We used the MBone tools and mrouted in several projects and courses from the MERCI project and forward. This report was published Mon Jun 23 1997 and has not been factually edited since that date.
The Multicast Backbone (MBone) was initially a virtual network backbone
built on top of the unicast Internet using IP-in-IP tunnels bridging
together multicast-enabled subnets. The reason for this was that at
that time, 1991-1992, production Internet routers could not carry
IP-multicast traffic. Thirty-two isolated multicast sites spread over
four countries were connected and the network was, among other things,
used to audiocast the 23rd Internet Engineering Task Force (IETF)
meeting. The MBone still exists today, but is gradually replaced by
IP-multicast support in Internet routers since late 1996. During the
five years of intense research, the initial audio tool (vt) was
complemented by several audio, video, whiteboard and session directory
tools.
The UCB/LBNL VIdeoConference tool (VIC) is one of the most successful
desktop video tools for packet-based networks. Unlike many of it's
predecessors, VIC is highly optimized for a typical Internet
environment with lossy connections and low-end desktop computers.
The source code is freely available and modular as described in [1].
This makes VIC a good platform for prototyping. The MASH research
group at the University of California, Berkeley [2] is extending
the TCL/C++ architecture of VIC into a multimedia networking
toolkit called the MASH shell, or simply mash. University College
London (UCL) is continuing the development of the original VIC,
keeping a revision series of their own.
VIC was designed with a flexible and extensible architecture to
support heterogeneous environments and configurations. For example,
in high bandwidth settings, multi-megabit full-motion JPEG streams
can be sourced using hardware assisted compression, while in low
bandwidth environments like the Internet, aggressive low bit-rate
coding can be carried out in software [3].
The original VIC provided the video portion of a suite of
applications for multimedia conferences developed at UCB; audio (VAT),
whiteboard (WB), and session control (SD) tools are implemented as
separate applications. VIC uses RTP version 2 for video transport
and for gathering awareness information and network statistics. To
provide confidentiality to a session, VIC implements end-to-end
encryption using the Data Encryption Standard (DES).
At writing time, the current version from UCL is version 4 [4].
Supported input video formats are Square pixel SIF (320x240 for NTSC
feed, 384x284 for PAL) and CIF. It can also do X11 screen capture.
The following codecs are supported:
Software H263
Software H263+
Software and hardware JPEG
Software BVC encoding
Raw YUV packetiser/codec
Software and hardware H.261 encoding
Software nv and nvdct
Software and hardware cellB
Audio-video synchronisation is supported with RAT version 3.2.
A User's Guide to McCanne's VIC 2.8 that I wrote for the laboration in the Telesystems course 1996. I also did a similar User's Guide for VAT, but never HTML:ed it.
The Robust-Audio Tool (RAT) developed at UCL allows users to
participate in audio conferences over the internet. Just as VIC,
RAT is based on IETF standards, using RTP version 2 above UDP/IP
as its transport protocol.
RAT features sender based loss mitigation mechanisms and receiver
based audio repair techniques to compensate for packet loss, and
load adaption in response to host performance. These features are
a result of experiences using the previously available audio
conferencing applications over the MBone for remote language
teaching [5]. Over the years, more and more features have been
added and the sound quality has improved significantly compared
to the previous audio tools. The current version is 4.0 [4] and
supports sampling rates of 8,16,32,48 kHz, mono and stereo, and
can do sample format conversion with alternative quality/cost
options. The codecs supported are
Wide Band ADPCM Speech Codec (16kHz, 64 kbps),
G726-2/3/4/5,
VDVI,
L16 (128 kbps, 16 bits linear),
PCM (64 kbps, 8 bits mu-law),
DVI (32 kbps, 16 bits differential),
GSM (13.2 kbps) and
LPC (5.8 kbps).
RAT can also do 3D positioning of audio sources and support lip
synchronization with VIC via a conference bus to VIC.
Vic and vat platforms and compatible applications
Maintained by Tobias Öbrink