Wissam Fawaz

Disruption-Tolerant Networking: A Comprehensive Survey on Recent Developments and Persisting Challenges

Nowadays, wireless networks are witnessing several deployments in various extreme environments where they suffer from different levels of link disruptions depending on the severity of the operating conditions. In all cases, their operation requirements are differently altered and their performance is negatively affected rendering them heterogeneous by nature. In the open literature, these networks are known as Intermittently Connected Networks (ICNs). The existing Internet protocols fail to operate properly in the context of ICNs, thus raising a variety of new challenging problems that are attracting the attention of the networking research community. Delay-/Disruption-Tolerant Networking emerged as a highly active area of research where networking experts compete in addressing the various ICN problems. Over time, unicast routing, one of the architectural key components common to all ICNs, became an almost independent field of research in which significant efforts continue to be invested. In contrast, network architectural designs, scheduling and forwarding issues dating from the early days of Inter-Planetary Networks (IPNs) have received relatively little attention and accumulate numerous pending challenges. Moreover, the gap caused by the lack of accurate ICN mathematical models is still large irrespective of some of the appreciated seminal works in this direction. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlight pending open issues in each of them.

Service level agreement and provisioning in optical networks

This article proposes a service level agreement applied to the optical domain (O-SLA), which is expected to be the near- and long-term network technology of the great bandwidth capacity offered by optical devices. After an exposition of the rationale behind an optical SLA, parameters that could be included in this O-SLA, as well as their values for four classes of services are proposed. Different client (wavelength or subwavelength) and service types (from leased wavelength to bandwidth on demand) are distinguished when necessary. The last part of this article presents issues related to the provisioning of services emanating from this O-SLA.

Probabilistic Bundle Relaying Schemes in Two-Hop Vehicular Delay Tolerant Networks

One class of Vehicular Delay-Tolerant Networks consists of two node types: stationary and mobile. Stationary nodes deployed along roadsides cannot directly communicate as they are considerably distant. Mobile nodes mounted over vehicles opportunistically entering the range of a stationary source serve as relays that carry bundles to the destination. In this letter, we introduce a novel relaying scheme that probabilistically determines a vehicles suitability to carry bundles. Hence, bundles are released to a present vehicle if and only if that latter contributes in minimizing the mean transit delay. Extensive simulations were performed to gauge the merit of the proposed scheme.

Space-Time Codes for MIMO Ultra-Wideband Communications and MIMO Free-Space Optical Communications with PPM

In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log2(M-1)/n log2(M).

Modeling and Delay Analysis of Intermittently Connected Roadside Communication Networks

Vehicular networks outline a challenging terrestrial application of the emerging delay-tolerant networking (DTN) paradigm where wireless links experience frequent disruptions. Thus, continuous end-to-end paths are unguaranteed. Under such conditions, mobile vehicles present opportunistic relaying capabilities that promote network connectivity, particularly between stationary and isolated roadside units. In this context, we investigate a challenging information-delivery-delay minimization problem. Information is encapsulated into bundles buffered at the source, and vehicles opportunistically transport them to the destination. Consequently, bundles undergo both queueing and transit delays. We propose a probabilistic bundle release scheme (PBRS) under which a roadside unit performs typical Internet-like forwarding where a single bundle is only released to an arriving relatively high-speed vehicle. This ensures a minimized bundle transit. In contrast, under a greedy bundle release scheme (GBRS), a bundle is released to any arriving vehicle, regardless of its speed. Two queueing models are developed to characterize a roadside unit and evaluate its performance under both schemes. A simulation framework is set up to validate these models. Results indicate the inefficiency of the typical Internet packet-like release mechanism as it incurs excessive bundle queueing delays. A bulk bundle release (BBR) extension is proposed as an effective solution. We show that GBRS-BBR outperforms PBRS-BBR.

Priority-enabled optical shared protection: An online efficiency evaluation study

The availability of an optical connection is considered to be a critical service differentiator in WDM optical networks. In this regard, the design of a protection scheme that is able to improve the availability of high priority connections while making efficient use of optical resources is a major concern for optical network operators. In a previous work, we proposed the so-called priority-aware shared protection as a potential survivability scheme for next generation WDM networks to deal with the previously exhibited concern. This paper develops an online study whose main purpose is to assess the efficiency of the aforementioned protection scheme. Through this study, we show that the priority-aware shared protection strategy is able to achieve both the best efficiency in terms of resource usage and in terms of availability satisfaction rate compared to existing protection solutions.

Which Vehicle To Select

In wireless networking, an Opportunistic Bundle Release Mechanism (OBRM) is a data bundle forwarding mechanism characterized by its ability to operate over Intermittently Connected Networks (ICNs) where end-to-end paths are not continuously available. Known for their intrinsic connectivity intermittence, vehicular networks constitute an ideal recreation ground for OBRMs. This letter, proposes the Optimal Vehicle Selection OBRM (OVS-OBRM) with the objective of minimizing the average bundle delivery delay.

A novel protection scheme for quality of service aware WDM networks

One of the major concerns of optical network operators is related to improving the availability of services provided to their highest-class clients through the use of different protection schemes. However, the majority of the work concerning protection schemes considered the primary connections as equally important when contending for the use of the backup resources. As a first contribution we therefore propose an improvement of the existing shared protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. Moreover, as a second contribution, we propose to include a novel service differentiation parameter, the service disruption rate of a connection, to provide differentiated services in a WDM mesh network, and we motivate the use of such a parameter with numerical examples. As a third contribution, we present a mathematical model for both the classical protection schemes and for the proposed priority-aware scheme. As a key distinguishing feature from existing literature we derive explicit analytic expressions for the average availability and service disruption rate resulting from the deployment of such schemes. By solving these models we then evaluate numerically the benefits of the service differentiation feature introduced in our scheme as well as the impact of the service disruption rate as service differentiator.

Deadline-based connection setup in wavelength-routed WDM networks

This article addresses the ubiquitous topic of quality of service (QoS) aware connection provisioning in wavelength-routed WDM optical networks. The impact of the connection setup time of an optical connection has not been adequately addressed in the open literature. As such, this paper presents a novel approach that uses the optical connection setup time as a service differentiator during connection provisioning. The proposed approach utilizes the Earliest Deadline First (EDF) queueing algorithm to achieve deadline-based connection setup management with the deadline being the setup time requirement of an optical connection. The proposed EDF-based approach would allow the network operator to improve the QoS perceived by the end clients. Performance of this novel scheme is analyzed by accurately calculating various parameters, such as the fraction of connections provisioned on-time (i.e. prior to deadline expiration) and the average time it takes to successfully setup a connection. In addition, the presented approach is validated by a simulation that analyzes the performance of the proposed connection setup scheme in the specific context of the National Science Foundation Network (NSFNET). The obtained results show that a deadline-based setup strategy can minimize blocking probability while achieving QoS differentiation.

Networking in E-textiles

The abundance of fabrics in our life offers immense possibilities for ubiquitous electronic integration. Electronic textiles (e-textiles) represent the merging of fabric and electronic technologies to be used in wearable and large-scale applications. The communication requirements of the computing elements of these systems will be presented along with a fault tolerant solution. The operation of the communication scheme will be studied analytically and compared to simulation results. The graceful deterioration of the performance with increasing faults will also be reported. Multiple e-textile application examples utilizing the networking scheme will be presented.