As we know how packets travel from one computer to another over the Internet. However what's in-between? Actually what makes up the Internet infrastructure or backbone?

Figure: Internet Backbone

Internet backbone is made up of many large networks, which interconnect with each other. These large networks are termed as Network Service Providers or NSPs. These networks peer with each other to exchange packet traffic. Every NSP is essential to connect to Network Access Points or NAPs. At NAPs, packet traffic can jump from one NSP's backbone to another NSP's backbone. NSPs interconnect at Metropolitan Area Exchanges or MAEs also. MAEs serve same purpose as NAPs though are privately owned. NAPs were original Internet interconnects points. Both MAEs and NAPs are referred to as Internet Exchange Points or IXs. NSPs also sell bandwidth to smaller networks, like ISPs and smaller bandwidth providers. Below is a picture demonstrating this hierarchical infrastructure.

This isn't a true representation of an actual piece of the Internet. Above figure is only meant to demonstrate how NSPs could interconnect with each other and smaller ISPs. None of the physical network components are demonstrated in this figure. This is because a single NSP's backbone infrastructure is a complex drawing by itself. Most NSPs publish maps of their network infrastructure on their web sites and may be found easily. To draw an actual map of the Internet will be nearly impossible because of its complexity, size and ever changing structure.