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

SGI
mrouted-3.8 from SGI

Applications

Notes

sdr

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.

scope/ttl

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:
Scope TTL
site 15
region 63
world 127

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 external world.

vic

turn on transmission

First read how to select video, and about network bandwidth consumption and its affects on audio quality and other Internet users.

video selection

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.

vat

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.

wb

session control

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 necessary.

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

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 display.

To import PostScript pages, create a file which associates a page label (name) with a postscript filename, one for each page. Example: 

dog  rover.ps
cat  ~/images/tabby.ps
tiger  /usr/local/lib/ghostscript/examples/tiger.ps
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

page orientation

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 buttons.
Chris Shenton
Last modified: Wed May 1 20:59:34 1996