Internet multicasting is a potentially powerful tool that involves sending individual streaming messages via video or audio, as well as text, to a selective group of people. It differs from unicasting (one-to-one) and broadcasting (one-to-all – broadcasts are blocked by routers, but can be received by anyone who knows the protocol for reception), in that a single user can select the specific people in the group who will receive the packet of content; the end user has to request to be involved in the multicast.
This can be achieved with great efficiency, lining a select group of people with large or small participants globally.
The multicasting process is more efficient than other forms of broadcasting since the path for reception is initiated on the user end. When the user requests to be a part of the multicast, routers open up from the user end in a progression towards the source, avoiding the involvement of routers that would otherwise block the multicast. In other words, only the routers that are necessary for conveying the packet are used in creating the multicast path to the user who requests it. Routers that do not have hosts who have requested the multicast, it is excluded from the tree of routers connected to the source. This provides greater efficiency and quality on the user end, as well as expediting bandwidth.
The protocol use for multitasking is called RTP (Real-time Transport Protocol) and it operates simultaneously with multicasting in order to send streaming audio, video, and other information over multicast networks. RTP determines how to convey information to the participants of the multicasting groups as well as monitor content quality as it is being delivered.
The IP Multicast protocol is a standard distribution protocol for delivering content to multiple participants. While the individual members of the participating group can easily change, depending on whether or not a host decides to join, stay with, or leave a particular group, and can also become a source by resending packets to another particular multicast group, as long as routers are "multicast enabled."
IP Multicast uses class D addressing. This is a unique form of an IP address that is specifically designed for multicasting.