Internet group management protocolT

Internet group management protocol
The internet group protocol is used to manage group memberships in local area networks.
A multicast router should know all groups having members in the local area network.
Accordingly,the multicast routing protocol subscribes packets for these groups.
The router does not have to know exactly who in the local area network belongs to group.
It is sufficient for the router to know that there is at least one receiver.
The reason is that, when the router transports a packet to the local area network,all stations subscribed to this group receive it automatically.
To avoid unnecessary data transmissions,the router checks periodically for multicast groups that are still desired.
For this purpose,it sends a membership query to all local computers within a specific time interval.