Patent Publication Number: US-RE42178-E

Title: Fiber optic conversion system and method

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates generally to fiber optic communication and-more particularly to a fiber optic conversion system and method. 
     BACKGROUND OF THE INVENTION 
     Electrical data systems that communicate over cables are sensitive to noise and generally limited in terms of distance between components coupled together by such cables. One solution to this problem is the use of fiber optic links between-components. 
     Fiber optic links are relatively insensitive to noise and allow for great distances between components. However, disadvantages associated with incorporating fiber optic links into existing electrical systems include the need for protocol logic processing or an enable status line. 
     Thus, fiber optic communication may not be possible in systems in which enable status lines are unavailable without complex protocol-specific fiber optic converters to convert the electrical signals into fiber optic signals. In addition, utilizing either protocol logic processing or an enable status line to implement a fiber optic converter is relatively expensive in terms of labor and equipment. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a fiber optic conversion system and method are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed systems and methods. In particular, fiber optic converters may be implemented without the use of protocol logic processing or an enable status line. 
     In one embodiment of the present invention, a fiber optic conversion method is provided that includes receiving a first electrical signal. A second electrical signal is received. The first and second electrical signals are compared. A float signal is generated when the first and second electrical signals comprise substantially a same electrical signal. A determination is made regarding whether optical signals are being received. A light signal is generated while optical signals are being received. A driver mode is entered in response to the float signal and the light signal being generated simultaneously. The driver mode is remained in while the light signal is being generated. 
     Technical advantages of one or more embodiments of the present invention include providing an improved fiber optic conversion method. In a particular embodiment, the fiber optic converter monitors the fiber optic link for a driver and becomes a driver itself when none is detected. The fiber optic converter becomes a receiver when fiber optic signals are no longer being received. Accordingly, there is no need for an enable status line or protocol monitoring circuitry. As a result, fiber optic links may be established between major nodes of existing electrical systems more inexpensively. In addition, fiber optic communication may be provided in systems in which enable status lines are unavailable. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like numerals represent like parts, in which: 
         FIG. 1  is a block diagram illustrating a fiber optic conversion system comprising fiber optic converters in accordance with one embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating the fiber optic converter of  FIG. 1  in accordance with one embodiment of the present invention; 
         FIGS. 3A and 3B  are schematic diagrams illustrating the fiber optic converter of  FIG. 1  in accordance with one embodiment of the present invention; and 
         FIG. 4  is a flow diagram illustrating a fiber optic conversion method for the fiber optic converter of  FIG. 1  in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram illustrating a fiber optic conversion system  10  comprising fiber optic converters  20  in accordance with one embodiment of the present invention. The conversion system  10  may comprise a commercial avionic system, a military avionic system, a data communication system, or other suitable system. 
     The conversion system  10  comprises two fiber optic converters  20  and two electrical systems  24 , in addition to two buses  30  and two fiber optic lines  34 . The two electrical systems  24  may be closely coupled together or may be remote from each other and located virtually anywhere with respect to each other, provided that fiber optic lines  34  are available to couple the fiber optic converters  20  to each other. 
     Each electrical system  24  is operable to communicate over a bus  30 . As used herein, “each” means every one of at least a subset of the identified items. Each bus  30  comprises at least two bi-directional lines, with one line carrying a digital signal and the other line carrying the complement of the digital signal carried on the first line. For example, the bus  30  may comprise an EIA-485 or other suitable bus. 
     Each fiber optic converter  20  is operable to communicate with its corresponding electrical system  24  through the corresponding bus  30 , as well as with another fiber optic converter  20  through the fiber optic lines  34 . Thus, the fiber optic converters  20  are operable to provide fiber optic communication between the electrical systems  24  through the buses  30  for the electrical systems  24 . 
     In accordance with one embodiment, fiber optic line  34 a may provide optical signals from fiber optic converter  20 a to fiber optic converter  20 b, while fiber optic line  34 b provides optical signals from fiber optic converter  20 b to fiber optic converter  20 a. However, it will be understood that the fiber optic lines  34  may be otherwise suitably implemented without departing from the scope of the present invention. For example, fiber optic line  34 a may provide optical signals from fiber optic converter  20 b to fiber optic converter  20 a while fiber optic line  34 b provides optical signals from fiber optic converter  20 a to fiber optic converter  20 b. 
     In operation, the electrical system  24 a may communicate with the electrical system  24 b by transmitting information through the bus  30 a to the fiber optic converter  20 a. The fiber optic converter  20 a is in a receiver mode at this point. The receiver mode corresponds to the mode in which the fiber optic converter  20  is receiving electrical signals from the bus  30  and generating optical signals for transmission over a fiber optic line  34 . 
     Thus, according to one embodiment, the fiber optic converter  20 a converts the electrical signals from the system  24 a into optical signals and transmits them to the fiber optic converter  20 b over the fiber optic line  34 a. The fiber optic converter  20 b is in the driver mode at this point. The driver mode corresponds to the mode in which the fiber optic converter  20  is receiving optical signals over a fiber optic line  34  and generating electrical signals for transmission over the bus  30 . The fiber optic converter  20 b enters the driver mode based on detecting floating lines for the bus  30 b and detecting optical signals on the fiber optic line  34 a, as described in more detail below. 
     After receiving the optical signals, the fiber optic converter  20 b converts the optical signals into electrical signals and transmits them to the system  24 b over the bus  30 b. The system  24 b may then transmit information back to the system  24 a in a similar manner, using fiber optic line  34 b. 
       FIG. 2  is a block diagram illustrating the fiber optic converter  20  in accordance with one embodiment of the present invention. The fiber optic converter  20  comprises a bus connector  50 , a driver  54 , a comparator/receiver  58 , a fiber optic transmitter  66 , a fiber optic receiver  70 , a voltage adjustment circuit  74 , a light monitor  78 , a delay circuit  82 , and a mode selector  92 . 
     Any or all of the bus connector  50 , the driver  54 , the comparator/receiver  58 , the fiber optic transmitter  66 , the fiber optic receiver  70 , the voltage adjustment circuit  74 , the light monitor  78 , the delay circuit  82 , and the mode selector  92  may comprise logic encoded in media. The logic comprises functional instructions for carrying out program tasks. The media comprises computer disks or other computer-readable media, application-specific integrated circuits, field-programmable gate arrays, digital signal processors, other suitable specific or general-purpose processors, transmission media or other suitable media in which logic may be encoded and utilized. 
     The bus connector  50  is operable to receive electrical input signals from the bus  30  and transmit electrical output signals to the bus  30  through terminal A  86  and terminal B  88 . The bus connector  50  also receives a power supply and a ground (not shown in  FIG. 2 ) from the bus  30  for use in the fiber optic converter  20 . 
     The driver  54  is coupled to the bus connector  50 . The driver  54  is operable to provide output signals to the bus connector  50  for transmission to the bus  30  when the fiber optic converter  20  is in the driver mode. 
     The comparator/receiver  58  is also coupled to the bus connector  50  and is operable to receive input signals from the bus  30  through the bus connector  50  when the fiber optic converter  20  is in the receiver mode. The comparator/receiver  58  is also operable to compare the signals received from the bus connector  50  and to provide a float signal to the mode selector  92  when the comparator/receiver  58  determines that the signals are floating, i.e., the signals are substantially the same, instead of being complementary as non-floating input signals from the bus  30  would be. 
     The fiber optic transmitter  66  is coupled to the comparator/receiver  58  and is operable to receive electrical input signals from the bus  30  via the bus connector  50  and the comparator/receiver  58 . The fiber optic transmitter  66  is also operable to convert the electrical input signals into optical signals and to generate optical signals for transmission along a fiber optic line  34  to another device, such as another fiber optic converter  20  coupled to a system  24  or other suitable receiving device. 
     The fiber optic receiver  70  is coupled to the delay circuit  82  and is operable to receive optical signals from a fiber optic line  34  to another device, such as another fiber optic converter  20  coupled to a system  24  or other suitable transmitting device. The fiber optic receiver  70  is also operable to convert the optical signals into electrical output signals and to provide the electrical output signals to the driver  54  via the delay circuit  82  for transmission to the bus  30  via the bus connector  50 . 
     The voltage adjustment circuit  74  is coupled to the bus connector  50 , the driver  54 , and the comparator/receiver  58 . The voltage adjustment circuit  74  is operable to cause the signals from the bus connector  50  to the driver  54  and to the comparator/receiver  58  to float to a specified common voltage potential. According to one embodiment, the specified common voltage potential comprises approximately 5.0 volts. However, it will be understood that the specified common voltage potential may comprise any suitable voltage potential without departing from the scope of the present invention. 
     The light monitor  78  is coupled to the fiber optic receiver  70 . The light monitor  78  is operable to determine whether or not the fiber optic receiver  70  is receiving optical signals. The light monitor  78  is also operable to provide a light signal to the mode selector  92  when the light monitor  78  determines that the fiber optic receiver  70  is receiving optical signals. 
     The delay circuit  82  is coupled to the fiber optic receiver  70  and to the driver  54 . The delay circuit  82  is operable to delay any electrical signals generated by the fiber optic receiver  70  in response to received optical signals before providing the electrical signals to the driver  54  for transmission to the bus  30  via the bus connector  50  when the fiber optic converter  20  is in the driver mode. As used herein, a first event is said to occur “in response to” a second event when the first event subsequently follows and is a result of the second event. The first event need not immediately follow the second event. 
     The mode selector  92  is coupled to the comparator/receiver  58  and to the light monitor  78 . The mode selector  92  is operable to receive a float signal from the comparator/receiver  58  and to receive a light signal from the light monitor  78 . Based on the presence or absence of these signals, the mode selector  92  is operable to place the fiber optic converter  20  into either the driver mode or the receiver mode by providing a corresponding signal to the driver  54 . 
     In addition, the mode selector  92  is coupled to the fiber optic transmitter  66  and is operable to enable the fiber optic transmitter  66 , such that the fiber optic transmitter  66  may transmit optical signals, when the fiber optic converter  20  is in the receiver mode and to disable the fiber optic transmitter  66 , such that the fiber optic transmitter  66  will not transmit optical signals, when the fiber optic converter  20  is in the driver mode. 
     In operation, the fiber optic converter  20  may begin in the receiver mode. While in the receiver mode, the bus connector  50  receives electrical signals from the bus  30  at terminals A  86  and B  88 . The comparator/receiver  58  receives these electrical signals from the bus connector  50  and provides them to the fiber optic transmitter  66  for transmission along a fiber optic line  34 . In addition, the comparator/receiver  58  does not generate a float signal for the mode selector  92  because the signals corresponding to terminals A  86  and B  88  are not substantially the same, but rather are complementary values. 
     After electrical signals are not received at terminals A  86  and B  88 , the voltage adjustment circuit  74  causes the signals corresponding to the terminals A  86  and B  88  to float to the specified common voltage potential. The comparator/receiver  58  then detects that the signals are substantially the same and generates the float signal for the mode selector  92 . The fiber optic converter  20  remains in the receiver mode, however, until the light monitor  78  detects light from the fiber optic receiver  70 . If no light is received, electrical signals may again be received at terminals A  86  and B  88  and the float signal will no longer be generated. 
     However, if the light monitor  78  does detect light from the fiber optic receiver  70 , the light monitor  78  generates the light signal for the mode selector  92 . If the mode selector  92  is receiving both the float signal and the light signal simultaneously, the mode selector  92  provides a signal to the driver  54  that converts the fiber optic converter  20  to the driver mode. 
     The delay circuit  82  delays the optical signal for a period of time sufficient to allow the fiber optic converter  20  to enter the driver mode such that the driver  54  is ready to process the optical signal when it is received from the fiber optic receiver  70 . 
     While in the driver mode, the fiber optic converter  20  receives optical signals at the fiber optic receiver  70 , the fiber optic receiver  70  converts the optical signals to electrical signals and provides them to the driver  54  through the delay circuit  82 , and the driver  54  provides the electrical signals to the bus connector  50  for transmission through terminals A  86  and B  88  to the bus  30 . 
     The fiber optic converter  20  remains in the driver mode until the light monitor  78  no longer generates the light signal. Thus, the float signal may be removed from the mode selector  92  once the fiber optic converter  20  has entered the driver mode, as will be the case when the signals corresponding to terminals A  86  and B  88  become complementary electrical signals for transmission over the bus  30 . 
     However, once the light signal is no longer generated by the light monitor  78 , the mode selector  92  returns the fiber optic converter  20  to the receiver mode. According to one embodiment, an adjustable delay may be included such that the light monitor  78  may continue to generate the light signal for an amount of time corresponding to the delay before the light monitor  78  no longer generates the light signal. 
     At this point, the fiber optic converter  20  may reenter the driver mode if the float and light signals are again received simultaneously at the mode selector  92 . Alternatively, the fiber optic converter  20  may remain in the receiver mode and begin receiving electrical signals. 
       FIG. 3  is a schematic diagram illustrating the fiber optic converter  20  in accordance with one embodiment of the present invention. According to this embodiment, the bus connector  50  comprises a 14-pin connector that is operable to receive and transmit signals from the terminals A  86  and B  88 . 
     The bus connector  50  is also operable to receive a power supply  100  and a ground  102  from the bus  30 . The power supply  100  supplies a higher potential than the ground  102 . According to one embodiment, the power supply  100  provides a potential of approximately 5.0 volts and the ground  102  provides a potential of approximately 0.0 volts. However, it will be understood that the power supply  100  and the ground  102  may provide any suitable potentials without departing from the scope of the present invention. 
     According to one embodiment, the driver  54  comprises an LTC-1485 or other suitable transceiver chip operable to drive an electrical signal. A resistor  104  may be used between the lines corresponding to terminals A  86  and B  88  to ensure proper transmission line impedance matching to the electrical system  24 . 
     According to one embodiment, the comparator/receiver  58  comprises a pair of LTC-1485 or other suitable transceiver chips  106  operable to receive electrical signals. For this embodiment, the comparator/receiver  58  also comprises a pair of diodes  108  for each transceiver chip  106  and a NOR gate  109 . The diodes  108  are operable to reduce the voltage of the signals received from terminals A  86  and B  88 . 
     Thus, for the upper transceiver chip  106 a, the signal from terminal A  86  is reduced approximately 1.2 volts by the diodes  108 a, while the signal from terminal B  88  is not reduced. For the lower transceiver chip  106 b, the signal from terminal B  88  is reduced approximately 1.2 volts by the diodes  108 b, while the signal from terminal A  86  is not reduced. According to one embodiment, the specified common voltage potential provided by the voltage adjustment circuit  74  comprises a voltage that is greater than the voltage drop from terminals A  86  and B  88  to the transceiver chips  106 . Thus, for the embodiment in which a pair of diodes  108  are used to reduce the voltage, the specified common voltage potential may comprise a potential greater than approximately 1.2 volts. 
     When the signals from terminals A  86  and B  88  are substantially the same due to the voltage adjustment circuit  74  causing the signals to float to the specified common voltage potential, the upper transceiver chip  106 a senses that the signal from terminal A  86  is less than the signal from terminal B  88 , while the lower transceiver chip  106 b senses that the signal from terminal B  88  is less than the signal from terminal A  86 . In this situation, the NOR gate  109  goes high based on the low signals from both transceiver chips  106 . This high signal from the NOR gate  109  is provided to the mode selector  92  as the float signal. 
     Similarly, when the voltage adjustment circuit  74  is not causing the signals to float to the specified common voltage potential, both transceiver chips  106  sense that the signal from the same terminal A  86  or B  88  is less than the other signal, resulting in a high signal for one of the transceiver chips  106 . In this situation, the NOR gate  109  goes low, and the float signal is not provided to the mode selector  92 . The fiber optic transmitter  66  comprises an HFBR-1414 or other suitable transmitter  110  operable to receive an electrical signal and generate an optical signal in response to the electrical signal. The transmitter  110  is also operable to be enabled by the mode selector  92  when the fiber optic converter  20  is in the receiver mode and to be disabled by the mode selector  92  when the fiber optic converter  20  is in the driver mode. 
     The fiber optic transmitter  66  also comprises a plurality of resistors  112 , a plurality of capacitors  114 , a plurality of NAND gates  116 , and a NOR gate  118 . These components  112 ,  114 ,  116  and  118  may be used to provide the appropriate electrical signal to the transmitter  110  to cause the transmitter  110  to generate an optical signal. For example, the NOR gate  118  may be used to invert the signal received from the mode selector  92 . 
     According to one embodiment, the resistor  112 a comprises a relatively high resistance, such as approximately 1300Ω, in order to ensure that no optical signal is inadvertently transmitted at the wrong moment. However, it will be understood that the resistor  112 a may comprise any suitable resistance, such as at least 270Ω, without departing from the scope of the present invention. 
     According to one embodiment, the resistors  112 b and  112 c each comprise a resistance of approximately 33.2Ω, the capacitor  114 a comprises a capacitance of approximately 100 nF, the capacitor  114 b comprises a capacitance of approximately 22 μF, and the capacitor  114 c comprises a capacitance of approximately 100 pF. However, it will be understood that the resistors  112 b and  112 c may comprise any suitable resistance and the capacitors  114  may comprise any suitable capacitance without departing from the scope of the present invention. 
     The fiber optic receiver  70  comprises an HFBR-2416 or other suitable receiver  120  operable to receive an optical signal and generate an electrical signal in response to the optical signal. The fiber optic receiver  70  also comprises a resistor  122  and a plurality of capacitors  124 . These components  122  and  124  may be used to generate the appropriate electrical signal in response to the received optical signal. 
     According to one embodiment, the resistor  122  comprises a resistance of approximately 10Ω, and the capacitors  124 a and  124 b each comprise a capacitance of approximately 100 pF. However, it will be understood that the resistor  122  may comprise any suitable resistance and the capacitors  124  may comprise any suitable capacitance without departing from the scope of the present invention. 
     The voltage adjustment circuit  74  comprises a plurality of resistors  126 . According to one embodiment, the resistors  126 a and  126 b each comprise a resistance of approximately 1330Ω. However, it will be understood that the resistors  126  may comprise any suitable resistance without departing from the scope of the present invention. 
     According to one embodiment, the light monitor  78  comprises a fiber optic data quantizer  130 , such as an ML4622 or other suitable fiber optic data quantizer. The quantizer  130  may be coupled to a plurality of capacitors  132 . An adjustable delay may be included such that the light monitor  78  may continue to generate the light signal for an amount of time corresponding to the delay before the light monitor  78  no longer generates the light signal. For example, the delay may be included by the fiber optic data quantizer and may be adjustable based on the capacitor bias associated with the quantizer. 
     According to one embodiment, the capacitor  132 a comprises a capacitance of approximately 100 nF, the capacitor  132 b comprises a capacitance of approximately 10 pF, and the capacitor  132 c comprises a capacitance of approximately 4.7 pF. However, it will be understood that the capacitors  132  may comprise any suitable capacitance without departing from the scope of the present invention. 
     According to one embodiment, the delay circuit  82  comprises a DS1000 chip. However, it will be understood that the delay circuit  82  may comprise any suitable components operable to delay the electrical signals generated by the fiber optic receiver  70  for a period of time sufficient to allow the light monitor  78  to generate the light signal for the mode selector  92 . 
     The mode selector  92  comprises a pair of cross-coupled NOR gates  134 , a resistor  136 , and a capacitor  138 . The two NOR gates  134  together function as a latch. The NOR gate  134 a is operable to receive the float signal from the comparator/receiver  58 , while the NOR gate  134 b is operable to receive the light signal from the light monitor  78 . 
     According to the illustrated embodiment, the float signal corresponds to a high signal, while the light signal corresponds to a low signal. Thus, when the float signal and the light signal are activated, the mode selector  92  activates the enable line  140 , which places the fiber optic converter  20  into the driver mode. 
     Because the NOR gates  134  function as a latch of the float signal, the enable line  140  remains high, keeping the fiber optic converter  20  in the driver mode, until the light monitor  78  no longer generates the light signal, i.e., until the signal goes high. Thus, when the light monitor  78  no longer detects light being received at the fiber optic receiver  70 , the signal goes high and the fiber optic converter  20  returns to the receiver mode. 
     According to one embodiment, the fiber optic converter  20  may also comprise a noise reducer  142 . The noise reducer is coupled to a ground for the fiber optic data quantizer  130  and is operable to reduce noise in the ground signal for the quantizer  130  by eliminating alternating current noise from the ground signal. 
     According to one embodiment, the noise reducer  142  comprises a plurality of capacitors  144  and an inductor  146 . The capacitors  144 a and  144 c each comprise a capacitance of approximately 22 μF, the capacitors  144 b and  144 d each comprise a capacitance of approximately 100 nF, and the inductor  146  comprises an inductance of approximately 15 μH. However, it will be understood that the capacitors  144  may comprise any suitable capacitance and the inductor  146  may comprise any suitable inductance without departing from the scope of the present invention. 
       FIG. 4  is a flow diagram illustrating a fiber optic conversion method for the fiber optic converter  20  in accordance with one embodiment of the present invention. The method begins at step  200  where the fiber optic converter  20  enters the receiver mode. At step  202 , the comparator/receiver  58  receives first and second electrical signals from the bus connector  50  based on the signals from terminals A  86  and B  88 . At step  204 , the comparator/receiver  58  compares the first and second electrical signals. 
     At decisional step  206 , the comparator/receiver  58  determines whether or not the first and second electrical signals are the same. According to one embodiment, the comparator/receiver  58  determines whether or not the first and second electrical signals are the same based on whether or not the voltages associated with each electrical signal are substantially the same. In addition, the electrical signals may be substantially the same as a result of the voltage adjustment circuit  74  causing the signals to float. However, it will be understood that the comparator/receiver  58  may determine whether or not the first and second electrical signals are the same based on any suitable criteria without departing from the scope of the present invention. 
     If the comparator/receiver  58  determines that the first and second electrical signals are not the same, the method follows the No branch from decisional step  206  and returns to step  202  where the comparator/receiver  58  continues to receive first and second electrical signals from the bus connector  50 . 
     However, if the comparator/receiver  58  determines that the first and second electrical signals are the same, the method follows the Yes branch from decisional step  206  to step  208 . At step  208 , the comparator/receiver  58  generates a float signal for the mode selector  92  while the first and second electrical signals remain the same. 
     At step  210 , the light monitor  78  monitors the fiber optic receiver  70  for the presence of light received over a fiber optic line  34 . At decisional step  212 , the light monitor  78  determines whether or not light is present. If light is not present, the method follows the No branch from decisional step  212  and returns to step  210  where the light monitor  78  continues to monitor the fiber optic receiver  70  for the presence of light. 
     However, if light is present, the method follows the Yes branch from decisional step  212  to step  214 . At step  214 , the light monitor  78  generates a light signal for the mode selector  92  while light remains present. At step  216 , the fiber optic converter  20  enters the driver mode when the float signal and the light signal are being generated simultaneously. 
     At decisional step  218 , the mode selector  92  determines whether or not the light monitor  78  is continuing to generate the light signal. According to one embodiment, the light monitor  78  may continue to generate the light signal for an amount of time corresponding to an adjustable delay before the light monitor  78  no longer generates the light signal. 
     If the light monitor  78  is continuing to generate the light signal, the method follows the Yes branch from decisional step  218  to step  220 . At step  220 , the fiber optic converter  20  remains in the driver mode. At this point, the method returns to decisional step  218 . In this way, the fiber optic converter  20  remains in the driver mode until the light monitor  78  is no longer generating the light signal. 
     Returning to decisional step  218 , if the light monitor  78  is no longer generating the light signal, the method follows the No branch from decisional step  218  and returns to step  200 , where the fiber optic converter  20  returns to the receiver mode. 
     In this way, a fiber optic converter  20  may be implemented without the use of protocol logic processing or an enable status line by allowing the fiber optic converter to monitor the fiber optic line  34  for a driver and to become a driver when no driver is detected. The fiber optic converter  20  also reverts back to being a receiver when optical signals are no longer being received. Therefore, fiber optic communication may be established relatively easily and inexpensively between existing electrical systems  24  and may be provided in electrical systems  24  in which enable status lines are unavailable. 
     Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.