Problems related to operation and administration of multi-user application programs, particularly real-time applications, in systems of networked computers are solved using an enhancement of a selected call control protocol, such as the H.323 or SIP protocol. Each client, server, gatekeeper, and optional firewall of a system is provided with a specific real-time codec with a common interface adapted to a multimedia call control protocol, such as H.323 or SIP. The codec is adapted to cooperate with each of the client, sever, gatekeeper, and optional firewall. Thus, for example, each client can use its data communication protocol of choice without the need for the same data communication protocol choice on the server side of the application.