Java connection architecture defines standard for connecting to different EIS from the J2EE application.
EIS vendors wirte J2C resource adapater similar to JDBC providers written by database vendors. A resource adapter is a driver that connects at the system level to backend EIS.
In keeping with the J2EE packaging model, resource adapters are packaged as modules, in thsi case as RAR files, with an extension of .rar. You would typically have a .rar file for each type of EIS that you are connecting to. A RAR file is esentially a JAR file with some specific content - bascially code and XML deployment descriptor with the filename ra.xml. The RAR file may also contain utility classes, native binary files and documentation.
The adapter can be installed could also be installed as a part of application install, but this practice is discoraged in favor of installing resource adapters separately to the container.
You cannot install resource adapter at cell level. WAS cell contains a heterogeneous mixture of servers, such as combination of windows and Unix machines. Resource adapaters often contain binary shared libraries and there is no distribution mechanism at the cell level for this. The adapters use native path to locate these executables, which could be different on some nodes or platforms. Because of these problems, J2C resource adapters have to be installed to nodes directly and this is enforced by both wasadmin and admin console. When using resource adapater in a cell environment, you should install to the nodes and then configure them at the cell scope.
J2C resources provide connection factories similar to datasources provided by JDBC resources. They provide common configuration and pool of connection for improving performance. Application code obtains connection from connection factory and then releases the connection when done. THe container taks care of making actual connection, connection pooling,..etc
J2C can use both container managed and component managed security identity propagation.