LAN data transmissions fall into three Classifications : Unicast, Multicast, and Broadcast. In each type of transmission, a single packet is sent to one or more nodes.
Unicast is a one to one transmission method in which the network carries a message to one receiver, such as form a server to a LAN workstation. In a Unicast environment, even though multiple users might ask for the same information from the same server at the same time, such as video clip, duplicate data streams are sent. Unicast sends separate data streams to each computer requesting the data, In turn flooding the network with traffic.
Multicast is a one to many transmission method in which the network carries a message to multiple receivers at the same time. Multicast is similar to abroadcasting, except that multicasting means sending to everybody, whether they want the traffic or not. When sending a large number of data, multicast saves considerable network bandwidth because the bulk of the data is sent only once. The data travels from its source through major backbones and is then multiplied, or distributed out, at switching points closer to the end users. This is more efficient then a unicast system, in which the data is copied and for warded to each recipient.
Broadcast is a one to all transmission method in which the network carries a packet to all devices at the same time, but a particular machice for which the packet is intended accepts it.