We recently tracked down, with the help of an internet service provider (ISP) and one of our hosting providers, a networking issue that could be contributing to some of the lag and packet loss that players with certain ISPs are experiencing. This post is to provide some technical details about the problem and how we’re planning to fix it.
The issue relates to how UDP network packets can be delivered to their destination in a different order than they were sent. This is a protocol that all programs using UDP for networking have to deal with, and Fortnite, by way of Unreal Engine 4, does handle it, but not as efficiently as it could.
To help understand the issue, here’s a simplified version of the high-level sequence of events that occur in a single frame in-game.
Try to read a packet from the network, if one is available, go to #2. Otherwise, skip to #4.
If the packet read was sent before a packet we’ve ...
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