Today Level 3 finally put up a nice CDN win: Funcom, as the exclusive CDN provider for the Age of Conan Hyborian Adventures online game . Of course, amongst most non-gamers, the first question was 'Funcom who?', but in the gaming world the Conan launch has been big news. It has a lot (700k) of initial users and a great start, and Funcom clearly hopes to be the next World of Warcraft smash hit, but it is still early in its lifespan. But from a telecom perspective, how bandwidth and CDNs work for gaming is a bit different than how it works for streaming or website acceleration, so I thought I'd at least try to clear some things up.
A game like Conan or World of Warcraft uses bandwidth in two ways. The first is in actual gameplay, where people run around killing monsters or each other etc. The realtime positions, movement, actions, chats, etc. All this traffic must go back to one location - it can't be cached because it is in real time, it doesn't come through a CDN. It isn't that much traffic either, because each player keeps most of the information locally - you don't download all another player's graphics when you see him in the game, all that you get is a bunch of integers: a player id and equipment ids etc which are enough to represent the current state of the game to your local software. This is done via IP transit and at rates per user that are low enough to survive very low broadband speeds, sometimes even dialup for those crazy enough to try.
So what do you need a CDN for? Everyone who has the game installed needs to have the same version of the software as everyone else. If a new place is created, or a new item, or a new kind of monster, or a new quest, it goes into a patch - along with bugfixes one would normally expect. That patch is generally quite large and has to be downloaded by each player when he logs in before he can actually play, else his local software will be out of synch. So when the game is updated, you have a massive surge in bandwidth usage as the patches go out as each user logs in, and this is what they use the CDN for. The patch is handed off to the CDN which caches it all over the place, thus distributing the load efficiently and absorbing the variability in user logins. This sort of patch happens frequently, especially in the first year of a game because they roll these games out with a minimal virtual world that the users quickly exhaust - they need to add places and things to do steadily as the game matures. In a way, the phrase 'patch' is a misnomer because it is less about patching bugs, it is really one expansion pack after another.
Anyhow, that's gaming bandwidth as I understand it, I welcome corrections or clarifications.
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