Hello JBSAHU
If you want to spped up the process then just use Ajax.
Just drag and drop the Script Manager on your page
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
For eg this is your City dropdownlist
<asp:DropDownList ID="drpCity" runat="server" AutoPostBack="True"
onselectedindexchanged="drpCity_SelectedIndexChanged" >
</asp:DropDownList>
And this is your College dropdownlist
<asp:UpdatePanel ID="UpdatePanel3" runat="server">
<ContentTemplate>
<asp:Dropdownlist ID="drpCollege" runat="server" Width="195px" >
</asp:Dropdownlist>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="drpCity" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
This will increase the speed of your application...
....Sachin....