QoS mechanisms for maintaining SLAs. In order to fulfill the requirements of the SLAs, the operator will necessarily use QoS mechanisms, and particularly on a wireless technology [7]: • Call Admission Control (CAC); • Resource Control (e.g. Radio Resource Management in radio networks); • Network Monitoring; • QoS Prediction; • Configuration Management. In wireless networks, the broadcasting nature of the channel mandates that the nodes control their transmissions in order to avoid collisions or interference. In WSNs, one can schedule the communications, according to algorithms such as the Traffic-Aware Scheduling Algorithm (TASA) [8], which uses matching and coloring heuristics to find a communication solution, given the nodes topology and the required traffic load. In WSNs, radio link quality estimation is crucial to predict if the agreed-upon QoS will be met [4]. It permits, alongside with other raw measures (e.g. remaining energy of the nodes [9], traffic statistics), to elaborate the composite metrics defined in the SLOs. Some of these metrics prove that the QoS requirement of each SLO is met, and guide the real-time control actions on the network. Others are defined as Key Performance Indicators (KPIs), and sent to the clients and the WSN operator to show them high level statistics of the network. The communication protocols for WSNs have for long been studied and implemented with the goal of meeting QoS constraints. A classification of the MAC layer mechanisms is proposed in [10]. At the routing layer, the IETF ROLL RPL [11] proposes the construction of the routing topology based on Objective Functions (OFs). The OFs include QoS constraints that the topology must meet at buildup. IETF CORE CoAP [12] is an application level protocol based on UDP and adapted for constrained nodes. Finally, one may design WSNs applicative behavior in order to provide easier resource allocation for concurrent applications [9]. Client A WSN Operator Clients Our concerns are: • what occurs when a new client comes with his nodes and asks to use the operator connectivity to access the data of his sensors? • what amount of additional traffic is the relay network currently able to stand? To answer this, the operator must have an infrastructure that: • collects information about the network performance and current capacity; • allows it to decide to admit or not the new client flows. If this infrastructure was incorrectly implemented, the WSN Fig. 2. Nodes infrastructure of an operated WSN.
