Internet multicasting is an IP-based networking technique used to broadcast various media types from a single source to multiple end-points.
Unlike the classic peer-to-peer internetworking which consumes large amounts of bandwidth, multicasting makes efficient use of bandwidth
because it implements a mainly asynchronous, one-to-many networking model, as illustrated here.
But many applications relays the same information to many.
Examples:Radio, TV, Conferencing, Distribution of control information, Distributed games
But in fact, few use native multicasting today, except control and IPTV
IP Multicast Summary
The Internet abstraction of hardware multicasting.
Prime architect: Steve Deering
Group addresses (class D)
Exploits multicast-capable networking hardware if available
Best-effort delivery semantics (unreliable)
Receiver-based multicast: Senders send to any group, Receivers join groups
Dynamic group membership: . Hosts leave and join groups dynamically
. (S, G) . specific sender S to group G
. (*, G) . all senders to group G
There is no multicast-TCP. Why?
Problem: how to deal with all acknowledgments: TCP-like ACKs would cause ACK-implosions
Acknowledgment aggregation points - keep copies of data for retransmission cases
Use NACKs (Negative acknowledgements)
Send redundant information so that lost information can be recomputed from the information received, i.e. use forward error correcting codes (FEC)
There is no general-purpose reliable multicast protocol for the Internet: Only application-specific
Multicasting supports video streaming, radio simulation, and Webcasts. Teleconferencing and videoconferencing also use multicasting, but they require more robust protocols and wider bandwidth.
Internet protocol (IP) multicasting is a variation on network multicasting. Unlike traditional Internet traffic that requires separate connections for each source-destination pair, IP multicasting allows many recipients to share the same source.
This means that just one set of data packets is transmitted for all the destinations. Thus for large amounts of data, IP multicasting is more efficient than normal Internet transmissions because the server can broadcast a message to many recipients simultaneously.
Standards are being developed to support multicasting over a TCP/IP network such as the Internet. These standards will allow users to join multicast groups easily.
There are several vendors of multicasting servers. Consider your needs carefully and compare their offerings before deciding on any one product.
The next lesson wraps up the module.