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Video Conferencing Standards


TANDBERG

Application Notes

D10740, Rev 2.3 TANDBERG

Videoconferencing Standards
D10740 Rev 2.2

2

ITU DEFINED STANDARDS
....................................................................................................................................3

V
IDEOCONFERENCING
(H.3
XX
)
.................................................................................................................................3

INTRODUCTION TO H.323
....................................................................................................................................4

C
OMPONENTS
..............................................................................................................................................................4

Terminals
................................................................................................................................................................4

Gatekeepers
............................................................................................................................................................5

Gateways
.................................................................................................................................................................5

INTRODUCTION TO H.320
....................................................................................................................................6

STANDARDS
..............................................................................................................................................................7

T
HE
A
UDIO
S
TANDARDS
:
..........................................................................................................................................7

T
HE
V
IDEO
S
TANDARDS
............................................................................................................................................8

T
HE
C
OMMUNICATIONS
S
TANDARDS
.....................................................................................................................9

D
ATA
C
OLLABORATION
T.120
...............................................................................................................................10

STANDARDS OVERVIEW
................................................................................................................................... 11

INTER-DEVICE COMMUNICATION
.................................................................................................................. 12

TANDBERG

Videoconferencing Standards
D10740 Rev 2.2

3
ITU Defined Standards

The International Telecommunications Union -- Telecommunications Standardization Sector
(ITU-T) is responsible for generating worldwide "recommendations" (non-binding standards)
for telecommunications. The ITU- T is divided into fourteen Study Groups. Each Study
Group studies "questions" (i.e., topics for study); the results of their study define these
recommendations. Study Group XVI is responsible for generating recommendations for data
collaboration and videoconferencing. The following summarizes salient recommendations for
multimedia communications produced by Study Group XVI.

Videoconferencing (H.3xx)
H.3xx are "umbrella" recommendations for videoconferencing. These recommendations
reference other recommendations that include the protocols for coding video/audio,
multiplexing, signalling, and control. The core H.3xx recommendations are:
H.320

Narrow-band videoconferencing over circuit-switched networks
(N-ISDN, SW56, dedicated networks)

H.321

Narrow-band videoconferencing over ATM and B-ISDN

H.323

Narrow-band videoconferencing over non-guaranteed quality-of-
service packet networks (LAN, Internet, etc.)

H.324

Very narrow-band videoconferencing over the general (dial-up)
telephone network

H.310

Wide-band (MPEG-2) videoconferencing over ATM and B-ISDN

For the H.3xx recommendations, referencing the T.120 recommendation for data
collaboration is optional
.

TANDBERG

Videoconferencing Standards
D10740 Rev 2.2

4
Introduction to H.323
H.323 is an International Telecommunications Union (ITU) standard that describes the
protocols, services and equipment necessary for multimedia communications including audio,
video and data on networks without guaranteed Quality of Service (QoS). These networks
technologies may include Ethernet, Fast Ethernet, and Token Ring and protocols like Internet
Protocol (IP) or Integrated Packet Exchange (IPX). Due to the need to communicate
between smaller networks connected to the Internet, H.323 will be more popular on IP
networks.

Today, the dominant method of Internet communications is email. However, there is a
growing need to increase communications to include audio, video and data. The explosion of
the Internet in the early 1990s has paved the way to higher bandwidth connections to
corporate offices, universities and even to the home. Now that the bandwidth is available,
the demand for multimedia communications over the Internet is growing.

Components
H.323 specifies several new standards to allow for communications between terminals on IP
networks. These standards dictate how different mandatory and optional components of the
H.323 standard interoperate with each other.

The major network components of H.323 include the mandatory terminal, and the optional
gatekeeper, gateway and multipoint control unit (MCU).

Terminals
The terminal or endpoint must support a minimum of G.711 audio, H.225, H.245, Q.931
and RTP. If the terminal supports video, it must support a minimum of H.261 QCIF. The
terminal may support T.120 data sharing although this support is optional. The TANDBERG
500, 800, 1000, 2500, 6000 and 7000 video conferencing systems all fit the definition of a
H.323 terminal.


TANDBERG

Videoconferencing Standards
D10740 Rev 2.2

5
Gatekeepers
The gatekeeper is an optional component of H.323 that is responsible for managing other
components of a H.323 network. It is a very important component to the managed network.
The gatekeeper has several responsibilities which include: translation of E.164 aliases to IP
or IPX addresses, bandwidth management of incoming or outgoing calls, call admission to
accept or deny calls, and zone management. Gatekeepers can also support an optional
feature that allows a call to be rerouted if there is no answer from the intended terminal.
Gatekeepers also help manage different H.323 zones and help manage H.323 MCU
sessions. It is important to remember that while gatekeepers are optional, the H.323 terminal
must make use of the gatekeepers services if the gatekeeper is present in the network.

Gatekeepers are typically software products that reside on a server. Although many H.323
MCUs and gateways have embedded gatekeepers, they usually offer less features than stand
alone gatekeepers.
Gateways
If there is a need for a H.323 terminal to communicate with another terminal on a H.320,
H.324 or analogue PSTN networks, a H.323 gateway is required to perform the translation.
This optional components typically have ISDN and IP network connections and support the
translation between these two networks. The number of simultaneous connections allowed
through a gateway is not specified in any standard, so there are different options available
from different manufacturers. Gateways typically have built in gatekeepers with minimal
features.

TANDBERG

Videoconferencing Standards
D10740 Rev 2.2

6
Multipoint Control Units
The last of the major components is the MCU which controls conferences between 3 or
more terminals. The H.323 MCU may be a separate component or may be incorporated
into a terminal. The TANDBERG 800, 2500, 6000 and 7000 have optional software
packages that enable internal H.323 MCU capabilities. The TANDBERG built-in multipoint
conference unit (MCU), Multisite
TF
, has the capability to establish meetings with up to 4
video sites (5 if at least one site is a telephone call, ISDN/analogue/mobile). A conference
can consist of any combination of ISDN/LAN sites. Up to 4 TANDBERG Multisite
TF

systems can be cascaded in one meeting. The maximum numbers of participants is 10 video
system and 4 telephones, see fig bellow.







Introduction to H.320
In 1991 the European Videophony Experiment (EVE) saw various manufacturers trailing
equipment using the CCITT standard H.320.
Simultaneously in Japan the HATS trial was initiated, also H.320 based and this included
some ISDN trial work.
Today the H.320 standard forms an umbrella for a whole host of standards adopted by the
main manufacturers of video conferencing equipment and ensures a fair degree of
interconnectivity. A group is currently being formed to help ensure interoperability and
promote the use of the H.320 set of standards.


H.320 is an overall standard and requires, as a minimum for VideoConferencing
intercommunication, that the following standards are used:
1. G.711
Audio
3KHz bandwith.
2. H.261
Video