Oracle ORAIn Feburary 2016 28,

In Feburary 2016 28,
Oracle servers run both an Oracle database and listener process. One Oracle listener, which you can configure to support multiple databases, receives and manages client connection requests. If the listener receives more requests than it can handle, user requests can time out; in this case, restarting the listener will resolve the error.
Database Connection
Oracle database connection requests aren't processed unless they include authentication information such as a user name, password and the name of the Oracle service. If the authentication services aren't running or the password name is incorrect, communication efforts will fail. Similarly, if the Oracle database locks up and fails to respond to database queries, Oracle will report a failure. According to “Oracle Dba on Unix and Linux” by Michael Wessler, if the Oracle database itself crashes, the program's background processes such as PMON and SMON will terminate, and you will receive an “ORA-12637 packet receive failed” or 'TNS: packet writer failure' message.
Server & Hardware
The Tnsnames.ora file on your computer contains references to Oracle servers with which it regularly communicates. If a server name is incorrect or incomplete, Oracle can't connect to it. If the port referenced in the Tnsnames.ora file isn't open, you may see an “ORA-12637 packet receive failed” message. Router and network interface controller, or NIC, card failures also cause this problem, as can insufficient server disk input/output and system memory.
Communication
Packet communication errors can occur when a network's data traffic is so great that the time-out limit hits before your computer receives a response from the Oracle server. If the packet sizes are too large for the server to process, you can change the transport date unit, or TDU, parameters in the Tnsnames.ora file. If a network router fails and the data packets are routed to other nodes that cannot handle the load, error messages will result. You also might see errors from a malicious denial-of-service attack, or hackers turning off the Oracle listener, although the latter appears as a process failure.
In Feburary 2016 28,