There is a critical need to design

Abstract-Agents in networks have two strategic choices: They can forward/process incoming service requests -or not, and they can establish additional contacts and maintain or terminate existing ones. In other words, an agent can choose both an action-selection and a link-selection strategy. So far, it is unclear which equilibria exist in such settings. We show that there are the following equilibria: First, an inefficient one where agents leave the network. Second, an equilibrium where agents process requests on behalf of others, i.e., they cooperate. In this second equilibrium, agents distribute their contacts uniformly, which is not efficient. We show that a strategy, we propose in this paper, yields an equilibrium that is optimal, i.e., that yields the highest sum of payoffs over all equilibria. If agents base their link-selection decisions on the processing times of their requests, optimal system states can be equilibria.

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Social search platforms like Aardvark or Yahoo Answers have attracted a lot of attention lately. In principle, participants have two strategic dimensions in social search systems: (1) Interaction selection, i.e., forwarding/processing incoming requests (or not), and (2) contact selection, i.e., adding or dropping contacts. In systems with these strategic dimensions, it is unclear whether nodes cooperate, and if they form efficient network structures. To shed light on this fundamental question, we have conducted a study to investigate human behavior in interaction selection and to investigate the ability of humans to form efficient networks. In order to limit the degree of problem understanding necessary by the study participants, we have introduced the problem as an online game. 193 subjects joined the study that was online for 67 days. One result is that subjects choose contacts strategically and that they use strategies that lead to cooperative and almost efficient systems. Surprisingly, subjects tend to overestimate the value of cooperative contacts and keep cooperative but costly contacts. This observation is important: Assisting agents that help subjects to avoid this behavior might yield more efficiency.