Telephony
Glossary
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µ-law: An algorithm used in companding
a pulse code modulated voice
signal. The µ-law algorithm is primarily used in North American T-1 telephone networks. (source)
ADC: See analog-to-digital converter.
analog-to-digital
converter: A device that converts continuous signals to discrete
digital numbers. It is often abbreviated as ADC,
A/D, or A to D. (source)
basic
rate interface ISDN: Also known as 2B+1D, it is an integrated services
digital network channel consisting of two 64 kpbs "bearer" (B)
channels and one 16 kbps "delta" (D) channel, giving a total data rate
of 144 kbps. The B channels are used for voice or user data, and the D
channel is used for control and signaling and/or X.25 packet
networking. BRI is the kind of ISDN interface most
likely to be found in residential service. (source)
BRI ISDN:
See basic rate interface ISDN.
CAS: See channel associated signaling.
cat 5: See category
5 cable.
category
5 cable: An unshielded twisted-pair type cable designed for high
signal integrity. The actual standard defines specific electrical
properties of the wire, but it is most commonly known as being rated
for its Ethernet capability of 100 Mbps. (source)
CCS: See common channel signaling.
central
office: A local telephone company facility where subscriber
lines are linked to switching equipment that connects subscriber lines
to each other, locally, or to long distance lines. (source)
channel bank:
A type of time division
multiplexer used in T-1 and E-1
multiplexing applications. (source)
channel
associated signaling: A form of signaling in which the signaling
information is associated with the specific circuit. In T-1
transmission, robbed-bit signaling
is a form of channel associated signaling. (source)
circuit
switching:
A method of routing traffic between an originator and a destination
through switching centers, from local users or from other switching
centers, whereby a continuous electrical circuit is established and
maintained between the calling and called stations until it is released
by one of those stations. Circuit switching has been used
extensively
for the public
switched telephone network. It is also called
connection-oriented and is the opposite of packet
switched or connectionless networking. TDM
voice channels are an example of circuit switching. (source)
CO: See central
office.
codec: A
combination of the words "Compressor-Decompressor", which describes a
device or program capable of performing transformations on a data
stream or signal. Codecs can both put the stream or signal into an
encoded form (often for transmission, storage or encryption) and
retrieve, or decode that form for viewing or manipulation in a format
more appropriate for these operations. (source)
common
channel signaling: A form of signaling in which the signaling
for all of the affected circuits is carried over a separate common
circuit. An example of common channel signaling in both
T-1 and E-1 transmission is the D channel used
in PRI ISDN signaling. (source)
CPE: See customer premises equipment.
customer
premises equipment: Terminal equipment such as computers, PBXs, and multiplexers connected to
the telephone network and residing on the customer’s premises. (source)
DAC: See digital-to-analog converter.
data
terminal equipment: Communications devices that transmit and
receive data traffic in a communications system. They may also provide
interfaces to users. Examples of data terminal equipment are computers
and multiplexers. (source)
demarcation
point: See line of demarcation.
digital-to-analog
converter: A device for converting a digital (usually binary)
code to an analog signal. It is often abbreviated as DAC,
D/A, or D to A. (source)
digital
signal processing: The study of signals in a digital
representation and the processing methods of these signals. Since the
goal of DSP is usually to measure or filter continuous real-world
analog signals, the first step is usually to convert the signal from an
analog to a digital form, by using an analog-to-digital converter.
Often, the required output signal is another analog output signal,
which requires a digital-to-analog
converter. (source)
DS-0:
Digital signal level 0. Standard term for a 64 kbps digital
telecommunications signal or channel corresponding to the capacity of
one voice-frequency-equivalent channel. The DS-0 rate forms the
basis for the North American digital multiplex transmission hierarchy.
Multiple DS-0s are multiplexed together on higher capacity circuits. 24
DS-0s make a DS-1 signal, which when carried on
copper is the well-known T-carrier system, T-1 (the
European equivalent is an E-1, containing 32 64
kbit/s channels). (source)
DS-1:
Digital signal level 1. A standard term describing the 1.544 Mbps
digital signal carried on a T-1 facility or the
2.048 Mbps digital signal carried on an E-1
facility. A DS-1 line is made up of 24 time division multiplexed DS-0 channels. T-1 and E-1 signals are primarily transmitted over DS-1 lines
composed of standard twisted-pair copper wire. One twisted-pair is used
for the transmit signal and a second twisted-pair is used for the
receive signal creating a full duplex
circuit. In order to offer additional features,
a DS-1 line can be administered with IDSN
protocols. (source)
DSP: See digital signal processing.
DTE: See data terminal equipment.
E-1: A
digital transmission facility used in Europe to primarily transmit 30
digital voice channels. The digital voice channels are time division multiplexed into
a single serial data stream of 2.048 Mbps. E-1 facilities are also used
to transport a mix of digital data, compressed video, and digital voice
in ISDN applications. (source)
frame: In T-1 and E-1 multiplexing, a frame
is a term used to define the results of one complete multiplexer scan
cycle in which a byte of data from each channel has been placed in its
respective time slot for transmission over
the T-1 or E-1 line. A T-1 frame consists of 24 time
slots and an E-1 frame consists of 32 time slots. The multiplexed data is transmitted
and received frame by frame. (source)
full duplex:
Capability for simultaneous data transmission between a sending station
and a receiving station. (source)
gateway:
In telecommunications, it is a network node equipped for interfacing
with another network that uses different protocols. A protocol
translation/mapping gateway, such as a TDM - VoIP gateway, interconnects networks with different
network protocol technologies by performing the required protocol
conversions. (source)
in-band
signaling: Signaling transmitted within a frequency range or
channel normally used for information transmission. (source)
integrated services
digital network: A digital service offered by both T-1 and E-1 providers for the
transport of digitized voice, digital data, and compressed video that
supports additional
features over a standard T-1 or E-1.
When offered at the full T-1 or E-1
data rate, this is known as primary
rate interface ISDN (PRI ISDN) as opposed
to basic rate interface ISDN (BRI ISDN). (source)
ISDN: See integrated services
digital network.
line
of demarcation: Also known as the demarcation point, it is the
point at which the telephone carrier's local loop network ends and
connects with the telephone system or wiring at the customer's
premises. In most cases, everything up to and including the demarcation
point is owned by the carrier, and everything past it is owned by the
property owner. (source)
out-of-band
signaling: Signaling transmismitted using frequencies or
channels outside the frequencies or channels normally used for
information transfer. Out-of-band signaling often is used for error
reporting in situations in which in-band signaling can be affected by
whatever problems the network might be experiencing. (source)
packet
switching: A communications paradigm in which packets (messages
or fragments of messages) are individually routed between nodes, with
no previously established communication path. The internet is a packet
switched network. It is also called connectionless and is the opposite
of circuit switched or
connection-oriented networking. VoIP voice
packets are an example of packet switching. (source)
PBX: See private branch exchange.
PCM: See pulse code modulation.
PRI ISDN:
See primary rate interface ISDN.
primary
rate interface ISDN: Also known as 23B+1D, it is an integrated services
digital network channel consisting of 23 64 kbps "bearer" (B)
channels (DS-0 channels 1-23) and one 64 kbps "delta" (D) channel (DS-0
channel 24), giving a total data rate of 1.544 Mbps. The B channels are
used for voice or user data, and the D channel is used for control and
signalling and/or X.25 packet networking. PRI is the kind of ISDN interface most likely to be found in business
service. PRI ISDN is an example of in-band
CCS. (source)
private
branch exchange: A telephone exchange located at a user’s
premise that provides switching services for local extensions as well
as access to the public
switched telephone network. (source)
pulse
code modulation: A method for converting analog voice to digital
voice. The analog voice signal is sampled at a rate of 8000 times
per second and each sample is described digitally using an 8-bit byte.
This results in a 64 kbps digital voice signal. (source)
PSTN: See public switched telephone
network.
public switched telephone
network: The concatenation of the world's public circuit switched telephone networks, in
much the same way that the internet is the concatenation of the world's
public IP-based packet switched
networks. Originally a network of fixed-line analog telephone systems,
the PSTN is now almost entirely digital, and now includes mobile as
well as fixed telephones. (source)
robbed-bit
signaling: An in-band signaling
method used in T-1 digital voice transmission where
the least significant bit is "robbed" from the 8-bit byte of each DS-0 channel’s time slot in
frames 6 and 12 of a superframe; and frames 6, 12, 18, and 24 of an extended superframe.
The robbed bits are used to convey signaling information for each
respective DS-0 channel. This is a form of channel associated signaling.
(source)
session
initiation protocol: An application-layer control (signaling)
protocol for creating, modifying, and terminating sessions with one or
more participants. These sessions include internet telephone calls,
multimedia distribution, and multimedia conferences. (source)
signaling
system 7: A global standard for telecommunications defined by
the International Telecommunications Union (ITU). This standard defines
the procedures and protocol by which network elements in the public switched telephone
network (PSTN) exchange information over a
digital signaling network to effect wireless (cellular) and wireline
call setup, routing and control. Signaling system 7 is an example of out-of-band CCS.
(source)
SIP: See session initiation protocol.
span: The
portion of a high speed digital system that connects two switching
centers (for example, central offices or
PBXs) and supports full duplex transmission. The industry term
for this is a trunk. (source)
SS7: See signaling
system 7.
T-1: A
digital transmission facility used in North America and Japan to
primarily transmit 24 digital voice channels. The digital voice
channels are time division
multiplexed into a single serial data stream of 1.544 Mbps. T-1
facilities are also used to transport a mix of digital data, compressed
video, and digital voice in ISDN applications. T-1
digital voice transmissions use robbed-bit
signaling and are an example of in-band
CAS. (source)
TDM: See time division multiplexing.
time
division multiplexing: A method in which digital information
from lower data rate channels is bit or byte interleaved into time slots on a higher data rate stream for
efficient transmission. The high speed data rate is typically the
aggregate of the data rate of all the lower speed channels. In time
division multiplexing, the data received on the high speed line is
de-multiplexed from the individual time slots
and directed to each of the lower data rate channels respectively. Time
division multiplexing is used in T-1 and E-1 transmission. (source)
time slot:
In T-1 and E-1 time division multiplexing, a
time slot is the amount of bandwidth allocated on the high speed line
for an 8-bit byte of digital information from each DS-0
channel being multiplexed. That channel’s time slot appears in the same
sequence in each T-1 or E-1 frame. (source)
transcoder:
A device that converts digital content from one (usually lossy) format
to another. It involves first decoding/decompressing the original data
to a raw intermediate format (ie. PCM for audio or
YUV for video) that mimics standard playback of the lossy content and
then re-encoding this into the target format. Compression
artifacts are cumulative, therefore transcoding between lossy codecs causes a progressive loss of quality with
each successive generation. (source)
trunk: A
dedicated aggregate telephone circuit that connects two switching
systems such as central offices and PBXs. (source)
voice over
IP: Also known as IP telephony and internet telephony, it is
technology that enables routing of voice conversations over the
internet or any other IP network. This departs from the traditional use
of dedicated, circuit switched voice
transmission lines, instead carrying the voice data over a
general-purpose packet switched
network. (source)
VoIP: See voice
over IP.