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Transfer an existing call to another telephone number after first consulting with the dialed party before the user hangs up.

Automated receptionist. Calls made to specific number cause a greeting to be played asking for the extension number of the person they wish to reach. The call will be transferred to the extension number entered.

Bandwidth is often used as a synonym for data transfer rate - the amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps).

Back-to-Back User Agent. SIP based logical entity that can receive and process INVITE messages as a SIP User Agent Server (UAS). It also acts as a SIP User Agent Client (UAC) that determines how the request should be answered and how to initiate outbound calls.Unlike a SIP proxy server, the B2BUA maintains complete call state and participates in all call requests.

Busy Call Forwarding

When dialed party's line is busy, the call is automatically transferred to a predetermined number.

Place a call on hold temporarily while you place a second call or answer another call.

Delivers the incoming call to the next available station or group when the called station in the group is unanswered.

Call Detail Record (CDR)

Information regarding a single call collected from the switch and available as an automatically generated downloadable report for a requested time period. The report contains information on the number of calls, call duration, call origination and destination, and billed amount.

The time interval between when the phone is taken off the hook and when it is put back on the hook.

The length of time, measured in seconds, required to establish a call between users.

A long distance company which uses primarily its own transmission facilities, as opposed to resellers which lease or buy most or all transmission facilities from carriers. Many people refer to any type of long distance company, whether it has its own network or not, as a carrier, so the term is not as restrictive as it used to be.

A type of network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Ordinary voice phone service is circuit-switched. The telephone company reserves a specific physical path to the number you are calling for the duration of your call. During that time, no one else can use the physical lines involved.

AT&T's name for the type of switch used in a telephone tandem office. In the past, Class 4 switches dealt only with high-speed, four-wire T1, T3 and OC-3 connections in contrast to two-wire local lines on Class 5 switches. Today, all switches support four-wire lines.

AT&T's name for the type of switch used in a local telephone end office. It provides customer services such as call waiting and call forwarding. In the past, a Class 5 switch implied two-wire ports from the customer and four-wire ports out the back end. Today, all switches support four-wire lines.

Voice encoding/decoding mechanism. Codecs are used to compress the voice signal into data packets. Each codec has different bandwidth requirements. The most popular codecs are: G.729, G.729A, G.723.1, G711A-Law, and G.711mU-Law.

Competitive Local Exchange Carrier (CLEC)

A U.S. telephone 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 (LEC) that were providing local service when the Telecommunications Act of 1996 was enacted.

A device used to connect multiple parties over the phone. A proctor or operator can man conference bridges, or the can be supervised. There are both stand-alone conference bridges and conference bridge functions built in to some PBXs (Private Branch Exchange). These systems have circuitry for summing and balancing the energy (noise) on each channel so everyone can hear each other. More sophisticated conference bridges have the ability to "idle" the transmit side of channels of non-speaking parties. Some conference bridges use "clVoxising" to idle or reject the input of touch tones or other signals.

Computer Telephony Integration. Telephone systems utilizing computer technology.

DID Direct Inward Dialing

The ability to make a telephone call directly into an internal extension without having to go through the operator.

DNIS Dialed Number Identification Service

A telephone function that sends the dialed telephone number to the answering service.

DTMF (Dual-tone multifrequency)

The system used by touch-tone telephones. DTMF assigns a specific frequency (made up of two separate tones) to each key so that it can easily be identified by a microprocessor. This is basically the technology behind touch tone dialing.

The international public telecommunication numbering plan. An E.164 number uniquely identifies a public network termination point and typically consists of three fields, CC (country code), NDC (national destination code), and SN (subscriber number), up to 15 digits in total.

The designation for the 2.048Mbps. ITU standard for Europe's 30-channel digital telephone service. It is the European version of T-1 (DS-1). The bandwidth is divided into two signaling channels (channels 15 and 31 starting from 0) and thirty bearer (voice channels). A&B bit signaling (robbed bit signaling) is not used here. E-1 uses one of the control channels for signaling and the other for clock synchronization.

SIP or H.323 terminal or Gateway. An endpoint can call and be called. It generates and terminates the information stream.

Facility-based carrier

A long-distance service provider that owns its own physical facilities. The bulk of the long-distance companies are resellers.

A feature that allows calls to find you wherever you are, ringing multiple phones (such as your cell phone, home phone, and work phone) all at once.

(foreign exchange office) is the interface on a VOIP device for connecting to an analog PBX extension.

(foreign exchange station) is the interface on a VOIP device for connecting directly to phones, faxes, and CO ports on PBXs or key telephone systems.

An ITU-T PCM half-duplex codec that uses either A-law or U-law compression (64 kbps, high quality, minimum processor load).

An ITU-T double rate CELP codec (6.4/5.3 kbps, medium quality, high processor load).

An ITU-T ACELP codec (8 kbps, medium quality, high processor load).

A device or computer that controls one or more gateways within a 'zone'. Gatekeepers are responsible for routing all calls to/from the gateways in a non-point-to-point situation. Gatekeepers can communicate with other gatekeepers, but usually only between those of the same manufacturer.

A gateway is basically a protocol converter, i.e. a network point that connects networks using different protocols so that data can be exchanged seamlessly between endpoints. For example, a POTS-to-VoIP Gateway connects PSTNs and packet-switched networks, translating the media into IP packets, so that "legacy" telephony becomes Voice-over-IP.

An ITU-T standard for handling video, data and voice call information. This standard was originally proposed for the PictureTel system, which allowed video/voice calls, but has been enlarged to encompass many types of media devices. This 'protocol' is actually a umbrella for multiple protocols, each responsible for different items such as packet format and transmission, video codecs, voice codecs, call signaling, conferencing, etc. Version 1 was formally approved in 1996 and the latest, version 4, was approved in November 2000.

Incumbent Local Exchange Carrier (ILEC)

A U.S. telephone company that was providing local service when the Telecommunications Act of 1996 was enacted. ILECs include the regional Bell operating companies. A "local exchange" is a carriers local "central office", where residential and business lines terminate. Local exchanges connect to other local exchanges within a local access and transport area or to interexchange carriers such as long-distance carriers like AT&T and Sprint.

Interexchange Carrier (IXC or IEC)

Synonymous in common usage with "long-distance carrier", an interexchange carrier (IXC) is a telephone company that provides connections between local exchanges in different geographic areas. Under the federal Telecommunications Act, an IXC carries communications traffic across LATA boundaries. BOCs, at this time, are only permitted to carry communications within LATA boundaries.

Any means of transmitting the human voice (real time or close to real time) over the internet. There are several components: 1) On the client side, a multimedia-equipped PC with special client software will digitize your voice. This can be done with a voice modem or other voice encoding method; 2) A direct or dial-up connection to the internet allows your voice to be transmitted in packet form to its destination; 3) Connection with the far side is achieved by IP address search, common servers or beacons to identify the called party (and to "ring" that person's phone); 4) A similar arrangement on the far end completes the call and allows both parties to speak. There are also PSTN/Internet gateways that allow regular telephone callers to make Phone-to-Internet-to-Phone connections. There are PC-to-Phone connections and Phone-to-PC connections.

Internet Service Provider. A business that provides subscriber-based access to the Internet. Subscribers can be individuals or businesses. According to Jack Rickard, publisher of Boardwatch Magazine, ISPs operate at the fourth or lowest level of the Internet. At the third level, regional providers aggregate traffic from lower-order ISPs to the second, backbone level. The highest level in North America is the NAP (Network Access Point), which act as peer-to-peer interconnection points for the largest backbones. There are three "official" NAPs located in San Francisco, Chicago and Pennsauken, New Jersey. ISPs use both Internet Routers, Servers and Rack-Mounted modems to provide a variety of services including Web Site hosting, FTP service, e-mail accounts, unified messaging, audio and video broadcasting and in some cases - Internet Telephony and Fax Gateway service.

The Internet Engineering Task Force is the organization responsible for defining standards that affect or use the IP network.

Internet Protocol (IP)

The method by which data is sent from one computer to another on the Internet.

Integrated Services Digital Network (ISDN)

A point-to-point signaling protocol designed to interface PBX equipment with central office switches.

IP Centrex delivers such services as call hold, call transfer, last number look-up and redial, call forward, three-way calling, but does it on a packet-based network.

IP PBX is a customer premises telephone system that manages telephones in the enterprise and acts as the gateway to external networks. Unlike a conventional PBX that requires two separate networks, one each for data and voice, an IP PBX is based on converged networks that enable true one-wire to the desktop connection. An IP PBX can be used with IP phones, softphones and traditional phones connected to Ethernet adapters (ATA) or PCs.

(Internet Protocol telephony, also known as Voice over IP Telephony) A general term for the technologies that use the Internet Protocol's packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN). The basic steps involved in originating an IP Telephony call are conversion of the analog voice signal to digital format and compression/translation of the signal into Internet protocol (IP) packets for transmission over the Internet or other packet-switched networks; the process is reversed at the receiving end. The terms IP Telephony and Internet Telephony are often used to mean the same; however, they are not 100 per cent interchangeable, since Internet is only a subcase of packet-switched networks. For users who have free or fixed-price Internet access, IP Telephony software essentially provides free telephone calls anywhere in the world. However, the challenge of IP Telephony is maintaining the quality of service expected by subscribers. Session border controllers resolve this issue by providing quality assurance comparable to legacy telephone systems.

Internet Telephony Service Provider.

International Telecommunications Unionthe international standards organization for all types of radio and telephony telecommunications.

International Telecommunications UnionTelecommunications sector. The part of the ITU responsible for both circuit-switched and packet-switched telecommunications.

Interactive Voice Response is a software application that accepts a combination of voice telephone input and touch-tone keypad selection and provides appropriate responses in the form of voice, fax, callback, e-mail and perhaps other media. IVR is usually part of a larger application that includes database access. Common IVR applications include: bank and stock account balances and transfers, surveys and polls, caller authorization centers (for example, the MCCP), etc.

(Also called Delay) The amount of time it takes a Packet to travel from source to destination. Together, Latency and Bandwidth define the speed and capacity of a network.

Local Access and Transport Area (LATA)

Defines that area, in a state served by a Bell telephone company, in which, under current federal Telecommunications Act rules, the company can provide service. Each Service Area may include one or more area codes or share a common area code. A connection between two local exchanges within the LATA is referred to as intraLATA. A connection between a carrier in one LATA to a carrier in another LATA is referred to as interLATA or 'long-distance' service.

Long Distance Carrier

A telephone company that provides connections between local exchanges in different geographic areas. Long-distance carriers provide interlocal access and transport area (interLATA) service as described in the Telecommunications Act of 1996. In the U.S., long distance carriers are called interexchange carriers (IXCs).

Local Exchange Carrier (LEC)

A public telephone company in the U.S. that provides ordinary local voice-grade telecommunications service under regulation within a specified service area. Some of the largest LECs are the 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 in 1983. In addition to the Bell companies, there are a number of independent LECs, such as GTE.

Mean opinion score (MOS)

A measurement of the subjective quality of human speech, represented as a rating index. MOS is derived by taking the average of numerical scores given by juries to rate quality and using it as a quantitative indicator of system performance.

The IETF name for the ITU-T H.248 protocol standard recommendation for controlling a media gateway when connecting telephone calls between a LAN and the PSTN. It handles many telephony issues such as redundant MGC systems that MGCP does not address. The Megaco protocol is similar to the MGCP protocol but is not backward-compatible with it, meaning a system using Megaco will not interoperate with a system using MGCP.

Media Gateway Control Protocol (MGCP)

A protocol designed to control various devices that can handle different types of media, e.g., voice, video, data, etc. It is designed to allow a Media Gateway Controller (MGC) to control one or more unintelligent Media Gateway (MG) devices.

Any device, such as a circuit-switched or IP gateway that converts data from the format required for one type of network to the format required for another. As defined in the Internet Engineering Task Force (IETF), a media gateway might terminate channels from a circuit-switched network as well as streaming media from a packet-switched network. Data input could be audio, video, or real-time multi-point communications, which the media gateway would handle simultaneously. The media gateway controller is sometimes called a softswitch.

Media Gateway Controller

A device that controls one or more media gateways and has enough intelligence to be able to control nearly all aspects of each media gateway, but does not have enough intelligence to control an entire call.

In computer telephony, any means of message store and forward. This includes fax mail, voice mail and broadcast messaging. This horizontal application is the most popular of all other voice solutions. Messaging systems provide for the store and forward of "non-real time" communication. For example, a recorded voice message can be stored for later play back either locally or remotely, or a fax can be received and stored before it is re-transmitted to the ultimate recipient. Messages, then, can vary in content and media type - the distinction being that they are recorded or stored for pick up in the future. The time between original storage and retrieval of a message can be created and stored by a sales manager for later retrieval by multiple (worldwide) sales people. The sales staff can listen to the message at different times over an extended period. This is due to the nature if random retrieval by the recipients in their respective time zones. Messaging systems are a kind of "shared tenant" answering machine, because messages that were intended for as many as a thousand or more users can be stored and controlled by the same system. If a community of users agree on some basic ground rules, messages can be shared, forwarded, and distributed to multiple recipients in the same fashion as e-mail.

A term used to refer to the PSTN network of other countries. It comes from the abbreviation for Post, Telephone and Telegraph, which used to be the government-owned company within other countries that owned and managed the national postal, telephone and telegraph systems.

A technique for routing data through a network by encapsulating the data in packets, labeling them with addresses and routing information (the packet header), and then routing the packets over various physical circuits (often times different for each packet) until they reach their intended destination. By breaking communication down into packets, packed-switched networks allow the same data path to be shared among many users in the network. Most traffic over the Internet uses packet switching.

Post-dial delay (PDD)

The time interval between when the caller presses the last digit of a number and when the phone on the other end begins to ring. It is the basic quantifier for routing speed as perceived by the user.

Point of Presence, equivalent of a local phone company's central office. The place your long distance carrier terminates your long distance lines just before those lines are connected to your local phone company's lines, or to your own direct hookup.

Plain Old Telephone Service. The term refers to the standard telephone service that most homes use. The POTS network is also called the PSTN.

Private Branch Exchange (PBX)

A very small, specialized switch similar that permits attached telephones to call each other using shorter numbers, and requires the caller to select an 'outside line' in order to call through the PSTN.

Public Switched Telephone Network (PSTN)

The world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. The PSTN is the aggregation of TDM circuit-switched telephone networks that has evolved from the days of Alexander Graham Bell. Today, it is almost entirely digital in technology except for the final link from the central (local) telephone office to the user. It is also referred to as the Plain Old Telephone Service (POTS) or the Switched Circuit Network (SCN).

ISDN connection control protocol, roughly comparable to TCP in the Internet protocol stack. Q.931 doesn't provide flow control or perform retransmission, because the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates bandwidth in fixed increments of 64 kbps. Q.931 does manage connection setup and breakdown. In H.323 scenario, this protocol is encapsulated in TCP and sent to port 1720.

A subjective rating of telephone communications quality in which listeners judge transmissions by qualifiers, such as excellent, good, fair, poor, or unsatisfactory.

Regional Bell operating company (RBOC) is a term describing one of the U.S. regional telephone companies (or their successors) that were created as a result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983. The seven original regional Bell operating companies were Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Bell, Southwestern Bell, and US WEST. Each of these companies owned at least two Bell operating companies (Bell operating company). The BOCs were given the right to provide local phone service while AT&T was allowed to retain its long-distance service. The RBOCs and their constituent BOCs are part of the class of local exchange carriers (LECs).

In addition to the RBOCs, there are more than 100 other franchised local telephone companies classed as local exchange carriers. Competitive local exchange carriers (CLECs) are additional companies allowed to compete with the LECs. These include AT&T in some localities and power companies. An interexchange carrier (IXC) is a long-distance carrier that carries traffic between LECs.

Under the Telecommunications Act of 1996, RBOCs and LECs are allowed to compete for long-distance telephone traffic under certain circumstances. RBOCs are generally in competition for digital data and Internet traffic with wireless service providers and cable TV companies. RBOCs are gradually making available new telephone carrier technologies such as ISDN and DSL.

A hardware and software system that directs data packets entering the router toward their intended destinations. Routers have various physical interfaces such as 100baseT Ethernet, T1, E1, DS3, OC-3, etc. Routing is based upon the destination address contained within the header of the IP data packet.

Resource Reservation Protocol. Protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams they want to receive. RSVP depends on IPv6. Also known as Resource Reservation Setup Protocol.

Real-Time Transport Protocol. Commonly used with IP networks. RTP is designed to provide end-to-end network transport functions for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP provides such services as payload type identification, sequence numbering, timestamping, and delivery monitoring to real-time applications.

Session border controller (SBC)

A new category of network equipment that enables interactive communications across IP network borders. SBCs closely integrate signaling and media control and serve as a transit point for all signaling and media streams going through the service provider's network. The ability to traverse firewalls and network address translators ensures ubiquity of network reach, whilst advanced routing and interworking capabilities maintain mission-critical quality of service.

Session Initiation Protocol (SIP)

A protocol designed to allow personal computers to place telephone calls on the Internet. It is often used by devices on the Internet and is currently used for telephone calls, most often 'SIP-enabled' telephones.

Signaling System 7 (SS7)

The international data network and signaling protocols that control the PSTN voice circuits and calls, ensuring that calls are set up securely and efficiently. Although SS7 is an international telecommunications standard, it has country-by-country variations.

(Also referred to as media gateway controller or call agent). The generic name for a new approach to telephony switching that has evolved to enable transporting voice traffic over packet-switched networks. At the most basic level, a softswitch is defined as media gateway controller software that provides call control and resource management for a media gateway. Call control relates to the setup and termination of calls, including call routing. A softswitch also provides call authentication and authorization, and accounting services by accessing information available in an existing Signaling System 7 (SS7) network.

A programming interface that allows Windows client applications to access voice services on a server.

A 1.544 Mbps point-to-point dedicated, digital circuit provided by the telephone companies. The monthly cost is typically based on distance. T1 lines are widely used for private networks as well as interconnections between an organization's PBX or LAN and the telco. The first T1 line was tariffed by AT&T in January 1983. However, starting in the early 1960s, T1 was deployed in intercity trunks by AT&T to improve signal quality and make more efficient use of the network.

A T1 line uses two wire pairs (one for transmit, one for receive) and time division multiplexing (TDM) to interleave 24 64-Kbps voice or data channels. The standard T1 frame is 193 bits long, which holds 24 8-bit voice samples and one synchronization bit with 8,000 frames transmitted per second. T1 is not restricted to digital voice or to 64 Kbps data streams. Channels may be combined and the total 1.544 Mbps capacity can be broken up as required. See DS, T-carrier, bipolar transmission, D4 and ESF.

Time Division Multiplexing (TDM)

The technique by which circuit-switched networks (PSTN) carry multiple voice calls over a single physical circuit.

A communications channel between two points, typically referring to large-bandwidth telephone channels between switching centers that handle many simultaneous voice and data signals.

Trunking means that several connections in a network may be established simultaneously, and that setup of connections proceeds automatically using the channels available at the time in question. In this way many users may share a few connections, and if the number of connections is increased, the capacity of the network is increased more than proportionally. This means that an optimal trunking effect is obtained in very large networks.

User Agent. A SIP UA is a device that transmits SIP packets over IP.

VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.

In addition to IP, VoIP uses the real-time protocol (RTP) to help ensure that packets get delivered in a timely way. Using public networks, it is currently difficult to guarantee Quality of Service (QoS). Better service is possible with private networks managed by an enterprise or by an Internet telephony service provider (ITSP).

Service providers can use this application to connect enterprise and call center customers directly to their VoIP network. By bypassing local operators and toll charges, the VoIP Trunking application enables service providers to offer attractive termination rates for both domestic and international long distance calling. This application connects seamlessly to the enterprise/call center's PBX, allowing employees to make off-net calls at reduced rates.

Glossary