The internet protocol suite is a set of computer networking communications protocols often referred to as TCP/IP—Transmission Control Protocol (TCP) and Internet Protocol (IP). The protocol specifies how data should be packetized, addressed, transmitted, routed, and received.
Most network protocol suites are structured as a series of layers, sometimes referred to collectively as a protocol stack. Each layer is designed for a specific purpose and exists on both the sending and receiving hosts.
The Open Systems Interconnect (OSI) model describes network activities as having a structure of seven layers, each of which has one or more protocols associated with it. The operations defined by the OSI model are conceptual and not unique to any particular network protocol suite.
The Open Systems Interconnect (OSI) Reference Model:
| Layer No. | Layer Name | Description |
|---|---|---|
| 7 | Application | Consists of standard communication services and applications that everyone can use |
| 6 | Presentation | Ensures that information is delivered to the receiving machine in a form that it can understand |
| 5 | Session | Manages the connections and terminations between cooperating computers |
| 4 | Transport | Manages the transfer of data and assures that received and transmitted data are identical |
| 3 | Network | Manages data addressing and delivery between networks |
| 2 | Data Link | Handles the transfer of data across the network media |
| 1 | Physical | Defines the characteristics of the network hardware |
The OSI model describes an idealized network communications protocol family. TCP/IP does not correspond to this model directly, as it either combines several OSI layers into a single layer, or does not use certain layers at all.
The TCP/IP Protocol Stack:
| OSI Ref. Layer No. | OSI Layer Equivalent | TCP/IP Layer |
|---|---|---|
| 5, 6, 7 | Application, Session, Presentation | Application |
| 4 | Transport | Transport |
| 3 | Network | Internet |
| 2 | Data Link | Data Link |
| 1 | Physical | Physical Network |