Abstract:
A method and apparatus are disclosed for redirecting traffic associated with an application so that the traffic advantageously traverses (or “hairpins”) through an application-layer gateway. Because the present invention advantageously redirects traffic without any participation by routers, no changes to or replacement of routers in a network is required. The illustrative embodiment is disclosed in the context of Internet telephony, but is also applicable to other kinds of applications and types of communication (e.g., Internet Protocol Television [IPTV], instant messaging [IM], videoconferencing, etc.)

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to telecommunications in general, and, more particularly, to mid-call redirection of traffic through application-layer gateways. 
       BACKGROUND OF THE INVENTION  
       [0002]    A modern telecommunications system often comprises one or more switched telephone networks and one or more Internet Protocol-based packet networks. These two different types of networks are sometimes interconnected by an application-layer gateway, which acts as a translator between the two types of networks, thereby enabling communications-based applications (e.g., Voice over Internet Protocol [VoIP] telephony, videoconferencing, Internet Protocol Television [IPTV], etc.) over multiple transport protocols end to end. In particular, one of the primary functions of an application-layer gateway is to convert between the different transmission and coding techniques used across the different networks. For example, a Voice-over-Internet-Protocol-capable (VoIP-capable) application-layer gateway performs the conversion between time-division multiplexed (TDM) voice streams that are transmitted and received by a switched telephone network telecommunications terminal, and VoIP datagrams that are transmitted and received by an Internet Protocol (IP) endpoint (e.g., a VoIP-capable telecommunications terminal, etc.). 
         [0003]    Other key functions of an application-layer gateway include voice and video compression and decompression, packetization, call routing, and control signaling. In addition, an application-layer gateway may provide features such as echo cancellation, tone detection, tone generation (e.g., dual tone multi-frequency tones, etc.), and conferencing, as well as interfaces to external controllers, billing systems, and network management systems. 
         [0004]      FIG. 1  depicts the salient elements of illustrative telecommunications network  100 , in accordance with the prior art. As shown in  FIG. 1 , telecommunications network  100  comprises Internet Protocol (IP) endpoints  131 - 1  and  131 - 2 , local enterprise network  140 , analog terminals  141 - 1  and  141 - 2 , Public Switched Telephone Network (PSTN)  150 , PSTN telecommunications terminals  151 - 1  and  151 - 2 , and Internet Protocol (IP) network  160 , interconnected as shown. 
         [0005]    Each of Internet Protocol (IP) endpoints  131 - 1  and  131 - 2  is a device capable of communicating in accordance with the Internet Protocol (e.g., an IP telephone, an IP headset, an IP handset, an IP softphone, an IP conference phone, etc.). In illustrative telecommunications network  100 , Internet Protocol endpoints  131 - 1  and  131 - 2  are capable of communicating with each other over Internet Protocol (IP) network  160 . 
         [0006]    Local enterprise network  140  provides for local distribution of analog signals, such as in an enterprise system, and comprises wiring between Internet Protocol (IP) network  160  and analog terminals  141 - 1  and  141 - 2 . 
         [0007]    PSTN terminals  151 - 1  and  151 - 2  are devices capable of communicating over Public Switched Telephone Network (PSTN)  150  (e.g., a Plain Old Telephone Service [POTS] telephone, an Integrated Services Digital Network [ISDN] telephone, a cell phone, etc.). 
         [0008]    Public Switched Telephone Network (PSTN)  150  comprises one or more transmission-related nodes such as switches that are used to direct call-related signals from one or more sources to the correct destinations of those signals. PSTN  150  is capable of handling either analog or digital bearer information in circuit-switched calls among two or more devices, such as PSTN terminals  151 - 1  and  151 - 2 . 
         [0009]    Internet Protocol (IP) network  160  comprises one or more transmission-related nodes that are used to direct packets from one or more sources to their appropriate destination(s) in accordance with the Internet Protocol. Internet Protocol (IP) network  160  is described in detail below and with respect to  FIG. 2 . 
         [0010]      FIG. 2  depicts the salient elements of Internet Protocol (IP) network  160 , in accordance with the prior art. As shown in  FIG. 2 , IP network  160  comprises application-layer gateways  210 - 1  and  210 - 2 , application server  220 , and Internet Protocol (IP) routers  230 - 1  through  230 - 8 , interconnected as shown. (As will be appreciated by those skilled in the art, the fact that Internet Protocol network  160  as depicted in  FIG. 2  comprises two application-layer gateways and eight Internet Protocol routers is merely illustrative.) 
         [0011]    Application-layer gateways  210 - 1  and  210 - 2  are data-processing systems that provide application-layer functions (e.g., Voice over IP functions, etc.) such as translation between different types of networks, compression, packetization, etc., as described above. In illustrative telecommunications network  100 , application-layer gateway  210 - 1  acts as a translator between local enterprise network  140  and Internet Protocol network  160 , and application-layer gateway  210 - 2  acts as a translator between Public Switched Telephone Network (PSTN)  150  and Internet Protocol network  160 . 
         [0012]    Application server  220  is a data-processing system that is capable of providing one or more services to support a particular application. For example, application server  220  might provide one or more Voice over Internet Protocol (VoIP) services such as call setup between two or more Internet Protocol endpoints, call modification, call termination, and so forth. 
         [0013]    Each Internet Protocol (IP) router  230 - i,  where i is an integer between 1 and 8 inclusive, is a device that is capable of receiving Internet Protocol packets via one or more incoming links and of forwarding the packets along one or more outgoing links. Typically Internet Protocol routers  230 - 1  through  230 - 8  maintain routing tables that are dynamic and enable the routers to alter the paths by which traffic is transmitted through Internet Protocol network  160 . For example,  FIG. 3  depicts a first path (via boldface arrows) through which packets might travel between Internet Protocol endpoints  131 - 1  and  131 - 2 , while  FIG. 4  depicts a second path through which packets might travel between Internet Protocol endpoints  131 - 1  and  131 - 2 . In accordance with the prior art, Internet Protocol routers  230 - 1  to  230 - 8  are capable of rerouting traffic along different paths over time in response to various conditions (e.g., link failures, congested routes, toll charges, etc.) 
       SUMMARY OF THE INVENTION  
       [0014]    The present invention enables traffic to be redirected in a network without any participation from routers. In particular, traffic associated with an application (e.g., Internet Protocol telephony, Internet Protocol Television, etc.) can be redirected to traverse (or “hairpin”) through an application-layer gateway when it is advantageous to do so, without participation from any routers. Such redirection might be advantageous for a variety of reasons, such as providing better quality of service (QoS) for a particular call, load balancing, fault tolerance, and so forth. 
         [0015]    In accordance with the illustrative embodiment, traffic redirection can be performed by any component of the telephony system, other than a router. For example, the traffic-redirection might be performed by one or more application-level gateways, or one or more application servers, or one or more telecommunications terminals (e.g., Internet Protocol endpoints, etc.), or some combination of these elements. The present invention is thus advantageous in that it enables traffic redirection without requiring any changes to or replacement of routers in a network. 
         [0016]    In accordance with the illustrative embodiment, traffic redirection can occur while a call is in progress (i.e., “mid-call redirection”). Moreover, the redirection is not restricted to the addition of an application-layer gateway to an existing path, but might instead replace an application-layer gateway in an existing path with a different application-layer gateway. The illustrative embodiment is disclosed in the context of Internet telephony; however, it will be clear to those skilled in the art, after reading this specification, how to make and use embodiments of the present invention for other kinds of applications and types of communication (e.g., Internet Protocol Television [IPTV], instant messaging [IM], videoconferencing, etc.) 
         [0017]    The illustrative embodiment comprises: generating a signal that causes communication between a first node in a network and a second node in the network to traverse a second path in the network in lieu of a first path in the network; wherein the network comprises one or more application-layer gateways; and wherein the first path does not include any of the application-layer gateways; and wherein the second path includes one of the application-layer gateways. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  depicts the salient elements of an illustrative telecommunications network of the prior art. 
           [0019]      FIG. 2  depicts the salient elements of Internet Protocol (IP) network  160 , as shown in  FIG. 1 , in accordance with the prior art. 
           [0020]      FIG. 3  depicts a first path through Internet Protocol network  160 , in accordance with the prior art. 
           [0021]      FIG. 4  depicts a second path through Internet Protocol network  160 , in accordance with the prior art. 
           [0022]      FIG. 5  depicts the salient elements of a telecommunications network in accordance with the illustrative embodiment of the present invention. 
           [0023]      FIG. 6  depicts a first illustrative path through telecommunications network  500 , as shown in  FIG. 5 , in accordance with the illustrative embodiment of the present invention. 
           [0024]      FIG. 7  depicts a second illustrative path through telecommunications network  500 , in accordance with the illustrative embodiment of the present invention. 
           [0025]      FIG. 8  depicts a flowchart of a method for redirecting an existing call, in accordance with the illustrative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0026]      FIG. 5  depicts the salient elements of telecommunications network  500 , in accordance with the illustrative embodiment of the present invention. As shown in  FIG. 5 , telecommunications network  500  comprises application-layer gateways  510 - 1  and  510 - 2 , application server  520 , Internet Protocol (IP) endpoints  531 - 1  and  531 - 2 , and Internet Protocol (IP) routers  230 - 1  through  230 - 8 , interconnected as shown. (As is the case for Internet Protocol network  160  of the prior art, the fact that telecommunications network  500  comprises two application-layer gateways and eight Internet Protocol routers is merely illustrative.) 
         [0027]    Application-layer gateways  510 - 1  and  510 - 2  are data-processing systems that are capable of providing application-layer functions (e.g., Voice over IP [VoIP] services, etc.) as in the prior art. Moreover, application-layer gateways  510 - 1  and  510 - 2  are also capable of participating in the performing of task  850  of  FIG. 8 , and optionally, one or more other tasks of  FIG. 8 , as described below. As will be appreciated by those skilled in the art, in some other embodiments of the present invention, application-layer gateways  510 - 1  and  510 - 2  might provide services for some other type of application (e.g., videoconferencing, Internet Protocol Television [IPTV], etc.), either instead of or in addition to Voice over IP. 
         [0028]    Application server  520  is a data-processing system that is capable of providing one or more services to support a particular application (e.g., Voice over IP [VoIP], Internet Protocol Television [IPTV], etc.), and is also capable of participating in the performing of one or more of the tasks described below and with respect to  FIG. 8 . In accordance with the illustrative embodiment, application server  520  is capable of providing Voice over Internet Protocol (VoIP) services such as call setup between two or more Internet Protocol endpoints, call modification, call termination, etc. As will be appreciated by those skilled in the art, in some other embodiments of the present invention application server  520  might provide services for some other type of application (e.g., videoconferencing, Internet Protocol Television [IPTV], etc.), either instead of or in addition to Voice over IP. 
         [0029]    Each of Internet Protocol (IP) endpoints  531 - 1  and  531 - 2  is a device capable of communicating in accordance with the Internet Protocol (e.g., an IP telephone, an IP headset, an IP handset, an IP softphone, an IP conference phone, etc.). Moreover, IP endpoints  531 - 1  and  531 - 2  are also capable of participating in the performing of one or more of the tasks described below and with respect to  FIG. 8 . 
         [0030]    Internet Protocol (IP) routers  230 - 1  through  230 - 8  remain unchanged from the prior art, as described above. 
         [0031]      FIG. 6  depicts a first illustrative path through telecommunications network  500 , in accordance with the illustrative embodiment of the present invention. The boldface arrows in  FIG. 6  indicate the path through which packets travel between Internet Protocol endpoints  531 - 1  and  531 - 2 . As shown in  FIG. 6 , the nodes along this first path, other than Internet Protocol endpoints  531 - 1  and  531 - 2 , consists solely of Internet Protocol routers—namely, routers  230 - 1 ,  230 - 2 , and  230 - 6 . 
         [0032]      FIG. 7  depicts a second illustrative path through telecommunications network  500 , in accordance with the illustrative embodiment of the present invention. This second path corresponds to a change in the first path that is effected during a Voice over IP call between Internet Protocol endpoints  531 - 1  and  531 - 2 , in accordance with the method of the illustrative embodiment described below and with respect to  FIG. 8 . As shown in  FIG. 7 , the second path now includes an application-layer gateway—namely gateway  510 - 2 —as a result of the redirection of the call. (The bidirectional link between IP router  230 - 8  and gateway  510 - 2  is depicted in  FIG. 7  as two uni-directional links in order to more clearly illustrate the second path.) 
         [0033]      FIG. 8  depicts a flowchart of a method for redirecting an existing call, in accordance with the illustrative embodiment of the present invention. As described above, in some embodiments the tasks of  FIG. 8  might be performed by one or more application-layer gateways  510 , while in some other embodiments the tasks of  FIG. 8  might be performed by application server  520 , while in still some other embodiments the tasks of  FIG. 8  might be performed by one or both of Internet Protocol endpoints  531 - 1  and  531 - 2 . 
         [0034]    In yet some other embodiments of the present invention, the tasks of  FIG. 8  might be divided among some combination of application-layer gateways  510 , application server  520 , and Internet Protocol endpoints  531 - 1  and  531 - 2 , where a respective device might perform a particular task, or where two or more of these devices might participate in the performing of a particular task. 
         [0035]    In any case, it will be clear to those skilled in the art, after reading this disclosure, how to make or program one or more of application-layer gateways  510 , application server  520 , and Internet Protocol endpoints  531 - 1  and  531 - 2  in order to implement the method of  FIG. 8 . 
         [0036]    At task  810 , the quality of service (QoS) provided by the current path for an existing call, as well as the QoS provided by one or more alternative paths for the existing call, is monitored, in well-known fashion. 
         [0037]    Task  820  checks for a particular condition pertaining to the quality of service of the current path. Examples of such conditions might include:
       whether QoS has decreased by a specified quantity;   whether QoS has dropped below a specified threshold;   whether QoS has decreased by a specified quantity in a given amount of time;   whether a problem in the network has been detected;   whether there is an alternative path whose QoS exceeds that of the current path by a specified threshold A;   etc.
 
If the condition tested for in task  820  is true, execution proceeds to task  830 , otherwise, execution continues back at task  820 .
       
 
         [0044]    Task  830  checks whether there is an alternative path for the current call with better quality of service (QoS) than that of the current path. This alternative path might add one or more application-layer gateways  510  to the current path, or might replace a particular application-layer gateway  510 - i  in the current path with another application-layer gateway  510 - j.  If such an alternative path is found, execution proceeds to task  840 , otherwise execution continues back at task  820 . 
         [0045]    At task  840 , a signal (e.g., a signaling protocol message such as H.323/SIP, etc.) is generated that indicates that the current call should be redirected along the specified alternative path. 
         [0046]    At task  850 , the existing call is redirected along the specified alternative path, in well-known fashion. After task  850  is performed, the method of  FIG. 8  terminates. 
         [0047]    As will be appreciated by those skilled in the art, in accordance with the illustrative embodiment, the redirection of the call in task  850 , as well as all of the other tasks  810  through  840 , is performed without any participation by any of Internet Protocol routers  230 - 1  to  230 - 8 . As noted above, the redirection is not necessarily restricted to the addition of an application-layer gateway to an existing path, but might instead replace an application-layer gateway in an existing path with a different application-layer gateway. Moreover, as will be appreciated by those skilled in the art, in some other embodiments of the present invention, there might be a plurality of paths exiting from an application-layer gateway, and traffic might be redirected from one such path out of the gateway to another such path. 
         [0048]    As will further be appreciated by those skilled in the art, although the illustrative embodiment of the present invention is disclosed in the context of Internet telephony, it will be clear to those skilled in the art, after reading this specification, how to make and use embodiments of the present invention for other kinds of applications and types of communication (e.g., Internet Protocol Television [IPTV], instant messaging [IM], videoconferencing, etc.) 
         [0049]    As will further be appreciated by those skilled in the art, although the illustrative embodiment of the present invention is disclosed in the context of the Internet Protocol, it will be clear to those skilled in the art, after reading this specification, how to make and use embodiments of the present invention for other types of packet-based protocols, as well as for circuit-switched networks, applications, and protocols. 
         [0050]    It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.