استراتژی مدیریت تحرک عملکرد بالای لایه پیوند برای شبکه های پهن باند خصوصی حرفه ای

In this paper, we present an innovative approach to solving the mobility management problem in the context of professional private broadband networks in the vehicular scenario. These heterogeneous communication networks are commonly deployed and managed by mission-critical organisations with the aim of supporting their specific and highly demanding services. Taking advantage of the specific characteristics of these networks, we propose to solve the mobility problem at Layer 2. This way, the mobility management overhead is reduced compared to solutions that operate at Layer 3 or above and therefore, shorter handover delays and better end-to-end application performances are achieved. The core element of our proposal is an intelligent mobile switch that makes use of the services provided by the IEEE 802.21 protocol to enhance vertical or heterogeneous handover performance. To validate our approach, we have developed a prototype implementation of the designed mobile switch with IEEE 802.11 and IEEE 802.16 support. Using this mobile switch implementation, we have carried out a set of experiments over a real testbed and measured some key indicators to assess the mobility management process. The obtained results show that our handover strategy comfortably meets the requirements of the ITU-T Y.1541 recommendation for highly demanding applications and ITU-R report M.2134 for high-speed handover. To the best of our knowledge, our contribution is the first proposal that solves the mobility management problem at Layer 2 while addressing the multi-access technology context in the vehicular professional private network scenario.

Currently, research and standardisation proposals for vehicular wireless networks do not converge towards a bottom-up standardised and fully defined communication architecture. Instead, the real picture is closer to an “amalgamation” of multiple wireless access technologies with their own technical specifications. In fact, known standardisation initiatives in this context, such as Communication Access for Land Mobiles from ISO (ISO CALM), the Intelligent Transport Systems initiative from the ETSI (ETSI ITS) and the Wireless Access in Vehicular Environment initiative from the IEEE (IEEE WAVE), do not propose a specific access technology under their global communication frameworks. All these technologies are expected to perform harmoniously and efficiently to meet the growing demand for ubiquitous and real-time communication services (Tafazolli, 2006). To achieve high performance in these demanding services, interest in developing new techniques and procedures to allow heterogeneous networks to behave as a single network has increased. In the vehicular context, the main challenge is to efficiently address the sequence of intra- and inter-technology handover processes executed by the mobile nodes along their trajectories. This is commonly understood as the mobility management problem, which is not clearly solved in a heterogeneous and general-purpose network architecture. Al-Surmi et al. summarise the most important current open issues and challenges in IP-based wireless systems in Al-Surmi et al. (2012). Instead of dealing with the mobility management problem in a general purpose communication network, in this study, we propose to address the mobility management problem in the specific context of professional private vehicular communication networks. Therefore, we tackle the issue with a context problem-solving approach. We understand that mobility requirements are common, but we have the benefit of the specific context of the professional private networks. We argue that under the professional private networks context, where a single organisation controls the entire IP-addressing scheme and the network elements of different link-layer technologies are configured under a common IP realm, the mobility management problem can be successfully and efficiently solved at Layer 2. Professional private broadband networks are mission-critical communication networks used in a wide variety of sectors, including public safety, public transport, oil and gas, utilities, mining industry and others. In these types of deployments, no commercial telecom operators are involved due to their mission-critical nature. The communication network is deployed and maintained by the specific company providing these mission-critical services. Professional private networks are generally demanded to provide high availability for a reduced number of users and often cover a large, extended area. Moreover, professional private networks, such as commercial networks, continue to face the demand for a multi-technology access scenario. They usually evolve from a set of multiple standalone networks into an integrated multi-technology access network. To obtain end-to-end high performance communications over a heterogeneous access network, it is essential to achieve a high performance during the handover process. In this regard, several studies indicate that the handover performance is closely linked to timely initiation of the handover process (McNair and Zhu, 2004 and Stevens-Navarro and Wong, 2006). To this end, two aspects are equally important: the handover policy (or the mechanism that rules the handover decision process) and the mechanism used to effectively communicate the decision to the different link-layer technologies. Regarding this last aspect, in the last few years, the IEEE has been working on the development of a standard that defines a Media Independent Handover (MIH) framework: IEEE 802.21 (2009). This standard defines an abstract framework that improves horizontal and vertical handovers' performance by exchanging information between the different access technologies involved in the handover process and the higher-layer mobility management applications. The major contribution of our paper is to present a novel mobility management strategy in the specific context of professional private broadband networks in the vehicular environment. The base of this strategy is to deal with the mobility management issue at Layer 2, instead of at Layer 3 or above. Taking the public transport sector as an example of the vehicular communication networks considered in this work, railway communication networks are one of the most demanding professional private networks. Consequently, aiming for a high performance mobility management solution for broadband professional private networks in the railway context, in this article, we propose a novel communication architecture based on our IEEE 802.21 mobile switch concept: a multi technology mobile switch with IEEE 802.21 support that enhances the handover performance by making use of MIH services and of an intelligent handover decision-making engine to initiate the handover process in a timely fashion. To validate our approach, we present a real testbed implementation involving a vertical handover between two different access technologies: IEEE 802.11 and IEEE 802.16. We consider this validation methodology very valuable, since real world deployments of new approaches are scarce. The obtained results show that our solution comfortably meets the performance requirements of the highly demanding real-time IP services indicated in the ITU-T Y.1541 (2011) recommendation, as well as the handover interruption times defined in the ITU-R report M.2134 (2008) for inter-frequency handovers. This paper is structured as follows. First, in Section 2, we introduce some background and preliminary concepts related to the motivation of our work. Section 3 describes the context and design assumptions of our proposal for the specific case study of a professional multi-technology broadband private network in the railway context, where a train migrates sequentially from an IEEE 802.16 access network to an IEEE 802.11 access network and vice-versa. Section 4 focuses on detailing our proposed vertical or intra-technology handover framework, describing our mobile switch and its major modules, procedures and interfaces. In Section 5, we describe our vertical handover process. Finally, 6 and 7 provide the details of our testbed implementation, obtained results and main conclusions.

In this paper, we have presented an effective and efficient mechanism to tackle the mobility management problem in the specific context of professional private networks in the vehicular environment. One of the key elements introduced in our solution is the innovative concept of a Layer 2 multi-technology access network. In other words, the proposed access network consists of a set of different link-layer technologies, each configured as a switched network. This results in a fully switched global access network. In this scenario, we introduce the heterogeneous mobile switch, a crucial component to manage network mobility, which is based on the IEEE 802.21 protocol. We have evaluated our proposed mobility management solution by means of a real testbed implementation, integrating IEEE 802.11 and IEEE 802.16 technologies. Commonly, research works in this area provide results based on simulation tools or analytical developments. Testbed implementations, instead, are not frequent due to their complexity. Therefore, the presented evaluation is by itself an important contribution of the paper. The obtained results show that our proposal comfortably meets the requirements of the ITU-T Y.1541 recommendation for real-time, highly interactive applications sensitive to jitter and the requirement specified by the ITU-R M.2134 report for inter-frequency handover interruption times. It is also worth mentioning that our approach provides competitive results when compared with network-based mobility management solutions like those detailed in Al-Surmi et al. (2012). Therefore, we conclude that our innovative and context aware Layer 2 mobility management approach may constitute an important step in the mobility management research area by promoting the definition of new mobility management solutions that benefit from the specific characteristics of the scenario in which they are to be deployed. As part of this research work, we are working on extending our performance evaluation by assessing the effect of different parameters, such as the speed of the mobile node. On the other hand, we are also interested in defining a more complex handover decision algorithm by including new parameters, such as the speed of the mobile node or power consumption. The modularity of the designed handover framework provides flexibility for the addition of new events for the definition of more complex handover strategies.