Editing Protocol data unit (section)

===OSI model===
Protocol data units of the [[OSI model]] are:<ref>{{Cite web |url=http://www.tcpipguide.com/free/t_DataEncapsulationProtocolDataUnitsPDUsandServiceDa.htm |title=Data Encapsulation, Protocol Data Units (PDUs) and Service Data Units (SDUs) |work=The TCP/IP Guide |access-date=2012-04-05}}</ref>

*The Layer 4: [[transport layer]] PDU is the [[Packet segmentation|segment]].
*The Layer 3: [[network layer]] PDU is the [[Network packet|packet]] or the [[datagram]].<ref>{{Cite web|url=https://www.cloudflare.com/learning/network-layer/what-is-a-packet/|title=What is a packet? {{!}} Network packet definition|work=Cloudflare}}</ref>
*The Layer 2: [[data link layer]] PDU is the [[Frame (networking)|frame]].
*The Layer 1: [[physical layer]] PDU is the [[bit]] or, more generally, [[Symbol (data)|symbol]].

Given a context pertaining to a specific OSI layer, ''PDU'' is sometimes used as a synonym for its representation at that layer.