[Ns-developers] PackMime-HTTP changes

[Michele Weigle]

Hi all,

I've just committed a significant update for PackMime-HTTP.  This change
allows much more flexibility in setting HTTP/1.1 behavior than
before.

If you want to use PackMime-HTTP's default behavior, your TCL
scripts will not need to be changed.  But, note that results generated
with PackMime-HTTP in HTTP/1.1 mode will be different with this code
than with the ns-2.30-release code even if you use the default
values.  The difference is because I separated out several random
variables that control things such as the number of pages per
connection, the number of objects per page, the time between objects,
the time between pages, etc.  I have put the full details of what random
variables are available in the PackMime chapter in the ns Manual.

The behavior of HTTP/1.0 is not changed and results generated
with PackMime-HTTP in HTTP/1.0 mode should not change.

 From conversation with users, I have discovered that there is a
misunderstanding about the client and server nodes in PackMime-HTTP.
I've added the following explanation to the beginning of the
PackMime-HTTP chapter in the ns Manual (which should appear in
the Nov 22 version of the manual):

"The goal of PackMime-HTTP is not to simulate the interaction between
a single web client and web server, but to simulate the TCP-level
traffic generated on a link shared by many web clients and servers.

A typical PackMime-HTTP instance consists of two ns nodes: a server
node and a client node.  It is important to note that these nodes do
not correspond to a single web server or web client.  A single
PackMime-HTTP client node generates HTTP connections coming from a
"cloud" of web clients.  Likewise, a single PackMime-HTTP server node
accepts and serves HTTP connections destined for a "cloud" of web
servers.  A single web client is represented by a single PackMime-HTTP
client application, and a single web server is represented by a single
PackMime-HTTP server application.  There are many client applications
assigned to a single client ns node, and many server applications
assigned to a single server ns node.

In order to simulate different RTTs, bottleneck links, and/or loss
rates for each connection, PackMime-HTTP is often used in conjunction
with DelayBox.  DelayBox is a module developed at UNC-Chapel Hill for
delaying and/or dropping packets in a flow according to a given
distribution."

-Michele

--
Michele Weigle
Assistant Professor
Department of Computer Science
Old Dominion University
Norfolk, VA 23539
mweigle at cs.odu.edu
http://www.cs.odu.edu/~mweigle
(757) 683-6001 ext. 5050