94 research outputs found
A Remote Capacity Utilization Estimator for WLANs
In WLANs, the capacity of a node is not fixed and can vary dramatically due to the shared nature of the medium under the IEEE 802.11 MAC mechanism. There are two main methods of capacity estimation in WLANs: Active methods based upon probing packets that consume the bandwidth of the channel and do not scale well. Passive methods based upon analyzing the transmitted packets that avoid the overhead of transmitting probe packets and perform with greater accuracy. Furthermore, passive methods can be implemented locally or remotely. Local passive methods require an additional dissemination mechanism in order to communicate the capacity information to other network nodes which adds complexity and can be unreliable under adverse network conditions. On the other hand, remote passive methods do not require a dissemination mechanism and so can be simpler to implement and also do not suffer from communication reliability issues. Many applications (e.g. ANDSF etc) can benefit from utilizing this capacity information. Therefore, in this thesis we propose a new remote passive Capacity Utilization estimator performed by neighbour nodes. However, there will be an error associated with the measurements owing to the differences in the wireless medium as observed by the different nodes’ location. The main undertaking of this thesis is to address this issue. An error model is developed to analyse the main sources of error and to determine their impact on the accuracy of the estimator. Arising from this model, a number of modifications are implemented to improve the accuracy of the estimator. The network simulator ns2 is used to investigate the performance of the estimator and the results from a range of different test scenarios indicate its feasibility and accuracy as a passive remote method. Finally, the estimator is deployed in a node saturation detection scheme where it is shown to outperform two other similar schemes based upon queue observation and probing with ping packets
Cooperation Between Stations in Wireless Networks
In a wireless network, mobile nodes (MNs) repeatedly perform tasks such as layer 2 (L2) handoff, layer 3 (L3) handoff and authentication. These tasks are critical, particularly for real-time applications such as VoIP. We propose a novel approach, namely Cooperative Roaming (CR), in which MNs can collaborate with each other and share useful information about the network in which they move. We show how we can achieve seamless L2 and L3 handoffs regardless of the authentication mechanism used and without any changes to either the infrastructure or the protocol. In particular, we provide a working implementation of CR and show how, with CR, MNs can achieve a total L2+L3 handoff time of less than 16 ms in an open network and of about 21 ms in an IEEE 802.11i network. We consider behaviors typical of IEEE 802.11 networks, although many of the concepts and problems addressed here apply to any kind of mobile network
Quality-Oriented Mobility Management for Multimedia Content Delivery to Mobile Users
The heterogeneous wireless networking environment determined by the latest developments in wireless access technologies promises a high level of communication resources for mobile
computational devices. Although the communication resources provided, especially referring to bandwidth, enable multimedia streaming to mobile users, maintaining a high user perceived quality is still a challenging task. The main factors which affect quality in multimedia streaming over wireless networks are mainly the error-prone nature of the wireless channels and the user mobility. These factors determine a high level of dynamics of wireless communication resources, namely variations in throughput and packet loss as well as network availability and delays in delivering the data packets. Under these conditions maintaining a high level of quality, as perceived by the user, requires a quality oriented mobility management scheme. Consequently we propose the Smooth Adaptive Soft-Handover Algorithm, a novel quality oriented handover management scheme which unlike other similar solutions, smoothly transfer the data traffic from one network to another using multiple simultaneous connections. To estimate the capacity of each connection the novel Quality of Multimedia Streaming (QMS) metric is proposed. The QMS metric aims at offering maximum flexibility and efficiency allowing the applications to fine tune the behavior of the handover algorithm. The current simulation-based performance evaluation clearly shows the better
performance of the proposed Smooth Adaptive Soft-Handover Algorithm as compared with other handover solutions. The evaluation was performed in various scenarios including
multiple mobile hosts performing handover simultaneously, wireless networks with variable overlapping areas, and various network congestion levels
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Adaptive load balancing metric for WLANs
As the number of mobile devices accessing large-scale WLANs such as campus
and metropolitan area networks increases, the need for load balancing among the
cells becomes crucial. In addition, the network must also support some minimum
handoff tolerance defined by an application.
A number of load balancing techniques have been proposed in the literature that
focuses on formulating new load metrics rather than using Received Signal
Strength Indicator (RSSI) as the association metric. These schemes consider a
variety of factors such as number of STAs, enhanced RSSI, channel utilization,
queue length, bandwidth, and throughput to achieve balanced load. However,
some of these techniques require protocol modifications to both APs and STAs or
need special agents such as admission control server, extra software, and
switches. Others do not consider Quality of Service (QoS) requirements of
applications, which vary from one application to another, and thus do not satisfy
users requiring minimized handoff latency and real-time services. Moreover, most
techniques ignored the hidden node problem, which causes packet collisions and
thus the presence of such nodes can severely affect the performance of WLANs.
This dissertation proposes a new metric that provides load balance as well as
timely handoffs for WLANs by taking into account both direct and hidden node
collisions as well as the types of traffics in order to support QoS. Another novel
feature of the proposed method is the use of probe requests during the discovery
phase to monitor the states of the channels to determine the best Access Point
(AP) for association. Our simulation results show that the proposed method is
significantly better than relying only on signal strength in term of utilization,
end-to-end delay, collision rate, and packet loss
Cooperation Strategies for Enhanced Connectivity at Home
WHILE AT HOME , USERS MAY EXPERIENCE A POOR I NTERNET SERVICE while being connected to their 802.11 Access Points (APs). The AP is just one component
of the Internet Gateway (GW) that generally includes a backhaul connection (ADSL, fiber,etc..) and a router providing a LAN. The root cause of performance degradation may be poor/congested wireless channel between the user and the GW or congested/bandwidth limited backhaul connection.
The latter is a serious issue for DSL users that are located far from the central office because the greater the distance the lesser the achievable physical datarate. Furthermore, the GW is one of the few devices in the home that is left always on, resulting in energy waste and electromagnetic pollution increase. This thesis proposes two strategies to enhance Internet connectivity at home by (i) creating a wireless resource sharing scheme through the federation and the coordination of neighboring GWs in order to achieve energy efficiency while avoiding congestion, (ii) exploiting different king of connectivities, i.e., the wired plus the cellular (3G/4G) connections, through the aggregation of the available bandwidth across multiple access technologies.
In order to achieve the aforementioned strategies we study and develop:
• A viable interference estimation technique for 802.11 BSSes that can be implemented on commodity hardware at the MAC layer, without requiring active measurements, changes in the 802.11 standard, cooperation from the wireless stations (WSs). We extend previous theoretical results on the saturation throughput in order to quantify the impact in term of throughput loss of any kind of interferer. We im- plement and extensively evaluate our estimation technique with a real testbed and with different kind of interferer, achieving always good accuracy.
• Two available bandwidth estimation algorithms for 802.11 BSSes that rely only on passive measurements and that account for different kind of interferers on the ISM band. This algorithms can be implemented on commodity hardware, as they require only software modifications. The first algorithm applies to intra-GW while the second one applies to inter-GW available bandwidth estimation. Indeed, we use the first algorithm to compute the metric for assessing the Wi-Fi load of a GW and the second one to compute the metric to decide whether accept incoming WSs from neighboring GWs or not. Note that in the latter case it is assumed that one or more WSs with known traffic profile are requested to relocate from one GW to another
one. We evaluate both algorithms with simulation as well as with a real test-bed for different traffic patterns, achieving high precision.
• A fully distributed and decentralized inter-access point protocol for federated GWs that allows to dynamically manage the associations of the wireless stations (WSs) in the federated network in order to achieve energy efficiency and offloading con- gested GWs, i.e, we keep a minimum number of GWs ON while avoiding to create congestion and real-time throughput loss. We evaluate this protocol in a federated scenario, using both simulation and a real test-bed, achieving up to 65% of energy saving in the simulated setting. We compare the energy saving achieved by our protocol against a centralized optimal scheme, obtaining close to optimal results.
• An application level solution that accelerates slow ADSL connections with the parallel use of cellular (3G/4G) connections. We study the feasibility and the potential performance of this scheme at scale using both extensive throughput measurement of the cellular network and trace driven analysis. We validate our solution by implementing a real test bed and evaluating it “in the wild, at several residential locations of a major European city. We test two applications: Video-on-Demand (VoD) and picture upload, obtaining remarkable throughput increase for both applications at all locations. Our implementation features a multipath scheduler which we compare to other scheduling policies as well as to transport level solution like MTCP, obtaining always better results
IEEE 802.21 in heterogeneous handover environments
Mestrado em Engenharia de Computadores e TelemáticaO desenvolvimento das capacidades tecnológicas dos terminais móveis, e das
infra-estruturas que os suportam, potenciam novos cenários onde estes dispositivos
munidos com interfaces de diferentes tecnologias vagueiam entre
diferentes ambientes de conectividade. É assim necessário providenciar meios
que facilitem a gestão de mobilidade, permitindo ao terminal ligar-se da melhor
forma (i.e., optando pela melhor tecnologia) em qualquer altura.
A norma IEEE 802.21 está a ser desenvolvida pelo Institute of Electrical and
Electronics Engineers (IEEE) com o intuito de providenciar mecanismos e
serviços que facilitem e optimizem handovers de forma independente da tecnologia.
A norma 802.21 especifica assim um conjunto de mecanismos que
potenciarão cenários como o descrito acima, tendo em conta a motivação e requerimentos
apresentados por arquitecturas de redes futuras, como as redes
de quarta geração (4G).
Esta dissertação apresenta uma análise extensiva da norma IEEE 802.21, introduzindo
um conjunto de simulações desenvolvidas para estudar o impacto
da utilização de mecanismos 802.21 em handovers controlados por rede, numa
rede de acesso mista composta por tecnologias 802.11 e 3G. Os resultados
obtidos permitiram verificar a aplicabilidade destes conceitos a ambientes de
próxima geração, motivando também uma descrição do desenho de integração
de mecanismos 802.21 a arquitecturas de redes de quarta geração.
ABSTRACT: The development of the technological capabilities of mobile terminals, and
the infra-structures that support them, enable new scenarios where these devices
using different technology interfaces roam in different connectivity environments.
This creates a need for providing the means that facilitate mobility
management, allowing the terminal to connect in the best way possible (i.e., by
choosing the best technology) at any time.
The IEEE 802.21 standard is being developed by the Institute of Electrical and
Electronics Engineers (IEEE) to provide mechanisms and services supporting
Media Independent Handovers. The 802.21 standard specifies a set of mechanisms
that enable scenarios like the one described above, considering the
motivation and requirements presented by future network architectures, such
as the ones from fourth generation networks (4G).
This thesis presents an extensive analysis of the IEEE 802.21 standard, introducing
a set of simulations developed for studying the impact of using 802.21
mechanisms in network controlled handovers, in a mixed access network composed
of 802.11 and 3G technologies. The obtained results allow the verification
of the applicability of these concepts into next generation environments,
also motivating the description of the design for integration of 802.21 mechanisms
to fourth generation networks
IMPROVING QoS OF VoWLAN VIA CROSS-LAYER BASED ADAPTIVE APPROACH
Voice over Internet Protocol (VoIP) is a technology that allows the transmission of
voice packets over Internet Protocol (IP). Recently, the integration of VoIP and
Wireless Local Area Network (WLAN), and known as Voice over WLAN
(VoWLAN), has become popular driven by the mobility requirements ofusers, as
well as by factor of its tangible cost effectiveness. However, WLAN network
architecture was primarily designed to support the transmission of data, and not for
voice traffic, which makes it lack ofproviding the stringent Quality ofService (QoS)
for VoIP applications. On the other hand, WLAN operates based on IEEE 802.11
standards that support Link Adaptive (LA) technique. However, LA leads to having a
network with multi-rate transmissions that causes network bandwidth variation, which
hence degrades the voice quality. Therefore, it is important to develop an algorithm
that would be able to overcome the negative effect of the multi-rate issue on VoIP
quality. Hence, the main goal ofthis research work is to develop an agent that utilizes
IP protocols by applying a Cross-Layering approach to eliminate the above-mentioned
negative effect. This could be expected from the interaction between Medium Access
Control (MAC) layer and Application layer, where the proposed agent adapts the
voice packet size at the Application layer according to the change of MAC
transmission data rate to avoid network congestion from happening. The agent also
monitors the quality of conversations from the periodically generated Real Time
Control Protocol (RTCP) reports. If voice quality degradation is detected, then the
agent performs further rate adaptation to improve the quality. The agent performance
has been evaluated by carrying out an extensive series ofsimulation using OPNET
Modeler. The obtained results of different performance parameters are presented,
comparing the performance ofVoWLAN that used the proposed agent to that ofthe
standard network without agent. The results ofall measured quality parameters hav
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