Abstract:
A high availability telephone instrument, comprising a primary communications link interface connected to a primary communications link; at least one backup communications link interface connected to at least one backup communications link; and a controller connected to for detecting failure of the primary communications link and in response selecting the at least one backup communications link for providing voice communication between the telephone instrument and the backup communications link.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to telephones, and more particularly to a telephone instrument that is connectable to any one of a plurality of different communications systems via multiple separate communications links of different type, to provide a high level of overall availability in the event of a failure in one of the associated communications systems.  
           [0003]    2. Description of the Related Art  
           [0004]    There are many situations requiring failsafe communication via a telephone having only a single communications system/link.  
           [0005]    For example, a business that relies on telephone communications for a significant portion of their revenue could be adversely affected by a failure in its communications system.  
           [0006]    Another example is a “teleworker”, in a remote location, who requires a telephone that is connected to an office communications system, which may be a significant distance away, but who also needs to be able to make emergency 911 or other local telephone calls.  
           [0007]    A further example is a person or organization that provides emergency service (e.g. fire, health, police, security) requiring a highly redundant communications system.  
           [0008]    In the past, a person requiring such failsafe communications would need multiple completely separate telephone instruments, where the number of such instruments varies depending on the degree of “availability” deemed necessary in the particular circumstances. This prior art approach is costly, confusing to the user and often requires excessive desk/wall space to accommodate the multiple separate telephone instruments.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an aspect of the present invention to provide a high level of overall availability in the event of a communication system failure.  
           [0010]    Therefore, according to the invention a telephone instrument is selectively connected to a plurality of communications links of different types (e.g. Ethernet LAN, an analog phone line, ISDN, radio link, etc.) By selectively connecting the telephone instrument to any of a plurality of communications links a high level of availability is provided in the event one or several of the systems fail.  
           [0011]    The minimum number of communications links required for increased availability according to the invention is two, whereas the maximum number of communications links is limited only by the economic tradeoff between cost and increasing availability.  
           [0012]    These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction, and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a block diagram of a telephone instrument according to the prior art.  
         [0014]    [0014]FIG. 2 is a block diagram of a high availability telephone instrument according to the present invention.  
         [0015]    [0015]FIG. 3 is a block diagram showing a fail-safe link selection mode of operating the high availability telephone instrument of FIG. 2.  
         [0016]    [0016]FIG. 4 is a block diagram showing a user-input link selection mode of operating the high availability telephone instrument of FIG. 2.  
         [0017]    [0017]FIG. 5 is a block diagram showing a dialed-number link selection mode of operating the high availability telephone instrument of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    A simplified block diagram of a traditional telephone instrument is shown in FIG. 1 to help illustrate the improvements that are the subject of this invention.  
         [0019]    The traditional telephone instrument of FIG. 1 includes a number of user interfaces such as input devices  100  and visual indicators  120  connected to a telephone controller and signaling generator  130 , audio transducers  140  and interfaces  150 . The controller  130  and audio interfaces  150  are connected to a communications link interface  160  that, in turn, is connected to an external communications link, which can be, for example, an analog connection, ISDN connection, radio connection (cell phone or Bluetooth or 802.11 wireless LAN, etc.), digital Local Area Network (LAN), etc. A power supply  170  provides operating power to the various telephone components. Although not shown, the telephone instrument also includes a hook switch and other well-known mechanical/electrical components for proper operation of the device.  
         [0020]    As discussed above, in the event of a communications link failure the telephone instrument user is no longer able to communicate. In some circumstances or applications, failure to communicate is not tolerable.  
         [0021]    A simplified block diagram of a high availability telephone according to the present invention is shown in FIG. 2. It will be noted that the telephone instrument of FIG. 2 incorporates the same user interfaces and a first or primary communications link interface  160  as the prior art device of FIG. 1, but additionally includes at least one additional (i.e. secondary) communications link interface  200  (up to N such interfaces  210  being shown).  
         [0022]    In operation, one of the communications links (e.g. the 1 st  link) is set as the default primary link. Failure of the primary link is detected by the associated communications link interface  160  in a well-known manner, such as by detecting the absence of a signal normally present on the link. For example, if the primary communications link is an analog telephone line then the interface  160  detects failure of the line due to a loss of battery voltage. Similarly, if the link is a radio connection then failure is detected based on loss of the carrier signal, or if the link is a LAN connection then loss of “link” status or loss of a higher layer protocol signal indicates a link failure. Failure of the link is reported to the controller  130  that, in turn, switches communication to the first backup link (e.g. communications link interface  200  to a radio link is enabled). Likewise, in the event of a failure of the backup link, any additional backup links are switched in. A detailed flow chart of the operation of controller  130  in this operating mode, is set forth in FIG. 3.  
         [0023]    As an alternative to the automatic link selection discussed above, it is contemplated that the telephone instrument may be provided with user input selection (e.g. similar to a key telephone set) for selecting which of a plurality of different types of communications links is to be used for a particular call. An incoming call on any of the communications links is sensed by the associated interface in the usual manner, for the particular type of link, and an indication of the specific link is provided to the user via indicators  120  (e.g. similar to a key button). The user then answers the call on that link if desired. A detailed flow chart of the operation of controller  130  in this operating mode, is set forth in FIG. 4.  
         [0024]    According to another alternative operating mode, the controller  130  select an appropriate communications link based on decoding the number dialed by the user and comparing it to a predefined routing criteria (e.g. E911, least cost call routing, or different levels of routing security). For example, recognition of an emergency number (e.g. 911) always activates the 2 nd  interface/link, recognition of calls to a certain area code activates the 1 st  interface/link for a lower cost routing, or calls to a specific number always use the 3 rd  interface/link for higher level of security. A detailed flow chart of the operation of controller  130  in this operating mode, is set forth in FIG. 5.  
         [0025]    The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.