SDU and PDUs

SDU (Service data Unit): The data unit, also called the Business Data Unit, is a dataset of the user service of the specified layer, and when the same protocol layer is transmitted to the receiver, the data is not changed, that is, the business part is then sent to the lower layer and the lower layer is encapsulated in the PDU. A Service data unit is a unit of information sent from a high-level protocol to a lower layer protocol. The nth tier service data unit is SDU, and the Protocol Data Unit (PDU) on the previous layer is one by one corresponding. According to the data of the protocol Data unit, sent to the receiving end of the specified layer.

PDU (N) = SDU (N-1)

SDU (n) = PDU (n + 1)

PDU: (protocolData Unit) Protocol units

Data passed between n-tier users and N-tier protocols is called Service Data Unit (SDU)
The data passed between N-layer protocol entities is called Protocol Data Unit (PDU), which is sent to the peer-to-peer protocol entity via the downlevel channel through the data Send/Receive management and the SDU of the user submitted in the form of PDU. Restore the PDU to SDU to the end user at the receiving end.
PDU Encapsulation/unpacking: In the sender, the user submitted SDU Plus Protocol control information PCI, encapsulated into a PDU, in the receiver, said the received PDU solution encapsulation, remove the PCI, revert to SDU sent to the receiver users.
SDU Segment/assembly: If the bandwidth of the lower channel does not meet the needs of the delivery SDU, it is necessary to divide a SDU into multiple segments, which are encapsulated into a PDU to be sent out (segmented), and then reassembled into SDU after the receiver has unpacked the PDU.
SDU Splicing/separation: stitching refers to the sender (N) layer protocol entity to encapsulate multiple short (n) sdu into one (n) PDU to send, in the receiving and then receive the (n) PDU solution encapsulation, the plurality (n) SDU separated. The purpose of splicing function is to improve the utilization of the channel.
PDU Segmentation/combination: PDU segmentation refers to the transmission side (N) layer protocol entity divides an (n) PDU into multiple (n-1) SDU, which is sent out in parallel from multiple (n-1) channels, and the receiving side then combines multiple (n-1) SDU received into one (n) PDU. Since this is an n-tier function, the combined operation is performed in n-tier, where N-tier first obtains multiple split (n) PDUs and then combines them into one (n) PDU.

SDU and PDUs