Internet structure

End systems connect to internet via ISPs

Access ISPs interconnected

  • Any 2 hosts can send packets to each other

Resulting network of networks is compllex

Complex because structure is driven by economy / national policies

O(N^2) if we connect every ISP to other access ISPs

Service view

Infra which provides services to applications

Provides programming interface to apps

hooks which allow sending & receiving app programs to connect to internet.

Provides service options, analogous to postal service.

What is a protocol


Each layer implements a service by performing actions within that layer, rely on services provided by the layer below it.

Internet protocol stack / Network stack