# Fuzzy Multi-Criteria Based Trust Management in Heterogeneous Federated Future Internet Testbeds
## 2 Related Work
In [19], the authors proposed a trust platform for NFV infrastructure that was responsible for the QoS guarantee of a Virtual Network Function (VNF) to fulfill the user's requirements. The reputation of VNF was quantified by local monitoring data and from trust information of other devices. FlowBroker [20] is a brokering agent architecture suitable for the coordination of distributed SDN controllers. The broker's reputation is based on metrics of the end-to-end delay, the max link utilization ratio and the packet loss ratio and is used by other agents in order to accept flow rule changes and peer broker forwarding updates. A machine learning method, named linear discriminant analysis, is adopted for the quantification of the reputation of each broker. An interesting category of trust and reputation systems is that implemented on Peer-to-Peer (P2P) networks. The following trust management frameworks are also applied to other distributed systems. The EigenTrust algorithm [21] was designed to protect P2P network users from downloading malicious or inauthentic files. It calculated and assigned a global trust value to every peer by using a recursive method and the users' opinions. The algorithm was based on power iteration and can be implemented both as a centralized and distributed service. The ROCQ mechanism [22] proposed a reputation-based trust management system that produced reputation values in order to represent the trustworthiness of peers in P2P networks. The evaluation of peers was provided after the end of each transaction between peers. The ROCQ system could be implemented in a distributed manner, and the reputation value was based on the user's opinion, the user's credibility produced by his/her previous evaluations and the quality that represented the confidence of a peer in the accuracy of his/her evaluation. There were very few studies that have proposed a reputation or trust management approach for different types of resources. FTUE [8] is a reputation-based trust management framework for federated testbeds. It utilized user feedback and monitoring data to compute the reputation metric per service per testbed. Four different scenarios were used to characterize the user's credibility, which was considered based on the reputation score. [PERSON] et al. [23] proposed an approach for federated trust in the context of the GENI project. The concept of trust had three different meanings, named credibility, endorsement and reliance. GENI provided an authentication and authorization mechanism to realize the trust operation between the federated entities. The overwhelming majority of the aforementioned approaches have focused only on a specific type of resource. In a federated environment, the calculation of reputation and trust value is more challenging, because there are many different metrics and requirements that must be considered. Compared with these studies, the main difference of our approach is that it can take simultaneously into account various QoS, QoE and SLA data from different types of resources and testbeds in a scalable way and without any assumption about the experimenter's willingness.