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| VoIP Glossary
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802.1p An IEEE standard for providing QoS using three bits (defined in 802.1q) to allow switches to reorder packets based on priority level.
802.1q 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.
AAL1 ATM Adaptation One. ATM adaptation layer. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.
AAL5 ATM Adaptation Five. ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic.
ADPCM Adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals.
AIM Advance Integration Module- Propriety to Cisco equipment.
ANI Automatic Number Identification; A telephone function that transmits the billing number of the incoming call (Caller ID, for example).
BLI Busy Lamp Indicator; A light or LED on a telephone that shows which line is in use.
BW Band width.
CBR Constant Bit rate. Constant bit rate. QoS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery.
CCS Common channel signaling. Signaling system used in telephone networks that separates signaling information from user data. A specified channel is exclusively designated to carry signaling information for all other channels in the system. See also SS7.
CELP Code excited linear prediction compression. Compression algorithm used in low bit-rate voice encoding. Used in ITU-T Recommendations G.728, G.729, G.723.1.
Circuit Switching Circuit switching is a WAN switching method in which
a dedicated Physical circuit through a carrier network is established, maintained, and
terminated for each communication session. Used extensively in telephone company networks,
operates much like a normal telephone call.
Circuit Based Refers to Using Circuit Switched technology.
CIR Committed Information rate. Rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics.
CODEC In Voice over IP, Voice over Frame Relay, and Voice over ATM, a DSP software algorithm used to compress/decompress speech or audio signals.
CRTP Compressed Real-Time Transmission Protocol- See RTP
CS-ACELP Conjugate Structure Algebraic Code Excited Linear Prediction. CELP voice compression algorithm providing 8 Kbps, or 8:1 compression, standardized in ITU-T Recommendation G.729.
DID Direct Inward Dialing; The ability to make a telephone call directly into an internal extension without having to go through the operator.
Diff-Serv Differentiated Services; The Diff-Serv model divides traffic into a small number of classes to provide quality of service (QoS).
DNIS Dialed Number Identification Service; A telephone function that sends the dialed telephone number to the answering service.
DTMF Dual-Tone Multifrequency; The type of audio signals generated when you press the buttons on a touch-tone telephone.
DASA Dial Access Stack Architecture
DLCI Data-link connection identifier. Value that specifies a PVC or SVC in a Frame Relay network. In the basic Frame Relay specification, DLCIs are locally significant (connected devices might use different values to specify the same connection). In the LMI extended specification, DLCIs are globally significant (DLCIs specify individual end devices).
DSP Digital Signal Processor
E1 The European counterpart to T1, which transmits at 2.048 Mbps.
FRF.11 Frame Relay Forum implementation agreement for Voice over Frame Relay (v1.0 May 1997). This specification defines multiplexed data, voice, fax, DTMF digit-relay and CAS/Robbed-bit signaling frame formats, but does not include call setup, routing or administration facilities.
FRF.12 The FRF.12 Implementation Agreement (also known as FRF.11 Annex C) was developed to allow long data frames to be fragmented into smaller pieces and interleaved with real-time frames. In this way, real-time voice and non real-time data frames can be carried together on lower speed links without causing excessive delay to the real-time traffic.
G.711 Describes the 64-kbps PCM voice coding technique. In G.711, encoded voice is already in the correct format for digital voice delivery in the PSTN or through PBXs. Described in the ITU-T standard in its G-series recommendations.
G.723.1 Describes a compression technique that can be used for compressing speech or audio signal components at a very low bit rate as part of the H.324 family of standards. This CODEC has two bit rates associated with it: 5.3 and 6.3 kbps. The higher bit rate is based on ML-MLQ technology and provides a somewhat higher quality of sound. The lower bit rate is based on CELP and provides system designers with additional flexibility. Described in the ITU-T standard in its G-series recommendations.
G.729 Describes CELP compression where voice is coded into 8-kbps streams. There are two variations of this standard (G.729 and G.729 Annex A) that differ mainly in computational complexity; both provide speech quality similar to 32-kbps ADPCM. Described in the ITU-T standard in its G-series recommendations.
H.323 Extension of ITU-T standard H.320 that enables videoconferencing over LANs and other packet-switched networks, as well as video over the Internet.
HDLC High-Level Data Link Control. Bit-oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
IP Internet Protocol
IOS Internetworking Operating System- Cisco.
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LDCELP Low-delay CELP. CELP voice compression algorithm providing 16 Kbps, or 4:1 compression. Standardized in ITU-T Recommendation G.728.
LMI Local Management Interface. Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing.
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.
MPLS Multi-Protocol Label Switching. Emerging industry standard upon which tag switching is based.
NEBS Network Equipment Building Systems. In OSS, the Bellcore requirement for equipment deployed in a central office environment. Covers spatial, hardware, crafts person interface, thermal, fire resistance, handling and transportation, earthquake and vibration, airborne contaminants, grounding, acoustical noise, illumination, EMC, and ESD requirements.
NTP Network Time Protocol. Protocol built on top of TCP that assures accurate local time-keeping with reference to radio and atomic clocks located on the Internet. This protocol is capable of synchronizing distributed clocks within milliseconds over long time periods.
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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.
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).
PSTN Public Switched Telephone Network; The worldwide voice telephone network.
Packet Switching Packet switching is a WAN switching method in which
network devices share a single point-to-point link to transport packets from a source to a
destination across a carrier network.
Packet Based Refers to using packet switched technology.
PCM Pulse Coded modulation.
PVC Permanent virtual circuit or connection. Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.
Q.O.S Quality of service.
RSVP Resource Reservation Protocol. Protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so forth) of the packet streams they want to receive. RSVP depends on IPv6. Also known as Resource Reservation Setup Protocol.
RTP Real-Time Transport Protocol. Real-Time Transport Protocol. One of the IPv6 protocols. RTP is designed to provide end-to-end network transport functions for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP provides services such as payload type identification, sequence numbering, time-stamping, and delivery monitoring to real-time applications.
RTCP RTP Control Protocol. Protocol that monitors the QOS of an IPv6 RTP connection and conveys information about the on-going session. See also RTP.
SIP Session Initiation Protocol; A protocol that provides telephony services similar to H.323, but is less complex and uses less resources.
SGCP Simple Gateway Control Protocol. Controls Voice over IP gateways by an external call control element (called a call-agent).
SS7 Signaling System 7. Standard CCS system used with BISDN and ISDN. Developed by Bellcore.
T1 A 1.544-Mbps point-to-point dedicated digital circuit provided by the telephone companies consisting of 24 channels.
TAPI Telephony API; A programming interface that allows Windows client applications to access voice services on a server.
TOS Type of Service; A method of setting precedence for a particular type of traffic for QoS.
Trunk A communications channel between two points, typically referring to large-bandwidth telephone channels between switching centers that handle many simultaneous voice and data signals.
TDM Time-division multiplexing. In TDM, information from each data Channel is allocated bandwidth based on preassigned time slots, Regardless of whether there is data to transmit.
Tag Switching High-performance, packet-forwarding technology that integrates network layer (Layer 3) routing and data link layer (Layer 2) switching and provides scalable, high-speed switching in the network core. Tag switching is based on the concept of label swapping, in which packets or cells are assigned short, fixed-length labels that tell switching nodes how data should be forwarded.
TOS Type of Service.
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VAD Voice activity detection. When enabled on voice port or a dial peer, silence is not transmitted over the network, only audible speech. When VAD is enabled, the sound quality is slightly degraded, but the connection monopolizes much less bandwidth.
VBR Variable bit rate. QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (RT) class and non-real time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples, but that still need a guaranteed QoS.
WEPD Weighted Early Packet Discard
WFQ Weighted fair queuing. Congestion management algorithm that identifies conversations (in the form of traffic streams), separates packets that belong to each conversation, and ensures that capacity is shared fairly between these individual conversations. WFQ is an automatic way of stabilizing network behavior during congestion and results in increased performance and reduced retransmission.
WRED Weighted Random Early Detection.
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