In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from source and creating copies automatically in other network elements, such as routers.
Multicast is most commonly implemented in IP multicast, which is often employed in Internet Protocol (IP) applications of streaming media and Internet television. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagram sent to a multicast destination address.
In multicast communication, there is one source and a group of destinations. The relationship is one-to-may. In this type of communication, the source address is a unicast address, but the destination address is a group address, which defines one or more destinations. The group address identifies the members of the group.
A multicast packet starts from the source S1 and goes to all destinations that belong to group G1. In multicasting, when a router receives a packet, it may forward it through several of its interfaces.
At the Data Link Layer, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits (P2MP) or Infini band multicast.
3.1.1 MULTICAST APPLICATION
Multicasting has many applications today such as access to distributed databases, information dissemination, teleconferencing and distance learning
Access to Distributed Databases
Most of the large databases today are distributed. That is, the information is stored in more than one location, usually at the time of production. The user who needs to have access to the database does not need to know the location of the information. The user’s request is multicast to all the database locations, and the location that has the information responds
Businesses often need to send information to their customers. If the nature of information is the same for everyone, the information can be multicast. For example, a software update can be sent to all purchasers of a particular software package.
Dissemination of News
In a similar manner, news can be easily disseminated through multicasting. One single message can be sent to those interested in a particular topic. For example, the statistics of the championship of a college tournament can be sent to the sports editor s of many newspapers.
Teleconferencing involves multicasting. The individuals attending a teleconference all need to receive the same information at the same time. Temporary or permanent groups can be formed for this purpose.
One growing area in the use of multicasting is distance learning. Lessons taught by one single professor can be received by a specific group of students. This is especially convenient for those students who find it difficult to attend classes on campus.
Mbone (short for “multicast backbone”) is a virtual network invented by Van Jacobson. The purpose of “Mbone” is to minimize the amount of dat a required for multipoint audio/video-conferencing. Since most Internet routers have IP multicast disabled due to concerns of bandwidth tracking and billing, the Mbone evolved to connect multicast-capable networks over the existing Internet infrastructure. The commercialization of multicast routers is difficult because there are no efficient access control capabilities to the multicast trees (multicast routers and their protocols), and because Internet service providers have difficulty computing charges for multicast traffic.
Some of its major characteristics are:
- Topology: combination of mesh and star networks
- IP addresses: 220.127.116.11; routing schemes: DVMRP, MOSPF
- Session registration: IGMP
Mbone uses a network of Mrouters that can support IP multicast, and enables access to real-time interactive multimedia on the Internet.
SELF ASSESSMENT EXERCISE
Give a concise description of the term ‘Multicast’
In this unit, we learnt that multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from source and creating copies automatically in other network elements.