# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 1 Introduction
There are different studies that bring out the limitations of the current proposed security solutions that need, therefore, further research. In this survey we present and discuss different security solutions intended to be applied to some BBN applications. A number of these issues has been considered in the literature, and synthesized by several surveys in order to discuss and compare them [19; 31; 32; 33; 34]. Namely, a recent survey [31] summarizes the WBAN routing protocols, while classifying them into posture-based, energy-efficient, QoS-based, mobility-based, etc., and highlighting the network design considerations provided by each. Besides, authors of [19] provide a comprehensive overview of the existing WBAN protocols covering the latest advances in architecture, energy, security and application aspects. Nevertheless, all of the aforementioned works provide WBAN solutions in the intra-WBAN context, either to optimize the energy consumption, to implement QoS-aware data management, to ensure secure transmissions, or to handle dynamic scenarios, in the communications between the body sensors and the sink, belonging to a single WBAN. Few works tackled the body-to-body concept and investigate a single or limited design axes [35; 36; 16; 3]. For example, real testbed-based experiments are conducted in [35] to explore the connectivity behavior in body-to-body communications under different network parameters (radio technology, interference conditions, mobility, data dissemination scheme, etc.). A body-to-body pointed study is also present in [3], especially a distributed routing protocol is introduced using an adaptive CSMA/CA cross-layer mechanism. Some other studies focused on the body-to-body channel characterization such as [15; 16; 36]. Even fewer works tackled the inter-WBAN coexistence issue [37; 38; 39; 32], some of which are discussed in detail in this survey hereafter. Yet, to the best of our knowledge, this survey is the first to synthesize the existing WBAN and BBN solutions to provide an overview of the candidate protocols that are suitable for BBN deployment, and to discuss the opportunities of their enhancement and adaptation to fit the BBN specific requirements. We would like to emphasize that all the previous issues, namely the energy, QoS, mobility and security design axes, will be carefully addressed and discussed in the tremendously challenging context of BBNs, and therefore our survey makes the big difference from all existing surveys on WBANs and co-existence of WBANs in the literature. To summarize, the main contributions of this survey are twofold. One is to synthesize existing WBAN surveys in order to extract relevant techniques and protocols suitable for BBNs. More specifically, _the first goal_ of our survey is to investigate the research trends in WBANs and draw the most suitable mechanisms for BBNs, which have additional particularities different from those of single WBANs. Indeed, it is generally presumed that a WBAN is not a dynamic network structure, sensor nodes are fixed on the human body, and intra-WBAN transmissions could be handled by time division multiple access (TDMA)-based MAC, for example [37]. However, in BBN context we would rather presume a dynamic structure where each WBAN member can join and leave the BBN network seamlessly, and without the need for any centralized infrastructure which would present additional constraints for inter-WBANs transmissions. Yet this survey differs from the existing WBAN surveys in underlying the latest and relevant results in this area and providing targeted requirements to pave the way for practical BBN use. The second goal is to present and discuss some open issues, which are of significant concern for BBNs, keeping in mind the emergence of new paradigms, such as IoT and cloud computing.