How to increase session time for login in asp.net

Question

how to increase the session time for logged in user.?

i knw in return i will get reply as in web.config file to be considered as below.

 <authentication mode="Forms">

        <forms loginUrl="CS.aspx"

               protection="All"

               timeout="2880"

               name=".USERLOGINCONTROLAUTH"

               path="/"

               requireSSL="false"

               slidingExpiration="true"

               defaultUrl="CS.aspx"

               cookieless="false"

               enableCrossAppRedirects="false"/>

      </authentication>

in dis above code highlifghted part tells the timeout n cookieless part.

but still session ends early den expected.

as example : gmail.com , facebook.com, etc where in user logged in session remains for longer time.

i need the same.

do give me proper n best solution for expertise please