Abstract:
Systems and methods for providing redundancy protection in a Y-cable-based signal transmitter arrangement having at least one first transmitter operating in an active mode and a second transmitter operating in a standby mode, wherein operating in the active mode includes transmitting data to a remote endpoint via a Y cable and a transmit interface, are disclosed. Data transmitted by the first transmitter to a remote endpoint is monitored for a loss of signal condition. Communications from the remote endpoint is monitored for a transmit failure indication. A determination is made as to whether to switch the second transmitter to the active mode based on a combination of the loss of signal and the transmit failure indication. In an alternative implementation, data transmitted by the first transmitter is not monitored and the decision to switch the second transmitter to the active mode is based primarily on transmit failure indications alone.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/616,651 entitled “Media Gateway Features”, filed Oct. 7, 2004, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The subject matter described herein relates to providing redundancy protection in signal transmission system. More particularly, the subject matter described herein relates to providing redundancy protection in a Y-cable-based signal transmitter arrangement.  
       BACKGROUND  
       [0003]     In telecommunications switches, Y cables are used to connect active and standby transmitters and receivers to a common I/O cable.  FIG. 1  illustrates a conventional Y cable  50 . In  FIG. 1A , Y cable  50  includes the first connector  52  with transmit and receive pins, a second connector  54  with transmit and receive pins, an active-side cable  56 , a standby-side cable  58 , a junction  60 , and a common cable  62 . In a typical application, connector  52  is connected to an active telecommunications switching module and connector  54  is connected to a standby telecommunications switching module. Signals transmitted by the active telecommunications switching module traverse cable  56 , junction  60  and are output via common cable  62 . Signals received from a remote endpoint traverse common cable  62  and are distributed to both the active and standby switching modules via cables  56  and  58 , respectively. If the active-switching module fails, the standby switching module begins operating in the active mode and transmits data to the remote endpoint via cable  58  and common cable  62 .  
         [0004]     Conventional Y-cable-based communications systems offer some level of redundancy to compensate for local equipment failures.  FIG. 1B  illustrates a conventional Y-cable-based communications system  100 . Y-cable-based communications system  100  includes an active transceiver module  102 , a standby transceiver module  104 , a remote endpoint  106 , such as a receiver, and a Y cable  50 . Active transceiver module  102  and standby transceiver module  104  communicate with the remote endpoint  106  via Y cable  50 . Here, it should be noted that active transceiver module  102  and standby transceiver module  104  include receiving capabilities (as discussed further below) and remote endpoint  106  will typically include transmitting capabilities.  
         [0005]     As described above, Y cable  50  includes an active-side cable  56 , a standby-side cable  58 , a junction  60  and a common cable  62 . Junction  60  connects common cable  62  to both active-side cable  56  and standby-side cable  58 . As shown in  FIG. 1 , Y cable  50  is typically bidirectional to accommodate bidirectional communications, which would be the case when transceivers are employed as discussed above. Junction  60  may be a hard-wired connection, a splitter, a coupler, or the like, and can include isolation to isolate each of the cables from each other while allowing signal propagation.  
         [0006]     During normal operation, a transmitter in active transceiver module  102  transmits signals via active-side cable  56  and standby transceiver module  104  does not transmit signals over standby-side cable  58 . When, however, an active transceiver module  102  failure is detected, some mechanism is employed to stop transmissions from active transceiver module  102  and begin transmissions from standby transceiver module  104 .  
         [0007]      FIG. 2  illustrates a Y cable-based signal transmitter arrangement  200  including conventional active-side monitoring capabilities.  FIG. 2  shows an active-side  202  and standby-side  204  that include active transceiver module  102  and standby transceiver module  104 , respectively. Active transceiver module  102  includes a transmitter  206 , a receiver  208 , a monitoring/processing/control block  210  and a monitor  212 . Standby transceiver module  104  includes a monitor  213 , a transmitter  214 , a receiver  216  and a monitoring/processing/control block  218 . Y cable  50  is also shown and includes a transmit interface comprising active-side transmit line  220 , standby-side transmit line  222  and common cable transmit line  224 . Y cable  50  also includes a receive interface comprising active-side receive line  226 , standby-side receive line  228  and common cable receive line  230 . The term “line” as used herein denotes one or more conductors, optical fibers, or waveguides. Junction  60  provides continuity for signal propagation within the transmit interface and separately within the receive interface, as shown. As can be appreciated from  FIG. 2 , active-side transmit line  220  and receive line  226  are part of active-side cable  56 , and standby-side transmit line  222  and receive line  228  are part of standby-side cable  58 .  
         [0008]     Monitors  212  and  213  monitor transmission signals about to be transmitted onto the Y cable by active-side and standby-side transmitters  206  and  214 , respectively, via lines  232  and  233  and junctions  234  and  235 . The signals are monitored prior to line drivers  236  and  238 , which drive the transmission signals onto the Y cable under the control of respective monitoring/processing/control blocks  210  and  218 . That is, monitors  212  and  213  do not monitor transmissions at the Y cable, since monitoring point junctions  234  and  235  are isolated from the Y cable by drivers  236  and  238 , respectively. Accordingly, standby-side monitor  213  does not monitor transmissions on the Y cable from active-side transmitter  206 .  
         [0009]     In operation, active transceiver module  102  operates to transmit and receive signals via transmitter  206  and receiver  208 , respectively. Monitoring/processing/control block  210  processes signals for transmission and forwards them to transmitter  206  and also processes signals received by receiver  208 . Monitoring/processing/control block  210  also monitors receiver  208  for receiver failure and active-side monitor  212  for alarms concerning a loss of transmission by transmitter  206 . Should either of these events occur on the active side  202  (and not on standby side  204 ) monitoring/processing/control block  210  stops transmissions from transmitter  206  and sends an instruction to monitoring/processing/control block  218  in standby-side transmitter module  104  to enabled transmitter  214  to begin transmitting in place of transmitter  206 .  
         [0010]     Some of the signals received at receiver  208  and/or receiver  216  provide an indication regarding whether or not the remote endpoint correctly received the transmission from either of transmitter  206  or transmitter  214 . For example, negative acknowledgment signals or commands indicating that the signal was incorrectly received at the remote endpoint may be received and processed by either or both of receiver  208  and receiver  216  in conjunction with monitoring/processing/control block  210  and processing/control block  218 , respectively. Signals such as these indicating an incorrect receipt of transmissions at the remote endpoint will be referred to herein as a transmit failure indication. One example of the transmit failure indication is a remote failure indication (RFI) that is sent by remote endpoints in a telecommunications switching system. RFIs from remote endpoints have conventionally been used to alert a transmitter as to whether a transmission should be repeated due to incorrect receipt, or no receipt of the signal. Failure indications, however, have not been used in determining whether a standby transmitter should be activated in a Y-cable-based transmitter system. The reason is because failure indications are received by both active and standby receivers  208  and  216  and conventional wisdom is that identical failure conditions therefore result on both active and standby sides  202  and  204  that would either cancel out each other or cause repeated switching back and forth between active and standby transmitters. In addition, transmissions by the active-side and standby-side transmitters are conventionally monitored at the transmitters before the line drivers, and not at the Y cable, as discussed above. Such monitoring has limited use in determining whether a standby transmitter should be activated in a Y-cable-based transmitter system.  
         [0011]     A need therefore exists for using transmit failure indications either alone or in conjunction with the monitoring of active and/or standby sides of the Y cable in determining whether a standby transmitter should be activated in a Y-cable-based transmitter system.  
       SUMMARY  
       [0012]     In one aspect of the subject matter disclosed herein, a method is disclosed for providing redundancy protection in a Y-cable-based signal transmitter arrangement having at least one first transmitter operating in an active mode and a second transmitter operating in a standby mode, wherein operating in the active mode includes transmitting data to a remote endpoint via a Y cable and a transmit interface. The method includes monitoring data transmitted by the first transmitter to the remote endpoint for a loss of signal condition and monitoring, via a receive interface connected to the Y cable, communications from the remote endpoint for a transmit failure indication. A determination is made as to whether to switch the second transmitter to the active mode based on a combination of the loss of signal condition and the transmit failure indication.  
         [0013]     In another aspect of the subject matter disclosed herein, a method is disclosed for providing redundancy protection in a Y-cable-based signal transmitter arrangement having at least one first transmitter operating in an active mode and a second transmitter operating in a standby mode, wherein operating in the active mode includes transmitting data to a remote endpoint via a Y cable and a transmit interface. The method includes monitoring, via a receive interface connected to a Y cable, communications from the remote endpoint for a first transmit failure indication. In response to detecting the first transmit failure indication, the second transmitter is switched to an active mode, communications from the remote endpoint are monitored for a second transmit failure indication, and a cause of the first transmit failure indication is determined based on whether the second transmit failure indication is detected.  
         [0014]     In another aspect of the subject matter disclosed herein, a system is disclosed for providing redundancy protection in a Y-cable-based signal transmitter arrangement having at least one first transmitter operating in an active mode and a second transmitter operating in a standby mode, wherein operating in the active mode includes transmitting data to a remote endpoint via a Y cable and a transmit interface. The system includes at least one monitor for monitoring data transmitted by the first transmitter to the remote endpoint for a loss of signal condition and at least one receiver for monitoring communications from the remote endpoint for a transmit failure indication via a receive interface and the Y cable. The system also includes a protection controller for receiving and processing information from the at least one receiver and at least one monitor and for determining whether to switch the second transmitter to an active mode based on a combination of the loss of signal condition and the transmit failure indication.  
         [0015]     In another aspect of the subject matter disclosed herein, a system is disclosed for providing redundancy protection in a Y-cable-based signal transmitter arrangement having at least one first transmitter operating in an active mode and a second transmitter operating in a standby mode, wherein operating in the active mode includes transmitting data to a remote endpoint via a Y cable and a transmit interface. The system includes at least one receiver for monitoring, via a receive interface and a Y cable, communications from the remote endpoint for a first transmit failure indication and a protection controller for, in response to detecting the first transmit failure indication, switching the second transmitter to the active mode, monitoring communications from the remote endpoint for a second transmit failure indication, and determining a cause of the first transmit failure indication based on whether the second transmit failure indication is detected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Objects and advantages of the present invention will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings, in which like reference numerals have been used to designate like elements, and in which:  
         [0017]      FIG. 1A  is a schematic diagram illustrating an example of a conventional Y cable;  
         [0018]      FIG. 1B  is a block diagram illustrating a conventional Y-cable-based transmission system;  
         [0019]      FIG. 2  is a block diagram illustrating a conventional Y-cable-based signal transmitter arrangement;  
         [0020]      FIG. 3  is a block diagram illustrating a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to an aspect of the subject matter disclosed herein;  
         [0021]      FIG. 4  is a block diagram illustrating a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to another aspect of the subject matter disclosed herein;  
         [0022]      FIG. 5A  is a block diagram illustrating one implementation of protection controller according to another aspect of the subject matter disclosed herein;  
         [0023]      FIG. 5B  is a block diagram illustrating another implementation of protection controller according to another aspect of the subject matter disclosed herein;  
         [0024]      FIG. 6  is a flow chart illustrating a method for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to an aspect of the subject matter disclosed herein;  
         [0025]      FIG. 7  is a flow chart illustrating a method for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to another aspect of the subject matter disclosed herein;  
         [0026]      FIG. 8  is a block diagram illustrating a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to yet another aspect of the subject matter disclosed herein;  
         [0027]      FIG. 9  is a flow chart illustrating a method for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to yet another aspect of the subject matter disclosed herein; and  
         [0028]      FIG. 10  is a block diagram illustrating a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to yet another aspect of the subject matter disclosed herein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     To facilitate an understanding of exemplary embodiments, many aspects are described in terms of sequences of actions that can be performed by elements of a computer system. For example, it will be recognized that in each of the embodiments, the various actions can be performed by specialized circuits or circuitry (e.g., discrete logic gates interconnected to perform a specialized function), by program instructions being executed by one or more processors, or by a combination of both.  
         [0030]     Moreover, the sequences of actions can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor containing system, or other system that can fetch the instructions from a computer-readable medium and execute the instructions.  
         [0031]     As used herein, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non exhaustive list) of the computer-readable medium can include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM).  
         [0032]     Thus, the invention can be embodied in many different forms, and all such forms are contemplated to be within the scope of what is claimed. Any such form of embodiment can be referred to herein as “logic configured to” perform a described action, or alternatively as “logic that” performs a described action.  
         [0033]      FIG. 3  illustrates a system  300  for providing redundancy protection in a Y-cable-based signal transmitter arrangement  302  according to an aspect of the subject matter disclosed herein. As shown in  FIG. 3 , a redundancy protection system  300  includes standby-side monitor  213 , standby-side monitoring/processing/control block  218 , active-side monitor  212 , and active-side monitoring/processing/control block  210 . Also included in redundancy protection system  300  are a protection controller  308 , an indicator  310 , and an operator reset  312 . Active-side monitor  212  monitors transmissions from the currently active transmitter ( 206  or  214 ) at an active-side transmit interface line  220  via line  232  and junction  234 . Standby-side monitor  213  monitors transmissions from the currently active transmitter ( 206  or  214 ) at a standby-side transmit interface line  222  via line  312  and junction  314 . Active-side monitor  212  and standby-side monitor  213  may alternatively be combined into a single monitor that performs the functions of both monitors. Note here that the monitoring is done at the active-side and standby-side transmit interface lines  220  and  222 , instead of at the transmitter and before the line driver as in conventional Y-cable-based systems. The remaining components in Y-cable-based signal transmitter arrangement  302  are similar to those described above in connection with  FIG. 2 .  
         [0034]     In operation, active-side monitor  212  and standby-side monitor  213  monitor transmissions from whichever transmitter is currently in the active-mode, which would initially be active-side transmitter  206 . When a loss of signal condition is detected, active-side monitor  212  and/or standby-side monitor  213  send an “alarm” signal to monitoring/processing/control block  210  and/or monitoring/processing/control block  218 , respectively. Similarly, when a transmit failure indication is received from the remote endpoint at receiver  208  and/or receiver  216 , the transmit failure indication is processed by monitoring/processing/control block  210  and/or monitoring/processing/control block  218 , respectively. It should be noted here that the signals transmitted and received can be electrical signals traveling via electrical conductors, optical signals traveling via optical fibers, microwave signals traveling via microwave waveguides, or any combination thereof. Also, as described above, the term “transmit failure indication” as used herein denotes a signal or message indicating or tending to indicate that a prior transmission was not received correctly by a remote endpoint. The exact makeup of the transmit failure indication will vary according to the transmission medium used and the particular protocol used, and will not be discussed in detail here. One of ordinary skill in this art, however, will appreciate that many signal transmission protocols include acknowledgment type messages that are returned in response to transmissions and that tend to indicate whether or not a transmission was received correctly by a remote endpoint. These messages are read and information therein is used by protection controller  308 .  
         [0035]     Loss of signal and transmit failure indication information is gathered by protection controller  308  and analyzed to determine whether to perform a switchover. That is, in one implementation, protection controller  308  determines whether or not to perform a switchover based on a combination of three inputs, one from each of active-side monitor  212  and standby-side monitor  213 , and a transmit failure indication from the remote endpoint. The term switchover is used herein to denote disabling the active-side transmitter  206  from transmitting via the Y cable and enabling the standby-side transmitter  214  to begin transmitting via the Y cable. During a switchover, standby-side transmitter  214  is transitioned from a standby mode in which it does not transmit to the remote endpoint via the Y cable to an active mode in which it does transmit to the remote endpoint via the Y cable, and the opposite case is true for transmitter  206 .  
         [0036]     Since there are three inputs, each having two possible states, there are 2 3 =8 possible combinations. One of the combinations correspond to no alarms from either of active-side monitor  212  and standby-side monitor  213  and no transmit failure indication from the remote endpoint, which corresponds to normal operation and need not be discussed further here since no protection-related actions are needed. The remaining seven combinations, along with the corresponding conclusions and actions, are shown in Table 1 below and numbered as scenarios 1.1 to 1.6. Note that scenario 1.1 includes two possible combinations of inputs that results in the same conclusion and action.  
                                                   TABLE 1                           Failure Conditions and Proposed Actions            Condition                            Transmit Failure                   Active-side   Standby-   Indication from       #   Monitor   Side Monitor   Remote Endpoint   Conclusion   Action               1.1   Alarm   Alarm   Yes or No   active transmitter failed   Switchover       1.2   Normal   Normal   Yes   common cable failed   None       1.3   Alarm   Normal   Yes   active transmitter failed and   Switchover                       standby-side monitor failed       1.4   Alarm   Normal   No   active-side monitor failed   Switchover       1.5   Normal   Alarm   No   standby-side monitor and/or   Standby-side unusable -                       standby-side cable failed   prevent switchovers       1.6   Normal   Alarm   Yes   active transmitter failed and   Switchover                       active-side monitor failed,                       or the active-side cable failed                  
 
         [0037]     As can be appreciated from Table 1, there are three possible actions for each combination of inputs. The three possible actions are switchover, no switchover, and preventing switchovers. In addition, there are several conclusions that can be reached by protection controller  308  and indicated to an operator through indicator  310 . Indicator  310  can be one or more status lamps or can be a display supported by a computing system. Indicator  310  can be located locally or can be remotely located and can communicate with protection controller either directly or through a network (not shown), such as a local area network, wide area network, the Internet, or any combination of these. The various scenarios 1.1 to 1.6 of Table 1 are discussed further below.  
         [0038]     When a switchover is performed, a switchover flag is set by protection controller  308 . The switchover flag is used to inform an operator that a switchover has taken place in an attempt to resolve a detected problem and to prevent excessive switchovers in cases when the switchover does not resolve the problem. Once the switchover flag is set, no further switchovers can take place for the same condition until an operator manually clears the flag. The switchover flag may be, for example, a register or other memory device accessible to protection controller  308  and either internal or external to protection controller  308 . When an operator resets the switchover flag, operator reset  312  sends an indication to protection controller  308 . For example, operator reset  312  may be a local momentary switch or a command received through a network from a remotely located operator&#39;s console.  
         [0039]      FIG. 4  illustrates an alternate system  400  for providing redundancy protection in a Y-cable-based signal transmitter arrangement  402  according to another aspect of the subject matter disclosed herein. As shown in  FIG. 4 , once again, redundancy protection system  400  includes standby-side monitor  213 , standby-side monitoring/processing/control block  218 , active-side monitor  212 , active-side monitoring/processing/control block  210 , protection controller  308 , an indicator  310 , and operator reset  312 . In this embodiment, however, active-side monitor  212  is connected to a standby-side transmit interface line  222  via line  404  and junction  314 . Likewise, standby-side monitor  213  is connected to an active-side transmit interface line  220  via line  406  and junction  234 . Accordingly, this arrangement is referred to herein as the cross-over arrangement. The remaining components in Y-cable-based signal transmitter arrangement  402  are similar to those described above in connection with  FIG. 2 .  
         [0040]     Functionally, the connection shown in  FIG. 4  may be similar to those illustrated in  FIG. 3  in that monitors  212  and  213  each monitor the output of the transmitter currently functioning in the active mode. In  FIG. 3 , however, the connection between the monitors and the transmitters on the opposite sides may be made via junction  60  in Y cable  50 . In the cross-over arrangement shown in  FIG. 4 , the connection between the monitors and the transmitters on the opposite sides may be made via wires that are separate from Y cable  50 , as indicated by reference numerals  404  and  406 .  
         [0041]     Returning to  FIG. 4 , in operation, active-side monitor  212  and standby-side monitor  213  initially monitor transmissions from active-side transmitter  206 . If a transmit failure is detected and a switchover occurs, both monitors will monitor transmissions from standby-side transmitter  214  (which is now functioning in the active-mode). Because each transmitter is connected via an additional line ( 404  or  406 ) to a monitor associated with the other side, which may be a different telecommunications switching card, the arrangement illustrated in  FIG. 4  provides increased redundancy over the arrangement illustrated in  FIG. 3 .  
         [0042]     Table 2 below shows the various combinations of inputs, along with the corresponding conclusions and actions, of the cross-over arrangement, which are numbered as scenarios 2.1 to 2.6. The actions and conclusions reached are different than those in Table 1, as can be appreciated from a comparison of Tables 1 and 2.  
                                                   TABLE 2                           Failure Conditions and Proposed Actions for Cross-over Arrangement            Condition                            Transmit Failure                   Active-Side   Standby-   Indication from       #   Monitor   Side Monitor   Remote Endpoint   Conclusion   Action               2.1   Alarm   Alarm   Yes or No   active transmitter failed   Switchover       2.2   Normal   Normal   Yes   common cable failed   None       2.3   Alarm   Normal   Yes   active transmitter failed and   Switchover                       standby-side monitor failed,                       or active-side cable failed       2.4   Alarm   Normal   No   active-side monitor failed and/or   Standby-side unusable -                       standby-side cable failed   prevent switchovers       2.5   Normal   Alarm   No   standby-side monitor failed   None       2.6   Normal   Alarm   Yes   active transmitter failed and   Switchover                       active-side monitor failed                  
 
         [0043]     As discussed above, protection controller  308  includes logic configured to analyze information obtained via monitoring/processing/control blocks  210  and  218  from each of active-side monitor  212 , standby-side monitor  213  and transmit failure indications received via either or both of receivers  208  and  216 . Protection controller  308  can take on many forms and can be separate from transmitter modules  102  and  104  or can be a part of either transmitter module  102  or  104  or both. Moreover, it will be recognized that protection controller  308  can take on any form, e.g., a system, apparatus, or device, such as a computer-based system or processor containing system, so long as the various actions described herein can be performed. For example, protection controller  308  can be implemented using specialized circuits or circuitry (e.g., discrete logic gates interconnected to perform a specialized function) or can be implemented via program instructions being executed by one or more processors, or by a combination of both. In addition, the sequences of actions described herein can be embodied in a computer-readable medium for use by or in connection with protection controller  308  to fetch the instructions from the computer-readable medium and execute the instructions.  
         [0044]     In any event, protection controller  308  receives monitor alarm and transmit failure indication information collected at monitoring/processing/control blocks  210  and  218 , analyzes the information and performs an action based on the information according to Table 1 for the standard arrangement shown in  FIG. 3 , or according to Table 2 for the cross-over arrangement shown in  FIG. 4 . In one embodiment, Tables 1 and/or 2 can be implemented as lookup tables stored in a memory (not shown) associated with protection controller  308 . When a set of input conditions is forwarded to and analyzed by protection controller  308 , protection controller  308  performs a lookup operation in a lookup table and fetches a corresponding action and conclusion. For example, assuming the standard arrangement of  FIG. 3  and a set of input conditions according to scenario 1.3 of Table 1, protection controller  308  would fetch the corresponding action from a lookup table corresponding to Table 1 and would initiate a switchover accordingly. In addition, protection controller  308  may also fetch the corresponding conclusion and indicate it to an operator, either locally or remotely, via indicator  310 .  
         [0045]     Further analysis of Table 1 yields the following observations regarding when a switchover is to occur. Switchovers occur for scenarios 1.1, 1.3, 1.4 and 1.6. In each of scenarios 1.1, 1.3 and 1.4, the active-side monitor  212  provides an alarm signal as input. This is not the case for non-switchover scenarios 1.2 and 1.5. In the only other switchover scenario, scenario 1.6, active-side monitor  212  is not in alarm, but standby-side monitor  213  is in alarm and a transmit failure indication is received. Once again, this is not the case for non-switchover scenarios 1.2 and 1.5. Accordingly, an exemplary implementation of protection controller  308  can be to initiate a switchover when either of these two conditions is detected. That is, a switchover is initiated when either (or both):  
         [0046]     1. active-side monitor  212  is in alarm; or  
         [0047]     2. standby-side monitor  213  is in alarm and a transmit failure indication is received.  
         [0048]      FIG. 5A  illustrates one implementation of protection controller  308  according to another aspect of the subject matter disclosed herein.  FIG. 5A  includes OR gate  500 , AND gate  502 , switchover determination  504 , active-side monitor status  506 , standby-side monitor status  508  and transmit failure indication status  510 . As can be appreciated by one of ordinary skill in this art, when active-side monitor status  506  is in alarm, i.e., is a logic ‘high’, switchover determination  504  will change accordingly, thus initiating a switchover. In addition, when both standby-side monitor status  508  is in alarm, i.e., is a logic ‘high’, and a transmit failure indication is received, switchover determination  504  will also change accordingly, thus initiating a switchover. Accordingly, protection controller  308  can be implemented as shown in  FIG. 5A  for determining when a switchover should take place.  
         [0049]      FIG. 5B  illustrates another implementation of protection controller  308  according to another aspect of the subject matter disclosed herein.  FIG. 5B  includes the same components as  FIG. 5A  and the addition of an XOR gate  512  and a second AND gate  514 .  FIG. 5B  corresponds to a simplification of Table 2 for the cross-over arrangement. In this case, a switchover is initiated for scenarios 2.1, 2.3, or 2.6. A switchover is therefore initiated when either (or both):  
         [0050]     1. both active side monitor  212  and standby-side monitor  213  is in alarm; or  
         [0051]     2. only one of active-side monitor  212  and standby-side monitor  213  is in alarm and a transmit failure indication is received. Such is the case in scenarios 2.1, 2.3, and 2.6, but not in non-switchover scenarios 2.2, 2.4, and 2.5.  
         [0052]     In addition to determining when to switchover, protection controller  308  may also determine when to prevent future switchovers from taking place until the cause of the current failure issue has been addressed. For example, scenario 1.5 of Table 1 and scenario 2.4 of Table 2 each determine that either the standby-side cable or the monitor currently monitoring the standby-side transmitter has failed and thus the standby-side transmitter should not be employed via a switchover.  
         [0053]      FIG. 6  is a flow chart illustrating a method for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to an aspect of the subject matter disclosed herein. In step  600 , protection controller  308  determines the status of active-side monitor  212  and standby-side monitor  213 , and whether a transmit failure indication has been received. If protection controller  308  determines there is an active-side monitor alarm in step  602 , the switchover flag is checked in step  604  and protection controller  308  determines in step  606  whether the switchover flag is set. If the switchover flag is not set, a switchover is performed in step  608 , the switchover flag is set in step  610  and an alert corresponding to the conclusion is displayed via indicator  310  in step  612 . Returning to step  606 , if protection controller  308  determines the switchover flag is set, no switchover is performed (step  614 ). This is to prevent excessive switchovers, as described above.  
         [0054]     Returning to step  602 , if protection controller  308  determines there is no active-side monitor alarm, protection controller  308  determines whether there is a standby-side monitor alarm in step  616 . If protection controller  308  determines that there is no standby-side monitor alarm in step  616 , no switchover is performed (step  614 ). If, however, protection controller  308  determines that there is a standby-side monitor alarm in step  616 , then protection controller  308  determines whether a transmit failure indication has been received in step  618 . If a transmit failure indication has been received, control transfers to step  604  where the switchover flag is checked and to step  606  where protection controller  308  determines whether the switchover flag is set. Once again, if the switchover flag is not set, a switchover is performed in step  608 , the switchover flag is set in step  610 , and an alert corresponding to the conclusion is displayed via indicator  310  in step  612 .  
         [0055]     Returning to step  618 , if protection controller  308  determines that no transmit failure indication has been received, this corresponds to scenario 1.5 of Table 1. Accordingly, future switchovers are prevented by setting the switchover flag in step  610  (even though no switchover has occurred) and the corresponding alert is displayed (step  612 ).  
         [0056]      FIG. 7  is a flow chart illustrating a method for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to another aspect of the subject matter disclosed herein. The method illustrated by  FIG. 7  corresponds to the cross-over arrangement of  FIG. 4 . In step  700 , protection controller  308  determines the status of active-side monitor  212  and standby-side monitor  213 , and whether a transmit failure indication has been received. If protection controller  308  determines there is both an active-side monitor alarm and standby-side monitor alarm in step  702 , the switchover flag is checked in step  704  and protection controller  308  determines in step  706  whether the switchover flag is set. If the switchover flag is not set, a switchover is performed in step  708 , the switchover flag is set in step  710  and an alert corresponding to the conclusion is displayed via indicator  310  in step  712 . Returning to step  706 , if protection controller  308  determines the switchover flag is set, no switchover is performed (step  714 ). This is to prevent excessive switchovers, as described above.  
         [0057]     Returning to step  702 , if protection controller  308  determines there is not both an active-side monitor alarm and standby-side monitor alarm, protection controller  308  determines whether there is only one of an active-side monitor alarm and a standby-side monitor alarm in step  716 . If protection controller  308  determines that there is neither an active-side monitor alarm nor a standby-side monitor alarm in step  716 , no switchover is performed (step  714 ). If, however, protection controller  308  determines that there is one of an active-side monitor alarm and a standby-side monitor alarm in step  716 , then protection controller  308  determines whether a transmit failure indication has been received in step  718 . If a transmit failure indication has been received, control transfers to step  704  where the switchover flag is checked and to step  706  where protection controller  308  determines whether the switchover flag is set. Once again, if the switchover flag is not set, a switchover is performed in step  708 , the switchover flag is set in step  710 , and an alert corresponding to the conclusion is displayed via indicator  310  in step  712 .  
         [0058]     Returning to step  718 , if protection controller  308  determines that no transmit failure indication has been received, protection controller  308  determines in step  720  if the one monitor alarm (from step  716 ) is an active-side monitor alarm, which, if true, corresponds to scenario 2.4 of Table 1. Accordingly, future switchovers are prevented by setting the switchover flag in step  710  (even though no switchover has occurred) and the corresponding alert is displayed (step  712 ). If, however, protection controller  308  determines that the one monitor alarm (from step  716 ) is a standby-side monitor alarm in step  720 , no switchover is performed (step  714 ).  
         [0059]      FIG. 8  illustrates a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement  800  according to yet another aspect of the subject matter disclosed herein. As shown in  FIG. 8 , redundancy protection system  802  includes standby-side monitoring/processing/control block  218 , active-side monitoring/processing/control block  210 , protection controller  308  and an indicator  310 . In this embodiment, however, active-side monitor  212  and standby-side monitor  213  are not required. The absence of a requirement to monitor outgoing transmissions makes this arrangement more attractive for implementation in current Y-cable-based systems that lack monitors. The remaining components in Y-cable-based signal transmitter arrangement  800  are substantially described above in connection with  FIG. 3 .  
         [0060]     In operation, when a transmit failure indication is received from the remote endpoint at receiver  208  and/or receiver  216 , the transmit failure indication is processed by monitoring/processing/control block  210  and/or monitoring/processing/control block  218 , respectively. Based on the receipt of a transmit failure indication, protection controller  308  automatically performs a switchover and then monitors for a second transmit failure indication. Based on the presence or absence of the second transmit failure indication, an alert is displayed via indicator  310 .  
         [0061]      FIG. 9  is a flow chart illustrating a method for providing redundancy protection in the Y-cable-based signal transmitter arrangement of  FIG. 8  according to yet another aspect of the subject matter disclosed. In steps  900  and  902 , protection controller  308  monitors for the receipt of a transmit failure indication. If protection controller  308  determines that a transmit failure indication has been received in step  902 , the switchover flag is checked in step  904 , and protection controller  308  determines whether the switchover flag is set in step  906 . If the switchover flag is not set, a switchover is performed in step  908  and the switchover flag is set in step  910 . If, however, the switchover flag is set, no switchover is performed in step  907 .  
         [0062]     In steps  912  and  914 , protection controller  308  monitors for the receipt of a second transmit failure indication. Here, for example, protection controller  308  monitors received messages for a predetermined period of time to see if a second transmit failure indication is received. If protection controller  308  determines that a second transmit failure indication has been received in step  914 , an alarm is issued via indicator  310  indicating that the common transmit cable failed or an incorrect transmission signal was received in step  916 . If, however, protection controller  308  determines that no second transmit failure indication is received, an alarm is issued via indicator  310  indicating that the active-side transmitter and/or transmit cable failed in step  918 . In either case, an indication is provided via indicator  310  that a transmit failure indication switchover has occurred and no further switchovers will take place until the failure issue is resolved in step  920 .  
         [0063]      FIG. 10  is a block diagram illustrating a system for providing redundancy protection in a Y-cable-based signal transmitter arrangement according to another aspect of the subject matter disclosed herein. As shown in  FIG. 10 , three modules  1000 ,  1002 , and  1004 , each include active transceiver module  102  and standby transceiver module  104  as sub-modules. Modules  1000 ,  1002 , and  1004  may be, for example, a printed circuit board that has a number of sub-modules. The transceiver sub-modules communicate with protection controller  308  via a protection bus  1006 . Alternatively, protection bus  1006  may be omitted and the transceiver modules may each communicate directly with protection controller  308 . As shown in  FIG. 10 , active transceiver sub-module  102  of module  1000  and standby transceiver sub-module  104  of module  1002  connect to the active-side and standby-side of a first Y cable  50 A, which is connected to a first remote endpoint  106 A. Similarly, active transceiver sub-module  102  of module  1002  and standby transceiver sub-module  104  of module  1004  connect to the active-side and standby-side of a second Y cable  50 B, which is connected to a second remote endpoint  106 B. Note here that the first and second remote endpoints may be associated with each other or may be the same endpoint. As can be appreciated, the pairs of active and standby transceiver sub-modules  102 , 104  connected to each Y cable  50 A,  50 B are associated with different modules  1000 ,  1002 ,  1004 , thus providing an additional layer of redundancy should one of the modules  1000 ,  1002 , or  1004  fail.  
         [0064]     In operation, when protection controller  308  determines that a switchover is needed for remote endpoint  106 A, standby transceiver sub-module  104  of module  1002  begins transmitting and active transceiver sub-module  102  of module  1000  stops transmitting. Similarly, when protection controller  308  determines, independently of the switchover determination above, that a switchover is needed for remote endpoint  106 B, standby transceiver sub-module  104  of module  1004  begins transmitting and active transceiver sub-module  102  of module  1002  stops transmitting. Using this arrangement, should an entire module  1000 ,  1002 , or  1004  fail, a corresponding standby transceiver sub-module (which is located on a different module) will still be operational to assume transmitting responsibilities after switchover. This cooperative arrangement can be extended to any number of modules beyond the three shown.  
         [0065]     It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the invention is defined by the claims as set forth hereinafter.