Reliability of Internet hosts: a case study from the end user's perspective

This paper presents the results of a 40-day reliability study on a set of 97 popular Web sites done from an end user's perspective. Data for the study was acquired by periodically attempting to fetch an HTML file from each Web site and recording the outcome of such attempts. Analysis of the acquired data revealed: (i) 94% of the HTML file fetch requests succeed on average; (ii) most failures last less than 15 minutes; (iii) the underlying network plays a dominant role in determining host accessibility: (a) network related-outages account for a major part of the failures, (b) some network-related outages rendered more than 70% of the hosts inaccessible, and (c) host-related failures tend to be shorter than failures that might involve the network; (vi) the network connectivity is high on the average with 93% of the sites being accessible at any given time; and (vii) the mean availability of the hosts is high (0.993).