The server is a user level program listening to a socket and accepting connections from clients. It uses portion of the local workstation's main memory to store the client's pages. When the client requests a page-in, the server transfers the requested page(s) over the socket. When the client requests a page-out, the server reads the incoming pages from the socket, and stores them in its main memory.
A backup server responds to page-out requests much like a primary server, but it does not respond to page-in requests unless the client has explicitly declared the primary server as crashed.