Optimizing the QoS of VoIP applications over WiFi through use of synchronized time
O Flaithearta, Padraig
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With a rapidly increasing volume of Internet content and connected devices, along with the development of cloud services and server virtualization, it's becoming clear that traditional network architectures are becoming increasingly ill-equipped to cater for todays enterprises, and end-users. The Internet has now evolved to a stage where the number of Internet enabled devices exceeds the global population and it is estimated that there will be 50 billion devices connected to the Internet by 2020. This growth is being driven by concepts such as the Internet of Things (IoT) and Cyber Physical Systems (CPS), facilitated by new paradigms such as Software Defined Networking (SDN) and is expected to be characterized by machine-to-machine com- munication. With such a growth in devices, the need to protect the Quality of Service (QoS) of certain traffic classes such as Real Time Communications (RTC) has never been more necessary. This is particularly so in the wireless domain where bandwidth provision is typically more problematic and where much of this connectivity will be centred. The ongoing development of communications and industrial applications over computer networks increasingly relies on accurate time synchronization. Precise and verifiable timing is a key requirement that current systems do not support, particular- ly in wireless networks. The Network Time Protocol (NTP) is widely used to synchronize computer clocks on the Internet where it can provide sub-millisecond accuracies on LANs; however it is typically much less accurate on WLANs due to their inherent asymmetry. The challenge of improving time synchronization in wire- less networks is part of other ongoing research at NUI Galway. This thesis focuses on evaluating the extent to which synchronized time can be used to improve the QoS of Real Time Communications (RTC) such as Voice over Internet Protocol (VoIP) applications over wireless networks. Although the IEEE 802.11 (WiFi) standard has a QoS extension, it has significant limitations that this thesis addresses. A dual approach of simulation and real-world experimentation is taken. The former is used to validate the core idea whereas the latter is used principally to assess the technical feasibility of the approach. Regarding the latter, an intelligent Access Point (iAP) is presented which integrates a number of key features that operate in real-time. It firstly dynamically calculates accurate one-way delays based on synchronized time. These values (as well as the loss rate) inform a QoS estimator to produce QoS ratings for individual VoIP calls and these values in turn are used by a VoIP traffic prioritization mechanism which prioritizes certain VoIP calls, if required, based on their QoS score. Results show that the approach is thus valid and feasible. The approach is also very much aligned with the emerging SDN paradigm and these linkages are discussed to put the thesis contribution into context. The core research questions addressed by this thesis are thus twofold. Firstly the use of synchronized time in wireless networks is shown to facilitate a significant improvement in QoS management of RTC over WiFi under certain conditions. Secondly, the thesis proves the feasibility of the approach through development of a proof-of- concept (PoC) implementation, based on the WLAN QoS protocol 802.11e.