Vancouver Webpages' Mbone Page

Mbone

The mbone, or experimental multicast backbone, is a scheme whereby multicast network segments are linked together by unicast tunnels between machines running a multicast router (mrouted).

Multicast Addressing

Loosely speaking, multicast is a scheme for using ip addresses 224.0.0.0 through 239.0.0.0 to broadcast to several machines simultaneously. Addresses between 224.0.0.0 and 224.0.0.255 are reserved for maintenance protocols and aren't forwarded off your subnet.

Usually one uses the session directory tool sd to pick addresses and port numbers. This tool sends a multicast message with information about the conference. Users at other machines simply click to join. Without using sd, one must give an address & port number to the tools. Typically one chooses a port above 2000.

Tools

There are four main classes of tool:

These tools may be used either point-to-point, or multicast via a multicast router.

Session Directory

The original tool "sd" is now superseded by the newer tool "sdr".

This tool (sd) receives session description packets from the MBone and displays them on an X-terminal. Users may connect to a conference by using sd to open it. sd's default behaviour (to launch nv, vat, wb) may be overridden by the users personal ~/.sd.tcl file, eg. to launch alternative tools such as vic or nevot.
Note that you may manually launch any of the tools, giving the address, port, and other information on the command line. sd is just a convenient way to do this automatically. (It's also used to get new, random addresses that don't conflict with existing sessions if you are creating your own conference.)

Whiteboard

Like Xpaint or Pbrush, it allows two or more users to simultaneously write on an X-window. It uses objects rather than bitmap, so is correspondingly more efficient in terms of bandwidth. It allows import of text files, and a slideshow of pre-prepared PostScript pages, subject to a 32Kb page limit. The whiteboard tool is the LBL conference tool wb. wb will run on any X11 display.

Video

 There are several video tools (vic, ivs, nv) which allow one to send and receive slow-scan video pictures. One, nv, allows the user to capture and send an arbitrary area of the X11 screen. Ideally the video tools should be run at a workstation to reduce local net traffic, though they will allow viewing at an X-terminal. A frame grabber is required to transmit video. The vic tool is now available for Win95/NT.

Audio

 The tools (vat, nevot, ivs) are available for audio-capable workstations. One versions operates with NCD's audio-capable X-terminals.

References

Tools

The tools run on a wide variety of Unix platforms, ranging from Silicon Graphics workstations down to a 486 running NetBSD, FreeBSD or Linux. Experimental versions run on Win95, WinNT and PowerMac.

Packages


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