Guild Wars Technology Interview
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Q: Will any of the technology help with the lag that plagues so many of these types of games?
A: Yes, our technology gives us great tools to address lag. Designing Guild Wars to overcome lag was a core issue for ArenaNet, even more so than it would be for most games, because Guild Wars is a global game and you maybe playing with people from anywhere in the world.
Our team has tremendous experience building low-latency gaming networks. After all, when we built Battle.net, there was no such thing as broadband. However, while it's important to note that bandwidth and lag are somewhat related, they are not completely tied to one another. So it is not enough simply to use small amounts of bandwidth, you also have to design the game interaction model to mask latency introduced by the Internet. With Guild Wars we have designed the game to do both.
One technology Guild Wars uses to reduce lag is its predictive motion model. Rather than the server sending a packet several times per second with absolute positions for every unit, it sends a unit vector (direction and speed) describing its motion. The client and server both model the game in this fashion and the server only needs to communicate with the client when it knows that something in the client world is incorrect. At this point, the server just sends correction information to correct the client model. This greatly reduces perceived latency and bandwidth requirements.
It is important to note that even though both the client and server are modeling the world, the server is always the boss and only provides information to the client when necessary. This reduces exploits such as map hacks that give information to the players before they should know it.
