Abstract:
In a packet data communications system ( 100 ) that supports VoIP communications via cable modem, a fail over detector ( 200 ) identifies trouble (eq, no dial tone, delayed dial tone, low quality of service, no voltage, no current, network busy) on or within the communications path. In response, voice communications are switched to a secondary path, such as, for example, the PSTN, or some other reliable and/or predictable communications network, thereby insuring uninterrupted voice communications.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to telephony services, and in particular, to a method and apparatus that provides fail over protection for voice over Internet protocol (VoIP) telephone services.  
         BACKGROUND OF THE INVENTION  
         [0002]    Voice over Internet protocol (VOIP) telephone services are known. Such systems allow voice calls using Internet Protocol (“IP”) networks such as the Internet as an alternative to traditional public switched telephone networks (“PSTN”). Unlike the PSTN, which is circuit-switched, the Internet is packet-switched. As such, communications on the Internet is accomplished by transmitting and receiving packets of data. In addition to data, each packet contains a destination address to ensure that it is routed correctly. The format of these packets is defined by the IP. One type of allowable data is encoded, digitized voice, termed voice over IP (VoIP). VoIP is voice that is packetized as defined by IP, and communicated over the Internet for telephone-like communication. Individual VoIP packets may travel over different network paths to reach the final destination where the packets are reassembled in correct sequence to reconstruct the voice information.  
           [0003]    While transmission over the Internet may be inexpensive relative to transmission over the PSTN, the Internet exhibits communication challenges that are not present in the PSTN. By way of example, and not by way of limitation, the transmission speed between any two Internet users can change drastically due to the dynamic number of users sharing the common transmission medium, their bandwidth requirements, the capacity of the transmission medium, and the efficiency of the network routing and design. Other challenges associated with VoIP service provision include the variability of the quality of the signal received at the destination (i.e., the number of transmission errors such as packet loss, packet delay, corrupted packets, etc.).  
           [0004]    Thus, while the Internet may be a suitable medium for voice communications, transmission quality is not guaranteed, which in turn, may result in inconsistent performance. While such inconsistent performance may be tolerable for purposes of data transmission, it will in general be intolerable for voice communications, and in particular be unacceptable when the call in question is of an emergency nature, such as, for example, a call to an emergency response team, or a call to a 911 dispatcher.  
           [0005]    Accordingly, there exists a need for a customer premise device to make reliable calls when the quality of service (QoS) for a particular call is unacceptable.  
         SUMMARY OF THE INVENTION  
         [0006]    The need is met and an advance in the art is made by the present invention, which provides a customer premise device with access to a reliable network when quality of service for a VoIP connection is unacceptable.  
           [0007]    In accordance with one aspect of the present invention a fail-over detector monitors the communications path of a communications network providing VoIP services. Based upon various performance characteristics and availability of a connection, the detector selects between a predictable (e.g., plain old telephone connection) and unpredictable (eg, cable-based Internet connection) communications network for use by a system subscriber for purposes of voice communication. In accordance with another aspect of the invention, the fail-over detector employs a digital signal processor (DSP) to process an input signal consisting of voice, data, video, and/or combinations thereof. A fail-over detector monitors a DSP output. Based upon various performance characteristics or availability of a connection, the detector selects between a predictable and unpredictable communications network for use by a system subscriber for purposes of voice communication.  
           [0008]    In accordance with another aspect of the invention, the fail-over detector is disposed within an Enhanced Multimedia Terminal Adapter (EMTA) such as, for example, a cable television modem.  
           [0009]    In another aspect of the invention, a method is provided for establishing fail over contingency. The method begins with the monitoring of a first (unpredictable) communications path for a set of performance characteristics such as, for example, voltage, current, impedance, clock signals, open circuits, and the like. The first communications path supports VoIP service provision. Upon detection of a fault condition, a second (predictable) communications path is used for the provision of voice communications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a block diagram of a multimedia communications system that provides voice over Internet protocol (VoIP) telephone services in accordance with the present invention; and  
         [0011]    [0011]FIG. 2 is a block diagram of a fail over detector in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    [0012]FIG. 1 is a block diagram of a multimedia communications system  100  that provides voice over Internet protocol (VoIP) telephone services. Multimedia communications system  100  includes, in part, a cable modem network  140  providing VoIP service, an Internet Protocol (IP) network  120  providing packet switched communications, and a public switched telephone network (PSTN) providing plain old telephone services (POTS). User terminals  102 ,  152  are typically telephone devices or modems that utilize well-known analog circuit switched protocols to couple to the communications system  100  and to transmit and receive data over subscriber lines  104 , comprised in part, of twisted wire pairs.  
         [0013]    With reference to FIG. 1, a cable modem network  140  includes user terminals  152  coupled to enhanced multimedia terminal adapters (EMTA)  150 . In the past, EMTA equipment, frequently referred to as a cable modem or a set top box, has been available by contacting a local cable television service provider, such as, for example, AT&amp;T Broadband. EMTA  150  is designed to receive an input and, in response, direct an appropriate output to one or more peripheral devices, such as terminal  152 , personal computer  154  (not shown), or television  156  (not shown). For example, EMTA  150  directs Internet data, such as Web pages, to PC  154 ; Internet voice data is directed to terminal  152 ; and cable TV signals are directed to TV  156 . As shown in FIG. 1, each EMTA  150  is coupled to a cable modem termination switch (CMTS)  144  via a communications link  142 . In accordance with a preferred embodiment, the communications link  142  is a coaxial cable, or the like.  
         [0014]    Each CMTS  144  is coupled together by means of a data network. In accordance with a preferred embodiment, the data network consists of IP network  120 , which may be the Internet (e.g., the World-Wide Web) or a dedicated intranet that employs IP routing techniques. As such, each CMTS  144  is shown coupled, one to the other, via data links  126 . As will be appreciated, such data links implement known packet-based protocols well within the knowledge of those skilled in the art.  
         [0015]    With further reference to FIG. 1, IP network  120  is shown coupled to PSTN gateway  124  via previously discussed data links  126 . PSTN gateway  124  is in turn coupled to PSTN  110  via communications link  122 . During operation, PSTN gateway  124  converts circuit-switched communications received from PSTN  110  to a packet data protocol acceptable to the IP network  120 . Conversely, PSTN gateway  124  converts packet data received from IP network  120  to a circuit-switched protocol acceptable to PSTN  110 . PSTN gateway  124 , data link  126 , and communications link  122  provide an interface for user terminal  102 . By virtue of this connection, a user terminal  102  is coupled to elements attached to the PSTN  110  and elements attached to the IP network  120 , such as a telephone  152  connected to EMTA  150 .  
         [0016]    In a similar fashion, CMTS  144  converts data received from EMTA  150  to a data protocol acceptable to the IP network  120 . Conversely, CMTS  144  converts data received from IP network  120  to a protocol acceptable to EMTA  150 . CMTS  144 , data link  126 , and communications link  142  provide an interface for user terminal  152 . By virtue of this connection, user terminal  152  is coupled to elements attached to the IP network  120 , such as a telephone  102  connected to PSTN  110 . In addition, user terminal  152  may couple to elements attached to the IP network  120 , such as a telephone  152  connected to another EMTA  150 . As will be appreciated after review hereof, a call placed between two user terminals  152  supports the provision of VoIP telephone services in accordance with the present invention.  
         [0017]    As anticipated, communication over IP network  120  may, in several instances, be less expensive than communication over PSTN  110 . For example, when EMTA 1 and EMTA 2 of FIG. 1 are separated by large geographic distances, communications over IP network  120  will generally avoid the long distance rate charges typically associated with placing a similar call over the PSTN  110 .  
         [0018]    Despite the potential cost advantage, IP network  120 , nevertheless exhibits performance characteristics that are not present in the PSTN  110 . First, IP Network  120 , like all IP-based communications systems is an unpredictable communications system. Unlike the PSTN  110 , IP network  120  uses shared, rather than dedicated resources to connect a call. This sharing tends to make IP network  120  less likely to achieve a connection path, and therefore unpredictable. In addition, the transmission speed between any two IP network  120  users can change drastically due to the dynamic number of users sharing the common transmission medium, the dynamic bandwidth requirements, the capacity of the transmission medium, and the efficiency of the network routing and design. Other deleterious performance characteristics include variability in the quality of the received signal due to transmission errors, lost packets, packet delay, corrupted packets, and the like. Thus, while the Internet may be a suitable medium for voice communications the suitability is not very consistent. Such inconsistency is completely intolerable when the call in question is of emergency status, such as, for example, a call to an emergency response team, or a call to a local 911 dispatcher.  
         [0019]    With further reference to FIG. 1, EMTA (1) is shown coupled to PSTN  110  via a communications link  130 . In accordance with a preferred embodiment of the present invention, the communications link  130  supports any of a number of reliable communications protocols including, but not limited to POTS, Ethernet, Integrated Services Digital Network (ISDN), Digital Subscriber Line (DSL), RF packet data, IEEE-802.11, Time Division Multiplex (TDM), Code Division Multiplex (CDM), Global System Mobile (GSM) and the like. As will be appreciated, after careful consideration of the invention disclosed herein, the communications link  130  affords the cable network  140 , or any similarly situated communications system providing VoIP services, fail-over protection in the instance that a VoIP call is beset by the unpredictable nature of IP network  120 . In that instance, EMTA (1) can elect to send a call via a predictable, as opposed to the unpredictable communications network. Such fail over protection greatly enhances the marketability of VoIP systems as they continue to compete with the PSTN  110  and other predictable communication networks.  
         [0020]    [0020]FIG. 2 is a block diagram of a fail over detector in accordance with the present invention. As shown, the detector  153  is disposed within EMTA  150 . In accordance with a preferred embodiment, detector  153  may be any of a number of detectors designed to monitor various performance characteristics of a signal in question. In accordance with the present invention, detector  153  may be a voltage detector, current detector, line detector, tone detector, clock signal detector, open circuit detector, and the like. Its primary function is to monitor the output from digital signal processor (DSP)  151  that is destined for terminal  152 . As shown, the signal in question is an analog telephone signal, as known in the art.  
         [0021]    By monitoring the analog telephone signal, detector  153  provides an indication of the current status of the communications path comprised of IP network  120 . Since IP network  120  is somewhat unpredictable, service disruptions and/or anomalies may be detected by detector  153  as a function of voltage, current, and/or impedance level, or the presence or absence of clock or tone within the analog telephone signal generated by DSP  151 .  
         [0022]    During operation, DSP  151  receives an input signal from CMTS  144 . As will be appreciated, this input may comprise a multimedia content consisting of voice, data, video, or combinations thereof. DSP  151  processes the input and generates separate and distinct outputs as depicted in FIG.2.  
         [0023]    Detector  153  controls the operation of switch S1. Under normal operating conditions switch SI connects terminal  152  to the analog telephone output from DSP  151 . Upon detection of a service disruption/anomaly, detector  153  causes switch S1 to connect terminal  152  to communications link  130  for purposes of voice communications. As previously discussed, communications link  130  is coupled to a reliable communications network. As such, voice communications within the otherwise unpredictable system defined by IP network  120  can now be assured by the access to a reliable communications path.  
         [0024]    In accordance with one embodiment of the present invention, communications via the reliable communications path sourced by communications link  130  is reserved for voice calls, only. In accordance with another embodiment of the present invention, communications via the reliable communications path is reserved for emergency calls, only. In yet another embodiment of the present invention, communications via IP network  120  is reestablished once a service disruption is no longer detected by detector  153 .  
         [0025]    In an alternate embodiment of the invention, detector  153 , in conjunction with DSP  151 , causes switch S1 to connect terminal  152  to communications link  130  (a reliable communications network), if a call setup procedure through CMTS  144  and IP network  120  is unsuccessful. For example, if no dial tone is received or is delayed at initiation of a call by terminal  152 , DSP  151  and detector  153  sense this condition and cause switch S1 to connect terminal  152  to communications link  130 . Other conditions that may cause a switch to a predictable network during call setup include network busy or an analytic measure of quality of service below an acceptable threshold. If a switching condition is sensed after terminal  152  has dialed digits identifying the called party, DSP  151  repeats those digits after a switch to communications link  130  in a manner consistent with the protocol expected by communications link  130  and its interface to the PSTN. Preferably, call setup sensing and protocol are accomplished by DSP  151  in conjunction with a stored program to implement the functions.  
         [0026]    In additional embodiments, a physical switch is provided for a user to select the network for a call. For example, a physical switch may be added to EMTA  150  to force switch Si to a desirable setting. A physical switch may also defeat, that is prevent, or enable, a fail over option as described above, including a selection of the criteria for the fail over option.  
         [0027]    Whereas the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art and it is intended that the invention encompass such changes and modifications as fall within the scope of the appended claims.