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Common VoIP Terms

Below you will find common terms and definitions related to the topics of Hosted PBX, Voice-over-IP and general networking.


In the world of VoIP a codec is used to encode voice for transmission access IP networks. Codec’s for VoIP use are also referred to as vocoders, for “voice encoders”. Codecs generally provide a compression capability to save network bandwidth. Some codecs also support silence suppression, where silence is not encoded or transmitted.

DHCP – Dynamic Host Configuration Protocol

DHCP is a protocl used by networked computers (clients) to obtain IP addresses and other parameters such as the default gateway, subnet mash, and IP addresses of DNS servers from a DHCP server. The DHCP server ensures that all IP addresses are unique.

DID – Direct Inward Dialing

Direct Inward Dialing is a feature offered by telephone companies for use with their customers PBX systems, whereby the telephone company (telco) allocates a range of numbers all connected to their customer’s PBX. As calls are presented to the PBX, the number that the caller dialed is also given, so the PBX can route the call to the desired person within the organization.

DTMF – Dual-tone Multi-Frequency

DTMF signaling is used for telephone signaling over the line in the voice frequency band to the call switching center. The version of DTMF used for telephone tone dialing is known as the trademarked term Touch-Tone.


G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. G.711 represents logarithmic pulse-code modulation (PCM) samples for signals of voice frequencies, sampled at the rate of 8000 samples/second.


G.729 is an audio data compression algorithm for voice that compresses voice audio in chunks of 10 milliseconds. Music or tones such as DTMF or fax tones cannot be transported reliably with this codec, and thus use G.711 or out-of-band methods to transport these signals.

IP Address

An IP address is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Procotol standard. Any participating network device can have their own unique address.

IVR – Interactive Voice Response

IVR or interactive voice response is a phone technology that allows a computer to detect voice and touch tones using a normal phone call. The IVR system can respond with pre-recorded or dynamically generated audio to further direct callers on how to proceed. IVR systems can be used to control almost any function where the interface can be broken down into a series of simple menu choices.

IP Phone

A IP Phone or Voice over IP phone is an entity used to make telephone calls over the Internet, or to leverage network wiring within an office for carrying phone conversations to a PBX. VoIP phones use one of serveral competing communication standards to send their calls through a network. An IP Phone looks identical to a regular telephone but instead of connecting to the normal POTS phone line jack on the wall, it connects into a router or wall jack using an RJ-45 Ethernet connector, this then becomes a fully operational phone with all software onboard, provided by the switch or system.

Key System

A key system or key telephone system is a multiline telephone system typically used in small office environments. Key systems are noted for their expandability and having individual line selection buttons for each connected phone line, however some features of a private branch exchange such as dialable intercoms may also commonly be present.

LNP – Local Number Portability

Local Number Portability refers to the ability to transfer either an existing fixed-line or mobile telephone number assigned by a local exchange carrier (LEC) and reassign it to another carrier. In most cases, there are limitations to transferability with regards to geography, service area coverage and technology.

PBX – Private Branch Exchange

PBX stands for Private Branch eXchange which operates as a connection between a private organization and the public switched telephone network (PSTN). It is a system which connects the outside telephone network to the internal telephones, fax machines and extensions within the business. Often a PBX will include features like speed dial, conference calling and music on hold.

PoE – Power over Ethernet

Power over Ethernet is a technology used to transmit electrical power along with data to remote devices over standard ethernet cable in a network. This technology is useful for powering IP telephones or network cameras where it would be costly to run power seperately.

POTS – Plain Old Telephone System

POTS is a term which means voice grade telephone service that remains the basic form of residential and business telephone service in most parts of the world. Since the introduction of POTS more advanced forms of telephone service such as ISDN, mobile phones and voice over ip have been introduced. It has been available almost since the introduction of the public telephone system.

PSTN – Public Switched Telephone Network

The public switched telephone network is the network of the world’s public circuit switched telephone networks. Originally the pstn was a entwork of analog telephone systems but now the pstn is entirely digital. The pstn is largely governed by technical standards created by the ITU-T and uses E.163/E.164 address (commonly known as telephone numbers) for addressing.

QOS – Quality of Service

Quality of Service in networking terms refers to the ability of a network to give guaranteed performance based on some metric usually by prioritising traffic. For example certain types of network traffic such as voice over ip can be prioritized on a network to make sure that a certain minimum level of quality is alway obtained.

Rate Center

A rate center is a geographical area used by an LEC to determine the boundaries for local calling, billing and assigning phone numbers. Typically a call within a rate center is a local, while a call from one rate center to another is a long-distance call.


RJ-11 is a physical interface often used for terminating telephone wires. It is the standard connector utilized on 2-pair (4-wire) telephone wiring and RJ stands for “registered jack”.

RTP – Real-time Transport Protocol

RTP defines a standardized packet format for delivering audio and video over the Internet.


A router is a device that determines the proper path for data to travel between different networks and forwards data packets to the next device along this path. They connect networks together; a LAN to a WAN for example, to access the Internet. Routers are available in both wireless and wired versions.

SIP – Session Initiation Protocol

SIP is the IETF protocol for VoIP and other text and multimedia sessions like instant messenging, video, online games and other services. SIP is very much like HTTP, the web protocol or SMTP. Messages consist of headers and a message body. SIP message bodies for phones calls are defined in SDP – the session description protocol.


A softphone is a software program for making telephone calls over the Internet using your computer rather than a dedicated telephone. A softphone is designed to mimic the functions of a real telephone and often appears to look like a regular telephone. A user will normally connect a headset to their computer via their soundcard or usb port.


A network switch is a computer networking device that connects network segments. Network switches are capable of inspecting data packets as they are received, determining the source and destination of that packet, and forwarding it appropriately. By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub.

TCP/IP – Transmission Control Protocol/Internet Protocol

TCP/IP were the first two networking protocols defined. Today’s IP networking represents a synthesis of two developments that began in the 1970’s, namely LANs (Local Area Networks) and the Internet, both of which have revolutionized computing.

Virtual Number

A virtual phone number is a telephone number without an associated phone line. Usually these numbers are programmed to be forwarded to either a Voice over IP service, or to a different phone line, fixed or mobile. Virtual numbers are sometimes used in conjunction with mail forwarding services to a create a virtual office in a remote place. For instance, a company may purchase a virtual phone number with area code 212, together with a mail forwarding service in New York to give the impression that the company is located in New York. Virtual numbers are especially appealing to technology companies (for technical support), exporters (to give the impression that the company is local) and service companies such as call centers.

VoIP – Voice over IP

Voice over Internet Protocol is the routing of voice conversations over the Internet or through any other IP-based network. Companies providing VoIP service are commonly referred to as providers, and protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols. Voice over IP protocols carry telephony signals as digital audio, typically reduced in data rate using speech data compression techniques.


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