Oracle12c: Session Data Unit(SDU)

Session Data Unit(SDU) is the session layer responsible for  sending/receiving data from transport layer.  See table below for OSI diagram. Generally increasing the value of SDU can result in improved performance, efficient network utilization when transmitting large amounts of data.  However until Oracle 11g  the SDU size was limited  to 64K. Starting with Oracle12c, support for  SDU  is increased to 2M thereby allowing efficient use of  high bandwidth network.

SDU can be set at  database level by configuring DEFAULT_SDU_SIZE parameter in sqlnet.ora or SDU listener.ora parameter. On the client size SDU can set be by configuring DEFAULT_SDU_SIZE parameter in client sqlnet.ora or SDU tnsnames.ora parameter.

Note: SDU size  actually used is the smaller of  the client and server value.

OSI Model

Layer# Name Description
7 Application Standard communication services and applications that everyone can use
6 Presentation Layer that takes data from application and presents it  in a format that is recognized by other layers; Functions like character set conversion is done by this layer
5 Session Establishes, maintain & end connections
4 Transport Delivers data without errors in sequence and no data loss or duplications. Large messages can be delivered but is constrained by message size limits imposed by the network layer.
3 Network Controls the way data will be sent to recipient ; Factors like the physical path the data should take based  etc are performed by this layer. This layer translates logical addresses, or names, into physical addresses, performs routing
2 Data Link Handles the transfer of data across the network ; It  establishes and terminates the logical link between two nodes.
1 Physical The lowest layer of the OSI  is generally concerned with the transfer of data medium like optical or electrical medium etc.
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