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<a accesskey="3" href="page.php?w=service_data_unit&amp;p=2">3.Next</a>
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<p>In <a href="page.php?w=Open_Systems_Interconnection">Open Systems Interconnection</a> (OSI) terminology, a <b>service data unit</b> (<b>SDU</b>) is a unit of data that has been passed down from an <a href="page.php?w=OSI_model">OSI layer</a> or <a href="page.php?w=sublayer">sublayer</a> to a lower layer.  This unit of data (SDU) has not yet been <a href="page.php?w=Encapsulation_%28networking%29">encapsulated</a> into a <a href="page.php?w=protocol_data_unit">protocol data unit</a> (PDU) by the lower layer. That SDU is then encapsulated into</p><p>
<a accesskey="3" href="page.php?w=service_data_unit&amp;p=2">3.Next</a>
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