Multicast IP Routing protocols are utilized for distributing data as for example, audio streaming or video streaming broadcasts for multiple recipients. Utilizing multicast, a source could send a single copy of data to a single multicast address, which would be then distributed to an entire group of recipients.

A multicast group would be identifying a set of recipients that would be interested in a particular data stream and is going to be represented by an IP address from a well-defined range. Data that would be sent to this IP address is going to be forwarded to all members of the multicast group.

Routers between the source and recipients are going to duplicate data packets and forward multiple copies wherever the path to recipients diverges. Group membership information is to be used for calculating the best routers at which to duplicate the packets in the data stream so as to optimize the use of the network.

A source host would be sending data to a multicast group by merely setting the destination IP address of the datagram to be the multicast group address. Any host could become a source and send data to a multicast group. Sources aren’t going to be needed to register in any way before they could be beginning to sending data to a group, and do not need to be members of the group themselves.

There are lots and lots of different multicast protocols and modes of operation, each would be optimized for a particular scenario. Many of these are still considered at an early stage of standardization. However, they would be all so as to operate in the same general way, as follows.

•  A Multicast Group Membership Discovery protocol is going to be utilized by receiving hosts to advertise their group membership in order to a local multicast router, enabling them to join and leave multicast groups. The main Multicast Group Membership Discovery protocols are IGMP (Internet Group Management Protocol) for IPv4 and MLD (Multicast Listener Discovery) for IPv6.
•  A Multicast Routing Protocol would be utilized to communicate between multicast routers and facilitate them to calculate the multicast distribution tree of receiving hosts. PIM (Protocol Independent Multicast) is considered to be the most important Multicast Routing Protocol.

The multicast distribution tree of receiving hosts would be holding the route to every recipient that would have joined the multicast group and is going to be optimized so that:

•  Multicast traffic doesn’t accomplish networks that don’t have any such recipients unless the network is a transfer network on the way to other recipients.
•  Duplicate copies of packets would be kept to a minimum.

IP Multicast:

IP multicast is considered as a technique for one-to-many and many-to-many real-time communication over IP infrastructures that are present in a network. It would be scaled to a superior receiver population would be required neither prior knowledge of a receiver’s identity nor prior knowledge of the number of receivers.

Multicast utilizes network infrastructures that would be efficiently by requiring the source to send a packet only once, even if it would be needed to deliver to a large number of receivers. The nodes in the network, typically network Switches and Routers, take care of replicating the packet so as to reach multiple receivers such that messages which are being sent over each link of the network only once.

The most common transport layer protocol that would be utilized multicast addressing is UDP (User Datagram Protocol). By its nature, UDP is not considered to be quite reliable messages may be lost or delivered out of order. Reliable multicast protocols like the PGM (Pragmatic General Multicast) have been developed so as to add loss detection as well as retransmission on top of IP multicast.

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

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