Improved performance for network simulation

Over the course of designing and implementing two discrete event simulators, the commercial simulator packages CSIM and DesmoJ were leveraged to allow for rapid development of both wired and wireless network models. However, the two resulting simulators demonstrated poor scalability due to the use of multi-threading to maintain state for simulation elements. By using a simple single-process discrete event simulation engine, the running-time showed a marked decrease when compared to multi-threaded simulators.In one case study, we simulate a simple two-link MPLS network which employs two congestion control mechanisms for inelastic traffic, namely preemption and adaptation. Performance metrics measured include: the per-class blocking probability, customer average fraction of time streams travel on the preferred path, customer average fraction of time at the maximum subscription rate, the customer average rate of adaptation, and the time average rate of preemption. We compare the performance of preemption and adaptation individually and collectively against the base case where neither congestion mechanism is used. At the cost of increased number of rate adaptations and preemption events for a range of regimes, we show that the combined use of preemption and adaptation improves the quality of service and alignment of high priority traffic while increasing the effective network capacity. As a performance enhancement to the simulator developed to conducted these experiments, we switched to a single-process discrete evnt simulation engine in place of multi-threaded simulator. We note a large improvement for the running time as the simulation time and capacity increase.A second case study was conducted on a wireless simulator. In an effort to simplify the simulator and improve performance we again moved from a commercial thread-based simulator (CSIM) to a single-process discrete event simulation engine. Results of the runningtime vs network size for the single-process simulator showed a constant-time improvement over the thread-based simulator. To further improve performance, a complementary technique known as model abstraction is also applied. Model abstraction is a technique that reduces execution time by removing unnecessary simulation detail. In this thesis we propose three abstractions of the IEEE 802.11 protocol. The Goodput Ratio vs Transmission Power and End-to-end delay vs offered load performance metrics are compared against the OPNET commercial simulator.M.S., Computer Engineering -- Drexel University, 200

Efficient Passive Clustering and Gateways selection MANETs

Passive clustering does not employ control packets to collect topological information in ad hoc networks. In our proposal, we avoid making frequent changes in cluster architecture due to repeated election and re-election of cluster heads and gateways. Our primary objective has been to make Passive Clustering more practical by employing optimal number of gateways and reduce the number of rebroadcast packets

Private and censorship-resistant communication over public networks

Society’s increasing reliance on digital communication networks is creating unprecedented opportunities for wholesale surveillance and censorship. This thesis investigates the use of public networks such as the Internet to build robust, private communication systems that can resist monitoring and attacks by powerful adversaries such as national governments. We sketch the design of a censorship-resistant communication system based on peer-to-peer Internet overlays in which the participants only communicate directly with people they know and trust. This ‘friend-to-friend’ approach protects the participants’ privacy, but it also presents two significant challenges. The first is that, as with any peer-to-peer overlay, the users of the system must collectively provide the resources necessary for its operation; some users might prefer to use the system without contributing resources equal to those they consume, and if many users do so, the system may not be able to survive. To address this challenge we present a new game theoretic model of the problem of encouraging cooperation between selfish actors under conditions of scarcity, and develop a strategy for the game that provides rational incentives for cooperation under a wide range of conditions. The second challenge is that the structure of a friend-to-friend overlay may reveal the users’ social relationships to an adversary monitoring the underlying network. To conceal their sensitive relationships from the adversary, the users must be able to communicate indirectly across the overlay in a way that resists monitoring and attacks by other participants. We address this second challenge by developing two new routing protocols that robustly deliver messages across networks with unknown topologies, without revealing the identities of the communication endpoints to intermediate nodes or vice versa. The protocols make use of a novel unforgeable acknowledgement mechanism that proves that a message has been delivered without identifying the source or destination of the message or the path by which it was delivered. One of the routing protocols is shown to be robust to attacks by malicious participants, while the other provides rational incentives for selfish participants to cooperate in forwarding messages