Videoconference - SpeedyLook encyclopedia

History

The videophone system a long time remained an alarming specter, already shown with the World Fairs of Brussels in 1958 and of Montreal in 1967, like installation in a way experimental (and expensive) with Biarritz. This stagnation came from the low flow of the lines of communication to the end user. Several factors of evolution made it possible to implement this service: numerical networks from beginning to end, falls of cost in the equipment like the video cameras, but especially progress in the techniques of coding (compression of the data) audio and video. The first university connections, in France, go back to 1987 (source RENATER).

To obtain this performance technically was a thing, to find the use of it was another, and the videoconference seemed very indicated in this time when one started in France to complain about the human disadvantages, physical and psychological, associated with the frequency of professional displacements.

The first applications of videoconference were done by using lines ISDN. One prefers to them today for reasons of cost the traditional supports of Internet: ADSL, cable for the private individuals or line dedicated for the professionals. ATM would well also lend itself to this kind of applications, since it was conceived from the beginning to combine transport of voice, images and data, which was not the case of TCP/IP (which fortunately evolved/moved to allow it partially since).

Standards of videoconference

The standards of videoconference define the protocols and standards which the manufacturers and operators must respect in order to be able interfonctionner.

Indication of the calls according to the type of network

Various protocols exist, according to the network used. They describe the entities present on the network, the indication of the calls, but also the Codecs audio/video used, which are standardized in addition.

On STN: H324 protocol. The videoconference on the commutated phone network is used very little because of its low quality, which had with the low flow available. Some manufacturers propose videophones respecting this standard.
On ISDN: H320 protocol. The videoconference on network ISDN was until recently the solution of choice for the videoconferences in the professional world. For reasons of cost and flexibility, a migration occurs towards the world Internet.
On ATM: protocol H321
On Internet: the protocols H.323 and more recently SIP. The standard of H323 videoconference was conceived by UIT-T (world of the télécoms) whereas SIP was conceived by IETF (world of Internet). Until today, H.323 was the standard mainly used in the professional field for the videoconference on IP. Protocol SIP is currently taking over, the operators and suppliers of material having integrated the offer.
On UMTS, for telephony 3G: protocols H324M (in circuit mode, with a flow of 64kbp/s) and IMS (derivative of protocol SIP).

Video codecs

The video codecs generally used are (older with most recent):

H.261
H.263/H.263+/H.263++
MPEG-4
H.264 (also called MPEG-4 or AVC).

The video formats are also standardized, such as:

QCIF: 176x144 pixels (used with low flow, for example on mobile phone)
CIF: 352x288 pixels (general format for a medium flow between 256 kbit/s and 768 kbit/s)
But also 4CIF (704x576), or VGA (640x480), to go towards the high-definition: XGA (1024x768), etc
Of the formats " personnalisés" can also be used, according to the solutions and the manufacturers.

Audio codecs

Qualité telephones (its sampled to 8 Khz): G.711 law driven /loi has, G.722, G.723, G.728, G.729, EVRC, etc
Radio Qualité, or FM, (its sampled to 16 Khz): G.722, G722.1, etc
Hifi Quality (its sampled to 24 Khz or more, possibly stereophony or multichannel): codecs owners.

Uses and services of videoconference today

The professional world

The companies distributed on distant locations use the videoconference to reduce the costs of displacement, while holding frequent meetings.

Several categories of systems are used with this fin :

systems of group. They consist of a dedicated terminal coupled to a television, a screen LCD or plasma.
systems of room, high-end. These relatively expensive systems generally offer a video of quality (screens with overhead projectors or screens plasma of big size), a its Hi-fi, and a well studied environment: lighting, aspects acoustic, etc
the personal systems, use dedicated terminals equipped with a big screen LCD or small videophones.
software of videoconference on PC, often associated with complementary services: directory, conference document, coupling with the telephone…

For a few years, very top-of-the-range systems have appeared on the market.

Certains systems proposes to it video high-definition, with resolutions equal or higher than 1024×768 pixels. As comparison, the traditional terminals generally offer a resolution CIF (352×288 pixels), even 4CIF (704×576 px). These systems offer also an audio “high-quality”, sampled with 24 Khz or 32 Khz, instead of 8 Khz (quality telephones) or 16 Khz for the traditional terminals.
Of the systems of téléprésence makes it possible to see its interlocutors on scale 1, with the feeling of being able to look at “the eyes in the eyes”. Thus, one does not find any more the effect “hypocrite” of the traditional systems, caused by the site of the video camera. These systems offer sometimes an audio stereo high-quality, or better (spatialized), which makes it possible to locate its interlocutors in space.

Yet not a long time ago, the professional world preferred the H320 protocol rather than H.323, the lines famous ISDN being more reliable in term of availability, of band-width, in addition to a reduced latency time. The rise to power of Internet and the channels serving it made that the tendency starts to be reversed.

The general public

Recently, the general public has to him also access to services of video-telephony, on different supports :

On Internet, of many software makes it possible to establish an audio/video communication of PC PC. Most known are the applications of instant messagings and VoIP. One can thus quote MSN Messenger, Yahoo! Messenger, IChat, XMeeting, Livecom of Orange and BestOfChat.
the mobile telephony of third generation (on the network UMTS) makes it possible to establish an audio/video communication between telephones 3G equipped with a camera.
On the fixed line, France Telecom proposes since 2004 a service of videoconference on ADSL called Maligne Visio, which uses a specific videophone. This service makes it possible to make a videophonic call towards the other terminals Maligne Visio, but also to call a traditional in audio only, one telephone 3G in audio/video telephone, or even the Livecom instant message software.

Many private individuals make use of Internet to communicate by telephone and videoconference abroad. With solutions software of routing of the calls on Internet (and of footbridges with traditional telephones) as Asterisk (PBX) one can as of today making true living rooms of videoconference between country by paying the price only one local subscription Internet.

Dedicated applications

One will quote in this category the de applications;:

Télémédecine
Tele teaching
Téléguichet®, VisioGuichet®, or “Visio terminals”

Presentation of data, groupware

In addition to the possibility of seeing and of hearing its interlocutors, the videoconference is often associated with a solution which makes it possible to present documents, and of working in a collaborative way.

With this intention, several solutions can be implemented.

T.120 : This standard contains a series of protocols which make it possible to exchange messages texts (cat), to transfer from the files, to use a divided white table, or to make division of applications. In particular, the division of applications makes it possible to remotely show a document, but also with the participants to take the remote control of an application to publish a document, after authorization of the owner. The standard T.120 was implemented on several terminals, such as Netmeeting. Complex to develop, T.120 with the major disadvantage not easily not to cross NAT and not to cross the corporate networks. This standard from now on is exceeded.
Division of documents thanks to a second video stream: each participant thus receives an interactive video stream, who allows to see his interlocutor, and a flow document, who can be a capture of a screen of computer, or a window of application. This second flow generally uses a highher resolution.
the conference Web: These solutions are from now on more " with the mode". Their major advantage is to cross the corporate networks and NAT, by using if necessary a tunnel on HTTP/HTTPS. Participants, where that they are, have thus to only connect itself on a Web server, which installs possibly an application making it possible to take part in the conference. The environment of these applications is generally neat, and it offers various functions: presentation of documents, remote takeover, management of the participants, conversation text, etc Webex is currently one of the most known solutions, but there exist many other actors. In France, Orange proposes for example the solution Multimedia conference. The other suppliers of access Internet more or less propose also to solutions owners and thus more or less compatible with the next generations of mobile phones.
Of other solutions exists, to meet specific needs, like the groupware on models 3D (for example).

Future of the videoconference

With the appearance of the mobile apparatuses of telephone being able at the same time servire of video camera and multi-media screen, one can expect a strong development of the videoconference. Parallèmement, the flows available in 3G make so that the calls videos are conveyed under good conditions (cuts, latencies).

One should thus expect a multiplication of the offers of operators Internet; by hoping that they are able to agree on a communication protocol which can be used by the consumer between various operators. If not, they are still the users who will pay the broken pots, as with the désatreuses ones normalizes H.323, confined with a small sector of the professional world because of a deplorable interworking.

Terminals and Applications

Open software of videoconference

Apart from the Software S associated with a service, there exist software of videoconference " ouverts" , compatible with the open standards of market (H.323 and SIP) and which can be used within the framework of third services.

One can quote in the alphabetical order:

EConf (supports H323, SIP, 3G-324M, MGCP)
Ekiga (free software in the past GnomeMeeting)
eyeBeam
Mirial, of Dylogic
OpenMCU, the project OpenH323
PVX of Polycom
ReachVisio, of IP Media (H323 supports)
Tandberg
VT Phone, of Dilithium
WengoPhone, of Wengo
XMeeting/OhPhoneX

Software of videoconference associated with a service

Several Logiciel S of instant messaging makes it possible to carry out an audio/video communication. In the same way, certain companies offer a service of videoconference paying, associated with an application software. Generally, this software can communicate only with the users of the same service and they are not open on outside.

One can quote in the alphabetical order:

6DEF.COM Video Driver
AOL Instant Messenger
Best Off Cat
Capuccino
Camfrog
Gizmo
IChat
Livecom (from now on OrangeLink), of Orange/Wanadoo
Mercury Messenger
meeting3D, Meeting on line with the video
MSN Messenger
NEOLINKS Visio
Paltalk
SightSpeed
Skype
Softiphone
VidRev
Videoconference Hotconference
Visioplace
VRVS
Yahoo! Messenger
yakforFREE
Meeting of office a solution in Flash

See too

Internal bonds

Voice on IP: With the increasingly widespread use of the Voice on IP, which uses the same protocols as videoconference IP (H.323 and SIP), one can expect a convergence of the uses.
VideoLan Videoconference
Asterisk (PBX)

External bonds

infovisio.fr Site of day before in French on the videoconference, the Voice on IP and the solutions of streaming
OpenH323.org, Site on the H.323 standard in Open sources

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