SCALING

in games & virtual worlds

The three months have turned into two years (and counting). I’ve found lots of new research challenges, but they all have to do with finding ways to make the environment for online games and virtual worlds scale. In the process, I have been introduced to a different world of computing, with different problems, different assumptions, and a different environment. At times I feel like an anthropologist who has discovered a new civilization. I’m still learning about the culture and practice of games, and it is a different world.

EVERY THING YOU KNOW IS WRONG

The first thing to realize in understanding this new world is that it is part of the entertainment industry. Because of this, the most important goal for a game or virtual world is that it be fun. Everything else is secondary to this prime directive. Being fun is not an objective measure, but the goal is to provide an immersive, all-consuming experience that rewards the player for playing well, is easy to learn but hard to master, and will keep the player coming back again and again.

Most online games center around a story and a world, and the richness of that story and world has much to do with the success of the game. Design of the game centers on the story and the gameplay. Design of the code that is used to implement the game comes quite a bit later (and is often considered much less interesting). A producer heads the team that builds the game or the virtual world. Members of the team include writers, artists, and musicians, as well as coders. The group with the least influence on the game consists of the coders; their job is to bring the vision of others to reality.

The computational environment for online games or virtual worlds is close to the exact inverse of that found in most markets serviced by the high-tech industry. The clients are anything but thin; game players will be using the highest-end computing platforms they can get, or game consoles that have been specially designed for the computational rigors of these games. These client machines will have as much memory as can be jammed into the box, the latest and fastest CPUs, and graphics subsystems that have supercomputing abilities on their own. These clients will also have considerable capacity for persistent storage, since one of the basic approaches

12 November/December 2008 ACM QUEUE

to these games is to put as much information as possible on the client.

The need for a heavyweight client is, in part, an outcome of the evolution of these games. Online games have developed from stand-alone products, in which everything was done on the local machines. This is more than entropy in the industry, however; keeping as much as possible on the client allows the communication with the server to be minimized, both in the number of calls made to the server and in the amount of information conveyed in those calls. This communication minimization is required to meet the prime directive of fun, since it is part of the way in which latency is minimized in these games.

Latency is the enemy of fun—and therefore the enemy of online games and virtual worlds. This is especially interesting in the case of online games, where the latency of the connection between the client and the servers cannot be controlled. Therefore, the communication protocol needs to be as simple as possible, and the information transmitted from the client to the server must fit into a single packet whenever possible. Further, the server needs to be designed so that it is doing very little, ensuring that whatever it is doing can be done very quickly so a response can be sent back to the player. Some interesting tricks have been developed to mask unavoidable latency from the player. These include techniques such as showing prerecorded clips during the loading of a mission or showing a “best guess” immediately at the result of an action and then repairing any differences between that guess and the actual result when the server responds.

The role of the server is twofold. The most obvious is to allow players to interact with each other in the context of the game. This role is becoming more important and more complex as these games and worlds become increasingly elaborate. The original role of the server was to allow players to compete with each other in the game. Now games and virtual worlds are developing their own societies, where players may compete but may also cooperate or simply interact in various ways. Virtual worlds allow users to try out new personalities; games let players cooperate to do tasks that they would be unable to complete individually. In both, players are finding that a major draw of the technology is using it to connect to other people.

The second role of the server is to be the arbiter of truth between the clients. Whether the client is running on a console or on a personal computer, control rests in the hands of the player. This means that the player has access to the client program, and the competitive nature of the games gives the player motivation to alter the

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