Mobile ad hoc networks are characterized by multi-hop wireless links, absence of any cellular infrastructure, and frequent host mobility.Design of efficient routing protocols in such networks is a challenging issue.A class of routing protocols called on-demand protocols has recently found attention because of their low routing overhead.We propose a technique that can reduce the routing overhead even further.The on-demand protocols depend on query floods to discover routes whenever a new route is needed.Our technique utilizes prior routing histories to localize the query flood to a limited region of the network.Simulation results demonstrate excellent reduction of routing overheads with this mechanism.This also contributes to a reduced level of network congestion and better end-to-end delay performance of data packets.

We evaluate several routing protocols for mobile, wireless, ad hoc networks via packet level simulations. The protocol suite includes routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, end-to-end delay and routing load for a given traffic and mobility model. It is observed that the new generation of on-demand routing protocols use a much lower routing load. However the traditional link state and distance vector protocols provide, in general, better packet delivery and delay performance.

The Convex Exemplar (SPP1000 and SPP2000 series) is a new commercial distributed shared-memory architecture. Using a set of system kernels and two application programs, we examine performance effects on network latency, hot spot contention, cache coherence and overall scaling capability, which result both from the choice of the network structure as well as from its CC-NUMA memory system feature. Since the KSR-1 was also targeted at scalable cache coherent shared-memory systems by using hierarchical interconnection networks, we compared the architecture and performance results with the KSR-1. Our experiments indicate that the memory access latency of the Exemplar is comparatively low due to its fast processor node and the unique network/system structure. In addition, the Coherent Toroidal Interconnect (CTI) rings are efficient in handling cache coherence activities on the Exemplar. However, the Exemplar synchronization primitives need further exploit its hierarchical architecture in a high contention environment. As we expect with extremely fast processors in a hierarchical memory structure, the high-speed cluster-based Exemplar system is more sensitive to data locality.

Hot spot contention on a network-based shared-memory architecture occurs when a large number of processors try to access a globally shared variable across the network. While multistage interconnection network (MIN) and hierarchical ring (HR) structures are two important bases on which to build large scale shared-memory multiprocessors, the different interconnection networks and cache/memory systems of the two architectures respond very differently to network bottleneck situations. In this paper, we present a comparative performance evaluation of hot spot effects on the MIN-based and HR-based shared-memory architectures. Both nonblocking MIN-based and HR-based architectures are classified, and analytical models are described for understanding network differences and for evaluating hot spot performance on both architectures. The analytical comparisons indicate that HR-based architectures have the potential to handle various contentions caused by hot spots more efficiently than MIN-based architectures. Intensive performance measurements on hot spots have been conducted on the BBN TC2000 (MIN-based) and the KSR1 (HR-based) machines. Performance experiments were also conducted on the practical experience of hot spots with respect to synchronization lock algorithms. The experimental results are consistent with the analytical models, and present practical observations and an evaluation of hot spots on the two types of architectures.>