The Digital Lecture Board

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 !!!