The Air Force Institute of Technology

As ad-hoc collaborative environments become more common, the need for access control becomes more imperative. Centralized access control determination fails to work in mobile ad-hoc networking environments, as the information necessary for pre-configuration is not available. This situation is exacerbated by the dynamic nature of the environment's membership, so that the time and resources expended in offline management are largely wasted. This paper presents a decentralized access control system that implements sociological trust constructs in a quantitative system to evaluate interaction partners. A distributed, node-centric approach to reputation management processes nodal behavior feedback and provides a reputation index that nodes use to determine trustworthiness their peers before establishing associations. The availability of a reputation index gives a measure of expectation of a peer's behavior, based on past performance, and makes a MANET a more distributed operational environment.

Toward a decentralized trust-based access control system for dynamic collaboration

A mobile ad hoc network (MANET) is a wireless network that uses multi-hop peer-to-peer routing instead of static network infrastructure to provide network connectivity. MANETs have applications in rapidly deployed and dynamic military and civilian systems. The network topology in a MANET usually changes with time. Therefore, there are new challenges for routing protocols in MANETs since traditional routing protocols may not be suitable for MANETs. For example, some assumptions used by these protocols are not valid in MANETs or some protocols cannot efficiently handle topology changes. 
Researchers are designing new MANET routing protocols and comparing and improving existing MANET routing protocols before any routing protocols are standardized using simulations. However, the simulation results from different research groups are not consistent with each other. This is because of a lack of consistency in MANET routing protocol models and application environments, including networking and user traffic profiles. Therefore, the simulation scenarios are not equitable for all protocols and conclusions cannot be generalized. Furthermore, it is difficult for one to choose a proper routing protocol for a given MANET application. 
According to the aforementioned issues, my Ph.D. research focuses on MANET routing protocols. Specifically, my contributions include the characterization of different routing protocols using a novel systematic relay node set (RNS) framework, design of a new routing protocol for MANETs, a study of node mobility, including a quantitative study of link lifetime in a MANET and an adaptive interval scheme based on a novel neighbor stability criterion, improvements of a widely-used network simulator and corresponding protocol implementations, design and development of a novel emulation test bed, evaluation of MANET routing protocols through simulations, verification of our routing protocol using emulation, and development of guidelines for one to choose proper MANET routing protocols for particular MANET applications. 
Our study shows that reactive protocols do not always have low control overhead, as people tend to think. The control overhead for reactive protocols is more sensitive to the traffic load, in terms of the number of traffic flows, and mobility, in terms of link connectivity change rates, than other protocols. Therefore, reactive protocols may only be suitable for MANETs with small number of traffic loads and small link connectivity change rates. We also demonstrated that it is feasible to maintain full network topology in a MANET with low control overhead. This dissertation summarizes all the aforementioned methodologies and corresponding applications we developed concerning MANET routing protocols.

Mobile ad-hoc network routing protocols: methodologies and applications

Behavior grading is crucial to the operation of a mobile ad-hoc network (MANET). Our Key Management System project has established a behavior grading and tracking mechanism through the use of X.509 v3 certificates with appropriate extensions. Our distributed, node-centric approach to reputation management processes nodal behavior feedback and provides a reputation index that nodes use to determine trustworthiness of their peers before establishing IPsec security associations. Behavior feedback is "aged" in a three-window weighted average, which emphasizes current behavior while conservatively approximating behavior trends over time. The windowed approach maintains non-reputable evidence, which supports the reputation calculation and facilitates the exchange of behavior information with new nodes as they join the network.

Calculating a node's reputation in a mobile ad hoc network

The integration of various network-level functions, including routing, management, and security, is critical to the efficient operation of a mobile ad hoc network. In this article we focus on network mobility (rather than node mobility), implying the movement of entire subnetworks with respect to one another, while individual users initially associated with one such subnetwork may also move to other domains. One example is a battlefield network that includes ships, aircraft, and ground troops. In this "network of networks", subnets (e.g. shipboard networks) may be interconnected via a terrestrial mobile wireless network (e.g., between moving ships). We discuss the design and implementation of a new ad hoc routing protocol, a suite of solutions for policy-based network management, and approaches for key management and deployment of IPsec in a MANET. These solutions, in turn, are integrated with real-time middleware, a secure radio link, and a topology monitoring tool. We briefly describe each component of the solution, and focus on the challenges and approaches to integrating these components into a cohesive system to support network mobility. We evaluate the effectiveness of the system through experiments conducted in a wireless ad hoc testbed.

/pdf/network-mobility-and-protocol-interoperability-in-ad-hoc-4n8xva6s69.pdf

Network mobility and protocol interoperability in ad hoc networks

Blind broadcast in a wireless ad hoc network means any mobile node will rebroadcast all received broadcast messages. One node may receive the same copy of a message from more than one neighbor, so unnecessary overhead is introduced. A connected dominating set (CDS) can be used to reduce broadcast overhead. We propose a proactive link state routing protocol, integrated with CDS discovery algorithms, as a promising approach for routing in wireless ad hoc networks. This paper presents approximation algorithms to find a minimal CDS for a given network. A prototype of a proactive link state routing protocol integrated with CDS algorithms is introduced. Both simulation and analytical results indicate better performance than other algorithms.

Minimal connected dominating set algorithms and application for a MANET routing protocol

We present an innovative routing protocol that utilizes multiple channels to improve performance in a mobile ad hoc network. The basic idea of the design is to provide nodes with the ability to use multiple channels effectively so that multiple useful transmissions can occur simultaneously, thus improving network capacity. The proposed scheme requires minor changes to existing proactive or table-driven routing protocols and no modifications to current the IEEE 802.11 medium access control protocol. To avoid inefficiencies due to transmission of periodic updates in proactive routing protocols, the proposed scheme divides the network layer into control and data planes. To demonstrate the multi-channel routing scheme, we extend the OSPF-MCDS routing protocol to a multi-channel version, OSPF- MCDS-MC. Simulation results indicate that OSPF-MCDS-MC successfully exploits multiple channels to improve network capacity. The routing protocol allows the network goodput to increase in proportion to the number of available channels, even as the number of nodes and network load increase, in both single- hop and multiple-hop networks.

OSPF-MCDS-MC: a routing protocol for multi-channel wireless ad-hoc networks

The availability of low-cost network interface cards (NICs) has made the IEEE 802.11 medium access control (MAC) protocol the de facto MAC standard for wireless mobile ad-hoc networks. Although the IEEE 802.11 MAC protocol is designed to have stations share a single channel in a network, many of the IEEE 802.11 physical (PHY) layer standards define multiple channels and allow the simultaneous, non-interfering use of some of these channels. Therefore, simultaneous communications can occur through different channels, offering the opportunity to increase effectivenetwork capacity. We present an innovative routing protocol that utilizes multiple channels to improve performance in a mobile ad hoc network. The key feature of the protocol is that nodes can effectively use multiple channels for simultaneous useful transmissions, thus improving networkcapacity. The proposed scheme requires minor changes to existing proactive or table-driven routing protocols and no modifications to current the IEEE 802.11 MAC protocol. To mitigate the overhead of periodic updates in proactive routing protocols, the proposed scheme divides the network layer into control and data planes. To demonstrate the multi-channel routing scheme, we extend the OSPFMCDS routing protocol to a multi-channel version, OSPFMCDS- MC or, more simply, OMM. Simulation and experimental results indicate OMM successfully exploits multiple channels to increase network capacity. The protocol allows the network goodput to increase in proportion to the number of available channels, even as the number of nodes and network load increase, in both single-hop and multiple-hop networks. We also present a prototype implementation for experimental validation of the proposed multi-channel routing protocol scheme. The implementation includes the multi-channel routing protocol and a virtual interface module, which acts as a buffer for outgoing packets and performs channel-related functions, such as channel selection and switching, while ensuring portability.

/pdf/routing-in-multi-channel-wireless-ad-hoc-networks-ospf-mcds-e43o0a0qgu.pdf

Routing in Multi-Channel Wireless Ad-hoc Networks: OSPF-MCDS-MC

: The integration of various network-level functions, including routing, management, and security, is critical to the efficient operation of a mobile ad hoc network (MANET). This paper focuses on network mobility, implying the movement of entire subnetworks with respect to one another, while individual users initially associated with one such subnetwork may also move to other domains. One example is a battlefield network that includes ships, aircraft, and ground troops. In this "network of networks," subnets (e.g., shipboard networks) may be interconnected via a terrestrial mobile wireless network (e.g., between moving ships). We discuss the design and implementation of a new ad hoc routing protocol, a suite of solutions for policy-based network management, and approaches for key management and deployment of IPsec in a MANET. These solutions are integrated with real-time middleware, a secure radio link, and a topology monitoring tool. We briefly describe each component of the solution and focus on the challenges and approaches to integrating these components into a cohesive system to support network mobility. We evaluate the effectiveness of the system through experiments conducted in a wireless ad hoc testbed.

Tao Lin

Papers

Network mobility and protocol interoperability in ad hoc networks

Minimal connected dominating set algorithms and application for a MANET routing protocol

OSPF-MCDS-MC: a routing protocol for multi-channel wireless ad-hoc networks

Routing in Multi-Channel Wireless Ad-hoc Networks: OSPF-MCDS-MC

Interoperable Security, Routing and Quality of Service for Ad-Hoc Network Mobility