MBONE Tools Sources
This is a collection of random notes on where to pick up MBONE tools,
and some hints on tunnel and session configuration. Locations of the
new tools (eg: sdr and alpha releases of vat and vic) is given, but
you should be able to get from there to older (or non-alpha) releases.
- mrouted-3.8 from SGI
initial dialogue box
The first time you use sdr (and some of the other tools), it will pop
up a dialog box with a bunch of text about X Resources. If you ignore
the tech-talk, you'll realize that all it really wants is your name,
affiliation, and contact information. This information is tranmitted
to identify you to other conference participants, and so they can
reach you if there is a problem.
if your applications go away
You may accidentally kill-off one of the MBONE applications,
especially nv, vic, and vat. This can be done by clicking on the Quit
button, or by hitting the Q key in the application window. The sdr
directory provides a convenient facility for recovering. In sdr, click
on the same session as you selected before; it will pop up a window
describing all the media available in that session (eg: audio, video,
whiteboard); just click on the media button for the application you
lost -- it will be restarted anew.
Sdr uses descriptive text to set the scope of how far application
packets will travel -- their time-to-live (ttl). The ttls
corresponding to the words selected when you create a session are:
These TTLs interact with the threshold parameter for
the MBONE tunnel specified in /etc/mrouted.conf. For
example, if you have a number of networks connected by mrouted tunnels
and you want them to all be included in the "site", then you need to
choose a threshold which allows packets to cross tunnels,
but not get off your site through an other tunnel to the Internet at
large. Since "site" has a TTL of 15, internal tunnels might chose
threshold of 8, and the external tunnel might use a
threshold of 32. An example mrouted.conf shows how the main
mrouted at INOVA separates internal tunnels from its tunnel to the
turn on transmission
First read how to select video, and about network bandwidth
consumption and its affects on audio quality and other Internet users.
On vic, you may have to select what video source you want to use. For
SGI machines I've had to do the following: select the
Menu from the main vic pane; then go to the new
pane's Encoder section, mouse on the
Port pull-down menu, and select the
Analog option. This uses the analog input of the
Indycam, or whatever analog camera you have connected to the SGI.
bandwidth and transmission
Video consumes a lot of network bandwidth. The default data rate for
vic is set to 128Kbps. The total bandwidth for the global MBONE is 256
or 512Kbps. If you consume a lot of network bandwidth and the scope of
your conference extends outside your network, you will rob other
Internet users of the resources they need. You will probably also get
some angry email.
It's tempting to crank up the tranmission rate as high as it
will go -- in order to get smoother video -- you make cause a lot of
problems. Generally, you shouldn't exceed 128Kbps: unless you're
absolutely certain your traffic won't leave your own network (nobody
minds if you melt down your own net! :-); see the discussion about
scope and TTLs in the sdr section.
Also realize that sending a lot of video traffic may impact the
quality of your audio and the audio you receive from the other
participants in your conference. Drop-outs and break-up are the usual
symptoms. While missing some packets may affect the quality of video,
dropped chunks of audio may render it unintelligible. If this is
occurring, you might consider decreasing the bandwidth used by the
video of the conference participants.
To set the transmission rate, click on vic's Menu button, then
adjust the slider to desired Kbps. This is right next to the button to
turn on the Transmit option.
bandwidth conservation and encoding
Vat can use different techniques to encoding the audio you send. As
with everything else, there is a trade-off between quality and
bandwidth (network usage). The default encoding is PCM2 which sounds
good but uses a fair amount of network resources; it's completely
useless over dialup PPP connections, for example, but this is an
extreme case. One symptom of overtaxing the network is audio
"drop-outs", missing chunks of audio that quickly render the
conversation meaningless. To reduce bandwidth requirements, you can
use a more frugal audio encoding. The GSM encoding is very efficient,
and the quality is not bad -- on a par with telephones; I've even been
able to use it (barely) over a 28.8 PPP link. I find the tighter
LPC4 encoding to have a sound that's too robotic to be of much use.
To select audio encoding, use the vat Menu button to get the vat
control panel. Then select the encoding you want, eg: GSM.
(Video consumes a lot of bandwidth; see the section on vic and nv
about transmission rates).
full and half duplex
Telephones allow you to listen and talk at the same time: this is
full-duplex. Feedback can occur, however if a microphone picks up the
audio from the speaker, as is typical using tools like vat. For this
reason, vat defaults to a half-duplex mode where incoming network
audio mutes your microphone. If you wear headphones, instead of having
the audio come out of the speaker, you can avoid the feedback problem
and use vat in full-duplex.
To change duplex modes, click on the vat Menu button, and change the
"spkr" options as desired.
The whiteboard is a document sharing tool, but there must be a
mechanism to control who is drawing on it and who sees what page. The
technique wb uses is that any time someone draws or types on the
whiteboard, it tells all the other whiteboards in the conference to
immediatly jump to that page; this is useful for "keeping everyone on
the same page". Obviously, if everyone is trying to draw on different
pages, document focus will shift a lot: it helps to have someone
coordinating with voice.
document size verus network
To share the documents, whiteboard sends the image representation of
the document to all other whiteboards. If the data is very large, this
can take a significant amount of time, and interactivity will be
low. For this reason, whiteboard limits the size of documents you can
import: ASCII text documents are split across multiple pages;
PostScript files are limited to some number of Kilobytes and can't be
loaded at all if they're too large.
Many applications create excessively large PostScript
documents. PowerPoint is particularly egregious in this regard: one
test I did of a document containing a single word produced a .ps files
which was hundreds of KBytes long. These applications typically bloat
the file with font definitions and other clutter that isn't
Also, I believe each page of a PostScript document must be contained
in a separate file. This is so whiteboard can corrleate document pages
to whiteboard pages.
I need to do more digging into this to find out what the limits are,
how to persuade rogue applications to trim the fat, etc.
Wbimport works with wb to -- oddly enough -- import documents and step
through document pages. It also works with a couple helper
applications to snarf images from a scanner, or from the X Window
To import PostScript pages, create a file which associates a page label
(name) with a postscript filename, one for each page. Example:
Then start wbimport and specify that filename as the only argument. Be
aware that if you use wbimport to flip through pages, you will be
forcing all the other participants to look at each of those pages;
this may not be what you intend.
wbimport of X Windows
To import X Windows, wbimport relies on a script "doWbXwd" to do its
work. This calls commands to capture an image, convert it to
PostScript, and compress it for faster network transmission. The
default depended on some things I didn't have, so I used this
dumbed-down version which only relied on common X utilities
xwd | xpr -gray 2 -device ps | lzps
Unfortunately, it renders colors as grays, and not very many shades of
that. A better one relies on image manipulation and conversion
software (the Pbmplus tools) and renders color very well:
xwd | xwdtopnm | pnmtops -noturn -rle -scale 10 | lzps
If the text is sideways or upside down and you're feeling disoriented,
you can right the image. Click on one of the page-orientation icons
near the bottom right of the whiteboard between the Undo and Print
Last modified: Wed May 1 20:59:34 1996