Asymmetric Digital Subscriber Line (ADSL): A type of broadband DSL service. Most homes and small business users are connected to an asymmetric DSL (ADSL) line. Download speeds are faster than upload speeds.

AHT (Average Hold Time): The average length of time between the moment a caller finishes dialing and the moment the call is answered or terminated.

Analog: An information form that is represented by a continuous and smoothly varying amplitude or frequency changes over a certain range such as voice or music.

ANI Automatic Number Identification: A telephone function that transmits the billing number of the incoming call (Caller ID, for example).

ANSI (American National Standards Institute): The American standardization body known for interface recommendations and standardization of programming languages. ANSI is a non-profit making, government-independent organization.

Area Code:
A three digit number that generally identifies a geographic area of a switch that provides service to a telephone device (for America and Canada).

AS (Autonomous System): A group of networks under mutual administration that share the same routing methodology.

ASP (Application Service Provider): An independent, third party provider of software-based services delivered to customers across a wide area network (WAN).

ASR (Answer-Seizure Ratio): The ratio of successfully connected calls to attempted calls (also called ‘Call Completion Rate’).

ATA (Analogue Telephone Adapter): Used to connect a standard telephone to a high-speed modem to facilitate VOIP and/or fax calls over the Internet.

ATM (Asynchronous Transfer Mode): A technology for switched, connection-

Backbone: A high-speed network spanning the world from one major metropolitan area to another.


Bandwidth: The maximum data carrying capacity of a transmission link. For networks, bandwidth is usually expressed in bits per second (bps). The higher the bandwidth available, the more information you are able to access in a given time.

Broadband: It is a general term for any Internet connection which receives and transmits at a bit rate of 100kbps or greater.

BLI Busy Lamp Indicator: A light or LED on a telephone that shows which line is in use.

Billing Increment: A call duration measurement unit usually expressed in seconds.

BLI (Busy Lamp Indicator): A light or LED on a telephone that shows which line is in use.


CALEA (Communications Assistance for Law Enforcement Act): A 1994 act that requires telecommunications services to provide wiretapping access. The act specifically excludes information services, so the question is whether VOIP is a telecommunications service, and thus covered by the act, or an information service, and thus exempted. VOIP providers are receiving pressure to comply with the act.

Call deflection: Call Deflection allows a called endpoint to redirect the unanswered call to another endpoint.

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.

Caller ID: Allows a person receiving a phone call to see who is calling before answering the phone. The caller’s telephone number and/or name is displayed either on your phone (if your phone has this feature).

Capacity: The maximum information carrying ability of a communications facility or system.

Cat5 Wiring: Category 5 unshielded twisted-pair wiring commonly used for 10BaseT and 100BaseT Ethernet networks.

Cat6 Wiring: Category 6 unshielded twisted-pair wiring commonly used for 1000BaseT (Gigabit) Ethernet networks.

Central Office (CO): The local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs.

Circuit-switched: Communication system that establishes a dedicated channel for each transmission. The copper-wire telephone system(POTS) uses circuit-switching, as do PBX systems. Dedicated channels mean strong reliability and low latency, but the downside is that only one type of communication can use the channel at any given time.

Class 5 switch: A Class 5 switch refers to a telephone switch or exchange located at the local telephone company’s central office, directly serving subscribers. Class 5 switch services include basic dial-tone, calling features, and additional digital and data services to subscribers using the local loop.

CLEC (Competitive Local Exchange Carrier): A telephone company that competes with the larger incumbent carriers (ILECs) through reselling the ILEC services and/or creating services that uses the ILEC’s infrastructure. The Regional Bells are ILECs; local phone companies are frequently CLECs.

Codec (Compression-decompression): A Codec converts analogue signals to a digital bit stream, and vice-versa.

Compression: Compression is used at anywhere from 1:1 to 12:1 ratios in VOIP applications to consume less bandwidth. The voice quality may decrease with increased compression ratios. The most popular codecs in VOIP are ITU-T G.723.1 and G.729 (AB).

Congestion: The situation in which the traffic presents on the network exceeds available network bandwidth/capacity.

Customer Premises Equipment (CPE): Terminating equipment (such as terminals, telephones, and modems) supplied by the telephone company, installed at customer sites and connected to the telephone company network. Can also refer to any telephone equipment residing on a customer site.


Data Packet: Data transmitted over the Internet occurs in blocks of digital data referred to as packets.

Digital: Information encoded into a stream of ones and zeroes.

Dial-peer (Addressable Call Endpoint): A software structure that binds a dialed digit string to a voice port or IP address of the destination gateway.

Dial-peer hunting: Process when the originating router tries to establish call on different dial peers if the originating router receives a user-busy invalid number or an unassigned-number disconnect cause code from a destination router.

DiffServ (Differentiated Services): A quality of service (QOS) protocol that prioritizes IP voice and data traffic to help preserve voice quality, even when network traffic is heavy.

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.

Downstream: The rate of data traveling from the server towards the user.

DSL (Digital Subscriber Line): DSL is a type of broadband Internet connection. It transmits data over the copper wires of the phone system, but bypasses circuit-switching allowing faster transmission than dial-up but slower than ADSL.

DTMF (Dual-Tone Multi Frequency): The type of audio signals generated when you press the buttons on a touch-tone telephone.

Duplex: Duplex communication is the transmission of voice and/or data signals that allows simultaneous 2-way communication.

Dynamic Jitter Buffer: Collects voice packets, stores them, and shifts them to the voice processor in evenly spaced intervals to reduce any distortion in the sound caused by delays in arriving packets.


E911 (Enhanced 911): Technology allowing 911 calls from cellular phones to be routed to the geographically correct emergency station (a.k.a. PSAP: Public Safety Answering Point). VOIP users currently have limited access to 911 services, and with some providers none, because VOIP is not geographically based.

E.164: 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.

Endpoint: SIP Terminal or Gateway. An endpoint can call and be called. It generates and terminates the information stream.

ENUM(TElephone NUmber Mapping) is a suite of protocols to unify the telephone numbering system E.164 with the Internet addressing system DNS by using an indirect lookup method, to obtain NAPTR records. The records are stored at a DNS database.

Ethernet: A digital networking system that is packet-based. Each client “broadcasts” their requests into the network and “hubs” or “switches” route the requests to their correct destinations. This process is called “packet switching”. Ethernet is the dominant technology used in computer network connections.


FCC (Federal Communications Commission): The regulator of telephone and telecommunications services in the United States. It’s not yet known the full extent to which the FCC will regulate VOIP communications. Part of the complication lies with determining the regulation of communications that begin or end on an FCC-regulated system, such as the standard telephone service.

Firewall: A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented as hardware, software, or a combination of both.

FoIP (Fax Over Internet Protocol): The term used for the technology that transports facsimiles over the Internet.

Full Duplex: Phone calls are full duplex, meaning both parties can speak at the same time. Not all voice cards can support full-duplex operation so if you are using your PC to talk rather than a telephone with an ATA, you may have a half-duplex voice card.

FXO (Foreign Exchange Office): Is the interface on a VOIP device for connecting to an analog PBX extension.

FXS (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.


G.711: An ITU-T PCM half-duplex codec that uses either A-law or U-law compression (64 kbps, high quality, minimum processor load).

G.723.1: An ITU-T double rate CELP codec (6.4/5.3 kbps, medium quality, high processor load).

G.726: An ITU-T ADPCM wave form codec (16/24/32/40 kbps, good quality, low processor load).

G.728: An ITU-T low delay CELP codec (16 kbps, medium quality, very high processor load).

G.729: An ITU-T ACELP codec (8 kbps, medium quality, high processor load).

G.7xx: A family of ITU standards for audio compression.

Gateway: In IP telephony, a network device that converts voice and fax calls, in real time, between the public switched telephone network (PSTN) and an IP network. The primary functions of an IP gateway include voice and fax compression/ decompression, packetization, call routing, and control signaling. Additional features may include interfaces to external controllers, such as Gatekeepers or Softswitches, billing systems, and network management systems.

Grace Period: The time interval at the beginning of a call, measured in seconds, that is not billed.


H.323: An ITU standard for real-time interactive voice and videoconferencing over LANs and the Internet. It is quickly being replaced by SIP.

Hairpin: Telephony term that means to send a call back in the direction that it came from. For example, if a call cannot be routed over IP to a gateway that is closer to the target telephone, the call typically is sent back out the local zone, back the way from which it came.

Half Duplex: Phone calls are half duplex, meaning only one party can talk and one party listen at the same time.

Hardware: All the physical parts of a telephone system or network.

Hop off: Point at which a call transitions from the IP network to the PSTN, typically at a gateway.

Hub: The hub is the common connection point for devices in a network-it has multiple ports to allow for those connections.

Incumbent Local Exchange Carrier (ILEC): Traditional telephone company. In the U.S., the Regional Bell Operation Companies (RBOCs) that were formed after the divestiture of AT&T and the Independent Operating Companies (IOCs) that usually are located in more rural areas or single cities are called ILECs.


IETF (Internet Engineering Task Force): One of two technical working bodies in the Internet Activities Board. The IETF meets three times a year to set technical standards for the Internet.

Internet: The current-day public and global computer network or “information super-highway.” The Internet is an outgrowth and combination of a variety of university and government sponsored computer networks. Today, the Internet is made up of millions upon millions of computers and sub-networks, almost entirely supported by commercial funds except in countries where deregulation has not occurred. The internet is the substrate and chief communications backbone for the World Wide Web (WWW), the “graphical interface” of the Internet.

IP Address (Internet Protocol Address): The numeric address for a computer or device that is connected to the Internet. Generally seen for example as

IP Centrex: 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 Telephony (Internet Protocol telephony): 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). Also commonly referred to as IP Phone Service, VoIP Phone Service, and Broadband Phone Service.

Internet Protocol (IP): Method or protocol by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet.

ISP (Internet Service Provider): A company that provides Internet access to consumers. When you connect to the Internet, you do so by connecting to your ISP, who is directly connected to the Internet.

ITSP (Internet Telephony Service Provider): Provider of IP telephony based services.

ITU-T: ITU standards for telecommunications.


Jitter: The variation in the amount of Latency among Packets being received.


Kbps (Kilobits per second): A measure of the speed of an Internet connection, giving a maximum figure for how much data it can send or receive in a given time period.

KBPS (KiloBytes per second): A measure of the speed of an Internet connection, giving a maximum figure for how much data it can send or receive in a given time period.


LAN (Local Area Network): A small computer network that connects together a small number of computers.

LAN (Local Area Network):A LAN is a group of computers and associated devices that share a common communications line or wireless link and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).

Latency: Also called Delay. The amount of time it takes a Packet to travel from source to destination. In telephony, the lower the latency, the better the communication. Together, Latency and Bandwidth define the speed and capacity of a network.


MGCP (Media Gateway Control Protocol): A protocol complementary to H.323 and SIP, designed to control media gateways from external call control elements in decomposed gateway architectures.

Modem: A device that allows a computer to transmit and receive data over telephone or cable lines. Computer information is stored digitally, however information transmitted over telephone lines is transmitted in analogue waves. A modem converts between analog and digital, and vice versa.


Network: A group of computers that are connected to each other, with or without wires.


Packets: In voice and data communications, piece of information transmitted over a packet switching network. Packets often follow different routes from source to destination, routing around bottlenecks or disruptions.

Packet-switched: Communication system that chops messages into small packets before sending them. All packets are addressed and coded so they can be recompiled at their destination. Each packet can follow its own path and therefore can work around problematic transmission segments.

PBX (Private Branch Exchange): An automated in-house telephone switching system that interconnects telephone extensions to each other, as well as to the outside telephone network.

POTS (Plain Old Telephone Service): Nothing more than a standard telephone line, the kind Ma Bell and then AT&T handled exclusively before the deregulation of the telephone industry.

Point-to-Point Protocol (PPP): Point-to-point protocol (PPP) is a connection oriented protocol that is established between two communication devices that encapsulates data packets (such as Internet packets) for transfer between two communication points. PPP allows end users (end points) to setup a logical connection and transfer data between communication points regardless of the underlying physical connection (such as Ethernet, ATM, or ISDN).

PRI Primary Rate Interface: An ISDN service that provides 23 64-Kbps B (Bearer) channels and one 64-Kbps D (Data) channel (23 B and D).

Protocol: A communications protocol is the set of standard rules for data representation, signaling, authentication, and error detection which is required to send information over a communications channel.

PSTN (Public Switched Telephone Network): This is the traditional phone system, using circuit switching to make and maintain connections for the duration of a phone call. Also referred to as the ‘landline’ network, it uses a copper wire network to carry analog voice data. It is also used for dial-up Internet and fax transmission.


QoS (Quality of Service): Measure of performance for a transmission system that reflects it’s

QOS (Quality of Service): Refers to the transmission quality and service availability of the voice call over a VOIP network. Latency, packet loss, network jitter, and many other factors contribute to QOS measurements.


RAS (Registration, Admission, Status): A management protocol between terminals and Gatekeepers.

Redundant: Redundant describes telephone system or network components, such switches, routers, and telecommunication links, that are installed to back up primary resources in case they fail.

RJ-11 connection: A modular connector that has 2 to 6 conductors that is commonly used to interconnect end-user telephone equipment.

RJ-45 connection: A standard 8 wire modular connector. RJ-45 connectors are commonly used in telephone and data communication systems.

Router: A device that connects two or more networks of computers together in Ethernet networks. Routers allow the connection of multiple computers at each end.

RSVP (Resource Reservation Protocol): A protocol that supports the reservation of resources across an IP network.

RTP (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 and video.


Symmetric DSL (SDSL): Refer to the DSL definition for more information on DSL. This connection, used mainly by small businesses, doesn’t allow you to use the phone at the same time, but the speed of receiving and sending data is the same.

SIP (Session Initiation Protocol): SIP is a signaling protocol used for establishing sessions in an IP network, such as a two-way telephone call or a conference session.

Softphone: A software application that gives you the ability to make and receive calls over the Internet using your PC and a headset or a microphone and speakers. A softphone’s interface can look like a traditional phone.

Softswitch: Software used to bridge a public switched telephone network and voice over Internet by separating the call control functions of a phone call from the media gateway (transport layer).

Software: Intangible instructions, composed entirely of data. Software includes all computer programs, applications, instructions or operating systems that tell a computer what to do.

Switch: A network device that connects two separate paths together.


T1 A 1.544-Mbps: point-to-point dedicated digital circuit provided by the telephone companies consisting of 24 64Kbps channels. Also referred to as a channelized T1.

TAPI (Telephony API): A programming interface that allows Windows client applications to access voice services on a server.

TCP (Transmission Control Protocol): Connection-oriented transport layer protocol that coordinates the transmission, reception, and retransmission of packets in a data network to ensure reliable communication. TCP is part of the TCP/IP protocol stack.

TOS Type of Service: A method of setting precedence for a particular type of traffic for QoS.

Trunk: 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: 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.


User Datagram Protocol (UDP): UDP is a high-level communication protocol that coordinates the one-way transmission of data in a packet data network. The UDP protocol coordinates the division of files or blocks of data information into packets and adds sequence information to the packets that are transmitted during a communication session using Internet Protocol (IP) addressing.

Universal Service: The availability of affordable telecommunications technology for all Americans, part of the 1966 Telecommunications Act, and regulated by the FCC. Current discussions revolve around the applicability of VOIP to universal services and whether or not VOIP providers should be taxed accordingly.

Upload: The process of transmitting a file or data from your home system to a remote destination via the Internet.

Upstream: The rate of data traveling from the user towards the server.


Voicemail: Similar to an answering machine used for conventional phones, except that the messages are saved and serviced at a central location, rather than at the individual telephone.

VOIP (Voice over Internet Protocol): VOIP is an IP telephony term for a set of facilities used to manage the delivery of voice information over the Internet. VOIP involves sending voice information in digital form in discrete packets rather than by using the traditional circuit-committed protocols of the public switched telephone network (PSTN).

VPN: Virtual Private Network. Enables IP traffic to travel securely over a public TCP/IP network by encrypting all traffic from one network to another. A VPN uses “tunneling” to encrypt all information at the IP level.

Virtual phone number: A feature of VOIP that allows you to attach additional phone numbers with different area codes to your basic VOIP service. This feature allows people to phone you without incurring long-distance charges from the same or adjacent non toll area codes. All outgoing calls, however, are billed as if coming from your main phone number.


Wi-Fi: A wireless Ethernet technology that allows people with laptop computers to connect to the internet while out and about at “hot spots”. It is also used to connect cordless phones with VOIP.

Wide Area Network (WAN): A communications network serving geographically separate areas. A WAN can be established by linking together two or more metropolitan area networks, which enables data terminals in one city to access data resources in another city or country.

WiMax: Commonly referred to as WiMAX or less commonly as WirelessMAN™ or the Air Interface Standard, IEEE 802.16 is a specification for fixed broadband wireless metropolitan access networks (MANs) that use a point-to-multipoint architecture. Published on April 8, 2002, the standard defines the use of bandwidth between the licensed 10GHz and 66GHz and between the 2GHZ and 11GHz (licensed and unlicensed) frequency ranges and defines a MAC layer that supports multiple physical layer specifications customized for the frequency band of use and their associated regulations. 802.16 supports very high bit rates in both uploading to and downloading from a base station up to a distance of 30 miles to handle such services as VoIP, IP connectivity and TDM voice and data.

Wireless: References the transmission of information (data, voice etc) over electromagnetic waves rather than over a wire connection.

World Wide Web (WWW): A service that resides on computers that are connected to the Internet and allows end users to access data that is stored on the computers using standard interface software (browsers). The WWW (commonly called the “web”) is associated with customers that use web browsers (graphic display software) to find, acquire and transfer information.