Glossary

CIF: Spatial size of image. Matches to the quarter of the resolution of the TV.

Speed rate: Speed of audio, video and data transmission during a video conference. During professional video conferencing, the most used speed rates are:

• 384 Kb/s for high audio-visual quality such as 15 frames per second in CIF resolution with a sound of 7-kHz bandwith (twice as good as telephone sound).
• 256 Kb/s for a medium audiovisual quality
• 128 Kb/s for a basic audiovisual quality, such as 10 frames per second in CIF resolution with a sound of 3 kHz bandwith

Firewall: Protection element serving as an interface between a private network and the Internet.

Audio Codec: The sound transmitted by video conference is coded according to three quality families:

• Basic phone quality, 3kHz bandwith (G711, G728, G723 codec)
• 7 kHz bandwith (G722, PT724, PT716 codec)
• 14Hz bandwith (Siren 14 codec)

Video Codec: Video conferencing images are of CIF size. They are coded spatially and temporally depending on the encoding standard,  H261 or H263.

H263 standard is newer and has greater efficiency (better spatiotemporal outcome) at low bandwith (128 Kb/s) than the H261 standard. The outcome of the video quality is proportional to the transmission rate. Thus a good result will be obtained at a rate of 384 Kb/s and degrades fairly linearly when we reduce the digital rate to 256 Kb/s and a fortiori to 128 Kb/s.

H264: Algorithm of video compression for low speed rate. Available only on Polycom products.

Intranet: VPN of applications shared between several remote HTML sites accessible by web browser.

IP : Internet Protocole : Asynchronous transfer mode by package used one the Internet and Ethernet private networks.

LAN : Local Area Network : Company LAN Ethernet type.

Multipoint port: Resource of a Multipoint video conferencing server allowing the connection of a remote site in a multi-site meeting.

ISDN : Integrated Service Digital Network. Public network using the copper pair standard telephone line to deliver a synchronous and symmetrical 128 Kb/s rate usable per basic access (144 Kb/s raw). Primary 2Mb/s accesses are also available.

T120: Transfer standard of computer data during video conferencing. Data can be exchanged at low speeds (LSD mode up to 6Kb/s) or broadband (HSD mode up to 38Kb/s) or in normalized mode (MLP whitout rate limiting).

Video streaming: Multimedia broadcasting service of on the Internet or private IP network. Available in two modes:

• On request, in real time, for example to attend a conference
• As a playback

WAN: Wide Area Network.Private IP network extended to several remote locations from the same company through rented public transmission sections.

Multisites : Connection of multiple sites at the same time when your conferences are held with more than two speakers.