Mobile collaborative work is a developing sub-area of Computer Supported Collaborative Work (CSCW). The future of this field will be marked by a significant increase in mobile device usage as a tool for co-workers to cooperate, collaborate and work on a shared workspace in real-time to produce artefacts such as diagrams, text and graphics regardless of their geographical locations. A real-time collaboration editor can utilise a centralised or a replicated architecture. In a centralised architecture, a central server holds the shared document as well as manages the various aspects of the collaboration, such as the document consistency, ordering of updates, resolving conflicts and the session membership. Every user's action needs to be propagated to the central server, and the server will apply it to the document to ensure it results in the intended document state. Alternatively, a decentralised or replicated architecture can be used where there is no central server to store the shared document. Every participating site contains a copy of the shared document (replica) to work on separately. Using this architecture, every user's action needs to be broadcast to all participating sites so each site can update their replicas accordingly. The replicated architecture is attractive for such applications, especially in wireless and ad-hoc networks, since it does not rely on a central server and a user can continue to work on his or her own local document replica even during disconnection period. However, in the absence of a dedicated server, the collaboration is managed by individual devices. This presents challenges to implement collaborative editors in a replicated architecture, especially in a mobile network which is characterised by limited resource reliability and availability. This thesis addresses challenges and requirements to implement group editors in wireless ad-hoc network environments where resources are scarce and the network is significantly less stable and less robust than wired fixed networks. The major contribution of this thesis is a proposed framework that comprises the proposed algorithms and techniques to allow each device to manage the important aspects of collaboration such as document consistency, conflict handling and resolution, session membership and document partitioning. Firstly, the proposed document consistency algorithm ensures the document replicas held by each device are kept consistent despite the concurrent updates by the collaboration participants while taking into account the limited resource of mobile devices and mobile networks. Secondly, the proposed conflict management technique provides users with conflict status and information so that users can handle and resolve conflicts appropriately. Thirdly, the proposed membership management algorithm ensures all participants receive all necessary updates and allows users to join a currently active collaboration session. Fourthly, the proposed document partitioning algorithm provides flexibility for users to work on selected parts of the document and reduces the resource consumption. Finally, a basic implementation of the framework is presented to show how it can support a real time collaboration scenario.

The number of electronic devices, equipped with a wireless interface has exploded over the last decades. Unfortunately, their usage is often restricted to the connection to a wired infrastructure, even for local communications. That is quite surprising as the research area of infrastructureless, or ad hoc, networks has flourished for years. The literature on ad hoc networks is very rich, but their usage almost inexistent. Potential users have plenty of solutions at hand, but do not exploit them. Even if ad hoc networks allow us to get rid of the infrastructure, they still require an implicit agreement on the solution to use. Nevertheless, it is very dicult to pick in the rich panel of protocols the best one, that would fit any ad hoc user in any ad hoc network. As an example, it has been demonstrated, for the routing, that each protocol has definite advantages and disadvantages, in every different scenario, and is well suited for certain situations. Yet, a salient feature of ad hoc networks is precisely that the panel of situations is very large. The ad hoc network conditions are influenced by the number of ad hoc users, their relative positions, their capabilities, their mobility pattern, the applications they use, the traffic load and type, and so forth. Moreover, the users may themselves be heterogeneous, with different hardware and software capabilities, mobile behaviour and communication needs. Hence, there is a particular need in ad hoc networking for flexible techniques. We contribute to this problem by studying the feasibility of overlay routing and giving some hints in that direction. We explain how the overlay members can avoid the expensive process of building an overlay topology, before using their customised routing application. The rationale exploits the broadcast nature of ad hoc networks, and is qualified as a Reactive Overlay Approach. We also detail an elementary reactive overlay routing application and test it, by simulations, in a variety of conditions, including the network and overlay densities. This performance study shows the feasibility and the efficiency of overlay routing applications developed according to the Reactive Overlay Approach. It also evidences the impact of using an appropriate value for the neighbourhood range, defined as the maximum number of hops between two overlay neighbours. Hence, we detail the critical neighbourhood range (CNR) problem, which, in short, consists in determining the minimum neighbourhood range value that generates a connected overlay. We solve it in the asymptotic case, i.e. when the number of nodes in the underlay or the size of the field tends to infinity. The mathematical results are interesting in the sense that they can be useful for a better understanding of the interaction between various typical characteristics of a connected overlay topology on an ad hoc network. However, the theoretical, asymptotic, CNR is not adequate in practice. We thus also explore heuristics for estimating the CNR. We present a simple protocol which estimates an appropriate neighbourhood range for overlay routing applications. For the purpose of its evaluation, we define general performance criteria based on overlay flooding. Namely, these are the delivery percentage, bandwidth consumption and time duration of flooding on the overlay. The main drawback of the Reactive Overlay Approach is the amount of bandwidth consumed during the flooding of overlay route requests. Hence, we also consider the Proactive Overlay Approach, which consists in building the overlay topology before the emission of any overlay broadcast message, and maintaining it. We compare the quality of various overlay topologies in the static case. We finally describe and evaluate the Overlay Topology Control (OTC) protocol, that maintains, in a mobile context, the overlay topology as close as possible to the overlay topology evaluated as the best. The main objection that would arise against overlay routing on ad hoc networks is that the ad hoc nodes do generally own poor resources and that overlay routing consumes them even more than native routing. The feasibility study we conducted with the reactive approach and the evaluation of OTC, designed in the context of the proactive overlay approach, confirm that the consumption of resources must be handled carefully. Nevertheless, they show that this problem is not insurmountable.

Gemeinsamer Workshop von Universitaetsrechenzentrum und Professur Rechnernetze und verteilte Systeme der Fakultaet fuer Informatik der TU Chemnitz. Der Vortrag bietet eine kurze Einführung in die Welt der Ad-Hoc-Netzwerke.

Στη διπλωματική εργασία μελετάμε τη δυνατότητα συν-λειτουργίας των HAPs και των ad-hoc δικτύων. Μέσα από τη θεωρητική μελέτη και τις προσομοιώσεις προσπαθούμε να μελετήσουμε τις επιδόσεις ενός τέτοιου υβριδικού συστήματος, όσον αφορά τη δρομολόγηση και την αξιοπιστία στη μετάδοση της πληροφορίας. Αρχικά, προχωράμε σε μια θεωρητική μελέτη των στρατοσφαιρικών πλατφόρμων (HAPs) και των ad-hoc δικτύων. Αναφέρουμε δυνατότητες, τεχνολογίες και εφαρμογές των δύο αυτών τηλεπικοινωνιακών τύπων τεχνολογίας. Στη συνέχεια, παρουσιάζουμε το τηλεπικοινωνιακό σενάριο πάνω στο οποίο στηρίχθηκε η προσομοίωση και, τέλος, παρουσιάζουμε αναλυτικά τα αποτελέσματα που προέκυψαν από την πειραματική διαδικασία με μορφή πινάκων και διαγραμμάτων καθώς και τα συμπεράσματα στα οποία καταλήγουμε βάσει των μετρήσεών μας. / --

<p>Peer-to-Peer networking technology is evolving rapidly. P2P networks overcome the limitations of client/server networks where each computer shares resources of other computer. There are different types of P2P networks depending upon their functionalities. Peer to peer networks provide long list of features like: selection of nearby peers, redundant storage, effi-cient search/location of data items, data performance or guarantees etc. It is important to see that how P2P can work with wireless ad hoc networks and why it is important. What are im-portant issues which come across by using P2P and wireless ad hoc networks together. How TCP/IP stack can be affected. How the whole system looks like in which P2P techniques are used with wireless ad hoc routing protocols to perform different tasks and services.</p>

Wireless ad hoc networks have been emerged to support applications, in which it is required/desired to have wireless ommunications among a variety of devices without relying on any infrastructure or central managements. In ad hoc networks, wireless devices, simply called nodes, have limited transmission range. Therefore, each node can directly communicate with only those within its transmission range and requires other nodes to act as routers in order to communicate with out-of-range estinations. One of the fundamental operations in ad hoc networks is broadcasting, where a node sends a message to all other nodes in the network. This can be achieved through flooding, in which every node transmits the first copy of the received message. However, flooding can impose a large number of redundant transmissions, which can result in significant waste of constrained resources such as bandwidth and battery power. One of the contributions of this work is to propose efficient broadcast algorithms which can significantly reduce the number of redundant transmissions. We also consider some of the security issues of ad hoc networks. In particular, we carefully analyze the effect of the wormhole attack, which is one of the most severe threats against ad hoc networks. We also propose a countermeasure, which is an improvement over the existing timing-based solutions against the wormhole attack. Finally, in the last chapter, we propose novel point compression techniques which can be used in Elliptic Curve Cryptography (ECC). ECC can provide the same level of security as other public key cryptosystems (such as RSA) with substantially smaller key sizes. Smaller keys can result in smaller system parameters, bandwidth savings, faster implementations and lower power consumption. These advantages make ECC interesting for ad hoc networks with restricted devices.

Peer-to-Peer networking technology is evolving rapidly. P2P networks overcome the limitations of client/server networks where each computer shares resources of other computer. There are different types of P2P networks depending upon their functionalities. Peer to peer networks provide long list of features like: selection of nearby peers, redundant storage, effi-cient search/location of data items, data performance or guarantees etc. It is important to see that how P2P can work with wireless ad hoc networks and why it is important. What are im-portant issues which come across by using P2P and wireless ad hoc networks together. How TCP/IP stack can be affected. How the whole system looks like in which P2P techniques are used with wireless ad hoc routing protocols to perform different tasks and services.

In this paper, a mobile network is combined with backbone structure to form a hierarchical ad hoc network. Usually, a mobile ad hoc network is assumed to be homogeneous such that each mobile node uses the same radio capability. However, a homogenous ad hoc network suffers from poor scalability. In this thesis we establish a physical (not logical) hierarchical network to solve this problem in which backbone nodes are employed to transmit for long distance using larger radio power at high tier and cluster structure is used to efficiently utilize resources in a wide and dynamic network. We propose a cluster head determination scheme based on the degree variations of nodes. The nodes with minimum degree variation in the neighborhood are considered more stable and will be selected as the cluster heads. The cluster heads form the backbone nodes and other nodes are the cluster members. The information of cluster members and the nodes in neighboring clusters are recorded in a table of cluster head. According to the information, we have the knowledge of whether the destination node is close to the source node and can determine how to route the transmission. Routing is divided into low tier and high tier routing to relieve the workload of backbone network. The simulation results demonstrate that the proposed hierarchical routing in two tiers (HRTT) improves some problems occurred in the flat network.

This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach is called Dynamic Age-Dependent Backoff (DADB) which is derived from the ADB scheme and aims to improve the ADB scheme when the traffic load is high. Improvement of our scheme are provisioned by adjusting the size of the persistent factor of high traffic categories taking into account both age time of frame and network conditions. We evaluate the performance of DADB through simulations and compare it with the ADB scheme proposed in the 802.11e. Results show that our scheme DADB is similar to ADB scheme which can improve the delay and jitter in wireless network. Especially at high traffic load conditions, DADB outperforms the basic ADB: our scheme improve the throughput of high priority traffic category and decrease collision rate when traffic load is heavy.

In wireless mobile ad hoc networks (MANETs), cooperation cannot be an im- plicit assumption anymore. Each profit-oriented network node has the intention to be selfish due to limited resource possession. In this dissertation, we investigate the truthful resource management that induces network nodes to reveal true information and stimulate cooperation. We propose the Transmission Power Recursive Auction Mechanism routing pro- tocol (TEAM) and the Truthful Topology Control mechanism (TRUECON) to cope with the selfish intention and achieve resource effciency in a non-cooperative envi- ronment. We prove both are strategy-proof and have some theoretic bounds on the performance. Compared with the existing routing protocols and topology control al- gorithms, TEAM and TRUECON are more effcient when dealing with the selfishness in MANETs. We conduct a study on anonymity enhancement in MANETs by reducing trans- mission power of network nodes. A routing protocol - Whisper is presented. Simu- lation results show that it has desirable properties in terms of anonymity and power effciency.