The concept of multicast was introduced by Steve Deering in the '80's. Adding
multicast to the internet does not alter the basic model of the network. Any host
can send multicast data, but with a new type of address called a host group address.
IPv4 has reserved class D addresses to support multicasting. A user can dynamically
subscribe to the group to receive multicast traffic by informing a local router
that it is interested in a particular multicast group. However, it is not necessary
to belong to a group to send multicast. The delivery of multicast traffic in the
internet is accomplished by creating a multicast tree, wit all of its leaf nodes
a scenario where a professor wants to conduct a real-time class with 50 students
participating through the network. If the multimedia application for the conferencing
employs unicasting, the professor's computer repeatedly sends out 50 audio streams
to the student's computers. Unicasting wastes bandwidth because it sends 50 duplicate
copies over the network, and causes a significant delay before the last student
hears the professor. The audio stream could also flood every corner of the network
and possibly bring the network down. Multicasting comes to the rescue by allowing
the multicast host to send out only one copy of the information, and only those
hosts that are part of that group receive it. In the class example, the professor's
computer sends only one audio stream to the network, and only the targeted 50
students receive the stream. The information utilizes the minimum required network
bandwidth and arrives at every student's computer without any noticeable delay.
application is an example of the practical use of multicast in everyday life.
The same is true for other applications like audio/video conferencing, multiplayer
online gaming, online/offline video distribution, news and so on. As illustrated
in Fig.1.1, it is clear that even if there are only three receivers of a multimedia
application, the bandwidth utilization between routers can be roughly reduced
up to one-third if we use multicasting.
Initial Support of multicast in the internet is done by adding multicast-capable
routers (mrouters) and using dedicated tunnels to facilitate multicasting packets
from one mrouter to another. A router is a device that connects a local area network,
such as an inter-office LAN, to a wide area network such as the Internet. The
router's job is to move information between the two networks. Most routers today
are unicast routers: They are designed to move information from a specific place
to another specific place. However, routers that include multicasting capabilities
are becoming more common. The job of each mrouter is to encapsulate and de capsulate
each multicast packet as a regular Internet Protocol (IP) packet and send it through
the tunnel to another mrouter. This set of mrouters in the internet is called
MBone (multicast backbone). Presently, some of the existing internet routers have
been enhanced to support multicast, and there is no need to set up dedicated tunnels
for them. This is called native multicast and the internet currently has a combination
IP supports dynamic joining
and leaving of a group by Group Management Protocol (IGMP). A user wishing to
join a multicast group sends an IGMP join message to its neighboring multicast
router. If the multicast router is not a member of the group, it forwards the
message upstream until it finds some router or source that is subscribing to the
group. In a domain, if there are routers performing IP multicasting, one of them
is elected as the multicast querier to control the multicasting in the domain.
The multicast router also keeps track of current membership of any group by sending
periodic messages to all hosts in the domain.
You may also like this : IMode, Blue Gene , Access gateways, Computer Forensics, Direct Memory Access , Crusoe, Digital Subscriber Line , Computer Memory Based on the Protein Bacterio-rhodopsin, DNA Based Computing, Free Space Optics , Freenet, Fiber Distributed Data Interface , Dynamic Virtual Private Network, Introduction to the Internet Protocols, Graphic processing Unit, High Altitude Aeronautical Platforms, Aspect-oriented programming (Aop) , Intel MMX Technology, Hyper-Threading technology , IMAX, Brain-Computer Interface , InfiniBand, Multicast , Inverse Multiplexing, Blue Tooth , Holographic Memory , Jini Technology, Bio-metrics, Magnetic Random Access Memory , Intrution Detection System, Multiterabit Networks, Neural Networks And Their Applications, Quantum Computers , Small Computer System Interface, OpenRAN , Quadrics Interconnection Network, Plan 9 Operating System , Structured Cabling, Quantum Cryptography , Speech Application Language Tags, Real- Time Systems and Real- Time Operating Systems, Parallel Computing In India , Steganography, Virtual LAN Technology, Artificial Neural Network (ANN), Tele-immersion, VHDL, Blue Eyes , Voice Over Internet Protocol, The Tiger SHARC processor, Computer Seminars Reports and PPT