VOIP GLOSSARY

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VOIP GLOSSARY

VoIP Glossary

A
TERM	DEFINITION
3DES - Triple Data Encryption Standard	A stronger form of the Data Encryption Standard (DES), 3DES follows a pattern of encryption/decryption/encryption. 3DES has many different variations.
AAL1 - ATM adaptation layer 1	One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.
ABR - available bit rate	QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the status of the network and its capability to successfully deliver data.
AR - access rate	The maximum data rate of the access channel, typically referring to access to broadband networks and network services. (2) A Frame Relay term that addresses the maximum transmission rate supported by the access link into the network, and the port speed of the device (switch or router) at the edge of the carrier network. The AR defines the maximum rate for data transmission or receipt. See also CIR.
ADPCM - adaptive differential pulse code modulation	A waveform process by which analog voice samples are encoded into digital signals.
APC - adaptive predictive coding	A narrowband analog-to-digital conversion technique employing a one-level or multilevel sampling system in which the value of the signal at each sample time is adaptively predicted to be a linear function of the past values of the quantized signals. APC is related to LPC in that both use adaptive predictors. However, APC uses fewer prediction coefficients, thus requiring a higher bit-rate than LPC.
Ad-Hoc conference	A conference call feature where a conference is started by an initiator and only the initiator of the conference can add people into the conference.
ARQ - admission request	An RAS admission message defined as an attempt by an endpoint to initiate a call.
AIM - advanced integration module	A module in some Cisco routers that provides enhanced processing capabilities to the routers.
ARPA - Advanced Research Projects Agency	Research and development organization that is part of Department of Defense (DoD). ARPA is responsible for numerous technological advances in communications and networking. ARPA evolved into Defense Advanced Research Projects Agency (DARPA), and then back into ARPA again (in 1994).
AF - Assured Forwarding	A means of providing different levels of forwarding assurances for IP packets. This method is used by providers who offer differentiated services to their customers.
AMI - alternate mark inversion	Line-code modulation type used on T1 and E1 circuits. In AMI, marks (or ones) cause a pulse in alternating positive and negative directions, while zeros never pulse. Two pulses of the same polarity are not allowed. AMI requires that the sending device maintain ones density. Ones density is not maintained independently of the data stream. Sometimes called binary coded alternate mark inversion.
ANI - automatic number identification	SS7 feature in which a series of digits, either analog or digital, are included in the call, identifying the telephone number of the calling device. In other words, ANI identifies the number of the calling party. See also CLID.
ANSI - American National Standards Institute	A voluntary organization composed of corporate, government, and other members that coordinates standards-related activities, approves U.S. national standards, and develops positions for the United States in international standards organizations. ANSI helps develop international and U.S. standards relating to, among other things, communications and networking. ANSI is a member of the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO).
API - application programming interface	The means by which an application program talks to communications software. Standardized APIs allow application programs to be developed independently of the underlying method of communication. A set of standard software interrupts, calls, and data formats that computer application programs use to initiate contact with other devices (for example, network services, mainframe communications programs, or other program-to-program communications). Typically, APIs make it easier for software developers to create the links that an application needs to communicate with the operating system or with the network.
AS5300	A series of Cisco gateways that provide reliable, scalable, and feature-rich data and voice gateway functionality. The Cisco AS5300 Series Universal Gateways include the Cisco AS5300 Access Server/Voice Gateway and the Cisco AS5350 Universal Gateway.
ATM - Asynchronous Transfer Mode	The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media, such as E3, SONET, and T3.

B
TERM	DEFINITION
B8ZS - binary 8-zero substitution	Line-code modulation type used on T1 circuits. In B8ZS, marks (or ones) cause a pulse in alternating positive and negative directions, while zeros never pulse. Two pulses of the same polarity are not allowed, except when inserting a code to represent eight zeros. B8ZS maintains ones density by inserting a special code in place of eight consecutive zeros. The special code contains intentional violations of the bipolar pattern.
BRQ - bandwidth change request	RAS bandwidth control message sent by endpoint to gatekeeper requesting an increase/decrease in call bandwidth.
BC - Basic call	A call between two users that does not require Advanced Intelligent Network Release 1 features (e.g., a POTS call).
Bc - committed burst	Negotiated tariff metric in Frame Relay internetworks. The maximum amount of data (in bits) that a Frame Relay internetwork is committed to accept and transmit above the CIR. See also Be and CIR.
Be - excess burst	Negotiated tariff metric in Frame Relay internetworks. The number of bits that a Frame Relay internetwork attempts to transmit after Bc is accommodated. Be data, in general, is delivered with a lower probability than Bc data because Be data can be marked as DE by the network. See also Bc.
BOC - Bell operating company	BOC is a term for any of the 22 original companies (or their successors) that were created when AT&T was broken up in 1983 and given the right to provide local telephone service in a given geographic area. The companies had previously existed as subsidiaries of AT&T and were called the ”Bell System.” The purpose of the breakup was to create competition at both the local and long-distance service levels. BOCs compete with other, independent companies to sell local phone service. In certain areas, long-distance companies, including AT&T, can now compete for local service. Collectively, companies offering local phone service are referred to legally as local exchange carriers (LECs). BOCs are not allowed to manufacture equipment and were initially not allowed to provide long-distance service. The Telecommunications Act of 1996 now permits them to engage in long-distance business under certain circumstances. As of 1996, the BOCs consisted of original and successor companies to: Bell Telephone Company of Nevada, Illinois Bell, Indiana Bell, Michigan Bell, New England Telephone and Telegraph Company, New Jersey Bell, New York Telephone Company, U S West Communications Company, South Central Bell, Southern Bell, Southwestern Bell, Bell Telephone of Pennsylvania, The Chesapeake and Potomac Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The Chesapeake and Potomac Telephone Company of Virginia, The Diamond State Telephone Company, The Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, and the Wisconsin Telephone Company.
BHCA - busy hour call attempts	A traffic engineering term that refers to the number of call attempts made during the busiest hour of the day.
BLF - busy lampfield	A visual display of the status of all or some of your phones. Your BLF tells you if a phone is busy or on hold. Your BLF is typically attached to or part of your operator phone.
BVM - BRI voice module	An optional device for Cisco modular routers providing four ISDN BRI ports for connection to ISDN PBXs or PINXs. The BVM has four ISDN BRI ports for voice traffic. Each BRI port supports two voice channels (ISDN B channels) and one signaling channel (ISDN D channel).

C
TERM	DEFINITION
CLID - calling line ID	Information about the billing telephone number from which a call originated. The CLID value might be the entire telephone number, the area code, or the area code plus the local exchange. Also known as Caller ID.
CAS - channel associated signaling	The transmission of signaling information in association with the voice channel. In T1 networks, CAS signaling often is referred to as “robbed-bit” signaling because the network is robbing user bandwidth for other purposes.
CBR - constant bit rate	QoS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery.
CBWFQ - class-based weighted fair queuing	Congestion management mechanism that extends the standard WFQ functionality to provide support for user-defined traffic classes.
CCIS - common channel interoffice signaling	A technology that uses a common link to carry signaling information for a number of trunks. CCIS is similar to ITU-T SS6 protocol that operated at low bit rates (2.4, 4.8, and 9.6 kbps) and transmitted messages that were only 28 bits in length.
CCITT - Consultative Committee for International Telegraph and Telephone	Former name for the International organization responsible for the development of communications standards. Now called the ITU-T. See also ITU-T.
CCS - common channel signaling	Signaling system used in telephone networks that utilizes a statistical multiplexing protocol for signaling. A specified channel is exclusively designated to carry signaling information for all channels in the system. An example is ISDN or SS7. See also SS7.
CDVT - cell delay variation tolerance	In ATM, a QoS parameter for managing traffic that is specified when a connection is set up. In CBR transmissions, CDVT determines the level of jitter that is tolerable for the data samples taken by the PCR. See also CRB.
CELP - code excited linear prediction	Compression algorithm used in low bit-rate voice encoding. Used in ITU-T Recommendations G.728, G.729, G.723.1.
CO - central office	The local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs.
centum call seconds	Units used to measure traffic load. A CCS is 1/36th of an erlang. The formula for a centum call second is the number of calls per hour multiplied by their average duration in seconds, all divided by 100.
CES - circuit emulation service	Enables users to multiplex or to concentrate multiple circuit emulation streams for voice and video with packet data on a single high-speed ATM link without a separate ATM access multiplexer.
CID - channel ID	Designates the Frame Relay subchannel ID for Voice over Frame Relay.
CIR - committed information rate	The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics. See also Bc.
Cisco AVVID - Cisco Architecture for Voice, Video and Integrated Data	Cisco AVVID is the architecture for Voice, Video and Integrated Data. Cisco AVVID includes three components: infrastructure, such as switches and routers; clients, such as IP Phones, H.323 videoconferencing equipment, and PCs; and applications, such as call control, that use a common IP network.
Cisco CallManager	Software-based call-processing agent. It is a component of the Cisco IP telephony solution, part of Cisco AVVID. The software extends enterprise telephony features and functions to packet telephony network devices such as IP Phones, media processing devices, VoIP gateways, and multimedia applications.
Cisco ICM software	Cisco Intelligent Call Management software. Software, which delivers an integrated suite of contact center capabilities. Cisco ICM software provides intelligent queue management in a contact center environment. It enables improved queue management across a variety of ACDs from different vendors as well as integrating IVRs, database and desktop applications, and CTI solutions
Cisco IOS	Cisco Systems software that provides common functionality, scalability, and security for all products under the CiscoFusion architecture. Cisco IOS software allows centralized, integrated, and automated installation and management of internetworks while ensuring support for a wide variety of protocols, media, services, and platforms.
Cisco IPCC	Cisco IP Contact Center. An integrated suite of products that enables contact center agents using Cisco IP Phones to receive both TDM and VoIP calls. IPCC provides ACD and IVR capabilities in a single-vender IP suite. The IPCC can be implemented in a single-site environment or integrated into an enterprise-wide multisite contact center.
Cisco IP Phone	The Cisco family of IP Phones provides a complete range of intelligent communication systems that use the data network while providing the convenience and ease of use of a business telephone.
Cisco IP SoftPhone	A Windows-based application for the PC. Used as a standalone end station or in conjunction with the Cisco IP Phone, it provides mobility, directory integration, user interface, and a virtual conference room.
CLEC - competitive local exchange carrier	A company that builds and operates communication networks in metropolitan areas and provides its customers with an alternative to the local telephone company. In the United States, a CLEC is a company that competes with the already established local telephone business by providing its own network and switching. The term distinguishes new or potential competitors from established local exchange carriers (LECs) and arises from the Telecommunications Act of 1996, which was intended to promote competition among both long-distance and local phone service providers. North American Telecom and Winstar Communications are examples of CLECs, which are generally listed as simply “local exchange carriers.”
CLI - command-line interface	An interface that allows the user to interact with the operating system by entering commands and optional arguments. The UNIX operating system and Microsoft MS-DOS provide CLIs.
CLID - calling line ID	Information about the billing telephone number from which a call originated. The CLID value might be the entire telephone number, the area code, or the area code plus the local exchange. Also known as Caller ID.
CNG - comfort noise generation	While using VAD, the DSP at the destination emulates background noise from the source side, preventing the perception that a call is disconnected.
“Codebook” excitation index	Used by the receiver to look up a set of excitation values. A codebook is a set of rules that helps to determine what conditions indicate a Cisco device fault.
CPE - customer premises equipment	Terminating equipment, such as terminals, telephones, and modems, installed at customer sites, and connected to the telephone company network. (2) Any telephone equipment residing on the customer site.
CRC - cyclic redundancy check	Error-checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and compares the calculated remainder to a value stored in the frame by the sending node.
cross-connect	Cross connect is a connection scheme between cabling runs, subsystems, and equipment, using patch cords or jumpers that attach to connecting hardware on each end. Cross-connection is the attachment of one wire to another, usually by anchoring each wire to a connecting block and then placing a third wire between them so that an electrical connection is made. The TIA/EIA-568-A standard specifies that cross-connect cables (also called patch cords) are to be made out of stranded cable.
CRTP - Compressed Real-Time Transport Protocol	A type of header compression designed to reduce the IP/UDP/RTP headers to two bytes for most packets in the case where no UDP checksums are being sent, or four bytes with checksums.
CS-ACELP - Conjugate Structure Algebraic Code Excited Linear Prediction	CELP voice compression algorithm providing 8 kbps, or 8:1 compression, standardized in ITU-T Recommendation G.729 or G.729A.
CTI - computer telephony integration	The name given to the merger of traditional telecommunications (PBX) equipment with computers and computer applications. The use of caller ID to retrieve customer information automatically from a database is an example of a CTI application.

D
TERM	DEFINITION
DACS - digital access and crossconnect system	A digital cross-connect system that provides grooming, switching, and aggregation.
DCD - data carrier detect	Signal from the DCE (modem or printer) to the DTE (typically your PC), indicating that the modem is receiving a carrier signal from the DCE (modem) at the other end of the telephone circuit.
dB - decibel	Unit for measuring relative power ratios in terms of gain or loss. The rule of thumb to remember is that 10 dB indicates an increase (or a loss) by a factor of 10; 20 dB indicates an increase (or a loss) by a factor of 100; 30 dB indicates an increase (or a loss) by a factor of 1000.
DCE - data circuit-terminating equipment	Devices and connections of a communications network that comprise the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and typically provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE.
DDS - digital data service	A class of service that is offered by telecommunications companies to transport data rather than voice. Originally called Dataphone Digital Service by AT&T in the late 1970s.
DE bits - discard eligible bits	Bits that are used to tag Frame Relay frames that are eligible to be discarded if the network gets congested.
delay budget	The maximum amount of delay in data, voice, and video applications. The total end-to-end delay when engineering a VoIP implementation should not exceed the 150- to 200-ms delay budget.
Delay Dial	A signaling method in which the terminating side remains off hook until it is ready to receive address information. The off-hook interval is the delay dial signal.
DHCP - Dynamic Host Configuration Protocol	Provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when hosts no longer need them.
dial plan mapper	Provides the mapping of IP addresses to telephone numbers. After enough digits are accumulated to match a configured destination pattern, the dial plan mapper maps the IP host to a telephone number.
dial up	Modem access to a data network. The use of a dial or push-button telephone to create a telephone or data call. Dialup calls are usually billed by time of day, duration of call, and distance traveled. It is a connection to the Internet, or any network, where a modem and a standard telephone are used to make a connection between computers.
dialup remote access server	A remote access server is computer hardware that resides on a corporate LAN and into which employees dial on the PSTN to get access to their e-mail and to software and data on the corporate LAN (for example, status on customer orders). Remote access servers are also used by commercial service providers, such as ISPs, to allow their customers access into their networks. Remote access servers are typically measured by how many simultaneous dial-in users (on analog or digital lines) they can handle and whether they can work with cheaper digital circuits, such as T 1 and E 1 connections.
DPNSS - Digital Private Network Signaling System	A common-channel, message-oriented signaling protocol commonly used by PBXs.
drop and insert	Allows DS-0 channels from one T1 or E1 facility to be cross-connected digitally to DS-0 channels on another T1 or E1. By using this method, channel traffic is sent between a PBX and a CO PSTN switch or other telephony device, so that some PBX channels are directed for long-distance service through the PSTN while the router compresses others for interoffice VoIP calls. In addition, drop and insert can cross connect a telephony switch (from the CO or PSTN) to a channel bank for external analog connectivity. Also called TDM Cross-Connect. See DACS.
DRQ - disengage request	RAS message sent by the gateway to the gatekeeper during the process of a call. The gateway waits for the DCF message before it sends the setup message to the new destination gatekeeper.
DS0 - digital service level zero	Single timeslot on a DS1 (also known as T1) digital interface—that is, a 64-kbps, synchronous, full-duplex data channel, typically used for a single voice connection on a PBX. Also, a single timeslot on an E1.
DSI - digital speech interpolation	An algorithm that analyzes voice channels for silence. It suppresses the voice bits to conserve packet-line bandwidth and inserts a code to indicate to the far end that these bits have been removed. Also referred to as VAD.
DSL - digital subscriber line	Public network technology that delivers high bandwidth over conventional copper wiring at limited distances. There are four types of DSL: ADSL, HDSL, SDSL, and VDSL. All are provisioned via modem pairs, with one modem located at a central office and the other at the customer site. Because most DSL technologies do not use the whole bandwidth of the twisted pair, there is room remaining for a voice channel.
DSP - digital signal processor	An electronic circuit that compresses voice signals, generates tones, and decodes received compressions. DSPs can also emulate modems for purposes of fax relay.
DTE - data terminal equipment	Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocol translators, and multiplexers.
DTMF - dual tone multifrequency	Tones generated when a button is pressed on a telephone to convey address signaling.
DTR - data terminal ready	EIA/TIA-232 circuit that is activated to let the DCE know when the DTE is powered up and not in test mode.

E
TERM	DEFINITION
E&M - ear and mouth. Earth and Magneto. recEive and transMit.	(1) Trunking arrangement generally used for two-way switch-to-switch or switch-to-network connections. Cisco analog E&M interface is an 8-pin modular connector that allows connections to PBX trunk lines (tie-lines). E&M also is emulated on E1 and T1 digital interfaces. (2) A type of signaling traditionally used in the telecommunications industry. Indicates the use of a handset that corresponds to the ear (receiving) and mouth (transmitting) component of a telephone.
ECMA - European Computer Manufacturers Association	Group of European computer vendors who have done substantial OSI standardization work.
E-lead	The wiring arrangement on an E&M circuit in which the signal side sends its signaling information.
ESF - Extended Superframe	Framing type used on T1 circuits that consists of 24 frames of 193 bits each, with the 193rd bit providing framing information and other functions. ESF is an enhanced version of SF. See also SF.
ETSI - European Telecommunication Standards Institute	ETSI is a nonprofit organization producing voluntary telecommunications standards used throughout Europe.

F
TERM	DEFINITION
FDM - frequency-division multiplexing	Technique whereby information from multiple channels can be allocated bandwidth on a single wire based on frequency. An example is DSL.
FIFO - first-in/first-out	Refers to a buffering scheme where the first byte of data entering the buffer is the first byte retrieved by the CPU. In telephony, FIFO refers to a queuing scheme where the first calls received are the first calls processed.
flash memory	A special type of electrically erasable programmable read-only memory (EEPROM) that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their basic input/output system (BIOS) stored on a flash memory chip so that it can be updated easily if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.
four-wire	One of two distinct types of audio interfaces (two-wire or four-wire). The four-wire implementation provides separate paths for receiving and sending audio signals, consisting of T, R, and T1, R1 leads.
frame forwarding	Mechanism by which frame-based traffic, such as HDLC and SDLC, traverses an ATM network.
FRTS - Frame Relay traffic shaping	Queuing method that uses queues on a Frame Relay network to limit surges that can cause congestion. Data is buffered and sent into the network in regulated amounts to ensure that the traffic can fit within the promised traffic envelope for the particular connection.
FXO - Foreign Exchange Office	An FXO interface connects to the PSTN central office. Cisco FXO interface is an RJ-11 connector that allows an analog connection at the PSTN’s central office or to a station interface on a PBX.
FXS - Foreign Exchange Station	An FXS interface connects directly to a standard telephone and supplies ring, voltage, and dial tone. Cisco FXS interface is an RJ-11 connector that allows connections to basic telephone service equipment, key sets, and PBXs.

G
TERM	DEFINITION
gatekeeper	(1) The component of an H.323 telephony system that performs call address resolution, admission control, and subnet bandwidth management. (2) Telecommunications: H.323 entity on a LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper can provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways. A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup and request admission to a call from the gatekeeper.
gateway	An H.323 term that describes the component of a H.323 telephony network that translates between one technology and another, typically between traditional telephony and TCP/IP.
generic traffic shaping	Shapes traffic by reducing outbound traffic flow to avoid congestion by constraining traffic to a particular bit rate using the token bucket mechanism.
GRQ - gatekeeper discovery request	gatekeeper discovery request. RAS gatekeeper discovery message sent by endpoint to gatekeeper.

H
TERM	DEFINITION
HDB3 - high density binary 3	A line coding method used to maintain synchronization by ensuring a sufficient number of binary ones. HDB3 is used on E1 circuits.
HDLC - High-Level Data Link Control	Bit-oriented synchronous data-link-layer protocol developed by International Organization for Standardization (ISO). See also SDLC.
Hoot and Holler	A broadcast audio network used extensively by the brokerage industry for market updates and trading. Similar networks are used in publishing, transportation, power plants, and manufacturing.
HSRP - Hot Standby Router Protocol	Provides high network availability and transparent network topology changes. HSRP creates a hot standby router group with a lead router that services all packets sent to the hot standby address. Other routers in the group monitor the lead router, and if it fails, one of these standby routers inherits the lead position and the hot standby group address.
HTTP - Hypertext Transfer Protocol	The protocol used by web browsers and web servers to transfer files, such as text and graphic files.
Hyperterm software	Terminal emulation software.

I
TERM	DEFINITION
IETF - Internet Engineering Task Force	Task force consisting of over 80 working groups responsible for developing Internet standards
ILEC - incumbent local exchange carrier	An ILEC is a telephone company in the United States that was providing local service when the Telecommunications Act of 1996 was enacted. ILECs include the former Bell operating companies (BOCs), which were grouped into holding companies known collectively as the regional Bell operating companies (RBOCs) when the Bell System was broken up by a 1983 consent decree. ILECs are in contradistinction to competitive local exchange carriers (CLECs). A “local exchange” is the local “central office” of an LEC. Lines from homes and businesses terminate at a local exchange. Local exchanges connect to other local exchanges within a local access and transport area (LATA) or to inter-exchange carriers (IXCs), such as long-distance carriers AT&T, MCI, and Sprint.
IMAP - Internet Message Access Protocol	Method of accessing e-mail or bulletin board messages kept on a mail server that can be shared. IMAP permits client e-mail applications to access remote message stores as if they were local without actually transferring the message.
IMT - Inter-Machine Trunk	A means to give service providers access to more favorable tariffs and rates. In SS7 environments, IMTs terminate bearer traffic on the voice gateways.
IN - Intelligent Network	A network that provides IP routing, QoS, network access and control, and network management services.
IP - Internet Protocol	Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Defined in RFC 791.
IP cloud	The area in which data travels through an IP network. Illustrated in diagrams as a cloud.
IP precedence	A 3-bit value in the ToS byte used for assigning precedence to IP packets.
IP RTP priority	A Frame Relay feature that provides a strict priority queuing scheme on a Frame Relay PVC for delay-sensitive data, such as voice.
ISDN - Integrated Services Digital Network	Communication architecture offered by telephone companies that permits customers to access digital networks to carry data, voice, and other source traffic.
ISUP - ISDN User Part	SS7 protocol layer that defines the protocol used to prepare, manage, and release trunks that carry voice and data between calling and called parties under the auspice of ISDN.
ITU - International Telecommunication Union	An organization established by the United Nations to set international telecommunications standards and to allocate frequencies for specific uses.
ITU-T - International Telecommunication Union Telecommunication Standardization Sector	International body that develops worldwide standards for telecommunications technologies. The ITU-T carries out the functions of the former CCITT. See also CCITT.
IVR - interactive voice response	Term used to describe systems that provide information in the form of recorded messages over telephone lines in response to user input in the form of spoken words, or, more commonly, DTMF signaling. Examples include banks that allow you to check your balance from any telephone, and automated stock quote systems.
IXC - inter-exchange carrier	Common carrier providing long-distance connectivity between local access and transport areas (LATAs). The three major IXCs are AT&T, MCI, and Sprint, but several hundred IXCs offer long-distance service in the United States.