Editing Protocol data unit (section)

==Examples==
===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.

===Internet protocol suite===
Protocol data units for the [[Internet protocol suite]] are:

*The [[transport layer]] PDU is the [[TCP segment]] for TCP, and the datagram for UDP
*The [[Internet layer]] PDU is the [[Network packet|packet]].
*The [[link layer]] PDU is the [[Frame (networking)|frame]].

On TCP/IP over Ethernet, the data on the physical layer is carried in [[Ethernet frame]]s.

===Internetwork packet exchange (IPX)===
* For [[IPX]], the IPX packet is the network layer PDU for IPX, and can simultaneously be used in the transport layer as well.
* The SPX packet on top of IPX, is a transport layer PDU.
* The link-layer PDU is the frame.

===ATM===
The data link layer PDU in [[Asynchronous Transfer Mode]] (ATM) networks is called a ''cell''.

{{Anchor|MPDU}}

===Media access control protocol data unit===
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.<ref name=":0">{{Cite web |date=2006 |title=Wimax MAC-Upperlayer Services |url=http://www.comlab.hut.fi/opetus/4210/presentations/37_wimax_mac.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.comlab.hut.fi/opetus/4210/presentations/37_wimax_mac.pdf |archive-date=2022-10-09 |url-status=live |website=www.comlab.hut.fi |pages=12–15}}</ref>

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]]. In systems where the MPDU is smaller than the MSDU, then one MSDU may ''generate'' multiple MPDUs as a result of [[packet segmentation]].<ref name=":0" />