Abstract:
A passive remote loop-back method and apparatus for optical circuit verification is described. The apparatus may be remotely controlled through either of a dial-up or a data connection. The apparatus is adapted to: perform loop-back of received optical signals; verify status on loss of carrier; and, verify the status of its dual power supplies. The apparatus is also adapted to report alarm conditions by dialing a predetermined telephone number. The advantage is a versatile apparatus that may be monitored by a remote manager, and which automatically reports alarms using a dependable alternate communications medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under Title 35, USC § 120 to U.S. patent application Ser. No. 60/115,347 filed Jan. 8, 1999. 
    
    
     TECHNICAL FIELD 
     This invention relates to remote management and monitoring of fiber optic circuits and, in particular, to a method and apparatus for enabling remote monitoring of a fiber optic circuit that terminates on the apparatus. 
     BACKGROUND OF THE INVENTION 
     The use of fiber optics as a signal distribution medium is becoming increasingly popular. This is due to several factors. Fiber offers by far the greatest bandwidth of any transmission system. Since fiber is dielectric, it is not susceptible to radio or electromotive interference. Neither does it emit radio or electromotive interference. Although light signals suffer from attenuation, they are less prone to attenuate than electrical signals on a copper medium. Fiber is also intrinsically secure, because it is virtually impossible to place a physical tap without detection. Since no light is radiated outside a fiber optic&#39;s cable, physical taps are the only means of signal interception. For all these reasons, the use of fiber optic delivery systems is becoming ubiquitous. 
     Optical fibers are of two basic types, multi-mode and single mode. Multi-mode fiber is less expensive to produce, but has lower performance than single mode fiber because the inner core is larger in diameter. As the light rays travel down a Multi-node fiber, they disperse due to a phenomenon known as modal dispersion. Although reflected back into the inner core by the cladding on the fiber strands, different light rays travel different distances and therefore arrive at different times. As a length of the circuit increases and the speed of transmission increases, the pulses of light tend to interfere with each other in a phenomenon known as pulse dispersion. At that point, the light detector is unable to distinguish between the individual pulses. As a result, multi-mode fiber is generally used in applications involving relatively short distances and lower speeds, such as within customer premises. 
     Single mode fiber has a thinner inner core. It therefore performs better than multi-mode fiber over longer distances and at higher transmission rates. Although more expensive to manufacture, single mode fiber is used in long distance transmission links and particularly in high bandwidth applications. 
     Carriers typically use single mode fiber for fiber circuits to deliver services to customer premises. Customers typically use multi-mode fiber because it is less expensive and normally adequate for service delivery within the restricted environment of the customer premises. An interface is required at the customer demarcation point to convert from single mode to multi-mode signals. Such interfaces are well known in the art. A problem frequently experienced with such interfaces is that faults are difficult to isolate. When a communications fault is reported to a service provider, the service provider frequently has no choice but to dispatch a customer service representative to isolate the problem. There therefore exists a need for an apparatus adapted to terminate a fiber circuit that is capable of self-monitoring as well as being capable of entering a command mode that permits remote testing of the fiber circuit by providing a loop-back function to enable the fiber circuit to be monitored by sending a signal to the apparatus and checking to determine whether the same signal is received from the apparatus. 
     There is also a need for an apparatus that is secure, to ensure that unauthorized individuals cannot assume control or influence the operation of the fiber optic circuit. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an apparatus for enabling remote testing of a fiber optic circuit between a first end point and the apparatus. 
     It is a further object of the invention to provide an optical repeater that is adapted to enable testing of fiber optic circuits to which it is connected. 
     The invention therefore provides an apparatus that enables remote testing of a fiber optic circuit between a first end point and the apparatus, and a second fiber optic circuit between the apparatus and a second end point. The apparatus comprises a first transceiver for terminating the first fiber optic circuit between the first end point and the apparatus, and a second transceiver for terminating the second fiber optic circuit between the apparatus and the second end point. The apparatus also includes a high speed multiplexer that interconnects the first and second transceivers. A control unit of the apparatus controls the high speed multiplexer and automatically monitors other predetermined functions of the apparatus. The apparatus also includes at least one communications port for remotely communicating with the control unit to permit a remote administrator to perform remote testing of the fiber circuit and to monitor the other predetermined functions of the apparatus. 
     Typically, the first end point for the first fiber optic circuit is a service provider&#39;s equipment, and the second end point is a customer premise equipment, a local area network (LAN), for example. The first and second end points may also be repeaters in a fiber optic link. 
     The first and second fiber optic circuits may operate in different transmission modes. Typically, the first fiber optic circuit operates in a single mode and the second fiber optic circuit operates in a multi-mode. The apparatus in accordance with the invention is adapted to automatically convert from one mode to the other, and vice versa. 
     The apparatus in accordance with the invention is also adapted to control the high speed multiplexer on command, to loop-back signals received by either the first and second transceivers. This permits a remote administrator to test the integrity of a fiber optic circuit by commanding the transceiver to loop-back a signal sent from one of the first and second ends and monitoring receipt of the same signal. If the looped-back signal is received, the fiber optic circuit is determined to be operational without dispatching service personnel. 
     Command control of the apparatus is effected through at least one telecommunications port. Preferably, a telephone modem interface and a data interface are both provided. Access through each interface is strictly controlled by programmed procedures that only accept communications sessions from selected addresses. Any attempt to establish a communications session from any other address raises an alarm. Preferably, the alarm is automatically reported by the apparatus, which establishes a communications session with a predetermined address to report the alarm. The communications session is preferably established through the Public switched Telephone Network (PSTN) using the telephone modem interface. 
     The invention also provides a method of monitoring a remote apparatus for providing a connection between first and second fiber optic circuits, the remote apparatus converting optical signals received from either of the first and second fiber optic circuits into electrical signals and converting the electrical signals back into optical signals sent through an appropriate one of the first and second fiber optic circuits. The apparatus includes a control unit for monitoring functions of the apparatus. In accordance with the method, the apparatus automatically cyclically monitors predetermined functions of the apparatus to determine whether each of the predetermined functions are operating within a predetermined range. If the apparatus determines that any one of the functions is not operating within the predetermined range, the apparatus raises an alarm. The apparatus preferably determines whether the alarm is an alarm to be reported. It the alarm is an alarm to be reported, the apparatus automatically establishes a communications session with a predetermined alarm report address and automatically reports the alarm. In accordance with a preferred embodiment of the invention, every alarm is an alarm to be reported. 
     Preferably, the apparatus in accordance with the invention monitors at least: a) carrier on the first fiber optic circuit; b) carrier on the second fiber optic circuit; c) status of the main power supply; and d) status of the backup power supply. The apparatus may also monitor status of lasers used for sending optical signals through the first and second fiber optic circuits. 
     The invention also provides a method of securing a remote apparatus for providing a connection between first and second fiber optic circuits, the remote apparatus converting optical signals received from either of the first and second fiber optic circuits into electrical signals and converting the electrical signals back into optical signals sent through an appropriate one of the first and second fiber optic circuits. The apparatus includes a control unit for controlling and monitoring functions of the apparatus. The control unit is automatically operated to monitor communications ports of the apparatus for a communications connection request. On receipt of a communications connection request, the control unit automatically determines whether the communications request originated from a predetermined address. The communications request is rejected by the control unit if the communications request did not originate from the predetermined address. Preferably, an invalid communications request raises an alarm condition. If an alarm condition is raised, the control unit preferably automatically establishes a communications session with a predetermined report address to report the alarm. 
     The invention also provides a method of testing a fiber optic circuit using the apparatus in accordance with the invention. The fiber optic circuit is tested by establishing a communications session with the apparatus and instructing the control unit to loop-back optical signals on the fiber optic circuit to be tested. An optical signal is then sent from an end of the fiber optic circuit to be tested. On receipt of the signal, the apparatus loops the signal back on the same fiber optic circuit, and the remote administrator monitors the fiber optic circuit for return of the same signal. If the same signal is returned, the fiber optic circuit is determined to be in a functional condition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which; 
     FIG.  1 . is a schematic block diagram of an apparatus in accordance with the invention; 
     FIG. 2 is a schematic diagram of networks used in establishing a dial-up communications session with the apparatus shown in FIG. 1; 
     FIG. 3 is a schematic diagram of the networks used in establishing a communications session through a data network with the apparatus shown in FIG. 1; 
     FIG. 4 is a flow diagram illustrating the control logic used for controlling access to the apparatus shown in FIG. 1; and 
     FIG. 5 is a flow diagram illustrating the logic used in monitoring predetermined functions of the apparatus shown in FIG.  1  and reporting alarm conditions. 
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a block diagram that schematically illustrates a preferred embodiment of an apparatus  10  in accordance with the invention. The apparatus  10  may serve as a demarcation point between a service provider fiber optic circuit and a customer premise fiber optic circuit or as a repeater in a fiber optic link. 
     The apparatus  10  includes a microprocessor based control unit  12  that controls functionality of the apparatus  10 , and automatically monitors certain functions of the apparatus, as will be explained below in more detail with reference to FIG.  5 . The apparatus  10  also includes a high speed multiplexer  14  which may be, for example, a Positive Emitter Collector Logic (PECL) multiplexer, which is well known in the art. The high speed multiplexer  14  receives data input from the fiber optic transceiver  16   a  connected to a service provider fiber optic circuit via data input  22   a . The high speed multiplexer  14  likewise receives data from a fiber optic transceiver  16   b  connected to a fiber optic circuit associated with a customer&#39;s premise, for example. Data from the fiber optic circuit  16   b  is passed through data input  20   b  to the high speed multiplexer  14 . During normal communications, data arriving at fiber optic transceiver  16   b  is passed over the input  20   b  to the high speed multiplexer which may perform a mode conversion before passing the data over data output  20   a  to the fiber optic transceiver  16   a  which outputs optical signals over the associated fiber optic circuit. Likewise, optical signals received at fiber optic transceiver  16   a  are converted to electrical signals that are transferred to the high speed multiplexer  14  over input  22   a  and output by the high speed multiplexer  14  over output  22   b  to the fiber optic transceiver  16   b , which converts the electrical signals to light signals output on the associated fiber optic circuit. A fiber signal detect circuits  24   a ,  24   b  enable the control unit  12  to monitor the carrier signal received by the respective fiber optic transceivers  16   a ,  16   b.    
     When fiber optic circuit verification is required, the control unit  12  is enabled to control the high speed multiplexer  14  by sending commands over control channel  18  to cause the high speed multiplexer  14  to loop-back signals received by either one or both of the fiber optic transceivers  16   a ,  16   b . This permits an administrator to send a signal over one of the fiber optic circuits associated with one or both of the fiber optic transceivers  16   a ,  16   b , and monitor receipt of the same signal. If the same signal is returned, integrity of the fiber optic circuit is verified. 
     The apparatus  10  also includes redundant power supplies  26  and  28 . The power supply  26  is connected to a primary source of power, such as a direct current (DC) input. The power supply  28  is connected to a backup power supply that provides operating power if the primary power supply  26  fails, or power is interrupted. Power monitor connections  30 ,  32  permit the control unit  12  to monitor the status of the respective power supplies  26 ,  28 . 
     The apparatus  10  also includes at least one communications port to permit a remote administrator to control the apparatus  10  for the purpose of testing either one of the fiber optic circuits  16   a ,  16   b . The telephone modem interface  34  is a standard dial-up interface well known in the art. A connector  38  enables communications between the control input  12  and the telephone modem interface  34 . The apparatus  10  is likewise preferably equipped with a data communications port  36 , such as an RS-232 level converter, which enables communication via a data network such as a Wide Area Network (WAN), for example. A communications connection  40  permits the control unit  12  to exchange data with the data port  36 . 
     FIG. 2 is a schematic diagram of the apparatus  10  in a typical environment in which the apparatus is installed at a demarcation point between a provider&#39;s fiber network and customer equipment. As shown in FIG. 2, a service provider premise  42  includes service provider equipment  44  and management workstation  46 . As will be understood by those skilled in the art, service provider premises are considerably more complex and the schematic illustration shown in FIG. 2 only illustrates those components related to the invention. The management workstation  46  is connected to a modem  48  in a manner well known in the art. The modem  48  can be used in a dial-up connection to access the apparatus  10  for testing and diagnostic purposes, as will be explained below with reference to FIGS. 4 and 5. Access is accomplished through the PSTN  50  in a manner well understood in the art. The modem  48  is connected to the PSTN  50  by a local loop  62 , for example, and the telephone modem interface  34  (FIG. 1) is connected to the PSTN by a local loop  64 . The service provider&#39;s equipment  44  is connected to the service provider&#39;s fiber network  52  and to the apparatus  10  by a first fiber optic circuit  58 . The customer equipment  56  is connected to the apparatus  10  by a second fiber optic circuit  60 . The management workstation  46  is able to access the apparatus  10  by dialing a telephone number associated with the apparatus  10  in a manner well known in the art. 
     FIG. 3 is a schematic illustration of communications connections used to access the apparatus  10  from a management workstation  46  through a data network  70 . The management workstation  46  is connected by a data connection  65  (a Local Area Network, for example) to a server, adapter or router  66 , for example. The server  66  is connected by a data link  68  to a data network  70 . A customer server, adapter or router  74  is connected to the data network  70  by a data link  72 . The apparatus  10  is connected to the server, adapter or router  74  by a data connection  76 , a LAN for example. The management station  46  is adapted to access the apparatus  10  by establishing a data connection using any one of a number of protocols well known in the art. 
     FIG. 4 is a flow diagram illustrating a process in which the management workstation  46  accesses apparatus  10  and enters a command mode used, for example, to test the fiber optic circuit  58  (FIGS. 2,  3 ). In step  80 , the apparatus  10  waits for a connect request by listening to each of the communications ports  34 ,  36  (FIG.  1 ). On receipt of a connect request, the apparatus  10  determines whether the request originates from communications port  34  or  36  in step  82 . If the request is a dial-up request, the apparatus  10  preferably extracts a Calling Line Identification (CLID) from the connect request and compares it with a stored CLID (pCLID) to determine whether the connect request is authorized. If it is determined in step  82  that the request is not a dial-up request, in step  86  the control unit  12  compares an address of the connection request (IP address, for example) with, for example, a range of acceptable addresses to determine whether the request originates from an authorized location (step  86 ). 
     If the communications request is determined to have originated from an authorized location in either of steps  84  or  86 , a variable (Tries) is set to “0” in step  90  and the administrator is requested to enter a password in step  92 . In step  94 , the password is compared with a stored password associated with the CLID or the IP address to determine whether the administrator has rights to access the apparatus  10 . If passwords do not match, the variable initiated in step  90  is incremented in step  96  and compared with a threshold (pTHRESHOLD) in step  98 . If the threshold is not exceeded, the control unit  12  again requests the password in step  92 . If the threshold is exceeded, the connect request is discarded and the communications port is disconnected in step  100 , an alarm is raised in step  102 , and the control unit  12  returns to the waiting state in step  80 . 
     If the password is accepted in step  94 , access is granted in step  104  and command mode is enabled in step  106 . In command mode, the control unit  12  waits for commands sent by the management station  46  (FIG. 2,  3 ) and responds to those commands. On receipt of a command in step  108 , the control unit  12  examines the command in step  110  to determine whether the command equals logoff. If not, the control unit  12  performs the command in step  112  and returns to the waiting state for a next command. If the command is a logoff command, the control unit  12  disables command mode in step  114 , disconnects in step  116  and returns to the wait state for a connect request. 
     FIG. 5 is a flow diagram that illustrates the logic of a preferred monitoring function performed by the control unit  12  when the control unit  12  is not in command mode. Preferably, the control unit  12  automatically and cyclically monitors certain predetermined functions of the apparatus  10  when it is not operating in command mode. Those functions include, for example, the status of the carrier signals on the fiber optic transceivers  16   a ,  16   b  (FIG.  1 ), the status of the power supply  26  and the power supply  28 , as well as the status of the communications ports  34  and  36 . Other functions including the status of output lasers (not shown) of the fiber optic transceivers  16   a ,  16   b  may likewise be monitored. 
     In a preferred automatic process, the control unit  12  monitors a function in step  150 , using methods well known in the art, and determines in step  152  whether the function is operating within a predetermined range. If the function is operating within the predetermined range, a next function is selected in step  154  and that function is monitored in step  150 . If the function is not operating within the predetermined range, an alarm is raised in step  156 . Preferably, an alarm log is updated in step  158  and the level of the alarm is compared with an alarm threshold in step  160 . If the alarm level does not exceed the threshold, the process returns to select a next function to be monitored in step  154 . If the alarm level exceeds the threshold, the control unit  12  is preferably programmed to establish a connection with system management in step  162  using one of the communications ports  34 ,  36 . For example, the control unit  12  may be programmed to dial a specified number using the telephone modem interface  34  in order to report alarms. After the communication session is established, the control unit  12  reports the alarm in step  164 . After reporting the alarm, the control unit may return to monitoring functions, or may enter a shutdown state, depending on the severity of the alarm and the nature of the malfunction. 
     It is therefore apparent that the apparatus  10  in accordance with the invention a useful tool which may be used as an interface between a service provider and a customer network, or as a repeater in a fiber optic link. Although the examples described above relate exclusively to the use of the apparatus  10  as an interface between two networks, it will be apparent to those skilled in the art that the apparatus may also be used as a repeater in a fiber optic link. As such, the apparatus  10  permits either portion of the link to be monitored for link integrity and any hardware problems associated with the apparatus  10  are automatically reported, as described above. 
     The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.