There are three layers:- 

a. Stub and Skeleton layer

This layer lies just under the view of the developer. This layer intercepts method calls made by the client to the interface reference variable and redirects these calls to a remote RMI service.

b. Remote Reference Layer.

This layer understands how to interpret and handle references made from clients to the remote service objects. The link is a one-to-one (unicast) link.

c. Transport layer

This layer is based on TCP/IP connections among machines in a network. It gives basic connectivity, as well as some firewall penetration strategies.