First back to the basics. The session data unit / SDU & transport date unit / TDU parameters are located in the tnsnames.ora and listener.ora files. SDU specifies the size of the packets to send over the network. The TDU is the default packet size used within Oracle*Net to group data together. The TDU parameter should ideally be a multiple of the SDU parameter. The default value for both SDU and TDU is 2,048, and the maximum value is 32,767 bytes.
NOTES: Never set SDU greater than TDU coz it wastes network resources and if users r connecting thru dial-up modem, it may want to set SDU and TDU to smaller values.
For an example for a typical parameters.
(SDU = 4202)
(TDU = 4202)
(SID_NAME = ORCL) (provide name during installation)
(GLOBAL_DBNAME = ORCL.WORLD)
(PROTOCOL = TCP)
(HOST = fu.bar)
(PORT = 1521)
(CONNECT_DATA = (SID = ORCL))
Link here for better concept and whole process on Oracle 10g-Linux.