Kamus tentang IT ( Video Conferencing )

A

Application Sharing
This is a feature that allows two or more people to work together when one the individuals does not have the same application, or same version of the application. In application sharing, one user launches the application and it runs simultaneously. All users can impute information and otherwise control the application using the keyboard and mouse. Files associated with the application can be easily transferred, so the results of the collaboration are available to all users immediately. The person who launched the application can lock out the other person from making changes, so the locked-out person sees the application running but cannot control it.


Application Viewing
In personal conferencing, the users sharing the application can see every keystroke or mouse movement made by the one user who is running the application. The other users have no control over the application.

ATM. Asynchronous Transfer Mode
High speed low-delay transport technology, integrating multiple data types (voice, video, and data). ITU has selected ATM as the basis for the future broadband network because of its flexibility and suitability for both transmission and switching. May be used in the phone and computer networks of the future.

Audio
Signals that carry sounds.

Audio Bridge
Equipment that mixes multiple audio inputs and feeds back composite audio to each station after removing the individual station's input.

Automatic Bandwidth Adjustment
Algorithm in H.323 endpoint for automatic increasing and decreasing video bit rate due to the network behavior.


B

B channel
The ISDN circuit-switched bearer channels, capable of transmitting 64kps of digitized information.

B-ISDN
Broadband ISDN. The ITU-T is developing the B-ISDN standard, incorporating the existing ISDN switching, signaling, multiplexing and transmission standards into a higher-speed specification that will support the need to move different types of information around the public switched network.

Bandwidth
A term that defines the information carrying capacity of a channel - its throughput. In analog systems, it is the difference between the highest frequency that a channel can carry and the lowest, measured in hertz. In digital systems the unit of measure of bandwidth is bits per second.

Bit. Binary Digit
The basic signaling unit in all digital transmission systems.

Bit rate
The number of bits of information transmitted over a channel in a given second. Typically expressed bps.

Bps
Bits per second, a unit of measurement of the speed of data transmission and thus of bandwidth.

BRI. Basic Rate Interface In ISDN there are two interfaces, the BRI and the PRI or Primary Rate Interface. The BRI offers two circuit-switched B (bearer) channels of 64 kbps each and one packet-switched 16 kbps D (delta) channel that is used for exchanging signals with the network.

Bridge
In videoconferencing vernacular, a bridge connects three or more conference sites so that they can simultaneously communicate. Bridges are often called MCUs - Multiple Conferencing Units. A bridge is also considered a device that interconnects LAN segments at the data-link layer of the OSI model to extend the LAN environment physically. They work with frames of data, forwarding them between networks. They learn station addresses and they resolve problems with loops in the topology by participating in the spanning tree algorithm. Finally, the term bridge can be used in audio conferencing to refer to a device that connects multiple (more than two) voice calls so that all participants can hear and be heard.

Broadcasting
In packet-switched networks, this means sending a packet to all users connected to the specific network.

C

Call
Multimedia communication between two or more H.323 endpoints.

Call Signaling Channel
Reliable channel used to convey call setup messages following Q.931

Centralized Multipoint Conference
A call in which all participating terminals communicate in a point-to-point fashion with an MCU.

Caller ID
An identification (number, name) of the party being called. This identification is of interest when you transfer or forward a call. For example, when an unanswered call is forwarded to a voice messaging system, the called-ID of the original call is used to locate the mailbox of the called party.

CCITT
Consultative Committee for International Telegraphy and Telephony. As of 1994 known as the International Telecommunications Union. See ITU.

CIF
Common Intermediate Format, an optional part of the ITU-T's H.261 and H.263 standards. CIF specifies 288 non-interlaced luminance lines, that contain 176 pixels. CIF is to be sent at frame rates of 7.5, 10, 15, or 30 per second. When operating with CIF, the number of bits that result can not exceed 256 K bits (where K equals 1024).

Circuit-switched
An ISDN bearer service that provides a 64 kbps (sometimes 56 kbps) path between two users for the duration of the call. The term is also used for the networks with behavior similar to ISDN.

CODEC
A sophisticated digital signal-processing unit that takes an analog input and converts it to digital on the sending end. At the receiving end, another codec reverses this by reconverting the digital signal back to analog. Codec is a contraction of code/decode (some experts in the video industry assert it also stands for compress/decompress). A codec takes the form of a set of hardware or software components, or a combination of both.

Compression
Reducing the representation of the information, but not the information itself. Reducing the bandwidth or number of bits needed to encode information or encode a signal, typically by eliminating long strings of identical bits or bits that do not change in successive sampling intervals (e.g., video frames). Compression saves transmission time or capacity. It also saves storage space on storage devices such as hard disks, tape drives, and floppy disks.

D

Decentralized Multipoint Conference
Conference in which the participating terminals multicast to all other participating terminals without an MCU.

Document Sharing
See Whiteboard

E

E.16
Address format for ISDN networks. See ITU Recommendation E. 164 (1991). Added as alias for H.323 terminals.

Endpoint
A Terminal, Gateway, or MCU.

Ethernet
A LAN running on coaxial or twisted pair wiring, at 10 or 100 mbps. In Ethernet, all terminals are connected to a single common highway or bus.

Ethernet switch
A device than connects local area networks (LAN). Ethernet switching is viewed as one solution to deliver 10 Base-T or 100 Base-T networks that are bandwidth-constrained because of a new requirement to carry multimedia messages and interactive videoconferencing communications. To qualify as an Ethernet Switch, a device must be capable of switching packets from one Ethernet segment to another "on the fly" and exhibit very low port-to-port latency.

F

Full-duplex
A communication protocol in which the communications channel can send and receive data at the same time. Compare to half-duplex, where information can only be sent or received in one direction at a time.

Full High Definition (Full HD)
Full HD refers to the resolution used for the display of the video images during video or television broadcast .Full definition refers to 1080p (1920 x 1080 pixels). "1080" stands for 1080 lines of vertical display resolution, while "p" stands for progressive, or non-interlaced, scan. 1080p assumes a widescreen aspect ratio of 16:9. 1080p models offer pictures with even finer detail and more subtle colors than 720p models.

G

G.711
An ITU-T Recommendation entitled, "Pulse Code Modulation (PCM) of Voice Frequencies". G.711 defines how a 3.1 kHz audio signal is encoded at 64 kbps using Pulse Code Modulation (PCM) and either mu-law (US and Japan) or A-law (Europe).

G.721
An ITU-T Recommendation that defines how a 3.1 kHz audio signal is encoded at 32 kbps using Adaptive Differential Pulse Code Modulation (ADPCM).

G.722
An ITU-T Recommendation that defines how a 7.5 kHz audio signal is encoded at a data rate of 64 kbps.

G.722.1
G.722.1 is an ITU-T standard audio codec meant for high quality, moderate bit rate (24 and 32 kbit/s) wideband (50 Hz - 7 kHz audio bandwidth, 16 ksps) audio coding

G.722.1 Annex C
G.722.1 Annex C delivers 14 kHz audio fidelity at 24, 32, or 48 kbps (kilobits per second).

G.723
An ITU-T Recommendation entitled, "Dual Rate Speech Coder for Multimedia Communication Transmitting at 5.3 and 6.4 kbps".

G.728
An ITU-T Recommendation for audio encoding using Low Delay Code Excited Linear Prediction (CELP). The bandwidth of the analog audio signal is 3.4 kHz whereas after coding and compression the digitized signal requires a bandwidth of 16 kbps.

G.729
G.729 is an audio data compression algorithm for voice that compresses voice audio in chunks of 10 milliseconds. G.729 is mostly used in Voice over IP (VoIP) applications for its low bandwidth requirement.

Gateway
The gateway allows H.323 systems to interoperated with other H.32x products. For instance, the gateway could link the H.323 session with an H.320 (ISDN-based) system; an H.321 (ATM-based) system; an H.322 (iso Ethernet-based) system; or an H.324 (POTS-based) system. At the present, most H.323 gateway implementations are concerned with linking H.323 and H.320/H.324 systems across a LAN/WAN connection.

GateKeeper
A gatekeeper is a utility that controls H.323 videoconference access on a packet-switched network. It requires that multimedia terminals register "at the gate", which is accomplished when the terminal provides its address. The gatekeeper translates network addresses and aliases to make connections. It can also deny access or limit the number of simultaneous connections to prevent congestion.

H

H.221
A framing portion of the ITU-T's H.320 Recommendation that is formally known as "Frame Structure for a 64 to 1920 kbps Channel in Audiovisual Teleservices". The Recommendations specifies synchronous operation in which the coder and decoder synchronize timing.

H.222
ITU-T Recommendation specifies generic coding of moving pictures and associated audio information.

H.223
Part of the ITU-T's H.324 standard specifying a control/multiplexing protocol, which is formally called "Multiplexing protocol for low bit rate multimedia communication".

H.231
A Recommendation added to the ITU-T's H.320 family specifying multipoint control unit used to bridge three or more H.320 compliant codecs together in a multipoint conference.

H.233
A multiplexing Recommendation that is part of the ITU-T family of video interoperability Recommendations. The Recommendation specifies how individual frames of audiovisual information are to be multiplexed onto a digital channel.

H.235
H.235 covers security and encryption for H.323 and other H.245 based terminals. The standard addresses authentication by means of several algorithms and privacy which allows for encryption also of the media streams.

H.239
The H.239 ITU-T recommendation is titled "Role management and additional media channels for H.3xx-series terminals". Practical importance of this recommendation is its setting forth a way to have multiple video channels (e.g., one for conferencing, another for presentation) within a single session (call).

H.242
Part of the ITU-T's H.320 family of video interoperability Recommendations. H.242 specifying the protocol for establishing an audio session and taking it down after the communication has terminated.

H.245
Part of the ITU-T's H.323 and H.324 families defining control of communications between multimedia terminals.

H.261
The ITU-T's Recommendations that allows dissimilar video codecs to interpret how a signal has been encoded and compressed, and to decode and decompress that signal. It also defines two picture formats: CIF and QCIF.

H.263
H.263 is an ITU-T videoconferencing Recommendation originally designed as a low bit-rate compressed format for videoconferencing.

H.264
H.264 is the latest ITU-T videoconferencing Recommendation that offers a new video compression scheme. The main benefits of H.264 are higher video quality at a given bit-rate, higher resolution and lower storage requirements.



H.320
An ITU-T standard including a number of individual recommendations for coding, framing, signaling and establishing connections (H.221, H.230, H.321, H.242, and H.261). It applies to point-to-point and multipoint videoconferencing sessions and includes three audio algorithms, G.711, G.722 and G.728.

H.323
The H.323 extends the H.320 to Intranet, Extranet or Internet over packet-switched networks: Ethernet, Token-Ring, and others that may not guarantee QoS. It also specifies procedures for videoconferencing over ATM including ATM QoS. It supports both point-to-point and multipoint operations.

H.323 Alias
User logical name used for remote party calling. Translated by Gatekeeper to the network address.

H.324
An ITU-T standard that provides point-to-point data, video, and audio conferencing over analog telephone lines (POTS). It can incorporate H.261 video encoding, but most implementations will probably use H.263, a scalable version of H.261 that adds a 128-by-96 Sub-QCIF (SQCIF) format. Because of H.263's efficient design, it may produce frame rates much like those of today's ISDN H.320 systems through inexpensive hardware-assisted modems. The H.324 family includes H.223, a multiplexing protocol. H.245, a control protocol, T.120, a suite of audiographics protocols and V.34, a modem specification.

High Definition (HD)
High definition refers to the resolution used for the display of the video images during video or television broadcast. HD refers to 720p (1280 x 720 pixels) or higher. "720" stands for 720 lines of vertical display resolution, while "p" stands for progressive, or non-interlaced, scan. 720p assumes a widescreen aspect ratio of 16:9. With high definition (HD) videoconferencing systems, the improvement in video quality over standard definition (SD) videoconferencing is dramatic since HD carries more than 9 times the pixel count of standard CIF videoconferencing images.

I

Interactive Multicast
This method of streaming is a hybrid of the IP multicast protocol and is a unique streaming method invented by Emblaze-VCON. Emblaze-VCON Interactive Multicast uses the bandwidth-efficient IP Multicast protocol, but adds a layer of interactivity, where the "chair" or host of the multicast can virtually move the podium to any other participant, allowing interaction between all on the call, while using only one stream of video and audio, thus preserving bandwidth. This technology is ideal for bandwidth conscious networks and satellite-based networks.

IP. Internet Protocol
The most popular network protocol in corporate and public networks. May be used by H.323 endpoints for audio, video, and data packets transfer.

Interoperability
The ability of electronic components produced by different manufacturers to communicate across product line. The trend toward embracing standards has greatly furthered the interoperability process.

ISDN
Integrated Services Digital Network. ISDN is an entirely digital telephone service that can be installed by the local telephone company to replace the old analog local loop (the connection to the telephone company's nearest central switching office) with a digital line. As long-distance lines are usually digital already, replacing the local loop with an ISDN line provides "end-to-end" digital service. Two types of ISDN are: BRI and PRI. ISDN BRI is the interface to connect the desktop to the digital long distance network. ISDN BRI provides two 64 kbps B ("bearer") channel to carry information content, the voice, video, and data substance of a transmission. A separate 16 kbps D ("data") channel is used for call setup and signaling. ISDN BRI is often called "2B+D" ISDN, for its combination of two B and one D channel.

ITU
International Telecommunications Union. One of the specialized agencies of the United Nations that is composed of the telecommunications administrations of 113 participating nations. Founded in 1865 before telephone were invented as a telegraphy standards body. It now develops international standards for interconnecting telecommunications equipment across networks.

K

kbps
Kilo-bytes per second - one thousand bits per second.


L

LAN
Local Area Network (LAN). A network of computer and other devices for communication within a restricted geographic area, such as a building or a campus.

M

mbps
Megabits per second or approximately one million bits per second.

MCU – Multipoint Control Unit
The MCU is a bridging device that enables multipoint videoconferencing (3 or more sites). Once a MCU bridge is set up it is possible to add multiple sites to a video call and simultaneously allow several additional locations to participate in the session. Basic Features include:

* Voice Activated Switching - Switches the camera to the speaker, so that they may be seen by all participants.
* Continuous Presence – All the participants appear on the screen simultaneously and the speaker is highlighted
* Lecture Mode - Allows the speaker to see a mix of all participants; all other participants see the lecturer in full screen mode.

Multicasting
Sending a packet that can be received by multiple recipients, all of whom are listening on a single multicast address.

Multiplex
A method of transmitting multiple signals onto a single circuit so that each can be recovered intact.

Multiplexer
Electronic equipment that allows multiple signal to share a single communications circuit.

Multiplexing
The process of combing multiple signals onto a single circuit using various means.

Multipoint
Communication configuration in which several terminals or stations are connected. Compare to point-to-point where communication is between two stations only.

Multipoint Control Unit (MCU)
A device that bridges together multiple inputs so that three parties or more can participate in a video conference.

Multipoint Processor (MP)
An entity which provides for the processing of audio, video, and/or data streams in a multipoint conference. The MP provides for the mixing, switching, transcoding, or other processing of media streams under the control of the MC.

N

Network
A group of stations (computers, telephones, or other devices) connected by communications facilities for exchanging information. Connection can be permanent, via cable, or temporary, through telephone or other communications links. The transmission medium can be physical (copper, wire, fiber optic cable etc.) or wireless, for example via satellite.

P


POTS
Plain Old Telephone Service. Conventional analog narrowband telephone line using twisted-pair copper wire for transmitting voice calls.

Q

Q.931
Call signaling protocol for setup and termination of calls.

Quality of Service (QoS)
Guarantees network resources for specific application requirements.

R

RAS Channel
An unreliable channel used to convey the Registration, Admissions and Status messages and bandwidth changes between two H.323 entities through a Gatekeeper.

Reliable Transmission
Connection-oriented data transmission which guarantees sequenced error-free, flow-controlled transmission of messages to the receiver.

Resource Reservation Protocol (RSVP)
IETF specification. Allows applications to request dedicated resources.

Real-Time Protocol/Real-Time Control Protocol (RTP/RTCP)
IETF specification for audio and video signal management. Allows applications to synchronize and spoil audio and video information.

Router
Equipment that facilitates the exchange of packets between autonomous networks (LANs and WANs) of similar architecture. Routers move packets over a specific path or paths based on the packet's destination, network congestion and the protocols implemented on the network.

S


Switch
A device that establishes, monitors, and terminates a connection between devices connected to a network.

Switching
The process of setting up a connection between an input and an output. It allows a subscriber to establish communications with multiple parties by sending their address to the switch, which will then attempt to make a connection.

Switched Circuit Network (SCN)
A public or private switched telecommunications network such as GSTN or ISDN.

Switch Type
The type of ISDN network you are connected to. This information is available from the ISDN provider and provided to the buyer when purchasing an ISDN line.

T


T.120
The ITU-T's "Transmission Protocols for Multimedia Data", a data sharing/data conferencing specification that lets users share documents during any H.32x videoconference. Like H.32x specifications, T.120 is an umbrella Recommendation that includes a number of other Recommendations. Data-only T.120 session can be held when no video communications are required, and the standard also allows multipoint meetings that include participants using different transmission media. The mandatory components of T.120 include recommendations for multipoint file transfer and shared-whiteboard implementation.

TCP. Transmission control protocol
A reliable transport layer on top of IP.

Teleconferencing
The use of telecommunications links to provide audio, video and graphics capabilities. These systems allow distant workgroups or individuals to meet. An endpoint which provides for real-time, two-way communications with ano.

U


UDP
User Datagram Protocol. An unreliable transport layer on top of IP.

Unicast
Application of conferencing, usually over packet-switched networks, where only one user receives data. In contrast to this, multicast application, where data is received by more than one user.

Unreliable Transmission
Connection-less transmission which provides best-effort delivery of data packets. Messages transmitted by the sender may be lost, duplicated, or received out of sequence.

V


Videoconferencing
A collection of technologies that integrate video with audio, data, or both to convey in real-time over distance for meeting between dispersed sites.

Video Server
A specialized file server with enormous hard disc capacities (often measured in terabytes or trillions of bytes). These servers store MPEG compressed audio and video images and provide service to end-users over high-speed LANs and WANs. Applications that require video servers include entertainment, training/education, and video-enabled databases.

W

WAN
Wide Area Network. A communications network that services a geographic area larger than that served by a local area network or metropolitan area network.

Whiteboarding
A term used to describe the placement of shared documents on an on-screen "shared notebook" or "whiteboard". Multiple users can simultaneously view and annotate a document.


Z

Zone
In H.323 specifications, a collection of all Terminals, Gateways and MCUs managed by a single Gatekeeper. A zone must include at least one Terminal and may include LAN segments connected using routers.