B2B Integration : A Practical Guide to Collaborative E-commerce

Integration Patterns 83
remote procedure call, let's review some of the key terms of RPC
protocol.
Client — A client is an application or program that makes remote
procedure calls to remote servers. Irrespective of the language in which
the client is developed, it needs to know the following in order to make
a remote call:
• The uniform resource locator (URL) and transmission control protocol
(TCP) port of the server;
• The name of the remote procedure;
• The kind and number of arguments that procedure expects; and
• The kind and number of return values.
Server — A server is a process that provides remote services to clients.
Remote Service — A remote service is a collection of one or more
remote programs available over the network.
Remote Program — A remote program implements one or more remote
procedures.
A remote procedure call involves a single thread that controls
two processes. One of the processes is that of the calling program
(caller's process) or application and the other one is that of the server
on which the call is being made (server's process). The caller process
initiates the communication by sending a message with the remote
procedure's parameters to the server process (see Figure 3.23). After
sending the message, the caller process can wait for the server process
to respond back with the results of the remote procedure (synchronous
communication) or continue on (asynchronous communication). The server
process, on the other hand, is dormant waiting for the client requests
and servicing them as the RPCs are invoked. Once it receives a message
from the client program, it executes the remote procedure and sends the
calling process the results in the form of messages.
In the above implementation example, there is only one process that
is active at any moment in time. RPC protocol supports simultaneous
execution of more than one process. For instance, in an asynchronous
RPC call, the client process can continue without waiting for the results
from the server process.