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9. Glossary

ANI Automatic Number Identification

A telephone function that transmits the billing number of the incoming call (Caller ID, for example).

MGCP Media Gateway Control Protocol

A protocol for IP telephony that enables a caller with a PSTN phone number to locate the destination device and establish a session.

BLI Busy Lamp Indicator

A light or LED on a telephone that shows which line is in use.

PBX Private Branch eXchange

An in-house telephone switching system that interconnects telephone extensions to each other as well as to the outside telephone network.

DID Direct Inward Dialing

The ability to make a telephone call directly into an internal extension without having to go through the operator.

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).

Diff-Serv Differentiated Services

The Diff-Serv model divides traffic into a small number of classes to provide quality of service (QoS).

PSTN Public Switched Telephone Network

The worldwide voice telephone network.

DNIS Dialed Number Identification Service

A telephone function that sends the dialed telephone number to the answering service.

SIP Session Initiation Protocol

A protocol that provides telephony services similar to H.323, but is less complex and uses less resources.

DTMF Dual-Tone Multifrequency

The type of audio signals generated when you press the buttons on a touch-tone telephone

T1 A 1.544-Mbps

point-to-point dedicated digital circuit provided by the telephone companies consisting of 24 channels.

E1 The European counterpart to T1

which transmits at 2.048 Mbps

TAPI Telephony API

A programming interface that allows Windows client applications to access voice services on a server.


An IEEE standard for providing QoS using three bits (defined in 802.1q) to allow switches to reorder packets based on priority level.

TOS Type of Service

A method of setting precedence for a particular type of traffic for QoS.


An IEEE standard for providing virtual LAN (VLAN) identification and QoS levels. Three bits are used to allow eight priority levels, and 12 bits are used to identify up to 4,096 VLANs.


A communications channel between two points, typically referring to large-bandwidth telephone channels between switching centers that handle many simultaneous voice and data signals.


An ITU standard for real-time interactive voice and videoconferencing over LANs and the Internet

VoIP Voice over (TCP/) IP

A method of sending voice information over a packet-switched network, such as the Internet, using TCP/IP.

Source: Internetwk.com

by redxii See Profile edited by KeysCapt See Profile
last modified: 2002-06-12 08:04:30

The Real-time Transport (RTP) Protocol provides end-to-end network transport functions suitable for applications transmitting real-time data such as audio, video or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of-service for real-time services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers. The protocol supports the use of RTP-level transla tors and mixers.

by KeysCapt See Profile

The H.323 standard provides a foundation for audio, video, and data communications across IP-based networks, including the Internet. H.323 is an umbrella recommendation from the International Telecommunications Union (ITU) that sets standards for multimedia communications over Local Area Networks (LANs) that do not provide a guaranteed Quality of Service (QoS). These networks dominate todays corporate desktops and include packet-switched TCP/IP and IPX over Ethernet, Fast Ethernet and Token Ring network technologies. Therefore, the H.323 standards are important building blocks for a broad new range of collaborative, LAN-based applications for multimedia communications. It includes parts of H.225.0 - RAS, Q.931, H.245 RTP/RTCP and audio/video codecs, such as the audio codecs (G.711, G.723.1, G.728, etc.) and video codecs (H.261, H.263) that compress and decompress media streams.

Media streams are transported on RTP/RTCP. RTP carries the actual media and RTCP carries status and control information. The signalling is transported reliably over TCP. The following protocols deal with signalling:

RAS manages registration, admission, status.
Q.931 manages call setup and termination.
H.245 negotiates channel usage and capabilities.
H.235 security and authentication.

by KeysCapt See Profile