IP Multicasting allows IP traffic to be distributed from one source to a number of destinations or from many sources to many destinations. This technique is efficient when sending the same information to many hosts, such as a TV service that distributes content as a payload of IP (termed IPTV). Multicasting employs Multicast Groups which hosts will join (using IGMP ) if they are interested in the content being delivered to that multicast group. As such, part of the IPv4 address space has been reserved for multicast group identification. Multicast data for a particular group will be sent to the multicast address of that group, with the routing network responsible for duplicating multicast content as necessary in order to deliver a copy of the packet to all interested parties.