Enabling Large-scale Network Simulations: A Selective Abstraction Approach

ions Abstraction is possible because most protocol architectures are layered such that one protocol makes use of another. In design or evaluation of a level-n protocol, we need information provided by level n-1 and below, but not necessarily (depending on the research questions) all the details of the lower level protocols. For instance, a multicast transport protocol may need multicast routing tables in order to forward multicast packets. The detailed exchange of messages to generate those routing tables is often not important. If we abstract away unnecessary details, the memory and time consumption that would have been used by these details can be conserved and used to simulate larger scale scenarios. Based on this reasoning, we proposed centralized computation and end-to-end packet delivery. These two techniques are aimed to abstract away, respectively, network layer and hop-by-hop transmission details that higher layer protocol studies may or may not require. Protocol complexity is only one dimension of the scaling problems. To be able to simulate very large networks and substantial amounts of traffic, we need to enhance those elements that construct network connectivity or generate traffic in the simulations. Currently, in most network simulators, the cost to construct network connectivity is proportional to the cost of creating nodes O(N), links O(L) and routing table O(N). For large topologies (N > 1000), routing table cost is the most significant. Hierarchical routing has the