the off hook detector to detect the electrical state of the subscriber line Note that there is no automatic on hook detection for the purpose of re connecting the off hook current detector to the s
83. osen via the present state of the output data bus 98 bits 3 These bits are inputted to a loop current detector multi plexer T40 for selection of which loop detector status line is outputted on a trunk status line a TS Y line to the PCC 12 22 The output data bus 98 bits 3 are also inputted to a relay select decoder T42 which selects which relay on the trunk interface 16 26 is to be actu ated The state of bit 3 determines whether the loop current multiplexer 40 or the relay select decoder T42 is actuated A trunk interface operate enable signal a TIOE Y signal strobes a relay actuation enable register T44 to load in and store the identity of the line selected via relay select decoder T42 for retaining the desired relay actuation selection once the output data bus 98 bits no longer contain relevant data When the data link is to be switched to another trunk and the subscriber line switched onto the trunk presently in use as a data link the updating of register T44 the TIOE Y strobe performs this task Again this is because the relays T30 are non latching Thus actuating a new selected relay 4 197 427 19 automatically causes relay previously selectively actuated by the register T44 to be released In the present embodiment to ease modification of the size of the concentrator 8 system the trunk interface 16 26 circuitry is split up such that eight circuits are contained on each board Consequently a total
84. osspoint the switch opera tively connected thereto being caused to actuate when said switch matrix is selected 14 The line concentrator system of claim 13 wherein said switches in each said switch matrix are arranged 4 197 427 41 such that when a given switch is actuated all other switches on the same X and Y axis corresponding to said actuated switch are caused to be released if said switches were formerly in an actuated state to insure thereby that no erroneous switch paths are generated in said switching means 15 The line concentrator system of claim 1 further comprising a battery operatively associated with one of said terminals for enabling the continuation of system operation and retention of terminal status data during external power supply loss 16 The line concentrator system of claim 1 further comprising system fault detection and diagnosis means 17 The line concentrator system of claim 16 wherein said system fault detection and diagnosis means in com bination with said data processor and control program comprises in each said terminal means for the real time performance of fault detection routines for detecting thereby system operational errors means for storing in said memory and displaying a specific trouble number to indicate the identity of the detected operational errors means for storing in said memory subsequently de tected faults means for displaying a maintenan
85. perform the initial send ing of a data link message and the central office termi nal 20 is caused to look for this message The central terminal 20 does not attempt to send its own message initially to the remote terminal 10 Only when it has detected the remote terminal message will it send a message which will be a response thereto In operation the PCC 12 in the RT 20 chooses the first available trunk In the trunk interface 26 the trunk relay T30 corresponding to this chosen trunk is actu ated by the PCC 22 such that a signal from the data link transmitter and receiver XMTR RCVR 50 is enabled to be coupled out over that given trunk The message transmitted is in the form of a 2 second leader pulse followed by message This message is transmit ted in a standard way as described above via the UART DL 10 in the RT 20 If a message error occurs or a timeout time occurs before a reply message is re ceived from the COT 10 the RT 20 releases the trunk relay T30 and attempts to communicate again on an other randomally chosen trunk in the same manner as just described In this way all trunks available for use by the RT 20 are rotated through communication at tempts of 2 seconds each with the COT 10 Should this process fail to establish a communications link with the COT 10 after 256 cycles of attempts through all avail able trunks have been run the process may be modified such that the trunk relays are not caused to
86. r signal mentioned above whenever all trunks or line links i e paths in the switch matrices are busy The reasons for the occur rence of these busy conditions will be discussed below Refer to the Switching Matrix section for discussion of line link busy and to the Trunk Interface section for discussion of trunk busy The reorder signal is created in a reorder generator L60 which may be external to the system and consists of a 120 impulse per minute tone that when switched onto the subscriber s line is heard by the person attempting to complete the call Since the 5 25 35 40 45 55 60 65 16 tone resembles a standard telephone busy signal but at a faster repetition rate the caller should realize that to get his call completed he must hang up and re attempt to make the call The relay 150 is driven by a standard relay driver circuit L52 controlled by a relay select decode L62 The decoder L62 selects which of the sixteen relays 50 on the board are to be actu ated The decoder L62 is controlled by four lines input ted to it from the PCC 12 on the output data bus 98 The four lines are output data bus 98 bits 4 7 The PCC 12 controls which board is selected and whether relay selection or line status is performed on the selected board by using the OE 1 OE 4 lines to select the board and and 1 lines to select the function performed on the board In the present em bodiment at the
87. ransmission a data bad message is returned by the far terminal This causes the near terminal to retransmit the previous six teen byte block of table data If more than a preset number of errors are detected during a block data trans mission the entire process is aborted and the communi cation scanning process is reentered to find a more operational trunk If the entire block is received without errors a data good message is returned by the far terminal thus allowing the near terminal to transmit a new block of data If all status data has been transmit ted the refresh process is ended and both terminals are enabled to resume subscriber call processing Due to the fact that switch matrix units may have been removed by maintenance personnel during the system failure time the terminal with the refreshed information will also check its equipment status The terminal receiving table refresh data will then compare this data with what that terminal has found to be its actual present equipment status If a discrepancy is found in a given operational unit a message is sent back to the terminal originating the refresh data to make unit unavailable When this process is completed therefore the status tables in both terminals will contain the same information as to the present operational status of the entire concentrator 8 system When both terminals need table refresh they send I am still disconnecting messages back an
88. rom the central office terminal 10 be successfully received back at the RT 20 a successful data link has been established The two terminals are then enabled to transmit requests as to the present equipment status of the lines trunks and switching ma trices in the two terminals The number of available lines switch paths etc available in each terminal is compared and the sum of this data is stored in duplicate in the RAM 76 status tables in each terminal Note that in this example since both the COT 10 and the RT 20 have just been powered up no switched path data is in either of the terminal s status tables therefore no inter terminal comparison of this data is needed A similar procedure is performed by each terminal when a data link path has been interrupted due to the fact that all trunks are busy with calls After a trunk goes idle the RT 20 sends a leader pulse out on this trunk and waits for a response from the COT 10 to thereby reinstate the data link If the concentrator 8 system had been operating and one of the terminals lost power temporarily the RAM 76 memory data in that terminal would be destroyed Therefore the trunk and line status tables in that termi nal would have to be refreshed by data in the other terminal s RAM 76 to enable the present operating of the concentrator 8 system to continue If table refresh were not possible the entire concentrator 8 system would have to restart from scratch since there wou
89. s information is stored in one of the above described status table locations This unit 104 also may turn on an alarm light and audible alarm to indicate the occurrence of such a condition In the preferred embodiment of the present invention a major alarm will occur if there is a loss of communi cations between the terminals a watchdog timer time out or the detecting of certain errors through diagnos tic routines to be described hereinbelow Minor alarm conditions include loop current seen on an idle trunk excessive communications errors table status miscom parison between the two terminals and the occurrence of a freeze mode among others Hardware alarm condi tions include a malfunctioning clock an open door at the remote terminal excessive temperature at the re mote terminal and power failure at the remote terminal The two reinitialize commands 18 and 19 enable maintenance personnel to force a reinitialization of a selected terminal of the concentrator 8 system Thus the system may be commanded to either force table refresh of RT 20 with status table data stored in the COT 10 or vice versa These commands along with commands for forcing a specific switch path for dis playing a memory location etc are especially useful for preliminary checkout of the system Commands 23 and 24 enable maintenance personnel to either disable or reenable data link communication switching i e preventing switching of the data link amon
90. said all trunks busy signal from the reorder generator to indicate to a subscriber that he should hang up and attempt a service re quest at a later time 10 The line concentrator system of claim 1 wherein said means for determining which trunks are idle com prises trunk interface means including a plurality of trunk loop current detectors one each operatively cou pled to a trunk each said detector outputting a signal when its associated trunk is in use said trunk interface means further including a loop current multiplexer for enabling the processor means to selectively readout the status of each said detector and means for enabling said processor means to verify the proper operation of a trunk having a service re questing line switched thereon 11 The line concentrator system of claim 1 wherein said means for determining and selecting an idle switch path through said switching means comprises means under the control of said data processor and control program for independently monitoring and storing in said memory in each terminal the present system opera tional status said status including the present state of said switching means the identity of the trunks cur rently in use and the identity of the lines currently in use and further independently monitoring and storing in said memory in each terminal the present system equipment status said status including the identity of the lines which are currently operational t
91. t the keyboard 110 is a TOUCH TONE style key board which also includes an asterisk and a number symbol key Keys on a teletype unit are also read able in a similar way via the TTY interface 108 in the PCC 12 22 The display 106 in each concentrator 8 terminal also provides an important function in the inputting of commands and in the overall information transfer process between maintenance personnel and the concentrator 8 system For example as described in more detail herein the display 106 automatically dis plays a trouble number if a system malfunction has TABLE II LINE COMMANDS The tine commands are as follows 39 Display administrative lockout status 2 Set real time clock 41 Display near terminal s line status 3 Decimal display of memory 42 Display far terminal s line status location contents 43 Displays line s trunk number 4 Continuous display of memory 44 Place line in service location contents 45 Release line s path 5 Display the far terminal s 46 Maintenance lockout trouble numbers 47 Remove maintenance lockout 9 Clear alarm 48 Administrative lockout 11 Clear keyboard 49 Remove administrative lockout 12 Clear near terminal s trouble 64 Display line group busy status numbers TRUNK COMMANDS 13 Clear far terminal s trouble The trunk commands are as follows numbers 51 Display near terminal s trunk status 14 Clear communication error counts 18
92. t will pass through this high pass filter DL 32 are leader pulses since they are over 4 ms in duration versus the data pulses which are less than 1 ms in duration The output of this high pass filter DL 32 is coupled to a flip flop DL 34 A leader pulse turns on this flip flop DL 34 thereby enabling the serial data which is following the leader to be coupled through to the UART DL 10 via AND gate DL 36 The UART DL 10 then reads in this serial bit string checks the parity and checks that the start and stop bit are in proper form Receipt of the stop bit changes the state of UART DL 10 s DR line This state change is sensed by the PCC 12 22 and indicates that a data word byte has been received If the bit string has been transmitted properly the UART DL 10 converts this bit string into an eight bit parallel word for output ting to the PCC 12 22 If however the UART DL 10 detects a parity or other error this error status is trans mitted to the receiving PCC 12 22 and as a result the message will be rejected After completion of the entire message the receiving PCC 12 22 will send a message back to the PCC 12 22 which had sent the defective message requesting that the message be retransmitted As further check even if all three bytes of data in a given link message have been properly received by the UART as reflected in correct parity for each byte the check sum data byte must also match the check sum calculated separately
93. taining ROM chips The register 78 functions to selectively enable the ad dressing of a given ROM chip based on the state of address bits A8 A13 Each ROM chip presently con tains 256 eight bit words so that address bits 7 are used to select a specific word location on the ROM chip selected by the register 78 It is within the scope of the present invention to incorporate ROM s of higher bit density as they become available e g ROMs having 2024 eight bit words 4 Input Output Devices As shown in FIG 2 there are eight latchable regis ters of eight bits each that comprise the output ports 66 and eight strobing output ports 70 of one bit each These output ports 66 70 communicate control functions and data to the respective devices corresponding to a given port that the microprocessor 60 wishes to access The ports 66 70 connect to subsystems both within the PCC 12 22 and external to it The means for choosing which port passes information to its respective subsystem com prises two output port select units 68 72 The port select 68 selects one of the eight latching output ports 66 for information transfer and the port select 72 selects one of the eight strobing ports 70 for information trans fer Each port select unit 66 72 decodes three input lines 9 11 from the address data bus 92 into eight output lines for individual selection of one of the eight output ports The OUT 1 and OUT 2 signals originat ing from
94. the identity of the idle trunk and switch path chosen Note that if the far terminal does not re ceive this message without error it will request that the message be repeated The last step in this portion of the PTASK is the starting of a leader and setting of a time out time after which time the sending terminal will look for a new message from the opposite terminal If a mes sage is not received after the time out time an error condition is indicated Control cycle fault diagnosis of such error conditions is described hereinbelow If there are no pending subscriber service requests other terminal messages of lesser priority are sent to the opposite terminal For example each terminal automati cally communicates status information to the other for comparison thereof This is to insure that the separate status tables in each terminal 10 20 continue to match one another The next PTASK test is the check of whether or not a primary time out has occurred in the XMTR RCVR 50 If this is found to be true the primary task associated therewith is then performed The most critical time dependent task 15 to make sure that the UART DL 10 the terminal is periodically accessed by the PCC 12 22 If data link data is not received by the PCC from the UART DL 10 every 10 milliseconds this data is lost since the next byte of data will be written over the old data PTASK control returns as seen in FIG 5B to a point above where the subscriber serv
95. the microprocessor 60 also input to the port select units Signal OUT 1 enables operation of port select 68 and signal OUT 2 enables operation of port 4 197 427 11 select 72 The output port 66 latchable registers remain in a chosen state until microprocessor 60 modification at a later time The strobing output ports 70 however only stay on as long as the port select pulse OUT 2 remains on Each output port 66 passes up to eight bits 7 from the address data bus 96 out to the selected device Each output port 70 only passes one bit per port In the present embodiment since the output port 70 is non latching the only circuitry existing in this unit is a buffer gate connecting the line selected by the port select 72 and the selected device For further details on the operation of these units consult the System Opera tion section of this specification The various units that are accessed and controlled via the output ports 66 include a switch matrix select unit 102 an alarm and power unit 104 and a teletype inter face 108 which are units within the PCC 12 22 and include the line interface 18 28 the trunk interface 16 26 and the XMTR RCVR 40 50 which are units exter nal to the PCC 12 22 The output port 66 also includes one port for the PCC output data bus 98 and one port for maintenance monitor 100 control In the present embodiment all of these above mentioned ports 66 contain eight output signal paths except
96. till communicating are possible applications for this test trunk There is also the ability to disable the test trunk input by the relay DL 80 controlled by the PCC 12 22 2 SYSTEM OPERATION A System initialization and recovery As previously mentioned the concentrator 8 system of the present invention includes two separate processor control units 12 22 having separate random access memories 76 therein with one each in a respective central office terminal 10 and remote terminal 20 Thus means are needed for the initialization of concentrator 8 system status as stored in these memories when the system is first powered up Further means are needed for enabling the concentrator 8 system to recover from a power failure or other system malfunction when sys tem status data in one or both of the RAMS 76 has been lost To insure that both terminals 10 and 20 know the present state of the other terminal s switching network and to insure that the two switching matrices 14 and 24 are in an identical state the PCC s 12 22 must establish interterminal data link communications Only after a data link has been established can initialization of the two terminals be completed During the initialization process system status information is transferred be tween one terminal and the other over the data link path If system status has only been lost at one of the two terminals 10 20 status information updating is performed mainly from the termi
97. to insure that a trunk is operational before a path is switched through it by periodically using this intended trunk as the temporary processor common control data link for intercommunication between the terminals If either of the process common control units find the trunk to be inoperative neither will switch in a sub scriber over this path but will instead search for a new idle trunk that is operational Yet still another object of the present invention is to provide for each processor common control to have the ability to automatically discover store and display system operational faults or errors to lock out the lines or trunks corresponding to these errors if possible until repaired and to tell maintenance personnel how to repair the detected errors to thereby minimize mainte nance personnel training required for maintaining proper system operation and to enable maintenance personnel interaction with the system to be minimal when such interaction is required Yet another object of the present invention is to pro vide automatic traffic usage analysis for determination of heavy subscriber usage on a particular line group of lines etc Such analysis enables the even distribution of high usage and low usage subscribers over all line groups BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the pres ent invention will become more apparent upon refer ence to the following description and the accompan
98. to be processed A freeze mode command must be entered to take the terminal out of the freeze mode Once the control cycle has tested for a freeze mode command and found none or if a freeze mode command has been removed the control cycle after again access ing the PTASK next performs various alarm process ing or on line diagnostic routines These various rou tines will be described in more detail hereinbelow Once the alarm processing or on line diagnostic rou tines have been completed the control cycle is caused to be branched back as seen in FIG 5A so that scan ning of subscriber service requests etc may be re peated Note that the above described control cycle operation is essentially identical in both the COT 10 and the RT 20 The times during which the various steps are performed however is asynchronous between the two terminals In other words the COT 10 may be in the process of performing a periodic task while the RT 20 is in the midst of scanning its off hook detectors for a subscriber service request Again the only interaction between the two terminals is via the data link whereby call processing information and other status information is transferred between the two terminals Referring again to FIG 5B and the periodic task routine it will become apparent that this routine pro vides the important timing functions for the various tasks needing to be performed by the given PCC 12 22 For examp
99. tored system status during system start up and reinitialization of stored system status also involves special provisions When the concentrator 8 is initially turned on both terminals establish data link communication on an arbitrary trunk If data link com munication is successfully established on this first trunk or if after an arbitrary number of attempts communica tion is not established over this trunk each PCC 12 22 records this fact in its trunk status table and then contin ues on to a next trunk to attempt communication on this new trunk This procedure is repeated until all trunks have been checked and their operational status re corded in trunk status tables for future reference These tables are stored in each terminal s respective RAM With the data link established on the last trunk checked by the PCC 12 22 the PCC s 12 22 begin their respec tive scans for subscriber requests for service while continuing to communicate one with the other as was briefly described above If either terminal loses its line and trunk status infor mation due to a power failure subscriber lines that are presently coupled through the concentrator 8 system are able to continue to be so since magnetically latching relays are used in the concentrator switching matrix 14 24 These relays do not require any power to retain their present state When power is returned to the terminal that has lost its data it indicates to the other terminal
100. ty low cost and expanded system control of co equally operating mi 4 197 427 3 croprocessor controlled terminals at both ends of the concentrator Another object of the present invention is to provide a system that takes advantage of the compactness and hardware simplifications inherently made possibly by state of the art microcircuits Yet another object of the present invention is to pro vide for data link communication between concentrator terminals over an idle trunk thus negating the need for a dedicated trunk useable only for such communication Note that in the present invention if all trunks are busy there is no need for data link communication A further object of the present invention is to enable performance of real time system maintenance checking from either terminal both automatically by the system and via maintenance personnel commands without requiring system shutdown Also enabled is the read out at either terminal of system errors discovered in cluding error diagnosis such that maintenance person nel are directed to specific repairs to be performed Still another object of the present invention is to take advantage of the processor common control in each terminal for the independent retention in both terminal of line and trunk status to enable the retention of system operational status by at least one terminal in case of power failure at the other end A still further object of the present invention is
101. ub scriber line As result the PCC 22 after it has detected by other means that a subscriber s use of the line has ended must access the line interface 28 board to release the corresponding relay L4 The PCC 22 receives subscriber line off hock detec tor status one line at a time The PCC 22 controls this status read out process by means of four output data bus 98 lines 0 3 These four data bus 98 lines are inputted to a line status multiplexer L30 which uses the state of the four lines to control which of the sixteen off hook detector status lines on a given board is read out on an LS Y line No OE Y signal is required for line status selection A separate LS line from each line interface board 1 5 1 1 5 4 connects to one of the PCC 22 input ports 62 The PCC 22 controls which of the L4 relays on each board is actuated and released also by means of the output data bus 98 lines 0 3 These lines are decoded into sixteen outputs in the L32 and L34 The decision of whether relay L4 actuation via L32 or relay L4 release L34 is accomplished is controlled by the and 1 lines Recall that each board is selected by a separate OE Y strobe line for relay L4 control Gates L40 and 142 enable this relay state selection process allowing either the or F1 signal to pass only to the 4 197 427 15 chosen relay control decoder 132 1 34 the one board that has its OE Y line strobed 2 Central
102. ubes that are filled with inert gas They are thus highly reliable in adverse operating conditions Two pole relays are used because two wires and tip and the ring as described in the Line Interface section of this specification are always switched as a pair for each subscriber line as inputted from the line interface 18 28 The eight concentrated output lines from each matrix 510 are coupled the trunk interface 16 26 described in the next section Since the relays contain magnetically latching coils once they are switched to a certain state they remain there until switched back No power is required to maintain either an actuated or a released state As can be seen this arrangement automatically protects the switch path of calls that are in progress when a line concentrator 8 power failure occurs For simplicity only the relay actuation cross points are illustrated in FIG 9 It should be noted that each line inputted to the 168 matrix 510 has the ability of being switched to any of the eight output lines That is each input line has eight unique relays attached to it each one of which can attach this input line to a separate one of eight output lines With eight relays tied to each 4 197 427 17 input line it is easy to see why total of 128 relays needed to provide full switching of 16 input lines The means for deciding which of the 128 relay actua tion cross points is actuated is determined by the swit
103. utted by the UART DL 10 a ninth bit indicating the odd parity of the previous eight bits is automatically generated by the UART DL 10 and outputted Finally a stop bit is generated to indicate to the other terminal s UART that the byte of data has been completely sent The UART DL 10 serial message is transformed into FSK signals the FSK encode DL 12 In the present embodiment the FSK signal is defined as being for logic 0 a pulse of 1000 cycles per second cps and for a logic 1 a pulse of 2000 cycles per second cps Therefore data is transmitted as different frequencies shifted from one frequency to another frequency based on whether or not it is a logic 0 or a logic As shown in FIG 7 the UART DL 10 message inputs to a gated oscillator DL 46 which actually gener ates the frequency shifting based on whether the DL 46 input is a logic 1 or a logic 0 The gated oscillator DL 46 output is shaped into a square wave in the square wave regenerator DL 48 which then divides the 4 197 427 21 frequency of gated oscillator input pulse by two This output is passed through a low pass filter DL 50 which generates a sine wave from the square wave input The output of the DL 50 is coupled by the inter nal data link bus DL 90 and an isolation transformer DL 60 to the trunk interface 16 26 to become the data link signal that is transmitted to the other concentrator 8 system terminal
104. witch matrix 10 thereby guaranteeing that the switch path created at a selected cross point is the only switch path created for each of the sixteen matrix input lines One problem with a finite number of switches in each switch matrix S10 is that if there is heavy demand for switch paths through a given matrix 510 e g a demand for more than 8 paths some call requests can t be ser viced This is the phenomenon of line link busy or in other words switch matrix S10 blocking If eight of the 25 30 35 40 45 60 65 18 16 inputs to the switch matrix 810 are in use no other lines can be switched through in that matrix If such a condition occurs a subscriber can only either wait on line until another line attached to the matrix S10 goes free or hang up and try again The microprocessor 60 provides an indirect solution to the blocking problem in that it allows one to do traffic surveys which monitor the use made of given lines during a given period Using such surveys one can spread out heavy users so that high use lines are not bunched together in any one switch matrix 510 Very high use subscribers might even be taken out of the concentrator 8 system entirely More on this survey capability is given below in the System Operation section D The Trunk Interface The trunk interface 16 26 provides interface circuitry between the switching matrix 14 24 in each terminal and the trunks T 1 T n which interconnect t
105. y ing drawings in which FIG 1 illustrates in general block diagram form a line concentrator system according to the present invention FIG 2 is a more detailed block diagram of the pro cessor common control unit shown in FIG 1 FIG 3 illustrates an embodiment of the microproces sor unit shown in FIG 2 FIG 4 is a block diagram depicting memory alloca tions of the RAM memory shown in FIG 2 25 35 45 55 65 4 FIGS 5A B illustrate a flow diagram of control program executed by the microprocessor unit of FIG 2 FIG 6 is a schematic of one of the trunk interface units shown in FIG 1 and related circuits FIG 7 illustrates an embodiment of the transmitter receiver and data link generator shown in FIG 1 FIG 8 is a detailed block diagram of a two stage switching matrix shown in FIG 1 FIG 9 illustrates the circuitry of one of the switch matrices of FIG 8 FIG 10 is a detailed block diagram of the remote terminal line interface unit shown in FIG 1 FIG 11 is a detailed block diagram of the central office terminal line interface unit shown in FIG 1 and FIGS 12A and B illustrate the timing and format of a typical data link message DESCRIPTION OF THE PREFERRED EMBODIMENT 1 GENERAL The line concentrator switching system 8 is illus trated in block diagram form in FIG 1 The concentra tor 8 is composed of a central office terminal COT 10 and a remote terminal RT 20 A serv

Dual-processor line concentrator switching system

Contents

Download Pdf Manuals

Related Search

Related Contents