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The link layer corresponds to the OSI data link layer and may include similar functions as the physical layer, as well as some protocols of the OSI's network layer. These comparisons are based on the original seven-layer protocol model as defined in ISO 7498, rather than refinements in the internal organization of the network layer.
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
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.
In the seven-layer OSI model of computer networking, packet strictly refers to a protocol data unit at layer 3, the network layer. [2] A data unit at layer 2, the data link layer, is a frame. In layer 4, the transport layer, the data units are segments and datagrams.
The network layer provides the means of transferring variable-length network packets from a source to a destination host via one or more networks. Within the service layering semantics of the OSI (Open Systems Interconnection) network architecture, the network layer responds to service requests from the transport layer and issues service requests to the data link layer.
TCP/IP protocol suite or Five-layer Internet model (Forouzan, [59] Kurose [60]) TCP/IP model (Stallings [61]) OSI model (ISO/IEC 7498-1:1994 [62]) Three layers: Four layers: Four layers: Four+one layers: Five layers: Five layers: Five layers: Seven layers: Application/ Process Application Application Application Application Application ...
Local area networking standards such as Ethernet and IEEE 802.3 specifications use terminology from the seven-layer OSI model rather than the TCP/IP model. The TCP/IP model, in general, does not consider physical specifications, rather it assumes a working network infrastructure that can deliver media-level frames on the link.
Layered architecture: A protocol layer at the level n consists of two (or more) entities that have a service interface through which the service of the layer is provided to the users of the protocol, and which uses the service provided by a local entity of level (n-1).