Networks of small devices, such as environmental sensors, introduce a number of new challenges for traditional protocols and approaches. In particular, the extreme resource constraints characteristics of these devices force the engineering of device and application-specific optimizations in order to reduce complexity. By offloading some, if not most, of the complexity out of the small device and into the network, we simplify the design of individual devices, and may make otherwise infeasible applications possible. We look specifically at the problem of global mobility, and its associated protocol Mobile IP (MIP). We introduce the mobility gateway which performs MIP processing on behalf of registered devices. The mobility gateway provides an interface between the optimized world of small devices and the larger Internet. Through simulation, we investigate the potential savings offered by this technique in terms of bandwidth and power. In a sample scenario, we find the total number of bytes transmitted over the wireless channel reduced by as much as 70%, and the battery life of the device extended by more than 100 hours.

The benefit derived from using multicast is seemingly dependent upon the shape of the distribution tree. We attempt to model interdomain multicast trees accurately. We measure a number of key parameters, such as depth, degree frequency, and average degree, for a number of real and synthetic data sets. We find that interdomain multicast trees actually do share a common shape at both the router and autonomous system levels. Furthermore, we develop a characterization of multicast efficiency which reveals that group sizes as small as 20 to 40 receivers offer a 55%-70% reduction in the total number of links traversed when compared to separately delivered unicast streams. A final contribution of our work consists in a number of data sets, compiled from multicast group membership and path data, that can be used to generate large sample trees, representative of the current multicast infrastructure.

We investigate two issues. First, what level of efficiency gain does multicast offer over unicast? Second, how does the shape of multicast trees impact multicast efficiency? We address the first issue by developing a metric to measure multicast efficiency for a number of real and synthetic datasets. We find that group sizes as small as 20 to 40 receivers offer a 60-70% reduction in the number of links traversed compared to separately delivered unicast streams. Addressing the second issue, we have found that almost all multicast trees have similar characteristics in terms of key parameters such as depth, degree frequency and average degree. A final contribution of our work is that we have taken multicast group membership data and multicast path data and compiled datasets which can be used to generate large, realistic multicast trees.

To further advance the deployment of multicast, many consider it necessary to provide a quantitative measure of the potential benefit of employing multicast rather than unicast. We approach this problem in three ways. First, we propose a rudimentary metric that can provide a reasonable measure of the benefit achieved by an active group using multicast instead of unicast. Second, we discuss many of the issues inherent in developing multicast metrics and how these issues may be addressed to improve the accuracy of our model. Third, we consider how characteristics of network topology and group distribution might offer a predictive estimate for the proposed metric. In general, we identify two rules for evaluating the efficiency of multicast: (1) multicast efficiency increases as the average path length increases, and (2) fan-out close to the source decreases multicast's efficiency.