You are hosting the frameset website, a drop down menu is required to navigate the website; but the common DHTML menu are unable to popup its sub menu in another frame page. In this case, you need a special cross-frame menu to navigate your frameset website:
let’s check the cross-frame menu sample:
Two Cross-frame Menus in One Page
All the cross-frame menus are made by Sothink DHTML Menu. If you are interested in building cross-frame menu, download this cross-frame menu builder to create your menu sample.