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About Multicast

Multicast technology represents a network service in which a single flow of data, coming from a given source, can be sent simultaneously to several interested receivers. It is up to the network infrastructure to transport this data flow, replicating it when necessary to all the receivers that show interest in getting these data.

In TCP/IP networks, these receivers are represented by a group address or a multicast address. This group address corresponds to an IP address belonging to the former D class; that is to say, between 224.0.0.0 and 239.255.255.255. Each source sends packages to a group address (for instance: 233.7.124.1), to which several receivers will be associated. These receivers, in turn, can get linked and unlinked in a dynamic way. It is up to the network devices, especially the routers, to determine which of their interfaces have interested receivers in a multicast group and which should receive a copy of the packages sent to that group.

Multicast is aimed at one-to-many and many-to-many applications. In these cases, it shows clear advantages when compared to the unicast and broadcast transmission mechanisms. In unicast, it is necessary that the source replicate several identical data flows in order to transmit them to each of the receivers, generating band waste. On the other hand, the broadcast system sends the data to all the network in an undiscriminated way. It also results in resource waste since it implies transporting the data to all the network stations, even if the number of receivers wishing to have that content is reduced. With multicast, the traffic source sends a single copy of the packages to a multicast group address. The network infrastructure replicates these packages in an intelligent way, directing the data according to the topology of receivers interested in that information.

Among the several applications that can benefit from the use of multicast are: videoconference; distance learning; distribution of software, news and market information; live concerts; database updating; distributed games; concurrent processing; distributed simulations; etc...