home | prodotti | soluzioni | dettagli tecnici | contatto | glossario | link


Asynchronous Transfer Mode (ATM) - (1) A standard for cell relay wherein information for multiple types of services (voice, video, data) is conveyed in small, fixed-size cells. ATM is a connection-oriented technology used in both LAN and WAN environments. (2) A fast-packet switching technology allowing free allocation of capacity to each channel. The SONET-synchronous payload envelope is a variation of ATM. (3) ATM is an international ISDN high-speed, high-volume, packet switching transmission protocol standard. ATM currently accommodates transmission speeds from 64 Kbps to 622 Mbps.

Algorithm - A set of specifications that define methods and procedures for transmitting audio, video, and data.

Amplifier - A device use in analog networks to boost the strength of a signal and extend its transmitted range. Equivalent to a repeater for digital networks.

Analog - A way of sending voice, video, or data that is "analogous" to the original signal. Analog transmission is associated with voice and data signals over conventional telephone lines. (Contrast with digital).

Analog gateway - A means of connecting dissimilar codecs. Incoming digital signal from one type of codec is decoded by a similar codec and converted to analog. The analog signal is then passed to the dissimilar codec, coded, and decoded at the far end. Analog gateways achieved interoperability in a nonstandard environment, but have the disadvantages of degrading video and audio quality and often reducing functionality.

Analog signal - An electrical signal that varies continuously in amplitude and frequency.

Asynchronous - Method of timing for transmission of multiplexed digital signals. The signal is in a framed format so the receiving end can identify the boundaries of the multiplexed channels.

Authentication - Authentication is a procedure that establishes the legitimacy of users and defines the parameters of the sessions they establish. As such, authentication can be thought of as a security measure that controls and defines network access. It is always the first part of a session; the range of authentication parameters that can be set depend upon the specific authentication system employed.

Basic Rate Interface (BRI) - User interface to the public ISDN network (usually through Centrex). Contains two B channels at 64 Kbps and a D channel that operates at 16 Kbps. The BRI line is the transmission path between the user's phone and the CO, where it is then switched by the CO to its eventual destination. Used for both data and signaling purposes.

Broadcast - One-way video, usually from a single transmitting site to many receiving sites. In some cases, the receiving sites can communicate to the transmitting site on an audio-only basis.

Backward compatible - The ability of a new technology or product to work with existing equipment.

Bit - One binary digit; a pulse of data.

Bits per second (bps) - The number of bits passing a point per second. The transmission rate for digital information.

Bps - Bits Per Second

Backbone - The part of the communications network intended and architectured to carry the bulk of traffic. Provides connectivity between subnetworks in an enterprise-wide network.

Bandwidth - Bandwidth is the data capacity of a service, measured in thousands of bits per second (kbps) or millions of bits per second (Mbps). Bandwidth is not a measure of speed. It is the size of the data payload of the service measured in bits per second. T1 service delivers 1.544 Mbps, whereas ISDN service delivers 128 kbps. The data travels over the line at the same speed, but for T1 lines, the capacity is twelve times that of ISDN. Speed and capacity are two different attributes. For example, if you send yourself two packages via an overnight service--a box with many pages of text, and an envelope with one page of text--the speed at which the packages travel is the same, but the capacity of the box is greater. You may wonder why modem speeds are different if data travels across the line at the same rate--all should deliver the same amount of data per second, right? Differences in encoding methods and compression give modems the ability to transmit data in more and more efficient ways. Signal-encoding schemes and software built into a modem determines its data rate. Advertised throughput, however, is decreased by latency.

BONDING - Bandwidth ON Demand Interoperability Group A consortium of over 40 data communications equipment vendors and service providers who are joined together to create a standardized inverse multiplexing protocol so that inverse multiplexers from different vendors can interoperate. Also refers to the resultant specification, sometimes known as the "BONDING specification."

Bridge - A device or setup that connects and passes data, voice, or video between two network segments, based on the destination field in the packet header. The Pipeline 25 is a learning bridge, because it passes all packets to the next network segment (the ISDN line), and builds a table to identify the destination addresses that are local and remote. After learning the addresses on both sides of a network, the bridge passes only packets for the remote network.

Broadband - A way of transmitting large amounts of data, voice, and video that is greater than standard voice grade transmission. In ISDN, broadband channels support rates above the primary rate (1.544 Mbps or 2.048 Mbps).

Channel Service Unit (CSU)- "A type of customer premise equipment that terminates a T1 access facility to a channel bank, PBX or other equipment capable of supporting a T1 interface."

CIF - Common Intermediate Format. A video resolution of 352 pixels horizontally and 288 pixels vertically. It is used primarily in higher bit rate (128Kbps and higher) video conferencing.

Codec (COder/DECoder) - "A device that encodes an incoming analog signal into a digital signal for transmission to another Codec. The digital signal is decoded into analog format. In videoconferencing, codec typically code an decode video and audio."

Circuit switching - Basic switching process whereby a circuit between two users is opened on demand and maintained for their exclusive use for the duration of thetransmission.

Connectivity - The ability of a device to connect to another. This includes not only the physical issued associated with the busses, connector topologies, and other such matters, but also the support of the protocols required to pass data successfully over the physical connection.

Central Office - A telephone company facility that joins subscriber telephone lines to switching equipment. This allows subscribers to connect to one another, through local and long distance connections.

Compression - Compression is a technique that reduces the quantity of bandwidth or bits required to encode a block of information. Compression saves transmission time and capacity, and can free up storage space on in-demand data lines. Compressed data can be compromised in quality, but the advantages of bandwidth savings are frequently worth the trade-off. Compression is not yet standardized.

Digital Service Unit (DSU) - A type of customer premises equipment that terminates a single DSO or fractional T1.

Digital Signal Processor (DSP) - A high-speed coprocessor designed to do real-time signal manipulation.

Dedicated line - (1) A communications circuit or channel provided for the exclusive use of a particular subscriber. Dedicated lines are used for computers when large amounts of data need to be moved between points. (2) A transmission circuit installed between two sites of a private network and "open", or available, at all times. Synonym private line leased line.

Encryption - Alteration of transmitting information to protect it from unauthorized tapping.

End-to-end digital connectivity - Signals are in digital form during their entire path through the network.

Ethernet - A local area network that connects devices like computers, printers, and terminals. Ethernet operates over twisted-pair or coaxial cable at speeds at 10 or 100 Mbps.

FCIF - Full Common Intermediate Format. A video resolution of 352 pixels horizontally and 288 pixels vertically. It is used primarily in higher bit rate (128Kbps and higher) video conferencing.

Frame relay - A packet switched networking technology used for low speed (T1 - 1.5Mbps and lower) WAN connections. Primarily used to connect a company's routers on their data network. Considered more efficient than X.25 which it is expected to replace. Frame relay technology can handle "bursty"communications that have rapidly changing bandwidth requirements.

Frame Rate - Frames per second (fps) displayed on a video monitor; 25-30 fps is "full motion."

Frames per second (fps) - "Frequency with which video frames appear on a monitor. Broadcast-quality video generally consists of 30 frames per second. Full-motion videoconferencing typically offers video in the range of 10 - 15 frames per second. At very low bandwidths, such as 56 or 112 Kbps, the frame rate may be lower." Full duplex - Method to transmit and receive in both directions simultaneously as in normal human conversation.

Full-duplex audio - Audio that lets local and remote conference participants speak simultaneously without losing audio contact.

Full-motion - In compressed video, picture quality that is generally acceptable to users although not of broadcast quality; typically from 10 - 30 frames per second depending on the bandwidth allocated.

Firewall - A hardware/software tool that allows a network administrator to determine what type of users can access the resources on the network. The firewall provides a mechanism to monitor and funnel data from authorized users (only) through the firewall to and from the network. A firewall may be a software program that runs on UNIX or other platforms, or it may be a part of a proprietary operating system.

Fractional T1 - Service offering data rates between 64 kbit/s (DS0 rate) and 1.536 Mbit/s (DS1 rate), in specified intervals of 64 kbit/s.

G.711 - 3KHz audio-coding at 64Kbps.

G.722 - 7KHz audio-coding at 64Kbps.

G.728 - 3KHz audio compression at 16Kbps (wideband audio).

Gateway - Gateways are points of entrance to and exit from a communications network. Viewed as a physical entity, a gateway is that node that translates between two otherwise incompatible networks or network segments. Gateways perform code and protocol conversion to facilitate traffic between data highways of differing architecture. In OSI terms, a gateway is a device that provides mapping at all seven layers of the OSI model. A gateway can be thought of as a function within a system that enables communications with the outside world.

H.221 - The ITU-T standard relating to communications protocol for videoconferencing.

H.230 - The ITU-T standard that defines call control and indication.

H.231 - Multipoint for linking three or more H.320 codecs.

H.233 - Encryption.

H.242 - Call set-up and disconnect of two point videoconferencing.

H.243 - Defines call control procedures between H.231 MCU and H.320 codecs.

H.261 - The ITU-T Px64 standard relating to the video compression algorithm.

H.320 - Umbrella standard for videoconferencing.

H.323 - A standard approved by the International Telecommunication Union (ITU) that defines how audiovisual conferencing data is transmitted across networks. In theory, H.323 should enable users to participate in the same conference even though they are using different videoconferencing applications. Although most videoconferencing vendors have announced that their products will conform to H.323, it is too early to say whether such adherence will actually result in interoperability.

H.324 - Video over POTS.

Hertz (Hz) - Cycles per second.

Half duplex - Method to either transmit or receive without the ability to do both simultaneously.

Half-duplex audio - Audio that permits only one site to speak at a time.

ISDN (Integrated Services Digital Networks) - A switched network service providing end-to-end digital connectivity for transmitting voice, data, and video simultaneously over a single line verses multiple. Uses high-speed, out-of-band signaling. There are two major forms of ISDN BRI and PRI.

ISDN BRI - A digital access line that is divided into three channels. Two of the channels, called B channels, operate at 64 Kbps and are always used for data or voice. The third D channel is used for signaling at 16 Kbps.

ISDN PRI- Based physically and electrically on an E1 circuit, but channelized so that two channels are used for signaling and 30 channels are allocated for user traffic. ISDN PRI is available in E1 and T1 frame formats, depending on country.

Internet Protocol (IP) - A Layer 3 (network layer) protocol that contains addressing information and some control information that allows packets to be routed.

Internet Service Provider (ISP) - (1) Any of a number of companies that sell Internet access to individuals or organizations at speeds ranging from 300 bps to OC-3. (2) A business that enables individuals and companies to connect to the Internet by providing the interface to the Internet backbone.

Internet telephony - A term used to specifically describe running voice telephony over the Internet, as opposed to any other IP network. Integrated presentation system - Presentations such as those created in Microsoft® PowerPoint®, can be displayed and presented to the far site while simultaneously being presented to remote users connected via the Internet/Intranet. Interoperability - Interoperable devices are compatible with the devices and services of multiple vendors, and can be integrated into a generic network containing a wide range of vendor products. Interoperability is a significant factor among expansion considerations, since any device must have the versatility to function in an expanding network structure. The technical elements of interoperability may include a bundle of protocols and a flexible architecture to accommodate upgrades. A remote access server should include capabilities such as translation, encapsulation, filtering, etc., that enable internetworking.

Inverse Multiplexer (Imux) - an electronic device that enables two or more signals to pass over a single communications circuit, whether analog or digital. An inverse multiplexer allows individually dialed channels across a network to be combined into a single, higher-speed data stream. Each end of the connection uses an inverse multiplexer, or inverse mux.

JPEG - Joint Pictures Experts Group. Still-frame graphics for multimedia.

Kilobits per Second (Kbps) - Measure of rate of digital transmission, often abbreviated Kbps.

Local Area Network (LAN) - A network covering a relatively small geographic area (usually not larger than a floor or small building). Compared to WANs, LANs are usually characterized by relatively high data rates. (2) Network permitting transmission and communication between hardware devices, usually in one building or complex.

Latency - The delay between the time a device receives a frame and the frame is forwarded out of the destination port.

Loopback - A diagnostic test where a signal is transmitted over a communications link or network and then returned to the sending device. Loopbacks are used to make sure the video equipment is working properly and as a way to demonstrate videoconferencing, maintenance, changing connections, etc.

MPEG - Motion Pictures Experts Group; a standard for motion video.

Megabit - One million bits.

Multiplexer - A device that permits subdivision of a given bandwidth to combine several channels to be carried by one line or fiber. For example, a T1 Multiplexer may divide a T1 line (1,544Kbps) into two capacities of 768Kbps each.

Multipoint control unit - Device which allows more than two sites to be connected in a videoconference. Sometimes called a digital switch or video bridge.

NTSC - A video signaling standard for North American TV sets with a display rate of 30 fps and 352-525 scan lines.

PAL (Phase Alternation Line) - A European alternative to NTSC, with better color resolution and an increase in scan lines to 625 over NTSC's 525.

Primary Rate Interface (PRI) - An ISDN subscriber line consisting of 23 64Kbps B channels and one 64Kbps D channel primarily used to linkPBXs and to connect a PBX to the PSTN.

Private Branch Exchange (PBX) - A small telephone network for customer premises. Provides local connectivity, switching and connections to the wide area voice network.

Packet - (1) A logical grouping of information that includes a header and (usually) user data. (2) Continuous sequence of binary digits of information is switched through the network and an integral unit. Consists of up to 1,024 bits (128 octets) of customer data plus additional transmission and error control information." packet loss rate - "The measure loss, over time, of data packets as a percentage of the total traffic transmitted.

Protocol - (1) A formal description of a set of rules and conventions that govern how devices on a network exchange information. (2) Set of rules conducting interactions between two or more parties. These rules consist of syntax (header structure) semantics (actions and reactions that are supposed to occur) and timing (relative ordering and direction of states and events). QCIF - Quarter Common Intermediate Format. A video resolution of _ the size of FCIF - 176 pixels horizontally and 144 pixels vertically. It is used primarily ion low bite rate (128Kbps and lower) videoconferencing.

Quality of Service (QoS) - Measure of performance for a transmission system that reflects its transmission quality and service availability.

RS-232 - Connectivity from the codec permitting data inputs for transmission from .3 to 190.2 Kbps.

RS-449 - Transmission interface between the codec and the transmission link that typically connects to a t1 Multiplexer. A user RS-449 port may also be available for data transfer.

SECAM - French standard for analog video format.

Switched 56 - Transmission network at 56Kbps that allows dial-up videoconferencing. Because picture quality at 56Kbps is often not acceptable, most dial-up videoconferencing takes place on two 56Kbps lines, for a total of 112Kbps (see Dual 56).

SPID - Service Profile Identifier. Your ISDN service provider (telephone company) uses this number at the Central Office switch to identify services on your ISDN line. This number is derived from a telephone number.

T.120 - Multilayer protocols for graphics/data transmission.

TCP/IP - The international standard protocol used on the Internet and company data networks. It provides worldwide connectivity and includes serves such as the World Wide Web, e-mail, file transfer and remote terminal login.

Twisted pair - Cabling commonly used in telephone networks. The typical twisted pair is two copper wires twisted together and bundled with any number of other twisted pairs. T1 - A leased digital line that provides 1.544 Mbps data rate (in North America; European T1 delivers 2.048 Mbps)

Transcoding - Allows participants with dissimilar codec speeds to participate in the same video conference.

10Base-T - An IEEE standard (802.3) for operating 10 Mbps Ethernet networks with twisted-pair cabling and a wiring hub, referred to as a 10Base-T hub.

V.35 - Transmission interface between the codec and the transmission link that permits Switched 56 connectivity.

Voice activated switching - In multiway videoconferencing, used so that all participating sites automatically see the site which is currently speaking.

Voice over internet protocol - The transmission of voice signals over the IP based Internet. Voice-tracking - camera automatically tracks the voice of the person speaking.

torna sopra