Abstract:
A method and apparatus for enhanced Internet telephony ensures that communication between a source and destination is not interrupted by common network address translation. According to one aspect of the invention, communication may continue through a router that employs network address translation.

Description:
[0001]    The present application is a divisional application that claims priority benefit of U.S. patent application Ser. No. 10/684,593 entitled “Method and Apparatus for Enhanced Internet Telephony” the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Today, most common residential broadband deployments are delivered via either cable or DSL modem. Such broadband deployment typically provides customers with a single Ethernet port that grants one public IP address to a single computer device. Given this situation, customers are restricted to using only one computer, and must purchase a router if they desire to share the broadband connection to access, for example, the Internet between more than one of the customer&#39;s computer devices. 
         [0003]    To transport media and telephone signaling, customers commonly use a Multi Media Terminal Adapter (MTA) coupled between their source device (e.g., a computer or telephone) and their broadband connection. One example of a common Media Terminal Adapter is the Cisco ATA 186 Analog to Telephone Adapter (ATA) manufactured by Cisco Systems, Inc. of San Jose Calif. In the case of Internet telephony, the Media Terminal Adapter operates as a handset to Ethernet adapter that converts traditional telephone analog signals into Internet packets. The packets are then sent using, for example, a standard protocol such as Session Initiation Protocol (SIP) on route towards their destination. 
         [0004]      FIG. 1  is a schematic representation of an example user Internet Telephony environment. In  FIG. 1 , a cable modem  10  provides access to the Internet  20 . In the  FIG. 1  example, the user employs an intermediate communication point, e.g., router  30  to provide multiple devices access to the Internet  20 . The router  30  assigns respective private dynamic IP addresses to the Media Terminal Adapter  40  and to the computer  50 . 
         [0005]    As shown in the  FIG. 1  example, the Media Terminal Adapter  40  is coupled to a common telephone handset  60 . The Media Terminal Adapter  40  receives signals from the handset  60 , creates packets and sends data packets to the Router  30 , which in turn sends them to the cable modem  10  and eventually to the Internet  20 . 
         [0006]    A major drawback of the above typical environment is the difficulty in accommodating the Network Address Translation (NAT) that is typically implemented by the router  30 . As is commonly understood, a Dynamic Host Configuration Protocol server running on the router  30  assigns private dynamic IP addresses to the Media Terminal Adapter  40  and computer  50 ; thus effecting Network Address Translation (NAT). 
         [0007]    When a user wishes to initiate a call and activates the telephone handset  60 , the handset sends signals to the Media Terminal Adapter  40 . The Media Terminal Adapter  40  then begins the communication/registration process with an Internet telephone service provider. The communication between the Media Terminal Adapter  40  and a server of the Internet telephone service provider employs a standard protocol such as Session Initiation Protocol. But, the router  30  performs the Network Address Translation on a timed basis. As is commonly known, typical routers used in home environments assign private IP addresses to devices connected to the router. But, those addresses are valid only for a limited time. Thus, after the limited time expires, the private address is no longer assigned to a given device, such as the Media Terminal Adapter  40 . As a result, the SIP messages sent from Internet telephone service provider&#39;s server are not passed by the router  30  to the Media Terminal Adapter  40 . Consequently, the Media Terminal Adapter  40  can send SIP messages, but is not able to receive packets from the Internet Telephone service provider&#39;s server due to the router  30  losing the originating outbound port and making communication to an MTA located behind a router impossible. 
         [0008]      FIG. 2  is a schematic representation of an example environment that addresses the issue of router  30  losing an outbound port during an Internet telephone connection. In the  FIG. 2  example, at the Internet telephone service provider, a destination, e.g., a pre-proxy server  70 , receives messages from the router  30 . Pre-proxy server  70  records the private IP address of the Media Terminal Adapter  40  during, for example, the SIP registration process. It also records the network address translation communication port assigned by the router  30  to the Media Terminal Adapter  40  to and from which it will send and receive messages, such as SIP messages. Upon registration, the Media Terminal Adapter  40  passes fields used to communicate with the pre-proxy server  70 . Examples of fields, that can be passed include, for example, the private IP address of the Media Terminal Adapter  40 , the public IP address of the router  30 , and port information. After the pre-proxy server  70  receives the information from the Media Terminal Adapter  40 , the pre-proxy server  70  periodically sends, for example, blank UDP messages to the Media Terminal Adapter  40 , which contain the same destination and source address as a typical SIP message would have. Other messages could be used instead of the UDP message. The message used should prompt the Media Terminal Adapter  40  to send a response to the pre-proxy server  70 . The pre-proxy server  70  sends, for example, the UDP message to the router  30  using the public IP address of the router  30  and the port information received in the message from the router  30 . The pre-proxy server  70  sends, for example, the UDP within the limited time that the router  30  maintains that private address assigned to the Media Terminal Adapter. The router  30  accordingly routes the message to the destination designated in the message from the pre-proxy server  70 . The pre-proxy server  70  also maintains the private and public IP addresses of the MTA and rewrites the headers in the actual SIP messages based on this information. 
         [0009]    The above solution worked, but it did not solve the network address translation problem for all routers. For example, some routers would close the outbound port if the device behind the router&#39;s network address translation did not send an outbound message. Thus, there is a need for a solution to the problem, in Internet telephony, of the network address translation that a router performs as a part of its intended operation. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a method and apparatus for enhanced Internet telephony that avoids the above drawbacks. 
         [0011]    It is another object of the present invention to provide a method and apparatus for enhanced Internet telephony that allows the use of Session Initiated Protocol technology. 
         [0012]    It is a further object of the present invention to provide a method and apparatus for enhanced Internet telephony that allows the use of Session Initiated Protocol technology within environments employing network address translation. 
         [0013]    It is still another object of the present invention to provide a method and apparatus for enhanced Internet telephony that allows the use of Session Initiated Protocol technology with routers employing network address translation. 
         [0014]    To achieve the above and other object, the present invention provides a method for providing enhanced Internet telephony that includes receiving a message from a source at an intermediate point; sending at least a portion of the message from the intermediate point to a destination over the Internet; sending a response to the message from the destination to the intermediate point over the Internet; sending the response from the intermediate point to the source; repeatedly sending other messages from the destination over the Internet to the intermediate point; sending at least a portion of corresponding ones of the other messages from the intermediate point to the source; and sending responses to the portions of the other messages from the source to the intermediate point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic representation of an example user Internet Telephony environment. 
           [0016]      FIG. 2  is a schematic representation of an example environment intended to address the issue of a router losing an outbound port during an Internet telephone connection. 
           [0017]      FIG. 3  is a schematic representation of an example environment employing the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]      FIG. 3  is a schematic representation of an example environment employing an embodiment of the present invention. In  FIG. 3 , a user initiates a call using a telephone handset  60 . As described above, the media terminal adapter  40  implements standard signaling between itself and an Internet telephony regional data center  80 . Once the user has been registered and the destination has provided a SIP acknowledgment of the SIP invite sent by the media terminal adapter  40 , communication between the caller  60  and a customer in a destination area  100  proceeds using, for example, Real-time Transport Protocol (RTP) between the caller and a customer in the destination area  100  via the Internet  20  and, for example, a RTP relay  90  in Internet telephony point-of-presence  110  in the destination area  100 . 
         [0019]    However, with the call set up as described above, the router  30  may close the outbound port after a timeout period. As a result, voice data from the customer in the destination area  110  will not reach the telephone handset  60  behind router  30 . To avoid the router  30  timing out and closing the outbound port, an embodiment of the present invention causes the media terminal adapter  40  to send an outbound message to the Internet telephony regional data center  80 . One way of accomplishing this is to have the pre-proxy server  75  periodically send an empty SIP notify message to the media terminal adapter  40 . The media terminal adapter  40  responds to this notify message in accordance with SIP standards by, for example sending an acknowledgment message. The sending of a message by the media terminal adapter  40  causes the router  30  to keep the outbound port open by, for example restarting the router&#39;s timeout period. 
         [0020]    Referring to the exemplary embodiment shown in  FIG. 3 , the Internet telephony regional data center  80  has the pre-proxy server  75  separated from the RTP relay  85 . While this separation is not necessary to the present invention, in some environments, it allows additional functionality to be more easily added to the pre-proxy server  75 . An example of such additional functionality is the dynamic allocation of the RTP relay  85 . The pre-proxy server  75  can allocate the closest RTP relay between the two calling parties. That allocation enables the ability to decrease latency and travel time of the RTP stream. Also as shown in  FIG. 3 , with the exemplary embodiment, only SIP messages get routed to the Internet telephony regional data center  80 . The RTP stream need not travel to the data center, and depending upon the location of the caller and the destination area  100 , can travel within a limited geographic area. For example, the telephone handset could be located in California, and the Internet telephony regional data center  80  could be located in New Jersey. If the destination area  100  is also in California, the Internet telephony point of presence in the destination area  90  would be allocated by the pre-proxy server  75  to also be in California. Thus, as noted above, the RTP stream would remain in California; tending to reduce latency and travel time of the RTP stream. 
         [0021]    In the above, the pre-proxy server  75  is shown and discussed as a separate computer. This is for convenience of discussion, for purposes of practicing the invention, it does not need to be separate. Instead, the discussed functions that typically would be implemented in a pre-proxy server can be implemented in a computer that is also functioning as a server.