On database server:

Add (SDU = 32768) to SID_DESC section for the instance under SID_LIST_LISTENER in listener.ora
SID_LIST_edwt =
  (SID_LIST =
    (SID_DESC =
      (SDU = 32768)
      (GLOBAL_DBNAME= edwt)
      (ORACLE_HOME= /app/oracle/product/edwt/8.1.6.3)
      (SID_NAME = edwt)
    )

Add this to sqlnet.ora (temporarily, for verification purpose only):
trace_level_server=16
trace_directory_server=/tmp
trace_file_server=server.trc


On the client:

Add (SDU = 32768) to DESCRIPTION section in tnsnames.ora:
edwt =
  (DESCRIPTION =
    (SDU = 32768)
    (ADDRESS =
                (PROTOCOL = tcp)
                (Host = janus.sgld.uc.com)
                (Port = 1526)
    )
    (CONNECT_DATA =
          (SID = edwt)
    )
  )

Add this sqlnet.ora (temporarily, for verification purpose only):
trace_level_client=16
trace_directory_client=/tmp
trace_file_client=client.trc
trace_unique_client = true

On server, lsnrctl reload

To verify,

Run a query in sqlplus. Check the trace files on server and client. Also check by

ps -ef | grep LOCAL or grep SDU on the server


truss -t pread -p <pid> (on Linux use strace) should show 32768 bytes are read
at a time when the file descriptor (first arg in pread()) is the SQL*Net
socket.