# Social Milieu Oriented Routing: A New Dimension to Enhance Network Security in WSNs
## 2 Related Work  
The OSTP selection with multiple end-to-end QoT constraints can be modeled as the classical multi-constrained optimal path (MCOP) selection problem [11]. In this section, we review some existing MCOP and OSTP selection algorithms. [PERSON] _et al._[14] first proposed an approximation algorithm H_MCOP to determine a feasible path that satisfies a set of constraints while maintaining high utilization of network resources. H_MCOP is a promising method. However, when the possible path with the maximal utility is not a feasible solution, H_MCOP will stop searching, which will lead to the failure of finding a near-optimal solution and sometimes returning an infeasible one even when a feasible solution exists. [PERSON] _et al._[15] studied the problem of service selection with multiple QoS constraints and proposed an approximation algorithm, MCSP-K based on H_MCOP. However, in the service candidate graph therein, there is a link between any two nodes in adjacent service sets. If this requirement cannot be satisfied in a network, MCSP_K will search all the paths from a source node to each intermediate, which will lead the time complexity to be exponential. Thus, this algorithm does not fit for large scale WSNs. In [16], [PERSON] _et al._ took the entities of distributed systems and the relationships between them into consideration and raised two issues. The first one is how to formalize the entities that compose a system and their relationships for a particular activity. The other one is how to evaluate trust in a system for this activity. They proposed answers to both questions. On the one hand, they proposed SocioPath, a meta-model based on first order logic, which allows one to model a system considering entities of the social and digital worlds and their relationships. On the other hand, the authors proposed two approaches to evaluate trust systems, namely, SocioTrust and SubjectiveTrust. The former is based on probability theory to evaluate users' trust in systems for a given activity. The latter is based on subjective logic to take into account uncertainty in trust values. However, their methods only take into account one parameter (_i.e.,_ trust) in their evaluation and cannot be applied to deal with the NP-complete problem mentioned in this paper. Most of the existing work considered only indirect trust computation methods and integrated trust computation methods into comprehensive indirect computation to calculate the indirect trust for indirectly linked users. Unlike the previous work, [PERSON] _et al._[17] proposed a trust evaluation scheme for user relationships (links) in a social network. Their approach comprises two aspects: the reliability degree measuring the trustworthiness of the link and the strength degree for evaluating the closeness between users. A trust calculation method was given, including direct trust for directly linked users and indirect trust for indirectly linked users, which is established based on the comment factor, the forwarding factor, and the approving factor. Then a link strength evaluation method was proposed to determine the trustworthiness of direct and indirect links between users considering comment stability, mutual trust, interaction frequency, and common neighbors and community similarity. In the end, they designed a link trust evaluation algorithm based on the link trust matrix synthesizing the reliability and strength of links. Unfortunately, similarly to [PERSON] _et al._'s work, their work cannot be used in the context of our paper. [PERSON]. _et al._[11] developed a novel efficient heuristic algorithm MFPB_HOSTP for OSTP selection in complex social networks, where multiple backward local social trust paths (BLPs) are identified and concatenated with one Forward Local Path (FLP), forming multiple foreseen paths. MFPB_HOSTP is one of the most promising algorithms in solving the OSTP selection problem as it outperforms prior exiting algorithms in both efficiency and the quality of delivered solutions.