IP TELEPHONY TERMINOLOGY

Accounting
A service which records the actions of an authenticated user.

Admission Control
A service (like COPS+) that controls which users or systems can request Quality of Service features.

Analog feature phone

An analog phone, which has extra buttons (sometimes programmable) that correspond to tones understood by the telephone switch or other equipment. (e.g. Bellcore ADSI).

Analog or 2500 set
A traditional analog telephone.

Analog Transmission
A way of sending signals--voice, video, data--in which the transmitted signal is analogous to the original signal.

Analog Trunk
A single FXO or analog E&M circuit.

ATM

Asychronous Transfer Mode. A high bandwidth, low-delay, connection-oriented, packet-like switching and multiplexing technique.

Authentication
A service which verifies who is communicating.

Authorization

A service which defines what an authentication user may do.

Automated Attendant
A device which answers callers with a digital recording, and allows callers to route themselves to an extension through touch-tone input in response to a voice prompt.

Billing
A system of using accounting information to generate a bill for services.

Call
A conversation of 2 or more parties, which consists of 1 or more call segments. Any demand to set up a connections.

Call Appearance Mapper
A service which translates a telephony identity (telephone number or username) to native telephony addresses (i.e. IP address and port number information, phone number on the PSTN, ATM NSAP address, or Frame Relay DLCI).

Call Leg
A unidirectional or bi-directional part of a call between two telephony devices endpoints (as defined by SGCP) on the same IP, DS0, Frame Relay, or ATM network

.
Call Quality
A measure of the expected quality as affected by the MOS of the codec (with or without voice activity detection), and the delay, jitter, and congestion on the network.

Call Route Quality
A measure of the best quality available across a call route.

Call Segment
A full duplex connection between a pair of telephony parties. A call segment consists of one or more call legs. A "conference call" normally consists of several call segments. A call segment may share multicast call legs with other call segments.

Call Segment Path
Two 1-way connections that may take different routes.

Capacity Monitor
A service which counts the number of timeslots available in a TDM network, and the amount of bandwidth available on an IP, Frame Relay, or ATM network. The Capacity Monitor must be directly or indirectly (using another service) aware of the layer 3 topology of the IP networks.

Channel or Timeslot
A single, bi-directional, direct connection between two TDM devices.

Codec
Short for COder/DECoder. An algorithm to represent speech, music, or video as a stream of bits and vice versa.

Codec quality
The best quality expected using a specific codec.

Conference
A single conversation consisting of 2 or more call segments. In a DS-0 network, a conference is typically setup as call segments radiating outward in a star from the party that setup the conference call.End Point Selection.

Conference Bridge or MCU
A device responsible for merging audio (and optionally other media) from many callers in a conference.

Desk set
Another name for "Telephone Set".

Digital Signal
A discontinuous signal. One whose state consists of discrete elements, representing very specific information.

DLCI
Data Link Connection Identifier. A frame relay term defining a 10-bit filed of the address field.

"Dog Bone"
A very traditional, popular, and comfortable handset design.

DS-0
Digital signal, level 0 is 64 kilobits. It is equal to one voice conversation digitized under PCM.

E1
The European equivalent of the North American 1544 million bits per second (T1) except that E1 carries information at the rate of 2.048 million bits per section

.
E&M Transmission
(Ear and Mouth Transmission) 4-wire analog line type. One pair is used for transmit (goes to the user's ear), the other pair is used for receive (comes from the users mouth).

End Point Selection
The process of selecting one or more telephony devices (telephone set or daemon) associated with a telephony address.

Four-wire Circuit
A high performance circuit which offers lots of bandwidth and which is capable of multi-channel communications.

Ethernet phone
A phone that connects directly to an Ethernet network. Also referred to as an IP-phone.

Frame Relay

An access standard defined by ITU-T. Frame relay services employ a form of packet switching analogous to a streamlined version of X.25 networks. The packets are in the form of "frames" which are variable in length.

FXO
Foreign Exchange Office. Foreign Exchange is a service that provides local telephony service from a central office which is outside the subscriber's exchange area.

G.711
ITU-T u-law and A-law compression. Pulse Code Modulation (PCM). A simple waveform codec that uses 64kbits/sec. There are two variations u-law used in T1 and J1 countries, and A-law used in E1 countries.

G.7323.1
ITU-T 5.3 kbps and 6.3 kbps ACELP/MPMLQ coders. Dual rate speech coder designed for H.323 and H.324 audio and video conferencing /telephony standards over regular phone lines.

G.728
Low Delay Code Excited Linear Predictive (LD-CELP). A 16k codec. G.728 is primarily intended for Digital Circuit Multiplication Equipment (DCME) and so features a low transcoding delay in order to avoid the creation of telephony sidetone echo. It is also becoming a defacto standard for videoconferencing audio.

G.729 and G.729a
Conjugate Structure Algebraic CELP (CSA-CELP). An 8k codec. The G.729A specification uses a Conjugate-Structure Algebraic-Cod-Excited Linear Prediction algorithm.

G.723 and G.723.1
Codecs that operate at from 5.3k to 6.3k.

Gateway
A functional unit that interconnects a local area network (LAN) with another network having different higher layer protocols.

H.323
Serves as an "umbrella" for a set of standards defining real-time multimedia communications for packet based networks.

H.323 terminal
Any telephone that connects with H.323.

Handset
The part of a telephone you hold in your hand.

IEEE Std. 312-1977

IEEE Standard Definitions of Term for Communication Switching

IVR
Interactive Voice Response

IP
The internet protocol. The IP protocol is a standard describing protocol that keeps track of the Internet's addresses from different nodes, routes outgoing messages, and recognizes incoming messages.

IP Phone
A phone that sends traffic over a TCP/IP network (often an H.323 or terminal).

ITU-T

International Telecom Union telephony. (Previously the CCIT-T) The standards body that deals with telecommunications standards.

J-Tapi
Java Telephony API. A set of modulerly designed application programming interfaces for Java based application development.

LDAP
Lightweight Directory Access Protocol. An emerging standard which acts as an Internet-based solution to the DAP.

Link
A layer 2 network segment (typically in the WAN). For example, a Frame Relay link (native), an ATM link (native), or an IP link running any layer 2 protocol). An IP tunnel is not a link.
Link quality

The ability of a link to reliably deliver guaranteed bandwidth without dropping packets, and therefore to deliver good sounding audio.

Low Bandwidth Codec
A codec which uses 16k of bandwidth or less.

MAC Address

An address that identifies a particular medium access control (MAC) sublayer service access point (SAP).

MOS
Mean Opinion Score. A subjective measure of sound quality from 1 to 5.

Multicast Call Leg

A call leg which (in one or both directions ) carries (audio, video, or data) traffic for any number of parties.

Native Address
A MAC address on Ethernet. A TCP/IP address or DNS hostname plus a port number on an IP network, a DLCI on Frame Relay, or an NSAP address on ATM.

Native mode phone
A phone that maintains state information.

NBX phone
A stateless Ethernet phone developed by NBX Communication. It sends PCM encoded audio over Ethernet frames. State for many NBX phones is maintained by an standalone chassis on the same Ethernet network.

NSAP
Network Service Access Point. The point at whithc the OSI Network Service is made available to a Transport entity.

Path
The set of links through an IP network which corresponds to an IP call leg.

PSTN or GSTN

Public (or General) Switched Telephone Network. The public telephone network.

Router
A functional unit that interconnects two computer networks that use a single network layer procedure but may use different data link layers and physical layer procedures.

SoftPhone
A PC or PC-type device that emulates the telephone with prompts and commands appearing on the PC's screen instead of the phone.

Soft set
Provides the features of a telephone using software on a computer (Internet Phone, etc.)

Subscriber Line

A connection to an analog, BRI, or proprietary digital telephone set.
Tapi
Telephone Application Programming Interface. A term that refers to the Windows Telephony API.

T1
A digital transmission link with a total signal speed of 1544 Mbps. T1 is a standard for digital transmission in North America.

TCP/IP
Transmission Control Protocol/Internet Protocol. The networking protocol that provides communication across interconnected networks between commuters with diverse hardware architectures and various operating systems.

TDM
Time Division Multiplexer--A device that manages DS-0s. Also a network which uses DS-0s.

Telephony Address

An address in one of many forms a Telephony Identity on any voice transport or a Native Address on the appropriate transport.

Telephony Gateway
Translates either from one transport to another (Vox to Vox) or one codec to another, or both.

Telephony Identity
An email address in the form "user@domain", or an E.164 address (phone number).

Trunk
1)A single DS-0 circuit between TDM switches 2) T1 or E1 consisting of several DS-0s 3) One hop of a TDM path, with one or more DS-0s. 4) One analog circuit between the central office and the PBX.

Trunk group
Multiple DS-0 circuits between TDM switches (1st sense of trunk).

Unified Communications
Provides integrated messages in a single in-box (voice, fax, email, images and video).

Voice over Dial-up
Voice sent over a standard phone line between a pair of V.80 modems.

Voice over DS-0
Voice over a 64k DS-0 channel of the traditional phone network.

Voice over Ethernet or NBX
Voice encapsulated in Ethernet frames at layer 2.

Voice over Frame Relay
(VoFR) Voice encapsulated in Frame Relay.

Voice over IP (VoIP)
Voice encapsulated in TCP/IP.

Voice over ATM
Structured (Nx64) or unstructured circuit emulation services on ATM.