SQL.EXPIRE_TIME in sqlnet.ora I have set sql.expire_time parameter to 10 which recommends me to keep in my two node RAC database. At times, my application gets the error ORA-3135, therefore I suspect that this parameter could have some role to play here.. 

What exactly does this parameter do? Does it have anything to do with the error im facing?

I do not have any firewalls between my database and app server.
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.