Last modified: Wed Jun 17 2009

Report on the MBone evaluations

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.

VIC

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.

RAT

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

References

  1. S. McCanne, Scalable Compression and Transmission of Internet Multicast Video, Ph.D. thesis, University of California Berkeley, UCB/CSD-96-928, December 1996.
  2. The MASH Project Home Page
  3. Steven McCanne and Van Jacobson, vic: A Flexible Framework for Packet Video. ACM Multimedia, November 1995, San Francisco, CA, pp. 511-522.
  4. Mbone Conferencing Applications.
  5. V. Hardman, M. A. Sasse, M. Handley & A. Watson, Reliable Audio for use over the Internet", In Proceedings INET'95, Hawaii, 1995.


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