segmentation and reassembly (SAR)

In a packet-switched telecommunication network, segmentation and reassembly (SAR, sometimes just referred to as segmentation) is the process of breaking a packet into smaller units before transmission and reassembling them into the proper order at the receiving end of the communication. Packets are made smaller to speed them through the network and specifically because of specified packet size restrictions in a given path. In the Open Systems Interconnection (OSI) model, SAR is performed in the Transport layer at both ends. A transport protocol determines the size of the smallest maximum protocol data unit (PDU) supported by any of the involved networks, and segments the packets accordingly.

SAR is used for asynchronous transfer mode (ATM) communications. In TCP/IP, the same process is known as fragmentation.

This was last updated in April 2007

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