segmentation and reassembly sublayer (ATM) (SAR)

The Segmentation and Reassembly Sublayer(SAR) is a sublayer of the ATM adaptation layer. The SAR sublayer is responsible for segmenting the information units of the higher layers in ATM cells and for the composition of cell contents.

Structure of the ATM adaptation layer

The SAR layer receives the Protocol Data Units( PDU) from the convergence sub layer and adds a header and a trailer to the individual data blocks. The newly created PDUs are called SAR PDUs. These are passed to the ATM layer at the Service Access Point( SAP), where they form the payload for the ATM cells as the ATM- SDU (Service Data Unit). The process in the SAR sublayer converts variable-length frames into fixed-length cells and performs the reverse functionality.