Implementation and performance measurement of an island multicast protocol

With the availability and penetration of multicast-capable routers, many local networks in today's Internet are multicast-capable. However, achieving global IP multicast is still hindered by many management and technical difficulties. This is because routers interconnecting these local multicast-capable networks, or so-called "islands," are often either multicast-incapable or multicast-disabled. Traditional application-level multicast (ALM) only makes use of unicast connections to form delivery trees and has not fully taken advantage of the local multicast capability of an island. As a result, these protocols are not very efficient. In order to achieve efficient global multicast, we propose and study island multicast (IM) where unicast connections are used between islands while IP multicast is used within islands. We present the detailed mechanisms of the IM centralized approach. IM is simple to implement and is based on minimum spanning tree, and hence is applicable to many-to-many communication. We have implemented the protocol and done real measurements on PlanetLab. We show that our protocol significantly improves network performance (in terms of stress, delay and nodal degrees) as compared to using ALM alone.