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PhoneFactortrade is a token-less two-factor authentication service for user remote logons. This allows users of an organization to be authenticated through an automated phone call to the user's phone before access is allowed. In this paper, we present the service management architecture of PhoneFactor that depends on both the Internet and the public switched telephone network (PSTN), and we identify two key quality of service parameters, the system response time and call blocking probability, where the latter can impact the former. Furthermore, through traffic analysis of the measurement data from the deployed PhoneFactor service, we found that the inter-arrival time of requests follows the generalized Pareto distribution while the system response time and the call duration (for the authentication part through the phone call) follow the log-normal distribution. Given these distributions, we then present system capacity design methodologies by comparing them to known results for systems that are analytically derivable.