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Different authors have interpreted the TCP/IP model differently, and disagree whether the link layer, or any aspect of the TCP/IP model, covers OSI layer 1 (physical layer) issues, or whether TCP/IP assumes a hardware layer exists below the link layer.
This article lists protocols, categorized by the nearest layer in the Open Systems Interconnection model.This list is not exclusive to only the OSI protocol family.Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers.
TCP/IP does recognize four broad layers of functionality which are derived from the operating scope of their contained protocols: the scope of the software application; the host-to-host transport path; the internetworking range; and the scope of the direct links to other nodes on the local network. [47]
The Internet protocol suite is therefore often referred to as TCP/IP. The first major version of IP, Internet Protocol version 4 (IPv4), is the dominant protocol of the Internet. Its successor is Internet Protocol version 6 (IPv6), which has been in increasing deployment on the public Internet since around 2006. [1]
[5] [6] This resulted in a networking model that became known informally as TCP/IP, although formally it was variously referred to as the DoD internet architecture model (DoD model for short) or DARPA model. [7] [8] [9] Later, it became the part of, and synonymous with, the Internet Protocol Suite.
Because the internet layer of the TCP/IP model is easily compared directly with the network layer (layer 3) in the Open Systems Interconnection (OSI) protocol stack, [4] [5] [6] the internet layer is often improperly called network layer. [1] [7]
Layer Protocol data unit (PDU) Function [3] Host layers 7 Application: Data: High-level protocols such as for resource sharing or remote file access, e.g. HTTP. 6 Presentation: Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption: 5 Session
The protocols in use today in this layer for the Internet all originated in the development of TCP/IP. In the OSI model the transport layer is often referred to as Layer 4, or L4, [2] while numbered layers are not used in TCP/IP. The best-known transport protocol of the Internet protocol suite is the Transmission Control Protocol (TCP).