Abstract:
A data communication system is provided comprising, at a plurality of locations, data terminal equipment. Communication equipment adapted to transmit and/or receive data from location to location is provided at each location connected to the terminal equipment and interconnected between locations through a suitable communications channel or media. An auxiliary signal processor is provided at each location interfaced with the communications equipment and deriving from the communications equipment on a noninterfering basis, information relating to the status of the channel, communications equipment, and data terminal equipment. A central controller is provided at a central location and auxiliary communication equipment is provided at each location interconnected with the central controller and with the auxiliary signal processor.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to data communications and in particular to a system for the detection and correction of faults in a data communications network from a central location. 
     In my copending, commonly assigned patent application, System For The Quantitative Measurement Of Impairments In The Communication Channel Of A Quadrature Amplitude Modulation Data Communication System, Ser. No. 16,912, filed Mar. 2, 1979 there is disclosed a technique for QAM eye pattern analysis which permits the quantitative evaluation of a communications channel or media interconnecting two remote communication equipments of a data communication network. The communications equipment, in the form of transmit and/or receive modems may be interconnected by a communication channel comprising dedicated or dialed up commercial, military or foreign voice-grade telephone lines and include PCM, carrier, satellite and cable links. 
     In my copending, commonly assigned patent application, In-Service Monitoring System For Data Communications Network, Ser. No. 17,042, filed Mar. 2, 1979 there is disclosed a technique for the non-interfering monitoring of the components of a data communications network including the detection and isolation of faults and potential failures within the network. 
     The techniques disclosed in the above mentioned patent applications solve many long felt needs since they permit the evaluation of the communication of data from location to location without interfering with such data communication. The systems also permit potential future problems to be located and corrected prior to a degradation of the communications system to a point where it interferes with data transmission. 
     While these copending cases solve many of the problems heretofore encountered they still require that at each location of a data communications network a monitoring function be performed. For multi-location networks this would be both costly and time consuming. 
     In view of the above, it is the principal object of the present invention to provide a system whereby the monitoring of the condition of components of a multi-location data communications network may be attained from a central location. 
     A further object is to provide such a system wherein adjustment or reconfiguration of the components of the network at the several remote sites may be attained from the central location. 
     Still further objects and advantages will be apparent from a review of the detailed description of a preferred embodiment of my invention. 
     SUMMARY OF THE INVENTION 
     The above and other beneficial objects and advantages are attained in accordance with the present invention by providing a data communications network consisting of data terminal equipment provided at at least two locations remote from each other. At each location, transmit and/or receive communications equipment is connected to the data terminal equipment and interconnected through a suitable communications channel, media or links. Auxiliary signal processors are provided at each location interfaced with the communications equipment and adapted to derive, on a non-interfering basis, information from the communications equipment relative to the status of the data terminal equipment, communications equipment, and communications channel. 
     An auxiliary communications equipment is also provided at each location interfaced with the auxiliary signal processor thereat. A central controller is provided at a central location which could, if desired, be the location of one of the data terminal equipments. The auxiliary communications equipments are each interconnected, through a communications link, with the central controller thereby providing a telemetry interface between the central controller and the auxiliary signal processors. 
     The auxiliary communications equipment may be comprised for example, of a low speed FSK modem which transfers data in a portion of the communications media bandwidth which is not utilized for normal data traffic. In a system which utilizes 2400 bps modems for the communications equipment which operate within a frequency range of 1000 Hz to 2,600 Hz for data traffic, the auxiliary communications equipment may operate at a rate of 110 bps within a frequency range of 340 Hz to 540 Hz. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic block diagram of the system in accordance with the present invention; 
     FIG. 2 is a schematic block diagram of the auxiliary communications equipment utilized in the system of the present invention; and 
     FIG. 3 is a waveform diagram depicting the separation of data and telemetry information. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is now made to the drawings and to FIG. 1 in particular wherein a data communications system 10 in accordance with the present invention is depicted. The system comprises at least two data terminal equipments 12 and 14 provided at locations remote from each other. At each location there is also located communications equipment 16 (or 18). The communications equipment are in the form of transmit/receive modems and pass customer data to each other over a suitable communications media or channel such as a telephone link. 
     In the preferred embodiment, the modems 16 and 18 employ PSK modulation transferring data at a rate of 2400 bps. The modems 16 and 18 are connected to their associated data terminal equipment 12 and 14 by means of an RS232-C interface in a manner described in more detail in the previously mentioned application Ser. No. 17,042, filed Mar. 2, 1979 for In-Service Monitoring System For Data Communications Network. 
     At each location there is also provided an auxiliary processing element 20 (or 22). Preferably the auxiliary processing element is contained in the same chassis as the communications element 16 (or 18). The details of the interface between the auxiliary processing element 20 (or 22) and communications element 16 (or 18) are also set forth in the previously mentioned copending applications. 
     In accordance with the present invention, there is also provided an auxiliary communications element at each location. Accordingly, a telemetry channel subsystem 24 is provided at the location of modem 16, and preferably within the same chassis and similarly a telemetry channel subsystem 26 is provided at the location of modem 18, preferably within its chassis. 
     The inputs and outputs of the auxiliary processing elements 20 and 22 are provided from and to the telemetry channel subsystems 24 and 26 respectively which comprise FSK modems which operate at a data rate of 110 bps. 
     Commands to the telemetry channel subsystems and information from them are provided to a central controller 28. The central controller 28 may be provided at the location of one of the data terminals or at a different location. The central controller comprises a mini-computer such as, for example, the model TI 990/10 available from the Texas Instruments Corp. 
     Reference is now made to FIG. 2 wherein the telemetry channel subsystem is depicted. 
     As shown, data or commands from the central controller pass to a local auxiliary processing equipment 20 along line 30. The data from the central controller is also supplied to a local FSK transmitter 32. The output of FSK transmitter 32 is fed to an adder 34 along with the output of a PSK transmitter and supplied to the telephone line. At the remote end, a high pass filter 36 is provided to remove the low frequency FSK and pass the resultant PSK signal to the PSK receiver along line 38. A low pass filter 40 is also provided to remove the PSK from the composite signal and to supply the remaining FSK signal to the FSK receiver 42. The FSK receiver output is fed to the remote auxiliary processing element 22. 
     Data from auxiliary processing element 22 is provided to the FSK transmitter 44 within its co-located auxiliary communications element 26. The data signal is summed, through adder 46 with the PSK transmitter output of modem 18. The composite output at the remote site is connected to a telephone channel and thereby to the local site (i.e., the location of communications equipment 16). High and low pass filters 48 and 50 separate the composite PSK and FSK signals at the local site and feed them respectively to the PSK input and FSK receiver 52. The FSK receiver data output is combined by means of OR gate 54 with the output of local auxiliary processing equipment 20 and fed to the central controller. 
     As will be noted from the following detailed description of the relationship between the auxiliary communications equipments and central controller, a key feature of the central controller is that it continually addresses and queries each auxiliary processing equipment in the network as to the status of that auxiliary processing equipment, the corresponding communications equipment, the corresponding data terminal and the status of the communications media with regard to channel impairments. If the equipments at the site queried are not in a normal state, an alarm response is returned to the central controller from the queried auxiliary processing equipment. The alarm response also includes both the address or identification of the auxiliary processing equipment generating the alarm as well as the class of parameter which is not within normal limits and generated the alarm. 
     FIG. 3 presents the output spectra of the PSK transmitter and FSK transmitter. The PSK energy is in a frequency band of 1,000 to 2,600 Hz and the FSK energy is in a frequency band of 340 to 540 Hz. Hence, both these signals may be simultaneously transmitted on a telephone channel without mutual interference. Also shown in FIG. 3 are the characteristics of high pass and low pass signal separating filters. 
     The command or interrogation signalling formats used by the central controller 28 is one of two types. Type 1 interrogations are used when the central controller automatically polls each auxiliary processing element 20 and 22 as to whether or not the auxiliary processing element has determined that any parameters relating to its data terminal equipment, communication media, communications equipment or the auxiliary processing equipment itself are at alarm level. The poll format expressed in bits is 000A 1  A 2  A 3  A 4  A 5  P1. The first bit is set to 0 to indicate a start bit of the character. The next two bits are set to 0 also. Next five address bits A 1  through A 5  occur. A parity check of the preceding seven bits follows and finally a 1 is included to indicate the end of the character. A second word composed of 
     
         0A.sub.6 A.sub.7 A.sub.8 A.sub.9 FFFP1 
    
     follows. The first bit is again a 0 to indicate start of character. Next four more address bits follow. Three format indicator bits, indicated by FFF follow. Finally, a parity bit and a 1 to indicate end of character are included. 
     If the format indicator bits are 000, the message is an auto scan query and the total message length is two characters. 
     If the format indicator bits are 001, the query contains a third character. This third character contains a specific command. The bit pattern for the command character is 
     
         0C.sub.1 C.sub.2 C.sub.3 C.sub.4 C.sub.5 C.sub.6 C.sub.7 P1 
    
     where the C k  s are employed to indicate the specific command type. 
     The response of the auxiliary processing equipment to an autoscan poll may be one of two types. If no parameters have reached an alarm limit level, the auxiliary processing equipment echoes back the query. If an alarm has occurred, the auxiliary processing equipment echoes the query plus two additional characters which indicate the cause(s) of the alarm(s). The 14 data bits contained in the two characters contain the following information: 
     
         ______________________________________B1               DTE interface AlarmB2               Phase Jitter AlarmB3               Signal to Noise Ratio AlarmB4               Signal Quality AlarmB5               Received Signal Level AlarmB6               Power Supply Voltage AlarmB7               SpareB1               Standby CE AlarmB2               CE in Test ModeB3               Message Front Panel Switch ONB4               SpareB5               External Input ONB6               SpareB7               Spare______________________________________ 
    
     The response to the status query is a 32 character message which is composed of the following characters: 
     
         ______________________________________CH.sub.1 -CH.sub.2       AddressCH.sub.3 -CH.sub.6       Status as detailed belowCH.sub.7    Phase Jitter ValueCH.sub.8    SpareCH.sub.9 -CH.sub.10       Sum of c.sup.2CH.sub.11 -CH.sub.12       Sum of d.sup.2CH.sub.13   CE Power Supply Voltage ValueCH.sub.14   Receiceived Signal Level ValueCH.sub.15 -CH.sub.16       LSD Alarm Timer Limit ValueCH.sub.17 -CH.sub.18       RTS Alarm Timer Limit ValueCH.sub.19 -CH.sub.20       CTS Alarm Timer Limit ValueCH.sub.21   RLS Alarm Limit ValueCH.sub.22   Phase Jitter Alarm Limit ValueCH.sub.23 -CH.sub.24       SNR Alarm Limit ValueCH.sub.25   Status as detailed belowCH.sub.26   Frequenty Offset ValueCH.sub.27   Release Number of ROMS in APECH.sub.28 -CH.sub.32       Spare______________________________________ 
    
     The 35 status bits in characters three, four, five, six and 25 are defined as follows: 
     
         ______________________________________B1         Transmit Data Activity -      normal or alarmB2         Receive Data Out - normal or alarmB3         Transmit Clock Out -      normal or alarmB4         Receive Clock - normal or alarmB5         Signal Quality - good or badB6         CE Muted - yes or noB7         CE in Test Mode - yes or noB8         ROM Release Number in Character 27 -      yes or noB9         CE 5v Supply Voltage - normal      or alarmB10        Standby CE 5v Supply Voltage -      normal or alarmB11        Analog Loopback - enabled or      disabledB12        Digital Loopback - enabled or      disabledB13        APE Self-test - passed or failedB14        CE Self-Test - passed or failedB15        DTE CTS - normal or alarmB16        DTE RTS - normal or alarmB17        Line Signal Detect - normal or alarmB18        CE Local Test Mode - yes or noB19-B20    CE Type      01 is 4800      10 is 2400      11 is 9600B21        Standby CE Available - yes or noB22        Data Set Ready - on or offB23        Data Terminal Ready - on or offB24        CE Stream Disabled - yes or noB25        CE Rate - high or lowB26        Dial Line Connected - yes or noB27        Auto Answer - enabled or disabledB28        CE is - remote or masterB29        CE in Control is - main or standbyB30        Standby CE Self-Test - pass or failB31        Customer Data Lines - leased or      dialedB32        Telemetry Data Lines - leased or      DialedB33        Standby CE - present or absentB34        Dial Backup Equipment - present or      not presentB35        Dial Under APE Control - yes or no______________________________________ 
    
     From a study of the two responses which have been discussed in detail, it is obvious that the central controller 28 may assess the condition of all communication equipment, auxiliary processing equipment, and the parameters which relate to the condition of the communication media in both directions. Additionally, as discussed in the previously mentioned copending applications, the information is obtained without interruption of normal customer data traffic. Numerous other commands may also be employed to provide reconfiguration functions such as: 
     
         ______________________________________1.         Switch in standby CE2.         Change data rate of CE3.         Cause CE to answer dialed call4.         Cause CE to perform bit error rate      test5.         Cause CE to perform detailed out-of-      service self test6.         Turn off CE______________________________________ 
    
     Hence, an operator at the central controller location may assess the performance of the total communication network and all elements of the network. Moreover, he may reconfigure the network or its elements to compensate for or offset degradations within the network. 
     Thus, in accordance with the above, the aforementioned objectives are effectively attained.