Load balancing through terminal based dynamic AP reselection for QoS in IEEE 802.11 networks Nikolaos Papaoulakis, Charalampos Patrikakis, Chryssanthi Stefanoudaki, Platon Sipsas, Athanasios Voulodimos School of Electrical and Computer Engineering National Technical University of Athens, Greece {npapaoul, bpatr, cstef}@telecom.ntua.gr, sipsas@hotmail.com, thanosv@mail.ntua.gr Abstract- In this paper, a mechanism for supporting Quality of Service in wireless networks through the dynamic reselection of Access Points (APs) according to a terminal based load balancing scheme is presented. The mechanism is analyzed, and a corresponding implementation on laptops is presented, while evaluation through both simulation and actual field trials are included. Implementation refers to both Linux and MS OS systems. For the evaluation of the mechanism in the field trials, a very demanding streaming video scenario is selected, and the results are assessed with respect to the improvements that can be introduced in the end user Quality of Experience, even over state of the art streaming adaptation solutions. Keywords-load balancing, smooth streaming, AP reselection, WLANs, QoS I. INTRODUCTION The use of IEEE 802.11 Wireless Local Area Networks (WLANs) has been constantly gaining ground over the use of traditional wired LANs in the last years, both in private and public networks. The main reasons behind this are the low cost of implementation in terms of equipment and infrastructure, as well as the flexibility and simplicity offered to end users [1], [2]. Originally, WLANs were used for simple office and home applications as they were destined to provide a wireless extension on the existing wired LANs (Ethernet IEEE 802.3). The main services that they were carrying out were typical IP services, like HTTP browsing, FTP and email. These services have specific Quality of Service (QoS) requirements [3], which WLANs’ well-tested MAC mechanisms like CSMA/CA, RTS/CTS and the Fragmentation mechanisms can easily satisfy. On the other hand, real time services based on multimedia streaming such as VoD, WebTV, and videoconferencing have stricter requirements that increase the significance of key performance indicators such as bandwidth, delay of packet delivery, jitter and error rate [2][3]. The inherent lack of supporting mechanisms for guaranteeing the values of the above indicators in the existing version of 802.11 standards hinders the achievement of enhanced end user experience. Thus, the need for new mechanisms that can introduce the necessary functionality for quality awareness and responsiveness to various network conditions is imperative. In this paper, we present an innovative mechanism that is able to introduce a quality aware feature in already existing WLANs without requiring changes in the protocols utilized or on the implementation and installation of infrastructure equipment. The mechanism is inspired from similar solutions in the media and content distribution fields [4][5] and tries to address the issue of quality in the offered services through the balancing of traffic load in a similar way that this can happen in a Content Distribution Network (CDN). Here, it should be noted that in contrast to the traditional implementations of CDNs, where central management of the infrastructure is easy to be performed, the ‘ad hoc’ nature of WLANs and the increased mobility of users demands a decentralized approach. Therefore, the proposed solution includes only terminal based experiments and decisions, while it tries to minimize the implementation cost that a commercial deployment of the solution could have. This introduces an extra requirement that the proposed solution should satisfy: the experiments for the discovery and selection of a new AP with better connection and service quality characteristics should affect neither the capability of the terminal as regards networking parameters, nor the quality offered through the existing connection to an AP. The idea of dynamic AP reselection in order to meet the demand for QoS has been proposed in the past through several approaches that focus on the change of the conventional criterion for AP selection in a WLAN, based on the received signal strength of the AP at the client’s device. All these attempts have the same target: to surpass the traditional approach of the “best (strongest) signal” choice and end to the “best quality” choice. The latter combines the classic AP selection procedure with other parameters of the network that define QoS. For this, changes in the 802.11 standard are proposed ([1][2]). The approach proposed here goes beyond the proposals presented so far since it does not introduce changes in the 802.11 standard, nor any hardware and firmware changes in the infrastructure equipment, thus relying on a terminal based, cross- layer solution. The rest of the paper is organized as follows: In Section 2, a reference to the core proposals about supporting QoS in IEEE 802.11 networks is provided. Emphasis is given in AP reselection. Section 3 provides the description of the proposed mechanism, together with details on implementation. Section 4 contains an evaluation based on simulation and actual field trials aimed at assessing the effectiveness of the mechanism. Finally, Section 5 closes the paper with conclusions and discussion on possible uses of the proposed mechanism.