Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if it needs to be delivered to a large number of receivers.
Of these, PIM-SM is the most widely deployed as of 2006[update];[citation needed] SSM and Bidir are simpler and scalable variations developed more recently and are gaining in popularity.
[citation needed] IP multicast operation does not require an active source to know about the receivers of the group.
The IP multicast model has been described by Internet architect Dave Clark as, "You put packets in at one end, and the network conspires to deliver them to anyone who asks.
The term reverse-path forwarding is used to describe this concept of routing packets away from the source, rather than towards the destination.
The following are some common delivery and routing protocols used for multicast distribution: Unicast packets are delivered to a specific recipient on an Ethernet or IEEE 802.3 subnet by setting a specific layer 2 MAC address on the Ethernet packet address.
There are switches that listen to IGMP traffic and maintain a state table of which network systems are subscribed to a given multicast group.
This table is then used to forward traffic destined to a given group only to a limited set of hosts (ports).
If no stations within the basic service set are in power save mode, multicast packets are sent immediately when they arrive.
The DTIM and beacon interval settings can be adjusted to improve multicast performance in wireless networks.
[8] Unlike Ethernet, most traffic in 802.11 is sent reliably using ACKs and NACKs so that radio interference doesn't cause unbearably high packet loss.
IP multicast is an internet communication method where a single data packet can be transmitted from a sender and replicated to a set of receivers.
In contrast, transmission of multicast on media that is point-to-point or point-to-multipoint requires the packet to be replicated for each link.
The replication process should occur in an optimal manner where a distribution tree is built within the network.
The security of the system is based on the ability to control the distribution of the keys only to those legitimate receivers.
For this, the IETF created the Group Domain of Interpretation (GDOI) protocol defined in RFC 6407.
Multicast, by its very nature, is not a connection-oriented mechanism, so protocols such as TCP, which allows for retransmission of missing packets, are not appropriate.
An expanded version, PGM-CC, has attempted to make IP Multicasting more "TCP friendly" by stepping the entire group down to the bandwidth available by the worst receiver.
IP multicast is widely deployed in enterprises, commercial stock exchanges, and multimedia content delivery networks.
[citation needed] In the hospitality industry IP multicast has become common for IPTV distribution in hotels, and in the retail sector IP multicast is now widely used for TV distribution and video advertising applications.
Pay-TV operators and some educational institutions with significant on-campus student housing have deployed IP multicast to deliver one-way streaming media such as high-speed video to large groups of receivers.
These are far less prevalent and are most often relegated to research and education institutions, which often have a greater degree of network capacity to handle the demands.
[citation needed] Another use of multicast within campus and commercial networks is for file distribution, particularly to deliver operating system images and updates to remote hosts.
IP multicast has also seen deployment within the financial sector for applications such as stock tickers and hoot-n-holler systems.
[citation needed] RFC 3170 (IP Multicast Applications: Challenges & Solutions) provides an overview of deployment issues.
IP multicasting was first developed by Steve Deering while at Stanford University for which he received the IEEE Internet Award.
While the MBONE is no longer operational, there is renewed interest in tunneling multicast traffic once again in order to make the service available to a wide array of end users.
CastGate was an attempt from the ETRO-TELE research group at the Vrije Universiteit Brussel to adopt IP multicast on the Internet.
Austrian Internet service provider Telekom Austria offers its digital subscriber line (DSL) customers a TV set-top box that uses multicast addressing in receiving TV and radio broadcasts.