ITU's Videoconferencing Standards

The impact of teleconferencing standards by the International Telecommunications Union (ITU) has been considerable. Since introduced in roughly 1996, costs for products have come down dramatically while quality has improved. Systems have become considerably easier to use, and designed more an consumer products.

These standards span both the classic phoneline infrastructure (H.320 for moderate and higher bandwidth, H.324 for lower bandwidth videophones) and the packet-based Internet Protocol (IP) infrastructure (H.323, SIP).

ITU-T recommendations, especially the H-series (for audiovisual and multimedia systems, e.g. H.32x for videoconferencing, H.26x for video codecs, H.28x for remote device control, H.233-5 for security/confidentiality/encription, H.350.x for director services architecture, H.450.x for call service features) and the G-series (for , e.g. G.72x for audio codecs). For a sample of conferencing solutions see the telemedical site.

• Audio codecs range from:
  • the more basic G.711 (pulse code modulation requiring 48-64 Kbps of the connection), very low time delay (under 1 ms)
  • the newer higher quality G.722 (7 KHz voice with 64/32/16 Kbps) that focus on quality of speech and low time delays (under 2 ms)
  • the clever codecs with more aggressive compression such as G.723.1, (multimedia speech coder at 5.3 or 6.3 Kbps, well within the cell phone range of 8-11 Kbps), but with more time delay (60-100 ms)
  • G.728 (coding at 16 Kbps using low-delay linear prediction), under 2 ms time delay.
• Video codecs include:
  • H.261 DCT algorithm
  • H.263 Improved DCT algorithm
  • H.264 Even more improved algorithm, still with DCT base

Each overall videoconferencing standard defines messaging protocols that govern transmission of audio, video and data between two (or more) systems, and specifies additional viable standards for video and voice codecs, security, privacy, and multiplexing and data control. Often they share some features, such as RTP/RTCP) for real-time messaging control and CIF (352 x 288) or QCIF (176 x 144) or the standard TV resolution of 4CIF (704 x 576).

Each is periodically updated. An example of this is the new H.264/MPEG-4 advanced video coding standard, an outgrowth of a concerted joint effort by two key international bodies developing video coding standards: the H.26x video coding standards group through ITU and the MPEG-4 computer multimedia transmission/storage standards group through ISO/IEC. It provides higher quality video at lower bit rates (same video quality at roughly half the bandwidth) and better error resilience. This is significantly improving quality-of-service, especially for broadband (e.g., LAN, cable-modem, DSL) but also for phone-based connections, and tips the scales to IP-based solutions. All of the top videoconferencing manufacturers, such as Polycom, VCON and Tandberg, are rapidly evolving to products that support both the H.323 and SIP and use the H.264 protocol. Similarly, the top digital video products used for streaming multimedia, multicasting or playing DVD movies, have or are migrating to the very flexible new MPEG-4 standard. As an example of this impact, the Mobile Usability Lab (MU-Lab) of the RERC-AMI recently abandoned the need to maintain protocols for “lower quality” and “higher quality” digital video storage (related to length of trials and concerns of file size), simply because the new MPEG-4 standard provides high quality storage even with relatively smaller files.

Advantages of conferencing/multimedia standards:

• gathers expertise, to reach consensus, discuss and lend support to strong technologies,
• provides core interoperability between products (e.g., communication across platforms and networks),
• provides compatibility of components and applications of varying sophistication,
• provides a degree of quality control and performance management (depending on whether performance measures are involved),
• provides improved reliability,
• may provide customer confidence and a form of consumer empowerment.

Possible disadvantages:

• consensus standards require a"common ground" and typically provide a set of minimal specifications that may be below the best in the field,
• may discourage innovation,
• require an infrastructure to periodically update,
• it can bedifficult to remove "obsolete" standards.

Thus it is common for companies to try to add value to their product that is over-and-above the standard. This helps explain why video and sound quality is often worse when products for different manufacturers connect during a teleconference - they connect so as to met the minmal standard, without value-added features.

Our Telerehab and Performance Assessment Lab has multiple examples of each of these standards, and you have an opportunity to experience systems supporting each of these standards.

See also a summary by the International Multimedia Telecommunications Consortium, a Detailed Videoconferencing Glossary or a shorter Glossary of Conferencing Terms

| telerehab outline || tele-standards | H.320 ISDN | H.324 POTS | H.323 & SIP | Wireless | Multi-Node |