Fragmentation and Reassembly (Segmentation -OSI) EXchange data between two entities Characterized as sequence of pDUs of some bounded size Application level message in the form of datagram or continuous data stream R∈ eason Lower-level protocols may need to break data up into smaller blocks Communications network may only accept blocks of up to a certain size OATM 53 octets Ethernet 1526 octets olEEE802.11 2304 octets More efficient error control o Smaller retransmission -Faer(公平 oPrevent station monopolizing medium(防止长期霸占) Smaller buffers Provision of checkpoint and restart/recovery operations4/76 Fragmentation and Reassembly (Segmentation – OSI) • Exchange data between two entities • Characterized as sequence of PDUs of some bounded size • Application level message in the form of datagram or continuous data stream • Reason: - Lower-level protocols may need to break data up into smaller blocks - Communications network may only accept blocks of up to a certain size oATM 53 octets oEthernet 1526 octets oIEEE802.11 2304 octets - More efficient error control oSmaller retransmission - Fairer(公平) oPrevent station monopolizing medium(防止长期霸占) - Smaller buffers - Provision of checkpoint and restart/recovery operations