Dependent Dropdown In Service Catalaog Form

Hi Folks,

    I am new to service now and I have a requirement.

I have two dropdown fields in our catalog form. in first dropdown there are two values and values in 2nd dropdown field is coming from a custom table.

The actual requirement is to filter the 2nd dropdown based on first dropdown selection. In our custom table there is an entry of the first dropdown value in all record. So we can filter based on that. But I dont know the process to do that.

Please help me to do the same.

Regards,

Sonu