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Abstract|Graphs are commonly used to model the topological structure of internetworks, to study problems ranging from routing to resource reservation. A variety of graphs are found in the literature, including xed topologies such as rings or stars, well-known" topologies such as the ARPAnet, and randomly generated topologies. While many researchers rely upon graphs for analytic and simulation studies, there has been little analysis of the implications of using a particular model, or how the graph generation method may a ect the results of such studies. Further, the selection of one generation method over another is often arbitrary, since the di erences and similarities between methods are not well understood.This paper considers the problem of generating and selecting graph models that re ect the properties of real internetworks. We review generation methods in common use, and also propose several new methods. We consider a set of metrics that characterize the graphs produced by a method, and we quantify similarities and di erences amongst several generation methods with respect to these metrics. We also consider the e ect of the graph model in the context of a speci c problem, namely multicast routing.

Active networks represent a signi cant step in the evolution of packet-switched networks, from traditional packet-forwarding engines to more general functionality supporting dynamic control and modi cation of the network behavior. However, the phrase active network" means di erent things to di erent people. This article introduces a model and nomenclature for talking about active networks, describes some possible approaches in terms of that nomenclature, and presents various aspects of the architecture being developed in the DARPA-funded active networks program. Potential applications of active networks are highlighted, along with some of the challenges that must be overcome to make them a reality.

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