Abstract:
An entertainment system that has improved failure recovery characteristics and reduces the connection components is disclosed. In one aspect, an inflight entertainment system comprises a plurality of physically interconnected head end line replaceable units and a plurality of serially-connected networking line replaceable units physically interconnected in a serial configuration, wherein two of the serially-connected networking line replaceable units at the edge of the serial configuration are physically interconnected with two of the head end line replaceable units, respectively, wherein a loop-free head end data path is maintained between active head end line replaceable units by regulating link participation in the head end data path, and wherein one or more loop-free serially-connected networking data paths are maintained between at least one of the two head end line replaceable units and active serially-connected networking line replaceable units by regulating link participation in the serially-connected networking data paths.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 14/185,599, entitled “SERIAL NETWORKING FIBER-TO-THE-SEAT INFLIGHT ENTERTAINMENT SYSTEM, filed Feb. 20, 2014, which is a continuation of U.S. application Ser. No. 12/847,924, entitled “SERIAL NETWORKING FIBER-TO-THE-SEAT INFLIGHT ENTERTAINMENT SYSTEM,” filed Jul. 30, 2010, now U.S. Pat. No. 8,659,990, which claims the benefit of U.S. provisional application No. 61/273,584, entitled “SERIAL NETWORKING FIBER-TO-THE-SEAT INFLIGHT ENTERTAINMENT SYSTEM,” filed on Aug. 6, 2009, and U.S. provisional application No. 61/274,726, entitled “SERIAL NETWORKING FIBER-TO-THE-SEAT INFLIGHT ENTERTAINMENT SYSTEM NETWORK MANAGEMENT,” filed on Aug. 20, 2009. Additionally, this application is a continuation of U.S. application Ser. No. 12/898,482, entitled “INFLIGHT COMMUNICATION SYSTEM,” filed Oct. 5, 2010, which claims the benefit of U.S. provisional application No. 61/278,246, entitled “INFLIGHT COMMUNICATION SYSTEM VIDEO DISPLAY UNIT WITH ENHANCED USER INTERFACE,” filed on Oct. 5, 2009; U.S. provisional application No. 61/278,261, entitled “INFLIGHT COMMUNICATION SYSTEM WITH HIGH RELIABILITY AND HIGHLY SYNCHRONIZED PUBLIC ADDRESS AUDIO OUTPUT,” filed on Oct. 5, 2009; and U.S. provisional application No. 61/278,309, entitled “INFLIGHT COMMUNICATION SYSTEM VIDEO DISPLAY UNIT WITH DETACHABLE USER INTERFACE MODULE,” filed on Oct. 5, 2009. The contents of all of the above-identified applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Inflight entertainment systems have evolved significantly over the last 25 years. Prior to 1978, IFE systems consisted of audio-only systems. In 1978, Bell and Howell (Avicom Division) introduced a group viewing video system based on video cassette tapes. In 1988, Airvision introduced the first in-seat video system allowing passengers to choose between several channels of broadcast video. In 1997, Swissair installed the first interactive video on demand (VOD) system. Currently, several inflight entertainment systems provide VOD with full digital video disc-like controls. 
         [0003]    One factor in the commercial viability of an inflight entertainment system is the system&#39;s line replaceable units (LRUs). The term “LRU” is a term of art generally describing a complex component (e.g. “black box”) on an airplane that is designed to be replaced quickly on the flight line or airport ramp area. LRU&#39;s are beneficial because they are generally self-contained units that can be rapidly swapped-out in the event that maintenance is required thus allowing the airplane to continue to operate with little down time. To be installed on an airplane, an LRU design must first be approved by the Federal Aviation Administration by means defined in Title 14 of the Code of Federal Regulations. LRUs of a single hardware design configuration may have different software installed. An inflight entertainment system&#39;s installation costs, operating costs, maintenance costs and passenger comfort depend greatly on the size, form factor, number and weight of its LRUs, as well as the number of distinct LRUs deployed in a single aircraft and across an airline&#39;s entire fleet of aircraft. 
         [0004]      FIG. 1  illustrates conventional inflight entertainment systems that employ a terrestrial-like VOD architecture (i.e. head end, distribution area, seat end). The left side of the figure shows components that are typically found at the head end of the system or in an electronics bay. The right side of the figure shows system components that are typically found at the seat end. The middle section of the figure shows system components that are typically found in a distribution area between the head end and the seat end. These components include area distribution boxes (ADBs) that fan-out data from the head end to the seat end. ADBs are typically connected to seat electronics boxes (SEBs) within each seat column, which distribute data forward and/or backward to an adjacent seat group in the same seat column. 
         [0005]    Inflight entertainment system vendors have recently made attempts to reduce the number of distinct LRUs at the seat end. Four examples of conventional seat end architectures are shown in  FIG. 1 . Boxes A and D show traditional seat architectures wherein SEBs are interposed between ADBs and seat end components such as VDUs and passenger control units (PCUs). Boxes B and C show newer seat architectures that reflect attempts to eliminate or reduce reliance on SEBs by moving SEB functionality to VDUs and/or PCUs. This shift has generally come at the expense of increased VDU and/or PCU size, weight and power. 
         [0006]    The inflight entertainment industry has been slower to reduce the number of distinct LRUs at the head end and in the distribution area. Moreover, conventional inflight entertainment systems require inter-area wiring and seat-to-seat wiring that varies across inflight entertainment system vendors and even across a single inflight entertainment system vendor&#39;s products, raising installation and maintenance costs. 
         [0007]    Some small players in the inflight entertainment industry have made advances at the head end and in the distribution area. For example, one recent inflight entertainment system has no head end or distribution area. However, this system has no parallel in terrestrial VOD systems and cannot easily leverage advancements and technology developments from the terrestrial world. Another recent inflight entertainment system has a simplified head end that integrates the audio, video and application servers in a single LRU. However, this system is proprietary and cannot easily leverage advancements in terrestrial VOD system technology. Moreover, the latter system requires a network of distribution area nodes between the head end and the seat end. 
         [0008]    On a conventional passenger aircraft equipped with an inflight entertainment (IFE) system, often each passenger seat is equipped with a VDU for the entertainment of the passenger. Generally, VDUs each have a user interface that includes user interface elements, such as an audio output jack. The user interface elements can be highly susceptible to malfunction or breakage as a result of normal wear and tear or passenger misuse. 
         [0009]    Unfortunately, VDUs are often integrated in a way that if one of the user interface elements malfunctions or breaks, the only way to restore full service to the passenger is to replace the entire VDU. This is a cumbersome task that is generally not attempted in flight. Moreover, such integration often requires an airline to maintain sufficient spare VDUs at a high number of its destination airports to maintain high availability of its IFE system. Additionally, the airline generally must bear the cost of maintaining (direct or through contract) trained maintenance personnel at its destination airports to service failed VDUs. Furthermore, mixed fleet airlines (i.e., airlines having both wide-body and narrow-body aircraft) may have to separately spare (e.g., keep an inventory of extras) and maintain wide-body VDUs and narrow-body VDUs since its wide-body VDUs may not be usable in narrow-body applications and vice versa, e.g., VDUs for wide-body applications may include different user interface elements than narrow-body VDUs. 
         [0010]    Furthermore, on a conventional passenger aircraft, each passenger seat is often equipped with access to a flight attendant call button and a reading light on/off button for the convenience and safety of the passenger. In a narrow-body aircraft, these buttons are typically positioned on the cabin ceiling above the passenger&#39;s head. Overhead positioning of these buttons can be inconvenient for the passenger since the buttons are out of the passenger&#39;s sight line and require the passenger to reach up to activate and deactivate them. In a wide-body aircraft, these buttons are typically positioned on one of the passenger&#39;s armrests. Armrest positioning of these buttons is in some respects more convenient for the passenger. However, these buttons are still out of the passenger&#39;s sight line and space constraints of passenger armrests limit the size of these buttons, which can make them difficult to find, activate and deactivate. 
         [0011]    In a narrow-body aircraft, there is typically no integration between the IFE system and these buttons. The flight attendant call button and the reading light on/off button are installed overhead as a separate system and maintained as a separate system, thereby adding cost and complexity to both the installation and operation of both systems. In a wide-body aircraft, the IFE system is typically integrated with these buttons. In such cases, the flight attendant call button and the reading light on/off button are integrated on a passenger control unit (PCU) installed in the passenger armrest. Installation of the PCU in the passenger armrest often adds cost and complexity to the installation and operation of the IFE system. 
         [0012]    Furthermore, in conventional IFE systems, a passenger typically receives entertainment audio through a headset connected to a headset jack located at or near the passenger&#39;s seat. One safety requirement for IFE systems is that such systems do not interfere with a passenger&#39;s ability to hear PA system announcements. Therefore, in most inflight communication systems, when the PA system is in use entertainment audio received via the headset is overridden with PA audio, which is typically accomplished by interfacing the cabin intercom system (CIS) with the head end of the IFE system. Moreover, an inflight communication system should maintain synchronization within at least 33-milliseconds between PA audio transmitted over the headset and PA audio transmitted over overhead loudspeakers, as latencies greater than 33 milliseconds are detectable by humans and may make PA audio difficult to understand. 
       SUMMARY OF THE INVENTION 
       [0013]    The fiber-to-the-seat (FTTS) system described in U.S. Patent Application Publication No. 2007/0077998, the contents of which are incorporated herein by reference, and summarized in  FIG. 2  has offered a more modular, scalable, extensible, future proofed, wired inflight entertainment system that leverages terrestrial VOD hardware and software advances and is packaged to minimize the number of distinct LRU not only in a single aircraft but across an airline&#39;s entire fleet of aircraft (i.e. regional jets to jumbo jets). However, this FTTS system has certain drawbacks. First, each server switch unit (SSU) is a single point of failure for all VDUs and any cabin management terminal (CMT) that connects directly to that SSU. Second, the implementation of a star wired network topology wherein each VDU has a dedicated optical fiber “home run” to a head end SSU adds cost and complexity to the system. For example, over two miles of fiber are required on a typical narrow body aircraft installation and over four miles of fiber are required on a typical wide body aircraft installation. The high cost of aircraft grade fiber and fiber optic connectors, coupled with the cost and complexity of installing these fiber components, make this architecture very expensive to implement. 
         [0014]    In some embodiments, the present invention provides an inflight entertainment system that offers advantages of the FTTS system described in U.S. Patent Application Publication No. 2007/0077998 while exhibiting superior failure recovery characteristics and having reduced fiber component requirements. The system, however, is not limited to the field of aviation; indeed other applications are contemplated, such as but not limited to buses, boats, automobiles, trains, and the like. 
         [0015]    In one aspect of the invention, such an inflight entertainment system comprises a plurality of head end line replaceable units physically interconnected in a ring configuration and a plurality of serially-connected networking line replaceable units physically interconnected in a serial configuration, wherein two of the serially-connected networking line replaceable units at the edge of the serial configuration are physically interconnected with two of the head end line replaceable units, respectively, wherein a loop-free head end data path is maintained between active head end line replaceable units by regulating link participation in the head end data path, and wherein one or more loop-free serially-connected networking data paths are maintained between at least one of the two head end line replaceable units and active serially-connected networking line replaceable units by regulating link participation in the serially-connected networking data paths. 
         [0016]    In some embodiments, the loop-free serially-connected networking data paths are maintained by removing a selected link from a previous serially-connected serially-connected networking data path. In some embodiments, the selected link is selected using hop count information. In some embodiments, the selected link is selected to minimize the maximum number of hops between any of the active serially-connected networking line replaceable units and either of the two head end line replaceable units. 
         [0017]    In some embodiments, the loop-free serially-connected networking data paths are maintained by adding a selected link to a previous serially-connected networking data path in response to detecting a failure on the previous serially-connected networking data path. In some embodiments, the failure is a link failure. In some embodiments, the failure is a line replaceable unit failure. 
         [0018]    In some embodiments, the loop-free head end data path is maintained by removing a selected link from a previous head end data path in response to detecting a loop on the previous head end data path. 
         [0019]    In some embodiments, the loop-free head end data path is maintained by adding a selected link to a previous head end data path in response to detecting a failure on the previous head end data path. In some embodiments, the failure is a link failure. In some embodiments, the failure is a line replaceable unit failure. 
         [0020]    In some embodiments, the plurality of serially-connected networking line replaceable units comprises at least one video display line replaceable unit. 
         [0021]    In some embodiments, the plurality of serially-connected networking line replaceable units comprises at least one cabin management terminal line replaceable unit. 
         [0022]    In some embodiments, the plurality of serially-connected networking line replaceable units comprises at least one on board network interface line replaceable unit. In some embodiments the on board network interface line replaceable unit provides connectivity to a public address system. In some embodiments the on board network interface line replaceable unit provides connectivity to a flight management system. 
         [0023]    In some embodiments, the plurality of serially-connected networking line replaceable units comprises at least one off board network interface line replaceable unit. 
         [0024]    In some embodiments, the plurality of serially-connected networking line replaceable units comprises at least one data loader line replaceable unit. 
         [0025]    In some embodiments, the plurality of head end line replaceable units comprises at least one application server. 
         [0026]    In some embodiments, the plurality of head end line replaceable units comprises at least one audio server. 
         [0027]    In some embodiments, the plurality of head end line replaceable units comprises at least one video server. 
         [0028]    In some embodiments, the plurality of head end line replaceable units comprises at least one file server. 
         [0029]    In some embodiments, the plurality of head end line replaceable units comprises at least one game server. 
         [0030]    In some embodiments, the plurality of head end line replaceable units comprises at least one passenger flight information system server. 
         [0031]    In another aspect of the invention, a first head end line replaceable unit for an inflight entertainment system comprises a plurality of fiber optic transceivers and a processor communicatively coupled with the transceivers, wherein under control of the processor in response to failure of a first link to a second head end line replaceable unit via a first one of the transceivers the first head end line replaceable unit activates a second link to a third head end line replaceable unit via a second one of the transceivers whereby a loop-free head end data path between a plurality of head end line replaceable units is restored. 
         [0032]    In another aspect of the invention, a serial networking line replaceable unit for an inflight entertainment system comprises a plurality of fiber optic transceivers and a processor communicatively coupled with the transceivers, wherein under control of the processor in response to failure of a first data path to a first head end line replaceable unit via a first one of the transceivers the serial networking line replaceable unit activates a second data path to a second head end line replaceable unit via a second one of the transceivers. 
         [0033]    In another aspect of the invention, a head end line replaceable unit for an inflight entertainment system comprises a plurality of fiber optic transceivers and a processor communicatively coupled with the transceivers, wherein under control of the processor the head end line replaceable unit transmits a presence message on a link via a first one of the transceivers, receives the presence message on a link via a second one of the transceivers, and in response to receiving the presence message removes one of the links from participation in a loop-free head end data path between a plurality of head end line replaceable units. 
         [0034]    In some embodiments, under control of the processor the head end line replaceable unit transmits to a serial networking line replaceable unit via a third one of the transceivers a second presence message having a hop count. 
         [0035]    In yet another aspect of the invention, a serial networking line replaceable unit for an inflight entertainment system comprises a plurality of fiber optic transceivers and a processor communicatively coupled with the transceivers, wherein under control of the processor the serial networking line replaceable unit receives a presence message having a received hop count on a link via a first one of the transceivers, increments the hop count and transmits the presence message having an incremented hop count on a link via a second one of the fiber optic transceivers, and wherein under control of the processor the serial networking line replaceable unit regulates participation of one of the links in a loop-free serial networking data path between a head end line replaceable unit and a plurality of serial networking line replaceable units based at least in part on the received hop count. 
         [0036]    Certain aspects of the present disclosure relate to inflight communication systems and, more particularly, to an inflight communication system having a public address (PA) system that bypasses the IFE head end servers when delivering PA audio to seat audio/visual (A/V) systems, and/or having a video display unit (VDU) having a detachable user interface module, and/or having a VDU with an enhanced user interface. 
         [0037]    In some embodiments, a VDU for an inflight communication system includes an integrally mounted detachable module having a plurality of user interface elements thereon. The VDU can facilitate recovery from failure of one of the user interface elements in that the detachable module can be replaced without replacing the entire VDU. In addition, the VDU can enable an airline to employ a single type of VDU base for its entire fleet of wide-body and narrow-body aircraft. In some embodiments, a narrow-body detachable module (e.g., having X user interface elements) may be coupled with the VDU base, and a wide-body detachable module (e.g., having X or more or fewer than X user interface elements) may be coupled with the same VDU base. 
         [0038]    In some embodiments, a VDU for an inflight communication system includes a VDU base having a video display, a network interface, and one or more processors operatively coupled with the network interface; and a detachable module integrally mounted to the VDU base and having a plurality of user interface elements operatively coupled with at least one of the processors. 
         [0039]    In some embodiments, the user interface elements include an auxiliary input. 
         [0040]    In some embodiments, the user interface elements include an audio output jack. 
         [0041]    In some embodiments, the user interface elements include a flight attendant call button. 
         [0042]    In some embodiments, the user interface elements include a reading light control button. 
         [0043]    In some embodiments, the detachable module has electrical contacts that interface with electrical contacts on the VDU base to render the user interface elements operative. 
         [0044]    In some embodiments, the detachable module is engaged with the VDU base by moving the detachable module into abutment with the VDU base. 
         [0045]    In some embodiments, the detachable module is held in engagement with the VDU base using a mounting screw. 
         [0046]    In some embodiments, the video display includes a touch screen. 
         [0047]    In some embodiments, the VDU base further includes a credit card reader. 
         [0048]    In some embodiments, a VDU base for an inflight communication system includes a video display, a network interface, one or more processors operatively coupled with the network interface, and electrical contacts operatively coupled with at least one of the processors, wherein the VDU base is adapted to interchangeably receive using integral mounting and render operative via the electrical contacts a first detachable module having a first set of user interface elements and a second detachable module having a second set of user interface elements, wherein the first and second sets include different user interface elements. 
         [0049]    In some embodiments, the first detachable module is a wide-body aircraft detachable module and the second detachable module is a narrow-body aircraft detachable module. 
         [0050]    In some embodiments, the second set of user interface elements is a subset of the first set of user interface elements. For example, in some embodiments each of the user elements in the second set of user elements is also included in the first set of user elements. 
         [0051]    In some embodiments, the first and second sets each include an auxiliary input and an audio output jack. 
         [0052]    In some embodiments, the first set includes a flight attendant call button and a reading light control button and the second set does not include a flight attendant call button and does not include a reading light control button. 
         [0053]    In some embodiments, a VDU assembly for an inflight communication system includes a VDU base having a video display, a network interface, one or more processors operatively coupled with the network interface and a module receiving area having electrical contacts, and a detachable module integrally mountable to the base at the module receiving area and having a plurality of user interface elements, wherein when the detachable module is integrally mounted to the base at the module receiving area the user interface elements are operatively coupled via the electrical contacts with at least one of the processors. 
         [0054]    In some embodiments, a VDU for an inflight communication system has an integral flight attendant call button and/or reading light control button. Incorporating one or more of these buttons into a VDU enables these buttons to be positioned on a seat back where they are in the passenger&#39;s sight line and where space constraints are less severe. Moreover, incorporating these buttons into a VDU can simplify or eliminate armrest PCUs and overhead passenger controls, which can reduce or eliminate the installation, operating and maintenance costs associated with a conventional line replaceable unit of an inflight communication system. 
         [0055]    In some embodiments, a VDU for an inflight communication system includes a user interface having a video display and a flight attendant call button, a network interface, and one or more processors operatively coupled with the user interface and the network interface, wherein under control of at least one of the processors in response to depressing the flight attendant call button the video display unit transmits via the network interface a signal indicative of status of the flight attendant call button. 
         [0056]    In some embodiments, the user interface further includes a reading light control button, and under control of at least one of the processors in response to depressing the reading light control button the video display unit transmits via the network interface a signal indicative of status of the reading light control button. 
         [0057]    In some embodiments, the video display unit is mounted to a seat back. 
         [0058]    In some embodiments, the flight attendant call button is a mechanical button. 
         [0059]    In some embodiments, the flight attendant call button is a touch screen button. 
         [0060]    In some embodiments, the network interface is communicatively coupled with an inflight entertainment distribution network. 
         [0061]    In some embodiments, a video display unit for an inflight communication system includes a user interface having a video display and a reading light control button, a network interface, and one or more processors operatively coupled with the user interface and the network interface, wherein under control of at least one of the processors in response to depressing the reading light control button the video display unit transmits via the network interface a signal indicative of status of the reading light control button. 
         [0062]    In some embodiments, the user interface further includes a flight attendant call button, and under control of at least one of the processors in response to depressing the flight attendant call button the video display unit transmits via the network interface a signal indicative of status of the flight attendant call button. 
         [0063]    In some embodiments, the video display unit is mounted to a seat back. 
         [0064]    In some embodiments, the reading light control button is a mechanical button. 
         [0065]    In some embodiments, the reading light control button is a touch screen button. 
         [0066]    In some embodiments, the network interface is communicatively coupled with an inflight entertainment distribution network. 
         [0067]    In some embodiments, an inflight communication system includes a cabin management system having one or more attendant call lights, and a seatback video display unit operatively coupled with the cabin management system via an inflight entertainment distribution network, wherein in response to a signal received from the seatback video display unit indicative of status of a flight attendant call button the cabin management system regulates power to one or more of the attendant call lights. 
         [0068]    In some embodiments, the attendant call lights include a galley section attendant call light and a passenger section attendant call light. 
         [0069]    In some embodiments, the signal indicates on/off status of the flight attendant call button and the cabin management system turns-on/off the attendant call lights in response to the signal. 
         [0070]    In some embodiments, the signal indicates “on” status of the flight attendant call button and a public address system outputs an audible tone in response to the signal. 
         [0071]    In some embodiments, the public address system outputs the audible tone periodically. 
         [0072]    In some embodiments, an inflight communication system includes a cabin management system having a passenger reading light, and a seatback video display unit operatively coupled with the cabin management system via an inflight entertainment distribution network, wherein in response to a signal received from the seatback video display unit indicative of status of a reading light control button the cabin management system regulates power to the passenger reading light. 
         [0073]    In some embodiments, the signal indicates on/off status of the reading light control button and the cabin management system turns on/off the passenger reading light in response to the signal. 
         [0074]    In some embodiments, the signal indicates dimmer status of the reading light control button and the cabin management system dims or brightens the passenger reading light in response to the signal. 
         [0075]    In some embodiments, an inflight communication system that bypasses IFE head end servers when delivering PA audio to seat A/V systems, thereby reducing or eliminating the risk of PA audio output failure on seat A/V systems due to IFE head end server failure and/or improving synchronization between PA audio outputted on public loudspeakers and seat A/V systems. In some embodiments, such an inflight communication system includes a CIS having a public loudspeaker and an IFE system operatively coupled with the CIS and having at least one IFE head end server and a plurality of seat A/V systems, wherein each seat A/V system receives an entertainment audio signal from the IFE head end server and a PA audio signal and keyline status signal from the CIS and outputs either the entertainment audio signal or the PA audio signal based on the keyline status signal. 
         [0076]    In some embodiments, each seat A/V system generates an audio selection signal based on the keyline status signal and outputs either the entertainment audio signal or the PA audio signal based on the audio selection signal. 
         [0077]    In some embodiments, the PA audio signal and the keyline status signal bypass the IFE head end server en route between the CIS and each seat A/V system. In some embodiments, the PA audio signal and the keyline status signal are routed from the CIS to an aircraft interface unit and directly to the IFE distribution network for routing to a seat A/V system. 
         [0078]    In some embodiments, each seat A/V system further receives an entertainment video signal from the IFE head end server and outputs either the entertainment video signal or a video interrupt signal based on the keyline status signal. 
         [0079]    In some embodiments, the CIS outputs the PA audio signal on the public loudspeaker. 
         [0080]    In some embodiments, the IFE system and the CIS are operatively coupled via an aircraft interface unit. 
         [0081]    In some embodiments, each seat A/V system is operatively coupled with the CIS and the IFE head end server via an IFE distribution network. 
         [0082]    In some embodiments, each seat A/V system receives packets having the entertainment audio signal, the PA audio signal and the keyline status signal. 
         [0083]    In some embodiments, a seat A/V system for an inflight communication system enables bypassing of IFE head end servers when delivering PA audio to the seat A/V system. In some embodiments, such a seat A/V system for an inflight communication system includes at least one A/V input, an audio output and an audio selection switch operatively coupled between the A/V input and the audio output, wherein the audio selection switch is adapted to output on the audio output either an entertainment audio signal or a PA audio signal received on the A/V input based on an audio selection signal. In some embodiments, the seat A/V system for an inflight communication system is communicatively linked to one or more IFE head end servers via an IFE distribution network. 
         [0084]    In some embodiments, the seat A/V system further includes an entertainment processor and a passenger safety processor operatively coupled between the audio selection switch and the A/V input, wherein the entertainment processor is adapted to provide the entertainment audio signal to the audio selection switch and the passenger safety processor is adapted to provide the PA audio signal to the audio selection switch. 
         [0085]    In some embodiments, the passenger safety processor is further adapted to provide the audio selection signal to the audio selection switch. 
         [0086]    In some embodiments, the seat A/V system further includes a network switch operatively coupled between the audio selection switch and the A/V input, wherein the network switch is adapted to segregate entertainment signals received on the A/V input from PA signals received on the A/V input, provide the entertainment signals to the entertainment processor, and/or provide the PA signals to the passenger safety processor. 
         [0087]    In some embodiments, an inflight communication system routes PA audio through an IFE system before outputting the PA audio on a public loudspeaker, thereby improving synchronization between PA audio output on the public loudspeaker and the seat A/V systems. In some embodiments, such an inflight communication system includes a CIS having a public loudspeaker, and an IFE system operatively coupled with the CIS and having a plurality of seat A/V systems and a loopback converter, wherein in response to a PA audio signal received from the CIS the IFE system outputs the PA audio signal on each seat A/V system and returns the PA audio signal to the CIS via the loopback converter whereupon the CIS outputs the PA audio signal on the public loudspeaker. 
         [0088]    In some embodiments, the CIS has a handset and the PA audio signal is received by the CIS via the handset. 
         [0089]    In some embodiments, the loopback converter and the seat A/V systems are of a single line replaceable unit (LRU) type. 
         [0090]    In some embodiments, the IFE system and the CIS are operatively coupled via an aircraft interface unit. 
         [0091]    In some embodiments, each seat A/V system receives an entertainment audio signal from an IFE head end server and the PA audio signal and a keyline status signal from the CIS and outputs the PA audio signal based on the keyline status signal. 
         [0092]    In some embodiments, each seat A/V system further receives an entertainment video signal from the IFE head end server and outputs a video interrupt signal based on the keyline status signal. 
         [0093]    In some embodiments, each seat A/V system generates an audio selection signal based on the keyline status signal and outputs the PA audio signal based on the audio selection signal. 
         [0094]    In some embodiments, the PA audio signal and the keyline status signal bypass the IFE head end server between the CIS and each seat A/V system. 
         [0095]    In some embodiments, each seat A/V system is operatively coupled with the CIS and the IFE head end server via an IFE distribution network. 
         [0096]    In some embodiments, the IFE distribution network includes fiber optics. 
         [0097]    In some embodiments, each seat A/V system receives packets having the entertainment audio signal, the PA audio signal and the keyline status signal. These and other aspects of the invention will be better understood by reference to the following detailed description taken in conjunction with the drawings that are briefly described below. Of course, the invention is defined by the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0098]      FIG. 1  shows known inflight entertainment systems. 
           [0099]      FIG. 2  shows a known FTTS inflight entertainment system. 
           [0100]      FIG. 3  shows an inflight entertainment system with serially-connected networking line replaceable unit chains and a head end line replaceable unit ring in accordance with some embodiments of the invention. 
           [0101]      FIG. 4  shows a head end line replaceable unit for an inflight entertainment system with serial networking line replaceable unit chains and a head end line replaceable unit ring in accordance with some embodiments of the invention. 
           [0102]      FIG. 5  shows a generic serial networking line replaceable unit for an inflight entertainment system with serial networking line replaceable unit chains and a head end line replaceable unit ring in accordance with some embodiments of the invention. 
           [0103]      FIGS. 6A through 6D  show serial networking data path maintenance in accordance with some embodiments of the invention. 
           [0104]      FIGS. 7A through 7D  show head end data path maintenance in accordance with some embodiments of the invention. 
           [0105]      FIG. 8  schematically shows an embodiment of an inflight communication system for an aircraft including an embodiment of a VDU. 
           [0106]      FIG. 9  schematically shows an embodiment of the cabin positioning of the elements of the inflight communication system of  FIG. 8 . 
           [0107]      FIG. 10  schematically shows the VDU of  FIG. 8  in further detail. 
           [0108]      FIG. 11  schematically shows an embodiment of a wide-body VDU assembly. 
           [0109]      FIG. 12  schematically shows an embodiment of a narrow-body VDU assembly. 
           [0110]      FIG. 13  schematically shows a conventional inflight communication system. 
           [0111]      FIG. 14  schematically shows an embodiment of an inflight communication system with high reliability PA audio output including some embodiments of seat A/V systems. 
           [0112]      FIG. 15  schematically shows an embodiment of a seat A/V system that is representative one of the seat A/V systems of  FIG. 14 . 
           [0113]      FIG. 16  schematically shows an embodiment of an inflight communication system with high reliability and highly synchronized PA audio output including an embodiment of a loopback converter. 
           [0114]      FIG. 17  schematically shows an embodiment of the loopback converter of  FIG. 16  in more detail. 
           [0115]      FIG. 18  schematically shows another embodiment of a loopback converter. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0116]      FIG. 3  shows an inflight entertainment (IFE) system with serial networking line replaceable unit (SN-LRU) chains  311 - 313  and a head end line replaceable unit (HE-LRU) ring  310  in some embodiments of the invention. As illustrated, SN-LRU chain  311  and HE-LRU ring  310  are positioned outside of the seats, while SN-LRU chains  312 ,  313  are positioned at the seats. In these embodiments, multiple HE-LRUs  309  are physically connected by ring via fiber optic links  308 . Multiple chains of SN-LRUs  301 - 305  are physically connected to HE-LRUs  309  at their edges (ends) via links  307 , for example fiber optics, such that the two edges of each chain are physically connected to a different one of HE-LRUs  309 . Many types of SN-LRUs can be employed, for example serial networking onboard network interface unit  301 , serial networking offboard network interface unit  302 , serial networking data loader  303 , serial networking CMT  304  (generally positioned in the galley), and serial networking VDUs  305 . 
         [0117]    Each SN-LRU  301 - 305  discovers through topology messaging the nearest HE-LRU  309 . In the illustrated embodiment, starting on one SN-LRU chain  311  edge, unit  301  is connected to one of HE-LRUs  309  via a link  307  in the upstream direction while connecting to unit  302  in the downstream direction via another link  306 . Unit  301  receives from the HE-LRU  309  in the upstream direction a presence message including a hop count to the HE-LRU  309 , increments the hop count, and passes the updated presence message along in the downstream direction to unit  302 . As the presence message progresses in the downstream direction, each successive SN-LRU in the chain (e.g.  302 ,  303 ,  304 ) increments the hop count. Continuing on this chain, unit  302  is connected in the downstream direction to data loader  303  over another link  306 . Data loader  303  is connected in the downstream direction to CMT  304  over another link  306 . In the final link of this SN-LRU chain  311 , CMT  304  at the edge of the chain is connected back to a different one of HE-LRUs  309  over yet another link  307 . In the other direction, CMT  304  receives from that HE-LRU  309  a presence message including a hop count, increments the hop count, and passes the updated presence message along in the upstream direction to data loader  303 . Each successive SN-LRU in the chain  311  increments the hop count accordingly. 
         [0118]    The IFE system can include at least one additional SN-LRU chain  312  and probably at least two additional SN-LRU chains  312 ,  313 . The additional SN-LRU chain or chains  312 ,  313  can consist of most any type of SN-LRU, such as VDUs  305 . On each edge of these additional SN-LRU chains  312 ,  313 , one of serial networking VDUs  305  is connected to one of HE-LRUs  309  over a link and within each of these SN-LRU chains serial networking VDUs  305  are connected over links. These additional SN-LRU chains  312 ,  313  generally disseminate presence messages and hop count information in the same manner as the previously described SN-LRU chain  311 . 
         [0119]    Separately, each HE-LRU discovers through topology messaging whether the HE-LRU ring  310  is closed or open. Each HE-LRU  309  receives a presence message from neighboring HE-LRUs  309  and relays the presence message on its non-ingress port until it is determined whether presence message loops-back to the originating HE-LRUs  309 , in which case it is revealed that the HE-LRU ring  310  is closed, or does not loop-back to the originating HE-LRUs  309 , in which case it is revealed that the HE-LRU ring  310  is open. 
         [0120]    Server functionality (e.g. application server, audio server, video server, game server, file server, passenger information system server) is integrated into HE-LRUs  309  in a modular, scalable, robust fashion that minimizes the impact on the IFE system in the event one or more of HE-LRUs  309  fails. Network management processors within HE-LRUs  309  and SN-LRUs restore network access of live SN-LRUs  301 - 305  to HE-LRUs  309  under the following scenarios: (a) a connection break along an SN-LRU chain  311 - 313 ; (b) failure of an SN-LRU  301 - 305  in an SN-LRU chain  311 - 313 ; (c) failure of an HE-LRU  309  at one end of an SN-LRU chain  311 - 313 . Moreover, network management processors within HE-LRUs  309  restore network access of SN-LRUs  301 - 305  as described with respect to  FIGS. 6A-7D  to live HE-LRUs  309  under the following scenarios: (a) a connection break between any two HE-LRUs  309 ; (b) failure of an HE-LRU  309 . While the number of SN-LRUs  301 - 305  in an SN-LRU chain  311 - 313  will vary, relatively short SN-LRU chains generally offer a higher level of redundancy and failover bandwidth to SN-LRUs. In some embodiments, error indications are provided, e.g. error codes, to facilitate identification, diagnosis, and/or location of the error. In some embodiments the error indications are transmitted to offboard monitoring and/or maintenance systems. 
         [0121]      FIG. 4  shows a representative HE-LRU  400  adapted for use in an IFE system with SN-LRU chains and an HE-LRU ring in some embodiments of the invention. In these embodiments, HE-LRU  400  has integrated servers of six different types, including one or more application servers  401 , video servers  402 , audio servers  403 , game servers  404 , file servers  405  and passenger flight information system servers  406 , all of which are connected to an integrated network management processor  407  over internal connections. By way of example, network management processor  407  may be a managed switch. 
         [0122]    Application servers  401  are system controllers that provide the following types of services: content management; channel packaging; transaction processing; billing system integration; services management; provisioning integration; system administration and management; encryption management (key servers, authentication etc.); software client management; server integration for audio, video, gaming and file servers or the like. Video servers  402  provide the following types of services: VOD, near VOD; pay per view; network personal video recorder; broadcast video or the like. Audio servers  403  provide the following types of services: audio on demand; broadcast audio or the like. Game servers  404  provide the following types of services: logic and programming for games; dynamically delivered web pages for browser based games or the like. File servers  405  provide the following types of services: cached Internet content; cached user data and user profile data or the like. Passenger flight information system servers  406  use inputs from the aircraft navigation system and compute various flight information including time to destination, speed, altitude, outside air temperature, time at destination, aircraft location for display to passenger either in text form or graphically such as a moving map display or the like. 
         [0123]    Processor  407  has N ports reserved for physical connections to SN-LRUs on the edges of chains and K ports reserved for physical connections to other HE-LRUs in a ring. The K ports reserved for HE-LRU ring connections are connected to K HE-LRU port transceivers  408  over internal connections. Port transceivers  408  are in turn connected to a fiber optic panel connector  420  over K internal fiber optic connections. Similarly, the N ports reserved for SN-LRU chain connections are connected to N SN-LRU port transceivers  410  over internal connections. Port transceivers  410  are in turn connected to panel connector  420  over N internal fiber optic connections. In some embodiments, the internal fiber optic connections are simplex by the time they connect to panel connector  420  (e.g. port transceivers  408  and  410  are bidirectional or a coupler is used to convert a unidirectional duplex transceiver output to bidirectional simplex format). Panel connector  420  blind mates with a connector  421  when HE-LRU  400  is installed in a rack at the head end. Connector  421  has K external fiber optic cables reserved for HE-LRU ports that connect to the corresponding HE-LRU internal fiber optic connections when HE-LRU  400  is installed in the rack. Similarly, connector  421  has N external fiber optic cables reserved for the SN-LRU chain ports that connect to the corresponding SN-LRU internal fiber optic connections when HE-LRU  400  is installed in the rack. K and N are each greater than one. Moreover, HE-LRU  400  has T data ports, where K+N is less than or equal to T. Under control of processor  407 , HE-LRU  400  provides presence information to any SN-LRU that is connected directly to HE-LRU  400  over one of the N external fiber optic cables reserved for SN-LRU chain ports (i.e. any edge SN-LRU). Under control of processor  407 , HE-LRU  400  also provides its own presence information to any HE-LRU that is connected directly to HE-LRU  400  over one of the K external fiber optic cables reserved for HE-LRU ports and relays on its non-ingress port any presence information (that HE-LRU did not originate) received on these ports from neighboring HE-LRUs. 
         [0124]      FIG. 5  shows a generic SN-LRU  500  adapted for use in an IFE system with SN-LRU chains and an HE-LRU ring in some embodiments of the invention. In these embodiments, SN-LRU  500  includes an LRU core  501  having hardware and software elements, a first fiber optic transceiver  503 , a second fiber optic transceiver  504  and a network management processor  502 , which may be a managed switch. Processor  502  is communicatively coupled with first transceiver  503  and second transceiver  504  via internal copper connections. Processor  502  is communicatively coupled with LRU core  501  via an internal connection, such as a copper connection. First transceiver  503  is physically connected via, for example, an external fiber optic link to an upstream HE-LRU or SN-LRU. Second transceiver  504  is similarly physically connected via an external fiber optic link to a downstream HE-LRU or SN-LRU. Processor  502  provides LRU core  501  network access to an upstream HE-LRU through first transceiver  503  or to a downstream HE-LRU through second transceiver  504 . The upstream and downstream directions have been arbitrarily assigned to the network path on the left and the right of the LRU respectively. 
         [0125]    The structure and function of LRU core  501  varies by SN-LRU type. An LRU core for on board network interface unit  301  enables access to public address audio and data for passenger convenience features such as reading light control, flight attendant call and flight information for applications such as moving maps, etc. An LRU core for off board network interface unit  302  enables communication with terrestrial networks generally through satellite- or ground-based radio frequency networks. This LRU core may enable bidirectional or unidirectional communication depending on implementation. Bidirectional versions enable connectivity with terrestrial networks (broadband connectivity). Unidirectional versions enable access to off aircraft broadcast data sources such as television (broadcast video). An LRU core for data loader  303  enables media content updates (movies, audio, games, Internet web pages, files, etc.), key updates and transaction data transfers. This LRU core enables data transfer using one of the following mechanisms: removable disk or tape inserted into data loader  303 , portable disk drive or tape drive carried on board and temporarily connected to the IFE system, wireless LAN, or other wireless link. An LRU core for CMT  304  enables flight attendants to perform system management and administration functions such as: LRU reboot, video channel preview, flight attendant override, attendant call status, reading light status, built in test, interrogation and system test. LRU cores for VDUs  305  each include a physical display device (e.g. flat panel display) that enables a passenger to view video content and navigate an IFE menu. These LRU cores may additionally provide PCU functionality, such as volume control, channel control, lighting control, attendant call button, menu buttons and/or menu selection buttons, via a display device touch screen or mechanically actuated buttons. LRU cores for display interface units (not shown) include a physical interface to an external display device (e.g. flat panel display) that enables a passenger to view video content and navigate an IFE menu. Like the LRU cores for VDUs, these LRU cores may additionally provide PCU functionality, such as volume control, channel control, lighting control, attendant call button, menu buttons and/or menu selection buttons, via a display device touch screen or mechanically actuated buttons. 
         [0126]      FIGS. 6A through 6D  illustrate serial networking data path maintenance in some embodiments of the invention.  FIG. 6A  shows physical wiring of an IFE system having a ring of four HE-LRUs and a single chain of four SN-LRUs physically wired to HE-LRU  1  and HE-LRU  2 . SN-LRUs keep apprised of the nearest HE-LRU through topology messaging and regulate link participation in serial networking data paths to establish and maintain loop-free data paths that minimize the maximum number of network hops of any SN-LRU to an HE-LRU.  FIG. 6B  shows the serial networking topology when there are no faults in the chain. The link between SN-LRU  2  and SN-LRU  3  has been removed from the data path, resulting in establishment of two loop-free data paths wherein the maximum number of hops to an HE-LRU is two.  FIG. 6C  shows the serial networking topology after reconfiguration upon detecting that the link between SN-LRU  1  and SN-LRU  2  has failed. This reconfiguration is made by adding the link between SN-LRU  2  and SN-LRU  3  to the data path to provide all SN-LRUs a least hop data path to an HE-LRU wherein the maximum number of hops to an HE-LRU is three.  FIG. 6D  shows the serial networking topology after reconfiguration upon detecting that SN-LRU  4  has failed. This reconfiguration is made by adding the link between SN-LRU  2  and SN-LRU  3  to the data path to provide all SN-LRUs that remain active a least hop data path to an HE-LRU wherein the maximum number of hops to an HE-LRU is three. The additions and subtractions of links illustrated in  FIGS. 6B through 6D  are made under control of the network management processor in SN-LRU  1 , SN-LRU  2  and/or SN-LRU  3  using hop count and/or presence information gleaned from topology messaging. For example, each SN-LRU may under control of its network management processor determine whether it is a middle SN-LRU of a chain by comparing the hop counts received on both of its ports. If the hop counts for both ports is the same or differ by only one hop, the SN-LRU self-identifies as a middle LRU; otherwise, the SN-LRU does not self-identify as a middle LRU. If the SN-LRU self-identifies as a middle LRU, the SN-LRU breaks the chain to create a loop-free network topology. If the hop counts for both ports differ by one hop, the SN-LRU under control of its network management processor blocks the port with the higher hop count (i.e. the port that has a longer path to the nearest HE-LRU) and unblocks the other port. If the hop count for both ports is identical, the SN-LRU under control of its network management processor blocks a predetermined one of the ports and unblocks the other port. 
         [0127]      FIGS. 7A through 7D  illustrate head end data path maintenance in some embodiments of the invention.  FIG. 7A  shows physical wiring of an IFE system having a ring of four HE-LRUs and a single chain of four SN-LRUs physically wired to HE-LRU  1  and HE-LRU  2 . When HE-LRUs detect a closed HE-LRU ring as a result of topology messaging, a designated HE-LRU removes one of its links from the data path to create loop-free data path between HE-LRUs, which link may later be restored to the data path to maintain the data path if an HE-LRU or a link fails.  FIG. 7B  shows the head end network topology after HE-LRU loop detection. In that topology, the link between HE-LRU  1  and HE-LRU  4  has been removed from the data path to eliminate the loop.  FIG. 7C  shows the head end network topology after reconfiguration upon detecting that the link between HE-LRU  3  and HE-LRU  4  has failed. This link between HE-LRU  1  and HE-LRU  4  has been restored to the data path to maintain network access to all HE-LRUs.  FIG. 7D  shows the head end network topology after reconfiguration upon detecting that HE-LRU  2  has failed. This reconfiguration similarly results in restoration of the link between HE-LRU  1  and HE-LRU  4  to the data path to maintain network access to all live HE-LRUs. The additions and subtractions of links illustrated in  FIGS. 7B through 7D  are made under control of the network management processor in HE-LRU  1 , HE-LRU- 3 , and/or HE-LRU  4  using loop information gleaned from topology messaging. In some embodiments, at least two of the HE-LRUs in an HE-LRU ring are of a single hardware design configuration. 
         [0128]    In some embodiments, links are added and removed from data paths by dynamically regulating the state of transceivers in HE-LRUs and SN-LRUs between a data forwarding state and a data blocking state under control of the network management processors. Naturally, transceivers and their associated ports and links will continue to carry presence messages and other management information even when they are not participating in a data path. 
         [0129]    In one embodiment, an important distinguishing feature of the present invention from conventional spanning tree protocols is that in the present invention networks in which the loop-free data path between HE-LRUs passes through an SN-LRU are not formed. It is to be understood that the word “serial” as used herein describes the way the devices described are networked together and does not refer to the type of communications or way that communications are sent over the network links. 
         [0130]      FIG. 8  shows a communication system  100  for a vehicle, e.g., an aircraft inflight communication system. The illustrated inflight communication system  100  includes an IFE system  110  communicatively coupled via one or more interface units  120  to a cabin management system  130  and a PA system  140 . 
         [0131]    Generally, the IFE system  110  includes IFE servers  112 , an IFE distribution network  114  and a VDU  116 . While only one VDU  116  is shown, a plurality of VDUs are typically provided, e.g., a VDU positioned at or near the seat for every passenger on the aircraft. The IFE distribution network can be any type of communicative connection, e.g., fiber optic, copper wire, coaxial cable, wireless system, or the like. 
         [0132]    The cabin management system  130  shown includes a galley section attendant call light  132 , a passenger reading light  136 , a passenger section attendant call light  138 , and a control system  139 . While only one passenger reading light  136  and passenger section attendant call light  138  are shown, a passenger reading light is typically provided to each passenger and a passenger section attendant call light is typically provided to a group of adjacent passengers, e.g., three adjacent passengers. 
         [0133]    Several types of signals can be communicated between VDU  116  and other elements of inflight communication system  100  via IFE distribution network  114 . For example, some embodiments communicate audio/video entertainment signals originating from IFE servers  112 , PA audio signals and PA keyline status signals originating from PA system  140 , touch screen input signals, card input signals, and/or auxiliary input signals originating from VDU  116  and destined for IFE servers  112 , and/or flight attendant call signals and reading light control signals originating from VDU  116  and destined for control system  139 . These signals are typically carried between VDU  116  and the other elements of inflight communication system  100  in packets, such as Ethernet packets. 
         [0134]      FIG. 9  schematically shows cabin positioning of elements of the inflight communication system  100  of the embodiment of  FIG. 8 . The illustrated cabin includes a galley section  210  and a passenger section  220 . Galley section attendant call light  132  is often mounted to the cabin ceiling in galley section  210 , though other locations in the aircraft are possible. Passenger reading light  136  and/or passenger section attendant call light  138  can be mounted to the cabin ceiling in passenger section  220 , such as above a passenger seat  223 . VDU  116  is generally mounted to the back of a passenger seat  222  for use by a passenger sitting in passenger seat  223  immediately behind passenger seat  222 . VDU  116  can include a touch screen video display  224 , a flight attendant call button  226 , and a reading light control button  228 , among other user interface elements. Generally, the IFE servers  112  ( FIG. 8 ) are located in an electronics rack that is, typically, outside of the passenger section  220 . 
         [0135]      FIG. 10  shows an embodiment of VDU  116  in more detail. The illustrated VDU  116  has a user interface  300 A that includes a touch screen display  224 , a card reader  308 A, an auxiliary input  310 A, an audio output jack  316 , a flight attendant call button  226  and a reading light control button  228 . Other embodiments of the VDU  116  can include a user interface  300 A with other user interface elements or other combinations of user interface elements. Typically, the touch screen display  224  is capable of displaying video. 
         [0136]    In the illustrated embodiment, VDU  116  includes a network switch  302 A having a network interface  301 A for transmitting and receiving packets to and from IFE distribution network  114 . Network switch  302 A segregates signals inbound on network interface  301 A between entertainment signals and passenger safety signals. Inbound entertainment signals include, for example, audio/video entertainment signals. Inbound passenger safety signals include, for example, PA audio packets and PA keyline status packets. Network switch  302 A delivers entertainment signals to an entertainment processor  304 A and delivers passenger safety signals to a passenger safety processor  312 A. 
         [0137]    Generally, the passenger safety processor  312 A regulates the audio signals outputted on audio output jack  316  based on PA keyline status and may regulate the video signals outputted on touch screen display  224 . When PA system  140  is not in use, audio output jack  316  outputs entertainment audio signals received from entertainment processor  304 A and touch screen video display  224  renders entertainment video signals received from entertainment processor  304 A. When PA system  140  is in use, audio output jack  316  outputs PA audio signals received from passenger safety processor  312 A and touch screen video display  224  may render PA interrupt video signals received from entertainment processor  304 A. 
         [0138]    In some arrangements, audio selection switch  314  selects PA audio signals as audio output signals based on an audio selection signal. For example, when passenger safety processor  312 A receives from network switch  302 A PA keyline status indicating that PA system  140  is in use, passenger safety processor  312 A transmits an audio selection signal to audio selection switch  314  instructing audio selection switch  314  to select for transmission to audio output jack  316  PA audio signals made available by passenger safety processor  312 A rather than selecting entertainment audio signals made available by entertainment processor  304 A. Moreover, passenger safety processor  312 A can return a PA in progress signal to network switch  302 A, in response to which network switch  302 A may transmit a PA in progress signal to entertainment processor  304 A, instructing entertainment processor  304 A to select for transmission to touch screen video display  224  an interrupt video signal rather than entertainment video signals. In some embodiments, the entertainment processor  304 A may select an interrupt video signal as a video output signal based on the PA in progress signal received from network switch  302 A. In some embodiments, passenger safety processor  312 A may transmit a PA in progress signal on a direct communication line (not shown) to entertainment processor  304 A. In some embodiments, network switch  302 A may transmit a PA in progress signal to entertainment processor  304 A without prompting from passenger safety processor  312 A. 
         [0139]    In some embodiments, the audio selection signal instructing audio selection switch  314  to select PA audio signals and the PA in progress signal are transmitted repeatedly for as long as PA keyline status indicates that PA system  140  is in use. In some embodiments, the audio selection signal instructing audio selection switch  314  to select PA audio signals and the PA in progress signal are transmitted only once. In some embodiments, the audio selection signal instructing audio selection switch  314  to select PA audio signals and the PA in progress signal are transmitted according to a time interval. 
         [0140]    When passenger safety processor  312 A does not receive PA keyline status indicating that PA system  140  is in use (for example, receives a PA keyline status signal indicating non-use of PA system  140 ) passenger safety processor  312 A transmits an audio selection signal to audio selection switch  314  instructing audio selection switch  314  to select for transmission to audio output jack  316  entertainment audio signals made available by entertainment processor  304 A rather than PA audio signals made available by passenger safety processor  312 A. Audio selection switch  314  selects entertainment audio signals as audio output signals based on the audio selection signal. In some embodiments, entertainment processor  304 A selects entertainment video signals as video output signals based on the absence of a PA in progress signal indicating that PA system  140  is in use. 
         [0141]    The video and audio signals outputted by touch screen video display  224  and audio output jack  316 , respectively, are typically analog signals. The video signals may be extracted from packets and converted to analog form by network switch  302 A, entertainment processor  304 A, and/or touch screen video display  224 , or by conversion and extraction logic not shown in  FIG. 10 . The audio signals may be extracted from packets and converted to analog form by network switch  302 A, passenger safety processor  312 A, audio selection switch  314  or audio output jack  316 , and/or by conversion and extraction logic not shown in  FIG. 10 . The PA keyline status signals, audio selection signals and PA in progress signals described in relation to  FIG. 10  may be transmitted in packets or analog form. 
         [0142]    Card reader  308 A receives card (e.g., credit card, debit card, gift card, frequent-flyer membership card, or the like) information when a card is read by the reader  308 A. The card reader  308 A can transmit card input signals representing the card information to entertainment processor  304 A, which in turn can transmit the card input signals to network switch  302 A for delivery to IFE distribution network  114  via network interface  301 A, and eventually to IFE servers  112  or other IFE component (not shown). In some embodiments, the card information is transmitted to an off-board receiver. 
         [0143]    Auxiliary input  310 A can receive auxiliary information from an attached device, such as a handset with passenger controls, and transmits auxiliary input signals carrying the auxiliary information to entertainment processor  304 A for use by entertainment processor  304 A applications. Entertainment processor  304 A may in turn transmit the auxiliary input signals to network switch  302 A for delivery to IFE distribution network  114  via network interface  301 A, and eventually to IFE servers  112  or other IFE component (not shown) depending on the specific application. Auxiliary input  310 A may be, e.g., a universal serial bus (USB) port, Ethernet port, ⅛ inch port, ¼ inch port, IEEE 1394 port, or the like. 
         [0144]    Flight attendant call button  226  is generally actuated when selected by a passenger. In some embodiments, the flight attendant call button  226  is a mechanically actuated button, though in other embodiments the flight attendant call button  226  is an electronic button, e.g., a selectable area rendered on the touch screen  224 . When actuated, flight attendant call button  226  transmits a flight attendant call signal indicating flight attendant call button status to passenger safety processor  312 A, which in turn transmits the flight attendant call signal to network switch  302 A for delivery to IFE distribution network  114  via network interface  301 A, and eventually to control system  139  ( FIG. 8 ). When flight attendant call button  226  is actuated to the “on” position, the flight attendant call signal instructs the control system  139  to illuminate the passenger section attendant call light  132  and/or the galley section attendant call light  138 . When flight attendant call button  226  is pressed into the “off” position, the flight attendant call signal instructs control system  139  to de-illuminate the passenger section attendant call light  132  and/or the galley section attendant call light  138  if there are no other pending calls. In some embodiments, flight attendant call signals prompt cabin management system  130  to provide other sensory output, such as audio output delivered via PA system  140 . In some embodiments, rather than a button the flight attendant call button  226  is another type of input indicator, e.g., a switch, toggle, slider, or the like. 
         [0145]    Reading light control button  228  can be actuated when selected by a passenger. In some embodiments, the reading light control button  226  is a mechanically actuated button, though in other embodiments the reading light control button  226  is an electronic button, e.g., a selectable area rendered on the touch screen  224 . When actuated, reading light control button  228  transmits a reading light control signal indicating reading light control button status to passenger safety processor  312 A, which in turn transmits the reading light control signal to network switch  302 A for delivery to IFE distribution network  114  via network interface  301 A, and eventually to control system  139  ( FIG. 8 ). When reading light control button  228  is actuated to the “on” position, the reading light control signal instructs control system  139  to illuminate the passenger reading light  136 . When reading light control button  228  is actuated into the “off” position, the reading light control signal instructs control system  139  to de-illuminate the passenger reading light  136 . In some embodiments, rather than a button, the reading light control button  228  is another type of input indicator, e.g., a switch, toggle, slider, or the like. 
         [0146]    Control system  139  can regulate the status, e.g., illuminated or de-illuminated, of attendant call lights  132 ,  138  based on flight attendant call signals received from VDU  116 . The control system  139  can regulate the status, e.g., illuminated or de-illuminated, of passenger reading light  136  based on reading light control signals received from VDU  116 . 
         [0147]    In some embodiments, the reading light control button  228  operates as a dimmer (e.g., can increase and/or decrease the brightness, intensity, and/or amount of light from the passenger reading light  136 ). In these embodiments, reading light control signals instruct the cabin management control system  130  as to a desired brightness for the passenger reading light  136 , wherein the reading light control signals are selected by the passenger safety processor  312 A based on, e.g., how long the reading light control button was pressed. 
         [0148]    In some embodiments, one or both of the flight attendant call button  226  or reading light control button  228  are integral to the touch screen display  224 , e.g., as one or more buttons rendered on the touch screen display  224 . In these embodiments, the passenger can control his or her corresponding attendant call light  138  and/or the passenger reading light  136  by selecting the button and/or buttons on the passenger&#39;s corresponding touch screen display  224 . In some embodiments, the entertainment processor  304 A instead of the passenger safety processor  312 A interfaces between these buttons  226 ,  228  and network switch  302 A. 
         [0149]      FIG. 11  illustrates an embodiment of VDU  116  in a state where a wide-body aircraft detachable user interface module  400 A has been detached from a VDU base  406 A. Detachable module  400 A has a plurality of user interface elements, including auxiliary input  310 A, audio output jack  316 , flight attendant call button  226 , and reading light control button  228 . Detachable module  400 A has electrical contacts  404 A that interface with electrical contacts at a module receiving area  408 A of VDU base  406 A to operatively couple user interface elements  310 A,  316 ,  226 ,  228  to one or more of processors  304 A,  312 A and render user interface elements  310 A,  316 ,  226 ,  228  operative. Detachable module  400 A is engaged with VDU base  406 A by moving detachable module  400 A into abutment with receiving area  408 A as indicated by the arrow. In the illustrated embodiment, detachable module  400 A is held in engagement with VDU base  406 A by a mounting screw  402 A that threadably engages with a mounting screw hole (not shown) on VDU base  406 A to mount detachable module  400 A to VDU base  406 A. Also shown in the figure are touch screen video display  224  and card reader  308 A that are integral with VDU base  406 A and not detachable from VDU  116  in these embodiments. 
         [0150]    In the event one or more of user the interface elements on the detachable user interface module  400 A becomes inoperative or begins to perform sub-optimally, full functionality may be restored by disengaging detachable module  400 A from VDU base  406 A and attaching a spare detachable module to VDU base  406 A. Similarly, detachable module  400 A may be readily replaced with a detachable module having a desired configuration of user interface elements, e.g., additional or different user interface elements. For example, in one arrangement the detachable module  400 A for the first class portion of the passenger cabin includes auxiliary input  310 A, audio output jack  316 , flight attendant call button  226  and reading light control button  228 ; and the detachable module  400 A for the economy class portion of the passenger cabin includes only the flight attendant call button  226  and reading light control button  228 . 
         [0151]      FIG. 12  illustrates an embodiment of a narrow-body VDU assembly  500 A. Detachable module  510  has a plurality of user interface elements, including an auxiliary input  512  and an audio output jack  514 , but does not include a flight attendant call button  226  or a reading light control button  228 . Detachable module  510  has electrical contacts that interface with electrical contacts on VDU base  502 A to render user interface elements  512 ,  514  operative when detachable module  510  is engaged with VDU base  502 A by moving detachable module  510  into abutment with a module receiving area  508  of VDU base  502 A as indicated by the arrow. In the embodiment depicted, detachable module  510  is held in engagement with VDU base  502 A by a mounting screw  516  that threadably engages with a mounting screw hole (not shown) on VDU base  502 A to mount detachable module  510  to VDU base  502 A. In the event one or more of user interface elements  512 ,  514  becomes inoperative or begins to perform sub-optimally, full functionality may be restored by disengaging detachable module  510  from VDU base  502 A and engaging a spare with VDU base  502 A. Likewise, detachable module  510  may be readily replaced with a detachable module having a desired configuration of user interface elements, e.g., additional or different user interface elements. 
         [0152]    In some embodiments, the VDU base  402 A,  502 A and or the detachable module  400 A,  510  includes indicia to indicate the function of the user interface elements or other features. For example, in  FIG. 11 , the card reader  308 A includes indicia to indicate that a card may be slidably received the in reader  308 A. Likewise,  FIG. 5  illustrates an instance of indicia (a symbolic representation of a pair of headphones) indicating the corresponding position of the audio output jack  514  when the detachable module  510  is mounted to the VDU base  502 A. 
         [0153]    In some embodiments, a VDU base may interchangeably receive and render operative wide-body detachable modules (e.g.,  400 A) and narrow-body detachable modules (e.g.,  510 ). Among other advantages, deployment of a VDU base that can interchangeably support both wide-body and narrow-body detachable modules allows an airline to maintain and spare a single VDU base hardware design configuration across its entire fleet of wide-body and narrow-body aircraft. 
         [0154]    Turning to  FIG. 13 , a conventional inflight communication system that integrates an IFE system and a PA system is shown. This inflight communication system includes a cabin intercom system (CIS)  1120  and an IFE system  1130  communicatively coupled via an aircraft interface unit  1106 . CIS  1120  has handsets  1100  that receive analog PA audio signals and a keyline signal from flight personnel. The keyline signal indicates whether the PA system is presently in use and may be activated by depressing a push-to-talk key on one or more of the handsets  1100 . The analog PA audio signals and keyline signal are fed into a cabin intercom control system  1102  that delivers the analog PA audio signals to an overhead loudspeaker  1104  and delivers the analog PA audio signals and keyline signal to an aircraft interface unit  1106 . Overhead loudspeaker  1104  outputs the analog PA audio signals. Aircraft interface unit  1106  digitizes the analog PA audio signals and delivers PA audio packets carrying the PA audio signals and keyline status packets indicating the keyline signal to IFE system  1130 . 
         [0155]    At IFE system  130 , IFE head end servers  1108  receive the PA audio packets and keyline status packets, temporarily suspend transmission of entertainment packets, and deliver PA audio override packets and the PA audio packets to IFE distribution network  1110 , which distributes the PA audio override and PA audio packets to seat audio/video systems  1112 . Seat A/V systems  1112  convert digital PA audio signals carried in the PA audio packets to analog form and output analog PA audio signals to passengers sitting in the seats. However, PA audio in the conventional inflight communication system of  FIG. 13  is routed through IFE head end servers  1108  en route to seat A/V systems  1112 , which leaves PA audio output at seat A/V systems  1112  vulnerable to IFE head end server failure and risks unacceptably high latency between the PA audio output on the overhead loudspeaker  1104  and the PA audio output on the seat A/V systems  1112 . 
         [0156]      FIG. 14  shows an embodiment of an inflight communication system with high reliability PA audio output. The system includes a CIS  1220  and an IFE system  1230  communicatively coupled via an aircraft interface unit  1206 . 
         [0157]    As illustrated, the CIS  1220  has handsets (or other types of input devices)  1200  that receive analog PA audio signals and a keyline signal from flight personnel. The keyline signal indicates whether the PA system is presently in use and may be activated by, for example, depressing a push-to-talk key on one or more of the handsets  1200 . The analog PA audio signals and keyline signal can be fed into a cabin intercom control system  1202  that delivers the analog PA audio signals to a public loudspeaker  1204  mounted to the cabin (e.g., in the ceiling) and/or to the analog PA audio signals and keyline signal to an aircraft interface unit  1206 . The public loudspeaker  1204  outputs the analog PA audio signals to the passenger cabin, specific areas of the passenger cabin, other areas of the aircraft, or elsewhere. Generally, the aircraft interface unit  1206  typically digitizes the analog PA audio signals and delivers PA audio packets carrying the PA audio signals and keyline status packets reflecting the keyline signal to IFE system  1230 . 
         [0158]    At IFE system  1230 , an IFE distribution network  1210  receives the PA audio packets and keyline status packets and distributes the packets to seat A/V systems  1212 , which convert the digital PA audio signals carried in the PA audio packets to analog form and output analog PA audio signals to passengers at times indicated by the keyline status packets. As shown in  FIG. 14 , the communication flow bypasses IFE head end servers  1208 , which can reduce or eliminate the risk of PA audio output failure on seat A/V systems  1212  due to server crashes and/or improves synchronization between PA audio output on public loudspeaker  1204  and the seat A/V systems  1212 . 
         [0159]      FIG. 15  shows an embodiment of a seat A/V system  1300 , which is representative of one of the seat A/V systems  1212 . Seat A/V system  1300  includes a network switch  1302  with a network interface  1301  for transmitting and receiving packets to and from IFE distribution network  1210 . Network switch  1302  segregates packets inbound on network interface  1301  between entertainment packets and passenger safety packets. Inbound entertainment packets include, for example, A/V entertainment packets. Inbound passenger safety packets include, for example, PA audio packets and PA keyline status packets. Network switch  1302  delivers entertainment signals related to inbound entertainment packets to an entertainment processor  1304  and delivers passenger safety signals related to inbound passenger safety packets to a passenger safety processor  1308 . 
         [0160]    Passenger safety processor  1308  generally regulates the audio signals outputted on an audio output jack  1312  based on PA keyline status and may also regulate the video signals outputted on video display  1306 . When none of handsets  1100  is in use, audio output jack  1312  outputs entertainment audio signals received (if any) from entertainment processor  1304  and video display  1306  renders entertainment video signals received (if any) from entertainment processor  1304 . When one or more of handsets  1100  is in use, audio output jack  1312  outputs PA audio signals received from passenger safety processor  1308  and video display  1306  may render PA interrupt video signals received from entertainment processor  1304 . 
         [0161]    In some embodiments, audio selection switch  1310  selects PA audio signals as audio output signals based on the audio selection signal. For example, when passenger safety processor  1308  receives from network switch  1302  PA keyline status indicating that one or more of handsets  1100  is in use, passenger safety processor  1308  can transmit an audio selection signal to audio selection switch  1310  instructing audio selection switch  1310  to select for transmission to audio output jack  1312  the PA audio signals made available by passenger safety processor  1308  rather than selecting entertainment audio signals made available by entertainment processor  1304 . In some arrangements, passenger safety processor  1308  returns a PA in-progress signal to network switch  1302 , in response to which network switch  1302  may transmit a PA in-progress signal to entertainment processor  1304  instructing entertainment processor  1304  to select for transmission to video display  1306  an interrupt video signal rather than entertainment video signals, and entertainment processor  1304  may select an interrupt video signal as a video output signal based on the PA in-progress signal received from network switch  1302 . The interrupt video signal may be, for example, a text message such as “Announcement in Progress” overlaid over a paused video frame. In some embodiments, passenger safety processor  1308  transmits a PA in-progress signal to entertainment processor  1304  on a direct communication line (not shown). In some embodiments, network switch  1302  may transmit a PA in-progress signal to entertainment processor  1304  without prompting from passenger safety processor  1308 . 
         [0162]    In some embodiments, the audio selection signal instructing audio selection switch  1310  to select PA audio signals and the PA in-progress signal are transmitted repeatedly for as long as PA keyline status indicates that one or more handsets  1100  is in use. In some embodiments, the audio selection signal instructing audio selection switch  1310  to select PA audio signals and the PA in progress signal are transmitted only once. In some embodiments, the audio selection signal instructing audio selection switch  1310  to select PA audio signals and the PA in progress signal are transmitted according to a time interval. 
         [0163]    Generally, when passenger safety processor  1308  does not receive PA keyline status indicating that one or more handsets  1100  is in use, passenger safety processor  1308  transmits an audio selection signal to audio selection switch  1310  instructing audio selection switch  1310  to select for transmission to audio output jack  1316  the entertainment audio signals made available by entertainment processor  1304  rather than PA audio signals made available by passenger safety processor  1308 . Audio selection switch  1310  typically selects entertainment audio signals as audio output signals based on the audio selection signal. In some embodiments, entertainment processor  1304  selects entertainment video signals as video output signals based on the absence of a PA in-progress signal indicating that one or more handsets  1100  is in use. 
         [0164]    The video and audio signals outputted by video display  1306  and audio output jack  1312 , respectively, are typically analog signals. The video signals may be extracted from packets and converted to analog form by network switch  1302 , entertainment processor  1304 , video display  1306 , and/or conversion and extraction logic not shown in  FIG. 15 . The audio signals may be extracted from packets and converted to analog form by network switch  1302 , passenger safety processor  1312 , audio selection switch  1314 , audio output jack  1312 , and/or conversion and extraction logic not shown in  FIG. 15 . The PA keyline status signals, audio selection signals, and PA in progress signals described in relation to  FIG. 15  may be transmitted in packets or analog form. 
         [0165]      FIG. 16  shows an embodiment of an inflight communication system with high reliability and highly synchronized PA audio output. The illustrated system includes a CIS  1420  and an IFE system  1430  communicatively coupled via an aircraft interface unit  1406 . CIS  1420  has handsets  1400  that receive analog PA audio signals and a keyline signal. The keyline signal generally indicates whether the PA system is presently in use and may be activated by, for example, depressing a push-to-talk key on one or more of the handsets  1400 . The analog PA audio signals and keyline signal can be fed into a cabin intercom control system  1402  that delivers the analog PA audio signals and keyline signal to an aircraft interface unit  1406 . As shown, the analog PA audio signals are not delivered directly to a public loudspeaker  1404 , but instead are looped-back to the public loudspeaker after passing through IFE system  1430 . Typically, aircraft interface unit  1406  digitizes the analog PA audio signals and delivers PA audio packets carrying the PA audio signals and keyline status packets reflecting the keyline signal to IFE system  1430 . 
         [0166]    At the IFE system  1430 , an IFE distribution network  1410  receives the PA audio packets and keyline status packets and distributes the packets to seat A/V systems  1412 , which convert the PA audio output signals to analog form and output analog PA audio signals to passengers at times indicated by the keyline status packets. In some embodiments, IFE distribution network  1410  distributes the packets to a loopback converter  1414  that converts the PA audio output signals and keyline status signals to analog form and returns analog PA audio signals and keyline signal to cabin intercom control system  1402  via a loopback interface. As shown, the cabin intercom control system  1402  can deliver the loopback PA audio signals to public loudspeaker  1404 , which outputs the looped-back PA audio signals. As shown, the communication flow bypasses IFE head end servers  1408 , which can reduce or eliminate the risk of PA audio output failure on seat A/V systems  1412  due to server crashes and/or improve synchronization between PA audio output on public loudspeaker  1404  and seat A/V systems  1412 . In some embodiments, the inflight communication system routes PA audio through the IFE system  1430  before outputting the PA audio on public loudspeaker  1404 , thereby further improving synchronization between PA audio output on public loudspeaker  1404  and seat A/V systems  1412 . 
         [0167]      FIG. 17  shows an embodiment of a loopback converter  1414  in more detail. Loopback converter  1414  can include a network switch  1502  having an A/V input for receiving PA audio packets and keyline status packets from IFE distribution network  1410 . Generally, the network switch  1502  delivers the PA audio and keyline status packets to conversion logic  1504 , which can extract PA audio and keyline status signals from packets. The network switch  1502  can return to the CIS  1420  ( FIG. 16 ) analog PA audio signals for outputting on public loudspeaker  1404  and/or keyline signal reflecting keyline status. 
         [0168]      FIG. 18  shows an embodiment of a common LRU loopback converter  1600  for use in an inflight communication with high reliability and highly synchronized PA audio output. In some embodiments, a single LRU type (i.e., an LRU of a particular hardware design configuration) is used for both seat A/V systems and converter  1600  to obviate the need for a specially designed loopback LRU and achieve cost savings. In the illustrated embodiment, converter  1600  has elements  1602 ,  1604 ,  1606 ,  1608 ,  1610  that perform the functions described above in relation to their counterpart elements  1302 ,  1304 ,  1306 ,  1308 ,  1310 , except that converter  1600  returns analog PA audio signals and keyline signal to the CIS  1420  instead of routing the PA audio signal to an audio output jack. 
         [0169]    It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character hereof. The present description is therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come with in the meaning and range of equivalents thereof are intended to be embraced therein.