Secure fast handoff in IEEE 802.11-based wireless mesh networks

Abstract

IEEE 802.11-based Wireless Mesh Networks (WMNs) have become a de facto alternative network solution for the widespread and rapid deployments of wireless metropolitan area networks in recent decade, in addition to traditional mobile cellular networks e.g. 3G/4G. It has drawn a huge amount of attention in both research and industry communities to explore its pros and cons and improve its performance. We embrace this future and envision that WMNs will keep up evolving and finally dominate the mainstream wireless wide area networks rather than 5G networks to serve mobile applications on pervasive smartphones in coming future, similar to what had happened between IP and ATM technology in the field of wired networks in late 90s in last century. 802.11-based WMN serves the purpose to provide pervasive mobile Internet access and intranet communications in enormous and sophisticated application scenarios. Despite time-insensitive applications such as web browsing and email, 802.11-based WMN faces a major challenge which is how to fully support time-sensitive mobile applications, e.g. streaming media, Voice over IP (VoIP), video conference, Internet of Things (IoT), and etc. These aforementioned mobile applications all require small delay and low packet loss encountered when there are interruptions of communication which are mainly caused by handoff procedures. Particularly, the challenge aggravates when more and more frequent handoffs occurred in a WMN with dense APs in real-world deployment. For an instance, when a Mobile Client (MC) moves randomly, it has to constantly change its point of association, e.g. Access Point (AP) or mesh router, due to the proximity of small coverage of the radio signal. The performance of streaming media demands such a delay to be less than 300ms while VoIP demands that less than 50ms, specified by International Telecommunication Union (ITU) standard [6]. When it comes to the newly emerged applications of IoT in recent years, the delay of packets between sensors and actuators and the back-end server needs to below 5ms. Nevertheless, the current legacy 802.11-based WMN handoff procedures could cause an end-to-end delay exceeding 1 second [2] so that it cannot guarantee such Quality of Service (QoS) at all. In order to respond to the aforementioned challenge, we explore the problem domain to understand the mechanisms behind and aim to improve the mechanisms of handoff procedures on multiple levels so as to support QoS of mobile applications. In general, it mainly covers Layer 2 (L2 i.e. Data link Layer) handoff and Layer 3 (L3, i.e. IP Layer) handoff respectively, and occasionally even involves higher layer. The L2 handoff deals with issues of probing for the most suitable AP, authentication of MC, and association with AP. The L3 handoff involves issues of IP acquaintance, IP mobility, authentication and security of IP connectivity. In this work, we address the problem of Secure Fast Handoff (SFH) which is to tackle the delay and packet loss issues while maintaining secure communication on L2 and L3 as well. In our research, we systematically investigate the related issues, generalize problems, and propose novel and effective mechanisms to solve the aforementioned challenge. We propose a theoretic framework to facilitate fast and secure handoff for all time-sensitive applications in 802.11-based WMNs on the basis of procedure parameter optimization, network-based proactive AP-probing schemes, and improved authentication protocols. Moreover, the mechanisms are implemented in a real-world testbed, evaluated and developed to improve the performance for mobile applications. The contributions of us are summarized as follows: First, we address the fast handoff problem with an empirical study on an 802.11-based WMN testbed HAWK (Heterogeneous Advanced Wireless Mesh Networks), which incorporates our reactive L2 and L3 fast handoff schemes: Background Selective Channel Scanning and Location Management-based Routing Update, on top of off-the-shelf hardware. It is a tradeoff between optimal performance and low practical cost so that it can apply to real-world scenarios as much as possible. A series of field tests are conducted to investigate and fine-tune key parameters of the above reactive schemes in order to evaluate the performance. Second and mainly, to address secure fast handoff problem in an 802.11-based WMN, a novel total solution comprised of Network-assisted Radio Signature (NRS) and Dual Re-Authentication (DRA) has been proposed. In particular, the NRS scheme is proposed to proactively obtain neighboring AP knowledge by measuring and profiling the radio characteristics and to determine the most suitable AP to associate prior to actual handoff. The Dual Re-authentication mechanism is proposed to enable fast handoff by granting the MC an immediate access based on a lightweight authentication as long as the associate AP is determined, while a strong authentication is executed within a period of timeslot. The proposed solution is optimized in terms of fast handoff at cost of a prior training stage in the deployment of the network and actualized authentication to secure communication afterwards. Furthermore, to address the handoff problem in an AP-dense 802.11-based WMN environment which has been more prominent, we advance our proposed technique NRS and further develop Temporal-NRS (T-NRS) scheme, which leverages historical knowledge of APs associated in time series to assist in handoff decision in addition to NRS technique based on spatial knowledge. The enhanced scheme improves the performance whilst greatly eliminates the inflexibility of the original approach. At last, to continue addressing the handoff problem in an AP-dense WMN environment, a novel handoff scheme called OppoScan (Opportunistic Scanning) supported by virtual radio is proposed. OppoScan opportunistically leverages nearby MCs and APs to produce the required information of neighboring AP for handoff, thus significantly decrease the number of switching channel of APs. Our evaluation based on experiments indicates that OppoScan can efficiently achieve low delay while maintaining handoff in more practical scenarios for 802.11-based WMN.