SLA Admitter. Controling the Admission of new clients The SLA Admitter (Fig. 6) acts as the interface between the human decisions and the SLA architecture. It answers the new SLA installation requests by analyzing their feasibility, regard- ing current WSN state. Hence, the installation of unfeasible SLAs should be forbidden. The SLA Admitter first manages the translation of the SLOs into resource needs for each relay node. The result of this translation includes: • the set of relay nodes connecting the client (e.g. kind of virtual source nodes, owned by the operator); • the amount of traffic the new SLA guarantees on the WSN operator source nodes; • the delay requirements of the new client flows; • the time frame of these guarantees (e.g. working hours) and their duration. Once the traffic shape is determined, the SLA Admitter consults the Service Registry. Based on the raw measures, it computes the current estimation of the network state: • the remaining capacity of the WSN operator source nodes; • the physical topology information (e.g. the connectivity graph of the WSN); • the delay each route induces; • the variations of this information during the time frame of the composite metrics. The analysis has to predict the impact of the new traffic flows on the relay nodes (energy, occupation, etc.). It must consider changes in the WSN configuration (e.g. new routing paths, load balancing on the relays, etc.). These QoS predictions on WSNs are complex, given the variability of the parameters, and still represent a research challenge [9], [10]. Note that the granularity of the SLO may vary according to the cost strategy of the WSN operator. Moreover, the WSN technology impacts the precision and form of the raw measures. Hence, the SLA Admitter is technology-dependent. In cases where the analysis fails to install the new SLA, the SLA Admitter must give a complete report of the reject to the WSN operator. The report permits to determine where are the hard points that have prevented the admission, and what can be done about it (e.g. deployment of new relays). The SLA Admitter accepts the SLA request by giving the corresponding node requirements to the SLA Manager. Indeed, Raw Measures Metric composition Req - Node K Bandwidth End-to-End Delay Loss Tolerance N1 N2 N3 Energy N1 Topology N2 N3 Require ments . . . . . . Traffic Command Analysis NK NK Time frame Service ID Required Measured WSN Operator Clients Information and alarms
