Relationship between SDU and PDU

In a layered network structure, for example, in an Open Systems Interconnection (OSI) model, a Protocol Data Unit (PDU) is established at each layer of the transmission system ). PDU contains information from the upper layer and the object attaching information of the current layer. The PDU is then transmitted to the lower layer. The physical layer actually transmits these PDUS in the form of a bit stream of frame encoding, but these PDUS are constructed by higher layers of the protocol stack. The receiving system transmits these groups from the bottom up through the protocol stack, and separates related information in the PDU from each layer of the protocol stack. It is important that the information that each layer attaches to the PDU is assigned to the same layer of another system.

In the telecom field, termsService Data Unit(SDU,SErviceDATAUNit), also knownBusiness Data UnitIs the user service data set at the specified layer. when the data is transferred to the receiver at the same protocol layer, the data does not change.

Service data units (SDU) are information units transmitted from high-level protocols to low-level protocols. Layer n service data unit SDU corresponds to the Protocol Data Unit (PDU) of the previous layer. The data is sent to the specified layer at the receiving end based on the data of different protocol data units.

PDU (n) = SDU (n-1)

SDU (n) = PDU (n + 1)

Reference: http://baike.baidu.com/view/451435.htm? From_id = 7291428 & type = SYN & fromtitle = protocol + Data + Unit & Fr = Aladdin

Http://baike.baidu.com/view/451431.htm? Fromtitle = Service + Data + Unit & type = SYN

Relationship between SDU and PDU