What is Multicast

  • Multicast traffic refers to packets that are sent from one source host address to a special group-based destination address. The destination represents only the hosts that are interested in receiving the packets, and no others. Two extremes are covered here, unicast, which travels from host to host, and a broadcast, which travels from one host to everyone on a segment. Multicast falls somewhere in the middle, where the intention is to send packets from one host to only the users that want to receive them, namely those in the designated multicast group. In the case of the Access Grid, this would be the different venues which people can join.

  • Ideally, the recipients of multicast packets could be located anywhere, not just on the local segment, with the advantage that only people that wish to receive the video presentation would be affected by the traffic without flooding all the rest of the network with unwanted traffic. In the case of video conferencing, the amount of traffic is very high, which could create a lot of bottle necks and delays in the network if multicast didnt exist, and it was necessary to send broadcast or multiple unicast streams instead.

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