I found these walkthrough about how to use the WDS and an article for multicasting with WDS. You can read them by the following links:
Windows Deployment Services:
Chapter 13: Multicasting with Deployment Server:
Here are some important notes for your reference:
1. Make sure your network infrastructure supports the Internet Group Management Protocol (IGMP).
2. If you are using the standard boot images (Boot.wim) from the media, it must match (or be newer than) the operating system of the install image.
3. Check whether the Transmission type is Auto-Cast or Scheduled-Cast.