Availability of network access "anytime and anywhere" will impose new requirements to presence services - server load sharing and privacy protection. In such cases, presence services would have to deal with sensor device information with maximum consideration of user's privacy. In this paper, we propose FieldCast: peer-to-peer system architecture for presence information exchange in ubiquitous computing environment. According to our proposal, presence information is exchanged directly among user's own computing resources. We illustrate our result of evaluation that proves the feasibility of our proposal.