10.6 RMI's Multiplexing Protocol

The purpose of multiplexing is to provide a model where two endpoints can each open multiple full duplex connections to the other endpoint in an environment where only one of the endpoints is able to open such a bidirectional connection using some other facility (e.g., a TCP connection). RMI use this simple multiplexing protocol to allow a client to connect to an RMI server object in some situations where that is otherwise not possible. For example, some security managers for applet environments disallow the creation of server sockets to listen for incoming connections, thereby preventing such applets to export RMI objects and service remote calls from direct socket connections. If the applet can open a normal socket connection to its codebase host, however, then it can use the multiplexing protocol over that connection to allow the codebase host to invoke methods on RMI objects exported by the applet. This section describes how the format and rules of the multiplexing protocol.