The Internet is a hierarchical structure linking different levels of service providers whose millions of devices supply all the interconnections. The three levels outlined in the book from the top down include .

The three levels  are

National service ProviderRegional Service ProviderInternet Service Provider .

Explanation:

The national service provider is Often known  ISP (Internet Service Provider) is recognized as the state service provider. This layout varies from smaller ISPs that serve as local suppliers.In the regional service Provider the internet cables are submerged cables or over the ground cables.In the regional Service provider the client includes private sector.An Internet Service Provider is an entity offering infrastructure for Internet access, use, or the  participation.