Create A WebService Coding for Cascading DropdownList 1 to Dropdown List 2

Question

Here I also included Sccript Manager & Update Panel as the AJAX Controls

Here i am having 2 dropdown lists in which an item displayed in Dropdown List1 should display the appropriate options in Dropdown List 2 likeways If I select TV in Dropdown List 1 then it should display TV.ON,TV.MUTE & TV.OFF only in Dropdown List 2 & using SQL table named TVOP as the backend.


I need all the whole thing using AJAX & ASP Controls

Please find a Solution For thiss issue

Please Help me how to create a WebService or any related Service File using ASP & AJAX