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Networking Fundamentals · Foundational

Segment

The Layer 4 PDU produced by TCP, consisting of a TCP header and a chunk of application data.

Definition

TCP divides an application byte stream into segments, each with sequence and acknowledgment numbers, ports, flags and a window value. Segment size is limited by the maximum segment size negotiated during the handshake. The word segment is also used for a section of physical network, which is a different meaning.

Example

A 1 MB file transfer is split into hundreds of TCP segments.

Exam tip

Strictly, TCP produces segments and UDP produces datagrams, though many exams accept "segment" for Layer 4 generally.

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