Performance Analysis of Transactional Traffic in Mobile Ad-hoc Networks

Mobile Ad Hoc networks (MANETs) present unique challenge to new protocol design, especially in scenarios where nodes are highly mobile. Routing protocols performance is essential to the performance of wireless networks especially in mobile ad-hoc scenarios. The development of new routing protocols requires com- paring them against well-known protocols in various simulation environments. The protocols should be analysed under realistic conditions including, but not limited to, representative data transmission models, limited buffer space for data transmission, sensible simulation area and transmission range combination, and realistic moving patterns of the mobiles nodes. Furthermore, application traffic like transactional application traffic has not been investigated for domain-specific MANETs scenarios. Overall, there are not enough performance comparison work in the past literatures. This thesis presents extensive performance comparison among MANETs comparing transactional traffic including both highly-dynamic environment as well as low-mobility cases

Fairness and transmission opportunity limit in IEEE 802.11e enhanced distributed channel access

Tämä diplomityö tutkii lähetysaikarajan vaikutusta verkon reiluuteen IEEE802.11e tehostettuun ja hajautettuun kommunikaatiokanavaan pääsyyn. IEEE802.11e tuo palvelunlaatuominaisuuksia IEEE802.11 langattomiin verkkoihin. Asemat, jotka käyttävät IEEE802.11e-ominaisuuksia jakavat liikenteen neljään kategoriaan. Kategorioiden välinen erottelu saavutetaan neljällä parametrilla, jotka kontrolloivat kanavaan pääsyä. Tämä työ tutkii yhtä näistä parametreistä, lähetysaikarajaa, joka kontrolloi lähetyksen kestoa. IEEE802.11e antaa referenssiarvoja parametreille, mutta näillä arvoilla verkon kuormituksen lisääntyessä, alemman prioriteetin liikenne kärsii nopeasti. Hyvin pian kuormituksen lisääntyessä alemman prioriteetin liikenne ei pääse verkosta läpi lainkaan. Tällöin myös verkon reiluus on matala. Reiluuden parantamiseksi, häiritsemättä korkean prioriteetin liikennettä, tämä työ tutkii ison lähetysaikarajan käyttöä. Ensimmäisessä simulaatiosarjassa alemman prioriteetin lähetysaikaraja on ääretön. Tämä tarkoitta sitä, että alemman prioriteetin jono voi lähettää kaikki pakettinsa kun se pääsee lähettämään. Tulokset osoittavat, että ääretön lähetysaikaraja parantaa reiluutta kun kanava on kuormittumassa. Tulokset osoittavat myös, että ääretön lähetysaikaraja ei merkittävästi heikennä korkean prioriteetin liikennettä. Toinen simulaatiosarja keskittyy sellaiseen verkon kuormitustilaan, missä äärettömän lähetysaikarajan vaikutus on suurin. Näissä simulaatioissa lähetysaikarajan arvo on staattinen. Simulaatiosta toiseen lähetysaikarajan arvo muutetaan toiseen arvoon väliltä nolla-suurin sallittu arvo. Tulokset näistä simulaatioista ovat hyvin samanlaiset kuin ensimmäisen simulaatiosarjan tulokset.This thesis investigates the effect of transmission opportunity limit on fairness in IEEE802.11e enhanced distributed channel access. IEEE802.11e brings quality of service features into IEEE802.11 wireless local area networks. In stations operating with IEEE802.11e, traffic is divided into categories. Differentiation between these categories is achieved by using four parameters to control the channel access. This thesis investigates one of these parameters, the transmission opportunity limit, which controls the channel access duration. With the reference parameter values given in IEEE802.11e, as the network congestion level increases, low priority traffic suffers quickly to a point where none of it gets transmitted. This makes the network overall fairness poor. To improve fairness while not disturbing high priority traffic, this thesis investigates the use of large transmission opportunity limit values. In the first set of simulations, the low priority traffic transmission opportunity limit values are set to infinite. This means that the low priority queue can send all its packets when it gains access to the channel. The results show that infinite transmission opportunity limit improves fairness when channel is getting congested. Also infinite transmission opportunity limit does not notably weaken high priority traffic performance. Second set of simulations focuses on the network congestion level where the effect of the infinite transmission opportunity limit is the largest. In these simulations the transmission opportunity limit is set to static value ranging from zero to a maximum allowed value. The results from these simulations are similar to the results of the first simulation set

Modeling and Measuring Performance of Data Dissemination in Opportunistic Networks

In this thesis we focus on understanding, measuring and describing the performance of Opportunistic Networks (ONs) and their applications. An “opportunistic network” is a term introduced to describe a sparse, wireless, ad hoc network with highly mobile nodes. The opportunistic networking paradigm deviates from the traditional end-to-end connectivity concept: Forwarding is based on intermittent connectivity between mobile nodes (typically, users with wireless devices); complete routes between sources and destinations rarely exist. Due to this unique property of spontaneous link establishment, the challenges that exist in ONs are specific. The unstructured nature of these networks makes it difficult to give any performance guarantees on data dissemination. For this reason, in Part I of this thesis we explore the dynamics that affect the performance of opportunistic networks. We choose a number of meaningful scenarios where our models and algorithms can be validated using large and credible data sets. We show that a drift and jump model that takes a spatial approach succeeds in capturing the impact of infrastructure and mobile-to-mobile exchanges on an opportunistic content update system. We describe the effects of these dynamics by using the age distribution of a dynamic piece of data (i.e., information updates) as the performance measure. The model also succeeds in capturing a strong bias in user mobility and reveals the existence of regions, whose statistics play a critical role in the performance perceived in the network. We exploit these findings to design an application for greedy infrastructure placement, which relies on the model approximation for a large number of nodes. Another great challenge of opportunistic networking lies in the fact that the bandwidth available on wireless links, coupled with ad hoc networking, failed to rival the capacity of backbones and to establish opportunistic networks as an alternative to infrastructure-based networks. For this reason, we never study ONs in an isolated context. Instead, we consider the applications that leverage interconnection between opportunistic networks and legacy networks and we study the benefits this synergy brings to both. Following this approach, we use a large operator-provided data set to show that opportunistic networks (based on Wi-Fi) are capable of offloading a significant amount of traffic from 3G networks. At the same time, the offloading algorithms we propose reduce the amount of energy consumed by mobiles, while requiring Wi-Fi coverage that is several times smaller than in the case of real-time offloading. Again we confirm and reuse the fact that user mobility is biased towards certain regions of the network. In Part II of this thesis, we treat another issue that is essential for the acceptance and evolution of opportunistic networks and their applications. Namely, we address the absence of experimental results that would support the findings of simulation based studies. Although the techniques such as contact-based simulations should intuitively be able to capture the performance of opportunistic applications, this intuition has little evidence in practice. For this reason, we design and deploy an experiment with real users who use an opportunistic Twitter application, in a way that allows them to maintain communication with legacy networks (i.e., cellular networks, the Internet). The experiment gives us a unique insight into certain performance aspects that are typically hidden or misinterpreted when the usual evaluation techniques (such as simulation) are used. We show that, due to the commonly ignored factors (such as the limited transmission bandwidth), contact-based simulations significantly overestimate delivery ratio and obtain delays that are several times lower than those experimentally acquired. In addition to this, our results unanimously show that the common practice of assuming infinite cache sizes in simulation studies, leads to a misinterpretation of the effects of a backbone on an opportunistic network. Such simulations typically overestimate the performance of the opportunistic component, while underestimating the utility of the backbone. Given the discovered deficiencies of the contact-based simulations, we consider an alternative statistical treatment of contact traces that uses the weighted contact graph. We show that this approach offers a better interpretation of the impact of a backbone on an opportunistic network and results in a closer match when it comes to modeling certain aspects of performance (namely, delivery ratio). Finally, the security requirements for the opportunistic applications that involve an interconnection with legacy networks are also highly specific. They cannot be fully addressed by the solutions proposed in the context of autonomous opportunistic (or ad hoc) networks, nor by the security frameworks used for securing the applications with continuous connectivity. Thus, in Part III of this thesis, we put together a security framework that fits the networks and applications that we target (i.e., the opportunistic networks and applications with occasional Internet connectivity). We then focus on the impact of security print on network performance and design a scheme for the protection of optimal relaying capacity in an opportunistic multihop network. We fine-tune the parameters of our scheme by using a game-theoretic approach and we demonstrate the substantial performance gains provided by the scheme

Resource Allocation for Cellular/WLAN Integrated Networks

The next-generation wireless communications have been envisioned to be supported by heterogeneous networks using various wireless access technologies. The popular cellular networks and wireless local area networks (WLANs) present perfectly complementary characteristics in terms of service capacity, mobility support, and quality-of-service (QoS) provisioning. The cellular/WLAN interworking is thus an effective way to promote the evolution of wireless networks. As an essential aspect of the interworking, resource allocation is vital for efficient utilization of the overall resources. Specially, multi-service provisioning can be enhanced with cellular/WLAN interworking by taking advantage of the complementary network strength and an overlay structure. Call assignment/reassignment strategies and admission control policies are effective resource allocation mechanisms for the cellular/WLAN integrated network. Initially, the incoming calls are distributed to the overlay cell or WLAN according to call assignment strategies, which are enhanced with admission control policies in the target network. Further, call reassignment can be enabled to dynamically transfer the traffic load between the overlay cell and WLAN via vertical handoff. By these means, the multi-service traffic load can be properly shared between the interworked systems. In this thesis, we investigate the load sharing problem for this heterogeneous wireless overlay network. Three load sharing schemes with different call assignment/reassignment strategies and admission control policies are proposed and analyzed. Effective analytical models are developed to evaluate the QoS performance and determine the call admission and assignment parameters. First, an admission control scheme with service-differentiated call assignment is studied to gain insights on the effects of load sharing on interworking effectiveness. Then, the admission scheme is extended by using randomized call assignment to enable distributed implementation. Also, we analyze the impact of user mobility and data traffic variability. Further, an enhanced call assignment strategy is developed to exploit the heavy-tailedness of data call size. Last, the study is extended to a multi-service scenario. The overall resource utilization and QoS satisfaction are improved substantially by taking into account the multi-service traffic characteristics, such as the delay-sensitivity of voice traffic, elasticity and heavy-tailedness of data traffic, and rate-adaptiveness of video streaming traffic