Availability and Latency of World Wide Web Information Servers

Authors:Viles, Charles, Department of Computer ScienceUniversity of Virginia French, James, Department of Computer ScienceUniversity of Virginia

During a 90 day period in 1994, we measured the availability and connection latency of HTTP (hypertext transfer protocol) information servers. These measurements were made from a site in the Eastern United States. The list of servers included 189 servers from Europe and 324 servers from North America. Our measurements indicate that on average, 5.0% of North American servers and 5.4% of European servers were unavailable from the measurement site on any given day. As seen from the measurement site, the day-to-day variation in availability was much greater for the European servers than for the North American servers. The measurements also show a wide variation in availability for individual information servers. For example, more than 80% of all North American servers were available at least 95% of the time, but 5% of the servers were available less than 80% of the time. The pattern of unavailability suggests a strong correlation between unavailability and geographic location. Median connection latency from the measurement site was in the 0.2 - 0.5s range to other North American sites and the 0.4 - 2.5s to European sites, depending upon the day of the week. Latencies were much more variable to Europe than to North America. The magnitude of the latencies suggest the addition of an MGET method to HTTP to help alleviate large TCP set-up times associated with the retrieval of web pages with embedded images. The data show that 97% and 99% of all successful connections from the measurement site to Europe and North America respectively were made within the first 10 s. This suggests the establishment of client-side time-out intervals much shorter than those used for normal TCP connection establishment.

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Source Citation:

Viles, Charles, and James French. "Availability and Latency of World Wide Web Information Servers." University of Virginia Dept. of Computer Science Tech Report (1994).

University of Virginia, Department of Computer Science
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