KeepAliveTime
The value of KeepAliveTime determines the interval in milliseconds on idle connections before TCP sends a keep-alive transmission (which is used to determine if the other participant in the TCP connection is still responsive).
The default value seems to be 7200000 which equals to 2 hours.
As per Oracle's MOS Note 226202.1, TCP Keep Alive needs to be active to prevent dead sessions from accumulating when SQL*Net Dead Connection Detection (SQLNET.EXPIRE_TIME) is set to 0 or unset in the sqlnet.ora file.
See also section
4.2.3.6 TCP Keep-Alives in
RFC 1122.