Assignment #4 for Computer Simulation (Spring 1999)
Situation:
You are the IS manager for a growing "Web Mall". Business has been so good
that the rate of requests arriving into the single Web server exceeds the
service rate of these requests. In other words, your Web server is
overflowing and you are losing real customers. You plan to install a
second mirrored Web server and distribute the incoming requests between
the two identical servers. You have found three request distribution
products on the market. They are:
- LoadSplit - A device that randomly assigns an incoming request to
one of two servers.
- TurnTaker - A device that alternates incoming requests to the two
servers.
- ShortQ - A device that sends incoming requests to the server with
the shortest queue length.
It is intuitively obvious (or is it?) that ShortQ will result in the
lowest delay for processing a request. However, ShortQ is a very
expensive product and you need to justify its purchase to your manager.
Requirement:
Assume that a Web server can process 10 requests per second with a
deterministic distribution (i.e., each request take exactly 100 milliseconds
to process). Assume also that requests arrive at a mean rate of 18 per
second with a Poisson distribution. Determine the response time for
processing requests given two Web servers and the above LoadSplit,
TurnTaker, and ShortQ products.
Guidelines and hints:
The SMPL M/M/1 simulation handed-out in class is a good place to start. You
will need to change the service time to deterministic (a trivially easy change!)
and add another server. Then, you will need to add some code to implement
the three methods of distribution of arrivals. Submit a hardcopy and
softcopy of your program and three numerical answers. Be sure to run
your simulation for a sufficient amount of time to get "good" answers.
Extra Credit (10 points):
Find at least four commercial products that do load distribution for
Web servers. Submit the name and a very brief description explaining
HOW the servers are selected for each product.
Last updated by
Ken Christensen on FEBRUARY 13, 1999