IP Multicast
Encyclopedia
IP multicast is a method of sending 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) 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 to a group of interested receivers in a single transmission. It is often employed for 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...

 applications on the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 and private network
Private network
In the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...

s. The method is the IP-specific version of the general concept of multicast
Multicast
In computer networking, multicast is the delivery of a message or information 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...

 networking. It uses specially reserved 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...

 blocks in IPv4
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

 and IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

. In IPv6, IP multicast addressing replaces broadcast addressing as implemented in IPv4.

History

IP multicast was first standardized in 1986. Its specifications have been revised to include group management and administratively scoped addresses.

Technical description

IP multicast is a technique for one-to-many
One-to-many
One-to-many may refer to:* Multivalued function, a one-to-many function in mathematics* Fat link, a one-to-many link in hypertext* Point-to-multipoint communication, communication which has a one-to-many relation-See also:*One-to-one...

 and many-to-many
Many-to-many
Many-to-many is a term that describes a communication paradigm and an associated media form. It is the third of three major Internet computing paradigms...

 real-time 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 (typically network switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...

es and routers) take care of replicating the packet to reach multiple receivers such that messages are sent over each link of the network only once. The most common low-level 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.

Key concepts in IP multicast include an IP multicast group address, a multicast distribution tree and receiver driven tree creation.

An IP multicast group address is used by sources and the receivers to send and receive multicast messages. Sources use the group address as the IP destination address in their data packets. Receivers use this group address to inform the network that they are interested in receiving packets sent to that group. For example, if some content is associated with group 239.1.1.1, the source will send data packets destined to 239.1.1.1. Receivers for that content will inform the network that they are interested in receiving data packets sent to the group 239.1.1.1. The receiver joins 239.1.1.1. The protocol typically used by receivers to join a group is called the Internet Group Management Protocol
Internet Group Management Protocol
The Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships....

 (IGMP).

With routing protocols based on shared trees, once the receivers join a particular IP multicast group, a multicast distribution tree is constructed for that group. The protocol most widely used for this is Protocol Independent Multicast
Protocol Independent Multicast
Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet...

 (PIM). It sets up multicast distribution trees such that data packets from senders to a multicast group reach all receivers which have joined the group. For example, all data packets sent to the group 239.1.1.1 are received by receivers who joined 239.1.1.1. There are variations of PIM implementations: Sparse Mode
Sparse multicast
Protocol Independent Multicast - Sparse-Mode is a protocol for efficiently routing Internet Protocol packets to multicast groups that may span wide-area and inter-domain internets...

 (SM), Dense Mode
Dense multicast
Dense mode multicast is one mode that multicast can use to construct a tree for sending packets to the multicast subscribers. It is the opposite of sparse multicast....

 (DM), Source Specific Mode
Source-specific multicast
Source-specific multicast is a method of delivering multicast packets in which the only packets that are delivered to a receiver are those originating from a specific source address requested by the receiver...

 (SSM) and Bidirectional Mode (Bidir, or Sparse-Dense Mode, SDM). Of these, PIM-SM is the most widely deployed ; SSM and Bidir are simpler and scalable variations developed more recently and are gaining in popularity.

IP multicast operation does not require an active source to know about the receivers of the group. The multicast tree construction is receiver driven and is initiated by network nodes which are close to the receivers. IP multicast scales to a large receiver population. The IP multicast model has been described by Internet architect Dave Clark
David D. Clark
David Dana Clark is an American computer scientist. He graduated from Swarthmore College in 1966. In 1968, he received his Master's and Engineer's degrees in Electrical Engineering from the Massachusetts Institute of Technology, where he worked on the I/O architecture of Multics under Jerry...

 as, "You put packets in at one end, and the network conspires to deliver them to anyone who asks."

IP multicast creates state information per multicast distribution tree in the network. If a router is part of 1000 multicast trees, it has 1000 multicast routing and forwarding entries. On the other hand, a multicast router does not need to know how to reach all other multicast trees in the Internet. It only needs to know about multicast trees for which it has downstream receivers. This is key to scaling multicast-addressed services. It is very unlikely that core Internet routers would need to keep state for all multicast distribution trees, they only need to keep state for trees with downstream membership. In contrast, a unicast router needs to know how to reach all other unicast addresses in the Internet, even if it does this using just a default route. For this reason, aggregation is key to scaling unicast routing. Also, there are core routers that carry routes in the hundreds of thousands because they contain the Internet routing table.

Addressing

There are four forms of IP addressing, each with its own unique properties.
  • 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:...

    : The most common concept of an IP address is in unicast addressing, available in both IPv4
    IPv4
    Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

     and IPv6
    IPv6
    Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

    . It normally refers to a single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but it is not a one-to-one correspondence. Some individual PCs have several distinct unicast addresses, each for its own distinct purpose. Sending the same data to multiple unicast addresses requires the sender to send all the data many times over, once for each recipient.

  • Broadcast: In IPv4 it is possible to send data to all possible destinations ("all-hosts broadcast"), which permits the sender to send the data only once, and all receivers receive a copy of it. In the IPv4 protocol, the address 255.255.255.255 is used for local broadcast. In addition, a directed (limited) broadcast can be made by combining the network prefix with a host suffix composed entirely of binary 1s. For example, the destination address used for a directed broadcast to devices on the 192.0.2.0/24 network is 192.0.2.255. IPv6 does not implement broadcast addressing and replaces it with multicast to the specially-defined all-nodes multicast address.

  • Multicast
    Multicast
    In computer networking, multicast is the delivery of a message or information 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...

    : A multicast address is associated with a group of interested receivers. In IPv4, addresses 224.0.0.0 through 239.255.255.255 (the former Class D
    Classful network
    A classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the address space for Internet Protocol Version 4 into five address classes. Each class, coded in the first four bits of the...

     addresses) are designated as multicast addresses. IPv6 uses the address block with the prefix ff00::/8 for multicast applications. In either case, the sender sends a single datagram from its unicast address to the multicast group address and the intermediary routers take care of making copies and sending them to all receivers that have joined the corresponding multicast group.

  • 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:...

    : Like broadcast and multicast, anycast is a one-to-many routing topology. However, the data stream is not transmitted to all receivers, just the one which the router decides is the "closest" in the network.Anycast implementations typically operate using the shortest-path metric of BGP routing
    Border Gateway Protocol
    The Border Gateway Protocol is the protocol backing the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems . It is described as a path vector protocol...

     and not take into account congestion or other attributes of the path.
    Anycast is useful for global load balancing and is commonly used in DNS
    Domain name system
    The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...

     communications.

Protocols and applications

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.

Since multicast is a different transmission mode from unicast, only protocols designed for multicast can be sensibly used with multicast.

Most of the existing application protocols that use multicast run on top of the 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). In many applications, the Real-time Transport Protocol
Real-time Transport Protocol
The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...

 (RTP) is used for framing of multimedia content over multicast; the Resource Reservation Protocol
Resource Reservation Protocol
The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...

 (RSVP) may be used for bandwidth reservation in a network supporting multicast distribution.

On the local network, multicast delivery is controlled by IGMP (on IPv4
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

 network) and MLD
Multicast Listener Discovery
Multicast Listener Discovery is a component of the Internet Protocol Version 6 suite. MLD is used by IPv6 routers for discovering multicast listeners on a directly attached link, much like IGMP is used in IPv4. The protocol is embedded in ICMPv6 instead of using a separate protocol. MLDv1 is...

 (on IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

 network); inside a routing domain
Routing domain
In computer networking, a routing domain is a collection of networked systems that operate common routing protocols and are under the control of a single administration...

, PIM
Protocol Independent Multicast
Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet...

 or MOSPF are used; between routing domains, one uses inter-domain multicast routing protocols, such as MBGP.

A number of errors can happen if packets intended for unicast are accidentally sent to a multicast address; in particular, sending ICMP packets to a multicast address has been used in the context of DoS attacks as a way of achieving packet amplification.

IP multicast protocols

  • Internet Group Management Protocol
    Internet Group Management Protocol
    The Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships....

     (IGMP)
  • Protocol Independent Multicast
    Protocol Independent Multicast
    Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet...

     (PIM)
  • Distance Vector Multicast Routing Protocol
    Distance Vector Multicast Routing Protocol
    The Distance Vector Multicast Routing Protocol , defined in RFC 1075, is used to share information between routers to facilitate the transportation of IP Multicast packets among networks...

     (DVMRP)
  • Multicast Open Shortest Path First
    Multicast Open Shortest Path First
    The Multicast Open Shortest Path First protocol is an extension to the Open Shortest Path First protocol to support multicast routing, allowing routers to share information about group memberships....

     (MOSPF)
  • Multicast BGP
    Multicast BGP
    Multiprotocol Extensions for BGP , sometimes referred to as Multiprotocol BGP or Multicast BGP and defined in IETF RFC 4760, is an extension to Border Gateway Protocol that allows different types of addresses to be distributed in parallel...

     (MBGP)
  • Multicast Source Discovery Protocol
    Multicast Source Discovery Protocol
    Multicast Source Discovery Protocol is a Protocol Independent Multicast family multicast routing protocol defined by Experimental RFC 3618. MSDP interconnects multiple IPv4 PIM Sparse-Mode domains which enables PIM-SM to have Rendezvous Point redundancy and inter-domain multicasting.MSDP uses...

     (MSDP)
  • Multicast Listener Discovery
    Multicast Listener Discovery
    Multicast Listener Discovery is a component of the Internet Protocol Version 6 suite. MLD is used by IPv6 routers for discovering multicast listeners on a directly attached link, much like IGMP is used in IPv4. The protocol is embedded in ICMPv6 instead of using a separate protocol. MLDv1 is...

     (MLD)
  • GARP Multicast Registration Protocol (GMRP)
  • Multicast DNS
    Multicast DNS
    Multicast DNS is a way of using familiar DNS programming interfaces, packet formats and operating , in a small network where no conventional DNS server has been installed....

     (mDNS)

Routing

Each host (and in fact each application on the host) that wants to be a receiving member of a multicast group (i.e. receive data corresponding to a particular multicast address) must use the Internet Group Management Protocol
Internet Group Management Protocol
The Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships....

 (IGMP) to join. Adjacent routers also use this protocol to communicate.

In unicast routing, each router examines the destination address of an incoming packet and looks up the destination in a table to determine which interface to use in order for that packet to get closer to its destination. The source address is irrelevant to the router.

However, in multicast routing, the source address (which is a simple unicast address) is used to determine data stream direction. The source of the multicast traffic is considered upstream. The router determines which downstream interfaces are destinations for this multicast group (the destination address), and sends the packet out through the appropriate interfaces. The term reverse path forwarding
Reverse path forwarding
Reverse path forwarding is a technique used in modern routers for the purposes of ensuring loop-free forwarding of multicast packets in multicast routing and to help prevent IP address spoofing in unicast routing.- Multicast RPF :...

is used to describe this concept of routing packets away from the source, rather than towards the destination.

Layer 2 delivery

Unicast packets are delivered to a specific recipient on an Ethernet or IEEE 802.3 subnet by setting a specific layer 2 MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...

 on the Ethernet packet address. Broadcast packets make use of a broadcast MAC address (FF:FF:FF:FF:FF:FF), which includes setting the broadcast/multicast bit in the address. The IANA
Internet Assigned Numbers Authority
The Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...

 owns the OUI
Organizationally Unique Identifier
An Organizationally Unique Identifier is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated Registration Authority...

 MAC address 01:00:5e, therefore multicast packets are delivered by using the Ethernet MAC address range 01:00:5e:00:00:00 - 01:00:5e:7f:ff:ff. This is 23 bits of available address space. The first octet (01) includes the broadcast/multicast bit.
The lower 23 bits of the 28-bit multicast IP address are mapped into the 23 bits of available Ethernet address space. This means that there is ambiguity in delivering packets. If two hosts on the same subnet each subscribe to a different multicast group whose address differs only in the first 5 bits, Ethernet packets for both multicast groups will be delivered to both hosts, requiring the network software in the hosts to discard the unrequired packets.

For IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

 Multicast addresses, the Ethernet MAC is derived by the four low-order octets OR'ed with the MAC 33:33:00:00:00:00, so for example the IPv6 address FF02:DEAD:BEEF::1:3 would map to the Ethernet MAC address 33:33:00:01:00:03.

Switches that do not understand multicast addresses broadcast traffic sent to a multicast group to all the members of a LAN; in this case the system's network card (or operating system) has to filter the packets sent to multicast groups they are not subscribed to.

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). This is done through the use of IGMP snooping
IGMP snooping
IGMP snooping is the process of listening to Internet Group Management Protocol network traffic. IGMP snooping, as implied by the name, is a feature that allows a network switch to listen in on the IGMP conversation between hosts and routers. By listening to these conversations the switch...

.

Additionally, some switches with layer 3 capabilities can act as an IGMP querier. In networks where there is no router present to act as a multicast router a switch with IGMP snooping enabled can be used to generate the needed IGMP messages to get users to subscribe to multicast traffic.

Reliable multicast

Multicast, by its very nature, is not a connection-oriented mechanism, so protocols such as TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

, which allows for retransmission of missing packets, are not appropriate. For applications such as streaming audio and video, the occasional dropped packet is not a problem. But for distribution of critical data, a mechanism is required for requesting retransmission.

One such scheme, proposed by Cisco, is PGM (originally Pretty Good Multicasting, but changed for trademark reasons to 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:...

), documented in RFC 3208. In this scheme, multicast packets have sequence numbers and when a packet is missed a recipient can request that the packet be re-multicast with other members of the Multicast group ignoring the replacement data if not needed. 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.

Two other schemes documented by the Internet Engineering Task Force
Internet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...

 (IETF) are NACK-Oriented Reliable Multicast (NORM), documented in RFC 3940 and RFC 5401, and File Delivery over Unidirectional Transport (FLUTE), documented in RFC 3926. Open-source, in addition to proprietary, implementations exist for these. Other such protocols exist, such as Scalable Reliable Multicast, and are defined by a variety of sources. Such protocols vary in the means of error detection, the mechanisms used in error recovery, the scalability of such recovery and the underlying ideas involved in what it means to be reliable. A list of reliable multicast protocols from the ACM SIGCOMM Multicast Workshop, August 27, 1996, documents a number of approaches to the problem.

Independent groups like the Internet Protocol Multicast Standards Initiative (IPMSI) have claimed that the lack of a truly scalable Secure Reliable IP Multicast protocol like the proposed Secure Multicast for Advanced Repeating of Television (SMART)
SMART Multicast
SMART Multicast is an experimental method of Secure Reliable IP Multicast. It allows a user to forward IP datagrams to an unlimited group of receivers...

 have hampered the adoption of IP Multicast in inter-domain routing. The lack of a widely adopted system that has AES level security and scalable reliability have kept mass media transmissions of sporting events (like the Super Bowl) and/or breaking news events from being transmitted on the Public Internet.

Reliable IP Multicasting protocols, such as PGM and SMART, are experimental; the only standards-track protocol is NORM (the standards-track revision of RFC 3941 is specified in RFC 5401, the standards-track revision of RFC 3940 is specified in RFC 5740).

Wireless (802.11) considerations

An 802.11 wireless network will handle multicast traffic differently, depending on the configuration of Delivery Traffic Indication Message (DTIM), and beacon interval settings. If no stations within the basic service set are in power save mode, multicast packets are sent immediately when they arrive. If there are one or more stations in power save mode, access points then only delivers multicast traffic after each DTIM interval, and transmit at one of the supported rates in the basic rate set. In most retail wireless access points/routers, this interval is 102.4 ms (DTIM=1 (beacon interval)) and the transmit rate is either 1 Mbps or 6 Mbps, depending on the operating band and protection mode. As a result, the DTIM and beacon interval settings should be adjusted for optimum performance when implementing multicast in wireless networks.

Implementations

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. Additionally, there have been some uses of audio and video conferencing using multicast technologies. 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. Some technical conferences and meetings are transmitted using IP multicast. Until recently many of the sessions at the IETF meetings were delivered using multicast.

Another use of multicast within campus and commercial networks is for file distribution, particularly to deliver operating system images and updates to remote hosts. The key advantage of multicast boot images over unicasting boot images is significantly lower network bandwidth usage.

IP multicast has also seen deployment within the financial sector for applications such as stock ticker
Stock Ticker
Stock Ticker is a now out of print board game that was popular upon its release and is still played today. It was released by Copp-Clark Publishing, a venerable Canadian publisher.-Game play:...

s and hoot-n-holler
Hoot-n-holler
Hoot-n-holler is a type of telecommunications system where you have a permanent open circuit between two or more parties. Anyone can speak at any time over a distance without having to pick up a phone or press a button...

 systems.

While IP multicast has seen some success in each of these areas, IP multicast is not widely deployed and is generally not available as a service for the average end user. There are at least two primary factors for the lack of widespread deployment, both somewhat related to the other. On the one hand, forwarding multicast traffic, particularly for two-way communication, requires a great deal of protocol complexity. On the other hand, there are a number of additional operational concerns in being able to run a multicast network successfully, largely stemming from the complexity of a widely-deployed implementation, not the least of which is the enabling of additional avenues of failure, particularly from denial-of-service attacks. Many of these issues are covered in further detail below.

RFC 3170 (IP Multicast Applications: Challenges & Solutions) provides an overview of deployment issues.

History and milestones

IP multicasting was first developed by Steve Deering
Steve Deering
Stephen Deering is a former Technical Leader at Cisco Systems, where he worked on the development and standardization of architectural enhancements to the Internet Protocol...

 while at Stanford University for which he received the IEEE Internet Award

The MBONE
Mbone
Mbone was an experimental backbone for IP multicast traffic across the Internet developed in the early 1990s. It required specialized hardware and software...

 was a long-running experimental approach to enabling multicast between sites through the use of tunnels. 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.

Commercial deployment

Starting in 2005, the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 has begun encouraging UK-based Internet service provider
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...

s to adopt multicast-addressable services in their networks by providing BBC Radio at higher quality than is available via their 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:...

-addressed services. This has also been supported by a variety of commercial radio networks, including GCAP
GCAP
GCAP may refer to:* Global Call to Action Against Poverty, a global anti-poverty movement/coalition* GCap Media - British commercial radio company* Grupo Capoeira Angola Pelourinho - Capoeira group by Mestre Moraes* Guanylate cyclase-activating protein...

, EMAP
EMAP
Emap Limited is a British media company, specialising in the production of business-to-business magazines, and the organisation of business events and conferences...

, and Virgin Radio
Virgin Radio
Absolute Radio is one of the UK's three Independent National Radio stations. The station rebranded to its current name at 7.45am on 29 September 2008.The station is based in London and plays popular rock music...

.

The German public-service broadcasters ARD
ARD (broadcaster)
ARD is a joint organization of Germany's regional public-service broadcasters...

 and ZDF
ZDF
Zweites Deutsches Fernsehen , ZDF, is a public-service German television broadcaster based in Mainz . It is run as an independent non-profit institution, which was founded by the German federal states . The ZDF is financed by television licence fees called GEZ and advertising revenues...

 and the Franco-German network Arte
Arte
Arte is a Franco-German TV network. It is a European culture channel and aims to promote quality programming especially in areas of culture and the arts...

 offer their TV program multicasted on several networks. Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

n Internet service provider Telekom Austria
Telekom Austria
Telekom Austria is a provider of a range of fixed line, mobile, data, and Internet communications services. The company has a 100 per cent share in telecommunications provider A1 Telekom Austria....

 offers its Digital Subscriber Line
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...

 (DSL) customers a TV set-top box that uses multicast addressing in receiving TV and radio broadcasts. In Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, T-Home, a brand of Deutsche Telekom
Deutsche Telekom
Deutsche Telekom AG is a telecommunications company headquartered in Bonn, Germany. It is the largest telecommunications company in Europe....

, offers a similar service.

IP multicast software

  • Media Tools Repository - a collection of tools for the MBone
    Mbone
    Mbone was an experimental backbone for IP multicast traffic across the Internet developed in the early 1990s. It required specialized hardware and software...

  • 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...

  • Xorp - 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...

     router with multicast (IGMP, PIM) support
  • Smcroute - a simple tool to manipulate multicast routes on the Linux kernel
  • SSM-ping - tool to test multicast connectivity
  • Host implementation of IGMPv3 on FreeBSD
  • [ftp://parcftp.xerox.com/pub/net-research/ipmulti/ IP multicast software from Xerox]
  • Java Reliable Multicast Service
  • PIM implementation - an implementation of the PIM protocol, now obsolete
  • qpimd - PIM Daemon for Quagga - PIM
    Protocol Independent Multicast
    Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet...

     module for the Quagga Routing Suite
    Quagga (Software)
    Quagga is a network routing software suite providing implementations of Open Shortest Path First , Routing Information Protocol , Border Gateway Protocol and IS-IS for Unix-like platforms, particularly Linux, Solaris, FreeBSD and NetBSD....

  • GateD - UNIX implementation of routing protocols, including multicast
  • PIM-DM code for GateD
  • NORM - Nack-Oriented Reliable Multicast from the U.S. Naval Research Laboratory, with an open source C++ implementation
  • ecmh (Easy Cast du Multi Hub) - IPv6 Multicast Daemon, allows IPv6 multicast to be used without the need for PIM.
  • MRD6
    Multicast Routing Daemon v6
    The Multicast Routing Daemon v6 is an Ipv6 multicast routing daemon developed by Hugo Santos. Its main features include:* Extensible modular design* MLDv1 and MLDv2 support* PIM-SM support * partial MBGP support...

     - Ipv6 multicast routing daemon
  • UFTP
    UFTP
    UFTP is a UDP-based file transfer protocol and the name of a tool that implements that protocol. It was developed by Dennis Bush, and is designed for particularly efficient file transfers under scenarios where the file is to be broadcast/multicast or the transfer occurs over a wireless link...

     - Encrypted UDP based FTP with multicast
  • GStreamer
    GStreamer
    GStreamer is a pipeline-based multimedia framework written in the C programming language with the type system based on GObject.GStreamer allows a programmer to create a variety of media-handling components, including simple audio playback, audio and video playback, recording, streaming and editing...

     - 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...

     multimedia framework
    Multimedia framework
    A multimedia framework is a software framework that handles media on a computer and through a network. A good multimedia framework offers an intuitive API and a modular architecture to easily add support for new audio, video and container formats and transmission protocols...

     that supports multicast video streaming

See also

  • Dense multicast
    Dense multicast
    Dense mode multicast is one mode that multicast can use to construct a tree for sending packets to the multicast subscribers. It is the opposite of sparse multicast....

  • Sparse multicast
    Sparse multicast
    Protocol Independent Multicast - Sparse-Mode is a protocol for efficiently routing Internet Protocol packets to multicast groups that may span wide-area and inter-domain internets...

  • Source-specific multicast
    Source-specific multicast
    Source-specific multicast is a method of delivering multicast packets in which the only packets that are delivered to a receiver are those originating from a specific source address requested by the receiver...

  • Core-based trees
    Core-based trees
    Core-Based Trees is a proposal for making IP Multicast scalable by constructing a tree of routers. It was first proposed in a paper by Ballardie, Francis, and Crowcroft. What differentiates it from other schemes for multicasting is that the routing tree comprises multiple "cores" . The...

  • IGMP snooping
    IGMP snooping
    IGMP snooping is the process of listening to Internet Group Management Protocol network traffic. IGMP snooping, as implied by the name, is a feature that allows a network switch to listen in on the IGMP conversation between hosts and routers. By listening to these conversations the switch...

  • 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...

  • Multicast
    Multicast
    In computer networking, multicast is the delivery of a message or information 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...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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