**** Columbia Network Research Group Seminar ****

Title:    The Effects of Wide-Area Conditions on WWW Server Performance
Speaker:  Dr. Erich Nahum
          Networking Research
          IBM T.J. Watson Research Center, Yorktown Heights
When:     Wednesday, November 28, 2001, 2 pm
Where:    Interschool Lab
          Columbia University
Host:     Prof. D. Rubenstein

ABSTRACT

   WWW workload generators are used to evaluate web server performance,
   and thus have a large impact on what performance optimizations are
   applied to servers.  However, current benchmarks ignore a crucial
   component:  how these servers perform in the the wide-area Internet.

   This talk shows how WAN conditions can affect WWW server performance. 
   We examine these effects using an experimental testbed which emulates
   WAN characteristics in a live setting, by introducing factors such as
   delay and packet loss in a controlled and reproducible fashion.  We
   demonstrate that when more realistic wide-area conditions are
   introduced, servers exhibit performance properties and scaling
   behaviors which are not exposed by existing benchmarks running on
   LANs.  We find that packet losses can reduce server throughput by as
   much as 50 percent and increase response time as seen by the client. 
   We show that using TCP SACK does not lower server throughput, and can
   reduce client response time.