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Data processing by two communicating OSI-compatible devices proceeds as follows: The data to be transmitted is composed at the topmost layer of the transmitting device (layer N) into a protocol data unit (PDU). The PDU is passed to layer N−1, where it is known as the service data unit (SDU).
OSI model 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).
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 .
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 OSI model, these are defined at layers 1 and 2 — the physical layer and the data link layer. A widely adopted family of transmission media used in local area network technology is collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3 ...
The Layer 4: transport layer PDU is the segment or the datagram. The Layer 3: network layer PDU is the packet. The Layer 2: data link layer PDU is the frame. The Layer 1: physical layer PDU is the bit or, more generally, symbol. Given a context pertaining to a specific OSI layer, PDU is sometimes used as a synonym for its representation at that ...
[4] A simple definition of packet switching is: The routing and transferring of data by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon completion of the transmission the channel is made available for the transfer of other traffic. [5] [6]