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In telecommunications, the term protocol data unit (PDU) has the following meanings: *Information that is delivered as a unit among peer entities of a network and that may contain control information, such as address information, or user data. *In a layered system, a unit of data which is specified in a protocol of a given layer and which consists of protocol-control information and possibly user data of that layer. For example: Bridge PDU or iSCSI PDU ==OSI model== PDUs are relevant in relation to each of the first 4 layers of the OSI model as follows:〔(【引用サイトリンク】title=Data Encapsulation, Protocol Data Units (PDUs) and Service Data Units (SDUs) )〕 *The Layer 1 (Physical Layer) PDU is the bit or, more generally, symbol (can also be seen as "stream") *The Layer 2 (Data Link Layer) PDU is the frame *The Layer 3 (Network Layer) PDU is the packet *The Layer 4 (Transport Layer) PDU is the segment for TCP or the datagram for UDP *The Layer 5-6-7 (Application Layer) PDU is the data, which can be clear text, encrypted, or compressed Given a context pertaining to a specific OSI layer, PDU is sometimes used as a synonym for its representation at that layer 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Protocol data unit」の詳細全文を読む スポンサード リンク
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