Session timeout Problem.

I am developing an web application in C#.Net. It contains two pages. I the first page it does a lot  of back end processing after that the session key values are sent to the next page for further processing. All the process is going correct when i gave small files for processing.
For large files the session values are not comming to the 2nd page.
I think session experiences the timeout problem. How can I overcome this problem?

Please Help me.
Thanks in Advance
Ramu Medida.