Communications processes handle communications between clients and the enterprise server instance, and consist of a number of service listeners. When an enterprise server instance is created it contains one communications process. If there is a communications failure for any reason, the enterprise server instance cannot process any work until the communications process is restarted. So, to improve the ability of an enterprise server instance to withstand communications failures, you can create one or more additional communications processes per enterprise server instance. You create an additional communications process by copying an existing one. The new communications process is an exact clone of the original, except that any fixed port numbers are not cloned. The first communications process in a newly created enterprise server, Communications Process 1, contains a Web Services and J2EE listener and a Web (deployment) listener. If you are creating a new enterprise server, you might want to modify this communications process definition before you copy it, depending on the particular workload you have planned for the server.
For fault tolerance you need at least two communications processes. You might need more than two to overcome operating system thread limits. The maximum is 32.