Last post, I gave some background on how we test multiplayer network games under adverse conditions - simulating poor Internet connections.  Today, I'll discuss one of the more significant things that we observed in the SFII Beta.

When the reports started rolling in on the Beta test forums regarding issues with large rollbacks / teleporting effects, we started an investigation.  Many of these issues didn't appear during our internal pre-Beta QA period, so it was interesting to see them reported so widely.

The first thing we attempted to do was to reproduce the rollbacks in the Capcom QA environment.  The cause wasn't entirely obvious at first, because the condition does not occur when two players have high latency connections alone - We can set up a match between two machines that have 200ms ping times and still not see the same problem.

After some experimentation, we discovered that large rollbacks could be reproduced when we combined 100+ms latency conditions WITH packet loss.

For some background information, it may be useful to explain how packet loss contributes to the overall network experience.  Once again, I'll turn to the Wikipedia for a description of Packet Loss  Packet Loss and Quality of Service (QoS)

If you look in the "Problems" section on QoS, you'll notice that any number of factors can contribute to packet loss in a network environment.  It seems, based on this Beta test, that 5%-10% packet loss is fairly common in the real world, particularly over wireless Internet connections.

Since packet loss occurs randomly, there is no guarantee that it will show up at the time that a matchmaking connection is underway.  As a result, our Beta testers can only make a determination of who to challenge based on ping rating.  [Note: We show the Xbox LIVE Quality of Service latency value, which is close, but not quite the same as the ping from a PC command shell]

 Next blog, I'll discuss some of the things that we've done to address these issues.