An ORA-03113 end-of-file on communication channel error is a very generic error that indicates that the connection has been lost. ORA-03113 is reported by the oracle client processes due to many reasons. ORA-03113 by itself does not indicate the cause of the issue and is accompanied by other messages that are either displayed on the client side or in the oracle database alertlog.

ORA-03113:end-of-file on communication channel
ORA-03113 issues are primarily caused by

Network Issues or Problems
Forceful Disconnection of a Server Session
Oracle Database Crash
Oracle Server Crash
Oracle internal errors like ORA-00600 or ORA-07445 causing aborts
Oracle Client or TNS layer inability to handle the connections
and so on...
An
example of this error is shown below. In this example, the ORA-3113 was
generated by unavailability of Oracle as shown in ORA-01034 which
indicates that either the oracle database session has been killed or the oracle database instance is down or has just crashed.

ORA-03113: end-of-file on communication channel
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist

You as the dba or the user should be aware that this error can be very misleading and is also a catch-all error in the oracle software. Similar errors include the ORA-00600 and you should realize that oracle can just report this error sometimes when ever it has an internal issue.

This error requires analysis as a whole based on the accompanying error messages and should be search in Oracle Metalink. Oracle metalink Note 17613.1 will help you further analyze and understand this issue.

ORA-03113 Cause: The connection between Client and Server process was broken
ORA-03113Action:
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.
ORA-03113 Notes :

Many users have posted here saying that this is occuring in Oracle ERP or SAP Systems, but it has nothing to do with Oracle ERP / Ebusiness Suite or SAP Software itself. It has more to do with the Oracle Database. So, focus on the database and not on the Oracle EBusiness or SAP Software.

If your Organization leverages ITIL manages your own problem database in a problem management system like HPSD or other software, please refer to any prior occurrences and try to investigate if there was any environment specific item that caused it.

ORA 3113 error can also occur in Oracle ERP or SAP or any other system
using an Oracle Backend. It has nothing to do with the software itself,
first start with a vanilla database connection from the location where
the error is being noticed and then drill down the actual cause.