ASP.net Page session timeout not working -

i having strange issue, no matter not stop page timing out. here scenario have couple of pages lots of data, client selects check boxes, select values various drop downs etc. times clients spend more 30 minutes selecting/setting values. when click on submit page timeouts , takes them login page. when login in set values gone. frustrating. 1 think selecting drop downs, entering data text boxes etc. considered doing activity on page should keep session alive. doesn't seem case. have tried increasing timeout value out success.

here code web.config

    <authentication mode="forms">         <forms loginurl="~/public/login.aspx" slidingexpiration="true" timeout="200" protection="all" name="sampleapp"/>     </authentication>     <sessionstate mode="inproc" cookieless="false" timeout="200"/>     <httpruntime maxrequestlength="204800" executiontimeout="3600" /> 

we have machinekey tag setup encryption keys.

appreciate help. in advance.

in asp.net, client-side activity not involve posting/sending data web server has no effect on forms authentication sliding expiration time out. if users selecting values in drop down without posting , scrolling through big page, not extend timeout period.

however, if problem can write empty asmx web service method nothing , returns void. call page's javascript code every 5 minutes using javascript interval timer i.e. setinterval. call send request web server , users not time out happening now. also, call light , quick users never know it's happening.