Industry Video Teleconferencing Profile - VTC001
All of the terms used in this part of the Profile are defined either in the referenced base standards (see Section 2), in the standards listed in annexes, or listed below.
Audio Mixing: The process of combining two or more audio signals to produce a single composite audio signal. This allows each participant in a conference to hear all other participants simultaneously.
Audio Switching: The process of switching the audio that all participants hear to that of the designated speaker. No other participants can be heard until they are selected as the audio source.
Bit-rate Allocation Signal (BAS): An eight-bit word within the frame structure of ITU-T Recommendation H.221 which is used to transmit commands, control and indication signals, and capabilities.
Call Association: The process of associating multiple channel calls to a individual VTU by an MCU. In a dial-in MCU configuration in which each call is placed over multiple channels (i.e., 2B channels) and there is a single network access (phone) number for all ports in a conference, this provides the means of associating each channel to the VTU making the call.
Cascading: The process of providing a conference involving more than one MCU, so that information must pass not only between VTU and MCU, but also from one MCU to another.
Chair Control: A method of providing the capability for one of the VTUs involved in a conference to exercise some measure of authority over the conference, particularly in making the decision of which video will be broadcast to the other VTUs.
Chair-control VTU: An enhanced VTU possessing the capability to exert a certain measure of authority over the operation of the multipoint conference. The chair-control assignment may be prearranged, assigned by an operator, or by protocol during the call. The person controlling need not be the actual chairperson of the meeting.
Chair-control Port: That port of the MCU serving the VTU to which chair-control has been assigned.
Common Intermediate Format: see Full Common Intermediate Format
CODEC: Acronym for COder/DECoder. In video teleconferencing, an electronic device that converts analog signals, typically video, voice, and/or data, into digital form and compresses them into a fraction of their original size to save frequency bandwidth on a transmission path. It also performs the inverse operation, decompressing received signals and converting them back to analog.
Conferencing: Programs and meetings which may be for the purpose of presenting and exchanging information, comparing views, learning, planning, and decision-making. Conferences can be held in one location or conducted simultaneously at multiple locations and linked together by telecommunications systems.
Directly-connected VTU: A VTU that is directly connected to the MCU in question, that is, it is not connected through another MCU. It may or may not be collocated with the MCU.
Dumb-bell Configuration: A network configuration in which there are two MCUs that are connected to each other.
Encoder: A device that encodes.
Encryption: The process of encrypting.
Frame: 1. When referring to an image, the set of all the picture elements in an image. 2. When referring to ITU-T H.221, a frame consists of 80 octets (bytes) of multiplexed signals.
Frame alignment: In the Industry Profile, frame alignment refers to the ITU-T H.221 frame, not the image frame.
Frame Alignment Signal (FAS): In ITU-T H.221, this signal also contains additional bits for status, control and error detection.
Freeze-Frame Video: A frame of visual information selected from a video signal and processed through the video CODEC for transmission to remote sites. Not to be confused with still image. See Still Image.
Full Common Intermediate Format (FCIF): A video format defined in ITU-T H.261 that is characterized by 352 luminance pels on each of 288 lines, with half as many chrominance pels in each direction.
Local MCU: That MCU to which the VTU in question is directly attached. It may or may not be collocated with the VTU.
Minimum Picture Interval: The minimum time between pictures selected for encoding. Allowable values are 1/29.97, 2/29.97, 3/29.97, and 4/29.97 seconds per picture.
Motion Compensation: A type of interframe coding used by CODECs in the compression of motion video images. The process relies upon an algorithm that examines a sequence of image frames to measure the motion that occurs between frames.
Multipoint Control Unit: A multi-port device, by means of which three or more VTUs may intercommunicate in a conference call. It can also be used with two VTUs, e.g., while beginning or ending a multipoint conference.
m-law: The PCM coding and companding standard used in Japan and North
America.
px64: Family of 5 ITU-T Recommendations. These include H.261, H.221, H.242, H.230, and H.320. These Recommendations form the basis for Video Teleconferencing (VTC) interoperability.
Primary VTU: A VTU that fully participates in the conference.
Principal MCU: An MCU that has been assigned a superior controlling function in a call where two or more MCUs are interconnected. Called "master" MCU in ITU-T Recommendations.
Quarter Common Intermediate Format: A video format defined in ITU-T H.261 that is characterized by 176 luminance pels on each of 144 lines, with half as many chrominance pels in each direction. QCIF has 1/4 as many pels as FCIF.
Restricted Channel: A digital communications channel for which each increment of p gives a useful capacity of only 56000 bits per second, instead of 64000 bits per second. This is currently common in North America, and was originally due to a ones density limitation in T1 circuits.
Satellite MCU: An MCU that has been assigned a controlling function that is inferior to a Principal MCU in a call where two or more MCUs are interconnected. Called "slave" MCU in ITU-T Recommendations.
Secondary VTU: A VTU that participates in the conference, but perhaps without the full range of services that primary terminals receive. For example, a secondary VTU may not be able to send or receive video.
Segmentation: The procedure whereby an MCU can simultaneously be used in more than one conference.
Selected Communication Mode: The common mode of communication that is selected by the MCU for communication during the call. The mode includes the transfer rate, and the audio, video, and data rates.
Service Definition: A standards document which defines the scope of the standardization effort of commercial standards. Service definitions for video teleconferencing have been written by the ANSI T1A1.5 committee, and by ITU-T Study Group 1.
Star Configuration: A network configuration of MCUs in which there is one MCU to which all other MCUs are directly connected. A chain of three MCUs, a dumb-bell configuration, and a single MCU are all degenerate forms of the star configuration.
Still Image: Non-moving visual information such as graphs, drawings, pictures, or video frames not processed by the video CODEC portion of the VTU. This differs from freeze-frame images which are processed by the video CODEC portion of the VTU.
Teleconferencing System: A collection of equipment and integral components (customer premises equipment and facilities) required to process teleconferencing programs and control data, less network interface devices.
Terminal Equipment: A device or devices connected to a network or other communications system used to receive or transmit data. It usually includes some type of I/O device.
Terminal ID: A form of identification that allows a VTU to be assigned an alpha-numeric string such as a name or location rather than just an arbitrary terminal number.
Terminal Number: A number assigned by an MCU to a VTU for identifying VTUs in a conference. Terminal numbering is necessary for call association, chair control, and video select capabilities.
Unrestricted Channel: A digital communications channel, in which for each increment of p, all 64000 bits per second (bit/s) are available for information transfer. ISDN is an example of a network that uses 64000 bit/s communication channels.
Video: That portion of a signal that is related to moving images.
Videoconferencing: See Video Teleconferencing.
Video CODEC: See CODEC.
Video Mixing: The process of combining two or more video signals to produce a single composite video image. This allows each participant in a conference to view more than one of the other participants in the conference simultaneously. For example, the composite video image may be a two by two array in which the video from four participants appear in four blocks within the array (i.e., Hollywood Squares).
Video Switching: The process of switching the video signal that a participant sees to one of the other participants. The participant that is seen can be determined by the chairman, the participants, or as a function of the audio signal (see Voice Activated Switching).
Video Teleconferencing (VTC): Two-way electronic form of communications that permits two or more people in different locations to engage in face-to-face audio and visual communication. Meetings, seminars, and conferences are conducted as if all of the participants are in the same room.
Video Telephony: Relating to video phones and video teleconferencing.
Voice Activated Switching: The process of determining the video seen by the participants in a conference based on the audio signal. Typically, the loudest speaker will be seen by all of the participants.
Wideband: In the case of wideband audio, G.722 specifies a bandwidth of 7 kHz.
Windowing: Capability to divide the video display into two or more separate regions with displays from different sources in each region. For example, four separate windows on the same display could simultaneously show a) data, b) motion video of the remote site, c) a still image, and d) motion video of the home site.