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In computer networking, multicast is the delivery of a message or information
Information
Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...

 to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires it.

Multicast is most commonly implemented in IP multicast
IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...

, which is often employed in Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 (IP) applications of streaming media
Streaming media
Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...

 and Internet television
IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....

s sent to a multicast destination address.

At the Data Link Layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....

, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

 (ATM) point-to-multipoint virtual circuits (P2MP) or Infiniband
InfiniBand
InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...

 multicast.

IP multicast

IP multicast
IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...

 is a technique for one-to-many communication over an IP infrastructure in a network. It scales to a larger receiver population by not requiring prior knowledge of who or how many receivers there are. 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. The nodes in the network take care of replicating the packet to reach multiple receivers only when necessary.

The most common transport layer
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...

 protocol to use multicast addressing is User Datagram Protocol
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 (UDP). By its nature, UDP is not reliable—messages may be lost or delivered out of order. Reliable multicast
Reliable multicast
A reliable multicast protocol is a computer networking protocol that provides a reliable sequence of packets to multiple recipients simultaneously, making it suitable for applications like multi-receiver file transfer or streaming media.-Overview:...

 protocols such as Pragmatic General Multicast
Pragmatic General Multicast
Pragmatic General Multicast is a reliable multicast transport protocol. PGM provides a reliable sequence of packets to multiple recipients simultaneously, making it suitable for applications like multi-receiver file-transfer.-Overview:...

 (PGM) have been developed to add loss detection and retransmission on top of IP multicast.

IP multicast is widely deployed in enterprises, commercial stock exchange
Stock exchange
A stock exchange is an entity that provides services for stock brokers and traders to trade stocks, bonds, and other securities. Stock exchanges also provide facilities for issue and redemption of securities and other financial instruments, and capital events including the payment of income and...

s, and multimedia content delivery networks. A common enterprise use of IP multicast is for IPTV
IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

 applications such as distance learning and televised company meetings.

Other multicast technologies

, most effort at scaling multicast up to large networks have concentrated on the simpler case of single-source multicast, which seems to be more computationally tractable.

Still, the large state requirements in routers make applications using a large number of trees unworkable using IP multicast. Take presence information
Presence information
In computer and telecommunications networks, presence information is a status indicator that conveys ability and willingness of a potential communication partner—for example a user--to communicate...

 as an example where each person needs to keep at least one tree of its subscribers, if not several. No mechanism has yet been demonstrated that would allow the IP multicast model to scale to millions of senders and millions of multicast groups and, thus, it is not yet possible to make fully general multicast applications practical. For these reasons, and also reasons of economics, IP multicast is not, in general, used in the commercial Internet backbone. The increasing availability of WiFi
WIFI
WIFI is a radio station broadcasting a brokered format. Licensed to Florence, New Jersey, USA, the station is currently operated by Florence Broadcasting Partners, LLC.This station was previously owned by Real Life Broadcasting...

 Access Points that support multicast IP is facilitating the emergence of WiCast WiFi Multicast that allows the binding of data to geographical locations.

Explicit Multi-Unicast (XCAST)
XCAST
The explicit multi-unicast is a variation of multicast that supports a great number of little multicast sessions. It is done by adding all the IP addresses in the destination field of the IP header, instead of using a multicast address...

 is an alternate multicast strategy to IP multicast that provides reception addresses of all destinations with each packet. As such, since the IP packet size is limited in general, XCAST cannot be used for multicast groups of large number of destinations. The XCAST
XCAST
The explicit multi-unicast is a variation of multicast that supports a great number of little multicast sessions. It is done by adding all the IP addresses in the destination field of the IP header, instead of using a multicast address...

 model generally assumes that the stations participating in the communication are known ahead of time, so that distribution trees can be generated and resources allocated by network elements in advance of actual data traffic.

Other multicast technologies not based on IP multicast are more widely used. Notably the Internet Relay Chat
Internet Relay Chat
Internet Relay Chat is a protocol for real-time Internet text messaging or synchronous conferencing. It is mainly designed for group communication in discussion forums, called channels, but also allows one-to-one communication via private message as well as chat and data transfer, including file...

 (IRC), which is more pragmatic and scales better for large numbers of small groups. IRC implements a single spanning tree
Spanning tree protocol
The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...

 across its overlay network
Overlay network
An overlay network is a computer network which is built on the top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network...

 for all conference groups. This leads to suboptimal routing for some of these groups however. Additionally, IRC keeps a large amount of distributed states that limit growth of an IRC network, leading to fractioning into several non-interconnected networks. The lesser known PSYC technology uses custom multicast strategies per conference. Also some peer-to-peer
Peer-to-peer
Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

 technologies employ the multicast concept when distributing content to multiple recipients.

See also

  • Ad hoc routing protocol list
    Ad hoc routing protocol list
    An ad-hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad hoc network ....

     for more multicast protocols
  • Anycast
    Anycast
    Anycast is a network addressing and routing methodology in which datagrams from a single sender are routed to the topologically nearest node in a group of potential receivers all identified by the same destination address.-Addressing methodologies:...

  • Broadcast address
    Broadcast address
    A broadcast address is a logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams...

  • CastGate
    CastGate
    CastGate is an attempt from the ETRO-TELE research group at the Vrije Universiteit Brussel to break the chicken and egg problem of multicast adoption on the internet....

    , an attempt at providing connectivity to the multicast network for hosts that have none
  • Comparison of streaming media systems
    Comparison of streaming media systems
    This is a comparison of streaming media systems. A more complete list of streaming media systems is also available.-General:The following tables compare general and technical information for a number of streaming media systems both audio and video...

  • Comparison of video services
    Comparison of video services
    The following tables compare general and technical information for a number of notable video hosting services. Please see the individual products' articles for further information...

  • Content delivery network
    Content Delivery Network
    A content delivery network or content distribution network is a system of computers containing copies of data placed at various nodes of a network....

  • Flooding algorithm
    Flooding algorithm
    A flooding algorithm is an algorithm for distributing material to every part of a connected network. The name derives from the concept of inundation by a flood....

  • Grid casting
    Grid casting
    Grid casting or gridcasting is a file and stream sharing system that cooperates transparently by using idle bandwidth on a user's computer to deliver large scale live or on-demand broadcasts...

  • HTTP(P2P)
    HTTP(P2P)
    HTTP is a protocol based on HTTP. It is intended to improve page and object retrieval performance when web servers suffer server-side congestion. Examples of server-side congestion include the Slashdot and Flash crowd effects...

  • IGMP
  • Internet television
    Internet television
    Internet television is the digital distribution of television content via the Internet...

  • IPTV
    IPTV
    Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

  • List of music streaming services
  • List of streaming media systems
  • Multicast address
    Multicast address
    A multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service...

  • NBMA Nonbroadcast Multiple Access Network
  • Overlay network
    Overlay network
    An overlay network is a computer network which is built on the top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network...

  • Packet forwarding
  • P2PTV
    P2PTV
    The term P2PTV refers to peer-to-peer software applications designed to redistribute video streams in real time on a P2P network; the distributed video streams are typically TV channels from all over the world but may also come from other sources...

  • Protection of Broadcasts and Broadcasting Organizations Treaty
    Protection of Broadcasts and Broadcasting Organizations Treaty
    The WIPO Protection of Broadcasts and Broadcasting Organizations Treaty or the Broadcast Treaty is a treaty designed to afford broadcasters some control and copyright-like control over the content of their broadcasts...

  • Push technology
    Push technology
    Push technology, or server push, describes a style of Internet-based communication where the request for a given transaction is initiated by the publisher or central server...

  • Session Announcement Protocol
    Session Announcement Protocol
    Session Announcement Protocol is a protocol for broadcasting multicast session information.A SAP listening application can listen to the SAP multicast IP address and construct a guide of all advertised multicast sessions...

  • Spanning tree protocol
    Spanning tree protocol
    The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...

  • Streaming media
    Streaming media
    Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...

  • Tri-cast
    Tri-cast
    The term Tri-Cast refers to the simultaneous broadcasting of audio using the three methods of transmission FM broadcasting, online streaming and podcasting....

  • Unicast
    Unicast
    right|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...

  • VideoLAN
    VideoLAN
    VideoLAN is a project that develops software for playing video and other media formats across a local area network . It originally developed two programs for media streaming, VideoLAN Client and VideoLAN Server , but most of the features of VLS have been incorporated into VLC, with the result...

    , a free software
    Free software
    Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

     multicasted video streaming application
    Application software
    Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

  • Web television
    Web television
    Web television, also commonly referred to as web TV, not to be confused with WebTV, Internet television or catch up TV, is an emerging genre of digital entertainment that is distinct from traditional broadcast television...

  • Webcast
    Webcast
    A webcast is a media presentation distributed over the Internet using streaming media technology to distribute a single content source to many simultaneous listeners/viewers. A webcast may either be distributed live or on demand...

  • XCAST
    XCAST
    The explicit multi-unicast is a variation of multicast that supports a great number of little multicast sessions. It is done by adding all the IP addresses in the destination field of the IP header, instead of using a multicast address...



External links

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