RMI-P4 

RMI-P4 refers to the development framework that is used to develop distributed remote Java objects applications on the J2EE Engine. It is based entirely on the P4 protocol. The framework and the protocol functions are logically concentrated in the P4 Provider Service.

The P4 protocol is an SAP proprietary protocol that facilitates communication between distributed objects from different namespaces (possibly different hosts). Conceptually, it is related to the Remote Method Invocation (RMI) and Common Object Request Broker Architecture (CORBA) technologies, and its implementation combines features of both of them.

RMI-related Features

The P4 protocol is designed exclusively to support Java-to-Java remote communication. It greatly simplifies and significantly speeds up the input-output operations for transferring objects. The protocol uses the standard Java Serialization techniques to transfer the objects, thereby providing full compatibility with all Java types. This also reduces the volume of data being transferred through the network by avoiding the requirement to align the data types (the latter is an exclusive requirement of the CORBA specification).

CORBA-related Features

The P4 protocol employs the concept of the Broker architecture defined by CORBA. This allows for the functional extension of the protocol, by adding information that is transmitted as an independent part of each remote call. Using that powerful mechanism, you can enhance the protocol by building other functional levels, such as a security layer or a transport layer, and so on, on top of it.

The P4 protocol is designed to work in both standalone and cluster environments. It is well-suited to the J2EE Engine cluster architecture and provides transparent, robust failover and load balancing mechanisms.