SQL.EXPIRE_TIME in sqlnet.ora
That is for DCD (Dead Connection Detection). 

Dead Connection Detection

SQLNET.EXPIRE_TIME

If a client suddenly "disappears", e.g it's powered off, or loses network, the connection still remains open on the database server, with the corresponding session as well.

When the above parameter is set, the database probes the connections to check if they are still alive. The above parameter controls the frequency of this check (in minutes).

It is a common misconception that setting this parameter to 10 results in any dead session being cleaned up in at most 10 minutes, but that is not how it works, read the above PDF for explanation.