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Protocol data unit
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<p>In <a href="/facts/Telecommunications/vxoj1cxR">telecommunications</a>, a protocol data unit (PDU) is a single unit of information transmitted among peer entities of a <a href="/facts/Computer_network/3w5RM99p">computer network</a>. It is composed of protocol-specific control information and <a href="/facts/Payload_(computing)/zN2Pgfq6">user data</a>. In the layered architectures of <a href="/facts/Communication_protocol/5uady7cB">communication protocol</a> stacks, each layer implements protocols tailored to the specific type or mode of data exchange. </p><p>For example, the <a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol</a> (TCP) implements a connection-oriented transfer mode, and the PDU of this protocol is called a <i>segment</i>, while the <a href="/facts/User_Datagram_Protocol/dxLU0D6q">User Datagram Protocol</a> (UDP) uses <a href="/facts/Datagram/TMHVctMz">datagrams</a> as protocol data units for <a href="/facts/Connectionless_communication/MfMys8t7">connectionless communication</a>. A layer lower in the <a href="/facts/Internet_protocol_suite/KNkxtSpw">Internet protocol suite</a>, at the <a href="/facts/Internet_layer/336eMWJu">Internet layer</a>, the PDU is called a <a href="/facts/Network_packet/xCYf8SJu">packet</a>, irrespective of its payload type. </p>