Abstract: The present invention relates to a communications system (1) for making multimedia calls. The system comprises two multimedia terminals (10,12) and communication means for making a multimedia call over a shared communications network (20), including a firewall (26) through which the multimedia call must pass, and which restricts certain types of communication. Each terminal (10,12) has a number of logical communication ports for the multimedia call, including at least one dynamically assigned port. In the course of setting up the multimedia call, at least one of the terminals (10,12) is adapted to send a request to the other of the terminals to open up one or more of the dynamic ports in the other terminal. The system includes a proxy server (40) between the terminals (10,12) that acts for each terminal as a proxy for the other terminal during the course of the call. The proxy server (40) has logical communication ports for communication with the terminals including one or more pre-assigned ports.

Abstract: A method of performing a multimedia communication session over a communication link using Transmission Control Protocol (TCP) and over a communication link using User Datagram Protocol (UDP), including the acts of: receiving a request, over the TCP link, to register from a client terminal located within a private network; a probe data packet to the client terminal, over the TCP link, requesting to send a data packet over the UDP link; and receiving a data packet from the client terminal that contains information relating to an address of the client terminal and a dynamic port over which the multimedia communication session is to be established.

Abstract: A method of performing a multimedia communication session over a communication link using Transmission Control Protocol (TCP) and over a communication link using User Datagram Protocol (UDP), including the acts of: receiving a request, over the TCP link, to register from a client terminal located within a private network; a probe data packet to the client terminal, over the TCP link, requesting to send a data packet over the UDP link; and receiving a data packet from the client terminal that contains information relating to an address of the client terminal and a dynamic port over which the multimedia communication session is to be established.

Abstract: The present invention relates to a communications system (1) for handling communications sessions, for example multimedia calls or voice calls. The communications system (1) comprises a local terminal (10), an external server (40), a proxy interface agent (PIA) (11) between the terminal (10) and a shared network (20). The communication means includes a NAT function (32) through which the communications session must pass. The communications session is carried over the network (20) over one or more logical channels between the terminal (10) and the external server (40), during which the first NAT function (32) applies network address mappings on the terminal's transport addresses (14). The PIA (11) acts on behalf of the terminal (10) in communications with the external server (40), and establishes a logical channel on an outbound connection to the server that serves as a control channel between the PIA (11) and the server (40).

Abstract: The present invention relates to a communications system (1) for making multimedia calls. The system comprises two multimedia terminals (10,12) and communication means for making a multimedia call over a shared communications network (20), including a firewall (26) through which the multimedia call must pass, and which restricts certain types of communication. Each terminal (10,12) has a number of logical communication ports for the multimedia call, including at least one dynamically assigned port. In the course of setting up the multimedia call, at least one of the terminals (10,12) is adapted to send a request to the other of the terminals to open up one or more of the dynamic ports in the other terminal. The system includes a proxy server (40) between the terminals (10,12) that acts for each terminal as a proxy for the other terminal during the course of the call. The proxy server (40) has logical communication ports for communication with the terminals including one or more pre-assigned ports.

Abstract: The present invention relates to a communications system (1) for handling communications sessions, for example multimedia calls or voice calls. The communications system (1) comprises a local terminal (10), an external server (40), a proxy interface agent (PIA) (11) between the terminal (10) and a shared network (20). The communication means includes a NAT function (32) through which the communications session must pass. The communications session is carried over the network (20) over one or more logical channels between the terminal (10) and the external server (40), during which the first NAT function (32) applies network address mappings on the terminal's transport addresses (14). The PIA (11) acts on behalf of the terminal (10) in communications with the external server (40), and establishes a logical channel on an outbound connection to the server that serves as a control channel between the PIA (11) and the server (40).