# Wireless Mesh Networking: An IoT-Oriented Perspective Survey on Relevant Technologies
## 4 Mesh in Bluetooth/BLE Networks  
### Standard  
Among the different releases of the Bluetooth protocol, the Bluetooth Low Energy (BLE) corresponds to its low-power variant and is a promising technology which allows to build low-power and low-cost networks composed by a large amount of nodes. BLE is presently raising more and more attention and is becoming one of the leading technologies for both IoT-oriented and industrial scenarios. Moreover, the relevance of BLE technology is due to the fact that it can be found as a natively implemented feature in the majority of current devices (e.g., laptops, smartphones, mobile tablets, and other smart devices), thus enabling users to interact with environmental BLE objects without the use of additional gateways. Despite that, most applications developed in last years focus on different network topologies, either point-to-point or star-based, where the smart device (i.e., a smartphone or another BLE-enabled device) acts as the center of the network. Looking at the technological aspects, BLE may be described as a short-range technology: in order to cover large areas or to allow complex networking behaviors, a multi-hop network is required. Therefore, BLE has recently shown a great attention even for its use as a reference technology to build mesh networks, in order to enable many-to-many communications in network scenarios. Hence, this general interest has led to the definition of a plethora of proprietary BLE-oriented networking solutions that generally lack of interoperabilty due to missing common mesh standards [30; 31; 32; 33]. A first change happened in 2017 thanks to the release of the official Bluetooth mesh networking standard specifications [34] by the Bluetooth Special Interest Group (SIG). With respect to the original and classical version of the Bluetooth protocol, able to achieve high-speed transmission, the low-power BLE protocol aims at significantly reducing the power consumption of a BLE node itself. Moreover, it is notable that BLE-enabled devices (especially those oriented to IoT) are generally battery-powered (by coin-cell batteries) and should operate for a long time (e.g., several years) with a limited duty cycle without the need for replacing the internal battery. Similarly to the classic Bluetooth, BLE uses frequencies in the range of 2402-2480 MHz, thus working in the 2.4 GHz band; at the opposite, BLE is provided with 40 2 MHz-spaced channels. Looking at the operating plane, BLE provides two different communication ways among the devices participating to the communication: (i) advertising mode, in which a BLE node broadcasting packets allows its neighbors (within its transmission range) to receive the transmitted data; and (ii) connection-oriented mode, where the packet transmission happens only between two BLE nodes which, through a handshake, establish a direct connection. Focusing on these modes, in 2013 the iBeacon protocol [35] has been announced by Apple with the goal of building applications and services in a location-aware fashion. Hence, in order to mark a BLE advertising packet as an iBeacon message, it has to contain the following information (useful for identifying the specific iBeacon device which sent the iBeacon message): (i) a 16-byte Universally Unique IDentifier (UUID), and (ii) two 2-byte fields identifying Major and Minor identifiers. Even though both advertising and connection-oriented communication strategies can be used to implement a BLE mesh network, the SIG selected the former one as backbone mode for the mesh standard. In the BLE standard, nodes composing the mesh network are denoted as \"nodes\" and those which are not are called \"unprovisioned devices\". The process which transforms an unprovisioned device into a node is called \"provisioning\": this is a secure procedure resulting in an unprovisioned device getting a series of encryption keys and being known to the Provisioner device (typically a tablet or a smartphone).