Telecom & VoIP Glossary A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z A Access Services
Access services are specified sets of information transfer capabilities furnished to users at
telecommunications network points-of-termination (POTs) to provide access to network transport
services. Two examples are the following: subscriber access lines, the connection between a
network POT (in this case more commonly known as a Network Interface NI) and a local
exchange carrier switching system; and trunks between interexchange carrier points-of-presence
and local exchange carrier switching systems (The POT at the POP is identified as the point of
interface POI). End-to-end connections require originating and terminating access services. Access Tandem (AT)
AT is a LEC switching system that performs concentration and distribution functions for inter-
LATA traffic originating or terminating within a LATA. ACD
automatic call distribution ACF
access coordination fee Address Signals
Address Signals convey destination information such as a called 4-digit extension number, central
office code, and when required, area code and serving IXC carrier code. These signals may be
generated by station equipment, or by a switching system. AMI
alternate mark inversion Analog Carrier System
An analog carrier system is a transmission system that uses repeaters that compensate for
analog medium impairments, and produce output signals that are linear-scaled versions of input
signals. Analog carrier systems can carry speech, data, video and supervisory signals although
they are best suited for speech signals. 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. ANI
automatic number identification ANSI
American National Standards Institute ASB
asynchronous balanced mode ASI
alternate space inversion Asynchronous Communication
A data communications method in which bits are sent
without using a clock signal for synchronization.
Instead, each character is transmitted surrounded by a
start and stop bit that designates the beginning and
ending points of the information. This as opposed to
synchronous communication where blocks of data are
transmitted using a synchronizing clock.
Asynchronous Transfer Mode (ATM)
ATM is a broad-bandwidth, low delay, packet-like (cell relay) switching and multiplexing
technique. It is essentially connection oriented, although it is envisioned to support all services.
ATM networks will accept or reject connections based on user's average and peak bandwidth
requirements providing flexible and efficient service for LAN-to-LAN, compressed video and other
applications that involve variable bit rate (VBR) traffic. ATM
asynchronous transfer mode (See 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. Audio Menu
A verbal choice provided by a recording over the phone. Audio choice menus are common in automated attendant, IVR and fax-on-demand systems. They are prompts for caller input. Audio menus can instruct you to speak commands or press keys on a touch-tone keypad as commands. Audio Response Unit (ARU)
A computer telephony system incorporating voice storeandforward technology. There are passive and interactive ARUs. Passive ARUs simply play out messages while interactive ARUs play messages based on input from callers. Audio Teleconferencing or Audio Conferencing
The original technology used for audio teleconferencing was based on PBX (Private Branch Exchange) conferencing circuits. Setting up conference calls through the PBX is cumbersome, the voice quality degrades as the number of people on a call increases, and there are capacity limitations, so specialized conference bridges were developed to improve capacity and voice quality. Conference bridges, however, require trained operator intervention to schedule and invoke most features. As a result, individual corporations found the cost of ownership prohibitive, and the market for such products has been concentrated on service bureau providers. Today’s PC-based systems provide the freedom of conference bridges. By installing a conference server on your voice networks, you can set up, attend, and manage your own conferences over any touch-tone telephone. Additionally, users can schedule meetings using desktop software from their e-mail systems, or from a web browser. AWG
American Wire Gauge. Back to the top of this telecom dictionary
| | B B8ZS
bipolar eight-zero substitution Backbone Network
A backbone network is a transmission facility designed to interconnect often lower-speed
distribution networks, channels, or clusters of dispersed terminals or devices. Backbone Wiring
In a premises distribution system, backbone wiring is the cable connecting telecommunications
closets and equipment rooms within a building, and/or between buildings in a campus. Backbone
wiring is sometimes referred to as the riser subsystem. 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. BFt
terminal framing bit BF
framing bit Binary digit
See Bit. Binding Post
A binding post is a screw with a small nut mounted on a terminal box. Wires are joined together
by wrapping them around a screw and then tightening the nut on them. 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. BIPS
billion instructions per second BISDN
broadband integrated services digital network Bit
A bit is the most fundamental and widely used form of digital signals are binary signals, in which
one amplitude condition represents a binary digit 1, and another amplitude condition represents
a binary digit 0. Thus a binary digit, or bit is one of the members of a set of two in a numeration
system that is based on two and only two possible different values or states. 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. BOM
Bill of Materials BOQ
Bill of Quantity Bridge Tap
Bridge tap is an undetermined length of wire attached between the normal endpoints of a circuit
that introduces unwanted impedance imbalances for data transmission. Bridges
In IEEE 802 local area network (LAN) standards, bridges are devices that connect LANs, or LAN
segments, at the data link layer. Bridges provide the means to extend the LAN environment in
physical extent, number of stations, performance and reliability. Bridges perform three basic
functions: frame (as opposed to packet) forwarding; learning of station addresses; and resolving
of possible loops in the topology by participating in the spanning tree algorithm. Self learning
bridges construct tables of network addresses by listening" to source address information
contained in data signal frames. Other functions include the ability to filter traffic to keep traffic
originating and terminating in one network segment from leaving that segment; restricting
specified traffic to one segment that might otherwise be routed to other segments; and collecting
and storing network management and control information obtained via traffic monitoring. BRI
basic rate interface Broadband Integrated Services Digital Network (BISDN)
CCITT is developing a BISDN umbrella standard, incorporating underlying standards for
integrated digital network switching, multiplexing and transmission facilities, that will be able to
meet expanding voice, data, video and other requirements well into the future. In one of the first
draft CCITT documents BISDN is simply defined as "a service requiring transmission channels
capable of supporting rates greater than the primary rate". In the U.S. the primary rate for
"narrowband" ISDN (as the current standard is sometimes referred to) is 1.544 Mbps. Brouters
Brouters are devices that combine the functions of bridges and routers. See bridges, routers. Bus
In digital systems, e.g., time division multiplexing equipment, a bus (also referred to as a
highway) is defined as one or more conductors (or some medium) that connect a related group
of devices. Business Applications
Business applications are unique aggregations of telecommunications services that satisfy
particular enterprise needs. Byte
A byte, generally, is an 8-bit quantity of information, used mainly in referring to parallel data
transfer, and data storage; also generally referred to in data communications as an octet or
character. Back to the top of this telecom dictionary
| | C CAB
Carrier Access Business Cable
A cable is a group of metallic conductors or optical fibers that are bound together, usually with a
protective sheath, a strength member, and insulation between individual conductors/fibers and
for the entire group. CABS
Carrier Access Billing System CALC
customer access line charges CAP
competitive access provider Carrier
A carrier is a local (intra-LATA) or long distance (inter-LATA) telecommunications service
providing organization. A waveform, pulsed or continuous, that is modulated by another
information bearing waveform. 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. CBR
continuous bit rate CCIS
common-channel interoffice signaling 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. CCSA
common-control switching arrangement CCS
centi-call seconds or common-channel signaling CDMA
code division multiple access Cell Relay
Call relay is the process of transferring data in the form of fixed length packets called cells. Cell
relay is used in high-bandwidth, low-delay, packet-like switching and multiplexing techniques.
The objective is to develop a single multiplexing/switching mechanism for dividing up usable
capacity (bandwidth) in a l-manner that supports its allocation to both isochronous (e.g., voice
and video traffic) as well as packet data communications services. Standards groups have
debated the optimum cell size. Small cells favor low delay for isochronous applications but involve
a higher header to user information overhead penalty than would be needed for most data
applications. The current CCITT specification for BISDN is for a 53-byte cell which includes a 5-
byte header and a 48-byte payload. Centi Call Seconds (CCS)
CCS is a unit of the average traffic intensity of a facility during a period of time, a CCS is 100 call
seconds of traffic during one hour. Therefore a single traffic source, e.g., one call that generates
traffic 100% of the time produces 36 CCS of traffic per hour, i.e., 3600 seconds of traffic every
3600 seconds. An equivalent amount of traffic could also be generated by 10 sources that only
generate traffic 10% of the time. That is, 10 sources of traffic generating 3.6 CCS each,
contributes the same total traffic as a single 36 CCS traffic source. An alternative measure for
traffic is erlangs where 1 erlang equals 36 CCS. CENTRal EXchange (Centrex)
Centrex is a LEC-provided switching service for business customers that permits station-to-station
dialing, listed directory number service, direct inward dialing and station number identification on
outgoing calls. The switching functions are usually performed in a central office. Digital Centrex
offers the advanced features of fourth generation PBXs, without the need to purchase or lease
equipment and, in most cases, eliminates the need for floor space, electrical prime power and
heating, ventilation and air conditioning. Central Offices (CO)
A central office is a telephone company building in which network equipment such as switches
are installed. Channel
A channel is a single communications path in a transmission medium connecting two or more
points in a network, each path being separated by some means; e.g., spatial or multiplex
separation, such as frequency or time division multiplexing. "Channel" and "circuit" are often
used interchangeably, however circuit can also describe a physical configuration of equipment
that provides a network transmission capability for multiple channels. The characteristics of
channels and circuits are determined by the network equipment and media used to support
them. 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 Associated Signaling
Circuit Associated Signaling is a technique that uses the same facility path for voice and signaling
traffic. Historically this approach was selected to avoid the costs of separate channels for
signaling and because the amount of traffic generated by signaling is small compared to voice,
minimizing the chance for mutual interference. Circuit associated signaling can be contrasted with
some common-channel signaling systems that use completely separate packet switched networks
for signaling traffic. 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. City Wide Digital Centrex
A city wide digital centrex is a capability to serve multiple business locations within a single NXX
(exchange code), using multiple LEC central office Centrex switches. Outside callers are unaware
that multiple business locations are involved. CMIP
common management information protocol Coaxial Cable
Coaxial Cable (also called coax cable or coax) consists of an insulated central conductor
surrounded by a second cylindrical conductor that is clad with an insulating sheath. The outer
conductor usually consists of copper tubing or copper braid. COC
central office connections 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. Communications
Communications is the process of representing, transferring, interpreting or processing
information (data) among persons, places, or machines. Communications implies a sender, a
receiver, and a transmission medium over which the information travels. The meaning assigned
to the data must be recoverable without degradation. Conditioning
Conditioning is an adjustment made to the electrical characteristics of a cable pair to improve its
performance for a specific use. Conductor
In electrical circuits, a conductor is any material that readily permits a flow of electrons (electrical
current) through itself. Analogously, optical fibers are sometimes said to conduct light waves and
are also referred to as conductors. Corporation for Open Systems (COS)
COS is a nonprofit organization composed of manufacturing, service, and user organizations in
the computer communications area. Seeks to facilitate the development of the international,
multi-vendor marketplace through the development, introduction, and verification of OSI and
ISDN standards and by ensuring vendor equipment interoperability. CO
central office CPU
central processing unit 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. CSDC
circuit-switched digital capability CSMA/CD
Carrier sense multiple access with collision detection; a local area network contention based
access control protocol technique by which all devices attached to the network "listen" for
transmissions in progress before attempting to transmit themselves and, if two or more begin
transmission simultaneously, are able to detect the "collision". In that case each backs off
(defers) for a variable period of time (determined by a preset algorithm) before again attempting
to transmit. (Defined by the IEEE 802.3 standard). CSR
Centrex station rearrangement CSU
channel service unit Customer Premises Equipment
Customer Premises Equipment is all telecommunications terminal equipment located on the
customer premises. except coin operated telephones. Back to the top of this telecom dictionary
| | D D type Channel Bank
A D type channel bank is channel termination equipment used for combining (multiplexing)
individual analog channel signals on a time division basis. D type channel banks provide
interfaces for "n" analog signal inputs. Each analog input signal is directed to a codec for en
coding to PCM samples. A part of a Tl carrier system. DACS
digital access & cross-connect system DARPA
Defense Advanced Research Projects Agency Data Compression
Data compression is a technique that removes redundancy in transmitted bit patterns to reduce
transmission rates by 20% to 200%. For example, a modem designed to send and receive data
at 1200 bps without data compression may be capable of supporting 2400 bps with data
compression, using the same network analog voice-grade channel. 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). Data Terminal Equipment (DTE)
DTE is any device that can send data, receive data or perform both functions. (Note: sometimes
DTE implies digital terminal equipment, a type of CPE used with digital Service--see CSU and
DSU.) DB Loss
Decibel (dB) is a unit of measure of signal strength, usually the relationship between a
transmitted signal and a standard signal source. Loss is measured when the signal received
across a communication circuit is less than what was transmitted by the signal generator. DCE
data circuit terminating equipment DCP
digital communications protocol DCS
digital cross-connect system DDD
direct distance dialing DDN
Defense Data Network Digit L
Digital L is another amplitude condition that represents a binary digit 0. See binary digit or bit. 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. Digital Subscriber Line (DSL)
A high speed digital switched service that uses existing copper pairs to connect subscriber CPE (customer premises equipment) to the CO (central office). DSL handles more data downstream (data flowing towards the subscriber) than upstream (flowing towards the network). Digital Termination Service (DTS)
DTS is a service provided by some carriers permitting opera tors of private networks to use
digital microwave equipment to gain access to carrier net works. The FCC has allocated a special
microwave band for DTS. Direct Inward Dialing (DID)
DID is PBX-to-central office trunks that allow incoming calls to a PBX to ring specific stations
without attendant assistance. DID greatly reduces the number of required console attendants,
compared with systems in which all calls must be extended by console attendants. Direct Outward Dialing (DOD)
DOD is PBX-to-central office trunks that allow outgoing calls to be placed directly by PBX stations. Dispersion
In dispersive media, dispersion are complex signals are distorted because the various frequency
components which make up the signal have different propagation characteristics and paths. Due
to the finite conductivity of copper, wire or cable media for guided wave transmission is
fundamentally dispersive. Dispersion limits the upper bit rate that a medium can support by
distorting the signal waveforms to the extent that transitions from one information state to
another cannot be reliably detected by receiving equipment, (e.g., logical l logical 0 value
changes). DLCI
data link connection identifier DOD
direct outward dialing DQDS
distributed queue dual bus DS"N" Digital Signal Hierarchy
A time division multiplexed hierarchy of standard digital signals used in telecommunications
systems. DS1 level in the hierarchy corresponds to a 1.544 Mbps TDM signal which comprises 24
DS0 signals. DS0 refers to individual digital signals at channel rates of 64 kbps. Four DS1 signals
digitally multiplexed produce a DS2 level signal, containing 96 DS0 channels, and requires a
transmission medium that supports 6.312 Mbps. A DS3 level signal results from the digital
multiplexing of 7 DS2 signals, supports 672 DS0 signals and requires a 44.736 Mbps transmission
medium. Finally a DS4 level signal supports 6 DS3 level signals, 4032 DS0 signals and requires a
274.176 Mbps transmission medium. The DS hierarchy accounts for non synchronism in the
multiplexing plan, hence the term "asynchronous digital hierarchy" and the use of overhead bits.
Note that bit rates at higher levels are not integer multiples of 64 kbps. DSP
digital signal processor DSS/BLF
direct station selection/busy lamp field DSS
digital subscriber service DSU
data service unit DTMF
dual tone multiple frequency DTS
digital termination service Dual-Tone Multiple Frequency (DTMF)
the generic name for the tone signaling scheme used to signal from telephones to switching
equipment, in which 10 decimal digits and two auxiliary characters are represented by selecting
two frequencies of the following group: 697, 770, 852, 941,1209,1336,1447 Hz. Back to the top of this telecom dictionary
| E E-1
The designation for the 2.048 Mbps ITU standard for Europe’s 30-channel digital telephone service. It is the European version of T-1 (DS-1). The bandwidth is divided into 2 signaling channels (channels 15 and 31 starting from 0) and 30 bearer channels (voice channels). A&B bit signaling (robbed bit signaling) is not used here. E-1 uses one of the control channels for signaling and the other for clock synchronization. E&M Leads Signaling
E&M Leads Signaling is an interface, used for connections between switches and transmission
systems and between transmission systems themselves. Signaling information is transferred
across the interface via 2-state voltage conditions on two leads, each with a ground return,
separate from the leads used for message information. The message and signaling information
are combined and separated by means appropriate to the transmission facility. E-mail electronic mail
electronic mail ECSA
Exchange Carriers Standards Assoc EKTS
electronic key telephone system Electrical Signal
An electrical signal is a signal consisting of an electrical current (i.e., a flow of electrons) that
varies with time or space in accordance with specified parameters. Electronic Mail
Electronic mail is a generic term for non-interactive communication of text, data, image or voice
messages between a sender and designated recipients using telecommunications. Electronic Switched Network (ESN) Service
ESN service is a private network service that provides user organizations with a uniform
numbering plan and numerous call-routing features. The electronic tandem switching functions
are furnished by either PBX or Centrex switching equipment. EMI
electromagnetic interference End Office (EO)
EO is a LEC (BOC or an ITC) switching system within a LATA where local loops to customer
stations are terminated for purposes of interconnection with each other and with trunks. CO
(central office) and EO are often used interchangeably. Entrance Facilities
1. in a premises distribution system, the point of interconnection be tween the building wiring
system and external telecommunications facilities (LEC networks, other buildings, etc.). Bellcore
defines the interface with LEC networks as end-user points of termination (POT). 2. has a further
specific meaning in interstate access, entrance facilities for interstate access (ENFIA). EO
end office EPSCS
enhanced private switched communications service Equipment Room
In a premises distribution system, an equipment room is a special purpose room(s), with access
to the backbone wiring, for housing elecommunications, data processing, security, and alarm
equipment. 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. See centicall seconds. ESF
extended superframe ESN
electronic switched network Exchange Carrier (or local exchange carrier LEC)
An exchange carrier is any company, BOC or independent which provides intra-LATA
telecommunications within its franchised area. Extended Superframe Format (ESF)
ESF is an extension of the superframe format of T1 carrier systems from 12 to 24 frames and the
use of framing bits for error checking, a facilities data link (FDL) as well as frame
synchronization. See superframe format. Back to the top of this telecom dictionary
| | F Facilities Based Private Switched Network Services
Facilities Based Private Switched Network Services is a private network for which LECs and IXCs
dedicate physical switching and transmission facilities for the exclusive use of a particular
customer. Fast Packet
Fast Packet is a term referring to a number of broadband switching and networking paradigms.
Implicit is the assumption of an operating environment that includes reliable, digital, broadband,
nearly error free transmission system. Fax Server
A computer based fax machine. Fax servers are “shared use” devices, typically installed on a LAN. Clients on the LAN can use the fax server from their PCs in much the same way they share a network-based (shared) printer. Faxes can be generated by users at their workstations and “printed” to the fax server for transmission. Likewise, fax servers can route incoming faxes to printers, file server directories, or to individual users. Fax servers save users from having to print documents, carry them to the fax machine, and subsequently wait for them to be transmitted after creating a cover page. FCC Federal Communications Commission
The FCC is a board of commissioners empowered by the U.S. Congress to regulate all interstate
and international communications, as well as use of the radio frequency media. www.fcc.gov FDDI
fiber-distributed data interface FDL
facility data link FDM
frequency division multiplexing FEP
front-end processor FIPS
Federal Information Processing Standard Foreign Exchange (FX)
FX is a service that provides a circuit(s) between a user station, a PBX, or a Centrex switch, and a
central office other than the one that normally serves the caller. Frame
In time division multiplexing systems, Frame is a sequence of time slots each containing a sample
from one of the channels carried by the system. The frame is repeated at regular intervals,
(normally the sampling rate used in analog-to-digital conversion processes for signals being
multiplexed) and each channel usually occupies the same sequence position in successive frames. Frame Relay
In data communications, Frame Relay is a packet switching method that uses available bandwidth only when it is needed. This fast packet switching method is efficient enough to transmit voice communications with the proper network management. Frequency
Frequency is acoustic waves and electrical signals might be made up of only a single tone, like a
single note on a piano. In this case the signal waveform is made up of repeating identical
"cycles" and is said to be of a single frequency, equal to the number of cycles that occur in one
second of time. In communications, frequency was traditionally expressed in cycles per second,
but is now expressed in hertz (Hz), still equal to one cycle per second. Thus, one thousand cycles
per second is equal to one thousand hertz, or a kilohertz (kHz). 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. FSS
fully separated subsidiary FTAM
file transfer access & management Full Duplex
In telephony and data communications, full duplex means the ability for both ends of a communication to simultaneously send and receive information without degrading the quality of the content.FX
foreign exchange Back to the top of this telecom dictionary
| | G GOSIP
Government Open Systems Interconnection Profile Grade Of Service (GOS)
GOS is an estimate of customer satisfaction with a particular aspect of service such as noise,
echo or blocking. For example the noise grade of service is said to be 95% if, for a specified
distribution of noise, 95% of the people judge the service to be good or better. In traffic
networks, GOS defines the percentage of calls that receive no service (blocking) or poor service
(long delays). GOS measures apply to all aspects of telecommunications networks. In many cases
the literature equates GOS only with the probability of a blocked call. When used without further
explanation, GOS generally refers to blocking probability. Ground Start
Ground start is a supervisory signal given at certain coin telephones and PBXs by connecting one
side of the line to ground. Guided Media
Guided media is media that constrain electromagnetic or acoustic waves within boundaries
established by their physical construction. Examples include paired metallic wire cable, coaxial
cable, and fiber optic cable. Back to the top of this telecom dictionary
| | H 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 Header
The header is control information appended to a segment of user data for control, synchronization, routing and sequencing of a transmitted data packet or frame. Hertz (Hz)
Hertz is the measurement that distinguishes electromagnetic waveform energy; number of
cycles, or complete waves, that pass a reference point per second; measurement of frequency,
by which one hertz equals one cycle per second. Horizontal Wiring
In a premises distribution system, horizontal wiring is the connection between the
telecommunications outlet in work areas and the telecommunications closet. Hub
In local area networks (LANs), a hub is a wiring concentrator equipment used in hierarchical star
physical wiring topologies. Those directly connected to terminals or other user devices are of ten
referred to as local hubs or concentrators. Central hubs are those at the highest hierarchical
level. Hubs often provide the means for interconnecting 10BaseT, coaxial or fiber optic cable LAN
segments. Intelligent hubs may implement multiport bridging and network management
functions. HVAC
heating, ventilation and air conditioning Back to the top of this telecom dictionary
| I Inter-Asterisk eXchange (IAX or IAX2)
IAX is the Inter-Asterisk eXchange protocol used by Asterisk, a dual licensed open source and commercial PBX server from Digium and other softswitches and PBXs. It is used to enable VoIP connections between servers, and between servers and clients that also use the IAX protocol. IAX now most commonly refers to IAX2, the second version of the IAX protocol. The original IAX protocol has been deprecated almost universally in favor of IAX2. I-MAC
isonchronous media access controller IDN
integrated digital network IEC
International Electrotechnical Commission Impairments
Impairments is the (e.g., transmission channel and signal impairments) degradation caused by
practical limitations of channels, (e.g., signal level loss or attenuation, echo, various types of
signal distortion, etc.) or interference induced from outside the channel (such as power-line hum
or interference from heavy electrical machinery). The measurement of transmission impairments
is an important aspect of predicting whether or not telecommunications systems will sustain the
business applications they are intended to support. Signal-to-noise ratio, percent distortion,
frequency response, and echo are measurements that define impairments most noticeable by
users in analog voice systems. 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. Inter-LATA Services
Inter-LATA services are revenues, functions, etc., that relate to telecommunications originating in
one LATA and terminating outside that LATA. An interexchange carrier (IXC) is a company which
provides telecommunications services between LATAs. (the domain of IXCs). Intermediate Cross Connects
In a premises distribution system, intermediate cross connects are cross-connects located
telecommunications closets. International Organization for Standardization (ISO)
ISO is a worldwide federation of national standards bodies (ISO National Bodies). The work of
preparing international standards is normally carried out through ISO technical committees. Draft
proposals for international standards adopted by the technical committees are circulated to the
National Bodies for approval before their acceptance as Draft International Standards by the
committee. Internet
The Internet consists of the world’s combined public IPbased packet-switched networks. The Internet is an outgrowth and combination of a variety of university and government sponsored computer networks. Federal and private sector subsidies supported the DARPA-NET, NSFnet (National Sciences Foundation,) and thousands of other subnetworks, which were used to do inter-agency research and communication. Today, the Internet is made up of millions upon millions of computers and subnetworks works—almost entirely supported by commercial funds except in countries where deregulation has not occurred. The Internet is the substrate and chief communications backbone for the world wide web (WWW). Internet Telephony
Any means of transmitting the human voice (real-time or near real-time) over the Internet. There are several components: 1) On the client side, a multimedia-equipped PC with special client software will digitize your voice. This can be done with a voice modem or other voice encoding method; 2) A direct or dial-up connection to the Internet allows your voice to be transmitted in packet form to its destination; 3) Connection with the far side is achieved by IP address search, common servers or beacons to identify the called party (and to “ring” that person’s phone); 4) A similar arrangement on the far end completes the call and allows both parties to speak. There are also PSTN/Internet gateways that allow regular telephone callers to make phone-to- Internet-to-phone connections. There are PC-to-phone connections and phone-to-PC connections.
Internet suite of protocols
The internet suite of protocols is a collection of computer-communication protocols originally
developed under DARPA sponsorship, including the transmission control protocol/internet
protocol (TCP/IP). Interoffice Channel
In LEC tariffs, Interoffice Channel is the channel connecting two serving COs (more accurately
serving wire centers). In IXC tariffs, the channel connecting two serving IXC POPs, interoffice
transmission facilities used to connect LEC switching systems. Intra-LATA
Intra-LATA are services, revenues, functions, etc., that relate to telecommunications originating
and terminating within a single LATA (the domain of LECs). IOC
interoffice channel IPX
internetwork packet exchange IP
internet protocol ISDN
integrated services digital network Isochronous Signals
Isochronous Signals are periodic signals in which the time interval that separates any two
corresponding significant occurrences or level transitions is always equal to some unit interval or
a multiple of that unit interval. For example, in digitized voice signals, ideally voice samples occur
isochronously at precisely the sampling interval or frame rate. Packet data signals are not
isochronous. ISO
International Organization for Standardization Internet Service Provider (ISP)
A business that provides subscriber-based access to the Internet. Subscribers can be individuals or businesses. According to Jack Rickard, publisher of Boardwatch Magazine, ISPs operate at the fourth or lowest level of the Internet. At the third level, regional providers aggregate traffic from lower-order ISPs to the second, backbone level. The highest level in North America is the NAP (Network Access Point), which acts as peer-topeer interconnection points for the largest backbones. There are three ”official” NAPs located in San Francisco, California; Chicago, Illinois; and Pennsauken, New Jersey. ISPs use Internet routers, servers and Rrack-mounted modems to provide a variety of services, including web site hosting, FTP service, e-mail accounts, unified messaging, audio and video broadcasting, and—in some cases—Internet telephony and fax gateway services. ITC
independent telephone company ITU
International Telecommunications Union Interactive Voice Response (IVR)
In computer telephony, IVR is a horizontal application wherein computer-based information is accessed over the phone by using a telephone instead of a computer. An IVR platform uses computer telephony components to translate callers’ touch-tones or voice commands into computer queries after the callers listen to an audio menu. For example: “Please enter your account number using the touch-tones on your telephone.” These queries are then “fetched” by the IVR platform from the host computer. In some cases, the information resides in the same platform (self-hosted). The information is converted into voice commands that are spoken over the phone to the caller. Back to the top of this telecom dictionary
| J JPEG
Joint Photographic Experts Group JTM
job transfer manipulation Back to the top of this telecom dictionary
| K Key Telephone System (KTS)
KTS is an arrangement of multi-line telephones and associated equipment that permits the
station user to depress buttons (keys) to access different central office or PBX lines, as well as to
perform other functions. Typical functions include answering or placing a call on a selected line,
putting a call on hold, using the intercom feature between phones at the same location, or
activating a signal buzzer. KSU
key service unit KTS
key telephone system Back to the top of this telecom dictionary
| L LAN (IEEE 802.3 10BaseT)
LAN (Local Area Network) is an Institute of Electrical and Electronic Engineers specification for a
class of LANs using four-pair unshielded twisted pair (UTP) cable. See Local Area Network. LAN
local area network LATA
local access and transport area LCR
least cost routing LDN
listed directory number; generally an organization's main telephone number that appears in the
telephone book. LDN
listed directory number LEC
local exchange carrier Line
See loop transmission facilities. Local Access And Transport Area (LATA)
LATA is a geographic area (called an "exchange" or "exchange area" in the MFJ) within each
BOC's franchised area that has been established by a BOC in accordance with the provisions of
the MFJ for the purpose of defining the territory within which a BOC may offer its telecommunications services. In 1989, there were 198 LATAs, also referred to as market service
areas (MSAs), in the United States. Local Area Network (LAN)
LAN is a premises high-speed (typically in the range of 10 Mbps) data communications system
wherein all segments of the transmission medium (typically coaxial cable, twisted pair or optical
fiber) are contained within an office or campus environment. Local Channel
In LEC tariffs, a local channel is the local loop that connects customer premises to serving LEC
wire centers. In IXC tariffs, the network components (transmission, switching, other) used to
connect customer premises to serving IXC POPs. Loop Length
Typically, loop length is a complete electrical circuit; the pair of wires that winds its way from the
central office to the telephone set or system at the customer's premises. Loop Signaling
Loop signaling is a method of signaling over dc circuit paths that utilizes the metallic loop formed
by the line or trunk conductors and terminating circuits. Loop Start
Loop start is a supervisory signal given at a telephone or PBX in response to closing the loop's DC
current path. Loop Transmission Facilities
Loop transmission facilities connect switching systems to customer premises equipment
throughout the serving area. A loop is a transmission path between a customer's premises and a
LEC central office. The most common form of loop, a pair of wires, is also called a line. A loop"
can be derived from digital loop carrier (DLC) systems also referred to as subscriber loop carrier
(SLC) systems. LSI
large-scale integrated circuit Back to the top of this telecom dictionary
| M MAAP
maintenance & administration panels MACSTAR
multiple access customer station rearrangement MAC
media access control or moves, adds, and changes Main Cross-Connects
In a premises distribution system, main cross-connects are the cross connects located in an
equipment room. MAN
metropolitan area network MCU
mobile control unit Media
See transmission medium; yielded media; unguided media. Messaging
In computer telephony, any means of storing and forwarding messages. This includes fax mail, voice mail, and broadcast messaging. This horizontal application is the most popular of all voice solutions. Messaging systems provide for the storing and forwarding of “nonreal time” communication. For example, a recorded voice message can be stored for later playback either locally or remotely, or a fax can be received and stored before it is re-transmitted to the ultimate recipient. Messages can vary in content and media type—the distinction being that they are recorded or stored for pick up in the future. Message Telecommunications Service (MTS)
MTS is a non-private-line intrastate and interstate long-distance that uses in whole or in part the
public switched telephone network (PSTN). MFJ
Modification of Final Judgment MFOTS
Military Fiber-Optic Transmission System MF
multiple frequency MHS
message handling system MIB
management information base MIC
Material Identification Code Microwave
In telecommunications, microwaves are frequencies above 1 GHz. MIPS
million instructions per second Modems (MOdulator/DEModulators)
Modems are devices that transform digital signals generated by data terminal equipments (DTEs)
to analog signal formats, suitable for transmission through the extensive, world-wide connectivity
of public and private, switched (dial up) and non-switched telephone voice networks. Modification Of Final Judgment (MFJ)
MFJ is a ruling issued by U.S. District Court Judge Harold Greene which concluded the U. S.
Justice Department's antitrust suit against AT&T by modification of an earlier (1956) consent
decree's final judgment. Modulation
Modulation is the process of varying certain parameters of a carrier signal i.e., a signal suitable
for modulation by an information signal by means of another signal (the modulating or
information bearing signal). MPEG
Moving Pictures Experts Group MSS
metropolitan switching system MTSO
mobile telephone switching office MTS
message telecommunications service Multiline Telephone
A multiline telephone is a telephone that incorporates visual displays and switches (keys) that
permit the station user to access more than one central office or other line and to perform other
desired functions. Typical functions include answering or originating a call on a selected line,
putting a call on hold, operating an intercom feature, a buzzer, etc. Displays can indicate busy,
ringing and message waiting status. 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). Back to the top of this telecom dictionary
| N NBEC
non-Bell exchange carrier NCP
network control point NCTE
network channel terminating equipment Network Control Point (NCP)
In virtual private networks, the Network Contol 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. Network Operating System (NOS)
NOS is software that controls the execution of network programs and modules. Structurally,
networking software comprises multiple modules, most residing in network servers, but some
must be installed in each terminal/station that can access network resources. Peer-to-peer NOSs
permit any terminal/station to act as a resource server or a client, and can be based on
Microsoft's Disk operating system (MS DOS) designed for IBM and compatible PCs. Since MS DOS
is not designed to run multiple programs and respond to many simultaneous users, most NOSs
designed for large networks with dedicated servers/superservers, have a multitasking and multi-
user architecture. Advanced NOS products support network management, diagnostics, and
administration, as well as, primary server, client, de vice and external network driver functions. Network Services
Network Services are specified sets of information transfer capabilities furnished to users
between telecommunications network points of termination. Network services categories include
access and transport, public and private, and switched and non-switched. NIC
network interface card NIST
National Institute of Standards and Technology NI
network interface NOC
network operations center NOS
network operating system NPA
numbering plan area NSEP
National Security & Emergency Preparedness NTSC
National Television System Committee NT
network termination Back to the top of this telecom dictionary
| O OA&M
operation administration & maintenance OCC
other common carriers Ohms Restriction
Ohms Restriction is the same as Ohms resistance. Ohms are measures of resistance. A resistance
of one Ohm allows one Ampere of current to pass at the electric potential of one Volt. 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. Operating Telephone Company
An operating telephone company is any Bell-operating company or independent telephone
company (termed exchange carrier in the MFJ) operating in North America. 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. OPX
off-premises extension OSC
operating system control 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. Back to the top of this telecom dictionary
| P P-MAC
packet media access controller Packet
A logically grouped unit of data. Packets contain a payload (the information to be transmitted), originator, destination, and synchronization information. The idea with packets is to transmit them over a network so each individual packet can be sent along the most optimal route to its destination. Packets are constructed on one end of the communication and de-constructed on the receiving end based on the header addressing information at the front of each packet. Routers in the network will store and forward packets based on network delays, errors, and re-transmittal requests from the receiving end. Packet Switching
A means of economically sending and receiving data over multiple network channels. Packet switching takes data and breaks it down into packets—small bundles of information containing the payload and routing information. The packets are then transmitted to the receiving end, where they are converted back to the original data format. One feature of packet switching is that packets
can be received out of order and then be quickly arranged into the correct order. There are slow packet switching networks—like the old SNA networks—and fast packet networks based on Frame Relay and ATM. Although traditionally used for data, packet networks— especially well-managed ones—are suitable for real-time transmission of voice and video. PAD
packet assembler-disassembler PCB
printed circuit board PDS
premises distribution system Personal Communications
Personal communications provides at least one human operator with direct terminal access and
real time or near real time interactive communications with a remote human opera tor or an
information system resource. Personal communications can refer to a broad range of services,
systems and equipment, e.g., facsimile machines, landline telephones, cellular tele phone
systems and emerging personal communication system (PCS) adjuncts, and a variety of radio
systems including pagers, hand-held remote data entry terminals, and autonomous citizen-band-
like radio systems. PHY
physical-layer protocol PMD
physical-layer media-dependent 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. Post Office Protocol (POP)
An Internet standard for storage and retrieval of email messages. POT
point of termination PPSN
public packet switched network Premises Distribution System (PDS)
PDS is the transmission network inside a building or among a group of buildings, for example an
office park or a campus. PDS is used in this book as a generic term although AT&T used it to
describe a specific product offering. The PDS connects desktop and other station equipment with
common host equipment, (e.g., switches, computers and building automation systems), and to
external telecommunications networks. Private Branch Exchange (PBX) or
Private Automatic Branch Exchange (PABX)
In telephony, a PBX system behaves as a customer’s premises over trunk lines (thus the term branch). At first, PBXs mimicked a small telephone company switchboard. Users would use an operator to make telephone calls to the PSTN (public switched telephone network). Now, users dial directly, without using an operator; computer telephony platforms such as automated attendants are able to route incoming calls automatically, too. 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.). PSN
packet switched network PSPDN
packet switched public data network Public Switched Telephone Network (PSTN)
The world’s combined public circuit-switched telephone networks make up the PSTN. At one time, the PSTN consisted of analog telephone systems, now the PSTN is almost entirely digital, and includes mobile telephones along with fixed telephones. PTT
postal, telephone, and telegraph 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. PVC
permanent virtual circuit Back to the top of this telecom dictionary
| | Q 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. Back to the top of this telecom dictionary
| R Real-Time
Communications wherein perceptible delays between the sender and receiver are minimal and easily tolerated are considered to take place in real-time. Regular telephone calls are real time. Point-to-point fax transmissions are near to real-time. Voice messaging is not real-time. RBHC
regional Bell holding company RBS
robbed bit signaling Regional Bell Holding Company (RBHC)
RBHC is one of 7 regional companies created by the AT&T divestiture to assume ownership of
the Bell operating companies. They are Ameritech, Bell Atlantic, Bell South, NYNEX, Pacific
Telesis, Southwestern Bell and US West. Registered Jack-11 (RJ-11)
The designation for connecting a tip and ring circuit to a standard, modular, 6-position jack.
Registered Jack-45 (RJ-45)
Eight-position modular connector used for data transmission over standard twisted or flat pairs. 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. RFC
request for comment RFE
Request for Engineering RFI
radio frequency interference RFP
request for proposal RF
radio frequency Routers
In IEEE 802 local area network (LAN) standards, routers are devices that connect autonomous
networks of like architecture at the network layer (layer 3). Unlike a bridge which operates
transparently to communicating end-terminals at the logical link layer (layer 2), a router reacts
only to packets addressed to it by either a terminal or another router. Routers perform packet (as
opposed to frame) routing and forwarding functions; they can select one of many potential paths
based on transit delay, network congestion or other criteria. How routers perform their functions
is largely determined by the protocols implemented in the networks they interconnect. RSU
remote switching unit Back to the top of this telecom dictionary
| S SAFENET
survivable adaptable fiber-optic embedded network Satellite Communications
Satellite communications entails microwave radio, line-of-sight propagation from a transmitting
earth terminal (i.e., usually ground-based but potentially ship or airborne) through the
atmosphere and outer space media to a satellite, and back to earthbound receiving terminals. In
essence, satellites are equivalent to orbiting microwave repeaters. Scenario
In SWAT, a scenario is an iteration of an RFW project. A scenario holds the design detail work
units that are associated with the project. By creating multiple scenarios, you can compare
pricing and scheduling options. A scenario has three different statuses. A Working status
indicates that the scenario is under review. A Posted status indicates that a scenario has been
identified as the official design. A Final Posted status indicates that a scenario is the "as-built"
version of the project. SDH
synchronous digital hierarchy SDN
software defined network Server
In a network, a server is equipment that makes available file, database, printing, facsimile,
communications or other services to client terminals/stations with access to the network. A
gateway is a server that permits client terminal/station access to external communications
networks and/or information systems. Service Management System (SMS)
In virtual private networks, SMS is a facility used to build and maintain a VPN database allowing
customers to program specific functions for unique business applications. The SMS contains
complete specifications of customer defined private network specifications including location
data, numbering plan, features, screening actions, authorization codes, calling privileges, etc.
This information is downloaded (transmitted) to network control points (NCPs) which implement
its instructions on a customer-by-customer basis. Service Order (SO)
A service order is a record that describes a customer request to establish, change, or terminate a
service. The service order contains all information required to meet a customer's needs. Service Provider
A company that provides services to Internet, telephone, and mobile phone users.
Signaling System #7 (SSY7)
The basis for routing traffic with out-of-band signaling. Its forerunner, CCIS (Common Channel Interoffice Signaling), used 4.8 kbps data links to transmit call set up and tear down messages to switching office adjunct computers and packet switches. SS7 in itself is not a network service offering, but rather the underlying infrastructure upon which many existing and proposed offerings are based. For example, local Basic Rate ISDN (BRI) services can tap into SS7, so 64 kbps packetized data can be routed with the help of the network’s out-of-band signaling capability. In addition, nationwide Primary Rate ISDN (PRI) services can use the same backbone. SF
single frequency Shielded Twisted Pair
Shielded twisted pair is twisted copper paired wire cable with an outer metallic sheath
surrounding insulated conductors. See unshielded twisted pair. Signal
A signal is usually a time-dependent value attached to an energy propagating phenomenon used
to convey information, for example, an audio or sound signal in which the data is characterized in
terms of loudness and pitch. 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. Simple Network Management Protocol (SNMP)
SNMP is the application protocol offering network management service in the Internet suite of
protocols. A structure for formatting messages and transmitting information between reporting
devices (agents) and data collection programs. Developed jointly by the Department of Defense,
industry and the academic community as part of the TCP/IP protocol suite; ratified as an Internet
standard in Request for (Comment (RFC) 1098. 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). Session Initiation Protocol (SIP)
The Session Initiation Protocol (SIP) is a signalling protocol used for establishing sessions in an IP network. A session could be a simple two-way telephone call or it could be a collaborative multi-media conference session. The ability to establish these sessions means that a host of innovative services become possible, such as voice-enriched e-commerce, web page click-to-dial, Instant Messaging with buddy lists, and IP Centrex services. SMDR
station message detail record SMDS
switched multimegabit data system SMT
station management technology SNA
Systems Network Architecture SNI
subscriber network interface SNMP
Simple network management protocol. See Simple Network Management Protocol (SNMP). SO
Service Order SONET
synchronous optical network Space Division
Space division is a switch that implements the switch matrix using a physical, electrical, spatial
link. Where older space division switches used electro-mechanical mechanisms with metallic
contacts, modern space-division switches are implemented electronically using integrated circuits.
(Usually denoted by "S" in combined time and space division switches). Special Services
Special services are any of a variety of LEC and IXC switched, non-switched, or special rate
services that are either separate from public telephone service or contribute to certain aspects of
public telephone service. Examples include PBX tie trunks, foreign exchange (FX) and private line
services. These services are important to business telecommunication planners/users. Speech Recognition
Speech recognition describes a technology that enable callers to speak words that are used to control applications.
Store and Forward
The method for storing a message or transmission for later playback or transmission. As opposed to real-time communication, store and forward is the basis for all messaging systems, including email, fax-on-demand, unified messaging, etc. In data communications, store and forward applies to momentary buffering of packets or other data strings.
SSN
switched service network SS
signaling system Station Equipment
Station equipment is a component of telecommunications systems such as a telephone or data
terminal, generally located on the user's premises. Its function is to transmit and receive user
information (traffic), and to exchange control information with the network to access
communications services. STM
synchronous transfer mode STP
shielded twisted pair or signaling transfer/point Superframe Format (SF)
Superframe format is a framing format (D3/D4--mode 3), the most widely used T1 carrier
framing format in which the bipolar bit stream is organized into superframes each consisting of
12 frames. To ensure timing, the signal must consist of at least one "1" bit in every 15 bits and at
least :3 " 1" bits in every 24 bits. See extended superframe. Supervisory Signals
Supervisory signals are signals used to indicate or control the states of circuits involved in a
particular switched connection. A supervisory signal indicates to equipment, to an operator, or to
a user that a particular state in the call has been reached and may simplify the need for action. 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. Switching
Switching refers to the process of connecting appropriate lines and/or trunks to form a desired
communications path between two station sets, or more generally, any two arbitrary points in a
telecommunications network. Included are all kinds of related functions such as signaling,
monitoring the status of circuits, translating address to routing instructions, alternate routing,
testing circuits for busy conditions, and detecting and recording troubles. Switching Systems
Switching systems are interconnect transmission facilities at various network locations and route
traffic through a network. Systems (Manual Circuits)
In Plant Records and Assignment, these terms refer to circuits whose network elements have
been assigned manually rather than by automatic assignment. Systems Network Architecture (SNA)
SNA is IBM's proprietary description of the logical structure, formats, protocols, and operational
sequences for transmitting information units through and controlling network configuration and
operation. Back to the top of this telecom dictionary
| T T-1 or T1
North American digital standard for high capacity transmission of telephony and data communications. In telephone T-1 provides a 1.544 Mbps link which is divided into 24 discrete, 64kpbs voice-grade channels. In data communications, T-1 links are used to directly connect CPE (Customer Premises Equipment) routers to the Internet and for Private Data Network or VPN 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. T-3
North American standard for DS-3. Operates at a signaling rate of 44.736 Mbps, or the equivalent of 28 T-1s. Tandem Switching System
A tandem switching system is a broad functional category describing systems that connect trunks
to trunks, and route traffic through a network. Tariff
A tariff is a published rate for a specific telecommunications service, equipment, or facility that
constitutes a public contract between the user and the telecommunications supplier (i.e., carrier);
tariff services and rates are established by and for telecommunications common carriers in a
formal process in which carriers submit filings for federal or state government regulatory review,
public comments, possible amendment, and approval. 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. Transmission Control Protocol (TCP)
The transport layer protocol developed for the ARPAnet which comprises layers 4 and 5 of the OSI model. TCP controls sequential data exchange in TCP/IP for remotely hosts in a peer-to-peer network. TDMA
time division multiple access TDM
time division multiplexing Telecommunications
Telecommunications is any process that enables one or more users to pass to one or more other
users information of any nature delivered in any usable form, by wire, radio, visual, or other
electrical, electromagnetic, optical means. The word is derived from the Greek tele, "far off," and
the Latin communicare "to share." Telecommunications Closet
In a premises distribution system, a telecommunications closet is an area for connecting the
horizontal and backbone wiring and for containing active or passive PDS equipment. Telecommunications Network
A telecommunications network is a system of interconnected facilities designed to carry traffic
from a variety of telecommunications services. The network has two different but related
aspects. In terms of its physical components, it is a facilities network. In terms of the variety of
telecommunications services that it provides, it can support a set of many traffic networks, each
representing a particular interconnection of facilities. Telecommunications Service
Telecommunications service is a specified set of information transfer capabilities provided to a
group of users by a telecommunications system. Telephony
Taken from Greek root words meaning “far sound”, telephony means the process of converting or transmitting voice or other signals over a distance, and then re-converting them to an audible sound at the far end. 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. Time Division Switch
A time division switch is a switch that implements the switch matrix using the TDM process, in a
time-slot interchange (TSI) arrangement (usually denoted by T in combined time and space
division switches). Token Passing Bus LAN (IEEE 802.4)
A token passing bus LAN is a LAN using a deterministic access mechanism and topology in which
all stations actively attached to the bus "listen" for a broadcast token or supervisory frame.
Stations wishing to transmit must receive the token before doing so; however the next logical
station to transmit may not be the next physical station on the bus. Access is controlled by pre-
assigned priority algorithms. Token Passing Ring LAN (IEEE 802.5)
A token passing ring LAN is a LAN using a deterministic access mechanism and topology, in
which a supervisory frame (or token) is passed from station to adjacent station sequentially.
Stations wishing to transmit must wait for the "free" token to arrive before transmitting data. In a
token ring LAN the start and end points of the medium are physically connected, leading to a ring
topology. TP
transaction processing Tracking
Tracking features user-defined approval levels and project milestone tables to generate project
cost and status information, which is tracked for reporting and review. As assigned tasks are
completed, supervisors make daily entries identifying the number of hours worked on a task,
materials used, and the number of work units completed. This information is then available for
project jeopardy tracking, cost tracking, and determination of contractor payments due. Traffic
Traffic is the flow of information within a telecommunications network. Transceiver
A transceiver is a generic term describing a device that can both transmit and receive. In IEEE
802 local area network (LAN) standards, a transceiver consists of a transmitter, receiver, power
converter, and, for CSMA/CD LANs, collision detector and jabber detector capabilities. The
transmitter receives signals from an attached terminal's network interface card (NIC) and
transmits them to the coaxial cable or other LAN medium. The receiver receives signals from the
medium and transmits them via the transceiver cable and NIC to the attached terminal. The
jabber detector is a timer circuit that protects the LAN from a continuously transmitting terminal. Transfer Mode
Transfer mode is a generic term for switching and multiplexing aspects of broadband integrated
services digital networks (BISDN), adopted by CCITT Study Group XVIII. Transmission control protocol/internet protocol (TCP/IP)
See "Internet suite of protocols" and "TCP/IP". Transmission Facilities
Transmission facilities provide the communication paths that carry user and network control
information between nodes in a network. In general, transmission facilities consist of a medium
(e.g., free space, the atmosphere, copper or fiber optic cable) and electronic equipment located
at points along the medium. This equipment amplifies (analog systems) or regenerates (digital
systems) signals, provides termination functions at points where transmission facilities connect to
switching systems, and may provide the means to combine many separate sets of call
information into a single "multiplexed" signal to enhance the transmission efficiency. Transmission Impairments
Transmission impairments is the degradation caused by practical limitations of channels (e.g.,
signal level loss due to attenuation, echo, various types of signal distortion, etc.), or interference
induced from outside the channel (such as power-line hum or interference from heavy electrical
machinery). Transmission Medium
Transmission medium is any material substance or "free space" (i.e., a vacuum) that can be, or
is, used for the propagation of suitable signals, usually in the form of electromagnetic (including
light waves), or acoustic waves, from one point to another; unguided in the case of free space or
gaseous media or guided by a boundary of material substance. Transport Services
Transport Services are network switching, transmission and related services that support
information transfer capabilities between originating and terminating access service facilities. 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. Back to the top of this telecom dictionary
| U UIS
Universal Information Services Unguided Media
Unguided media is any medium in which boundary effects between "free space" and material
substances are absent. The "free space" medium may or may not include a gas or vapor.
Unguided media including the earth's atmosphere and outer space support terrestrial and satellite
radio and optical transmission. UNI
user-network interface UNIX
A multi-user, multi-tasking operating system originally developed in 1969 by Ken Thompson of AT&T Bell Laboratories. UNIX is used in telephone companies and mission-critical applications. 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. See
cable; conductor. UTP
Unshielded twisted pair. See Unshielded Twisted Pair. Back to the top of this telecom dictionary
| V VAD
value-added distributor VAN
value-added network VAR
value-added reseller VBR
variable bit rate VCI
virtual circuit identifier VCS
virtual circuit switch Very Small Aperture Terminal (VSAT)
VSATs are earth terminals using small antennas (1.5 6 feet in diameter). This technology typically
operates in the Ku band (11/14 GHz), and Ka band (20/30 GHz). Video Conferencing
Video conferencing is the real-time, usually two-way transmission of voice and images between
two or more locations. Today, both voice and video analog signals are digitized by video codices
before transmission which can involve wide bandwidths. To conserve bandwidth, some systems
employ "freeze frame," where a television screen is only "repainted" every few seconds. Codecs
for higher quality full motion video attempt to minimize bandwidth requirements by taking
advantage of intervals with relatively little motion (which require smaller bandwidths), and by
trading off smooth motion tracking and picture resolution. Voice Over IP (VoIP)
Voice over IP or VoIP is a term used in IP telephony for a set of facilities that use the Internet Protocol (IP) to deliver voice information. In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public
switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that they avoid the tolls charged by ordinary telephone service. The term VoIP derives from the VoIP Forum, an effort by major equipment providers, to promote the use of ITU-T H.323, the standard for sending voice (audio) and video using IP on the public Internet and within an intranet. The Forum also promotes the use of directory service standards so that users can locate other users and the use of touch-tone signals for automatic call distribution and voice mail.
In addition to IP, VoIP uses the real-time protocol (RTP) to ensure that packets get delivered in a timely way. Because the nature of public networks such as the Internet makes it difficult to guarantee Quality of Service (QoS), better service is usually possible with private networks
managed by an enterprise or by an Internet telephony service provider (ITSP).
Enterprises use VoIP gateways to enter into the VoIP environment. A gateway receives packetized voice transmissions from users within the company and then routes them to other parts of the company’s intranet (local area or wide area network) or—using a T-carrier system or E-carrier interface—sends them over the public switched telephone network.
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. VPI
virtual path identifier VPN
virtual private network VRU
voice response unit VSAT
very small aperture terminal Back to the top of this telecom dictionary
| W WAN
wide area network WARC
World Administrative Radio Consortium WATS
Wide-area telecommunications services. See Wide-area telecommunications services. Waveform
amplitude (magnitude) versus time representation of signals. Web Browser
Client software used to view information on WWW
servers. Web browsers are also packaged with email
clients, newsreaders and IP telephony clients. Web Server
On the world wide web, a server dedicated to storing data (such as web pages in HTML format) and distributing it to users. Web browsers are able to download video, text, still images and audio from web pages. Some servers support Unified Messaging. Wide-Area Telecommunications Services (WATS)
WATS is a service permitting customers to make (OUTWATS) or receive (INWATS) long distance
voice or data calls and to have them billed on a bulk rather than an individual call basis. The
service is provided by means of special private access lines connected to WATS equipped central
offices. A single access line permits inward or outward service but not both. Wink-Start
Wink-Start is a supervisory signal that consists of an off-hook followed by an on-hook signal,
exchanged between two switching systems. The wink-start signal is generated by the called
switch to indicate to the calling switch that it is ready to receive address signal digits. WO
Work Order Work Area
In a premises distribution system, a work area is an area containing stations and the connections
between those stations and their telecommunications (information) outlets. Work Order
A work order is the basic engineering document that adds, modifies, or removes network
components (capital assets). It is the tracking mechanism that all telecommunication companies
use to add or remove components from their capital base. Back to the top of this telecom dictionary |
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