
The Digital Lecture
Board
A Teaching and Learning
Tool for
Synchronous, Collaborative,
Remote Instruction
© 1998 University of Mannheim
LS Praktische Informatik IV
L 15, 16
D-68161 Mannheim
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Installation
Postscript rendering
The digital lecture board (dlb) relies on ghostscript,
pssplit and lzps
for rendering postscript documents. Make sure these components are installed
properly on your system. A version of pssplit and lzps comes with the dlb
distribution. Make sure that the PATH variable is set to the location
of those files and to the location of ghostscript (gs). The dlb always
looks in the local directory and then in the PATH variable for the files.
Setup
Type setup to start installation. The setup tool creates a .dlbrc
directory in your home directory and copies configuration files
and files needed during runtime to this directory. If not available, a
new .rtpDefaults file is created.
Starting the dlb
The digital lecture board comes with the reliable multicast protocol smp.
There are two different ways to start the dlb:
1. Just type dlb in the
dlb directory. The reliable multicast protocol is launched automatically
with a default port. When finishing the dlb, smp is also automatically
killed.
2. Type smp&
once. Smp runs now in the background and can be reused several times.
Then type dlb -a 0
to start the digital lecture board.
In both cases, the dlb uses default ip addresses and default port numbers
for data transmission. Check the command line section for setting your
desired ip and port values.
You may also want to use the dlb with the MBone session directory sdr.
Please copy the sdr2.plugin.S22.whiteboard.udp.dlb.dlb
plugin file to the ~/.sdr/plugin directory in your home directory.
Make sure your PATH variable contains the path to the dlb binaries otherwise
sdr won't install the plugin. Note: If sdr is installed, the dlb setup
tool automatically copies the plugin file to the plugin directory.
Command line options
usage: dlb [-l {0,1}] [-a {0,1}] [-e{0,1}] [-p smpport] [-t ttl] [dest/port]
-l {0,1}
disable/enable late join (defaults to 1)
-a {0,1} disable/enable
automatic start of smp (defaults to 1)
-e {0,1} disable/enable
encryption on startup (defaults to 0)
-p smpport set port number for the connection to
the reliable multicast protocol smp (defaults to 5000)
-t ttl
set time-to-live to ttl (defaults to 16)
dest/port set destination
ip address and destination port (defaults to 224.101.102.58/61000)
Example: dlb -a 0 -p 6789
-t 63 224.2.3.4/50000
In this example, you need smp listening at port number 6789 prior to
start the dlb. To start smp with a different port, type:
smp -p 6789
You may also wish to disable the multicast loopback option of smp. To
disable multicast loopback, use the -l command line option of smp:
-l {0,1}
disable/enable multicast loopback
Using the digital lecture board
Check our brief user guide available through the dlb user interface or
the help file included in the package.
Known limitations and bugs
The current version does not support scaling of gifs. The late join algorithm
is still unstable and does not always work properly. The built-in
security mechanisms are still incomplete. So don't use them for the transmission
of highly secure data. This will be fixed in the next release. Your help
in improving this software is very appreciated. Please send detailed bug
reports to Werner Geyer (geyer@pi4.informatik.uni-mannheim.de).
Disclaimer
Permission to use, copy, and distribute this software and its documentation
for any purpose and without fee is hereby granted. We make no representations
about the suitability of this software for any purpose. This Software
is provided by the University of Mannheim and contributors ``AS IS''
and any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose
are disclaimed. In no event shall the University of Mannheim or contributors
be liable for any direct, indirect, incidental, special, exemplary, or
consequential damages (including, but not limited to, procurement of substitute
goods or services; loss of use, data, or profits; or business interruption)
however caused and on any theory of liability, whether in contract, strict
liability, or tort (including negligence or otherwise) arising in any way
out of the use of this software, even if advised of the possibility of
such damage.
!!! Note that this is an alpha prerelease which has not been tested
in a real-life session for several hours !!!