  Multicasting technology uses the minimum network resources to serve multiple
clients by duplicating the data packets at the closest possible point to the
clients. This way at most only one data packets travels down a network link at
any one time irrespective of how many clients receive this packet.
Traditionally multicasting has been implemented over a specialized network
built using multicast routers. This kind of network has the drawback of
requiring the deployment of special routers that are more expensive than
ordinary routers. Recently there is new interest in delivering multicast
traffic over application layer overlay networks. Application layer overlay
networks though built on top of the physical network, behave like an
independent virtual network made up of only logical links between the nodes.
Several authors have proposed systems, mechanisms and protocols for the
implementation of multicast media streaming over overlay networks. In this
paper, the author takes a critical look at these systems and mechanism with
special reference to their strengths and weaknesses.
