Client/Server Sessions

A client/server session consists of a collection of players, or clients, connected to a central server. As far as Microsoft?DirectPlay?is concerned, a client has no knowledge of any other clients, only the server. The messaging needed to run the game is between the individual clients and the server. DirectPlay does not provide direct client-to-client messaging, as it does for peer-to-peer sessions.

A client/server session requires two distinctly different applications.

The server application runs on a remote server. At a minimum, it serves as a central messaging hub and game host. The server must receive and handle all incoming messages from the clients, and send appropriate messages back out. Any transfer of data from one client to another must be handled by the server application.
A client application runs on each players' computer. The primary function of this application is to handle the UI, and keep the player's game state synchronized with the server.

There are certain aspects of the session that can be handled by only one of these applications. For instance, updating a player's video display can only be done by the client application. However, many aspects of the processing needed to maintain the game universe can, at least in principle, be done by either application. Writing an effective client/server game requires some careful consideration of how to divide the processing chores between the two applications.

This document describes the basic principles of client server games, and outlines how to implement client and server applications.