## 4 The IEEE 802.15.5 WPAN Mesh Standard
Trade-off & & redundancy and & & & & & \\  & with scalability & & bottlenecks & & & & & \\ \hline \multirow{2}{*}{**Self-**Organization**} & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Yes \\ \hline \multirow{2}{*}{**Support for**} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Provided by CoRE [33]} & \multirow{2}{*}{Yes} & \multirow{2}{*}{N/A} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Not considered in the current spec.} \\  & & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \multirow{2}{*}{**End-to-end**} & No & No & Unknown & N/A & Yes & Yes & Not considered in the current spec. \\  & Reliability & & & & & & & \\ \hline \multirow{2}{*}{**Security**} & Yes & No & Unknown & N/A & Yes & Yes & No \\ \hline \multirow{2}{*}{**Mobility**} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Unknown} & \multirow{2}{*}{No} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Yes} & \multirow{2}{*}{Yes} \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & &As defined by the IEEE 802.15.5 standard, a _mesh_ topology consists of a logical tree topology with additional local links among those nodes that are in coverage range (neighbor nodes). The logical tree topology provides transmission of information by means of parent-child pairs, and additional local links allow to select alternative paths between any given source-destination (path redundancy), which improves robustness and link reliability [2]. Under these premises, the appropriate generation and operation of a _LR-WPAN mesh_ network is done by means of _four mandatory functions_, namely: (1) start-up and generation of a logical tree multi-hop topology; (2) addressing scheme; (3) generation of local links; and, finally, (4) the unicast data transmission. In particular, functions 1-3 are controlled and coordinated by a unique node called by the standard the _mesh coordinator_ (MC), while function 4 must be carried out by every node of the mesh network (including the MC). This means that network nodes (with the exception of end-devices) have the self-organization capability in order to forward the information received from the neighbors, as well as to face different network concerns such as device failures or new devices joining the network, among others. In order to better understand the operation of these four mandatory functions, Figure 3 exemplifies a _LR-WPAN mesh_ network composed of 14 TelosB devices [56], where device A is the MC and the rest are nodes that belong to the mesh topology. Observing Figure 3(a), the creation of the tree network (mandatory function 1) is as follows: the MC is the device in charge of generating the logical tree network (comprising the tree level 0) by firstly setting different configuration parameters such as frequency channel, network identifier (unique for the entire network), addressing scheme (preferably based on 16-bit IEEE addresses), and energy saving mechanism if it was selected by the user of the application. In particular, all nodes are configured with the same single frequency channel selected by the MC, and employ only this specific channel during the entire network operation. However, other wireless technologies such as Wi-Fi may interfere with the mesh network under consideration. In this case, the MC selects a new single frequency channel and reports it to all network nodes. Following with the formation of the logical tree network, new nodes which are located within the MC's coverage range (e.g., nodes B, C, and D)  
Figure 3: Example of an IEEE 802.15.5 mesh network consisting of 14 TelosB devices: (**a**) Tree formation (function 1) and addressing (function 2); (**b**) Local links generation (function 3) and unicast forwarding (function 4). accomplish a discovery process. This is divided into two stages. Firstly, new nodes transmit beacon requests to the MC with the aim of learning about the configuration parameters established by the MC.