ORA-03135: connections lost contact Process ID

Good Day All

We are receiving the following error when from our application connecting to Oracle database

ORA-03135: connections lost contact Process ID

We no no firewall between the application server and database , also I have checked

SQL> select * from user_resource_limits a where a.resource_name in ('IDLE_TIME','CONNECT_TIME');

RESOURCE_NAME                    LIMIT

-------------------------------- ----------------------------------------

IDLE_TIME                        UNLIMITED

CONNECT_TIME                     UNLIMITED

SQL>

I have also added in the sqlnet.ora the below

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

SQLNET.EXPIRE_TIME =100

SQLNET.INBOUND_CONNECT_TIMEOUT = 300

SQLNET.SEND_TIMEOUT = 300

SQLNET.RECV_TIMEOUT = 300

No luck , application still receiving the error ORA-03135: connections lost contact Process ID  , any advice for me