VoIP Dictionary

The following provides a glossary of terms and definitions that are commonly used in Voice over IP Solutions. We hope this will provide a good reference for you during your introduction to the world of VoIP. If you think that important terms or definitions related to VoIP are missing from this page, or there is something you were looking for but could not find then please use our comment form below to ask us.

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A device that enables something to be used in a different way from which is was intended, or makes different pieces of equipment compatible.


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.

Analog Telephone Adapter (ATA):

A device that converts the analog signals from a conventional phone into a format acceptable for transmission over an internet connection, and vice versa at the receiving end. This device is commonly used for Voice over IP Phone Services.

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).

Asymmetric Digital Subscriber Line (ADSL):

Most homes and small business users are connected to an asymmetric DSL (ADSL) line. Refer to DSL definition below for more info on DSL. ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit (most of the time).

Asynchronous Transfer Mode (ATM):

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.

Answer Seizure Ratio (ASR):

This is the ratio of successfully connected calls with respect to attempted calls (seizures). It is an important term for defining network quality.

Automatic Call Distributor (ACD):

Automatic Call Distribution is the system that routes incoming calls. Think of a call center scenario where a high volume of incoming calls occur and they must be routed to agents that are available.

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Bits per second (bps) or Bandwidth:

The most common measurement for data transmission. It indicates the number of bits that can be transferred to or from a communications device in one second.


The use of cable to provide data transfer using analog (radio-frequency) signals. Digital signals must be passed through a modem and transmitted over one of the frequency bands of the cable. Multiple channels carry data on a single physical cable. Cable TV is an example of broadband transmission. The term is commonly associated with high speed data transfer connections.

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Caller Identification (ID):

A phone service feature that allows the recipient of a phone call to see the phone number of the originating caller (person). This would be a typical feature included with your Phone Service.

Call Detail Records (CDR):

These are detailed records about phone calls that originate, terminate or pass through the exchange. Used for billing purposes.

Call Forwarding:

A phone service feature that allows the customer to forward their phone to another phone number (for example, you can forward your home phone number to your cell number if you know you are going to be away from home). This would be a typical feature included with your service.

Call Waiting:

A phone service feature that notifies a telephone user that another incoming call is waiting to be answered. This is typically provided by a short tone on the phone, or by use of the caller ID feature. This would be a typical feature included with your service.


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 switching:

A process of connecting two points in a communications network where the path (switching points) through the network remains fixed during the operation of a communications circuit. While a circuit switched connection is in operation, the capacity of the circuit remains constant regardless of the amount of content (e.g. voice or data signal) that is transferred during the circuit connection.

Class 5 switch:

Telephone company switch.

Codec (coder/decoder):

A technique used to compress/decompress speech or audio signals.

Competitive Local Exchange Carrier (CLEC):

A company that builds and operates communication networks in metropolitan areas and provides its customers with an alternative to the local telephone company.

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.

Customer Relationship Management (CRM):

This is a method to manage a company's interactions with customers. Think of software such as that provided by Salesforce. This is important for VoIP as many solutions integrate the digital phone service with a CRM so a salesperson can see the customer's details when a phone call comes in.

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1) A general term for information.
2) A collection of interrelated, unique data items or records, in one or more computer files.

Data Communications:

The transmission and reception of data between locations. Data communications require a combination of hardware (terminals, modems, multiplexers, and other hardware) and software.


This is always measured in seconds or fractions of seconds. There are delays through every electronic device even if it's only nano seconds. 1ns is 0.000000001 seconds. In a system like the internet delays are caused by the electronics(this is usually negligible), queuing delays, transmission distances and software delays.


Data characters coded in discrete, separate pulses or signal levels.

Digital Subscriber Line (DSL):

A high-speed digital switched service using existing copper pairs to connect subscriber CPE (Customer Premises Equipment) to the Central Office. DSL handles more data downstream (data flowing towards the subscriber) than upstream (towards the network).


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

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E1 Link:

A wide area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048Mbps.


A process of sending text messages in electronic form. The messages can also include images and video clips.


Ethernet is a packet based transmission protocol that is primarily used in LANs.

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A process of converting optical images into electrical signals for transmission over communication systems (phone line, internet etc). When the electrical signal is received, it is converted back to an optical format for display or printing of the original image. This process is commonly called FAXing.

Fax Machine:

A device that allows the user to fax information over a communication line.

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.

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A device that acts as an interface between two or more networks to connect dissimilar communications systems. A gateway translates from one set of protocols to another, at levels from the Physical layer (Level 1) up through the Application layer (Level 7) of the OSI Reference model.

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A standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks.

Half Duplex:

Best way to think of half-duplex is a walkie-talkie where only one party can talk and one party listen at the same time.


A measurement unit for frequency that is equal to the number of cycles per second of a waveform.

Hypertext Transfer Protocol (HTTP):

A protocol that is used to transmit hypertext documents through the Internet. It controls and manages communications between a Web browser and a Web server.


A hub is a communication device that distributes communication to several devices in a network through the re-broadcasting of data that it has received from one (or more) of the devices connected to it.

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IEEE 802.16:

Also known as WiMAX or WirelessMAN so please refer to that section below for further information.

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.


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.

Internet Protocol (IP):

This is the what the protocol is referred to for digital traffic that communicates over the Internet. IP Addresses are used to identify endpoint devices.

IP Telephony (Internet Protocol Telephony):

Simply another term that is used to refer to IP based telecommunications. 

ISP (Internet Service Provider):

A business that provides subscriber-based access to the Internet. ISPs use 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.

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A socket connector designed for the insertion of a plug, commonly used for audio devices (e.g. used for connecting your headphones to your audio equipment).


Jitter when applied to Voice over IP is a variation in packet transit delay. The causes of jitter are typically queuing, contention and serialization effects on the path through the network. Faster, higher bandwidth networks tend to have less jitter whereas slower networks tend to have more congestion and more jitter. A QoS device like an ATA can help eliminate some of this jitter.

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Kilo-bits per second (Kbps):

A measure of the number of one thousand bits transferred over a 1 second period.

Kilo-Hertz (KHz):

A measurement unit of the number of one thousand cycles per second of a waveform.

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Local Area Network (LAN):

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).


An expression of how much time it takes for a packet of data to get from one designated point to another.

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Media Gateway Control Protocol (MGCP):

An Internet Engineering Task Force (IETF) draft standard for controlling voice gateways through IP networks.

Mega-bits per second (Mbps):

A measure of the number of one million bits to be transferred over a 1 second period.

Mega-Hertz (MHz):

A measurement unit of the number of one million cycles per second of a waveform.


A modem converts the serial digital (binary) data from a transmitting terminal into a form suitable for retransmission over an analog telephone channel. A second modem reconverts this signal to binary data for acceptance by the receiving terminal.

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A system of computers linked together by communication channels allowing the flow of data between the linked computers.

Network Interface Card (NIC):

An adapter circuit board installed in a computer to provide a physical connection to a network.

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A reference to a user being actively connected to the internet.

OSI Reference Model:

A reference model to standardize communication systems. The model standardized nomenclature across existing protocols and provided guidelines for new protocols using 7 layers.

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The unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network.

Packet loss:

Occasionally in complex systems like the internet packets get lost. The packets sometimes take so long to reach the destination that they are no longer useful, sometime packets get corrupted and the data in them is no longer reliable. .

Packet Switching:

A means of economically sending and receiving data over alternate, multiple network channels. The premise for packet switching is the packet, a small bundle of information containing the payload and routing information. Packet switching takes data, breaks it down into packets, transmits the packets and does the reverse on the other end. Packets can be sent in order and then be received in a different order - only to be put back in the correct order in fractions of a second.

Private Branch eXchange (PBX):

An automated telephone switching system serving one company, located on the company's premises, and connecting to the public telephone network.

Post Dial Delay (PDD):

This is the time between the last digit dialed for a phone number and when the ring tone is heard.

Phone Adaptor:

See ATA.

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).


1) A strictly defined procedure and message format allowing two or more systems to communicate over a transmission medium.
2) A formalized set of rules that computers use to communicate. Because of the complexity of communications between systems and the need for different communications requirements, protocols have been divided into modular layers, in which each layer performs a specific function for the layer above.

Visit this page for more information on VoIP Protocols.

Public Switched Telephone Network (PSTN):

The world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. Also referred to as the Plain Old Telephone Service (POTS).

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Quality of Service (QoS):

The idea that transmission rates, error rates, and other characteristics can be measured, improved, and, to some extent, guaranteed in advance.

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Rate-Adaptive DSL (RADSL):

This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.

Real-time Transport Protocol (RTP):

RTP is a packet based communication protocol that adds timing and sequence information to each packet to allow the reassembly of packets to reproduce real time audio and video information. RTP is a transport used in IP audio and video environments.

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.


A device that connects multiple networks together and forwards packets (of data) between them.

Check out our Router Setup for VoIP guide for more information.

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Session Initiation Protocol (SIP):

A standard protocol for initiating an interactive user session that involves multimedia elements such as video, voice, chat, gaming, and virtual reality. For more details on this protocol, visit the SIP page.

Softphone (Software Telephone):

A software program that runs on your PC (desktop or laptop) that allows you to make and receive calls over the Internet. You can use a headset, or a microphone and speakers, in place of a telephone. A softphone's interface typically looks like a traditional phone dial pad. A softphone typically provides all the features and benefits associated with VoIP Solutions.


A device that connects two separate paths together.

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.

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A wide area digital transmission scheme used predominantly in North America and Japan that carries data at a rate of 1.544Mbps.

Transmission Control Protocol (TCP):

A session layer protocol that coordinates the transmission, reception, and retransmission of packets in a data network to ensure reliable (confirmed) communication. The TCP protocol coordinates the division of data information into packets, adds sequence and flow control information to the packets, and coordinates the confirmation and retransmission of packets that are lost during a communication session. TCP utilizes Internet Protocol (IP) as the network layer protocol.


A device that converts your speech into an analog signal suitable for transmission over a phone line.

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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. This allows the receiving end to receive and re-sequence the packets to recreate the original data file or block of data that was transmitted. UDP adds a small amount of overhead (control data) to each packet relative to other high-level protocols such as TCP. However, UDP does not provide any guarantees to data delivery through the network.

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Very High Bit Rate DSL (VDSL):

Refer to DSL definition for more information on DSL. VDSL is a fast connection, but works only over a short distance.


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.

Check out our 10 Voicemail Greeting Tips guide for more information in setting up voicemail.

Voice over IP (VoIP):

Term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP).

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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.


This is also IEEE 802.16 and is occasionally known as WirelessMAN™. The MAN acronym refers to Metropolitan Access Networks where point-to-multipoint technology is used at a bandwidth between 10GHz and 66GHz and also for the range between 2GHz and 11GHz.


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.

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Approved by the CCITT (now the ITU-T) in the 1970s as a popular standard for packet-switching networks. It defines standard physical layer, data link layer and network layers (layers 1 through 3) of the OSI Reference Model. It was developed to describe how data passes into and out of public data communications networks. X.25 networks are in use throughout the world.

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