1.  Database crash

2.  Network disconnect

3.  Server terminated the session

4.  Server crash

5.  Oracle internal errors - 600 or 7445

On oracle 10.2.0.3, when issues oerr ora 3113 you get the following:

oerr ora 3113
03113, 00000, "end-of-file on communication channel"
// *Cause: The connection between Client and Server process was broken.
// *Action: There was a communication error that requires further investigation.
//          First, check for network problems and review the SQL*Net setup.
//          Also, look in the alert.log file for any errors. Finally, test to
//          see whether the server process is dead and whether a trace file
//          was generated at failure time.

This is what user was doing:  Using sqlldr to load the database to a simple table with simple control file.

However, intermittenly the ORA-03113: end-of-file on communication  error was reported by the user even though the database was fine, no network issue and there were no other errors reported by any other user.  There were still active connections being made by other users and everything else was working fine. 

here is some snipits:

Ora-7445 reported intermittently during SQL*Loader task to 10.2.0.3 db with no stack captured
and no interruption seen to the database service:

ling_load1.log:

SQL*Loader: Release 10.2.0.3.0 - Production on Sat Aug 28 02:56:59 2010

. . . . . . .

Record 11509334: Rejected - Error on table CUSTDATA.MX_LING2_MAX.

ORA-03113: end-of-file on communication channel

This was also reported in alert log:

Wed Aug 25 03:07:59 2010
Errors in file /u01/app/oracle/admin/PRODDB/udump/proddb_ora_12627.trc:
ORA-07445: exception encountered: core dump [<0x3449825>] [SIGSEGV] [Address not mapped to object] [0x000000018] [] []
Wed Aug 25 03:09:19 2010
Errors in file /u01/app/oracle/admin/PRODDB/udump/proddb_ora_11532.trc:
ORA-07445: exception encountered: core dump [<0x3449825>] [SIGSEGV] [Address not mapped to object] [0x000000018] [] []
.

.

.

After this patch, it fixed it.  

Suprisingly, the ora 3113 ora error doesn't necessarily is a result of a crash or disconnect.  It could also be from iternal errors.

Hope this helps.