Glossary

CIF

An abbreviation for Common Intermediate Format. This format allows communication between different color systems (NTSC and PAL).

352 pixels × 288 lines

Codec

An abbreviation for Coder-Decoder. An integrated device of a coder that converts an analog audio/video signal to a digital data stream and compresses it, and a decoder for expanding to restore the original analog signal.

DHCP

An abbreviation for Dynamic Host Configuration Protocol. Manages IP addresses in the network.

DNS

An abbreviation for Domain Name System. Defines the domain name system server.

Echo Canceller

Device to eliminate echo that occurs when transmitting audio.

Frame rate

The number of frames which can be encoded/decoded in one second.

G.711

Audio encoding/decoding format recommended by the ITU-T. A phone bandwidth audio signal is converted to a digital signal with a data rate of 64 kbps. It can be transmitted with a data rate of 56 kbps.

G.722

Audio encoding/decoding format recommended by the ITU-T. A 7-kHz bandwidth audio signal is converted to a digital signal with a data rate of 48 kbps, 56 kbps or 64 kbps.

G.728

Audio encoding/decoding format recommended by the ITU-T. A phone bandwidth audio signal is converted to a digital signal with a data rate of 16 kbps.

G.729

Audio encoding/decoding format recommended by the ITU-T. A phone bandwidth audio signal is converted to a digital signal with the data rate of 8 kbps.

Gatekeeper

Controls the access of H.323 videoconference devices on a network. Administers the zone, access limitation, audio/ video bandwidth, and alias etc.

H.225.0

Frame structure for a 64 to 1920 kbps channel in audiovisual teleservices.

H.239

ITU-T standard for sharing data and presentations with video. This supports dual streaming, enabling endpoints to receive and transmit video and presentation data simultaneously.

H.261

Video codec for audio/visual services as p × 64 kbps. Videoconferencing standard that defines a video coding algorithm, picture format and error correcting technology for communication between different manufacturers’ video codecs.

H.263

A video coding algorithm based on the H.261 standard. This format enables communication via a lower bit rate.

H.263+

Video encoding/decoding format based on the H.263 standard, added by the Annex I to T (I, J, K …… T), that

allows enhanced picture quality and error resistance. Normally, this format is a profile used with a combination of some of the Annex for H.263/H.263+.

H.264

Avideo coding algorithm standardized by the ITU-T in May 2003. This format realizes high-quality picture via a lower bit rate. It provides an equal picture quality via half as low bit rate as the H.263 format. The H.264 format is also called as MPEG4 Advanced Video Coding (AVC).

H.323

This enables communications on the non-QOS (Quality of Service) LAN.

HMLP

See “MLP”.

Lip synchronization

A function that synchronizes sound with motion. Sound processing is much faster than motion processing, thus sound and motion sometimes get out of step with each other.

MCU

An abbreviation for Multipoint Control Unit. When connecting a MCU, a multipoint videoconference can be held.

Appendix

Glossary 121