Akamai's State of the Internet quarterly reports are the only authoritative source I'm familiar with that confidently publishes at a global data scale. They have one of the only true global networks, that reach basically into every market. They're the only global network that I know that publishes routine detailed information like that. It's not perfect, I'm not aware of anything better however. They've been publishing it for a number of years, so there's a decent tracking history of trends over time.
