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.