###### Abstract
Other aspects are also covered, in particular security and privacy, and health device integration. Different communication standards were used to deploy CRIP, such as Near Field Communication (NFC), biometrics (fingerprints) and Bluetooth. In most of the above-mentioned applications, wireless communication is inevitable between various types of devices including sensors, actuators, coordinators, and gateways. Additionally, with the advent of body-to-body networks (BBNs or B2B), the communication is extended from classical \"on-body networks/body area networks (BANs)\" to modern \"body-to-body networks (BBNs)\" as shown in Figure 1. Consequently, wearable wireless networks (WNNs) are emerging as a new frontier for future smart applications in Internet of things (IoT) and Internet of humans (IoH). From the viewpoint of WWN \"connectivity\" in IoT and IoH, BBNd provide multi-hop device-to-device (D2D) communication to extend the end-to-end network coverage. This coincides with the vision of 5G, setting up new challenges towards cooperative and collaborative D2D communication among heterogeneous devices. Figure 1: Wearable wireless networks: extending on-body communication to body-to-body and off-body communication. BAN: on-body network. The \"connectivity\" between devices can not be merely ensured by establishing and executing a hand-shaking protocol. For example, if the packet reception ratio is as low as 50% it means that half of the time devices are disconnected, or in other words, the packets delay recorded is 2 times higher than the given application constraint. Additionally, it also means that only 50% of the time the considered devices are connected. Consequently, connectivity is an indispensable aspect in WWNs and IoT. To have deeper understanding in this article, we take a closer look at the BAN and BBN communication in WWNs. In particular, we accentuate on the network connectivity challenges in WWNs while considering a first responder rescue and critical operation as a case study. The contributions of this paper are the following:  
* _Potential technologies for BAN and BBN wireless networks for the considered application:_ A comprehensive overview of existing technologies is presented with potential candidates for BAN and BBN communication. We consider various cross-layer design parameters that can have a direct or indirect impact on the connectivity. Most appropriate standards and supported technologies are selected for both BAN and BBN communication in the application context (use case: disaster and relief operations). * _Impact of space-time channel variations, co-channel interference for on-body connectivity_: On-body connectivity is addressed from the view points of space-time channel variations and dynamic mobility as well as co-channel interference under the constraints of low power, latency and packet delivery ratio (PDR). * _Real testbed to evaluate and analyze end-to-end connectivity and end-to-end round trip time delay for BBN wireless communication_: The analysis of the end-to-end connectivity and the end-to-end round trip time delay behavior for BBN communication is discussed with regards to the data dissemination strategies. Then, the experiment scenario is presented and the testing is detailed based on the newly proposed dedicated routing strategy for a disaster context [6] (Optimized Routing Approach for Critical and Emergency Networks (i.e., ORACE-Net)). This work is a rare implementation of BAN and BBN technologies in the disaster context. It does not only evaluate the considered implementation, but it also provides a strong guidance for possible future emerging candidates for wireless BAN and BBN technologies.