| The Virtual Node Layer (VNLayer) is a cluster based programming abstraction for a Mobile Ad-Hoc Network. VNLayer defines fixed or predictably mobile geographical regions. In each region, a number of mobile nodes collectively emulate a virtual node, which provides services and relays packets for client processes.;As a clustering scheme with state replication, the VNLayer approach can theoretically improve the efficiency and reliability of MANET protocols. As a general programming abstraction, the VNLayer hides underlying complexities from protocol developers and can be shared by multiple applications. However, the VNLayer also introduces extra control overhead and prolongs data forwarding delay, which could be prohibitively expensive in terms of performance.;Based on an existing VNLayer implementation [1], we developed an ns-2 based software package, VNSim. VNSim can be used to simulate VNLayer based applications in a MANET of up to a few hundred mobile nodes, in order to better understand the impact of the VNLayer approach on efficiency and reliability.;With VNSim, we did our first case study on a VNLayer based MANET address allocation protocol, VNDHCP. Simulation results proved that the VNLayer approach can be used to adapt a wireline protocol to MANET.;We also did an extensive simulation study on VNLayer based MANET routing. A wireline routing protocol, RIP, was adapted to run over the VNLayer. With the support provided by the VNLayer, the adapted protocol, VNRIP, was implemented very quickly and can provide reasonable performance.;During the study of VNLayer based MANET routing, we identified a number of major performance limitations in the existing VNLayer implementation and the models it is based on. To tackle the limitations, we created a more realistic link layer model, extended the VNLayer model and optimized our VNLayer implementation.;With the optimized VNLayer implementation, we implemented VNAODV, an adapted version of AODV, over the new link and VNLayer models. Simulation results indicate that VNAODV delivers more packets and creates more stable routes than standard AODV in a dense MANET with high node motion rate and moderate data traffic.;This research validated the intuition that the VNLayer approach can be used to adapt wireline protocols quickly to MANET and to improve the performance of MANET protocols. This research also provided us some insights on how to implement and optimize cluster based MANET protocols. |
