Overview of the AWS Global Network
Networks like those run by AT&T, Comcast, NTT, Tata, or Zayo are known as Tier-1. This means they can reach the entire internet through settlement-free peering. These are the biggest players on the internet, with the most resources. Nevertheless, even Tier-1 ISPs oversubscribe their networks.
This means they sell more bandwidth to their customers than they can deliver – all at once, anyway. They rely on the fact that most customers don’t hammer their full bandwidth allocation 24 hours a day. This is why your ISP probably gives you less upload than download speed, and why they implement data caps. They also use complex QoS mechanisms to deal with the inevitable periods of congestion that result.
Over the years, they have become good at predicting how much oversubscription they can get away with before losing customers to competitors. For context, an ISP that only oversubscribes 25:1 is considered a good one. Ratios as high as...
