Telecommunications
Glossary
Analog Signal
An analog signal is a continuous electrical signal that
varies in direct correlation with an impressed phenomenon,
stimulus, or event that bears intelligence. Sound waves
and their electrical analogs are characterized by loudness
(amplitude) and pitch. Analog signals can assume any of
an infinite number of amplitude values or states within
a specified range, in accordance with or analogous to,
an impressed stimulus. Pitch refers to how many times
per second the signal swings between high and low amplitudes,
i.e., its frequency.
ANSI
American National Standards Institute
ATM
Asynchronous transfer mode.
Automatic
Call Distribution (ACD)
ACD is a means for efficiently directing and managing
large numbers of incoming calls to specific departments/terminals
within an organization.
Bandwidth
Bandwidth is a frequency range, usually specified by the
number of hertz in a band or between upper and lower limiting
frequencies. Alternatively, the frequency range that a
device is capable of generating, handling, passing or
allowing.
Bipolar
Signals
Bipolar signals are signals in which positive and negative
pulses, always alternating, represent one binary signal
state only. The absence of pulses represents the other
binary state. Bipolar has two forms, AMI and ASI. In alternate
mark inversion (AMI) the pulses correspond to ls; in alternate
space inversion (ASI) the pulses correspond to 0s.
Bit
Error Rate (BER)
BER is the ratio of the number of bits received with errors
to the total number of bits transmitted. BER and the average
number of error-free seconds are the principal impairment
measurements for digital channels.
Bit
Rate
Bit rate is the capacity characteristic of digital signals
as defined by the number of bits (or bytes) per second
that a channel will support. For example, a transmission
facility that can support information exchange at the
rate of I megabit per second (1 Mbps or 1,000,000 bits
per second) delivers the same quantity of information,
i.e., throughput, as a 1 kilobit per second (kbps or 1,000
bits per second) facility, but, in only 1/1000 of the
time.
BOC
(Bell-operating Company)
BOC is the common term for one of 24 local exchange carrier
telephone companies that were part of the Bell System
prior to divestiture. All but two of the BOCs (Southern
New England Telephone in Connecticut and Cincinnati Bell
in Ohio) are owned and managed by one of 7 regional Bell
holding companies (RBHCs). Approximately 80% of America's
local exchange users are served by the BOCs.
Carrier
System
A carrier system is a transmission system for transmitting
one or more channels of information by processing and
converting to a form suitable for the transmission medium
used. Carrier systems are classified as either analog
carrier systems or digital carrier systems.
CCITT
CCITT is the International Consultative Committee for
Telephone and Telegraph, a consultative committee to the
International Telecommunications Union (ITU) which recommend
international standards for telephone and telegraph services
and facilities to aid international connectivity and interoperability.
CDMA
code division multiple access
Channel
Service Unit (CSU)
Channel Service Units (CSUs) and Data Service Units (DSUs)
are required to connect digital customer premises equipment
(CPE) to carrier networks. A CSU is network channel terminating
equipment (NCTE) attaching as CPE to telephone company's
digital circuits, and protecting the network from harm.
Other CSU functions include line conditioning and equalization,
error control (e.g., bipolar signal violations), and the
logical ability to respond to local and network loop back
circuit testing commands. See Data Service Units (DSU).
Circuit
Switching
Circuit switching is a process that establishes connections
on demand and permits the exclusive use of those connections
until released. Packet and message switching, primarily
used in data communications networks are alternative switching
techniques.
Codec
Codec is a contraction of coder and decoder; a device
that encodes analog signals into digital signals, for
transmission through a network in digital format, and
decodes received digital signals back into analog signals.
Common
Channel Signaling (CCS)
CCS is a signaling system developed for use between stored
program control digital switching systems, in which all
of the signaling information for one or more trunk groups
is transmitted over a dedicated signaling channel, usually,
but not always completely separate from the user traffic
bearing facilities.
Common
Management Information Protocol (CMIP)
CMIP is the OSI protocol for network management. A structure
for formatting messages and transmitting information between
reporting devices (agents) and data collection programs,
developed by the International Standards Organization
and designated ISO/IEC 9596.
Cross
Connect
1 In a premises distribution system, equipment used to
terminate and administer communications circuits. In a
wire cross connect, jumper wires or patch cords are used
to make circuit connections, between horizontal and backbone
wiring segments. 2. in transmission systems a patch panel
for connecting circuits.
Data
Service Units (DSU)
DSUs are channel service units (CSI's) and data service
units (DSUs) are required to connect digital customer
premises equipment (CPE ) to carrier networks. A hardware
device providing an interface between a digital line and
a unit of data terminal equipment. DSUs provide transmit
and receive control logic, synchronization and timing
recovery across data circuits. DSUs may also
convert ordinary binary signals generated by CPE to special
bipolar signals. Bipolar signals are designed specifically
to facilitate transmission at up to 1.544 Mbps rates over
UTP cable, a media originally intended for 3 kHz, voice
bandwidth signals. See Channel Service Units (CSU).
Digital
Carrier Systems
Digital Carrier Systems are carrier systems for digital
signals that uses regenerative versus linear repeaters
and time division multiplexing.
Digital
Cross Connect System (DCS)
DCS is a new generation of switching/multiplex equipment
that permits per-channel DS0 (64 kbps) electronic cross-connection
from one T1 transmission facility to another, directly
from the constituent DSl signals. Commonly referred to
as "DACS" (digital access and cross connect
system), although this is a trademark of AT&T.
Digital
Signal
A digital signal is a signal (electrical or otherwise)
in which information is carried in a limited number of
different (two or more) discrete states. The most fundamental
and widely used form of the digital signal is binary,
in which one amplitude condition represents a binary.
Erlang
An erlang is an international dimensions unit of the average
traffic intensity of a facility during a period of time;
one erlang of traffic is equivalent to a single user who
uses a single resource 100% of the time.
FDDI
Fiber-distributed data interface
Frequency
Division Multiplexing (FDM)
FDM divides the frequency bandwidth (spectrum) of a broadband
transmission circuit into many
subbands, each capable of supporting a single, full time
communications channel on a non-
interfering basis with other multiplexed channels. FDM
multiplexing is generally suitable for use
with analog carrier transmission systems.
Full
Duplex
Full duplex is a transmission path capable of transmitting
signals in both directions
simultaneously.
Half
Duplex
Half duplex is a transmission path capable of transmitting
signals in both directions, but only in one direction
at a time.
HDLC
High-level data link control
Inbound
Signaling
Inbound signaling uses not only the same channel path
as the voice traffic, but the same frequency range (band)
used for the voice traffic.
Independent
Telephone Company (ITC)
ITC is a local exchange carrier that is not one of the
22 divested Bell-operating companies. ITCs are not generally
subject to the restrictions of the MFJ, although some
of the larger ones are bound by separate consent decrees.
Southern New England Telephone and Cincinnati Bell are
generally considered ITCs from a regulatory point of view.
Integrated
Services Digital Network (ISDN)
ISDN consists of a set of standards being developed by
the CCITT and various U.S. standards setting organizations.
The CCITT formal recommendations, adopted in October,
1984, first defined ISDN as ". . . a network, in
general evolving from a telephony integrated digital network,
that provides end-to-end digital connectivity to support
a wide range of services, including voice and non-voice,
to which users will have access by a limited set of standard
multipurpose user-network interfaces." The concept
of user access to an existing integrated digital network
(IDN) underlies the ISDN.
IOC
Interoffice channel
IPX
Internetwork packet exchange
IP
Internet protocol
Multimode
Optical Fiber(S)
Multimode fibers, with much wider cores than single mode
fibers, allow light to enter at various angles, and reflect
(bounce off of) core-clad boundaries as electromagnetic
(light) wave propagates from transmitter to receiver.
From a technical performance trade-off point of view,
single mode fiber exhibits bandwidths of up to 100,000
MHz (MHz = 1,000,000 hertz or cycles per second = one
megahertz) while multimode band width is in the range
of 1,000 to 2,000 MHz (1,000 MHz = one billion hertz =
one gigahertz = 1 GHz). See optical fiber(s); single modefiber(s).
Multiplexing
Multiplexing is a technique that enables a number of communications
channels to be combined into a single broadband signal
and transmitted over a single circuit. At the receiving
terminal, demultiplexing of the broadband signal separates
and recovers the original channels. Multiplexing makes
more efficient use of transmission capacity to achieve
a low per channel cost. Two basic
multiplexing methods used in telecommunications systems,
are frequency division multiplexing (FDM) and time division
multiplexing (TDM).
Network
Control Point (NCP)
In virtual private networks, the Network Control Point
is a centralized database that stores a subscriber's unique
VPN definition. Highly sophisticated, this database screens
every call and applies call processing control in accordance
with customer-defined requirements.
NOC
network operations center
Open
Systems Interconnection (OSI) standards
OSI standards are standards for the exchange of information
among systems that are "open" to one another
by virtue of incorporating ISO standards. The OSI reference
model segments communications functions into seven layers.
Each layer relies on the next lower layer to provide more
primitive functions and, in turn, provides services to
support the next higher layer.
Optical
Fiber(s)
Optical fibers are light guides for electromagnetic waves
in the infrared and visible light spectrum composed of
concentric cylinders made of dielectric materials with
different indices of refraction (i.e., velocity of propagation
normalized to the velocity of light in free space). At
the center is a core comprising the glass or plastic strand
or fiber in which a light wave travels. A low index of
refraction clad surrounds the core and is itself enclosed
in a light-absorbing jacket that prevents
interference among multi-fiber cables. Multi-fiber cable
can be purchased with between 2 and 136 fibers.
OSI
open systems interconnection
OSS
operations support systems or operational support system
Out
Of Band Signaling
Out of band signaling uses the same channel path as the
voice traffic but signaling is in a frequency band outside
that used for the voice traffic. In digital systems, out-of-band
signaling may take the appearance of an allocated bit
position or a dedicated channel or time slot.
Point-of-presence
(POP)
A POP is a physical location within a LATA that an IXC
establishes for the purpose of gaining access to BOC/LEC
networks within the LATA using LEC provided access services.
An IXC may have more than one POP within a LATA and the
POP may support public and private, switched and non switched
services.
POT
point of termination
Private
Branch Exchange (PBX)
A PBX is a premises switching system, serving a commercial
or government organization, and usually located on that
organization's premises. PBXs provide telecommunications
services on the premises or campus, (e.g., internal calling
and other services), and access to public and private
telecommunications network services.
Private
Network
A private network is a network made up of circuits and,
sometimes, switching equipment, for the exclusive use
of one organization.
PRI
primary rate interface
Protocols
Protocols are strict procedures for the initiation, maintenance
and termination of data communications. Protocols define
the syntax (arrangements, formats and patterns of bits
and bytes) and the semantics (system control, information
context or meaning of patterns of bits or bytes) of exchanged
data, as well as numerous other characteristics (data
rates, timing, etc.).
Public
Switched Telephone Network (PSTN)
A Public Switched Telephone Network (PSTN) denotes those
portions of the LEC and IXC networks that provide public
switched telephone network services.
PUC
public utility commission
Pulse
Code Modulation (PCM)
Pulse Code Modulation (PCM) is a modulation scheme involving
conversion of a signal from analog to digital form by
means of coding. See also modulation.
Quantizing
Noise
In any analog to digital conversion process, e.g., PCM,
quantizing noise is the difference between the converted
binary value and the actual analog signal's amplitude.
Repeater
In digital transmission, a repeater is equipment that
receives a pulse train, amplifies it, retimes it, and
then reconstructs the signal for retransmission. In IEEE
802 local area network (LAN) standards, a repeater is
essentially two transceivers joined back to back and attached
to two adjacent LAN segments. See transceiver.
Signaling
Signaling is the process of generating and exchanging
information between components of a telecommunications
system to establish, monitor, or release connections (call
handling functions) and to control related network and
system operations (other functions).
Signaling
System No. 7, SS #7
SS#7 is an international common channel signaling system
recommendations established by the CCITT.
Simplex
Simplex is a transmission path capable of transmitting
signals in only one direction.
Single
Mode Optical Fiber(s)
Single mode optical fibers have sufficiently small core
diameters in relation to the wavelength (frequency) of
operation that electromagnetic (light) wave is constrained
to travel in only one transverse path from transmitter
to receiver. This requires the utmost in angular alignment
of light emitting devices at points where light enters
the fiber and results in higher transmitter/termination
costs than multimode fiber systems. See multimode optical
fiber(s).
SONET
Synchronous optical network
Switch
Matrices
Switch matrices are the mechanism that provides signal
paths between its input and output terminations. Modern
matrices are electronic and involve either time or space
division switching. A time division switch employs a TDM
process, in a time-slot interchange (TSI) arrangement.
In space division, a physical, electrical, spatial link
is established through the switch matrix. Whereas older
space division switches used electro-mechanical mechanisms
with metallic contacts, modern space-division switches
are implemented electronically using integrated circuits.
T1
Carrier
A T1 carrier is a time-division multiplexed digital transmission
facility capable of supporting 24 voice channels, (each
encoded as a 64 kbps PCM DS0 signal), producing an aggregate
multiplexer output signal at the 1.544 Mbps DS1 rate.
Developed in the 1960s, the T1 carrier is designed to
operate full duplex over two pairs in unshielded twisted
pair (UTP) cable.
TA
Terminal adapter
TCP/IP
Transmission control protocol/internet protocol. TCP/IP
is the transport layer and Internet layer, respectively,
of the Internet suite of protocols. TCP corresponds to
layer 4 of the OSI protocol stack: IP performs some of
the functions of layer 3. It is a connectionless protocol
used primarily to connect dissimilar networks to each
other.
TCP
Transmission control protocol
TDMA
Time division multiple access
TDM
Time division multiplexing
Terrestrial
Microwave Radio
Terrestrial microwave radio is a transmission systems
consisting of at least two radio transmitter/receivers
(transceivers) connected to high gain antennas (directional
antennas which concentrate electromagnetic or radiowave
energy in narrow beams) focused in pairs on each other.
The operation is point-to-point, that is, communications
are established between two and only two antennas (installations)
with line-of-sight visibility. This can be contrasted
to point-to-
multipoint systems like broadcast radio or television.
TIA
Telecommunications Industry Association
Time
Division Multiplexing (TDM)
Time Division Multiplexing is a transmission facility
shared in time (rather than frequency), i.e., signals
from several sources share a single channel or bus by
using the channel or bus in successive time slots. A discrete
time slot or interval is assigned to each signal source.
Trunk
In a network, a trunk is a communications path connecting
two switching systems used to establish end-to-end connections
between customers.
Twisted
Pair
Twisted pair is the most common type of transmission medium,
consisting of two insulated copper wires twisted together.
The twists or lays are varied in length to reduce the
potential for interference between pairs. In cables greater
than 25 pair, the twisted pairs are grouped and bound
together in a common cable sheath. See unshielded twisted
pair.
Unshielded
Twisted Pair (UTP)
UTP is a two wood pulp or plastic insulated copper conductors
(wires), twisted together into pairs, capable of propagating
electromagnetic waves. The twists, or lays, are varied
in length to reduce the potential for signal interference
between pairs, in multi-pair cables. Wire sizes range
from 26 to l9 gauge (i.e., 0.016 to 0.036 inch in diameter)
and are typically manufactured in cables of from 2 to
3600 pairs. Shielded twisted pair cable is similar to
UTP, but the twisted pairs
are surrounded by a cylindrical metallic conductor that
is clad with an insulating sheath.
Very
Small Aperture Terminal (VSAT)
VSATs are earth terminals using small antennas (1.5 feet
in diameter). This technology typically operates in the
Ku band (11/14 GHz), and Ka band (20/30 GHz).
Virtual
Private Networks (VPN)
VPNs are services using public network facilities augmented
by network control point and service management system
facilities wherein traffic is routed through the public
network under computer control in a manner that makes
VPN service indistinguishable from dedicated facilities
based private networks. Customers can define, change and
control network resources with the same or more flexibility
as afforded by facilities based private networks.
Wireless
Application Protocol (WAP)
WAP
- a protocol developed by WAP forum is the protocol used
for accessing internet on WAP based mobile phones.
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