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In telecommunications, a protocol data unit (PDU) is a single unit of information transmitted among peer entities of a computer network. It is composed of protocol-specific control information and user data. In the layered architectures of communication protocol stacks, each layer implements protocols tailored to the specific type or mode of ...
Each PDU contains a payload, called the service data unit (SDU), along with protocol-related headers or footers. Data processing by two communicating OSI-compatible devices proceeds as follows: The data to be transmitted is composed at the topmost layer of the transmitting device (layer N) into a protocol data unit (PDU). The PDU is passed to ...
In the seven-layer OSI model of computer networking, packet strictly refers to a protocol data unit at layer 3, the network layer. [2] A data unit at layer 2, the data link layer, is a frame. In layer 4, the transport layer, the data units are segments and datagrams.
Smart card application protocol data unit. In the context of smart cards, an application protocol data unit (APDU) is the communication unit between a smart card reader and a smart card. The structure of the APDU is defined by ISO/IEC 7816 -4 Organization, security and commands for interchange. [1]
Modbus defines a protocol data unit (PDU) independently to its lower layer protocols in its protocol stack. The mapping of MODBUS protocol on specific buses or network requires some additional fields, which are defined as application data unit (ADU). ADU is formed by a client inside a Modbus network when the client initiates a transaction.
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. [2] The data link layer provides the functional and procedural means to transfer data between network entities and may also ...
In the OSI model of computer networking, a frame is the protocol data unit at the data link layer. Frames are the result of the final layer of encapsulation before the data is transmitted over the physical layer. [1] A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a packet." [2]
Service data unit. In Open Systems Interconnection (OSI) terminology, a service data unit (SDU) is a unit of data that has been passed down from an OSI layer or sublayer to a lower layer. This unit of data (SDU) has not yet been encapsulated into a protocol data unit (PDU) by the lower layer. That SDU is then encapsulated into the lower layer's ...