A central server stores a database of global IP addresses for establishing TCP/IP sessions with other users of computer networks. One user system transfers a data call request to the central server system over a public data network. The central server system identifies the global IP addresses of the calling and called users and determines which ones of the calling and called users is connected to the public data network via a firewall. Depending upon the presence of firewalls, the central server configures the data call to enable direct, point-to-point packet transmission of network packets between the calling and called users without relaying them through the central server.