How to Call Controllers in External Assemblies in an ASP.NET Web form?

I have an Asp.net web form which uses web API to transfer files, when user selects files by an <input type="file" />, an Ajax function is called:

var ajaxRequest = $.ajax({
            type: "POST",
            url: './api/fileupload/uploadHugeFile',
            contentType: false,
            processData: false,
            data: FD
        });

Then in Global.asax, in Application_Start I added:

GlobalConfiguration.Configure(config =>
            {
                config.MapHttpAttributeRoutes();

                config.Routes.MapHttpRoute(
                     name: "DefaultApi",
                     routeTemplate: "api/{controller}/{action}/{id}",
                     defaults: new { id = System.Web.Http.RouteParameter.Optional }
                     );
        });

It's obvious that if I add a class named fileuploadController.cs in App_Code folder and create an uploadHugeFile() public method as an action, it works like a charm.

The problem is when I want to make this a control in company with many other controls to create a single dll file (using class library).

This should be referenced by a namespace then, the question is how can I add that namespace instead of url: './api/fileupload/uploadHugeFile', I thought of something like the namespaces: new[] {"MyNameSpace"} at the end of MapHttpRoute().