What is the protocol data unit (PDU) at layer 4 of the OSI model?

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What is the protocol data unit (PDU) at layer 4 of the OSI model?

In the OSI model, the Transport layer handles end-to-end delivery and the segmentation of data for reliable or best-effort transport. The PDU at this layer is called a segment, because the transport layer takes data from the higher layers, breaks it into smaller pieces, and adds a transport header with information like port numbers, sequencing, and control flags. This enables multiplexing multiple applications over a single network connection and, when using TCP, ensures reliability and proper ordering. The other terms belong to different layers: a frame is the Data Link layer unit, a packet is the Network layer unit, and a datagram is a term often used with UDP but is not the standard OSI naming for the transport layer.

In the OSI model, the Transport layer handles end-to-end delivery and the segmentation of data for reliable or best-effort transport. The PDU at this layer is called a segment, because the transport layer takes data from the higher layers, breaks it into smaller pieces, and adds a transport header with information like port numbers, sequencing, and control flags. This enables multiplexing multiple applications over a single network connection and, when using TCP, ensures reliability and proper ordering. The other terms belong to different layers: a frame is the Data Link layer unit, a packet is the Network layer unit, and a datagram is a term often used with UDP but is not the standard OSI naming for the transport layer.

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