Scalability and topological stability are two of the most challenging issues in current wireless mesh networks (WMNs) deployments. In the literature, both the scalability and the topological stability of WMNs are described as likely to suffer from poor performance due to the ad hoc nature of the underlying IEEE 802.11 mechanisms. The main contribution of this article is a comprehensive review of the main topological stability and scalability-related issues in IEEE 802.11s-based networks. Moreover, the most relevant proposed solutions are surveyed, where both the drawbacks and the merits of each proposal are highlighted. At the end of the article, some open research challenges are presented and discussed. It is expected that this work may serve as motivation for more and deeper research on these issues to allow the design of future more stable and scalable IEEE 802.11s mesh networks deployments. 672 S. SAMPAIO, P. SOUTO AND F. VASQUES Figure 1. IEEE 802.11s network elements described in the standard [5].are combined with node H as it provides connectivity to the BSS B3-so, acting as mesh gate-and also connects the MBSS to a non-802.11 LAN, so acting as a portal. Note that any mesh gate is also a mesh STA.The aforementioned mesh properties enable, among other, fast deployment, low installation cost, and reliable communication. Consequently, their application spans a wide range of application domains from broadband home, community, and neighboring-enterprise-metropolitan areatransportation systems to building automation, health, medical, and security surveillance networks [6]. Nevertheless, current IEEE 802.11s mesh network deployments are typically small-sized, and it is yet unclear if they can scale to realistic network sizes, and support more demanding types of traffic such as real-time communication § .The challenge of introducing mesh capabilities in both medium access control (MAC) and physical (PHY) layers, while keeping compatibility with other IEEE 802.11 standards, makes the recently released IEEE 802.11s standard a hot topic of interest by researchers in the WMN's field. This article addresses the challenges to ensure scalability and topological stability in this networks.Scalability is a well-known issue in multi-hop networking, such as the IEEE 802.11s. Basically, when the size of the network increases, its performance behavior may significantly degrade [10]. It is an important factor for the performance of a mesh network [11]. However, this issue has not been studied in depth in the IEEE 802.11s; hence, there are still few research works in the literature about the scalability of IEEE 802.11s WMNs. The cause, as emphasized by Srivathsan et al. in [12], may be that network providers are beginning to implement their own mechanisms. Topological stability means that the self-organization process should be robust enough to sustain the assignment of links over a reasonable period without performance degradation or breakage; on the other hand, that the topology change and vicinity conditions (e.g., neighbors ...
