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A protocol data unit (PDU) is an open-system interconnection (OSI) term used in telecommunications that refers to a group of information added or removed by a layer of the OSI model. Each layer in the model uses the PDU to communicate and exchange information, which can only be read by the peer layer on the receiving device and is then handed over to next upper layer after stripping.
A protocol data unit is information delivered as a unit among peer entities of networks containing control information, address information or data. In layered systems, PDU represents a unit of data specified in the protocol of a given layer, which consists of protocol control information and user data.
PDU is a significant term related to the initial four layers of the OSI model. In Layer 1, PDU is a bit, in Layer 2 it is a frame, in Layer 3 it is a packet and in Layer 4 it is a segment. In Layer 5 and above, PDU is referred to as data.
PDU has four fields: the destination service access point, source service access point, control field and information field. In packet-switched data networks, PDU is related to a service data unit.