#    Copyright (c) 1998 University of Southern California.
#    All rights reserved.                                            
#                                                                   
#    Redistribution and use in source and binary forms are permitted
#    provided that the above copyright notice and this paragraph are
#    duplicated in all such forms and that any documentation, advertising
#    materials, and other materials related to such distribution and use
#    acknowledge that the software was developed by the University of
#    Southern California, Information Sciences Institute.  The name of the
#    University may not be used to endorse or promote products derived from
#    this software without specific prior written permission.
#    
#    THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
#    WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
#    MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

LSAM OBJECT SCHEDULING
======================
LSAM Authors: Lars Eggert, Amy Hughes
$Revision: 1.16 $ ($Date: 1998/07/06 23:02:47 $)
More Information: http://www.isi.edu/lsam/scheduling


Introduction
------------
The LSAM server supports different service classes for requests. Requests may
either be foreground (FG) or background (BG) requests. Responses to requests
may be sent in the FG or BG as well. This can be thought of as a form of
differentiated services.

FG requests and responses are being received, processed and/or sent out using
the normal apache methods. BG requests and responses, however, are dealt with
in a special way as to minimize their impact on FG performance.  This may
include delaying them longer or maybe not processing them altogether,
depending on the FG load.

BG requests and responses will be used for cache preloading in the future.

The current version of the object scheduler is limited in the following ways:

Unicast Only:
	Responses can only be unicast, there is no support for multicast yet.

Distinguishing between FG and BG requests:
	There is currently no inherent way to distinguish a FG from a BG
	request. Instead, the server listens on two ports, a "FG port" and
	a "BG port". All requests arriving on the FG port are assumed to
	be FG requests and treated as such, while all requests arriving at
	the BG port are treated as BG requests.


Demonstration
-------------

Due to the lack of a fully functional status page, demonstrating background
scheduling in this release is a little difficult. You may follow these steps:

1. Copy a large file to apache/htdocs - preferably an HTML or text file that
   is serveral hundred KB long. Let us assume that you call this file
   bg_test.html.

2. Change the permissions of bg_test.html so it is world readable:

   % cd apache/htdocs
   % chmod a+r bg_test.html

3. Start the server, if it not already running:

   % apachectl.lsam start

4. Open a browser of your choice, and request bg_test.html twice, once from
   the foreground port and once from the background port. Under the default
   configuration, these URLs will work:

   http://www.your.server:8080/bg_test.html for the foreground request
   http://www.your.server:8081/bg_test.html for the background request

5. Notice that receiving the background response takes considerably longer,
   because it is being sent rate-limited at 1.0 Mbps (under the default
   configuration.)

   If you do not see a significant difference in loading time, your background
   rate limit is probably too close to your available network bandwidth along
   the path to the server. You can change the rate limit through the
   "Foreground/background Scheduling" page. Set it to a small value
   (i.e. 0.1) and repeat the steps above.



Upcoming Features
-----------------
	* support for multicast responses

Acknowledgments
---------------

      Portions copyright 1994, 1995, 1996, 1997, 1998, by Cold
      Spring Harbor Laboratory. Funded under Grant
      P41-RR02188 by the National Institutes of Health. 

      Portions copyright 1996, 1997, 1998, by Boutell.Com, Inc. 

      GIF decompression code copyright 1990, 1991, 1993, by David
      Koblas (koblas@netcom.com). 

      Non-LZW-based GIF compression code copyright 1998, by
      Hutchison Avenue Software Corporation
      (http://www.hasc.com/, info@hasc.com). 

      Permission has been granted to copy and distribute
      gd in any context, including a commercial application,
      provided that this notice is present in user-accessible
      supporting documentation. 

      This does not affect your ownership of the derived work itself,
      and the intent is to assure proper credit for the authors of gd,
      not to interfere with your productive use of gd. If you have
      questions, ask. "Derived works" includes all programs that
      utilize the library. Credit must be given in user-accessible
      documentation. 

      Permission to use, copy, modify, and distribute this software
      and its documentation for any purpose and without fee is
      hereby granted, provided that the above copyright notice
      appear in all copies and that both that copyright notice and this
      permission notice appear in supporting documentation. This
      software is provided "as is" without express or implied
      warranty.