Oracle Database B10772-01 Administrator's Manual page 109

REQUESTED
REQUIRED
The default value for each of the parameters is ACCEPTED.
REJECTED
Select this value if you do not elect to enable the security service, even if required by
the other side.
In this scenario, this side of the connection specifies that the security service is not
permitted. If the other side is set to REQUIRED, the connection terminates with error
message ORA-12650. If the other side is set to REQUESTED, ACCEPTED, or
REJECTED, the connection continues without error and without the security service
enabled.
ACCEPTED
Select this value to enable the security service if required or requested by the other
side.
In this scenario, this side of the connection does not require the security service, but
it is enabled if the other side is set to REQUIRED or REQUESTED. If the other side
is set to REQUIRED or REQUESTED, and an encryption or integrity algorithm
match is found, the connection continues without error and with the security
service enabled. If the other side is set to REQUIRED and no algorithm match is
found, the connection terminates with error message ORA-12650.
If the other side is set to REQUESTED and no algorithm match is found, or if the
other side is set to ACCEPTED or REJECTED, the connection continues without
error and without the security service enabled.
REQUESTED
Select this value to enable the security service if the other side permits it.
In this scenario, this side of the connection specifies that the security service is
desired but not required. The security service is enabled if the other side specifies
ACCEPTED, REQUESTED, or REQUIRED. There must be a matching algorithm
available on the other side—otherwise the service is not enabled. If the other side
specifies REQUIRED and there is no matching algorithm, the connection fails.
REQUIRED
Select this value to enable the security service or preclude the connection.
Configuring Network Data Encryption and Integrity for Oracle Servers and Clients 3-7
How To Configure Data Encryption and Integrity