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OSI had two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols. The OSI reference model was a major advance in the standardisation of network concepts. It promoted the idea of a consistent model of protocol layers, defining interoperability between network ...
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).
The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite.
The TCP checksum is a weak check by modern standards and is normally paired with a CRC integrity check at layer 2, below both TCP and IP, such as is used in PPP or the Ethernet frame. However, introduction of errors in packets between CRC-protected hops is common and the 16-bit TCP checksum catches most of these.
A media access control protocol data unit (MAC PDU or MPDU) is a message that is exchanged between media access control (MAC) entities in a communication system based on the layered OSI model. [ 2 ] In systems where the MPDU may be larger than the MAC service data unit (MSDU), the MPDU may include multiple MSDUs as a result of packet aggregation .
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.
The TCP/IP model describes the protocols used by the Internet. [3] The TCP/IP model has a layer called the Internet layer, located above the link layer.In many textbooks and other secondary references, the TCP/IP Internet layer is equated with the OSI network layer.
An application layer is an abstraction layer that specifies the shared communication protocols and interface methods used by hosts in a communications network. [1] An application layer abstraction is specified in both the Internet Protocol Suite (TCP/IP) and the OSI model. [2]