PDU (Protocol Data Unit)

PDU (Protocol data Unit)The Edit Protocol Data unit PDU (Protocol Data Unit) refers to the data units passed between peer levels. The PDU on the physical layer of the Protocol Data Unit (Protocol Data unit) is the data bit (bit), the PDU on the data link layer is the data frame (frame), the PDU on the network layer is the packet (packet), the transmission layer PDU is the data segment (segment), and the other higher level The PDU is a message (message). Chinese name Protocol Data unit foreign name PDU full name Protocol Data unit interpretation peer level Catalogue1 Definition 2 Classification definitionEditing in a hierarchical network structure, such as in an open system Interconnect (OSI) model, a Protocol data unit (PDU) is established at each layer of the transport system. The PDU contains information from the upper layer, as well as the entities attached to the current tier. The PDU is then transferred to the next lower layer. The physical layer actually transmits these pdus in the form of a bit stream of a frame, but these PDUs are built from the higher layers of the protocol stack. The receiving system transmits these packets from the bottom up through the protocol stack and separates the relevant information from the PDU at each layer of the protocol stack. It is important that the information that is attached to the PDU for each layer is the same layer assigned to the other system. This is how the peer layer does a communication session coordination. The data segment is processed by stripping the header from the transport layer, performing Protocol data detection to determine the data for the protocol segment that is part of the data in the transport layer, and performing flag validation and stripping. also provides techniques for working with data segments, which receive the header portion of the Protocol data unit. Use the Received header section to determine the number of bytes of data that will be stored in the application space. Furthermore, the received header portion is used to determine the next header portion of the next protocol data unit. Then, issue a peek command to get the next header section. It also provides techniques for performing cyclic redundancy checks using the stored partial cyclic redundancy check summary and remaining data. categoryEdit SNMP Specifies 5 protocol data unit PDUs (that is, SNMP messages) that are used to exchange between management processes and agents. Get-request action: Extracts one or more parameter values from the agent process; Get-next-request action: Extracts the next parameter value immediately following the current parameter value from the agent process. Set-request action: Sets one or more parameter values for the agent process; Get-response action: Returns one or more parameter values. This operation is issued by the agent process, which is the response of the previous three operations, trap operation: The agent process unsolicited messages, notifying the management process that something has happened. Get-request, Get-next-request, set-request operations are issued by the management process to the agent process, the following get-response, Trap is the agent process sent to the management process, for the sake of simplification, the previous 3 operations are called get , Get-next, and set operations. Note that receiving a GET or set message is 161 ports, and the trap message is using 162 ports. Each layer of data plus control information is a PDU.