for example, In a Company named ABC have many clients. When the client requests to the webserver and he response to the client. Then the client can access some data from his account. All the data are stored in another Server. When the client can access his account, he request to the server to itsown port 1000 (store area server) and he response to the client request. then after the response the client can access and or see the all the details about it.
Client request->Webserver --Client request-> Data Server port 1000 <-response <-Server response