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Glossary of VOIP Terms - Page 2 |
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100baseT - The 100/10 megabits/second Ethernet standard that uses twisted pair wires with RJ-45 connectors. |
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Access Tandem - An Access Tandem switch interconnects with CO switches and other access tandem switches to form the PSTN
network. It is often called a “class 4” switch, a reference to the original AT&T hierarchal network structure. |
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Application Server - An application server is an IETF concept. It is most often a computer that implements applications, such as prepaid
calling, “class 5” services, automated operator services, etc., and interfaces with a softswitch in order to permit
interactions with a caller. |
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Bandwidth - Bandwidth is a term used to describe the capacity of a physical circuit or piece of equipment to transport or switch
information and is often expressed in terms of bits per second. Common abbreviations are Kbits, Mbits, and Gbits for
kilobits (thousands of bits), megabits (millions of bits), and gigabits (billions of bits), respectively. |
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Bearer Circuits - Bearer circuits refer to specific circuits that carry only voice and are never used to carry data messages for call
signaling, such as the ISDN or SS7 data links |
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CLEC - A Competitive Local Exchange Carrier is a local telephone company available to subscribers within a geographic area
that is not the original local telephone company. See ILEC.
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CO - Central Office refers to the type of PSTN switch to which telephones and PBX systems are attached. A CO switch
implements features such as call waiting, call forwarding, etc. and interconnects with tandem switches. It is often
called a “class 5” switch, a reference to the original AT&T hierarchal network structure. |
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DTMF - Dual-Tone Multi-Frequency is a set of 16 tones used for in-band signaling between PSTN switches and telephones.
The tones can also be used for signaling between switches. |
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G.711 - This vocoder is used in the PSTN, and is commonly called PCM (Pulse Code Modulation). There are two flavors of its
algorithm; mu-law used in North America and Japan, and A-law used in the rest of the world. This vocoder algorithm
produces a bit rate of 64 Kbits/second and has no silence suppression, meaning silence is transmitted and occupies
bandwidth. |
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G.723 - This vocoder is commonly used in VoIP gateways and is the vocoder in Microsoft’s NetMeeting software. It is called
the Multi-rate Coder and has two bit rates, 5.3 and 6.4 Kbits/second. This vocoder algorithm has silence suppression,
meaning silence is not transmitted and does not occupy bandwidth, and is patented, the use for which a license must be
paid. |
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G.726 - This vocoder, commonly called ADPCM (Adaptive Differential Pulse Code Modulation), is used in the NACT IPAX
gateway for the playback of voice messages such as authorization code and destination number prompts. This vocoder
algorithm can produce bit rates of 16, 24, 32, and 40 Kbits/second. The NACT IPAX voice prompts are recorded at 32
Kbits/second. This vocoder has no silence suppression, meaning silence is transmitted and occupies bandwidth. |
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G.727 - This vocoder, commonly called Variable-Rate ADPCM, is available in the NACT IPAX VoIP vocoder suite. This
vocoder algorithm allows bit rates of 16-40 Kbits/second for sending and receiving voice. The bit rates can be
different in each direction. It has no silence suppression. |
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G.728 - This vocoder, sometimes known by the abbreviation LD-CELP (Low-Delay Code Excited Linear Prediction), is used
in some VoIP gateways. It has a bit rate of 16 Kbits/second. |
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G.729 - This vocoder, sometimes known by the abbreviation CS-ACELP (Conjugate Structure Algebraic-Code Excited Linear
Prediction), is used in many VoIP gateways. It has a bit rate of 8 Kbits/second. This vocoder algorithm has silence
suppression, meaning silence is not transmitted and does not occupy bandwidth. This is a patented vocoder algorithm
for which a license fee must be paid. |
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Gatekeeper - A gatekeeper is an H.323 concept and a device or computer that controls one or more gateways within a “zone”. It is
responsible for routing all calls to/from the gateways in a non-point-to-point situation. Gatekeepers can communicate
with other gatekeepers, but usually only between those of the same manufacturer. |
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Gateway1 - A gateway in the circuit-switched network is a switch that bridges or interfaces two separate PSTN networks, for
example., the mu-law PCM, SS7 signaling-based, North American network with the A-law PCM, C7 signaling-based,
European network. Such switches are often called international gateway switches because they interface with and
connect the national networks of two or more countries. Examples of such switches are the Nortel DMS 300 and the
Lucent 5ESS. |
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Gateway2 - A gateway is a hardware and software system that converts one type of media to another type of media (e.g., G.711
T1/E1 (TDM-based) to G.723 RTP (IP-based)). In general telephony terms it converts voice from one form to another,usually from circuit-switched to packet-switched. In the ISC/IETF VoIP model, a gateway is a dumb device that
mainly converts the voice media.
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