Passing & keeping values between forms

Hi,

I am struggling how to do this.

I have a site master page which has a menu. The menu has a link to an asp.net page which has a link in a day cell. My problem is as below.

If I click on a menu. the query string collects an employee ID via url param passing in Employee event page.

Employee event page has a calendar  which users can add/delete/update events. If users add or modify an event, it will return back to Employee event asp.net. After that users lost all inforamtion such as employee id and current selected year month. is there any good solution for keeping the values? which is best, using session variable or viewState etc?

1. site.master

    Menu: http://localhost/EmployeeEvent.aspx?employeeID=2222

 2. Employee Event.aspx

    Calendar control->select Dec ...