Wireless Multi Hop Access Networks and Protocols

As more and more applications and services in our society now depend on the Internet, it is important that dynamically deployed wireless multi hop networks are able to gain access to the Internet and other infrastructure networks and services. This thesis proposes and evaluates solutions for providing multi hop Internet Access. It investigates how ad hoc networks can be combined with wireless and mesh networks in order to create wireless multi hop access networks. When several access points to the Internet are available, and the mobile node roams to a new access point, the node has to make a decision when and how to change its point of attachment. The thesis describes how to consider the rapid fluctuations of the wireless medium, how to handle the fact that other nodes on the path to the access point are also mobile which results in frequent link and route breaks, and the impact the change of attachment has on already existing connections. Medium access and routing protocols have been developed that consider both the long term and the short term variations of a mobile wireless network. The long term variations consider the fact that as nodes are mobile, links will frequently break and new links appear and thus the network topology map is constantly redrawn. The short term variations consider the rapid fluctuations of the wireless channel caused by mobility and multi path propagation deviations. In order to achieve diversity forwarding, protocols are presented which consider the network topology and the state of the wireless channel when decisions about forwarding need to be made. The medium access protocols are able to perform multi dimensional fast link adaptation on a per packet level with forwarding considerations. This i ncludes power, rate, code and channel adaptation. This will enable the type of performance improvements that are of significant importance for the success of multi hop wireless networks

Micro mobility and internet access performance for TCP connections in Ad Hoc networks

In ad hoc mobile networks nodes typically communicate over wireless channels and are capable of movement. These are networks that support multihop communication and can be formed on a temporary basis. This paper evaluates a solution that allows mobile nodes to access the wired Internet and roam from base station to base station. The solution is based on the extension of Mobile IP capabilities to the ad hoc network while a micro-mobility protocol is adapted to support local migration. We evaluate the performance of this solution with regard to reliable transport layer connections. It is shown that a high throughput is possible to achieve for high mobility speeds. It is also observed that, as the number of hops between a mobile node and the base station increases, the throughput is decreased because of the characteristics of the wireless environment and the medium access layer protocol

Performance and implementation of routing and wireless transport layer connections in micro mobility Ad hoc networks

In mobile ad hoc networks wireless nodes communicate over multi hop links and are capable of movement. This paper evaluates a solution that provide these networks with Internet Access and the capability to roam between different access points. Design and implemenation consideration are discussed that focus on behaviour and criterias for performing handover. Simulation result show that the main factor affecting transport performance during micro mobility are link breaks, where choice of TCP flavour and advanced window freezing behaviours have little effect It is also shown that a new kind of TCP unfairness arise when different TCP flavours compete among each other

Performance of Internet Access Solutions in Mobile Ad Hoc Networks

Although an autonomous mobile ad hoc network (MANET) is useful in many scenarios, a MANET connected to the Internet is more desirable. This interconnection is achieved by using gateways, which act as bridges between a MANET and the Internet. Before a mobile node can communicate with an Internet host it needs to find a route to a gateway. Thus, a gateway discovery mechanism is required. In this paper the MANET routing protocol ad hoc on-demand distance vector (AODV) is extended to achieve the interconnection between a MANET and the Internet. Moreover, the paper investigates and compares three approaches for gateway discovery. The question of whether the configuration phase with the gateway should be initiated by the gateway, by the mobile node or by mixing these two approaches is being discussed. We have implemented and simulated these three methods and we discuss the advantages and disadvantages of the three alternative

Cross layer routing and media access control with channel dependant forwarding in wireless ad-hoc networks

Wireless ad hoc networks have the last 10 years gained a lot of attention within the research community. A wireless ad hoc network is a special type of wireless network where nodes are typically mobile and doesn’t rely on any fixed infrastructure to operate correctly. Much work has been done on developing robust and stable routing algorithms that consider the dynamic nature of an ad hoc network: nodes are very mobile and enter and leave the network in random ways. Much work has also been done on developing medium access control (MAC) algorithms that consider many wireless characteristics such as interference and the hidden terminal problems. Little work has so far been done on developing joint routing and MAC layer solutions that consider the variations of the wireless channel. We present a solution where the routing protocol can cooperate with the MAC layer to provide power control and channel dependent forwarding. By establishing non-disjoint multiple paths between each source and destination, nodes may be able to avoid links that are currently in a deep signal fade by choosing a more beneficial next hop path

Urban mesh ad hoc networks

Mesh networking is currently gaining much attention, within both academia and industry. Mesh networking allows cheap and fast deployment of wireless services. It is regarded as a very promising solution for urban deployment scenarios as well as for temporary emergency response situations. Another related promising field is that of ad hoc wireless networking, which consists of mobile nodes that dynamically create and maintain a network without the need for any infrastructure. We propose a solution and architecture for urban mesh ad hoc networks, a network that combines mesh networking with ad hoc networks for urban environments. We present four types of ad hoc mesh and ad hoc mesh networks. The most general one consists of mesh nodes, called mesh points (MP), that act as a type of access point for user nodes (UN). The MPs have at least two interfaces: one which is used to communicate with UNs, and one which is used to maintain the mesh access network and transport data. These two interfaces can basically use any type of technology (IEEE 802.11 a/b/g, WiMax, etc.), and for capacity reasons it is generally regarded that the best solution is to let the mesh interface operate on a separate high-capacity channel or channels. An intricate part of these types of networks are routing and location services. In our solution, UN devices operate in ad hoc mode running an ad hoc routing protocol. This allows UNs that wish to communicate to connect directly in an ad hoc manner, or through an MP. An important question is therefore whether two UNs that wish to communicate should connect through the mesh or connect directly. We show that from a capacity point of view whether a UN should route its packets to the closest available MP, or through a ad hoc network, depends on the environment the network is located, the amount traffic and the type of protocols used. Since MPs need to know where to route packets within the mesh, i.e., locating the MP closest to the destination UN, each UN run a small application that registers the UN to the mesh network. In addition to the above features we have developed a new MAC that quickly queries two candidate nodes, which picks the candidate with the currently best radio conditions. This enable nodes to cope with deep dips in signal strength due to fast fading, a well-known problem in urban environments. We show that this new protocol achieves significantly lower delays. We also show that in dense urban environments performance and battery lifetime can be improved if ad hoc technologies are used

Routing in hybrid ad hoc networks using service points

In mobile ad hoc networks, nodes are often modeled as having the same capabilities. However, there are many cases in which certain nodes host special services to other nodes in the network. Examples of such services are Internet access, DNS proxy or AAA servers. We refer to these special nodes as netmarks. Because there is a high likelihood that netmarks will communicate with the rest of the network, routes to netmarks are discovered and maintained proactively. By forming a virtual overlay between netmarks, we can provide location and routing services as well as Internet access for the common nodes. This hybrid routing approach is called netmark overlay routing protocol, NOR

Internet connectivity for mobile ad hoc networks

The need for ad hoc networks arises when a number of mobile nodes gather in one particular location and form autonomous networks. Ad hoc networks can be adjoined to the Internet, introducing routing and addressing issues that require new features from ad hoc networking protocols. The Internet Gateway can offer global addressability and bidirectional Internet connectivity to every node in the ad hoc network. This can be done in such a way that mobile wireless nodes can migrate between wireless access points that have direct access to the wired Internet and the wireless ad hoc networks that do not have any such local access point infrastructure. Mobile IP can be employed to make such movement seamless (whenever physically possible), even though it occurs between domains with previously incompatible routing models. We believe that IPv6 and Mobile IPv6 afford important advantages for making such attachments, especially regarding router advertisement and address autoconfiguration. In this paper, we show how general ad hoc networks can be connected to the Internet by Internet Gateways, and then describe our specific experiments with Ad hoc On-Demand Distance Vector Routing (AODV) for IPv6 (AODV6). After demonstrating the basic principles allowing access to the Internet, we then detail our further experiments using Mobile IPv6. Copyright (C) 2002 John Wiley Sons, Ltd

Dynamic combination of multiple host-based anomaly detectors with broader detection coverage and fewer false alerts

The original publication is available at www.springerlink.comTo achieve broader detection coverage with fewer false alarms, a POMDP-based anomaly detection model combining several sate-of-the-art host-based anomaly detectors is proposed in this paper. An optimal combinatorial manner is expected to be discovered through a policy-gradient reinforcement learning algorithm, based on the independent actions of those detectors, and the behavior of the proposed model can be adjusted through a global reward signal to adapt to various system situations. A primarily experiment with some comparative studies are carried out to validate its performance.Zonghua Zhang and Hong She