Distributed and Mobile Computing Laboratory, Graduate School of Information and Communication, Ajou University, Suwon 442-749, Korea.|Distributed and Mobile Computing Laboratory, Graduate School of Information and Communication, Ajou University, Suwon 442-749, Korea.|Distributed and Mobile Computing Laboratory, Graduate School of Information and Communication, Ajou University, Suwon 442-749, Korea.|Distributed and Mobile Computing Laboratory, Graduate School of Information and Communication, Ajou University, Suwon 442-749, Korea.|Distributed and Mobile Computing Laboratory, Graduate School of Information and Communication, Ajou University, Suwon 442-749, Korea.