Glossary: Asterisk Terms

CODEC

Coder/Decoder
A software library that contains the algorithms necessary to convert an analog signal to and from a digital one. See also: Encode, G.711, G.729, GSM

Context

The dialplan is composed of one or more extension contexts. Each extension context is itself simply a collection of extensions. Each extension context in a dialplan has a unique name associated with it. The use of contexts can be used to implement a number of important features, such as security, routing, autoattendant, multilevel menus, authentication, callback, privacy, macros, etc... See also: Dialplan

Dialplan

Detailed definition See also: Context

E&M

Ear & Mouth
A type of signaling commonly used over T1 and E1 interfaces.

Encode

The process of converting an analog signal into a digital signal that can be manipulated easily by a computer. See also: CODEC

FXO

Foreign Exchange Office
A device usually found on the customer end that is powered by the channel and can interface into the telephone company's network. Digium makes FXO modules that interface with PSTN lines using FXS signalling in either Loopstart(fxs_ls) or the more common Kewlstart(fxs_ks) modes. See also: PSTN, REN

FXS

Foreign Exchange Station
A device usually located on the telephony company's property, a FXS device send power through a channel to a phone on the other end. Digium makes FXS modules that interface with PSTN phones using FXO signalling in either Loopstart(fxo_ls) or the more common Kewlstart(fxo_ks) modes. See also: PSTN, REN

G.711

An uncompressed codec that samples a 64kbps channel at 8 bits per sample using pulse code modulation. The Two varients of G.711 are known formally as uLaw and aLaw. See also: CODEC, G.729, GSM

G.729

The G.729 codec is an industry standard which allows for stuffing more calls in limited bandwidth to utilize IP voice in more cost effective ways. A typical call consumes 64Kbps of voice bandwidth. G.729 reduces the call to 8Kbps (normal IP overhead adds to this number). Many people are using Asterisk with G.729 to replace expensive gateways. See also: CODEC, G.711, GSM

GSM

A compressed speech codec that uses a rate of 13 kbps. See also: CODEC, G.711, G.729

H.323

A VOIP protocol that was deployed early and is widely adopted. See also: IAX, MGCP, SIP, VoIP

IAX

Inter-Asterisk eXchange
A VOIP protocol designed to be much more NAT friendly. IAX currently only transports audio. See also: H.323, MGCP, SIP, VoIP

IVR

Interactive Voice Response
An automated voice system that allows callers to navigate a phone system and be directed to the correct extension by pressing a series of numbers on a tuch-tone phone. (I.E. Push 1 for sales, push 2 for support, etc..)

MGCP

Media Gateway Control Protocol
A VOIP Protocol that has both signaling and control and was designed to reduce complexity between media gateways. See also: H.323, IAX, SIP, VoIP

Open source

Detailed definition

PBX

Detailed definition

PRI

Primary Rate Interface
A PRI is a truly digital circuit, containing 24 ISDN channels. One of these channels is a dchannel and used for signaling. The rest are bchannels and used to transport audio.

PSTN

Public Switched Telephone Network
This refers to the analog telephone network that's very common in residential networks. PSTN lines are usually much cheaper then T1 lines, but only provide one channel. Digium's FXO and FXS modules interface with this network. See also: FXO, FXS

REN

Ringer Equivalency Number
A number which represents the ringer loading effect on a line. A ringer equivalency number of 1 represents the loading effect of a single traditional telephone set ringing circuit. Most modern telephones probably will have a REN lower than 1. The total REN expresses the total loading effect of the equipment on the ringing current generator (FXS). The REN of a Digium FXS board is 5 (representing "extension," i.e., parallel-connected telephones). The actual number of devices on the line may be greater than the REN limit, if their respective individual RENs are less than 1. See also: FXO, FXS

SIP

Session Initiation Protocol
An IP protocol used for transporting many forms of media, including video and voice. SIP is currently the most common VOIP protocol. See also: H.323, IAX, MGCP, VoIP

TDM

Time Division Multiplexing
A processes of splitting one medium into two or more channels by using timed segments to transmit information.

Transcode

The process of converting a channel with one type of encoding to a different type of encoding in real time.

VoIP

Voice Over Internet Protocol
A general method for transporting voice through the internet. VOIP commonly refers to the general method and not a specific protocol. SIP is currently the most widely used VOIP protocol. See also: H.323, IAX, MGCP, SIP

Zaptel

Detailed definition