The analysis of achieving TCP fairness in IEEE 802.11 infrastructure WLAN

This paper raising the TCP fairness issues that reviewed from three aspects; per-flow, per-station, and per-rate based on the IEEE 802.11 Wireless Local Area Networks (WLANs) environment.Due to the strong drive towards wireless Internet access via mobile devices, these issues must be carefully handled in order to build improved systems. We succinctly review and categorize the TCP fairness characteristic and then outline the problems and solutions from previous works through comparative table.Finally, we considered the future direction for solving these problems.Overall this paper summarizes current state of knowledge of the WLAN TCP fairness

Multi-layer traffic control for wireless networks

Le reti Wireless LAN, così come definite dallo standard IEEE 802.11, garantiscono connettività senza fili nei cosiddetti “hot-spot” (aeroporti, hotel, etc.), nei campus universitari, nelle intranet aziendali e nelle abitazioni. In tali scenari, le WLAN sono denotate come “ad infrastruttura” nel senso che la copertura della rete è basata sulla presenza di un “Access Point” che fornisce alle stazioni mobili l’accesso alla rete cablata. Esiste un ulteriore approccio (chiamato “ad-hoc”) in cui le stazioni mobili appartenenti alla WLAN comunicano tra di loro senza l’ausilio dell’Access Point. Le Wireless LAN tipicamente sono connesse alla rete di trasporto (che essa sia Internet o una Intranet aziendale) usando un’infrastruttura cablata. Le reti wireless Mesh ad infrastruttura (WIMN) rappresentano un’alternativa valida e meno costosa alla classica infrastruttura cablata. A testimonianza di quanto appena affermato vi è la comparsa e la crescita sul mercato di diverse aziende specializzate nella fornitura di infrastrutture di trasporto wireless e il lancio di varie attività di standardizzazione (tra cui spicca il gruppo 802.11s). La facilità di utilizzo, di messa in opera di una rete wireless e i costi veramente ridotti hanno rappresentato fattori critici per lo straordinario successo di tale tecnologia. Di conseguenza possiamo affermare che la tecnologia wireless ha modificato lo stile di vita degli utenti, il modo di lavorare, il modo di passare il tempo libero (video conferenze, scambio foto, condivisione di brani musicali, giochi in rete, messaggistica istantanea ecc.). D’altro canto, lo sforzo per garantire lo sviluppo di reti capaci di supportare servizi dati ubiqui a velocità di trasferimento elevate è strettamente legato a numerose sfide tecniche tra cui: il supporto per l’handover tra differenti tecnologie (WLAN/3G), la certezza di accesso e autenticazione sicure, la fatturazione e l’accounting unificati, la garanzia di QoS ecc. L’attività di ricerca svolta nell’arco del Dottorato si è focalizzata sulla definizione di meccanismi multi-layer per il controllo del traffico in reti wireless. In particolare, nuove soluzioni di controllo del traffico sono state realizzate a differenti livelli della pila protocollare (dallo strato data-link allo strato applicativo) in modo da fornire: funzionalità avanzate (autenticazione sicura, differenziazione di servizio, handover trasparente) e livelli soddisfacenti di Qualità del Servizio. La maggior parte delle soluzioni proposte in questo lavoro di tesi sono state implementate in test-bed reali. Questo lavoro riporta i risultati della mia attività di ricerca ed è organizzato nel seguente modo: ogni capitolo presenta, ad uno specifico strato della pila protocollare, un meccanismo di controllo del traffico con l’obiettivo di risolvere le problematiche presentate precedentemente. I Capitoli 1 e 2 fanno riferimento allo strato di Trasporto ed investigano il problema del mantenimento della fairness per le connessioni TCP. L’unfairness TCP conduce ad una significativa degradazione delle performance implicando livelli non soddisfacenti di QoS. Questi capitoli descrivono l’attività di ricerca in cui ho impiegato il maggior impegno durante gli studi del dottorato. Nel capitolo 1 viene presentato uno studio simulativo delle problematiche di unfairness TCP e vengono introdotti due possibili soluzioni basate su rate-control. Nel Capitolo 2 viene derivato un modello analitico per la fairness TCP e si propone uno strumento per la personalizzazione delle politiche di fairness. Il capitolo 3 si focalizza sullo strato Applicativo e riporta diverse soluzioni di controllo del traffico in grado di garantire autenticazione sicura in scenari di roaming tra provider wireless. Queste soluzioni rappresentano parte integrante del framework UniWireless, un testbed nazionale sviluppato nell’ambito del progetto TWELVE. Il capitolo 4 descrive, nuovamente a strato Applicativo, una soluzione (basata su SIP) per la gestione della mobilità degli utenti in scenari di rete eterogenei ovvero quando diverse tecnologie di accesso radio sono presenti (802.11/WiFi, Bluetooth, 2.5G/3G). Infine il Capitolo 5 fa riferimento allo strato Data-Link presentando uno studio preliminare di un approccio per il routing e il load-balancing in reti Mesh infrastrutturate.Wireless LANs, as they have been defined by the IEEE 802.11 standard, are shared media enabling connectivity in the so-called “hot-spots” (airports, hotel lounges, etc.), university campuses, enterprise intranets, as well as “in-home” for home internet access. With reference to the above scenarios, WLANs are commonly denoted as “infra-structured” in the sense that WLAN coverage is based on “Access Points” which provide the mobile stations with access to the wired network. In addition to this approach, there exists also an “ad-hoc” mode to organize WLANs where mobile stations talk to each other without the need of Access Points. Wireless LANs are typically connected to the wired backbones (Internet or corporate intranets) using a wired infrastructure. Wireless Infrastructure Mesh Networks (WIMN) may represent a viable and cost-effective alternative to this traditional wired approach. This is witnessed by the emergence and growth of many companies specialized in the provisioning of wireless infrastructure solutions, as well as the launch of standardization activities (such as 802.11s). The easiness of deploying and using a wireless network, and the low deployment costs have been critical factors in the extraordinary success of such technology. As a logical consequence, the wireless technology has allowed end users being connected everywhere – every time and it has changed several things in people’s lifestyle, such as the way people work, or how they live their leisure time (videoconferencing, instant photo or music sharing, network gaming, etc.). On the other side, the effort to develop networks capable of supporting ubiquitous data services with very high data rates in strategic locations is linked with many technical challenges including seamless vertical handovers across WLAN and 3G radio technologies, security, 3G-based authentication, unified accounting and billing, consistent QoS and service provisioning, etc. My PhD research activity have been focused on multi-layer traffic control for Wireless LANs. In particular, specific new traffic control solutions have been designed at different layers of the protocol stack (from the link layer to the application layer) in order to guarantee i) advanced features (secure authentication, service differentiation, seamless handover) and ii) satisfactory level of perceived QoS. Most of the proposed solutions have been also implemented in real testbeds. This dissertation presents the results of my research activity and is organized as follows: each Chapter presents, at a specific layer of the protocol stack, a traffic control mechanism in order to address the introduced above issues. Chapter 1 and Charter 2 refer to the Transport Layer, and they investigate the problem of maintaining fairness for TCP connections. TCP unfairness may result in significant degradation of performance leading to users perceiving unsatisfactory Quality of Service. These Chapters describe the research activity in which I spent the most significant effort. Chapter 1 proposes a simulative study of the TCP fairness issues and two different solutions based on Rate Control mechanism. Chapter 2 illustrates an analytical model of the TCP fairness and derives a framework allowing wireless network providers to customize fairness policies. Chapter 3 focuses on the Application Layer and it presents new traffic control solutions able to guarantee secure authentication in wireless inter-provider roaming scenarios. These solutions are an integral part of the UniWireless framework, a nationwide distributed Open Access testbed that has been jointly realized by different research units within the TWELVE national project. Chapter 4 describes again an Application Layer solution, based on Session Initiation Protocol to manage user mobility and provide seamless mobile multimedia services in a heterogeneous scenario where different radio access technologies are used (802.11/WiFi, Bluetooth, 2.5G/3G networks). Finally Chapter 5 refers to the Data Link Layer and presents a preliminary study of a general approach for routing and load balancing in Wireless Infrastructure Mesh Network. The key idea is to dynamically select routes among a set of slowly changing alternative network paths, where paths are created through the reuse of classical 802.1Q multiple spanning tree mechanisms

Improving Performance for CSMA/CA Based Wireless Networks

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based wireless networks are becoming increasingly ubiquitous. With the aim of supporting rich multimedia applications such as high-definition television (HDTV, 20Mbps) and DVD (9.8Mbps), one of the technology trends is towards increasingly higher bandwidth. Some recent IEEE 802.11n proposals seek to provide PHY rates of up to 600 Mbps. In addition to increasing bandwidth, there is also strong interest in extending the coverage of CSMA/CA based wireless networks. One solution is to relay traffic via multiple intermediate stations if the sender and the receiver are far apart. The so called “mesh” networks based on this relay-based approach, if properly designed, may feature both “high speed” and “large coverage” at the same time. This thesis focusses on MAC layer performance enhancements in CSMA/CA based networks in this context. Firstly, we observe that higher PHY rates do not necessarily translate into corresponding increases in MAC layer throughput due to the overhead of the CSMA/CA based MAC/PHY layers. To mitigate the overhead, we propose a novel MAC scheme whereby transported information is partially acknowledged and retransmitted. Theoretical analysis and extensive simulations show that the proposed MAC approach can achieve high efficiency (low MAC overhead) for a wide range of channel variations and realistic traffic types. Secondly, we investigate the close interaction between the MAC layer and the buffer above it to improve performance for real world traffic such as TCP. Surprisingly, the issue of buffer sizing in 802.11 wireless networks has received little attention in the literature yet it poses fundamentally new challenges compared to buffer sizing in wired networks. We propose a new adaptive buffer sizing approach for 802.11e WLANs that maintains a high level of link utilisation, while minimising queueing delay. Thirdly, we highlight that gross unfairness can exist between competing flows in multihop mesh networks even if we assume that orthogonal channels are used in neighbouring hops. That is, even without inter-channel interference and hidden terminals, multi-hop mesh networks which aim to offer a both “high speed” and “large coverage” are not achieved. We propose the use of 802.11e’s TXOP mechanism to restore/enfore fairness. The proposed approach is implementable using off-the-shelf devices and fully decentralised (requires no message passing)

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

LTE Optimization and Resource Management in Wireless Heterogeneous Networks

Mobile communication technology is evolving with a great pace. The development of the Long Term Evolution (LTE) mobile system by 3GPP is one of the milestones in this direction. This work highlights a few areas in the LTE radio access network where the proposed innovative mechanisms can substantially improve overall LTE system performance. In order to further extend the capacity of LTE networks, an integration with the non-3GPP networks (e.g., WLAN, WiMAX etc.) is also proposed in this work. Moreover, it is discussed how bandwidth resources should be managed in such heterogeneous networks. The work has purposed a comprehensive system architecture as an overlay of the 3GPP defined SAE architecture, effective resource management mechanisms as well as a Linear Programming based analytical solution for the optimal network resource allocation problem. In addition, alternative computationally efficient heuristic based algorithms have also been designed to achieve near-optimal performance