To transmit a single message to a select group of recipients. A simple example of multicasting is sending an e-mail message to a mailing list. Teleconferencing and videoconferencing also use multicasting, but require more robust protocols and networks.
Standards are being developed to support multicasting over a TCP/IP network such as the Internet. These standards, IP Multicast and Mbone, will allow users to easily join multicast groups.
Note that multicasting refers to sending a message to a select group whereas broadcasting refers to sending a message to everyone connected to a network.
The terms multicast and narrowcast are often used interchangeably, although narrowcast usually refers to the business model whereas multicast refers to the actual technology used to transmit the data.
Introduction to IP Multicast routing This paper, from 3Com, describes the benefits of multicasting, the Multicast Backbone (MBONE), Class D addressing, and the operation of the Internet
Group Management Protocol (IGMP) and explores a number of different algorithms that may potentially be employed by multicast routing protocols.
Multicast Routing This page, from Cisco Systems, describes design considerations for multipoint communications.
