Abstract:
Streamer redundancy. At least some illustrative embodiments are methods including: in a streamer towed by a survey vessel, sensing a first interconnection of a daisy chain the first interconnection between a first networked unit and a second networked unit, wherein the first networked unit and the second networked unit comprise a portion of a plurality of networked units; and determining that a fault condition exists on the first interconnection in response to the sensing; disabling the first interconnection responsive to the fault condition; enabling a second interconnection responsive to the fault condition, wherein the second interconnection couples the first networked unit and a third networked unit of the plurality of networked units and wherein the second interconnection does not couple to the second networked unit; and reporting information indicative of the fault condition to the survey vessel via the second networked unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/897,533 filed Oct. 30, 2013 and titled “Method for Streamer Redundancy”, which provisional application is incorporated by reference herein as if reproduced in full below. 
    
    
     BACKGROUND 
     Seismic and electromagnetic surveys may be two common types of geophysical survey. Geophysical survey equipment typically includes complex apparatus containing various components and connections. For example, a streamer commonly used in geophysical survey operation typically contains many sensors, sensor digitizing units, telemetry units, power units, navigation units, control units, and/or auxiliary units. All of these units are connected to a control/recording system onboard of a survey vessel, by way of one or multiple telemetry and power connections. When one of these units fails during operation, replacing the faulty unit (or “failed unit”) may result in operating downtime, increased operating cost/time and other inefficiencies. Thus, systems and methods that mitigate downtime arising from the replacement of faulty devices in the streamer would provide a competitive advantage in the marketplace. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows an overhead view of a marine survey system in accordance with at least some embodiments; 
         FIG. 1A  shows portions of the marine survey system of  FIG. 1  in further detail. 
         FIG. 2  shows a block diagram of a set of networked units in accordance with at least some embodiments; 
         FIG. 3  shows a block diagram of a control unit in accordance with at least some embodiments; 
         FIG. 4  shows a flow chart of a method in accordance with at least some embodiments; 
         FIG. 5  shows a block diagram of a set of networked units in accordance with at least some embodiments; 
         FIG. 6  shows a block diagram of a control unit in accordance with at least some embodiments; and 
         FIG. 7  shows a flow chart of a method in accordance with at least some embodiments. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, different companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections. 
     “Cable” shall mean a flexible, load carrying member that also comprises electrical conductors and/or optical conductors for carrying electrical power and/or signals between components. 
     “Rope” shall mean a flexible, axial load carrying member that does not include electrical and/or optical conductors. Such a rope may be made from fiber, steel, other high strength material, chain, or combinations of such materials. 
     “Line” shall mean either a rope or a cable. 
     “Downstream” as used herein means, in the context of the relationship between daisy chain units, such units disposed in the direction of, or more proximal to, the survey vessel. 
     “Upstream” as used herein means, in the context of the relationship between daisy chain units, such units disposed in the direction opposite of, or more distal to, the survey vessel. 
     “Daisy chain” means, in the context of an interconnection between devices, an interconnection in which signals or power, as the case may be, are transmitted end-to-end through each device so interconnected. 
     “Networked unit” means a device deployed in a streamer and having input and output ports configurable to couple to a daisy chain interconnection. Examples of networked units include sensor digitizing units, telemetry units power units, navigation units control units and auxiliary units. 
     “Exemplary, as used herein, means “serving as an example, instance, or illustration.” An embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure or the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure or the claims, is limited to that embodiment. 
       FIG. 1  shows an overhead view of a marine survey system  100  in accordance with at least some embodiments. In particular,  FIG. 1  shows a survey vessel  102  having onboard equipment, herein referred to collectively as recording system  104 , such as navigation, energy source control, and data recording equipment. Survey vessel  102  is configured to tow one or more streamers  106 A-F through the water. While  FIG. 1  illustratively shows six streamers  106 , any number of streamers  106  may be used. 
     The sensor streamers  106  are coupled to towing equipment that maintains the streamers  106  at selected depth and lateral positions with respect to each other and with respect to the survey vessel  102 . The towing equipment may comprise two paravane tow lines  108 A and  108 B each coupled to the vessel  102  by way of winches  110 A and  1108 , respectively. 
     Electrical and/or optical connections between appropriate components in the onboard recording system  104 , and components on the streamers  106 , such as sensors  116  may be made using inner lead-in cables  126 A-F via networked units  109  as described further herein below and in conjunction with  FIGS. 2 and 3 . 
     In a seismic survey, sensors  116  may include one or more instruments such as hydrophones, geophones or accelerometers to detect seismic signals. In an electromagnetic survey, sensors  116  may include electric field detector, a magnetic field detector or a combination electric field and magnetic field detector. 
     In either type of survey, a substantial number of sensors  116  may be interconnected via a communication pathway along a length of a streamer  106 , which may, in some embodiments reach lengths of tens of kilometers. The sensors  116  may be accompanied by networked units  109  which may include telemetry units as well as power, navigation, control, and auxiliary units. Sensors  116  and networked units  109  may be disposed within an outer surface  107 ,  FIG. 1A , of streamers  106 , in which communication pathway  125  and rope  127  may also be disposed. In some embodiments, outer surface  107  may be distinguished by an outer jacket at least partially covering streamer  106 ; by way of example, polyurethane jackets, mesh jackets, or impermeable jackets with cutouts distributed along the length of streamer  106 . Rope  127  may be provided as a strength member. These networked units may be connected to recording system  104  by one or more telemetry and/or power connections coupled together in “daisy chain” fashion. For example, as described further in conjunction with  FIG. 2 , data from sensors  116  may be digitized by a sensor digitizing unit and provided to telemetry units in digital form. The digitized data may then be modulated onto a carrier for example, which may then be transmitted to recording system  104 . The telemetry signals may be transmitted to the survey vessel  102  via the daisy-chained telemetry connections. Networked units  109  may also include auxiliary units and power units. Power units may supply conditioned power to other networked units  109 . Although networked units  109  are illustrated within streamers  106 , in some embodiments networked units may span multiple streamer sections, and in still other embodiments a single networked unit may span an entire length of a streamer. Further, in some embodiments, networked units may be located in connector modules between streamer sections, and in other embodiments networked units may be located in connector modules in some locations of the streamer and embedded or otherwise enclosed within the streamer in other locations of the streamer. 
       FIG. 2  illustrates a block diagram of a portion  200  of a set of such networked units, comprising telemetry units  202 A-C, power unit  204  and auxiliary unit  206 . Telemetry units  202 A-C may receive data from sensors  116  via sensor digitizing units  210 A-D and may communicate the data to the shipboard recording system  104 . Power units  204  may provide controlled power to other networked units. 
     Telemetry units  202 A-C may receive data from sensors  116  via sensor digitizing units  201 A-D may and communicate data to the shipboard recording system  104 . Telemetry units may communicate such data in digital form. Telemetry units  202 A-C are shown coupled to sensors  116 A-H via sensor digitizing units  210 A-D. In at least some embodiments sensor digitizing units  210 A-D may include an analog-to-digital converter (ADC). In still other embodiments, sensor digitizing units  210 A-D may be data acquisition computer, field programmable gate arrays or the like. In some embodiments the ADCs may be implemented as integrated in the telemetry units, and in yet other embodiments the sensor digitizing units may be implemented as discrete units as illustrated in  FIG. 2 . The sensor digitizing units may be coupled to the telemetry units electrically, optically or by any other suitable interface. In at least some embodiments, sensor digitizing units  210 A-D may be coupled to the telemetry units via a daisy chain interconnection. While, for the purpose of illustration three sensors are shown coupled to sensor digitizing unit  210 A, two sensors coupled to each of sensor digitizing units  210 B and  210 D, and a single sensor coupled to sensor digitizing units  210 C, in an embodiment of a streamer  106 , a sensor digitizing unit may be coupled to and receive data from one to about twelve sensors. In some embodiments, a sensor digitizing unit may couple to as many as 32 sensors. In any case, the specific number of sensors coupled to a sensor digitizing unit is not limiting, and any number of sensors may, in principle, be coupled to a sensor digitizing unit. Similarly, for the purpose of illustration, each of telemetry units  202 A-B are depicted as being coupled to a single sensor digitizing unit,  210 A and  210 B respectively, and telemetry unit  202 C is depicted a being coupled to two sensor digitizing unit s,  210 C and  210 D. In an embodiment of sensor streamer  106 , each telemetry unit may be coupled to and receive data from as many as about twenty-four to about one hundred digitizing units. However, the specific number of sensor digitizing units coupled to a telemetry unit is not limiting, and any number of sensor digitizing units may, in principle, be coupled to a telemetry unit. 
     The digitized data may then be provided to modulators  212 A-C which may modulate the digitized data onto a carrier for transmission to the onboard recording equipment. Examples of modulation which may be used include frequency shift keying (FSK), phase shift keying (PSK) quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK) or discrete multi-tone (DMT). 
     For the purpose of illustration, assume that telemetry unit  202 C represents a device proximal to the survey vessel and telemetry unit  202 A represents a device distal to the survey vessel. Telemetry signals from a telemetry unit, say telemetry unit  202 A may be transmitted toward the recording system  104  and pass through the downstream telemetry units  202 B and  202 C. Failure of one of these telemetry units, or a connection therebetween, could prevent the telemetry data from telemetry unit  202 A from reaching the survey vessel. Thus, the daisy-chained networked units may be coupled by bypass interconnections which provide for bypassing such a failed networked unit or connection, in accordance with the principles now described in further detail. 
     In the illustrated embodiment, each of the networked units includes two input ports and two output ports. In some embodiments, the input ports may be configured to connect to telemetry, communications or data channels, and in at least some embodiments, the ports may be configured to connect to power transmission lines or buses. And in still other embodiments, the ports may be configured to connect to both telemetry, communications or data channels and power transmission channels. Telemetry unit  202 A includes daisy chain input port  214 A and daisy chain output port  216 A. Likewise, telemetry unit  202 B comprises daisy chain input port  214 B and daisy chain output port  216 B, power unit  204  comprises daisy chain input port  214 C and daisy chain output port  216 C, telemetry unit  202 C includes daisy chain input port  214 D and daisy chain output port  216 D, and auxiliary unit  206  comprises daisy chain input port  214 E and daisy chain output port  216 E. Daisy chain interconnection  218 A coupling daisy chain output port  216 A of telemetry unit  202 A to daisy chain input port  214 B of telemetry unit  202 B and similar daisy chain interconnections  218 B,  218 C and  218 D also comprise a daisy chain interconnection between the respective networked units, namely telemetry unit  202 B, power unit  204 , telemetry unit  202 C and auxiliary unit  206 . A second set of interconnections,  220 A,  220 B and  220 C, provide a bypass path to allow routing around a faulty networked unit or daisy chain connection. Thus, bypass interconnection  220 A couples output port  217 A of telemetry unit  202 A to input port  215 C of power unit  204 . Likewise, bypass interconnection  220 B couples output port  217 B of telemetry unit  202 B to input port  215 D of telemetry unit  202 C and interconnection  220 C couples output port  217 C to input port  215 E of auxiliary unit  206 . Bypass interconnections  220 D and  220 E provide similar redundant paths coupling input port  215 B and output port  217 D to networked units upstream and downstream of portion  200  (not shown in  FIG. 2 ), respectively. In this way, a failure of, for example, telemetry unit  202 B, or the daisy chain interconnections,  218 A,  218 B therebetween, may be bypassed via bypass interconnection  220 A. On detection of such failure condition by telemetry unit  202 A, telemetry unit  202 A may enable bypass interconnection  220 A, and communication may then proceed toward recording system  104 . Similarly, output port  217 E may provide a bypass interconnection for auxiliary unit  206  to networked units downstream of portion  200 , and input port  215 A may provide a bypass interconnection to networked units upstream of portion  200 . In some embodiments, interconnections may be electrical and communication via electrical signals. In other embodiments, interconnections may be optical and communications by optical signals and in yet other embodiments, combination thereof may be used. In still other embodiments any suitable communication method may be used. Further, daisy chain interconnections  218 A-D and bypass interconnections  220 A-E may also carry electrical power as well as telemetry signals, as set forth above. Although an exemplary failure has described above in terms of a telemetry signal failure, a failure of a daisy chained power connection or unit coupled to such a power connection may also be similarly bypassed via bypass interconnections  220 A-E. 
     Power unit  204  may be included to provide power to other networked units. Networked units connected to power unit  204 , such as telemetry unit  202 C, may receive electrical power via power unit  204 , and power unit  204  may control the state of the electrical power supplied to the networked units daisy chained with power unit  204 . Thus, if a failure occurs in such a networked unit, a for example a short circuit or power consumption in excess of a predetermined specification, power unit  204  may detect the anomaly and disable the power to the failed unit. However, in this case, as described above, daisy chained units both upstream and downstream of the malfunctioning unit would also lose power. 
     Alternatively, by enabling a bypass interconnection, a power unit  204  may bypass a malfunctioning networked unit and maintain power to at least units that are otherwise daisy chained with the malfunctioning unit. For example, if telemetry unit  202 C fails whereby its current consumption exceeds a predetermined specification, power unit  204  may disable daisy chain interconnection  218 C. Power unit  204  may also enable bypass interconnection  220 C, thereby bypassing telemetry unit  202 C, and continue to supply power to networked units downstream of telemetry unit  202 C, such as auxiliary unit  206 . Although bypass interconnection  220 C has been described in conjunction with supplying power to networked units, as previously described bypass interconnection  220 C may also transport daisy chained communication signals between telemetry units  202  and the survey vessel  102 , for example. Such communication signals may, in at least some embodiments, be bidirectional. Power unit  204  may also detect a malfunction of a daisy chained telemetry signal, and bypass daisy chain interconnection  218 C and select redundant bypass interconnection  220 C. 
     An interconnection controller within a networked unit may be used to detect malfunction on a daisy chain interconnection and select a bypass interconnection to bypass the malfunction. In the exemplary embodiment of telemetry units  202 , power unit  204  and auxiliary unit  206  include an interconnection controller  222  which may monitor the daisy chain interconnections  218  for fault conditions and change between the daisy chain interconnections and bypass interconnections  220  accordingly. A fault condition on an interconnection may arise from an anomaly in a downstream networked device or on, for example, a power or telemetry channel between networked units. 
     This may be further understood by referring now to  FIG. 3 , showing a block diagram of an exemplary interconnection controller  222  in accordance with an embodiment. Interconnection controller  222  may include an interconnection enable unit  302 , telemetry fault detector  304 , a power fault detector  306  and an interconnection controller  308 . Interconnection enable unit  302  may connect daisy chain input port  214  to one of daisy chain output port  216  or output port  217  based on the state of the downstream interconnections and/or devices. Further, input signals and power may be received on either daisy chain input port  214  or input port  215  depending on the state of upstream interconnections or devices. In other words, an upstream device may have itself bypassed a faulty intervening unit or connection to reach the particular device including interconnection controller  222 . Input sense circuitry  310  may detect which of input ports  214  and  215  is active in that it is receiving telemetry and/or power from an upstream unit. For example, input sense circuitry  310  may detect the presence of power on one of input ports  214  and  215 . In at least some embodiments, input sense circuitry may detect telemetry data on the active one of daisy chain input port  214  and input port  215 . In some embodiments, telemetry units (such as units  202 , FIG.  2 ) may provide a heartbeat signal at a predetermined interval which may be detected by input sense circuitry  310 . Such a heartbeat signal may be used in embodiments where telemetry but not power is provided in a daisy chain configuration, and particularly in such embodiments where telemetry data rates are low, whereby a change in input ports by an upstream device may otherwise escape detection. Input sense circuitry  310  may connect the active input port to node  312  which may be input to output select circuitry  314 . 
     Connection controller  308  may select the state of output select circuitry  314  in response to signals received from telemetry fault detector  304  and power fault detector  306 . If daisy chained downstream devices or interconnections are free of fault conditions, both telemetry fault detector  304  and power fault detector  306  may provide respective output signal values to connection controller  308  in a first predetermined state denoting a fault-free condition on the daisy chain interconnection downstream. Connection controller  308  may then set a first predetermined value on control line  316  whereby output select circuitry  314  connects node  312  to daisy chain output port  216 . Conversely, if either of telemetry fault detector  304  or power fault detector  306  determines that a downstream fault condition exists on the daisy chain interconnection, the respective one of telemetry fault detector  304  and power fault detector  306  may provide an output signal having a predetermined value denoting a fault condition exists in the daisy chain interconnection. Connection controller  308  may then set a second predetermined value on control line  316  whereby output select circuitry  314  connects node  312  to output  317 , thereby enabling the bypass interconnect and disabling the daisy chain interconnect. Output select may connect node  312  to output  317  by, for example in at least some embodiments, electronic switches, optical switches or address table remapping, or any other suitable means as may be reflected by the communication pathway architecture. 
     For example, power fault detector  306  may monitor the daisy chain power interconnection for an overcurrent condition. Such a condition may represent a short circuit or other failure occurring in the device downstream of the particular networked unit sensing the overcurrent condition. Connection controller  308  may then signal output select circuitry  314  to select output port  217  thereby bypassing the failed device. In at least some embodiments, power fault detector  306  may employ a Hall effect current sensor to sense the current in the daisy chain power interconnections. 
     Similarly, telemetry fault detector  304  may monitor the daisy chain telemetry interconnection for a loss of telemetry signal. In particular, the telemetry fault detector may monitor the telemetry interconnection for upstream telemetry communications from survey vessel  102 . A loss of upstream communication for a predetermined interval of time may be indicative of a failure in a downstream telemetry unit. In at least some embodiments, telemetry units (such as telemetry units  202 ,  FIG. 2 ) may send a beacon or heartbeat signal which may be used by telemetry fault detector  304  to sense a fault condition on daisy chain telemetry interconnections. In such embodiments, a loss of the heartbeat signal may be indicative of a fault condition. In response to a telemetry interconnection fault condition, connection controller  308  may then signal output select to connect to output port  217 , as previously described. 
     Because a fault condition may be detected locally, the site of the failed unit or daisy chain interconnection may be determined. Thus, in an embodiment, connection controller  308  may be coupled to a telemetry unit, such as a telemetry unit  202 , and reporting information indicative of the detected fault to survey vessel  102 , for example via the telemetry unit. Such information may include information identifying the particular connection controller, a serial number for example. The reported information may then be used to locate the faulty unit or daisy chain connection which may facilitate repair of the streamer including the faulty unit. 
     In the exemplary embodiment of  FIG. 2 , the interconnection controller (e.g. interconnection controller  222 ,  FIG. 2 ) is shown disposed within the networked units themselves. In at least some embodiments interconnection controllers may be deployed in a separate control unit, however the principles of operation would be substantially unaffected by the form of deployment. 
       FIG. 4  shows a flow chart of a method  400  for bypassing a networked unit in accordance with an example embodiment. The method starts in block  402  and in block  404 , the method determines if a telemetry fault condition is detected on the telemetry daisy chain interconnection. A telemetry fault condition may be detected in block  404  as described in conjunction with  FIG. 3 . If no telemetry fault condition has been detected, block  404  falls through the “No” branch to block  406 . In block  406 , method  400  determines if a power fault condition is detected on the power daisy chain interconnection. A power fault condition may be detected in block  406  as described above in conjunction with  FIG. 3 . If no power fault condition is detected, block  406  falls through the “No” branch to return to block  404  wherein method  400  continues to monitor the state of the daisy chain interconnections. 
     Returning to blocks  404  and  406 , if either a telemetry fault condition is detected (block  404 ) or a power fault condition is detected (block  406 ) on the daisy chain interconnections, the blocks fall through the respective “Yes” branch, depending on the type of fault condition detected. And, in block  408 , the daisy chain interconnection may be disabled by bypassing it. In at least some embodiments, block  404  may bypass the daisy chain interconnection as described above in conjunction with  FIGS. 2 and 3 . In block  410 , information indicative of the fault condition is reported to the survey vessel. Such information may include a serial number or other identifier of the unit bypassed, or an analogous identifier of the reporting unit, and the nature of the fault condition (e.g. telemetry, power) which information may be logged and used to facilitate repair of the streamer. Method  400  ends at block  410 . 
     Refer now to  FIG. 5  showing a block diagram of a portion  500  of a set of networked units in accordance with another embodiment. Portion  500  includes networked units  502 A-E, which may comprise telemetry units, power units, sensor digitizing units, and auxiliary units as previously described. Networked units  502 A-E may be interconnected in daisy chain fashion via input ports  504  and output ports  506  having interconnections  508  therebetween. Further networked units  502 A-E may be selectably interconnected via bypass interconnections  510  and  512 , as described in further detail below in conjunction with  FIG. 6 . 
     Bypass interconnections  510  may connect two networked units  502 , bypassing an intervening unit in the daisy chain configuration. Thus, for example interconnection  510 A may couple an output port  511 A of networked unit  502 A to an input port  509 C of networked unit  502 C, bypassing networked unit  502 B. Similarly, interconnection  510 B may connect output port  511 B of networked unit  502 B to input port  509 D of networked unit  502 D, bypassing networked unit  502 C. Bypass interconnection  510 C may connect output port  511 C of networked unit  502 C to input port  509 E of networked unit  502 E bypassing networked unit  502 D. Bypass interconnection  510 M may connect input port  509 B of networked unit  502 B to a device (not shown) upstream of portion  500 . Similarly input port  509 A of networked unit  502 A may be connected to a device upstream of portion  500 . Bypass interconnect  512 D may connect output port  511 D of networked unit  502 D to a device downstream (not shown) of portion  500 . 
     Portion  500  also may include a second set of bypass interconnections  512 . Bypass interconnections  512  may connect two networked units  502  while bypassing two intervening networked units in the daisy chain configuration. For example, bypass interconnection  512 A couples output port  507 A of networked unit  502 A to input port  505 D of networked unit  502 D, bypassing networked units  502 B, C. In similar fashion, interconnection  512 B couples output port  507 B of networked unit  502 B to input port  505 E of networked unit  502 E, bypassing networked units  502 C, D. Bypass interconnections  512 C, D may connect output ports  507 C and  507 D  502 C, D, respectively to networked units (not shown) downstream of portion  500 . Bypass interconnections  512 M, N may connect input ports  505 B, C of units  502 B, C, respectively to networked units (not shown) upstream of portion  500 . Input port  505 A of networked unit  502 A may likewise connect via a bypass interconnection to a networked unit (not shown) upstream of portion  500 . 
     The disabling of a daisy chain interconnection by the enabling of a bypass interconnection may be controlled by an interconnection controller  520 . In the exemplary embodiment of  FIG. 5 , interconnection controllers  520  are shown as disposed within networked units  502 . However, in other embodiments, interconnection controllers  520  may be deployed in a separate control unit. In still other embodiments, a portion of interconnection controllers  520  may be disposed within some networked units  502  and another portion may be deployed in separate control units. 
     Turning to  FIG. 6 , an interconnection controller  520  in accordance with an embodiment is shown in further detail. Interconnection controller  520  includes an interconnection enable unit  602 , a telemetry fault detector  604 , power fault detector  606  and interconnection controller  608 . Interconnection enable unit  602  includes an input sense circuitry  610  and output select unit  614 . The operation of input sense circuitry  610  may be similar to the operation of input sense circuitry  310 ,  FIG. 3 . However, input sense circuitry  610  senses daisy chain input port  504  and bypass input ports  505  and  509  to determine which input port is active, as described above. The active input port is connected to node  612 . 
     Telemetry fault detector  604  and power fault detector  606  may be similar to telemetry fault detector  304  and power fault detector  306  described above in conjunction with  FIG. 3 . However, in the embodiment of interconnection controller  520 , these devices may be connected both to daisy chain output port  506 , via lines  613 A, B, respectively, but also to bypass interconnection output port  511 , via lines  615 A,B, respectively. Thus, if a fault condition on the daisy chain interconnection is sensed by one or both of telemetry fault detector  304  and power fault detector  606 , interconnection controller  608  may signal output select unit  614  to enable the bypass interconnection through bypass output port  511 . Recall, a bypass interconnection via an output port  511  may bypass a single unit in the daisy chain configuration. If, however a pair of units, for example, have failed or otherwise present a fault condition, enabling output port  511  may not clear the fault condition. In that case, one or both of telemetry fault detector  604  and power fault detect unit  606 , depending on the type of fault condition, may continue sense the fault condition on output port  511  via lines  615 , and maintain its fault assertion with respect to interconnection controller  608 . Interconnection controller  608  may then signal output select unit  614  to disable the interconnection via bypass output port  511  and enable the bypass interconnection via output port  507  (e.g. a bypass  512 ,  FIG. 5 ). In this way, a failure of two units in a daisy chain configuration that have failed may be bypassed. 
     This may be further understood by referring to  FIG. 7 , illustrating a flow chart of a method  700  for disabling a networked unit in accordance with an example embodiment. The method starts in block  702  and senses the daisy chain interconnection output port (e.g. an output port  506 ), block  703 . In block  704 , the method determines if a telemetry fault condition is detected on the telemetry daisy chain interconnection. A telemetry fault condition may be detected in block  704  as described in conjunction with  FIG. 3 . If no telemetry fault condition has been detected, block  704  falls through the “No” branch to block  706 . In block  706 , method  700  determines if a power fault condition is detected on the power daisy chain interconnection. A power fault may be detected in block  706  also as described above in conjunction with  FIG. 3 . If no power fault condition is detected, block  706  falls through the “No” branch to return to block  704  wherein method  400  continues to monitor the state of the daisy chain interconnections. 
     Returning to blocks  704  and  706 , if either a telemetry fault condition is detected (block  704 ) or a power fault condition (block  706 ) on the daisy chain interconnections, the blocks fall through the respective “Yes” branch, depending on the type of fault condition detected. In block  708 , method  700  branches depending on which of the output ports is being sensed. If the daisy chain interconnection is being sensed, block  708  falls through the “Yes” branch and in block  710  the daisy chain interconnection is bypassed via the first bypass interconnection (e.g. via an output port  511 ), thereby disabling it. In at least some embodiments, the first bypass may be enabled as described in conjunction with, inter alia,  FIG. 6 . Method  700  then senses the bypass interconnection enabled in block  710 , block  712 . In block  713 , information indicative of the fault condition is reported to the survey vessel. Such information may include a serial number or other identifier of the unit or units bypassed, or an analogous identifier of the reporting unit, and the nature of the fault (e.g. telemetry, power) which information may be logged and used to facilitate repair of the streamer. Method  700  returns to block  704  to determine if the fault is cleared in response to the bypassing of the downstream unit. If a fault condition is not cleared, i.e. the fault condition remains, one of blocks  704  and  706  fall through its respective “Yes” branch to block  708 . Because the bypass interconnection is being sensed via block  712 , block  708  proceeds by the “No” branch to block  714 . In block  714 , the second bypass interconnection is enabled (e.g. via an output port  507 ). In at least some embodiments, the second bypass may be enabled as described in conjunction with, inter alia,  FIG. 6 . In block  716 , information indicative of the fault condition is reported to the survey vessel, similarly to block  713 . Method  700  ends at block  718 . 
     References to “one embodiment”, “an embodiment”, “a particular embodiment”, and “some embodiments” indicate that a particular element or characteristic is included in at least one embodiment of the invention. Although the phrases “in one embodiment”, “an embodiment”, “a particular embodiment”, and “some embodiments” may appear in various places, these do not necessarily refer to the same embodiment. 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, the principles disclosed herein may be applied to embodiments wherein N+1 connections may be used to bypass N faulty units and/or interconnections, or combinations thereof. It is intended that the following claims be interpreted to embrace all such variations and modifications.