Internet Protocol Suite

The Internet protocol suite is the conceptual model and set of communications protocols used in the internet and similar computer networks. It is commonly known as TCP/IP because the foundational protocols in the suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP).

The Internet protocol suite provides end-to-end data communication specifying how data should be packeized, addressed, transmitted, routed and received. This functionality is organized into four abstraction layers, which classify all related protocols according to the scope of networking involved. From lowest to highest, the layers are the link layer, containing communication methods for data that remains within a single network segment (link); the internet layer, providing internetworking between independent networks; the transport layer, handling host-to-host communication; and the application layer, providing process-to-process data exchange for applications.

Application Layer

The application layer is the scope within which applications, or processes, create user data and communicate this data to other applications on another or the same host. The applications make use of the services provided by the underlying lower layers, especially the transport layer which provides reliable or unreliable pipes to other processes. The comminucations partners are characterized by the application architecture, such as the client-server model and peer-to-peer networking. This is the layer in which all application protocols such as SMTP, FTP, SSH, HTTP operate. Processes are addressed via ports which essentially represent services.

Transport Layer

The transport layer performs host-to-host communications on either the local network or remote networks separated by routers. It provides a channel for the communication needs of applications. UDP is the basic transport layer protocol, providing an unreliable connectionless datagram service. The Transmission Control Protocol provides flow-control, connection establishment, and reliable transmission of data.

Internet Layer

The internet layer exchanges datagrams across network boundaries. It provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections. It is therefore also the layer that establishes internetworking. Indeed, it defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite. The primary protocol in this scope is the Internet Protocol, which defines IP addresses. Its function in routing is to transport datagram to the next host, functioning as an IP router, that has the connectivity to a network closer to the final destination.

Link Layer

The link layer defines the networking methods within the scope of the local network link on which hosts communicate without intervening routers. This layer includes the protocols used to described the local network topology and the interfaces needed to affect transmission of Internet layer datagrams to next-neighbor hosts.

References: https://en.wikipedia.org/wiki/Internet_protocol_suite