I am a bit confused with Multicast. I know receivers that want to join a specific multicast group use IGMP to request to join to the group (lets say 220.127.116.11). My question is on the source side. Does the source also use IGMP to join the group? Or how does the source join the multicast group? If anyone has an example would be appreciated. Thank you.
To add to Joseph's explanation, for PIM specifics are:
https://tools.ietf.org/html/rfc7761#section-3.1 + section 3.2