Telecoms Glossary

A collection of Telecommunications Terms & definitions... use the search box to zoom in on a term.

10Base-T	10 Mbps Ethernet over twisted-pair copper cable.
100Base-T	100 Mbps Ethernet over twisted-pair copper cable.
1000Base-T	1000 Mbps Ethernet over twisted-pair copper cable.
16-QAM	16 (points) Quadrature Amplitude Modulation
AAB	Auto Answer Back
Advanced Audio Coding (AAC)	An audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves higher sound quality than MP3 at the same bit rate.
Abandoned Cable	Any cabling, from Riser closet to server room to end-user, which is no longer being used, is the wrong cable type (i.e. riser in a plenum ceiling) or not tagged for future use. It is defined as Installed communications cable that is not terminated at both ends at a connector or other equipment and not identified For Future Use with a tag.
AC (power)	Alternating Current (AC power)
ACD	Automatic Call Distribution. A telephone system feature which distributes incoming calls to an agent or representative and keeps statistics on each call. Typically used in high-volume call center environment.
ACD Agent	Someone who handles telephone calls in a call center. Other common names for the same job include operator, Telephone Service Representative (TSR), attendant, and representative.
ACK	ACKnowledge (char 06 - 06H)
A/D or ADC	Analog to Digital Converter
ACF	ADMISSIONS CONFIRM message - A RAS message that the Gatekeeper sends to the calling point, accepting the ARQ.
Acoustic Coupler	A device that allows a conventional telephone handset to feed its signal into a modem, as opposed to direct couplers, which feed the modulated/demodulated signal directly into the phone line.
Acoustic Echo	Duplication of sound as the result of feedback generated on a phone from the speaker to the mic.
Acoustic Echo Canceller	All speakerphones have some form of adaptive echo canceller that produces a synthetic replica of the potential echo to subtract from the transmit audio. Most units have a center clipping echo suppressor to remove the residual echo from the transmit signal. The goal of the acoustic echo canceller is to reduce the amount of direct and reverberant loudspeaker coupling to the microphone to prevent echo. To achieve this, the algorithms used in today’s devices require an audio system that is feedback stable.
Acoustic Echo Return Loss (AERL)	The minimum loss experienced by a sound in traveling from the loudspeaker to the microphone in a conference room. It is expressed in dB or decibels. A 0-dB loss corresponds to a perfectly reflective room or to very close coupling between loudspeaker and microphone. In practice, AERL figures can range from 0 to -30 dB, with a poor room having the former figure.
Acoustic Echo Return Loss Enhancement (AERLE)	The maximum echo cancellation provided by the acoustic canceller. Typical figures will vary from 6 to 18 dB. The larger the number the better. It is important to note whether the figure is quoted with the center clipper enabled or disabled. If quoted with center clipper disabled, it is a true measure of the cancellation provided by the echo canceller rather than the attenuation provided by the center clipper.
Acoustic Modem	A modulator-demodulator unit that converts data signals to telephone tones and back again.
ADSL	Asymmetrical Digital Subscriber Line
ADPCM	Adaptive Differential Pulse Coded Modulation
Address Resolution	A mechanism for identifying the address of a called endpoint in terms of the network, such as an IP address.
Address Translation	The ability of a Gatekeeper to translate an alias address, such as a name or e-mail address, to a transport address. One method of translation uses a Translation Table, which is updated by the Registration messages on the RAS channel.
AFC	Automatic Frequency Control
AGC	Automatic Gain Control
Agent	Staff member who works from within the telephone support service of a company.
AKA	Also Known As
Apple Lossless Audio Codec (ALAC)	An audio coding format developed by Apple Inc. for lossless data compression of digital music. After initially keeping it proprietary from its inception in 2004, in late 2011 Apple made the codec available open source and royalty-free.
Alias	An alternative identification string for an IP address. An alias can be a name, a URL address, an e-mail address, a transport address in the form of "IP address port number", or a Party Number.
Algorithm	1. Rule of thumb for doing something with a semblance of intelligence. For example, a descrambling algorithm will yield a clear, unscrambled message from an apparently meaningless one. 2. The procedure used for performing a task.
Alternate Gatekeeper	Support for an Alternate Gatekeeper enables you to make Gatekeeper failures transparent to the endpoints that are registered to the Gatekeeper. In RADVISION implementations, a backup Gatekeeper (the "Secondary" Gatekeeper) runs in parallel to each online Gatekeeper (the "Primary" Gatekeeper).
Analog	Commonly used term for analog signal transmission. Analog telephony has been largely replaced by digital ISDN. However, in many countries, analog telephone lines are still in use.
Analog Line	Phone line using an analog wave form for transmission of speech.
ALI	Automatic Location Identification – A 911 feature by which the name, address and responding agencies associated with the number of the telephone used to dial 911 is displayed at the PSAP at the time the call is answered.
Analog	A transmission method using continuous electrical signals, varying in amplitude or frequency in response to changes of sound, light, position, etc. impressed on a transducer in the sending unit. The opposite of analog is DIGITAL.
Analog-to-Digital, A/D Conversion	The conversion of an analog signal into a digital equivalent. An A/D converter samples or measures an input voltage and outputs a digitally encoded number corresponding to that voltage.
Analog Telephone Adapter (ATA)	A device that is used to incorporate analog devices into a VoIP environment by converting analog signals into IP packets.
Analog Transmission	Transmission of a continuously variable signal as opposed to a discrete signal. Physical quantities such as temperature are described as analog while data characters are coded in discrete pulses and are referred to as digital.
AM	Amplitude Modulation
AM/FM	Automatic Mapping / Facility Management
AMI	Alternate Mark Inversion
AMPS	Advanced Mobile Phone System (TIA 553)
ANI	Automatic number identification. Used in telco networks to identify the calling party.
ANI/DNIS Routing	Custom routing of phone calls based on ANI (Automatic Number Identification) that gives the caller’s phone number, and DNIS (Dialed Number Identification Service) which is the phone number that was dialed by the caller. An example would be for call centers that are outsourcers and handle the calls for many other companies. The outsourcer would know where to route the call based on which number the caller dialed.
Announcement	A recorded verbal message played to a caller.
ANS	Automatic Noise Suppression. Reduces background noise from audio signal.
ANSI	American National Standards Institute.
Application Level Gateway	Application Level Gateways (ALGs) serve as communicators between two networks. ALGs are protocol-aware entities that examine application protocol flows and only allow messages that conform to security policies to pass. See also proxy server.
Area Code	Numeric string that defines a specific region or country as part of a telephone number. Area codes include country codes, cities or even municipalities. Also called NPA (Number Plan Area).
ARJ	ADMISSIONS REJECT Message - A RAS message that the Gatekeeper sends to the calling point, rejecting the ARQ.
ARP	Address Resolution Protocol (Layer 3)
ARQ	Automatic Repeat reQuest
ARQ	ADMISSIONS REQUEST Message - A RAS message send by an endpoint placing a call or an endpoint receiving a call asking for bandwidth allowance and permission to continue the Call Setup.
ARCnet	Attached Resource Computer NETwork
ASCII	American Standard Code for Information Interchange (7 bits -
ASA	American Standards Association
ASK	Amplitude Shift Keying
Asterisk	A free computer software that offers a wide range of functions of telephone systems. More about Asterisk.
AVC	Automatic Volume Control
AT	Apple Talk
AT	ATtention (Hayes Modems Command Prefix)
AT&T	American Telegraph & Telephone
ATE	Automatic Test Equipment
ATM	Automated Teller Machine
ATM	Asynchronous Transfer Mode. A high bandwidth, controlled-delay, fixed size packet switching and transmission system. Uses fixed size packets, also known as "cells"; ATM is often referred to as "cell relay". ATM will provide the basis for the future broadband ISDN standards.
AUI	Attachment Unit Interface (Ethernet, 15-pin)
ATB (All Trunks Busy)	The state of a trunk group when all trunks are in use and not additional inbound or outbound calls can be accepted or made.
Attendant	An operator of a PBX console or telephone switchboard.
Attenuation	A reduction in power or amplitude of the transmitted signal. In cables, it is generally expressed in decibels per unit length.
Audio Bridge	An audio bridge connects the telephones at remote sites, equalizes the noise distortion and background noise for a live audio teleconference.
Audio Teleconferencing	Two-way electronic voice communication between two or more groups, or three or more individuals, who are in separate locations.
Authentication	The process of verifying the identity of a user trying to log on to a system, or of the sender of a message.
Automated Attendant	Voicemail-based menu tree that helps direct callers to appropriate information or destinations.
Automatic Call Distribution (ACD)	In order to ensure the best possible handling of incoming calls, an ACD system automatically takes and distributes calls to certain employees within a company. Particularly, call groups can be specified and assigned to the digits of the telephone keypad. An incoming call then automatically gets routed depending on the digit pressed by the caller.
Automatic Call Screening	A feature for busy people that allows them to separate calls into the ones requiring immediate action and those that are less or not important. It’s the modern version of screening calls by letting a call go to voicemail and listening in. Users can set up actions like automatic transfer to voicemail, play a special ring tone for certain callers or just ending the calls. Different profiles can be set up to route calls differently based on your location as well.
Automatic Ring Back	Normally, when a line is busy, you try redialing every few minutes. With automatic ring back, a code is dialed into the telephone keypad to enable the phone to notify you with a ring when your call goes through. Your phone will ring with a distinctive ring, so you know it’s an automatic ring back. When you pick up the phone, it redials the number, so you can complete your call.
Avaya	An American multinational technology company headquartered in Durham, North Carolina, that specializes in cloud communications and workstream collaboration solutions.
AWG	A standard method used to measure wire. The numbering system works backwards from what people would think, the thicker (heavier) the wire, the lower the number. For example: a 24AWG wire is thicker / heavier than a 26AWG wire.
B&W	Black and White (TV)
B8ZS	Binary Eight Zero Suppression. An encoding scheme for transmitting data bits over T1 transmission systems.
BABT	British Approval Board for Telecommunications
BACnet	Building Automation and Control NETwork
Backbone Cabling	Cable and connecting hardware that comprises the main and intermediate cross-connects, as well as cable runs that extend between telecommunications rooms, equipment rooms, and entrance facilities.
Balance	An indication of signal voltage equality and phase polarity on a conductor pair. Perfect balance occurs when the signals across a twisted-pair are equal in magnitude and opposite in phase with respect to ground.
Balanced Signal Transmission	Two voltages, equal and opposite in phase with respect to each other, across the conductors or a twisted-pair (commonly referred to a tip and ring).
Balun	BALanced-UNbalanced, typically a small transformer used for converting one to the other.
Bandwidth	Determines the rate at which information can be transmitted across a medium. The rates are measured in bits (b/s), kilobits (Kb/s), megabits (Mb/s) or gigabits per second (Gb/s). Typical transmission services are 56Kb/s, 64Kb/s, 1.544Mb/s (T1) and 45Mb/s (T3).
BCD	Binary Coded Decimal
BCM	The Avaya Business Communications Manager is a Linux based IP/TDM PBX convergence system for small and medium enterprises
Bearer Channel	Term used to define a channel that carries voice, data or video information.
BER	Bit Error Rate
BERT	Bit Error Rate Tester
BFT	Binary File Transfer
BGP	Border Gateway Protocol
Bit	Contraction of the term Binary digiT. The smallest unit of information a computer can process, representing one of two states (usually indicated by "1" or "0").
BISDN	Broadband ISDN. In 1995-1996, BISDN began to offer dedicated circuits, switched circuits and packet services at rates of 155Mb/s and above. BISDN is still relatively in the conceptual stage. The goal is to take advantage of the raw bandwidth, which has been made available by the proliferation of fiber optic cable plants.
BIOS	Basic Input/Output System
B-ISDN	Broad band Integrated Services Digital Network
BISUP	Broad band ISdn User Part
BISYNC	BISYNChronous (BSC IBM)
bit	BInary digiT
BITNET	Because It's Time NETwork
BIX	Belden IBDN BIX/GigaBIX is a Cross-Connect System which allows for very high termination density while maintaining optimal ease of administration. Up to 300 pairs can be terminated in a small area with easy cable management.
BNC	Bayonet (Baby? ) Normalized Connector
Blanking Level	The level of the front and back porches of the composite video signal.
bpi	Bits Per Inch
BPSK	Binary Phase Shift Keying
BQFP	Bumpered Quad Flat Pack
bps	Bits per second - A unit of measurement of the speed of data transmission and thus of bandwidth (lower case is significant).
Bps (or BPS)	Bytes (8-bit) bytes per second. A unit of measurement of the speed of data transmission and thus of bandwidth (upper case is significant).
Bonding	Method for making several BRI lines look like one high-rate line by use of an IMUX (inverse multiplexer).
Bonding	The permanent joining of metal parts to form an electrically conductive path that will assure electrical continuity and the capacity to conduct safely any current likely to be imposed on it.
BRA	Basic Rate Access
BRI	Basic Rate Interface. An ISDN subscriber line, consisting of two 64Kb/s B channels (bearer channels) and one 16Kb/s D channel (used for signaling and synchronization purposes.) - often referred to as 2 B's and a D.
Bridge	A device, which interconnects three or more telecommunication channels, such as telephone lines. A telephone conference audio bridge links three or more telephones (usually operated assisted). Usually a meet-me audio bridge or provides a teleconference direct dial access number. Both connect remote sites and equalize noise distortion.
Bridged Tap	The multiple appearances of the same cable pair or fiber at several distribution points. Also known as parallel connections.
Bridges, Gateway, Routers	Devices that convert LANs to other LANs, computers, and WANs by allowing systems running on different media (copper wire, fiber optics, etc.) and protocols (rules to communicate).
Bridging	A means of providing through connections between conductors or pairs that are terminated on connecting blocks. These through connections are commonly provided by means of individual metallic bridging clips or multiple bridging clips that are housed in a plastic insulator.
Bridging Amplifier	An amplifier connected directly into the main trunk of the CATV system. It serves as a sophisticated tap, providing isolation from the main trunk, and has multiple high-level outputs that provide signal to the feeder portion of the distribution network. Synonymous with Bridger and distribution amplifier.
Broadband	A method of transmitting larger amounts of data, voice and video than telephony networks allow. In ISDN, broadband channels support rates above the primary E1 (2.048 Mbps) and T1 (1.544 Mbps) rate.
Broadcast	Transmission of data to everybody on the network or network segment.
BSC	Binary Synchronous Communication protocol (BISYNC - IBM)
BSD	Berkeley System Distribution (Unix)
BSI	British Standards Institution (London)
Buffer	See jitter buffer.
Buffering	Buffering is the process of storing packets temporarily during the transmission of information to create a reserve of packets that can be used during packet transmission delays or requests. While a packet buffer is commonly located in the receiving device, it may also be used in the sending device to allow the rapid selection and retransmission of packets when they are requested by the receiving device.
Buffer Bloat	An excessive amount of latency caused when a router or switch is configured to use extremely large buffers. Packets in a first-in-first-out system become queued for long times causing higher latency which degrades VoIP quality as well as other time sensitive applications on a network.
Building Distributor	The international term for intermediate cross-connect. A distributor in which the building backbone cable(s) terminates and at which connections to the campus backbone cable(s) may be made.
Bundled Cable	An assembly of two or more cables continuously bound together to form a single unit prior to installation (sometimes referred to as loomed, speed-wrap or whip cable construction).
Busy	SIP status that can be sent when a telephone is called that is already involved in another conversation.
Busy Override	Allows the calling party to break into an ongoing conversation.
Busy Lamp Field (BLF)	Show the status (busy, ringing, available) of phones of other users that are connected to your phone system. Often exists in combination with speed dial keys.
Byte	A group of bits treated as a unit used to represent a character in some coding systems. Typically, eight bits equals a byte.
B Channel	Bearer Channel. In ISDN communications, a B channel transmits data or voice at 64 or 56 Kbps.
CAS	Channel Associated Signaling, also known as per-trunk signaling (PTS), each channel contains its own signaling. CAS voice channels are 56kbit/s each, due to robbed-bit (in-band) signaling (RBS)
CCS	Common Channel Signaling, or common-channel interoffice signaling (CCIS) uses a single dedicated channel for signaling. CCS voice channels are 64kbit/s each, 8 bits sampled at 8 kHz with G.711 encoding. CCS is used for ISDN.
Call	Attempt to establish a telephone conversation.
Call Acceptance	Acceptance or rejection of calls from an H.323 terminal. The Gatekeeper may reject calls from a terminal because of restricted access to or from particular terminals or Gateways, or restricted access during certain periods of time. Call Authorization is an optional Gatekeeper service.
Call Center	Company or department that is responsible for handling incoming calls. Usually found in departments with high call volume. Outbound Call Centers perform calls to the outside world, usually calling clients and potential clients.
Call Control	Also called Call Processing. Refers to the signaling involved in setting up, monitoring, transferring, and disconnecting (tearing down) a call.
Call Detail Records	List of calls that have been conducted through a telephone or a PBX.
Call Feedback	Support for Call Feedback enables you to configure a Gatekeeper Forwarding policy to deal with cases such as Gatekeeper failure to resolve a destination address in IP network, lack of Gatekeeper bandwidth resources, or unsuccessful Call Setup to the destination endpoint due to network failure.
Call Flow	Graphical call schedule that allows to process incoming calls automatically. Call Flows allow easy implementation of complex telephony scenarios.
Call Flow Editor	Graphical editor that allows the display of complex call flows as diagrams easily by drag and drop. Learn more about Askozia’s Call Flow Editor
Cabling	A combination of cables, wire, cords and connecting hardware used in telecommunications infrastructure.
Call Center	A communications solution centered on inbound and/or outbound calls that uses PBX features such as attendants, queues, predictive dialing, etc. to manage voice calls.
Call Logging	This feature captures, records and provides cost information for telephone usage. It can track both inbound and outbound calls, call ring outs, etc.
Call Blocking	A feature that allows recipients of calls from a specified number to no longer allow that number to call in. It is helpful when trying to stop a repeated annoyance caller from calling again and again.
Call Forwarding	Service to send calls to another location, available in several forms, generally Busy, Don’t Answer, or All. The form describes the condition under which calls are sent to an alternate telephone number.
Call Group	Logical linking of several telephony devices into groups, allowing phones within the same call group to be reached through the same phone number and ring simultaneously.
Call on Hold	Allows incoming calls to be suspended and/or retrieve a call placed in suspension.
Call Park	Allows you to put a call on hold at one telephone set and continue the conversation from any other telephone set once you’ve entered the “park code”.
Call Pick-Up	Allows you to answer someone else’s telephone from your extension.
Call Queuing	Allows calls to be placed on hold without handling the actual call or transferring callers to a desired party. Callers are placed in line and can be played pre-recorded music or greetings while waiting, as well as be given updates on their place in line and or likely time until an agent will be with them.
Call Recording	Automatic or agent-controlled recording of phone conversations generating a permanent audio record of phone calls. There are several ways to do this and save the recordings. Accessing the recordings can be the most difficult part but is getting better all of the time. The recordings can be used to settle disputes, train staff and provide individual feedback to agents. Call recording is also required by law for some industries like financial services.
Call Routing	This is a system that can route callers to specific people or departments based on input from callers.
Call Screening	The process of identifying an incoming caller and designating a specific response to that call. At a basic level, the call can be accepted, rejected, or sent to voicemail.
Call Transfer	Sending an existing call to another telephone extension.
Call Tree	See Auto Attendant.
Call Timer	Clocking phone conversation connection time.
Call Waiting	A feature that provides audible or visual indicators to let a single-line-phone user know that there is another call waiting.
Callee	Receiver of a phone call.
Caller	Person that initiates a phone call.
Caller ID	Used to identify phones. Usually sent as a combination of name and number of the caller. It is shown on the display of the callee’s phone.
Camp-On	In PBX and hybrid environments, a method of putting an incoming or outgoing call intended for a busy extension or line into a hold-like state where it remains until a line becomes available.
Campus Backbone	Cabling between buildings that share telecommunications facilities.
Campus Distributor	The international term for main cross-connect. The distributor from which the campus backbone cable emanates.
Carrier	Vendor of transmission services operating under terms defined by the FCC as a common carrier. Owns a transmission medium and rents, leases or sells portions for a set tariff to the public via shared circuits. (AT&T, Sprint, MCI, Ameritech, etc.)
Cascaded MCU	The MCU allows you to combine two or more conferences resulting in a larger conference with many more participants. This is called Cascading. Cascading creates a distributed environment that helps reduce the drain on network resources.
Cat3	A twisted pair cable with a maximum frequency of 16 MHz. Typically used for analog voice and low speed networks.
Cat5	A twisted pair cable used for networks and mulit-line phone systems. It has a maximum frequency of 100 MHz and can transmit up to 10/100Mbps. Category 5 (Cat5) was defined in ANSI/TIA/EIA 568A, but is not used with ANSI/TIA/EIA 568B.
Cat5e	A twisted pair cable used for networks and mulit-line phone systems. It has a maximum frequency of 100 MHz and can transmit up to 10/100/1000Mbps. Category 5 Enhanced (Cat 5e) will work with ANSI/TIA/EIA 568A and ANSI/TIA/EIA 568B. It is the current standard for installing networks. If you see a higher MHz rating on a Cat5e cable you are being scammed, the hardware that uses these cables conforms to the standards set forth by TIA/EIA.
Cat6	A twisted pair cable used for networks and multi-line phone systems. It has a maximum frequency of 250 MHz and can transmit up to 10/100/1000Mbps. If you see a higher MHz rating on a Cat6 cable you are being scammed, the hardware that uses these cables conforms to the standards set forth by TIA/EIA.
Cat6a	A twisted pair cable used for networks, it has a maximum frequency of 500 MHz and can transmit up to 10/100/1000Mbps and 10Gbps.
Central Office (CO)	A facility of a telecommunications common carrier where calls are switched. In local area exchanges, central offices switch calls within and between the 10,000-line exchange groups that can be addressed uniquely by the area code and first three digits of a phone number.
Centranet	Phone switching system, usually installed in a service provider’s central office that provides dial tone and features to customers. The name is unique to Verizon.
CATV	Community Antenna (CAble?) TeleVision
CB	Citizens Band
CBR	Constant Bit Rate
CCTV	Closed Circuit TeleVision
CD	Carrier Detect (V24)
CDP	Co-ordinated Dialing Plan. When linking PBX's, dialing 4 digits to reach a four digit external extension can be set up using CDP. This will give the caller the impression that the call-destination is "on-switch".
Centrex	Phone switching system, usually installed in a service provider’s central office that provides dial tone and features to end user customers. The name is unique to AT&T.
CCITT	Consultative Committee on International Telephony and Telegraphy. An international standards group.
CD	Compact Disc
CD-R	Compact Disc Rewriteable
CD-ROM	Compact Disc Read Only Memory
CDMA	Code Division Multiple Access (Cellular, IS-95)
CDR	Call Detail Record - Information in a simple text format that can be used as input to third party billing programs or other software for billing purposes.
Centi-Call Seconds (CCS)	A unit used for the measurement of telephone traffic analysis, equivalent to one hundred seconds of telephone usage.
CEPT	The European Conference of Postal and Telecommunications Administrations (CEPT) was established on June 26, 1959 by nineteen European states in Montreux, Switzerland, as a coordinating body for European state telecommunications and postal organizations.
CERT	Computer Emergency Response Team (cert@cert.org - 412 268 7090)
Channel	A signal path of specified bandwidth for conveying information such as voice, data and video.
Chat Room	A virtual room where a chat session takes place. Technically, a chat room is really a channel, but the term room is used to promote the chat metaphor.
Chip Sets	Application-specific integrated circuits (ASICS) are being developed for use in video application products such as codecs, desktop video and home satellite entertainment. ASICS operate more like computer hardware. Programmable chips operate much like computer software. The chip sets meet the CCITT H.261 compression standard and will be the driving force in the widespread use of video communications technology because they will lower the cost and open up the technology to a much larger group of users.
CIDR	Classless InterDomain Routing
CIF	Common Intermediate Format. The CCITT standard that addresses the incompatibility between the European television standard PAL (Phase Alternation Line) and SECAM (Systeme Electronique pour Couleur Avec Memoire) and those in most areas of the rest of the world that utilize NTSC (National Television System Committee). In the encoding process, CIF is divided into 12 GOBs (Groups of Blocks).
CIRC	Cross Interleaved Reed-salomon Code
Circuit	1. Means of two-way communication between two or more points. 2. In communications systems, an electronic, electrical or electromagnetic path between two or more points capable of providing a number of channels.
Circuit Switching	A networking technology that provides a temporary but dedicated connection between two stations regardless of the number of switching devices through which data is routed. Analog circuit switching (FDM) has been replaced by digital circuit switching (TDM). The digital technology still maintains the connection until one speaker hangs up.
Circular Hunting	Calls are distributed "round-robin". If a call is delivered to line 1, the next call goes to 2, the next to 3. The succession throughout each of the lines continues even if one of the previous lines becomes free. When the end of the hunt group is reached, the hunting starts over at the first line. Lines are skipped only if they are still busy on a previous call.
Cisco Proxy	The Cisco H.323 Proxy is a device that acts like a Gateway and relays H.323 data between H.323 zones.
Class of Service Restrictions	This feature can prevent callers from placing certain types of calls such as long-distance, international or 900 numbers.
Clustered MCUS	The Multipoint Controller (MC) and Media Processor (MP) unit components of the MCU operate independently. The MCU can be set up in a clustered layout to use a single MCU to control several units configured to operate only as MP units performing media processing. MCUs configured as MP Only units have their MC component disabled. The controlling MCU unit also makes use of the local MP component.
CMIP	Common Management Information Protocol (ISO)
CNAM	Caller ID with name.
CO Lines	The lines connecting your office to the CO (Central Office or telephone company).
Coax	For a cable to be considered coaxial it must contain a center core conductor, and a second conductor wrapped around it. The second conductor can be made from different types of braided conductors (typically au - gold, cu - copper, and al - aluminum) or a metal foil. This outer wire is typically the ground.
Codec	COder-DECoder. A video codec converts the analog video signals from a video source to digital signals for transmission over digital circuits, then converts the digital signals back to analog signals for display. An audio codec converts the audio signals to digital signals for transmission over digital circuits, then converts the digital signal back to analog for reproduction.
Code C signaling	ITT European Code C. This signaling system was DC based and used on early electronic PABX's. The telephones had a push button unit that had 12 buttons numbered 1 - 0 and included * and #. The # button was used for recall/transfer purposes as it sent an earth condition to each wire. The * button was generally unused. This system was effectively superseded by MF signaling.
Common Carrier	Usually a telecommunications company that owns a transmission medium and rents, leases or sells portions for a set tariff to the general public via shared circuits through published and nondiscriminatory rates. (MCI, etc.)
Compression	The method of taking raw data and processing it so that it may be represented with less information (or bits in the digital world.) Compression falls into two categories: lossless - the original data may be completely recovered - and lossy - the representation of the original data contains errors.
Compressed Video	Processed video images; transmits changes from one frame to the next which reduces the bandwidth to send them over a telecommunications channel which reduces cost. Also called bandwidth compression or bit rate reduction.
Computer Telephony Integration (CTI)	Software that enables connection of VoIP phones and computers, allowing to control the functions of a telephone from a computer.
Conference Bridge	Allows callers to call in and enter a code to join a conference. There is usually a host who has control over the functionality of the conference and can do things like mute attendees or separate attendees out into sub-conferences.
Conference Call	Having more than 3 people on the same call, depending on the type of business telephone system or Conference Bridge this can be up to hundreds of people.
Consolidation Point	A location for interconnection between horizontal cables that extend from building pathways and horizontal cables that extend into work area pathways.
Consult Hold	Allows you, while on an established call, to place the original call on hold & call any other station inside or outside the telephone system.
Conference Call	Merges several communication channels to allow multiple participants to join a meeting and communicate with each other at the same time.
Connection	In terms of telephony, connection usually refers to an established conversation channel for sending audio and video signals.
Convergence	Referred to in the telecom and IT worlds as the integration or connection of different systems. It allows for communication and “meeting” of separate systems to allow greater efficiency.
Cookbook	Technical recipes, how-to guides, and information for installers, technicians, and tinkerers.
CPE	Customer Premises Equipment
cpi	Characters Per Inch
cps	Characters Per Second
CPU	Central Processor Unit
CR	Carriage Return (char 13 - 0DH)
CRC	Cyclic Redundancy Check
CRCC	Cyclic Redundancy Check Character
Cross-Connect	A facility enabling the termination of cables as well as their interconnection or cross-connection with other cabling or equipment. Also known as a distributor.
Cross-Connection	A connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers to attach to connecting hardware on each end.
Crossbar (matrix) switch	A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which a connection may be established by closing a switch located at each intersection, the elements of the matrix.
Crosstalk	Noise or interference caused by electromagnetic coupling from one signal path to another.
CRT	Cathode Ray Tube
Conference Hunting	The purpose of Conference Hunting in RADVISION implementations is to maintain conferences and ignore Line Hunting where necessary.
Conferencing Service	The Conferencing Service is a mechanism supported on the RADVISION MCU which defines the qualities, compatibilities and management policies of a conference.
Continuous Presence	Continuous Presence (CP) allows you to view multiple participants in one screen at the same time. Incoming participant images are combined into a video image layout set according to the policies of the conferencing service. The range of video layouts available depends on the type of media processing supported.
CPE	Customer Premise Equipment. Terminal equipment located on the customer premises which connects to the telephone network.
CSMA/CD	Carrier Sense with Multiple Access/Collision Detection
CSU	Channel service unit. Used to terminate a T1 facility.
dB	DeciBel
dBm	DeciBels (relative to 1 mw)
D Channel	The data signaling channel of an ISDN line. This channel is used to carry call control messages between the ISDN terminal and the public switch.
D/A or DAC	Digital to Analog Converter (DAC)
DASS signaling	The Digital Access signaling System (DASS) is the UK proprietary standard created by BT to provide ISDN services in the UK. The first incarnation DASS1 is now obsolete and has been replaced by DASS II. This itself will become obsolete over the coming years as Q.931, a European standard becomes widely adopted in the EEC.
DASS II	A protocol used to control data flow across the ISDN doing a similar job to the protocols used with modems when sending the data over the analogue PSTN. It is more highly specified and controlled and operates at higher speeds.
DB9	A DB9 (RS-488) connector is a 9 pin serial connection used on most laptop and desktop computers, as well as token ring connections. DB connectors are gender specific: A DTE port (PC) = Male, a DCE port (Modem) = Female.
DB15	A gender specific connector (Male / Female) with 15 pins (DB15) used for connecting to Mac Monitors or PC Joysticks. DB connectors are gender specific (Male / Female).
DB25	A DB25 (RS-232) connector is a 25 pin connection used on most desktop computers to connect serial or parallel ports together. DB connectors are gender specific: A DTE port (PC) = Male, a DCE port (Modem) = Female.
DC (power)	Direct Current (DC power). Typically, -48VDC (positive ground) is still the standard in communications facilities for powering equipment.
DCE	Data Communications Equipment, eg: Modem (female). Connect DCE to DTE devices using a straight through serial cable (female-to-male). Connect DCE to DCE, or DTE to DTE devices using a null modem adaptor.
DTE	Data Terminal Equipment, eg: a PC COM port (male). Connect DTE to DCE devices using a straight through serial cable (male-to-female). Connect DCE to DCE, or DTE to DTE devices using a null modem adaptor.
DCT	Discrete Cosine Transform. A compression algorithm.
Dedicated Line	Leased telecommunications circuits that are devoted to a specific application; a circuit designated for exclusive use by two users; i.e., for interactive portion of a teleconference.
Default Extension	Any endpoint on the network that has been defined as an alternative destination for incoming calls routed by a Gateway.
Definition	Also called resolution. The fidelity with which detail is reproduced by a television or video display system ranging from fuzzy to sharp appearance.
Delay	The time taken for a signal to pass through a videoconference from the sending station to the receiving station.
Delay Skew	The difference in propagation delay between the fastest and slowest pair in a cable or cabling system.
Demarcation Point (Demarc)	The point of interconnection between the local exchange carrier’s telecommunication facilities and the telecommunications systems wiring and equipment as the end user’s facility. This point is located on the subscriber’s side of the telephone company’s protector or the equivalent thereof in cases where a protector is not required.
DES	Data Encryption Standard. An algorithm for encrypting (coding) data designed by the National Bureau of Standards so it is impossible for anyone without the decryption key to get the data back in unscrambled form.
Desktop Videoconferencing	Videoconferencing on a personal computer - Most appropriate for small groups or individuals. Many desktop videoconferencing systems support document sharing.
DFSK	Double Frequency Shift Keying
DIMM	Dual In line Memory Module
DIP	Dual In-line Package
DIU	Data Interface Unit
DHCP	Dynamic Host Configuration Protocol - In a DHCP environment, IP policy is dynamic. This means that a terminal does not have a constant IP address. Management keys for identifying endpoints in a DHCP environment are the alias name or phone number of an endpoint.
Dial Pattern	Combination of digits assigned to a specific decision, such as which provider to choose or whether a call is addressed internally or externally.
Dial Plan	Specifies how to interpret dialed numbers, for example as internal extensions, local numbers, long distance or international numbers.
Digital Enhanced Cordless Telecommunications (DECT)	An international standard for wireless telecommunication, especially for cordless phones. Learn more about DECT.
Do Not Disturb (DND)	Telephone function that has all incoming calls rejected and not signaled on the device.
Dual Tone Multi Frequency (DTMF)	Transmission method for telephone numbers that is used to transmit numbers through the telephone keypad. For IP telephony, SIP messages are sent instead of tones.
Direct Inward Dialing (DID)	A method in which incoming calls are routed directly to endpoints, without operator intervention.
Digital	Discrete bits of information in numerical steps. A form of information that is represented by signals encoded as a series of discrete numbers, intervals or steps, as contrasted to continuous or analog circuits.
Digital Dial-Up Bandwidth	Communications channels created by signaling to the network from the caller's site the intended destination of the connection. These channels may be terminated when the caller or called party chooses. The user pays for the bandwidth only when it is used. Digital Dial-Up Bandwidth operates in a fashion similar to the dialed voice telephone network, but the resultant connections are digital and of specified bandwidth.
Digital Media	Refers to any type of information in digital format including computer-generated text, graphics and animations, as well as photographs, animation, sound and video.
DIN	Deutsche Industrie Norm (Germany)
Direct Mode	Routing of the Call Setup channel (Q.931) and the control channel (H.245) to form a direct connection between two endpoints without Gatekeeper intervention. See also Call Setup routing.
Directional Microphone	A microphone that detects and transmits sound from only a certain direction. Useful in preventing unwanted sound from being transmitted.
Display	The visual presentation on the indicating device of an instrument.
Distance Learning	Incorporation of video and audio technologies so that students can "attend" classes and training sessions presented at a remote location.
DLE	Data Link Escape (char 16 - 10H))
DNIC	Data Network Identification Code (X-121)
DNS	Domain Name Server - On TCP/IP networks, DNS converts the domain name (URL) of a host computer into a numeric IP address using the following format xxx.xxx.xxx.xxx.
Document Sharing	A videoconferencing feature that enables multiple participants to view and edit the same computer document.
Double-Talk	The situation where parties at both ends of a conference are speaking simultaneously. A quality echo canceller will provide a continuous speech path I-directionally during double-talk.
Downspeeding	The ability of a Gateway to maintain a ISDN video call by reconnecting the call at a lower rate when one of the B channels is lost. Downspeeding contributes to a higher percentage of call completion on the network.
DPDT	Double-Pole Double-Throw (switch)
DPNSS signaling	Digital Private Network signaling System (DPNSS) is, in a way, the 'odd man out' in the list of ISDN protocols. It is not formally regulated, but is a voluntary standard developed by the exchange and large PBX manufacturers, over the last decade, in conjunction with BT to allow interconnection between their equipment over the ISDN network.
DPSK	Differential Phase Shift Keying
DQPSK	Differential Quaternary Phase Shift Keying
DSO	One 64 Kb/s unit of transmission bandwidth. A worldwide standard for digitizing one voice conversation and more recently for data transmission. Twenty four DSO's equal one DS1 (64Kb/s x 24) or a T-1.
DS1	One 544Mb/s unit of transmission bandwidth in North America or one 2.048Mb/s unit of transmission bandwidth elsewhere in the world. A telephony term describing a 1.544 or 2.048Mb/s digital signal carried on a T1 circuit.
Digital subscriber line (DSL)	A technology that brings high-bandwidth information services to the home or small business over telephone loop plant. DSL technology enables a loop to simultaneously carry voice, which takes little bandwidth, and high speed data.
DSP	Digital Signal Processing
DSS1	Digital Subscriber signaling System 1 (tel)
DSU	Data Service Unit
DTL	Diode-Transistor Logic
Dynamic Bandwidth Allocation	The process of determining current traffic loads over a channel and automatically increasing or decreasing the bandwidth of the channel to optimize the utilization of bandwidth efficiency
Direct Inward System Access (DISA)	The ability to access internal features from an outside telephone line.
Distributor	The term used for the functions of a collection of components (e.g. patch panels, patch-cords) used to interconnect cables.
Direct Outward Dialing (DOD)	Direct Outward Dialing. A feature that allows telephone system users to dial an access code and a telephone number from their desk.
DS0	Network facility with bandwidth of up to 64kb.
DS1	Network facility with bandwidth of 1.544 MB, sometimes channelized to provide 23 or 24 channels.
DS3	Network facility with bandwidth of 45 MB, sometimes channelized to provide multiple T1 facilities.
DTMF	Dual-tone multi-frequency standard signaling used for touch-tone dialing.
DTR	Data Terminal Ready
Drain Wire	An uninsulated wire inside a shielded cable that runs the length of the cable and acts as a grounding point for the shield.
Duplex	In data communications, duplex defines the direction of the transmission. Duplex transmissions are bi-directional as opposed. Duplex are able to transmit in both directions, however, only one at a time, this is known as half duplex. A full duplex transmission can send and receive information at the same time.
E1 2.048Mb/s	European 1 (2048 bps, 30-channel PCM). Common European equivalent of a T-1.
E1 Primary Rate Interface (E1 PRI)	E1 connections have 32 channels in total. Typically, for E1 CCS and CAS protocols, 30 channels are used as B-channels and 2 channels are used as D-channels. For this reason, the frame structure of an E1 PRI connection is said to be 30B+2D where the 2 D-channels are located on timeslots 0 and 16 and the remaining channels are used as B-channels. Hence; Channel 0 → D-channel (Used for clocking and synchronisation) Channel 1-15 → B-channels (Voice) Channel 16 → D-channel (Signalling) Channel 17-31 → B-channels (Voice) Note, certain protocols allow for a different D-channel configuration, eg, SS7.
E.164	The term "E.164 number" differentiates an "absolute" telephone number from the number you must dial to reach an endpoint form a specific location. E.164 numbers include country codes, national destination codes and subscriber numbers.
E911	Enhanced 911 service is a system dedicated to connecting mobile and Internet phone users to emergency services.
E-box	Electronics box (the main codec box) of a group videoconferencing system.
Echo Cancellation	An algorithm that can be implemented both in hardware or software and which ensures that echoes are suppressed during audio transmission through a telephone line.
Echo Canceller	Eliminates audio transmission echo. A telephone line echo canceller produces a synthetic replica of the echo it expects to see returning and subtracts it from the transmitted speech. The replica it creates is based on the transmission characteristics of the telephone cable between echo canceller and the telephone or videoconferencing system. Device that allows for the isolation and filtering of unwanted signal caused by echoes from the main transmitted signal.
Echo Effect	A time-delayed electronic reflection of a speaker's voice. This is largely eliminated by modern digital echo cancellation.
Echo Suppression	A technique for reducing annoying echoes in the audio portion of a videoconference by temporarily deadening the communication link in one direction.
Electronic Blackboard	A device or whiteboard that looks like an ordinary blackboard or whiteboard, but has a special conductive surface for producing free hand information that can be sent over telephone lines.
Endpoint	A network element at the end of the network such as an H.323 terminal, a Gateway, a Multipoint Controller Unit (MCU), a PC terminal, IP or ISDN phone, or video conference.
Entrance Facility	An entrance to a building for both public and private network service cables (including antennae), including the entrance point at the building wall and continuing to the entrance room or space. Entrance facilities are often used to house electrical protection equipment and connecting hardware for the transition between outdoor and indoor cable.
EOF	End Of File
EOF	End Of Frame
EOP	End Of Packet
ESC	ESCape (char 027 - 1BH)
ETSI	European Telecommunications Standards Institute. A France-based non-profit making organization that produces telecommunications standards to be used throughout Europe and beyond.
E Phone	Slang. See Emergency Phones.
E&M signaling	A type of supervisory line signaling that uses DC signals on separate leads, called the "E" lead and "M" lead, traditionally used in the telecommunications industry between telephone switches. Various mnemonic names have been used to memorize these letters, such as Ear and Mouth, the most common variation.
ESF	Extended Super Frame T1 framing scheme.
EST	Eastern Standard Time
ETB	End of Text Block (char 023 - 17H)
ETC	Enhanced Throughput Cellular
Ethernet	A LAN physical and data link protocol running over the lowest two layers of the OSI Reference Model.
Ethernet	Local area network used for connection computers, printers, workstations, or terminals. Generally provided over twisted pairs or coaxial cable, offering speeds of 10 Mbps or 100 Mbps. 1 and 10 Gbps are possible.
ETSI	European Telecommunications Standards Institute (Cedex - F)
ETX	End of TeXt (char 3 - 03H)
Euro ISDN (Q931)	The Euro-ISDN, Q.931, is a further protocol development building upon the features and facilities offered by DASS II and developed for implementation on networks throughout the EEC. It will eventually replace DASS II in the UK and the systems used by other EEC member countries to become the single ISDN standard used throughout Europe.
Exit Zone	When you define a prefix for the Exit Zone Service, you need to dial the prefix to reach an endpoint in another zone. This can be useful for restricting unauthorized users from making calls to other zones. The Exit Zone prefix affects the way in which the Gatekeeper tries to complete calls to other zones.
External Call	General term for both incoming and outgoing calls with dialogue partners from outside of the own network.
Facsimile (FAX)	Analog transmission of documents as images through the telephone networks.
Fallback	A modem speed that is lower than its normal (that is, maximum) speed of operation.
Fast Connect	Also called Fast Start and H.323 Fast Start. A procedure for shortening the time it takes to start a call by skipping the H.245 phase and transferring channel parameters in the Call Setup messages.
Fast Start	See Fast Connect.
FCC	Federal Communications Commission. An independent US government agency charged with regulating interstate and international communications by radio, television, satellite and cable.
FCIF	Full Common Intermediate Format or Full CIF. Used when distinguishing between CIF and QCIF. See CIF and QCIF.
FEC	Forward Error Correction
FECC	Far-End Camera Control.
F-Connector	F-Connectors are used on coaxial cable, typically used with in Cable TV, VCR's, Security Systems, Satelitte Systems and other Video applications. The most common cables used are RG58, RG59 and RG6. The connectors come either in a single or 2 piece piece set. THey can either be crimped, soldered, or twisted on.
Fiber	A thin strand of glass or plastic optical fiber that transmits light impulses.
Fiber Optics	A communications medium utilizing laser or "light" transmission. Uses a glass or plastic fiber carrying light to transmit voice, data and video signals. Each fiber can carry from 90 to 150Mb/s.
Field	One half of a video frame. One field contains all of the odd or all of the even scanning lines of the picture.
FIFO	First In, First Out
File Transfer Protocol (FTP)	A standard communication protocol used for transfering files from a server to a client on a computer network. Authentication (username and password) is in plain-text. Replaced with Secure File Transfer Protocol (SFTP).
Firestop	A material, device, or assembly or parts installed in a cable pathway at a fire-rated wall or floor to prevent passage of flame, smoke or gases through the rated barrier (e.g. between cubicles or separated rooms or spaces).
Firewall	A barrier device placed between two separate networks. A firewall can be implemented in a single router that filters out unwanted packets or it can use a variety of technologies in a combination of routers and hosts. Today many firewalls combine filtering functionality with Network Address Translations (NAT) functions.
Floor Distributor	The international term for horizontal cross-connect. The distributor used to connect between horizontal cable and other cabling subsystems or equipment.
Flow Control	Comprised of the hardware, software and procedure for controlling the transfer of IP packets between two points on a network.
Foot-candle	The unit of illumination equal to one lumen per square foot.
Foreign Exchange Office (FXO)	An 'office' interface requests dial-tone by on-hook/off-hook indication (loop closure). It's a PBX trunk port, or the plug on a phone, it receives dial-tone from an FXS device/port.
Foreign Exchange Station (FXS)	A 'station' or 'subscriber' interface provides dial-tone, battery current, and ring voltage to a subscriber device, eg. a telephone or fax. It's a PBX station port, or the plug on the wall, it sends dial-tone to an FXO device/port.
Forwarding	Allows to redirect calls from one phone to another one, without the need to answer the call first.
Four-wire Circuit	A circuit that uses two pair of conductors (four wires), one pair to transmit the signals and one pair to receive; allows two parties to communicate simultaneously.
Fps	Frames per second (video).
Frame	Full screen or frame of video made up of two fields. Thirty frames is one second of video.
Frame Rate	The rate at which individual pictures (frames) in a sequence are displayed in a video conference. Frame rate is measured in frames per second (fps).
Frame Relay	Method for sending high-bandwidth data in frames (not video frames, but "blocks" of data). Uses packet switching, not circuit switching.
Frequency	The number of cycles or waves per second, expressed in Hertz, (Hz). In structured cabling the information carrying capacity (bandwidth) is measured in Hz.
FTTB	Fiber to the Building: fiber reaches the boundary of the building, such as the basement in a multi-dwelling unit, with the final connection to the individual living space being made via alternative means.
FTTC	Fiber to the Curb: similar to FTTN, but the street cabinet or pole is closer to the user’s premises, typically within 1,000 feet (300 m).
FTTD	Fiber to the Desktop: in an office, fiber connection is installed from the main computer room to a desk or fiber media converter near the user's desk
FTTH	Fiber to the Home: fiber reaches the boundary of the living space, such as a box on the outside wall of a home.
FTTN	Fiber to the Node (or neighborhood): fiber is terminated in a street cabinet, possibly miles away from the customer premises, with the final connections being copper. FTTN is often an interim step toward full FTTH (fiber to the home).
FTTP	Fiber to the Premises: used as a blanket term for both FTTH and FTTB, or where the fiber network includes both homes and small businesses.
FTTR	Fiber to the Router: fiber connection is installed from the router to the ISP's fiber network.
Full Duplex	A signal or transmission where the transfer of data can go in both directions at the same time. Full duplex signals allow more information to be transfered.
Full-duplex audio	Two-way audio may be captured and reproduced simultaneously. With full-duplex audio, the microphone may capture local audio for transmission while the far end audio may be heard clearly. Interruptions and double-talk are possible.
Full-motion Video	Not compressed. A standard video signal of thirty frames per second (fps), 525 horizontal lines per frame, capable of complete action.
G.711	3.4kHz bandwidth audio transmitted at 48, 56 or 64Kb/s - narrow-band audio, sounds like a telephone speakerphone.
G.722	7kHz bandwidth audio transmitted at 48,56 or 64Kb/s - wide-band audio, ISDN telephony standard, sounds like a telephone, more bandwidth allows for better quality. Much less long-term fatigue from user when wide-band audio is used.
G.722.1	An ITU-T standard for speech codecs that compresses 50Hz-7KHz audio signals into one of two bit rates, 24 or 32 Kbps.
G723.1	An ITU-T standard for speech codecs that provides good quality audio at 5.3 or 63 Kbps.
G.728	3kHz bandwidth audio transmitted at 16Kb/s - newest technology, best quality, requires lower bit rate leaving more room for video.
G.729 A/B	An ITU-T standard for speech codecs that provides near-toll quality audio at 8 Kbps. G.729 Annex A is a reduced complexity codec and G.729 Annex B supports silence suppression and comfort noise generation.
Gain	An increase in signal power in transmission from one point to another; usually expressed in decibels.
Gatekeeper	In H.323 IP telephony, a Gatekeeper is an optional server that is responsible for network-based services including a registration, admission, and status, for which it uses a special protocol called RAS. Gatekeeper functions include address translation, call authorization and bandwidth management, as well as providing accounting information.
Gatekeeper Zone	A group of endpoints together with their Gatekeeper constitute a zone. You can configure a zone by predefining endpoints that are entitled to register with the Gatekeeper. See also predefined endpoint, registered endpoint, zone.
Gateway	A network element that performs conversions between different coding and transmission formats. The gateway does this by having many types of commonly used transmission equipment and / or circuits from different carriers to provide a means of interconnection. See Bridge.
Gateway Redundancy	The Gateway Redundancy feature enables the Gatekeeper to request that other Gatekeepers search their zones to locate a request when Line Hunting fails to find a suitable service provider. If no service is found, the Gateway Redundancy policy enables the Gatekeeper to complete the call by referring the call to other Gatekeepers.
Gateway Supported Prefixes	H.323 version 2 enables a Gateway to specify prefixes that the user should dial before the WAN number in order to make a call using a certain media. GCF:GATEKEEPER CONFIRM Message -A RAS message that the Gatekeeper sends to the requesting endpoint, accepting the GRQ.
Gender Changer	A small adapter that changes the gender of a connector. The adapter will have the same gender on both sides. For example: If you have a female ended cable that needs to connect to a female device you will use a Male Gender Changer to convert/couple the two female connections.
Geographic Redundancy	The replication of data in two geographically separate sites so that if a disaster should happen, your applications can switch from one site to another.
Geographic Redundancy	A Survivable Media Gateway (SMG) will attempt to register with an Alternate Call Server in the event of the Primary Call Server not being reachable.
GIGO	Garbage In, Garbage Out
GMT	Greenwich Meridian Time
GND	GrouND (0V)
GRJ	GATEKEEPER REJECT Message - A RAS message that the Gatekeeper sends to the requesting endpoint, rejecting the GRQ.
Group Hunting	Group Hunting enables a Gatekeeper to perform load balancing for a group of H.323 endpoints defined with the same alias.
GRQ	GATEKEEPER REQUEST Message - A RAS message that an endpoint sends to locate a Gatekeeper to which the endpoint can register.
GSM	Global System for Mobile Communications - The standard digital cellular phone service of Europe, Japan, Australia and elsewhere.
GOB	Groups of Blocks. In the encoding process, each picture is subdivided into groups of blocks and then further divided into macro blocks.
Ground	A conducting connection, whether intentional or accidental, between an electrical circuit (telecommunications) or equipment and earth, or to some conducting body that serves in place of the earth.
Ground Start	Way of signaling initiation of a call from a PBX to the CO by briefly grounding one side of a line.
HMLP	High-speed multi-layer protocol. Standard for high-speed transmission. T.120 systems must use this for high-speed transfer. HMLP channels must be multiples of 64Kb/s.
HSD	High-speed data standard. HSD channels must be multiples of 64Kb/s.
H.221	A CCITT standard describing a method of inverse multiplexing for videoconferencing terminals, to be used with PX64 videoconferencing.
H.225.0	H.225.0 specifies that procedures and messages applicable to Gatekeepers, including the RAS protocol for Registration, Admission and Status.
H.235 Security	H.235 Security ensures the authentication of each endpoint and the integrity of messages. The basis of the security process is the shared secret between the endpoint and the Gatekeeper.
H.239	ITU-T standard for role management and additional media channels for H.300 - series terminals.
H.243	Standard for multipoint communication in H.320.
H.244	A CCITT standard that is an enhanced version of H.221. H.221's logical successor.
H.245	The ITU-T standard used for the Control Protocol for Multimedia Communication. H.245 is included in the H.225.0 Recommendation. H.245 provides signaling for the proper operation of the H.323 terminal, including capabilities exchange, opening and closing of logical channels together with a full description of these channels, mode preference requests, flow control messages, and general commands and indications.
H.245 Proxy	The H.245 Proxy enables routing H.245 channels in a point-to point H.323 call. The H.245 Proxy is a natural extension of a Gatekeeper.
H.245 Tunneling	H.245 tunneling decreases the time between the point at which and endpoint initiates a call and the point at which the call participants are ready to open multimedia channels. The endpoint must also support H.245 tunneling.
H.248	The ITU-T standard for signaling and control between circuit-switched PSTNs and VoIP networks.
H.261	A CCITT standard describing a protocol for digitally encoding and decoding video images to allow videoconferencing terminals from different manufacturers to interoperate.
H.263	Video compression standard created and required for H.324. Is also an optional mode of the other H-series standards.
H.264	The ITU-T standard for compression that allows higher quality calls to pass over a lower bandwidth for advanced video coding in generic audiovisual services.
H.320	A set of CCITT standards describing a method of interoperability between videoconferencing terminals from different manufacturers.
H.323	Suite of standards for multimedia conferencing on traditional packet-switched LANs.
H.323 Fast Start	See Fast Connect.
H.324	Suite of standards for multimedia conferencing on analog phone lines POTS.
H.331	Standard, which specifies how H.320 terminals can be used in a one-way broadcast mode.
H.350	ITU-T standard for directory services architecture for multimedia conferencing.
H.324/M	The Third Generation Partnership Project (3GPP) has adopted the ITU-T Recommendation H.324 Annex C, also referred to as H.324/M (Mobile) or H.324M (with very few changes), on their 3G-324M as the standard for multimedia telephony over 3G circuit switched cellular networks.
H.450	See Supplementary Services.
Half Duplex	A signal or transmission where the transfer of data can go in both directions, however, it can only be sent in one direction at a time.
Handset	Part of a telephone that contains both microphone and earphone.
Headset	A combination of headphones and microphone, can be connected to a phone or to a computer to communicate through a soft phone.
Hertz (Hz)	A unit used in the measurement of frequency equal to one cycle per second. Frequency is generally measured in Kilohertz (KHz) or Megahertz (Mhz).
HD15 (VGA)	A gender specific connector (Male / Female) with 15 pins (HD15 / VGA) used for connecting PCs to PC Monitors. When ordering or connecting an HD connector, make sure you have the correct gender on the cable.
Hold	If a dialogue partner is set on hold, the audio connection gets interrupted. The waiting dialogue partner can listen to hold music until being transferred or retrieved back into the conversation.
Home-Run Cabling	A distribution method in which individual cables are run directly from the horizontal cross-connect to each telecommunications outlet. This configuration is also known as star topology.
Horizontal Cabling	The cabling between and including the telecommunications outlet and the horizontal cross-connect.
Horizontal Cross-Connect	A cross-connect of horizontal cabling to other cabling, e.g. horizontal, backbone or equipment.
Hosted VoIP	Also known as Cloud Based PBX and/or Hosted PBX is where the PBX hardware and software that handle calls for a business resides with the provider off-site on the Internet. Through signaling, calls and other communications are initiated and routed to other parties.
Hot Desk (Hotelling)	A method of supporting unassigned seating in an office environment or temporary physical operation of a workspace.
HDTV	Higher than normal definition TV. HDTV is generally defined as a system that offers double the horizontal and vertical resolution compared to existing systems and provides compact disc quality sound.
HT	Horizontal Tab (TAB, char 09 - 09H)
HTML	HyperText Mark-up Language (WWW)
Hub	Equipment that serves as the centralized connection point for a network or portion thereof. Hubs are used for multiplexing, multi-port bridging functions, switching and test access. They can be either passive or active and are not considered to be a part of the cabling infrastructure.
Hunt Group	The method of distributing phone calls from a single telephone number to a group of several phone lines. If a hunt group is called, all telephones belonging to that group ring one after the other in a pre-defined order until the call is answered or the caller hangs up.
HVAC	Heating, Ventilation and Air Conditioning
ICMP	Internet Control Message Protocol
IDEC	Integrated Dynamic Echo Canceller patented by PictureTel. Dynamically eliminates conference echo so that true full-duplex audio is possible.
IDE	Integrated Drive Electronics (interface)
IDF	Intermediate Distribution Frame (tel)
IEEE	Short for Institute of Electrical and Electronics Engineers (typically pronounced I triple E). This group has set most of the LAN standards through the 802 series.
IETF	Internet Engineering Task Force. Formed in 1986, the IETF sets the technical standards that run the Internet. IETF working groups seek the advice of the Internet community through RFCs (requests for Comment), and then submit recommendations to the IETF for final approval.
IMTC	International Multimedia Teleconferencing Consortium. Industry forum for promoting interoperability trials.
IMUX	Inverse Multiplexer. Device that bonds two or more BRI lines to form a higher rate channel.
Impedance	A measure of the total opposition to current flow in an alternating current circuit, made up of two components. With higher speed and bandwidth networks, the impedance of the cable plant as a whole can affect the networks performance.
Impact Tool	Impact Tools have a spring loaded head that when used will punch down the on the conductor and into the block. If you're setting up a phone or network system you may need to use an impact tool to wire up the large patch panels. Typical blades that are used in impact tools are 66, 88, and 110.
In-band signaling	Signaling made up of defined bits which pass within the data transmission stream.
Instant Messaging (IM)	A communications service that enables you to create a private chat room with another individual in order to communicate in real time over the Internet.
Incoming Call	External call received from the outside world on a PBX or telephone.
Incoming Call Routing	See default extension, DID, MSN, sub-addressing, TCS4.
Inverse Multiplexing	The creation of a single higher speed data channel by combining and synchronizing two or more lower speed data channels. IMUX - Equipment RPM.
INMARSAT	INternational MARitime SATellite
INTELSAT	INternational TELecommunications SATellite organization
I/O	Input/Output
IP	Internet Protocol (layer 3). Packet-based protocol for delivering data across networks.
IPng	Internet Protocol Next Generation (IETF)
IPv6	Internet Protocol Version 6
Internet Protocol (IP)	The principal communication protocol for delivering data packages through the internet from the source to the destination based on IP addresses.
IP Address	A unique numerical label assigned to each device connected to a network that uses the Internet Protocol for communication. Allows to identify and locate devices within a telecommunications network to enable data transfer. IP addresses are 32 bits long. Each octet is represented in decimal and is separated by dots.
IP Multicast	A means of simultaneous transmission of data from a server to a group of selected users on a TCP/IP network, (internal, intranet or Internet). IP multicast is used for streaming audio and video over the network.
IP Network	A network t hat uses the TCP/IP protocol.
IP Telephony	A set of technologies that enables voice, data and video collaboration over existing IP-based LANS, WANs, and the Internet. IP technology uses open IETF and ITU standards to move multimedia traffic over any network that uses IP.
IPX	Internet Packet Exchange (Netware, layer 3)
IR	InfraRed
IRQ	INFORMATION REQUEST Message. - A RAS message in which the Gatekeeper asks the endpoint for its current status.
IRR	INFORMATION REQUEST RESPONSE Message - A RAS message that the Gatekeeper sends to the calling endpoint, rejecting the IRQ.
Integrated Services for Digital Network (ISDN)	Telecommunication standard established for replacing the analog telephone network in the mid 90s, integrating both speech and data on the same communication lines.
Inter-Asterisk-Exchange (IAX)	A protocol used by Asterisk telephone systems to connect between multiple Asterisk servers or between an Asterisk server and a device.
Interbuilding Backbone	Telecommunications cable(s) that are part of the campus subsystem that connect one building to another.
Intercom	Two-way talk paths over a phone base speaker with or without announcement, for group announcement or limited public dialogue with everyone in the group.
Intercom Groups	Two-way talk paths over a phone base speaker with or without announcement, for group announcements, or limited public dialogue with everyone in the group.
Intermediate Cross-Connect	The connection point between a backbone cable that extends from the main cross-connect (first-level backbone) and the backbone cable from the horizontal cross-connect (second-level backbone).
Immediate Start	Analog 'start dial' signaling type, where the originating switch places trunk off hook and originating switch transmits dial digits.
Interconnect	A company or vendor selling customer premises equipment, generally PBXs and other types of office telephone systems. An interconnect company is typically an independent distributor of products from more than one manufacturer.
Interactive Voice Response (IVR)	Enables a computer to interact with humans by using voice recognition and DTMF tones input via a phone keypad, enabling automated interaction e.g. between customers and a company’s telephone system and thus simplifying call management and forwarding.
Internal Call	A call between two users which are logged on to the same phone system, and thus does not require to build up an external connection.
ISDN Rollover	In RADVISION implementations, Gateway support for the ISDN Rollover feature ensures that a call is completed even when call volume is high. ISDN Rollover requires support by the PSTN.
ISO	International Standardization Organization. International standards body concerned with non-telecommunications issues.
ISP	Internet Service Provider
ITSC	International Telecommunications Standards Conference
ITU	International Telecommunications Union. Organization composed of the telecommunications administrations of the participating nations. Focus is the maintenance and extension of international cooperation for improving telecommunications development and applications.
ITU-R	ITU Telecommunications Union - Radio Communications Sector
ITU-T	Standards body under the jurisdiction of the United Nations. Responsible for all international telecommunications standards.
ITU-TS	ITU Telecommunications Standardization
IVDS	Interactive Video and Data Services. The name for the license which will be granted by the FCC for devices called Interactive TV Appliances (ITAs). ITAs include TV answer, a two-way television service for consumers for game shows, sporting events and respond instantly to new polls, interactive advertising as well as distance learning. The system will allow viewers to shop, bank, pay bills and order a pizza.
IVR	Interactive Voice Response is a two-stage incoming call routing method supported by the Gateway. It enables DID to a LAN terminal, even when the ISDN lines do not have multiple numbers allowing direct dialing to an endpoint.
IXC	Inter Exchange Carrier. Common carrier providing communications channels between local companies (LECs, or Local Exchange Carriers). Also known as long distance carriers such as AT&T, LCI, LDDS, MCI, US Sprint, WilTel, etc.
ISDN Line	Integrated Services Digital Network. ISDN lines are generally either BRI (2b+d) or PRI (23b+d), where b = the number of bearer channels and d = a control channel. BRI service is usually provided to a telephone-type end point, whereas PRI is usually used to connect two switches.
Jack	A connecting device to which a wire or wires of a circuit may be attached, and which is arranged for the insertion of a plug.
Jitter	The result of a change in latency or the tendency towards lack of synchronization caused by mechanical or electrical changes. Technically, jitter is the phase shift of digital pulses over a transmission medium.
Jitter Buffer	A portion of memory specifically allocated to storing IP packets awaiting transmission, or to storing received IP packets. The buffer facilitates flow control by capturing IP packets and then transmitting packets as "playback" using speeds and rates of delay that the destination device can handle without causing packet loss through overloading.
Jitter Buffer Management	Jitter buffer management represents the trade-off between a larger buffer and increased rates of jitter.
JPEG	Joint Photographic Expert Group. JPEG is an industry standard for still image compression that has moved into full motion video. JPEG is a compression technique based upon intraframe encoding technology. It allows for the full restoration of symmetrically compressed images.
Jumper Wire	An assembly of twisted-pairs without connectors on either end used to join telecommunications links at a cross-connect.
Key System	A multiline telephone system offering a limited range of features; key systems are popular among smaller businesses as their main telephone system. They are also found in large businesses as a form of extension to their big primary phone system. Key systems are characterized by manual selection of outgoing lines, their small size, and relatively low price.
KB	KiloBytes
KB	Knowledge Base (AI)
Kbps	Kilobits per second. A unit of measure of data of 1,000 bits per second.
Kilo	A measurement referring to 1000 as in kilometer (1000 meters), kilohertz (1000 hertz), kilobit (1000bits) etc. There are other forms of measurements such as mega (1,000,000) and giga which is one billion.
LAN	Local Area Network. A private transmission network interconnecting offices within a building or a group of buildings used to convey voice, data and video traffic.
LAN/WAN Connectivity	The practical set of tools, from operating system layer protocols to support services that make a remote access device an effective link between LANs and WANs.
Landline	Traditional wired phone service.
LAP	Link Access Procedure
LAP-B	Link Access Procedure, Balanced (Multilink operation procedure, X25)
LAP-D	Link Access Procedure, D Channel
LAP-M	Link Access Procedure for Modems
Latency	A measure of accumulated waiting time or delay, representing the length of time required for information to pass through a network.
Layer 7: Application	The application layer is used by end-user software such as web browsers and email clients. It provides protocols that allow software to send and receive information and present meaningful data to users. A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).
Layer 6: Presentation	The presentation layer prepares data for the application layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end. The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer.
Layer 5: Session	The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer—if the session is interrupted, devices can resume data transfer from the last checkpoint.
Layer 4: Transport	The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end. It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer. The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again.
Layer 3: Network	The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network. The network layer uses network addresses (typically Internet Protocol addresses) to route packets to a destination node.
Layer 2: Data Link	The data link layer establishes and terminates a connection between two physically-connected nodes on a network. It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts—Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.
Layer 1: Physical	The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.
LCF	LOCATION CONFIRM Message - A RAS message that a Gatekeeper sends to the requesting Gatekeeper/endpoint accepting the LRQ.
LDAP	Lightweight Directory Access Protocol - A protocol for accessing online directory services. LDAP is both an information model and a protocol for querying and manipulating the model.
Leaky PBX	The name given to the practice of using a local PBX to leak calls from country A into the network in country B, disguising them as local calls.
Leased Lines	A term used to describe the leased or rented use of dedicated lines between two points.
LEC	Local Exchange Carrier. Carriers that can carry only intra-LATA traffic. Local telephone companies such as Cincinnati Bell, Ohio Bell, Illinois Bell, Pacific Bell in California, etc.
LED	Light Emitting Diode. A display technology that uses a semiconductor diode that emits light when charged. LEDs usually indicate both correct and problematic operation.
Line	The term telephone line remains from the past, where a two-wire cable was required for each phone conversation.
Line Appearance	A button/lamp on the telephone base linked to a phone line that indicates availability. You can see the status of the line by looking at the phone. When the lamps are lit, they indicate lines are in use, on hold, ringing, or available.
Line Card	The circuit in the Telco switch or PABX to which your telephone is connected.
Line Hunting	A Gateway supports a list of prefixes (services). Gateway unavailability to receive a call means that the Gateway cannot accept calls with the particular prefix in question. The Line Hunting function of a Gatekeeper searches for a Gateway which is free to accept calls with this prefix.
Linear Hunting	Calls are always delivered to the first line, unless it is busy — then the second, third, and remaining lines are considered in succession.
Local Loop	Referred to as the "last mile" between the LEC and the customer premise.
Log	Collects system messages that provide information to the user on certain events or errors in the telephone system.
Loop Back	A diagnostic test in which a signal is transmitted across a medium while the sending device waits for its return. It is helpful in isolating problem devices.
Loop Start	Way of signaling initiation of a call by creating a loop across the two wires of a telephone pair.
Load Balancing	The practice of splitting communication into two (or more) routes. By balancing the traffic on each route, communication is made faster and more reliable.
LRN (Local Routing Number)	A 10-digit code that represents a specific carrier. This code is “attached” to each phone number to indicate which carrier the phone number currently is subscribed with for routing purposes.
LRQ	LOCATION REQUEST Message - A RAS message that a Gatekeeper/endpoint sends to another Gatekeeper requesting the location of an endpoint.
LRJ	LOCATION REJECT Message - A RAS message that a Gatekeeper/endpoint sends to the requesting Gatekeeper rejecting the LRQ.
Lumen	Unit of light flux.
MAC	Multiplexed Analog Components (TV)
MAC address	Hardware address for network-enabled devices that is set by the manufacturer of the device and cannot be changed. Thus, enabling globally distinct identification of the device.
Macintosh	The Macintosh (Mac) is a family of personal computers designed, manufactured, and sold by Apple Inc. (originally as Apple Computer, Inc.) since January 1984.
macOS (OS X)	macOS (previously Mac OS X and later OS X) is a proprietary graphical operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers.
Mailbox	Also Voice Mailbox or Inbox. A Software that automatically takes calls and provides the opportunity to the caller to leave a voicemail for the callee.
Main Cross-Connect	A cross-connect for the first level backbone cables, entrance cables, and equipment cables.
Master	The side in communications which initiates and controls the session. The "slave" is the other side that responds to the master's commands.
Mbps	Megabits per second. A unit of measure of data of 1,000,000 bits per second.
MCDN	Meridian Customer Defined Network
MCU	Multipoint Controller Unit. videoconferencing equipment which allows multiple individual videoconference units to connect together to form a multi-party videoconference session. See Bridge #2
MDF	Main Distribution Frame (tel)
Mega	A prefix denoting 1,000,000 (1 million). In data communications this term is used in describing the speed of data transfer in megabits per second, the bandwidth of a given system in megahertz.
Megabit Per Second (Mbps)	A measurement of the transmission speed of a piece of equipment or network equal to 1 million bits per second.
Megabyte (MB)	Megabytes is typically how the hard drive memory of computers are measured. Since hard drives are becoming so large in size, gigabyte's (GB) are used to measure them.
Megahertz (MHz)	A unit of frequency measurement equal to 1 million Hz or cycles per second. Megahertz is one measurement of bandwidth, or information carrying capacity of a network, cable or connectors. Generally, Hz should not be confused with Bps (bits per second).
MF signaling	In telephony, multi-frequency signaling (MF) is a type of signaling that was introduced by the Bell System after World War II. It uses a combination of audible tones for address (telephone number) transport and supervision signaling on trunk lines between central offices. The signaling is sent in-band over the same channel as the bearer channel used for voice traffic.
MGCP/MEGACO	Media Gateway Control Protocol/MEdia GAteway Controller - An IP telephony signaling protocol from the IETF. MGCP was the original protocol, which evolved into MEGACO. Both protocols are designed for implementation in IP phones that are cheaper than SIP or H.323 phones.
MIB	Management Information Base - An SNMP structure that describes the particular device being monitored.
MIL	MILitary standard (USA)
MILSPEC	MILitary SPECification (USA)
MIME	Multipurpose Internet Mail Extensions
MLP	Multi-layer protocol for data (in H.221). MLP data and audio can only be placed in the first 64Kb/s channels of a connection. T.120 must use the MLP or HMLP channel.
MLHG	Multi-Line Hunting. The ability of a switching system to connect calls to another phone in a group when other numbers in the group are busy. Types include serial or circular. Serial always begins with the number originally dialed and hunts to the next in line until the end of the group is reached. Circular, begins with the number originally dialed and hunts to the next through the entire group even if the originally dialed number is in the middle.
Modem	MOdulator-DEModulator
MP3	A coding format for digital audio developed largely by the Fraunhofer Society in Germany. MP3 uses lossy data-compression to encode data using inexact approximations and the partial discarding of data. This allows a large reduction in file sizes when compared to uncompressed audio.
MPEG	Motion Pictures Experts Group. Multimedia compression standard for professional and consumer applications such as digital video, digital audio and systems compression. MPEG compresses similar frames of video, tracks elements which change between frames and discards the redundant information.
MPEG-4	Moving Pictures Experts Group. MPEG is a series of standards designed to reduce the storage requirements of digital video. MPEG-4 provides the standardized technological elements for the integration of interactive graphics applications and interactive multimedia.
MSN	Multiple Subscriber Number - A method of incoming call routing in which a group of phone numbers is assigned to a particular ISDN line by the telephone company. PRI ISDN lines are usually assigned multiple numbers in the US and in Europe.
MTBF	Mean Time Between Failures
Multiplexing	The process of combining a number of individual channels into a common frequency band or into a common bit stream for transmission. The converse equipment or process for separating a multiplexed stream into individual channels is called a demultiplexer.
Multipoint	A call involving three or more parties.
Multipoint Videoconferencing	Videoconference with more than two sites. The sites must connect via a video bridge.
Multi-Unicast	Transmission of duplicate data streams, one to each used. In multi-unicast, multiple users request the same data from the same server at the same time. Contrast with IP multicast, unicast.
Music-on-Hold	An audio file is played to callers if they have to wait in a call queue or are set on hold.
NAT	Network Address Translation - NAT devices translate IP addresses so that users on a private network can see the public network, but public network users cannot see the private network users.
NC	Network Congestion (No Connection)
NANP	The North American Numbering Plan (NANP) is a telephone numbering plan for World Zone 1, which comprises twenty-five distinct regions in twenty countries primarily in North America, including the Caribbean. Some North American countries, most notably Mexico, do not participate in the NANP.
NANPA	North American Numbering Plan Administration – An organization that oversees the NANP for Canada, the US and it’s territories as well as some Caribbean countries.
Neighbor Gatekeeper	A mechanism by which the RADVISION H.323 Gatekeeper optimizes inter-zone communication. A list of Neighbor Gatekeepers and their IP addresses allows the Gatekeeper to resolve destination IP addresses when the source endpoint is not in the same zone as the destination endpoint.
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 communication links. The transmission medium can be physical (fiber optic cable) or wireless (satellite).
Network Load Balancing	See RAI/RAC
NIC	Network Interface Card
Night Service	After hours incoming calls are automatically redirected by the switchboard to telephones or central voice mail.
Noise	A random and/or persistent induction of unwanted electrical or radio frequency signals onto a cable which interferes with and/or degrades the quality of the signal.
Non-Composite Video Signal	A signal which contains only the picture signal and the blanking pulses.
NPA	Number Plan Area. The first three digits of the 10-digit NANP telephone number, commonly called the Area Code.
NPA-NXX	The first six digits of a NANP telephone number (or of an LRN). Eg: (555) 222-3333, the NPA is “555” and the NXX is “222”.
NPA-NXX-X	The NPA-NXX-X represents a pooled thousand block drawn from the NPA-NXX.
NXX	The three digits of a phone number immediately following the area code, also called the “exchange” or the “Central Switching Office Designation.
Nortel	Nortel Networks Corporation (Nortel), formerly Northern Telecom Limited, was a Canadian multinational telecommunications and data networking equipment manufacturer headquartered in Mississauga, Ontario, Canada.
Nortel Meridian	A private branch exchange telephone switching system. It provides advanced voice features, data connectivity, LAN communications, computer telephony integration (CTI), and information services for communication applications ranging from 60 to 80,000 lines.
NSF	Network Specific Facility - The Network Specific Facility Information Element (NSF IE) feature enables system administrators to coordinate their network and service requirements with Service Providers.
NTP	Network Time Protocol
NTP	Nortel Networks technical publication
NT1	Network termination equipment for ISDN BRI. Turns a U interface into an S/T interface. Not needed when connecting to most digital PBXs.
NTSC	National Television System Committee. Defined the 525 line color video frequency spectrum used in the US, Canada, Mexico, Japan and a few other countries.
NRAM	Non Volatile RAM
NRZ	Non Return to Zero
Null Modem	A small device (or cable) which permits two RS-232 data terminal devices (DTE) to communicate with each other directly, without using modems or other communication equipment (DCE). To achieve this, the most obvious connection is that the transmit (TD) signal of one device must be connected to the receive (RD) input of the other device (and vice versa).
NVRAM	Non-Volatile RAM
OC-1	Optical Carrier using a SONET Optical signal, capacity of 51.840 Mbps.
OC-3	Optical Carrier using a SONET Optical signal, capacity of 155 Mbps.
OC-12	Optical Carrier using a SONET Optical signal, capacity of 622.08 Mbps.
OC-48	Optical Carrier using a SONET Optical signal, capacity of 2.4 Gbps.
OEM	Original End-product Manufacturer
OSI model	The Open Systems Interconnection model is a conceptual model that characterises and standardises the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.
Ohm	A unit of resistance. The measurement of the opposition to the flow of direct current is resistance. One volt will cause 1 ampere to flow through 1 Ohm of resistance.
Ohms Law	The mathematical relationship between Ohms(R), volts(V) and Amps(I). Technically is states that current (I) is directly proportionate to voltage and inversely proportionate to resistance. The mathematical equations are: V = I x R or I = V/R or R = V/I.
Online Endpoint	When an endpoint registers with a Gatekeeper, the endpoint is active and ready to receive calls. By registering, the endpoint informs the Gatekeeper that it is online.
OQPSK	Offset Quad Phone Shift Keying
OTDR	Optical Time Domain Reflectometer
Outgoing Call	Call that leaves the internal network and leads to the outside world, becoming an external call.
Off-Hook	A telephone set in use – the handset is removed from its cradle, thus sending an electrical signal to the central office that a circuit needs to be opened.
Off-Premises System	Refers to a teleconferencing room or equipment located outside of a user organization’s facility; e.g., a video teleconferencing room operated by a vendor and available to the public for a fee.
Offline	Frequent synonym for being disconnected and consequently unreachable
On-Hook	The normal state of the phone in which the handset rests in the cradle and the circuit to the central office conducts no electrical signal.
Online	Frequent synonym for being connected and consequently reachable
Packet	A block of data used for transmission in packet-switched systems.
Packet Loss	During a transmission some of the data that is sent in packets are lost due to latency, congestion at a router or other network problems. It is specifically problematic to VoIP and even a small amount can result in significant voice degradation.
Packet Re-Ordering	Packet reordering ensures that all packets reach their destination in the correct sequential order.
Packet Switching	A network technology that breaks up a message into smaller packets for transmission and switches them to their required destination.
PAL	Phase Alternation by Line. The 625 line, 25 frame per second TV standard used in Western Europe, India, China, Argentina and parts of Africa. Brazil uses PAL-M, a 525 line variant.
Parent Filters	When the RADVISION Gatekeeper fails to resolve a destination address, the Gatekeeper searches for the destination first among its Children, then among its neighbors and then via its parent. Parent filters enable the Gatekeeper to avoid unnecessary searches among its Children and Neighbor Gatekeepers.
Party Number	The dialing number of an endpoint. This number can be a telephone number or a number used by other mechanisms on various networks, such as telex and ISDN.
PABX	Private Automatic Branch eXchange
PBX (also called PABX)	Private Branch Exchange. A telephone switching system usually installed at a business location as opposed to a service providers central office.
Paging	A service designed to deliver numeric or alphanumeric messaging to a person whose location is uncertain – paging services make use of radio communications.
Patch Cord	A length of cable with connectors on one or both ends used to join telecommunications links at a cross-connect.
Patch Panel	Connecting hardware that typically provides means to connect horizontal or backbone cables to an arrangement of fixed connectors that may be accessed using patch cords or equipment cords to form cross-connections or interconnections.
PCAP (Packet Capture)	An application programming interface (API) that allows for capturing network traffic. It can be useful in diagnosing connectivity issues on VoIP networks and equipment.
PCM	Pulse Code Modulation
PCMCIA	Personal Computer Memory Card International Association
PDN	Primary Directory Number. The telephone number that the physical telephone set is associated with. Generally, the first telephone number listed on a multi-line set.
PDN (alt.)	Public Data Network. A digital data network, usually X.25 protocol that is accessible by dialing a public telephone number.
Picture Signal	That portion of the composite video signal which lies above the blanking level and contains picture brightness information.
Pickup Group	Logical linking of several telephony devices into a pickup group allows to pickup calls from other phones of this group.
PINX	Private Integrated Services Network Exchange, eg, a PINX DN is used to detect and prevent tromboning.
PIP	Picture in Picture. In videoconferencing, the ability to view the near end (you) in a small, segmented portion of the monitor screen while viewing the far end (them) simultaneously in a larger segmented portion of the screen.
Pixel	The smallest controllable element that can be illuminated on a display screen. Related to resolution.
Plenum	A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.
Plenum Cable	Plenum rated cable has been specifically engineered to be placed in the plenum air space above a suspended ceiling. In the event of a fire, the components of the jacket and conductor insulation will not give off toxic fumes and are slower to burn. A plenum rated cable will have on it one or both of the following markings: FT-6 or CMP. Both of these markings are recognized in the United States and Canada.
Point to Point	A videoconference between only two points.
Point to Multipoint	A videoconference between one location to many.
POP	Point of Presence. A central office where the inter-exchange carrier's responsibilities for the line begins and the local exchange carrier's responsibility ends. Location of a communications carrier's switching or terminal equipment. (Cincinnati to AT&T)
Port	The Hardware connection of a device.
Porting	The procedure of transferring a DID (phone number) from one carrier to another.
PORTL	A pathway into and out of a computer or a network device, such as a switch or a router.
POTS	Plain Old Telephone Service. Dial tone.
Power over Ethernet (PoE)	Indicates devices that are powered through the network cable or can supply other devices themselves.
Predefined Endpoint	An endpoint entitled to register with a specified Gatekeeper.
Prefix	A prefix is a part of the dialing sequence used to access a service or conference type. See also Gateway supported prefixes and conferencing service.
PRA	Primary Rate Access (2Mb/s - ISDN)
Primary Rate Interface (T1 PRI)	An ISDN subscriber line (1.544 Mbps) with 24 total channels: twenty three 64 Kb/s B bearer (user) channels, and one 64 Kb/s D channel for signaling and synchronization. Used in North America and Asia
Primary Rate Interface (E1 PRI)	An ISDN subscriber line (2.048 Mbps) with 32 total channels: thirty 64 Kb/s B bearer (user) channels for voice or data, one 64 Kb/s D channel for signaling, and one clock channel for synchronization. Used in Europe and Australia.
Projection Television	A combination of lenses and / or mirrors that project an enlarged video picture on a screen.
Protocol	A set of rules and procedures for establishing and controlling the transmission on a line. The set of messages has specific formats for exchanging communications and assuring end-to-end integrity of links, circuits, messages, sessions and application processes.
Provider	Businesses that offer services allowing (among others) phone calls or internet connections.
Provisioning	Configuration of an IP phone through the IP telephony server, or PBX. An automated provisioning does not require manual configurations on the phone.
Proxy Server	An application that breaks the connection between sender and receiver. All input is forwarded out on a different port, closing a straight path between two networks and preventing a cracker from obtaining internal addresses and details of a private network.
PSDN	Public Switched Digital Network. A term used to describe the set of digital dial-up services offered by the carriers (IXC and LEC).
PSTN	Public Switched Telephone Network - The worldwide voice telephone network. Once only an analog system, the heart of most telephone networks today is all digital. In the US, most of the remaining analog lines are the ones from your house or office to the telephone company's central office.
PSK	Phase Shift Keying
PTT	Post, Telegraph and Telephone
PTZ	Pan-Tilt-Zoom. Camera functionality.
PT724	PictureTel's enhanced audio mode delivering 7 kHz bandwidth at 24Kb/s. Provides excellent audio quality using less bandwidth than industry standards. This allows for improved video and data transmission.
PWM	Pulse Width Modulation
Public Network	A network operated by the carriers (IXC and LEC) which includes network-based services and network-based switching.
Public Switched Telephony Network (PSTN)	Usually refers to analog and ISDN transmissions.
Px64	A common reference to the CCITT standards (H.261 et al.) which describe methods to allow for videoconferencing system interoperability.
Private Branch Exchange	See PBX.
Propagation Delay	The amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a cable or cabling.
Punch Down	A method for securing wire to a quick clip in which the insulated wire is placed in the terminal groove and pushed down with a special tool. As the wire is seated, the terminal displaces the wire insulation to make an electrical connection. The punch down operation may also trim the wire as it terminates. Also called a cut-down.
Punch down tool	Also called a punch tool, IDC tool, krone tool, BIX tool, etc, is a small hand tool used by telecommunication and network technicians. It is used for inserting wire into insulation-displacement connectors on punch down blocks, patch panels, keystone modules, and surface mount boxes (also known as biscuit jacks).
Q.931	A protocol for Call Signaling, consisting of Setup, Teardown and Disengage. Q.931 is included in the H.225.0 Recommendation.
Q.931 + H.245 Routed Mode	The routing of the Call Setup channel (Q.931) and the Control channel (H.245) through the Gatekeeper. See also Call Setup routing, Routed Mode.
QSIG	Q-Sig is the Euro ISDN based equivalent of DPNSS. Unlike DPNSS it is a regulated standard, but like DPNSS the feature list is optional after the basic of call set up and handling have been implemented, so the interoperation of any two switches will be dependant upon the common features of the implementations of the connected telephone systems.
QAM	Quadrature Amplitude Modulation
QCIF	Quarter Common Intermediate Format. The QCIF format employs half the spatial resolution of CIF (both horizontal and vertical) and is the mandatory H.261 format. During encoding, a QCIF picture is subdivided into 3 GOBs (Groups of Blocks) Versus CIFs 12 GOBs.
QOS	Quality of Service - The ability to define a level of performance in a data communications system. For example, the ATM networks specify modes of service that ensure optimum performance for traffic such as real-time voice and video.
QPSK	Quadrature/Quaternary Phase Shift Keying
Queue	A call queue puts incoming calls in line until someone is available and typically plays on-hold music to the callers in the meantime. Several agents can be assigned and logged into a queue in order to answer the calls together.
Radius	Remote Access Dial-In User Service - A server for authentication, authorization and accounting of endpoints and endpoint aliases.
RAI/RAC	Resource Available Indication / Resource Available Confirmation - The RAI/RAC function automatically manages load balancing on the network. RAI/RAC messages are exchanged between a Gatekeeper and a Gateway to determine whether the Gateway is available to receive calls.
RAID	Redundant Array of Inexpensive Disks
RAM	Random Access Memory
RARP	Reverse Address Resolution Protocol
RAS	A protocol for Registration, Admission and Status. In an H.322 audio or video system, the RAS is a control channel over which H.225.0 signaling messages are sent.
Raster	The scanned (illuminated) area of a television picture tube.
RBOC	Regional Bell Operated Company. The name given to the seven telephone companies created subsequent to the break-up of AT &T. Often, RBOC's own the local exchange carrier (LEC). For instance, Ameritech (RBOC) owns Ohio Bell (LEC).
RCF	REGISTRATION CONFIRM Message. A RAS message that a Gatekeeper sends to the calling endpoint accepting the RRQ.
Real-Time	The processing of information that returns a result so rapidly that the interaction appears to be instantaneous. Videoconferencing is an example of a real-time application.
Real-Time Streaming	Delivery of a real-time stream of a live videoconference while the conference is in progress.
Redundancy	See Gateway Redundancy
Registered Endpoint	A registered endpoint is an endpoint that has informed the Gatekeeper that it is online, active and ready to receive calls, and has received confirmation from the Gatekeeper of its registration request.
Request for Command (RFC)	RFC documents are official documents of internet specifications, communications protocols, procedures, and events, published by the Internet Engineering Task Force (IETF) and the Internet Society.
RFP	Request for proposal. A bid that specifies and describes a system in industry terminology which the vendors understand. An RFP will prompt vendors to respond to questions about installation, training, maintenance, warranty, purchase terms and other relevant issues.
RG-58	A 50 Ohm coaxial cable frequently used for radio frequency, low power, and possibly older network applications.
RG-59	A 75 Ohm coaxial cable used with Cable TV. It is the old standard for home installations, now installers are using the new RG6 cable.
RG-6	A 75 Ohm coaxial cable used with Cable TV, Satellite and High Definition TV. It is also becoming the minimal standard for home installations due to it's full frequency capacity.
RG-6, Quad Shield	A 75 Ohm coaxial cable used with Cable TV, Satellite and High Definition TV. It is also becoming the minimal standard for home installations due to it's full frequency capacity. This cable is quad shielded which will help prevent line interference and noise.
RGB	Method of transmitting video signals that feeds red, green and blue channels over separate wires; provides the highest quality video signal and is the format for most computer equipment.
Ring Group	A group of phone numbers, extensions or physical telephones that ring together, simultaneously, when one extension number or extension is dialed.
RIP	Router Information Protocol
RJ-11	Registered jack telephone connector. RJ-11 is the common connector for plugging a telephone into the wall and the handset into the telephone.
RJ-45	An 8 wire connector used to connect Ethernet connections in computers, routers and other Internet devices. This connector is slightly larger than a (RJ-11) telephone connector.
rlogin	Enables a user to log in on another server using TCP network port 513. rlogin communicates with a daemon, rlogind, on the remote host. rlogin is similar to the Telnet command, but is not as customizable and is able to connect only to Unix-like hosts.
RMON	Remote MONitoring
Robbed-bit Signaling (RBS)	The robbed-bit signal scheme is used in the super frame circuit (SF). It takes the least significant bit of each channel in every sixth frame and utilizes it to convey on or off hook, and busy signal status on telephone lines. The first bit of every six is called A bit, the second bit is called B bit.
Routed Mode	The routing of the Call Setup channel (Q.931) and the Control channel (H.245) through the Gatekeeper. See also Call Setup routing, Q.931 + H.245 Routed Mode.
Router	A device or setup that finds the best route between any two networks, even if there are several networks to traverse. Like bridges, remote sites cab be connected using routers over dedicated or switched lines to create WANs.
Routing	The way calls are passed through a telephone system as determined by the programming done when the system is set up.
RRJ	REGISTRATION REJECT message. A RAS message that a Gatekeeper sends to the requesting endpoint rejecting the RPQ.
RRQ	REGISTRATION REQUEST. A RAS message in which an endpoint identifies itself to a specific Gatekeeper and asks for service. The RRQ message binds the endpoint aliases-names or phone numbers- to the IP addresses of the endpoint.
RS-232	A serial connection used with computers, data terminals (printer) and modems. An RS-232 connection is good to about 50 feet at a 20Kbps transmission speed, using a 25 pin (DB25) cable. RS232 COM ports are configured as either a DTE (Data Terminal Equipment, eg: PC) port or a DCE (Data Communications Equipment, eg: Modem) port. A straight cable connects DTE to DCE.
RS-366	A standard for providing dialing commands to network access equipment. In a videoconferencing application, an RS366 links the video codec and the network access equipment in order to facilitate dialing from the video codec. (e.g., IMUX)
RSA	Rivest Shamir & Adleman (encryption)
RTC	Real Time Clock
RTF	Rich Text Format
RTOS	Real Time Operating System
RTP/RTCP	Real Time Transport Protocol / Real Time Control Protocol-RTP is an IP protocol that supports real-time transmission of voice and video. It is widely used for IP telephony. RTCP is a companion protocol that is used to maintain QoS.
RTP Redundancy	A method of overcoming packet loss by doubling packet payload without increasing the number of packets sent.
RTS	Request To Send
RTT	Round Trip Time
RX	Reception
RXD (RD)	Received Data
SC Connector	A type of fiber optic connector that uses a push to snap on / push to snap off connector. The SC connector can be used with both multimode and singlemode fiber.
SDN	Secondary Directory Number. A telephone number that is picked up on a telephone set, but which is a PDN on another instrument.
SDN (alt.)	Software Defined Network. A virtual private network.
SDSAF	Switched Digital Services Applications Forum. A consortium of equipment vendors, service providers and users, with the goal of advancing the state of switched digital services.
SCR	Silicon Controlled Rectifier
SCS	Silicon Controlled Switch
SCSI	Small Computer System Interface
ScTP	SCreened Twisted Pair (FTP)
SDF	System Data Format
SDH	Synchronous Digital Hierarchy (SDH) and synchronous optical network (SONET) refer to a group of fiber-optic transmission rates that can transport digital signals with different capacities.
SDLC	Synchronous Data Link Control
SDMA	Space Division Multiple Access
SDSL	Symmetric Digital Subscriber Line
SDU	Service Data Unit
SDTL	Station Directed Tie Line
SEAL	Simple and Efficient Adaptation Layer (AAL5 - ATM)
SECAM	SEquentiel Couleur Avec Memoire (TV). The 625 line, 25 frame per second color television system used in France, Eastern Europe, USSR and parts of Africa.
Secure Shell (SSH)	Network protocol to enable encrypted and secure connections to a remote network device and this way, for example, to access the console of the device.
Serial Interface	A channel that transfers digital data in a serial fashion, one bit after the other over one wire or fiber. The serial port on a PC is a serial interface that is used to attach modems and scanners. Serial interfaces may have multiple lines, but only one is used for data. See also V.35 and x.21.
Service Prefix	The prefix identifies the service and can usually be a numeric code, an alphanumeric string, a name, or phone number.
Service Provider	A telecommunications provider that owns circuit switching equipment.
Services	A service is a function that is supported by a subset of endpoints in a zone. Access a service by dialing a prefix attached to the name or phone number. Services allow you to dynamically add more resources, such as a Gateway, into the system. In RADVISION implementations you can define access privileges per endpoint for each service.
Secure File Transfer Protocol (SFTP)	An extension of the Secure Shell protocol (SSH) version 2.0 to provide secure file transfer capabilities.
SG4	PictureTel's proprietary Software Generation 4. Based on SG3; improvements include transmission over standard H.221 multiplex, better motion coding, and contrast enhancement.
Short Code	IP Office uses short codes to match the number dialed to an action. The number dialed (or part of it) can be used as a parameter.
Signaling	There are three analog signaling types, mainly used on trunk side: Start Dial signaling, Ground start signaling and E & M signaling. These are used in analog telephony as supervisory signaling.
Signaling or Signalling	US vs. UK spelling: one L in American English, two L's in British English.
Silence Suppression	Silence information within the audio stream can consume LAN bandwidth and burden MCU voice processing. Using compression techniques, Silence Suppression can greatly reduce the wasted bandwidth in a multipoint conference and on congested networks.
SIMM	Single In-line Memory Module
Simultaneous Ring	See Ring Group
Singlemode Optical Fiber	An optical fiber that will allow only one mode to propagate; this fiber is typically step-index fiber.
SINAD	SIgnal, Noise And Distortion
Single Station MCU	In RADVISION implementations, a solitary RADVISION MCU that is facilitating a conference.
SIP	Single In-line Package
SIP	Session Initiation Protocol - An IP telephony signaling protocol developed by the IETF. SIP is a text-based protocol that is suitable for integrated voice-data applications. SIP is designed for voice transmission and uses fewer resources and is considerably less complex than H.323.
SLA	Service-Level Agreement
Slave	The side in communications which responds to session commands. The "master" is the other side that initiates and controls the session.
SLIP	Serial Line Internet Protocol
SM	Single Mode (fiber)
SM	Surface-Mount
SMA	SubMiniature A connector (RF-FO)
SMD	Surface-Mounted Device
SMDS	Switched Multimegabit Data Service
SMF	Single Mode Fiber
Survivable Media Gateway (SMG)	A SMG will attempt to register with an Alternate Call Server in the event of the Primary Call Server not being reachable.
SMDR (Station Message Detail Reporting)	Information recorded by a computer attached to the phone system, providing cost accounting information such as the number of calls, both local and long-distance, made from an extension during a certain time period.
SMPTE	Society of Motion Pictures and Television Engineers
SMTP	Simple Message Transfer Protocol (Internet - RFC 822)
SNI	Switch Node Interface. The link(s) between a PPN and an EPN over which control information is passed. Phone calls can be routed over these facilities as well, but this is generally not the case at USC.
SNMP	Simple Network Management Protocol. Standard for retrieving and transmitting management information (configuration, control, performance monitoring, etc.). Information is formatted according to MIBs (Management Information Base.
Softphone	Software that provides telephony functions on a PC as an alternative to SIP-based desk phones.
SOH	Start Of Header (char 01 - 01H)
Speed Dial	Phone numbers or commands can be placed on speed dial keys of the telephone, allowing to call them by pressing a single key.
SPID	Service Provider Identification Number.
SPST	Single Pole Single Throw (switch)
SPX	Sequenced Packet Exchange (layer 4, Netware)
Sonet	Synchronous Optical Network
SQE	Signal Quality Error (Heartbeat) (Ethernet)
S/NR	Signal to Noise Ratio. Final relationship between the video or audio signal level to the noise level. Ratio of the signal power to the noise power in a specified bandwidth, expressed in dbW.
SQCIF	Sub Quarter Common Intermediate Format. A video format usually used to refer to video with dimensions of 88 x 72 pixels.
SS7 / CCS	Signaling System 7. An internationally standardized, general-purpose Common Channel Signaling protocol. It defines the signalingbackbone for the public switched telephone network.
Survivable Remote Gateway 50 (SRG50)	A Nortel survivable IP telephony branch office solution (BCM) that provides public switched telephone network (PSTN) failover for voice over IP (VoIP) networks.
SRT	Source Route Transport (Token Ring)
SRP	Source Routing Protocol
Still-Image Video	System by which still images are transmitted over standard telephone lines, usually allowing for real-time interaction between locations.
ST Connector	A fiber optic connector that uses twist-on / twist-off.
Stations	In the voice world, a station is any terminal equipment that utilizes a port on the switch. Generally, one port is used by one station.
STP	Shielded Twisted Pair.
Strowger	The name Strowger is used to describe mechanical step by step telephone systems. The name originates from the "founder" of automated telephony, Mr Almon Strowger. BT used to call Strowger exchanges, TXS. All UK Strowger exchanges have now been recovered and replaced by Digital types.
STX	Start of TeXt (char 02 - 02H)
Sub-Addressing	Sub-addressing is a one-stage DID dialing mechanism in which a phone sends two numbers. One number is for routing on the circuit-switched network. The other number is forwarded to the Gateway inside a Q.931 Sub-addressing Information Element for IP address resolution by the Gatekeeper.
Sub-Conference	The current version of the RADVISION MCU allows the creation of audio sub-conferences to which selected participants in an existing conference can be temporarily diverted. When the sub-conference is over, the participants return to the main conference.
Subnet	A subnet is a portion of an IP network defined by a subnet mask. Devices on the same subnet have the same subnet mask.
Supplementary Services	The ITU-T H.450 Recommendation comprises a number of separate Recommendations for implementing Supplementary Services, of the H.450.x series. For full details of the H.450.x Recommendations, please refer to the appropriate ITU documents.
Survivable Media Gateway (SMG)	A Geographic Redundancy feature, whereby a Media Gateway can register with an Alternate Call Server in the event of the Primary Call Server not being reachable.
Switch	A mechanical or solid state device that opens and closes circuits, changes operating parameters or selects paths for circuits on a space or time division basis.
Switch	A device that keeps a record of the MAC addresses of all devices connected to it and then channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination.
Switched 56	A dial-up network-based service providing a data channel operating at a rate of 56Kb/s. Also a type of network access line, used to provided access to switched 56 network services.
Switched 64	A dial-up network-based service providing a data channel operating at a rate of 64Kb/s.
Switched 384	A dial-up network-based service providing a data channel operating at a rate of 384Kb/s.
Switched 1536	A dial-up network-based service providing a data channel operating at a rate of 1536Kb/s.
Switched Network	Any network in which switching is present and is used to direct messages from the sender to the recipient. Usually, switching is accomplished by disconnecting and reconnecting lines in different configurations in order to set up a continuous pathway between the sender and the recipient.
Switch module	Generic term used to describe a cabinet(s) containing the memory, processors, circuitry, and equipment necessary to support a group of stations.
Switch Node Interface	See SNI.
System X	Processor controlled electronic digital telephone exchange used by BT throughout British Isles. Designed and produced in collaboration with GEC and Plessey.
System Y	Processor controlled electronic digital telephone exchange used by BT throughout British Isles. Made by Ericsson and also called Axe 10.
T1	A digital transmission link with the capacity of 1.544Mb/s, used in North America. Typically channelized in 24 DSO's, each capable of carrying a single voice conversation or data stream. Uses two pairs of twisted pair wires.
T1 Primary Rate Interface (T1 PRI)	T1 connections have 24 channels in total. Typically, for T1 ISDN (CCS) protocols, 23 channels are used as B-channels and 1 channel is used as a D-channel. For this reason, the frame structure of a T1 PRI connection is said to be 23B+1D where the D-channel is located on timeslot 23 (channels numbered from 0 to 23) and the remaining channels are used as B-channels. Hence; Channel 0-22 → B-Channel (Voice) Channel 23 → D-Channel (Signalling) For T1 CAS protocols (for which there is only one; T1 Robbed Bit), all 24 channels are used as B-channels.
T.120	Standard for data conferencing and conference control for interactive multimedia communication - multipoint & point-to-point.
T.120 Data Standard	Data sharing protocol for multipoint data communication in a multimedia conferencing environment. T.120 enables white board collaborations, file transfers, graphic presentations and application between participants in a conference.
T.126	T.120 still image transfer and annotation protocol.
T.127	T.120 binary file transfer protocol.
T.128	Formally called "T-share", used in multi-point data conferencing.
T3	Network facility with bandwidth of 44.736 MBPS, channelized to provide 28 T1s.
TAPI	Telephone Application Program Interface
Tariff	Documents filed by a regulated telephone company with a state public utility commission (PUC) or the Federal Communications Commission (FCC). Document details services, equipment and pricing publicly offered by the telephone company.
TAT	Trunk Anti-Tromboning, with TRO, detects and avoids needless trunk loops created by call transfers or call forwards.
Transfer	PBX function that allows to forward active calls to another callee. There are two types of transfers, blind (without notice) and attended (with notice). For blind transfers, the call is passed to the new callee without preliminary notification. Contrary, for attended transfer, the transferring party and the new callee first have a brief consultation whereas the caller is put on hold and hears music.
TCAP	Transaction Capabilities Application Part. TCAP is the application layer of the Transaction Capabilities protocol that is used for messages between end offices and remote databases.
TCM Loop	Time Compression Multiplexing (TCM) is the standard communication protocol used by Nortel digital telephones on a 2-wire tip and ring circuit. Each digital phone line terminates at a station port on a Digital Voice Card (DVC) in the PBX.
TCC	Telephone Country Code
TCM	Trellis Coded Modulation
TCP	Tape Carrier Package
TCP	Transmission Control Protocol (layer 4)
TCP/IP	Transmission Control Protocol / Internet Protocol. Transmission Control Protocol/Internet Protocol. A set of protocols developed by the Department of Defense to link dissimilar computers across many kinds of networks, including unreliable ones.
TCO	Total Cost of Ownership.
TCS4	TCS4 is a special routing method for incoming H.320 video calls. TCS4 allows direct inward dialing to an endpoint on the IP network via the Gateway when DID is not available.
TDM	A method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.
TDMA	A channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM)
TDR	Time Domain Reflectometry
Telco	Generic name for telephone companies.
Telecommunications	Communicating over a distance. Use of wire, radio, optical or other electromagnetic channels to transmit and receive signals for voice, data and video communications.
Telephone	Communication device, transmitting sounds, languages and video. Available for different transmission techniques such as SIP, ISDN and analog.
Telephone Connection	The technical infrastructure provided by a network operator to connect to the public switched telephone network (PSTN) and establish phone calls.
Telephony	The word used to describe the science of transmitting voice over a telecommunications network.
Telephony Server	Alternative term for PBX, and furthermore referring to the AskoziaPBX hardware systems (formerly also called appliances).
Telnet	Telnet is a client-server protocol, used to establish a connection to TCP port 23, where a Telnet server application (telnetd) is listening. Telnet, however, predates TCP/IP and was originally run over Network Control Program (NCP) protocols.
Text-to-Speech (TTS)	Texts are transformed into computer generated synthesised speech, for example as part of an IVR system.
TFTP	Trivial File Transfer Protocol
THD	Total Harmonic Distortion
TIA	Telecommunications Industries Association
TIA-568B	The standard which governs the installation of cabling and components in a commercial building. The full name is ANSI/TIA/EIA 568B, although it more commonly goes by 568B.
TIA-569	The standards document published by the TIA governing the design and installation of pathways and spaces for cable used in those pathways and spaces as they relate commercial buildings. The full name is ANSI/TIA/EIA 568A, although it more commonly goes by 569A.
TIFF	Tag Image File Format
Tone start	Analog 'start dial' signaling type, where the originating switch places trunk off hook, receiving switch generates dial tone and dial digits are transmitted.
Topology Islands	IP subnets, characterized by homogeneous and fast LAN connectivity. Dividing the network into islands enables a Gatekeeper to direct calls through the most optimal routes, thus avoiding slow connections or bottlenecks as much as possible.
TPKT	A standard way of defining blocks of data in a TCP stream, since TCP does not have delimiters. During configuration you can define the maximum number of TPKT channels allowed.
Transcoding	Audio transcoding is the conversion of one audio transmission format into another using various algorithms to achieve different audio quality levels at reduced bandwidth levels.
TTL	Time to Live. A set maximum amount of time a packet is allowed to propagate through the network before it is discarded. TTL is a time, typically in seconds, after which the fragment can be deleted by any device on the network.
Twisted Pair	A pair of wires used in transmission circuits and twisted about one another to minimize coupling with other circuits.
TCP/IP	Transmission Control Protocol / Internetworking Protocol. A protocol developed to allow dissimilar devices to communicate across many kinds of networks.
TG	Trunk Group. A quantity of network facilities that complete calls.
Tie	Also, Tie Line. A specific type of trunk that is used to connect two switches.
Tip and ring	Tip and ring are the names of the two conductors of an analog telephone line, named after the parts of the plug to which the wires were connected. In many European countries, tip and ring are referred to as the A and B wires.
Tip Conductor	A telephony term used to describe the conductor of a pair that is grounded at the central office when the line is idle. This term was originally coined from its position as the first (tip) conductor of a tip-ring-sleeve switchboard plug.
TRO	Trunk Route Optimisation is the process of determining the most cost-efficient route for the call.
Tromboning	See TAT and TRO
Trunk	A communication line between two switching systems. The term switching systems typically includes equipment in a central office (the telephone company) and PBXs. A tie trunk connects PBXs. Central office trunks connect a PBX to the switching system at the central office.
Trunks	Individual channels or circuits that can be grouped. This is the smallest denominator for a network facility.
Trunking	IAn IP PBX’s process of merging data from multiple calls into a single set of packets to reduce transmission overhead.
Trunk Group	IA number of telephone channels, which are functionally related. Most common is the Hunt Group. Other common types include Incoming Trunk Groups and Outgoing Trunk Groups.
TSR	Terminate and Stay Resident (DOS)
TTL	Transistor-Transistor Logic
TTX	TeleTeXt
TTY	TeleTYpe
Twisted Pair Cable	A cable consisting of individual conductors twisted in pairs around each other. The purpose of twisting the conductors around each other is to reduce the affects of crosstalk.
TXD (TD)	Transmitted Data
TX	Telex
TX	Transmission
TXT	TeXT
TWT	Traveling Wave Tube
UART	Universal Asynchronous Receiver - Transmitter
UCF	UNREGISTRATION CONFRIM Message - A RAS message that a Gatekeeper or an endpoint sends accepting the URQ.
UDP	User Datagram Protocol (layer 4) - A transport protocol within the TCP/IP protocol suite that is used in place of TCP when a reliable delivery is not required.
UHF	Ultra High Frequency (300-3000 MHz)
UMTS	Universal Mobile Telecommunications System
UPC	Universal Product Code (bar code)
UPS	Uninterruptible Power Supply
UPS	United Parcel Service (USA)
UPT	Universal Personal Telecommunications
URL	Universal Resource Locator (Internet)
Unicast	A means of transmitting a message from one station to another; contrast with IP.
Unrecognized Alias	An alias that is not in the registration database of the Gatekeeper.
Unregistered Endpoint	An endpoint that is no longer online and registered with a Gatekeeper.
URJ	UNREGISTRATION REJECT message. A RAS message that a Gatekeeper or an endpoint sends rejecting the URQ.
URL	Uniform Resource Locator - An Internet address. The address that defines the route to a file on a computer connected to the Internet.
URQ	UNREGISTRATION REQUEST Message. - A RAS message sent when an endpoint wishes to terminate its session with a Gatekeeper.
Umbilicals	Specialized connections between a remote module(s) and the main host in the 5ESS switch. Similar to a SNI facility, these carry control information.
UNI	User to Network Interface
USAT	Ultra-Small Aperture Terminal
USB	Universal Serial Bus (Intel)
USD	United States' Dollar
USDC	United States' Digital Communications
UT	Universal Time
UTC	Universal Time Coordinated
UTE	Union Technique de l'Electricit‰ (Paris)
UTP	Unshielded Twisted Pair (UTP) cable is used for networking and traditional telephones. There several different types (categories) of UTP cable, with CAT5e being the most popular.
UUCP	Unix to Unix Copy Protocol
UV	UltraViolet
V.35	An ITU standard for group band modems that achieve higher data rates by combining the bandwidth of several telephone circuits. Typically used for modem-to-multiplexer communication. See also serial interface and X.21
VBR	Variable Bit Rate
VCO	Voltage Controlled Oscillator
VCS	Video Conferencing System.
VDSL	Very-high-rate Digital Subscriber Line
Video Bit Rate	Bit rate is the speed at which bits are transmitted, in bits per second.
Video Bridge	Computerized switching system which allows multipoint videoconferencing.
Videoconferencing	The use of digital video transmission systems to communicate between sites using video and voice. Digital video transmission systems typically consist of camera, codec, network access equipment, video and audio system.
Video on Demand Streaming	Delivery of a Video on Demand stream to a viewer upon request at any given time. Contrast this to a real-time stream that is delivered when the conference is in progress.
VMS	Voice Message System
VOD	Video On Demand
Voicemail	Voice message by a caller that is recorded by the mailbox and can be listened to later by the callee.
Voicemail System	System that specifically supports the voice mail application and is connected to the telephone switch. Calls are passed between the two systems, which communicate with each other to light the light on your telephone when you have a message.
Voice-Activated Video Switching	Automatic switching of a video image viewed at each conference terminal according to the voice level of a each participant.
Voice Switched Video	Type of video conference in which the cameras are activated by voice signals to send a picture of a particular person in the group. Not all participants are seen at any one time in contrast to continuous presence video.
VOIP	Voice over Internet Protocol (VoIP) is a protocol optimized for the transmission of voice through the Internet or other packet switched networks. VoIP is often used abstractly to refer to the actual transmission of voice (rather than the protocol implementing it). VoIP is also known as IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband. "VoIP" is pronounced voyp.
Virtual Private Network (VPN)	Virtual Private Network - VPN modules create closed secure tunnels for communication between two firewalled LANs. VPN technology is one of the approached being used today for providing secure communications over IP networks.
Video Phone	A telephone with a video display that allows simultaneous video and audio transmission in real-time.
Video Codecs	Algorithms that compress and encode, or decompress and decode digital video. Once a video gets compressed to reduce its size and increase data transfer speed, it permanently loses some of it’s information, that is to say quality, dependent on the chosen video codec.
Video Telephony	The transmission of video data in parallel to speech during a telephone conversation by means of videophones.
VTR - VCR	Video Tape Recorder or Video Cassette Recorder. Equipment capable of recording or playing back pre-recorded video.
VoIP	Voice over IP. A technique that allows voice to be carried in a portion of the bandwidth of an Ethernet signal that is carrying IP traffic.
W3	World Wide Web (WWW)
W3C	World Wide Web Consortium
WAN	Wide Area Network. A data network typically extending a LAN outside a building or beyond a campus, over IXC or LEC lines to link other LAN's at remote sites. Typically created by using bridges or routers to connect geographically separated LANs.
Wavelength	The distance between adjacent peaks/crests in a sound wave or eletromagnetic wave.
Web Conferencing	Enables two or more logged in users to set up a typed, real-time, online conversation across the World Wide Web.
Whiteboard	A term used to describe the placement of shared documents on an on-screen "shared notebook". See also document sharing.
Wildcard Digit Manipulation	A mechanism which enables a Gatekeeper to manipulate an incoming call source number before searching for the destination endpoint.
Wink start	Analog 'start dial' signaling type, where the originating trunk goes off hook first, remote switch transmit off hook pulse, and originating switch transmits dial digits.
wpm	Words Per Minute
WORM	Write Once, Read Many
WRU	Who aRe yoU
WWAN	Wireless Wide Area Networks
WWW	World Wide Web
WYSIWYG	What You See Is What You Get
X.21	An ITU standard protocol for a circuit switched network. See also serial interface and V.35.
XMS	eXtended Memory Specification (>1024kB)
XOR	eXclusive OR
YIQ	Y(luminance) Intensity Q(crominance) (color NTSC)
XTP	eXpress Transfer Protocol
ZIF	Zero Insertion Force
Zoiper	Softphone supporting SIP and IAX.
Zone	An H.323 zone is a logical collection of terminals, Gateways and Multipoint Control Units (MCUs) managed by a single Gatekeeper. A zone must include at least one terminal and may include several LAN segments connected by routers. See also Gatekeeper Zone.
Zone Prefix	Zone prefixes are similar to telephone are codes. If an endpoint in a zone dials a zone prefix before its number, and the Gatekeeper cannot resolve it in its zone, the Gatekeeper attempts to locate and route the call to the appropriate zone of the Neighbor Gatekeeper.