Multicast

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Routing schemes
Unicast

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Broadcast

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Multicast

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Anycast

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In computer networking, multicast is a type of group communication where data transmission is addressed to a group of destination computers simultaneously. [1] Multicast can be one-to-many or many-to-many distribution. [2] [3] Multicast differs from physical layer point-to-multipoint communication.

Contents

Group communication may either be application layer multicast [1] or network-assisted multicast, where the latter makes it possible for the source to efficiently send to the group in a single transmission. Copies are automatically created in other network elements, such as routers, switches and cellular network base stations, but only to network segments that currently contain members of the group. Network assisted multicast may be implemented at the data link layer using one-to-many addressing and switching such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM), point-to-multipoint virtual circuits (P2MP) [4] or InfiniBand multicast. Network-assisted multicast may also be implemented at the Internet layer using IP multicast. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagrams sent to a multicast destination address.

Multicast is often employed in Internet Protocol (IP) applications of streaming media, such as IPTV and multipoint videoconferencing.

Ethernet

Ethernet frames with a value of 1 in the least-significant bit of the first octet of the destination address are treated as multicast frames and are flooded to all points on the network. This mechanism constitutes multicast at the data link layer. This mechanism is used by IP multicast to achieve one-to-many transmission for IP on Ethernet networks. Modern Ethernet controllers filter received packets to reduce CPU load, by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.

Ethernet multicast is available on all Ethernet networks. Multicasts span the broadcast domain of the network. Multiple Registration Protocol can be used to control Ethernet multicast delivery.

IP

The relationship between the multicast group management protocol family and the multicast routing protocols family based on the network topology terms. Multicast Protocols-en.svg
The relationship between the multicast group management protocol family and the multicast routing protocols family based on the network topology terms.

IP multicast is a technique for one-to-many communication over an IP network. The destination nodes send Internet Group Management Protocol join and leave messages, for example in the case of IPTV when the user changes from one TV channel to another. IP multicast 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 protocol to use multicast addressing is User Datagram Protocol (UDP). By its nature, UDP is not reliable —messages may be lost or delivered out of order. By adding loss detection and retransmission mechanisms, reliable multicast has been implemented on top of UDP or IP by various middleware products, e.g. those that implement the Real-Time Publish-Subscribe (RTPS) Protocol of the Object Management Group (OMG) Data Distribution Service (DDS) standard, as well as by special transport protocols such as Pragmatic General Multicast (PGM).

IP multicast is always available within the local subnet. Achieving IP multicast service over a wider area requires multicast routing. Many networks, including the Internet, do not support multicast routing. Multicast routing functionality is available in enterprise-grade network equipment but is typically not available until configured by a network administrator. The Internet Group Management Protocol is used to control IP multicast delivery.

Application layer

Application layer multicast overlay services are not based on IP multicast or data link layer multicast. Instead they use multiple unicast transmissions to simulate a multicast. These services are designed for application-level group communication. Internet Relay Chat (IRC) implements a single spanning tree across its overlay network for all conference groups. [5] The lesser-known PSYC technology uses custom multicast strategies per conference. [6] Some peer-to-peer technologies employ the multicast concept known as peercasting when distributing content to multiple recipients.

Explicit multi-unicast (Xcast) is another multicast strategy that includes addresses of all intended destinations within each packet. As such, given maximum transmission unit limitations, Xcast cannot be used for multicast groups with many destinations. The Xcast model generally assumes that 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. [7]

Wireless networks

Wireless communications (with exception to point-to-point radio links using directional antennas) are inherently broadcasting media. However, the communication service provided may be unicast, multicast, or broadcast, depending on if the data is addressed to an individual node, a specific group of nodes, or all nodes in the covered network, respectively.

Television

In digital television, the concept of multicast service sometimes is used to refer to content protection by broadcast encryption, i.e. encrypted pay television content over a simplex broadcast channel only addressed to paying viewers. In this case, data is broadcast to all receivers but only addressed to a specific group.

The concept of interactive multicast, for example using IP multicast, may be used over TV broadcast networks to improve efficiency, offer more TV programs, or reduce the required spectrum. Interactive multicast implies that TV programs are sent only over transmitters where there are viewers and that only the most popular programs are transmitted. It relies on an additional interaction channel (a back-channel or return channel), where user equipment may send join and leave messages when the user changes TV channel. Interactive multicast has been suggested as an efficient transmission scheme in DVB-H and DVB-T2 terrestrial digital television systems, [8] A similar concept is switched broadcast over cable-TV networks, where only the currently most popular content is delivered in the cable-TV network. [9] Scalable video multicast in an application of interactive multicast, where a subset of the viewers receive additional data for high-resolution video.

TV gateways converts satellite (DVB-S, DVB-S2), cable (DVB-C, DVB-C2) and terrestrial television (DVB-T, DVB-T2) to IP for distribution using unicast and multicast in home, hospitality and enterprise applications

Another similar concept is Cell-TV, and implies TV distribution over 3G cellular networks using the network-assisted multicasting offered by the Multimedia Broadcast Multicast Service (MBMS) service, or over 4G/LTE cellular networks with the eMBMS (enhanced MBMS) service.

See also

Related Research Articles

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In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP does not require prior communication to set up communication channels or data paths.

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 addressing can be used in the link layer, such as Ethernet multicast, and at the internet layer for Internet Protocol Version 4 (IPv4) or Version 6 (IPv6) multicast.

In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the payload. Control information provides data for delivering the payload. Typically, control information is found in packet headers and trailers.

<span class="mw-page-title-main">Communication channel</span> Physical or logical connection used for transmission of information

A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for information transfer of, for example, a digital bit stream, from one or several senders to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.

<span class="mw-page-title-main">Anycast</span> Network addressing and routing methodology

Anycast is a network addressing and routing methodology in which a single IP address is shared by devices in multiple locations. Routers direct packets addressed to this destination to the location nearest the sender, using their normal decision-making algorithms, typically the lowest number of BGP network hops. Anycast routing is widely used by content delivery networks such as web and name servers, to bring their content closer to end users.

A broadcast address is a network address used to transmit to all devices connected to a multiple-access communications network. A message sent to a broadcast address may be received by all network-attached hosts.

An overlay network is a computer network that is layered on top of another network. The concept of overlay networking is distinct from the traditional model of OSI layered networks, and almost always assumes that the underlay network is an IP network of some kind.

IP multicast is a method of sending Internet Protocol (IP) datagrams to a group of interested receivers in a single transmission. It is the IP-specific form of multicast and is used for streaming media and other network applications. It uses specially reserved multicast address blocks in IPv4 and IPv6.

In computer networking, a reliable protocol is a communication protocol that notifies the sender whether or not the delivery of data to intended recipients was successful. Reliability is a synonym for assurance, which is the term used by the ITU and ATM Forum.

<span class="mw-page-title-main">Broadcasting (networking)</span> Network messaging to multiple recipients simultaneously

In computer networking, telecommunication and information theory, broadcasting is a method of transferring a message to all recipients simultaneously. Broadcasting can be performed as a high-level operation in a program, for example, broadcasting in Message Passing Interface, or it may be a low-level networking operation, for example broadcasting on Ethernet.

Multimedia Broadcast Multicast Services (MBMS) is a point-to-multipoint interface specification for existing 3GPP cellular networks, which is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network. For broadcast transmission across multiple cells, it defines transmission via single-frequency network configurations. The specification is referred to as Evolved Multimedia Broadcast Multicast Services (eMBMS) when transmissions are delivered through an LTE network. eMBMS is also known as LTE Broadcast.

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In packet switching networks, traffic flow, packet flow or network flow is a sequence of packets from a source computer to a destination, which may be another host, a multicast group, or a broadcast domain. RFC 2722 defines traffic flow as "an artificial logical equivalent to a call or connection." RFC 3697 defines traffic flow as "a sequence of packets sent from a particular source to a particular unicast, anycast, or multicast destination that the source desires to label as a flow. A flow could consist of all packets in a specific transport connection or a media stream. However, a flow is not necessarily 1:1 mapped to a transport connection." Flow is also defined in RFC 3917 as "a set of IP packets passing an observation point in the network during a certain time interval." Packet flow temporal efficiency can be affected by one-way delay (OWD) that is described as a combination of the following components:

<span class="mw-page-title-main">Xcast</span>

The explicit multi-unicast (Xcast) is a variation of multicast that supports a great number of multicast sessions with a small number of recipients in each. It adds all the destination IP addresses in the IP header, instead of using a multicast address. The traditional multicast schemes over Internet Protocol (IP) scale to multicast groups with many members, but they have scalability problems for a great number of groups. Multicast schemes can be used to minimize the bandwidth consumption. Xcast minimizes bandwidth consumption for small groups, by eliminating the signaling protocols and state information for every session of the standard IP multicast scheme.

Generic Stream Encapsulation, or GSE for short, is a Data link layer protocol defined by DVB. GSE provides means to carry packet oriented protocols such as IP on top of uni-directional physical layers such as DVB-S2, DVB-T2 and DVB-C2.

Multimedia Broadcast multicast service Single Frequency Network (MBSFN) is a communication channel defined in the fourth-generation cellular networking standard called Long-Term Evolution (LTE). The transmission mode is intended as a further improvement of the efficiency of the enhanced Multimedia Broadcast Multicast Service (eMBMS) service, which can deliver services such as mobile TV using the LTE infrastructure, and is expected to compete with dedicated mobile/handheld TV broadcast systems such as DVB-H and DVB-SH. This enables network operators to offer mobile TV without the need for additional expensive licensed spectrum and without requiring new infrastructure and end-user devices.

<span class="mw-page-title-main">Broadcast, unknown-unicast and multicast traffic</span> Computer networking concept

Broadcast, unknown-unicast and multicast traffic is network traffic transmitted using one of three methods of sending data link layer network traffic to a destination of which the sender does not know the network address. This is achieved by sending the network traffic to multiple destinations on an Ethernet network. As a concept related to computer networking, it includes three types of Ethernet modes: broadcast, unicast and multicast Ethernet. BUM traffic refers to that kind of network traffic that will be forwarded to multiple destinations or that cannot be addressed to the intended destination only.

<span class="mw-page-title-main">Multicast routing</span> Computer networking protocol for forwarding transmissions from one sender to multiple receivers

Multicast routing is one of the routing protocols in IP networking.

Deterministic Networking (DetNet) is an effort by the IETF DetNet Working Group to study implementation of deterministic data paths for real-time applications with extremely low data loss rates, packet delay variation (jitter), and bounded latency, such as audio and video streaming, industrial automation, and vehicle control.

References

  1. 1 2 Media-communication based on Application-Layer Multicast
  2. ↑ Lawrence Harte, Introduction to Data Multicasting , Althos Publishing 2008.
  3. ↑ Li, Bing; Atwood, J. William (2016-06-19). "Secure receiver access control for IP multicast at the network level: Design and validation". Computer Networks. 102: 109–128. doi:10.1016/j.comnet.2016.03.010. ISSN   1389-1286.
  4. ↑ M. Noormohammadpour; et al. (July 10, 2017). "DCCast: Efficient Point to Multipoint Transfers Across Datacenters". USENIX. Retrieved July 26, 2017.
  5. ↑ A Discussion on Computer Network Conferencing. sec. 2.5.1. RFC   1324 .
  6. ↑ White paper, EU: PSYC.
  7. ↑ Rick Boivie; Nancy Feldman; Yuji Imai; Wim Livens & Dirk Ooms (November 2007). "Explicit Multicast (Xcast) Concepts and Options". Internet Engineering Task Force. doi:10.17487/RFC5058 . Retrieved May 25, 2013.{{cite journal}}: Cite journal requires |journal= (help)
  8. ↑ M. Eriksson, S.M. Hasibur Rahman, F. Fraille, M. Sjöström, ”Efficient Interactive Multicast over DVB-T2 - Utilizing Dynamic SFNs and PARPS”, 2013 IEEE International Conference on Computer and Information Technology (BMSB’13), London, UK, June 2013.
  9. ↑ N. Sinha, R. Oz and S. V. Vasudevan, “The statistics of switched broadcast”, Proceedings of the SCTE 2005 Conference on Emerging Technologies, Tampa, FL, USA, January 2005
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