mgpm - a multicast-enabled mgp

mgpm is a multicast-enabled version of the MagicPoint presentation tool. A techreport describing the application is available as mgpm990713.ps.gz.

Snapshots of the basic version of MagicPoint are available at ftp://sh.wide.ad.jp/WIDE/free-ware/mgp-snap

mgpm is designed as a one-to-many application, where a master node can unidirectionally transmit a presentation to a potentially large number of receivers.

The application uses a FEC-based reliable multicast protocol to distribute the presentation data to the receivers, and a special-purpose protocol to deliver commands (e.g. page changes, annotations, etc.) from the master sender to the receivers. In order to achieve scalability, the protocol is fully unidirectional and uses no feedback whatsoever from the receivers.

Transmission is done using RTP-encapsulated packets over a number of multicast groups. The application uses a congestion-controlled version of our Reliable Multicast Data delivery Protocol (RMDP) which is based on the RLC congestion control scheme. More info on RMDP and RLC is available at my research page http://www.iet.unipi.it/~luigi/research.html

RLC and RMDP are joint works with Lorenzo Vicisano and Jon Crowcroft.

Download and install info

You can choose between a binary (currently for FreeBSD, Windows and Linux) and a source distribution.

Binary install
- For FreeBSD 2.2.x, Download the binary distribution: mgpm990112.freebsd.bin.tgz and extract them with cd /usr/local ; tar xvzf mgpm990112.freebsd.bin.tgz
- For Windows (95/98/NT) Download the binary distribution: mgpw990211.zip
  extract binaries and dll from the zip file and put them in the path
- For Linux, Download the binary distribution: mgpm990112.linux.bin.tgz and extract them with cd /usr/local ; tar xvzf mgpm990112.linux.bin.tgz
This will install the following binaries and shared libraries:
```
    bin/mgpm, bin/sen-sample, bin/rec-sample,
    lib/libttf.so.2.0 (FreeBSD only)
```
(you don't need to install things in the system's directory, but then make sure that the bin/ directory in your PATH and LD_LIBRARY_PATH contains the lib/ directory with the above shared libs.
Source install
Sources are structured as a set of FreeBSD ports so you will have an easy time in installing/removing it. For other operating systems you might need some work to actually compile things.
You need to download the following files into /usr/ports/distfiles:
Then do the following:
```
    cd /usr/ports/misc (or some other directory you like)
    tar xvzf /usr/ports/distfiles/rlc981215.tgz
    tar xvzf /usr/ports/distfiles/rmdp981215.tgz
    tar xvzf /usr/ports/distfiles/mgpm981222.tgz

    cd rlc-port
    make install
    cd ../rmdp
    make install
    cd ../mgpm
    make
    cp work/kit/mgp /usr/local/bin/mgpm
```

Usage

mgpm behaves essentially as mgp, with only a few extensions. To use it for multicast presentations, the sender node needs to start it as follows:

   mgpm [options] -M group/port/ttl filename

whereas receivers can start the program as

   mgpm [options] -S rmdp://group:port/

With the above command, the sender runs an RMDP session on the specified multicast group addresses, and a command session on the group address immediately before. The receiver will in turn launch an RMDP receiver to download the presentation, then starts displaying the current slide and execute any command coming from the sender.

Other combinations are possible, e.g. the receiver can load the presentation from a local file or using http, just replacing the URL of the file with a local filename or a generic URL (e.g. /tmp/a.mgp or http://host/file).

In this case the address to be used for the control stream can then be specified with the option -r group/port on the receiver, and -s group/port on the sender. Unicast addresses can be used, in which case they should reflect the receiver's IP.

Security alert

Be warned, an mgp presentation can request the execution of commands on the host. The "-S" flag on the client is there to prevent a nasty sender to be able to run things on your machine. Remove it only if you know what you are doing.

Miscellanea

mgpm is still in being actively developed. We are working on various aspects of the application:

on the command protocol to make it more robust to losses, packet reordering, etc.;
on the user interface, to allow better control of the tool with a Pen, or to permit keyboard annotations, etc.
We are considering the idea of making the tool a little bit more interactive, e.g. allow the sender to receive notes/msgs from the receivers;

From my experience, the annotation ("rakugaki") mode in mgp is not very useful unless you have a graphic tablet and a pen. With that, and a tiny little bit of training, you can really use mgp as a {black|white}board, and do real-time drawings with the same ease. I have had good success with a Wacom PenPartner, which is a low cost (about 100US$) tablet with a passive pen using a button and an eraser. XFree86 fully support the tablet through the XIE interface, by simply adding the following lines to /etc/XF86Config:

    Section "Files"
    ...
      ModulePath  "/usr/X11R6/lib/modules"
    EndSection

    Section "Module" 
      Load "xf86Wacom.so"
    EndSection

    Section "Xinput" 
      SubSection "WacomStylus"
	Port "/dev/cuaa1"
	DeviceName "Wacom" 
	Mode Absolute 
	Suppress 6 
	AlwaysCore
      EndSubSection 
    EndSection

In this way you can have both the mouse and the pen active at all times.
NOTE: The XFree86 3.3.3 version of xf86Wacom.so has a bug in that it reports the eraser side of the pen as Button1, instead of Button3 as the previous version (3.3.2) did. The problem has been reported to the xf86Wacom developers and will be hopefully fixed in future releases. In the meantime i will try to provide a patch and possibly modified binaries.

Luigi Rizzo
Dipartimento di Ingegneria dell'Informazione -- Univ. di Pisa
via Diotisalvi 2 -- 56126 PISA
tel. +39-050-568533 Fax +39-050-568522
email: l.rizzo@iet.unipi.it