BGP

Chapter 12. Interconnecting with Other Networks

When your network has a low traffic volume, it makes sense to pay one or more ISPs to handle traffic you exchange with all destinations on the Net. Because the amount of traffic you exchange with each individual destination network is very small, there is no point in arranging direct connections to these networks. But as your traffic volume grows, at some point the economy of interconnecting with other networks swings the other way. For networks with a high traffic volume, it doesn’t make much sense to pay ISPs to handle all this traffic. Few ISPs differentiate between “cheap” traffic that can be delivered to another network locally or regionally, and “expensive” traffic that has to be carried over great distances. Handling the cheap traffic yourself will cost less than paying your ISP the average traffic costs over it. In addition, the economies of scale are a little peculiar for networking. At first, the cost per unit of traffic goes down as the amount of traffic goes up, but at some point, the cost per unit starts to go up again because the fastest routers and the fastest interfaces are more expensive than a combination of several midrange routers and slower interfaces with the same aggregate bandwidth. At some point, a larger number of direct connections will become more attractive than one or two big pipes to ISPs.

Peering

Although the word “peering” is used for different things, it’s usually assumed in the Internet business to ...