Multicasting vs. unicasting or broadcasting

Multicasting differs in certain important respects from unicasting and broadcasting as a transmission technique.

A distinction can be made between multicasting traffic at the network layer (based on special class D IP addresses) and at the data link layer (based on multicast MAC addresses). The general differences how multicasting can be distinguished from unicasting and broadcasting are highlighted in the following sections.

Multicasting vs. unicasting

In unicasting, the transmitted datagrams are intended only for a single host having a unique address. In multicasting, the data is transmitted likewise to a single address (that is, the multicast group address), but the actual data reaches all hosts that belong to the group identified by the multicast address. This way the data needs only to be sent once, and not separately to each host. This naturally saves bandwidth.

Multicasting vs. broadcasting

In broadcasting, the data is sent from a host to other hosts within a given network, so they must all use their resources to process the data. In contrast, in multicasting, the hosts that do not belong to a multicast group do not have to use their resources for multicast data. Moreover, multicasting is not restricted to a single network. Hosts on remote networks can receive IP multicast datagrams if they belong to a specific host group, and that there are multicast routers forwarding the traffic. Thus, IP multicasting can in principle be used globally whereas broadcasting is limited to a single network.