Restricted Mobility Improves Delay-Throughput Trade-offs in Mobile Ad-Hoc Networks

In this paper we revisit two classes of mobility models which are widely used to repre-sent users ’ mobility in wireless networks: Random Waypoint (RWP) and Random Direction (RD). For both models we obtain systems of partial differential equations which describe the evolution of the users ’ distribution. For the RD model, we show how the equations can be solved analytically both in the stationary and transient regime adopting standard mathematical techniques. Our main contributions are i) simple expressions which relate the transient dura-tion to the model parameters; ii) the definition of a generalized random direction model whose stationary distribution of mobiles in the physical space corresponds to an assigned distribution

Scalable Routing Easy as PIE: a Practical Isometric Embedding Protocol (Technical Report)

We present PIE, a scalable routing scheme that achieves 100% packet delivery and low path stretch. It is easy to implement in a distributed fashion and works well when costs are associated to links. Scalability is achieved by using virtual coordinates in a space of concise dimensionality, which enables greedy routing based only on local knowledge. PIE is a general routing scheme, meaning that it works on any graph. We focus however on the Internet, where routing scalability is an urgent concern. We show analytically and by using simulation that the scheme scales extremely well on Internet-like graphs. In addition, its geometric nature allows it to react efficiently to topological changes or failures by finding new paths in the network at no cost, yielding better delivery ratios than standard algorithms. The proposed routing scheme needs an amount of memory polylogarithmic in the size of the network and requires only local communication between the nodes. Although each node constructs its coordinates and routes packets locally, the path stretch remains extremely low, even lower than for centralized or less scalable state-of-the-art algorithms: PIE always finds short paths and often enough finds the shortest paths.Comment: This work has been previously published in IEEE ICNP'11. The present document contains an additional optional mechanism, presented in Section III-D, to further improve performance by using route asymmetry. It also contains new simulation result

Huge networks, tiny faulty nodes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 87-91).Can one build, and efficiently use, networks of arbitrary size and topology using a "standard" node whose resources, in terms of memory and reliability, do not need to scale up with the complexity and size of the network? This thesis addresses two important aspects of this question. The first is whether one can achieve efficient connectivity despite the presence of a constant probability of faults per node/link. Efficient connectivity means (informally) having every pair of regions connected by a constant fraction of the independent, entirely non-faulty paths that would be present if the entire network were fault free - even at distances where each path has only a vanishingly small probability of being fault-free. The answer is yes, as long as some very mild topological conditions on the high level structure of the network are met - informally, if the network is not too "thin" and if it does not contain too many large "holes". The results go against some established "empyrical wisdom" in the networking community. The second issue addressed by this thesis is whether one can route efficiently on a network of arbitrary size and topology using only a constant number c of bits/node (even if c is less than the logarithm of the network's size!). Routing efficiently means (informally) that message delivery should only stretch the delivery path by a constant factor. The answer again is yes, as long as the volume of the network grows only polynomially with its radius (otherwise, we run into established lower bounds). This effectively captures every network one may build in a universe (like our own) with finite dimensionality using links of a fixed, maximum length and nodes with a fixed, minimum volume. The results extend the current results for compact routing, allowing one to route efficiently on a much larger class of networks than had previously been known, with many fewer bits.by Enoch Peserico.Ph.D

Simulation-based Performance Evaluation of MANET Backbone Formation Algorithms

As a result of the recent advances in the computation and communications industries, wireless communications-enabled computing devices are ubiquitous nowadays. Even though these devices are introduced to satisfy the user’s mobile computing needs, they are still unable to provide for the full mobile computing functionality as they confine the user mobility to be within certain regions in order to benefit from services provided by fixed network access points. Mobile ad hoc networks (MANETs) are introduced as the technology that potentially will make the nowadays illusion of mobile computing a tangible reality. MANETs are created by the mobile computing devices on an ad hoc basis, without any support or administration provided by a fixed or pre-installed communications infrastructure. Along with their appealing autonomy and fast deployment properties, MANETs exhibit some other properties that make their realization a very challenging task. Topology dynamism and bandwidth limitations of the communication channel adversely affect the performance of routing protocols designed for MANETs, especially with the increase in the number of mobile hosts and/or mobility rates. The Connected Dominating Set (CDS), a.k.a. virtual backbone or Spine, is proposed to facilitate routing, broadcasting, and establishing a dynamic infrastructure for distributed location databases. Minimizing the CDS produces a simpler abstracted topology of the MANET and allows for using shorter routes between any pair of hosts. Since it is NP-complete to find the minimum connected dominating set, MCDS, researchers resorted to approximation algorithms and heuristics to tackle this problem. The literature is rich of many CDS approximation algorithms that compete in terms of CDS size, running time, and signaling overhead. It has been reported that localized CDS creation algorithms are the fastest and the lightest in terms of signaling overhead among all other techniques. Examples of these localized CDS algorithms are Wu and Li algorithm and its Stojmenovic variant, the MPR algorithm, and Alzoubi algorithm. The designers of each of these algorithms claim that their algorithm exhibits the highest degree of localization and hence incurs the lowest cost in the CDS creation phase. However, these claims are not supported by any physical or at least simulation-based evidence. Moreover, the cost of maintaining the CDS (in terms of the change in CDS size, running time, and signaling overhead), in the presence of unpredictable and frequent topology changes, is an important factor that has to be taken into account -a cost that is overlooked most of the time. A simulation-based comparative study between the performance of these algorithms will be conducted using the ns2 network simulator. This study will focus on the total costs incurred by these algorithms in terms of CDS size, running time, and signaling overhead generated during the CDS creation and maintenance phases. Moreover, the effects of mobility rates, network size, and mobility models on the performance of each algorithm will be investigated. Conclusions regarding the pros and cons of each algorithm will be drawn, and directions for future research work will be recommended

Hierarchical Routing in Low-Power Wireless Networks

Steen, M.R. van [Promotor

Elements of the Theory of Dynamic Networks

The challenge of computing in a highly dynamic environment.</jats:p