We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks.

/pdf/gpsr-greedy-perimeter-stateless-routing-for-wireless-59gz21qf8y.pdf

GPSR: greedy perimeter stateless routing for wireless networks

https://www.cs.montana.edu/courses/csci566/Ref/CR-Survey.pdf

NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey

Advances in processor, memory and radio technology will enable small and cheap nodes capable of sensing, communication and computation. Networks of such nodes can coordinate to perform distributed sensing of environmental phenomena. In this paper, we explore the directed diffusion paradigm for such coordination. Directed diffusion is datacentric in that all communication is for named data. All nodes in a directed diffusion-based network are application-aware. This enables diffusion to achieve energy savings by selecting empirically good paths and by caching and processing data in-network. We explore and evaluate the use of directed diffusion for a simple remote-surveillance sensor network.

/pdf/directed-diffusion-a-scalable-and-robust-communication-4tsx5vxsas.pdf

Directed diffusion: a scalable and robust communication paradigm for sensor networks

"A Survey of Mobility Models for Ad Hoc Network Research," Wireless Comm. & Mobile Computing (WCMC) : Special issue on Mobile Ad Hoc Networking : Research

In the performance evaluation of a protocol for an ad hoc network, the protocol should be tested under realistic conditions including, but not limited to, a sensible transmission range, limited buffer space for the storage of messages, representative data traffic models, and realistic movements of the mobile users (i.e., a mobility model). This paper is a survey of mobility models that are used in the simulations of ad hoc networks. We describe several mobility models that represent mobile nodes whose movements are independent of each other (i.e., entity mobility models) and several mobility models that represent mobile nodes whose movements are dependent on each other (i.e., group mobility models). The goal of this paper is to present a number of mobility models in order to offer researchers more informed choices when they are deciding upon a mobility model to use in their performance evaluations. Lastly, we present simulation results that illustrate the importance of choosing a mobility model in the simulation of an ad hoc network protocol. Specifically, we illustrate how the performance results of an ad hoc network protocol drastically change as a result of changing the mobility model simulated.

/pdf/a-survey-of-mobility-models-for-ad-hoc-network-research-ygkxat400x.pdf

A survey of mobility models for ad hoc network research

This paper considers the problem of Byzantine fault-tolerance in distributed multi-agent optimization. In this problem, each agent has a local cost function, and in the fault-free case, the goal is to design a distributed algorithm that allows all the agents to find a minimum point of all the agents' aggregate cost function. We consider a scenario where some agents might be Byzantine faulty that renders the original goal of computing a minimum point of all the agents' aggregate cost vacuous. A more reasonable objective for an algorithm in this scenario is to allow all the non-faulty agents to compute the minimum point of only the non-faulty agents' aggregate cost. Prior work shows that if there are up to f (out of n) Byzantine agents then a minimum point of the non-faulty agents' aggregate cost can be computed exactly if and only if the non-faulty agents' costs satisfy a certain redundancy property called 2f-redundancy. However, 2f-redundancy is an ideal property that can be satisfied only in systems free from noise or uncertainties, which can make the goal of exact fault-tolerance unachievable in some applications. Thus, we introduce the notion of (f,e)-resilience, a generalization of exact fault-tolerance wherein the objective is to find an approximate minimum point of the non-faulty aggregate cost, with e accuracy. This approximate fault-tolerance can be achieved under a weaker condition that is easier to satisfy in practice, compared to 2f-redundancy. We obtain necessary and sufficient conditions for achieving (f, e)-resilience characterizing the correlation between relaxation in redundancy and approximation in resilience. In case when the agents' cost functions are differentiable, we obtain conditions for (f, e)-resilience of the distributed gradient-descent method when equipped with robust gradient aggregation; such as comparative gradient elimination or coordinate-wise trimmed mean.

Approximate Byzantine Fault-Tolerance in Distributed Optimization

Recent years have witnessed the widespread deployment of IEEE 802.11 LANs in areas such as airports, campuses, and enterprises. These networks allow users to access network services and the Internet in remote locations and without the need Tor wires. The data rates for 802.11a, b and g far surpass that of wide-area cellular networks, however, the range of transmission of 802.11 is much less than that of cellular (250m versus 20km). Employing ad-hoc mode in 802.11 can extend traditional WLANs to multiple hops, thus increasing coverage and reducing the need for additional infrastructure. The amount of network extension (in terms of wireless hops) is limited by the density of the network (i.e., the availability of wireless devices that can serve as relays for other devices), and the scalability of stand-alone wireless ad-hoc networks. In this paper, we introduce a k-hop architecture and routing protocol utilizing a "beaconing" approach for route discovery and maintenance. We demonstrate through simulations the efficiency and reliability of our routing protocol in the presence of mobility and high node density.

A routing protocol for k-hop networks

Beamforming antennas have been shown to improve spatial reuse in wireless networks. Protocols that aim to exploit beamforming antennas have leveraged benefits from directional transmission as well as directional reception. We argue that exploiting antenna characteristics for transmission and reception alone, is not sufficient Controlling the antenna during the idle state of a node is necessary to attain further improvements. A node that does not control its antenna during the idle state will waste time in receiving packets not intended for it. These packets will eventually be dropped at the MAC layer, reducing channel utilization. With suitable beamforming, a node might be able to utilize this time for concurrent communication. We call this the problem of MAC-layer Capture in view of a node getting engaged in receiving unproductive packets. We present MAC and routing protocols to address MAC-layer capture. Simulation results show that improvements from avoiding MAC-layer capture can be substantial in static mesh networks.

/pdf/mac-layer-capture-a-problem-in-wireless-mesh-networks-using-2lr6n2an1s.pdf

MAC-Layer Capture: A Problem in Wireless Mesh Networks using Beamforming Antennas

This paper explores the problem of reaching approximate consensus in synchronous point-to-point networks, where each directed link of the underlying communication graph represents a communication channel between a pair of nodes. We adopt the transient Byzantine link failure model [15, 16], where an omniscient adversary controls a subset of the directed communication links, but the nodes are assumed to be fault-free.

/pdf/iterative-approximate-consensus-in-the-presence-of-byzantine-447yl2p066.pdf

Iterative Approximate Consensus in the Presence of Byzantine Link Failures

This report deals with the design and evaulation of a "two-level" failure recovery scheme for distributed systems. In our previous work [30, 32], we motivated a "two-level" recovery approach that tolerates the more probable failures with a low overhead, and less probable failures with possibly higher overhead. The two-level approach can achieve a smaller overhead as compared to traditional recovery schemes. In this report, we present and evaluate a "two-level" recovery scheme that is suitable for a network of workstations, each workstation having a local disk. The recovery scheme presented in the report can tolerate trasient processor failures with a low overhead, while other failures require a larger overhead. The report presents analysis of the average (expected) task completion time using the proposed scheme. This scheme has been implemented on a workstation cluster. Our analysis indicates that the proposed two-level recovery scheme can achieve better performance as compared to existing "one-level" recovery schemes. The report also evaluates the impact of checkpoint latency on the performance of the recovery scheme. To our knowledge, no analysis of the performance impact of checkpoint latency has been carried out previously. Experimental measurements of checkpoint latency for four applications are presented.

Nitin H. Vaidya

Papers

Approximate Byzantine Fault-Tolerance in Distributed Optimization

A routing protocol for k-hop networks

MAC-Layer Capture: A Problem in Wireless Mesh Networks using Beamforming Antennas

Iterative Approximate Consensus in the Presence of Byzantine Link Failures

Another Two-Level Failure Recovery Scheme