There are two possible ways of having a tiered system - one is to degrade competitors/those who don't pay, and the other is to offer a premium service to those who do pay.
The only way I know of to offer a premium service on the same network as a non-premium service is to delay non-premium packets. This artificial packet delay is known as "Quality of Service" or QoS because it degrades the quality of service to some users in order to allow other users unobstructed use of the network. You see the same thing in road networks when the police block certain intersections to allow a parade or an important diplomat to move along the streets with no obstructions. This type of policing can also be used in networks. But there is another way. If you provide enough bandwidth so that your peak traffic levels can travel through the network without ever being buffered at any of the core network interfaces, then everybody is a king. If you charge your customers a higher fee for such a network than your competitors do, then we have a tiered Internet. This unobstructed network was pioneered by Sprint on it's zero-CIR frame relay network and they carried this forward into their IP network as well. Other companies have carried forward this architecture as well. --Michael Dillon