Server keeps timing me out

So me and a friend of mine have been playing on this server for I'd say around a month or two now, and we haven't experienced any problems up until now. Recently during the last couple days the server has been timing both me and him out after around 10-20 minutes of playing. This is unusual because we're in the current version of Minecraft and we don't have any mods or plugins. I've checked the log after the server times out, and nothing seems to tell me that it's even crashed in the first place. Anyone have any idea what could be the cause of this, and/or how I can fix it?