glossary of Common Telecommunications Terms, EECS 663
Glossary Of Common Telecommunications Terms
- Acknowledgment (ACK)
Message returned from receiver to transmitter to indicate successful
reception of transmission. Also communications control character used for
- Adaptive Differential Pulse Code Modulation (ADPCM)
A form for the digital coding voice signals, typically at 32 Kbps.
- Add/Drop Multiplexer (ADM)
A multiplexer that allows for the insertion and removal of embedded data
channels without the demultiplexing of the entire bit stream.
- Address Resolution Protocol (ARP)
A protocol used to adjust addresses between different networks or domains.
- Advanced Intelligent Network (AIN)
A system that allows the telecommunications providers a mechanism to quickly
and economically create and/or modify services for their customers.
- Alarm Indication Signal (AIS)
Algorithm for multiple access in which any station transmits when ready,
determines whether collision has occurred, and then retransmits if necessary.
- Alternate Route
A secondary path between the source and destination that will be used if the
primary path is unavailable.
- American National Standards Institute (ANSI)
Standards body in United States responsible for a number of
telecommunications standards. ANSI was formed for the purpose of
establishing voluntary industry standards.
- Amplitude Modulation (AM)
The strength of the radio frequency carrier is made proportional to the
- Automatic Number Identification (ANI)
The display for the number of the calling telephone.
- Analog-to-Digital Conversion (A/D)
Conversion of analog signals, e.g., voice or video, into a digital format.
- Application Layer
Highest layer of OSI Reference Model. Layer 7 of the OSI model. This layer
determines the interface of the system with the user and provides useful
American Standard Code for Information Interchange. The standard code,
using a coded character set consisting of 7-bit coded characters (8 bits,
including the parity check), used for information interchange among data
processing systems, data communications systems, and associated equipment.
The ASCII character set consists of control characters and graphic
- Asynchronous Transmission
Random start and stop of data which requires special start and stop
information embedded in the data flow.
- Asynchronous Balanced Mode (ABM)
HDLC mode defined for balanced point-to-point configurations with two
combined stations. Either end can initiate transmission without waiting
for a poll from the other end.
- Asynchronous Response Mode (ARM)
HDLC mode for systems with one primary and one or more secondaries; if more
than one secondary is present, all but one must be quiescent. With one
primary and one active secondary, either active station may initiate
transmission at any time without waiting for a poll or an F bit.
- Asynchronous Transfer Mode (ATM)
Broadband ISDN mode similar to asynchronous time division multiplexing. ATM
uses small fixed length packets called cells.
- ATM Adaptation Layer (AAL)
A protocol layer that segments incoming data into ATM cells.
- Automatic Repeat Request (ARQ)
A feature that automatically initiates a request for retransmission when an
error in transmission is detected. An error correction technique. When the
receiving DTE detects an error, it signals the transmitting DTE to resend
- Basic Rate ISDN
Two B channels at 64kbps and one 16 kbps signaling channel.
- Baud Rate
Number of signal changes per second used to convey information. Often
misused to denote bit rate of digital signal.
- B Channel
Full duplex 64 kbps. ISDN channel used for user data.
- Bell Communications Research (Bellcore)
The research and development organization for the RBOC's.
- Bell Operating Companies (BOCs)
The 22 telephone companies that were members of the Bell system before
divestiture. Before the divestiture of AT&T, the 22 Bell Operating
Companies were AT&T subsidiaries that built, operated, and maintained the
local and intrastate networks and provided most of the day-to-day service
for customers. After divestiture, the BOCs retain their identity within
seven regional companies (RBOCs) and are responsible for local service as
defined by local access and transport areas (LATAs).
- Bell System
The collection of companies headed by AT&T and consisting of the 22 Bell
Operating Companies and the Western Electric Corporation. The Bell System
was dismantled by divestiture on January 1, 1984.
- Bit Error Rate (BER)
A measure of the quality of a digital transmission facility.
- Bit Interleaved Parity (BIP)
A parity check method used in SONET.
- Bit Stuffing
The insertion of extra bits into a data stream to avoid the appearance of
unintended control sequences.
- Bit-oriented protocol
A communications protocol that uses only one special character, called the
flag character, to mark the beginning and end of a message. All other
combinations of bits are treated as valid data characters.
Blocking exist if a request for network resources can not be satisfied by
A device for connecting like LAN's, e.g., Ethernets. Bridges operate at the
data link layer.
- Broadband ISDN (BISDN)
A second generation of ISDN. The key characteristic of broadband ISDN is
that it provides transmission channels capable of supporting rates greater
than the primary ISDN rate. Standards being developed for ISDN to handle
applications such as video requiring high bandwidth.
- Busy hour
The hour of the day when the traffic carried on a network is the highest.
- Call Set-Up Time
The time requires to establish a dedicated end-to-end path in a circuit
- Carrier sense multiple access (CSMA)
Medium access technique involving first sensing medium to see if other
signals are already present, then transmitting if no signal is present.
Several algorithms handle cases where signal is already present.
- Carrier sense multiple access with collision detection (CSMA/CD)
A communications protocol frequently used on local area networks in which
stations, upon detecting a collision of data caused by multiple simultaneous
transmissions, wait a random period of time before retransmitting.
Combination of CSMA with sensing to detect collisions during transmission.
Standard medium access technique in some LANs, including Ethernet.
See Common Channel Signaling.
See Common Channel Signaling System #7.
- Centa Call Seconds (CCS)
A measure of equipment or circuit utilization. One centa call second
is 100 seconds of utilization.
- Central Office (CO)
In the United States, the place where communications common carriers
terminate customer lines and locate the equipment that interconnects those
- Central Office Switch
The equipment in a telephone company central office that allows any circuit
to be connected to any other.
- Channel Service Unit (CSU)
The interface to the T-1 line that terminates the local loop.
- Circuit Switching
A method of communicating in which a dedicated communications path is
established between two devices through one or more intermediate switching
nodes. Unlike packet switching, information is sent as a continuous stream
of bits. Data rate is guaranteed, and delay is essentially limited to
propagation time. In circuit switching there is a temporary establishment of
a connection between two pieces of equipment that permits the exclusive use
until the connection is released. The connection is set up on demand and
discontinued when the transmission is complete. An example is a dial-up
telephone connection. This type of switching is used in ordinary telephone
service, with dedicated path between source and destination set up for
duration of call.
- Code Division Multiple Access (CDMA)
A spread spectrum technique to share bandwidth among a set of users.
Result of multiple attempts to transmit at same time on multiple access
medium. Usually all colliding transmissions wipe each other out and require
- Common Carrier
In the United States, companies that furnish long-distance telecommunication
services to the public. Common carriers are subject to regulation by
federal and state regulatory commissions.
- Common Channel Interoffice Signaling (CCIS)
An AT&T system for sending signals between central offices.
- Common Channel Signaling (CCS)
A method of signaling in which signaling information relating to a
multiplicity of circuits, or function or for network management, is conveyed
over a single channel by addressed messages. Signaling systems being used
and installed in many telephone networks. CCS completely separates
signaling information from user data by sending it over separate signaling
- Common Channel Signaling System#7 (CCSS#7)
Version of CCS used in ISDN architecture.
A device that allows multiple end-point to share a common transmission
- Connectionless Transmission
Data transmission without prior establishment of a connection.
- Constant Bit Rate (CBR)
A traffic type that generates a continuous flow of information, e.g., 64
Kbps voice or fixed rate video.
- Connection-Oriented Transmission
Data transmission technique involving setting up connection before
transmission and disconnecting it afterward.
- Consultative Committee for International Telegraph and Telephone (CCITT)
International standards committee responsible for substantial portion of
telecommunications network standards. CCITT is an international standards
organization that is part of the International Telecommunications Union,
which is an arm of the United Nations.
The condition that arises when two or more users simultaneously request
access to the same network resource.
- Crossbar Switch
A relay-operated device that makes a connection between one line in each of
two sets of lines. The two sets are physically arranged along adjacent
sides of a matrix of contacts or switch points.
- Customer Premises Equipment (CPE)
Telecommunications hardware located at the users site.
- Cyclic Redundancy Check (CRC)
An error detecting code in which the code is the remainder resulting from
dividing the bits to be checked by a predetermined binary number.
Packet or short message transmitted through network without previously
setting up a connection. Different datagrams are handled independently of
each other. In packet switching, a self-contained packet, independent of
other packets, that does not require acknowledgment and that carries
information sufficient for routing from the originating data terminal
equipment (DTE), without relying on earlier exchanges between the DTEs and
- Data Circuit Terminating Equipment (DCE)
The termination point for the network circuit. For example, a modem
terminates the network circuit, the local loop, and is considered as the
DCE. The users device in this example the remote terminal is considered the
data terminal equipment (DTE).
- Data Encryption Standard (DES)
A standard security technique for scrambling information.
- Data Link Layer (DLL)
Layer 2 of OSI Reference Model and most other networking architecture's.
Converts an unreliable transmission channel into a reliable one.
- Data Link Connection Identifier (DCLI)
The address used in frame relay networks.
- Data Terminal Equipment (DTE)
Typical the end-user devices, e.g., terminals or computers.
- Digital-to-Analog Conversion (D/A)
The conversion of digital data to an analog signal.
- Digital (Data) Service Unit (DSU)
Converts the terminal interface, e.g., RS-232, to line coding for
transmission on the local loop.
- Digital Speech Interpolation (DSI)
A voice compression technique based on the talk-spurt/silence property of
- D Channel
Full duplex 16 Kbps or 64 Kbps ISDN channel (in basic rate and
primary rate interfaces, respectively) used to transmit control data or user
- Distributed Queue Dual Bus (DQDB)
A protocol for metropolitan area networks, the bases for the IEEE 802.6
Digital service level-0, a 64kbps channel primarily used for digital voice.
Digital service level-1, a 1.544 Mbps channel in North America or a 2.048
Mbps channel in CCITT countries. Typically composed of multiple DS-0
channels. Typically a DS-1 is composed of 24 DS-0 signals.
Digital service level-3 a 44.736 Mbps digital signal, typically carries 28
DS-1's. Sometimes referred to as T3.
- Dual Tone Multi-Frequency (DTMF)
The transmission of two tone (frequencies) that is used for dialing.
- Electronic Document Interchange (EDI) -
The use of telecommunications to transmit documents electronically.
- Electronic Mail (E-Mail)
The use of telecommunications for sending
textual messages from one person to another. The capability to store the
messages in an electronic mailbox is normally a part of the electronic mail
- Electrical-Optical (E/O)
Electrical to Optical conversion.
The addition of control information by a protocol entity to data obtained
from a protocol user.
- End Office
A class 5 office of a local telephone exchange where a subscriberÕs loop
A measure of communications equipment or circuit usage. One Erlang is one
hour of equipment usage or 36 CCS.
- Erlang B
Blocking Formula The formula which characterizes the probability of blocking
for a M/M/N/N system, i.e., a system that can hold N calls and has N
servers. the systems has a Poisson Arrival process and a random exponentially
distributed service or holding time.
A local area network that uses 1 persistent CSMA/CD protocol on a baseband
- Explicit Congestion Notification (ECN)
A mechanism used by the network to warn user equipment that the network is
- Extended Binary Coded Decimal Interchange Code (EBCDIC) -
The extended character set used in IBM hosts.
- Facsimile Machine (FAX)
A machine that scans a sheet of paper and converts the light and dark areas
to electrical signals that can be transmitted over telephone lines.
- FDDI Fiber Distributed Data Interface
FDDI is a high-speed (100 Mbps) communications architecture standardized by
ANSI, primarily for fiber optic links.
- Fiber-Optic Link (FOL)
- Federal Communications Commission (FCC)
A board of commissioners appointed by the president under the Communications
Act of 1934; the commissioners regulate all interstate and foreign electrical
telecommunications systems originating in the United States.
- Fiber Distributed Data Interface (FDDI)
A 100 Mbps token ring LAN.
- File Transfer Protocol (FTP)
A protocol for transferring files within TCP/IP networks.
- First-in-first-out (FIFO)
Queueing in the order that calls or transactions arrive. Calls that arrive
first get serviced first.
- Flag (1)
Any of various types of indicators used for identification. (2) A bit
sequence that signals the occurrence of some condition, such as the end of
a word. (3) In high-level data link control (HDLC), the initial and final
octets of a frame with the specific bit configuration of 01111110. A single
flag may be used to denote the end of one frame and the start of another.
- Flow Control
Regulation of traffic allowed into specific portions of a network to avoid
excessive congestion. Flow Control is performed by a receiving entity to
limit the amount or rate of data sent by a transmitting entity.
- Forward Error Correction (FEC)
Approach to error control in which redundancy is included in transmitted
messages to allow correction of errors at receiver without retransmission.
Data unit generated by data link layer, consisting of user data plus all
pertinent headers and trailers.
- Frame Relay (FR)
A telecommunications service/network that relies on simplified link-by-link
protocols, high speed transmission (up to 45 Mbps), low link BER, virtual
circuits, and end-to-end error recovery.
- Frequency-Division Multiplexing (FDM)
Division of a transmission facility into two or more channels by splitting
the frequency band transmitted by the facility into narrower bands, each of
which is used to constitute a distinct channel.
- Frequency Modulation (FM)
The frequency of the radio frequency carrier is made to be proportional to
the information signal.
- Full Duplex Channel
A full duplex channel is capable of transmission in both directions
A device that allows for the interconnection of dissimilar networks.
Gateways provide protocol translation, address translation, and code
translation between the connected networks. All seven layers of the OSI
model may be needed to perform these functions.
- Geosynchronous Orbit
The position at which communications satellites will remain in orbit above
the same location on the earth, about 23,000 miles above the surface.
- Giga (G)
One billion. For example, 1 gigahertz equals 1,000,000,000 hertz. One
gigahertz also equals 1000 megahertz and 1,000,000 kilohertz.
- Half Duplex Channel
A half duplex channel is capable of transmission in only one direction at a
- High-Level Data Link Control (HDLC)
A data link layer protocol.
- High Speed Network (HSN)
High-Speed Peripheral Parallel Interface (HiPPi) A computer channel
interface clocked at 25 MHz, a 32 bit wide bus is used for a 800 Mbps
channel while a 64 bit wide bus for a 1.6 Gbps rate. Primarily used to
- Holding time
The duration of a switchboard call. Most often applied in traffic studies to
the duration of a telephone call.
- IEEE 802
Set of standards for LANs being developed by IEEE 802 Committee.
- IEEE 802.2
Logical link control protocol developed by IEEE 802 Committee.
- IEEE 802.3
CSMA/CD-MAC protocol developed by IEEE 802 Committee.
- IEEE 802.4
Token bus MAC protocol developed by IEEE 802 Committee.
- IEEE 802.5
Token ring MAC protocol developed by IEEE 802 Committee.
- IEEE 802.6
Metropolitan Area Network MAC protocol developed by IEEE 802 Committee that
uses the Distributed Queue Dual Bus (DQDB) protocol.
- In-Band Signaling
The transmission of control information in the same 4kHz channel used for
- Integrated Services Digital Network (ISDN)
Worldwide telecommunication service that will use digital transmission and
switching technology to support voice and digital data communications. ISDN
is being developed by telephone companies to serve all data communications
needs of users.
- Interexchange Carrier (IXC)
Long distance carriers. Contrast with local exchange carrier (LEC).
- International Standards Organization (ISO)
An organization established to promote the development of standards to
facilitate the international exchange of goods and services, and to develop
mutual cooperation in areas of intellectual, scientific, technological, and
economic activity. This international standards organization is responsible
for telecommunications networking standards including OSI Reference Model.
- International Telecommunications Union (ITU)
The specialized telecommunications agency of the United Nations, established
to provide standardized communications procedures and practices, including
frequency allocation and radio regulations, on a world-wide basis.
A conceptual entity that embodies one or more functions between an upper and
a lower logical boundary.
- Layered Network Architecture
Currently the basis of all telecommunication network architecture standards,
with functions allocated to different layers and standardized interfaces
- Local Access and Transport Area (LATA)
Within a LATA the LEC can carry all the traffic. The LEC is restricted from
carrying traffic between LATA's, i.e., interLATA traffic can not be
transmitted by the LEC.
- Local Area Network (LAN)
Network spanning an area of not more than a few kilometers in diameter.
- Local Exchange Carrier (LEC)
The BOCs and the independent telephone companies.
- Local Loop
A channel connecting the subscriberÕs equipment to the line-terminating
equipment in the central office exchange. A transmission path, generally
twisted pair, between the individual subscriber and the nearest switching
center of a public telecommunications network. Also referred to as a
- Logical Link Control (LLC)
Upper half of data link layer in IEEE 802 architecture.
- M/M/1 Queue
A queue with infinite buffer space with a Poisson Arrival process and a
random exponentially distributed service time (or message length).
- Management Information Base (MIB)
A description of a network element that is used for network management
- Manufacturing Automation Protocol (MAP)
Networking architecture, based on token bus protocol, developed by General
Motors for automating manufacturing processes.
- Medium Access Control (MAC)
Lower half of data link layer IEEE 802 architecture; handles medium access
functions. Used to keep stations sharing common communications link from
interfering with each other.
- Message Switching
Switching technique involving transmission of messages from node to node,
with storage at intermediate nodes until next portion of path available. (1)
In a data network, the process of routing messages by receiving, storing,
and forwarding complete messages. (2) The technique of receiving a complete
message, storing it, and then forwarding it to its destination unaltered.
- Metropolitan Area Network (MAN)
Network spanning area up to a few dozen kilometers in diameter. A network of
limited geographic scope, generally defined as within a 50-mile radius.
Standards for MANs are being defined by the IEEE.
- Modem (Modulate/Demodulate)
A device the converts a binary information stream into an analog signal for
- Multiplexer (MUX)
A device capable of interleaving the events of two or more activities or
capable of distributing the events of an interleaved sequence to the
(1) In data transmission, a function that permits two or more data sources to
share a common transmission medium such that each data source has its own
channel. (2) The division of a transmission facility into two or more
channels either by splitting the frequency bank transmitted by the channel
into narrower banks, each of which is used to constitute a distinct channel
(frequency division multiplexing), or by allotting this common channel to
several different information channels, one at a time (time division
- Network Element (NE)
- Network Layer
Layer 3 of OSI Reference Model. Responsible for routing data through a communication network.
- Network Management Protocol (NMP)
A protocol used to control and manage network resources.
- Network-Node Interface (NNI)
Point-to-Point interface between two switches in B-ISDN.
Any request for network resources can be satisfied independent
of the condition (state) of the system.
Activated (in regard to a telephone set). By extension, a data set
automatically answering on a public switched system is said to go off-hook.
Contrast with on-hook.
Deactivated (in reference to a telephone set).
A telephone not in use is on-hook. Contrast with off-hook.
- Open Systems Interconnection (OSI) Reference Model
A model of communications between cooperating devices. It defines a 7-layer
architecture of communication functions. The OSI reference model is a
telecommunication networking architecture developed by International
Organization for Standardization (ISO) and adopted as an international
standard; also known as Reference Model for Open Systems Interconnection.
- Operations, Administration, Maintenance, and Provisioning (OAM&P)
day-to-day execution of functions within the telecommunications network
needed to provide service to the customers.
- Optical Carrier -N (OC-N)
Line rates used in SONET optical transmission
systems. The base rate is 51.84 Mbps, the higher OC-N rates are N X 51.84
Mbps, e.g., OC-12 is at 622Mbps.
- Optical-Electrical (O/E)
Optical to electrical conversion.
The information added to the users data to facilitate its transport through
A sequence of binary digits (including data and call control
signals) that is switched as a composite whole. The data, call control
signals, and possible error control information are arranged in a specific
- Packet Switching
Switching technique involving breaking long messages up into shorter packets
transmitted individually through network, with storage at intermediate nodes
until next portion of route available. A method of transmitting messages
through a communications network, in which long messages are subdivided into
short packets. Each packet is passed from source to destination through
intermediate nodes. At each node, the entire message is received, stored
briefly, and then passed on to the next node.
- Permanent Virtual Circuit (PVC)
A virtual circuit that is an assigned connection over a packet switched
network and is not switchable by the users.
- Personal Communications Network (PCN)
The network that supports Personal Communications Services.
- Personal Communications Services (PCS)
A family of end-to-end telecommunications services that provide: 1)
Reception/Initiation of voice or data calls via a personal number that is
associated with the customer rather than a physical location, i.e., a plug
in the wall, or specific terminal device. 2) Access to wire line services
using a wireless terminal device. 3) The quality and security comparable to
that of the wireline network.
- Physical Layer
Layer 1 of the OSI model. Concerned with the electrical,
mechanical, and timing aspects of signal transmission over a medium.
The inclusion of an acknowledgment of a previously-received protocol data
unit in an outgoing protocol data unit.
- Plain Old Telephone Service (POTS)
Basic telephone service with no special features.
- Possion Arrival Process
A common model for the random arrivals to a queue, or telecommunication
server where the number of arrivals, n, in a time interval t follow a Poisson
probability mass function. The random interarrival time follows an
exponential probability density function.
- Postal, Telegraph, and Telephone (PTT)
A government organization that operates a nationalized public
- Presentation Layer
Layer 6 of the OSI model. The presentation layer is responsible for code
conversion, data encryption, and data compression.
- Primary Rate ISDN
Twenty three B channels an one D channel for control signaling.
- Private Automatic Branch Exchange (PABX)
A private automatic telephone exchange that provides for the transmission of
calls to and from the public telephone network. See also private branch
- Private Branch Exchange (PBX)
A private telephone exchange connected to the public telephone network on the
userÕs premises. A PBX provides a circuit switching facility for
telephones on extension lines within the building and access to the public
A formal statement of the procedures that are adopted to ensure communication
between two or more functions within the same layer of a hierarchy of
functions. (1) A specification for the format and relative timing of
information exchanged between communicating parties. (2) The set of rules
governing the operation of functional units of a communications system that
must be followed if communications are to be achieved. A protocol is a set
of mutually agreed upon rules of procedure stating how two or more parties
are to interact to exchange information.
- Protocol Data Unit (PDU)
Type of data unit used by a particular protocol. Often preceded by letter to
indicate protocol layer--for example, NPDU and TPDU for network and
transport layers. A PDU is the information that is delivered as a unit
between peer entities of a network and may contain control information,
address information, or data.
- Public Switched Telephone Network (PSTN)
The dial up public telecommunications network.
- Pulse Code Modulation (PCM)
A process in which a signal is sampled, and the magnitude of each sample with
respect to a fixed reference is quantized and converted by coding to a
- Quality of Service (QoS)
- Queued Packet Synchronous exchange (QPSX)
The old name for DQDB.
- Random Access
Unscheduled access to communications medium in which stations transmit when
ready (possibly after sensing medium), and later resolve any conflicts that
- Regional Bell Operating Company (RBOC)
One of the seven corporations formed when divestiture occurred and that
comprise the 22 Bell Operating Companies.
- Registered Jack (RJ)
The connector of user network interface, the standard telephone jack is the
The signal made by a telephone to indicate an incoming call.
- Segmentation and Reassembly (SAR)
The protocol that divides packets into cells and combines cells into
- Session Layer
Layer 5 of OSI Reference Model. Manages a logical connection (session)
between two communicating processes or applications.
- Service Access Point (SAP)
The logical address of a session within a physical terminal.
The exchange of information specifically concerned with the establishment and
control of connections, and with management, in a telecommunication network.
- Simple Network Management Protocol (SNMP)
A management protocol based on TCP/IP and MID's.
- Sliding Window Flow Control
Type of flow control in which transmitter is given permit to transmit
ÒwindowÓ of packets or other data units, and not allowed to transmit
more until it receives another permit.
Modification of ALOHA medium access technique in which time is divided into
slots of duration equal to packet duration and each transmission is required
to start at the beginning of a slot.
Synchronous Optical Network is a standard for optical transmission. It is
a physical layer framing structure at rates from about 51.84 Mbps through
over 9.9 Gbps.
- Step-by-step Switch
A switch that moves in synch with a pulse device, such as a rotary telephone
dial. Each digit dialed moves successive selector switches to carry the
connection forward until the desired line is reached.
- Stop-and-Wait Protocols
Protocols in which the sender sends one frame and
then waits for an acknowledgment before sending the next frame.
- Store-and-Forward System
An application in which input is transmitted,
usually to a computer, stored, and then later delivered to the recipient.
- Strowger Switch
A step-by-step switch named after its inventor, Almon B. Strowger. See
also step-by-step switch.
- Subscriber Line Interface Circuit (SLIC)
A SLIC is the interface between the local loop and the switch. SLIC
functions include, -48 V dc battery, ringing voltage supply, overload
protection, and loop supervision.
A measure of a network's ability to withstand failures in links and nodes.
- Switched Multimedia Data Service (SMDS)
A Bellcore data MAN service offered by telecommunications carriers.
- Switched Virtual Circuit (SVC)
A temporary logical connection in a packet switched network.
- Synchronous Transmission
Data bit and characters are transmitted at a fixed rate with the transmitter
and receiver synchronized at the bit and character level.
- Synchronous Transport Signal -N (STS-N)
The electrical equivalent of the OC-N.
- T-1 Carrier System
Digital telephone carrier system developed by Bell Labs in United States as
first purely digital carrier system.
The standards committee responsible for the transmission issues in the US.,
corresponds to the ETS1 in Europe and the Telecommunications Technology
Committee in Japan.
- Technical Office Protocol (TOP)
A set of standard protocols aimed at office automation.
Using telecommunications to work from home or other locations instead of on
the businessÕs premises.
A measure of system efficiency.
- Time Assignment Speech Interpolation (TASI)
Also known as Digital Speech Interpolation (DSI) A technique of
multiplexing telephone calls by taking advantage of the pauses in normal
speech and assigning the channel to another call during the pause.
- Time Division Multiplexing (TDM)
Communication channel sharing technique carrying different signals in
different time slots. The division of a transmission facility into multiple
channels by allotting the facility to different channels, one at a time.
- Time Shared Space Division Switch
A crosspoint array where each input is a TDM bus and which can reconfigure
the connection on each time slot. Known as the S stage in a multi-stage
- Time-Slot Interchange (TSI)
The interchange of time slots within a time-division multiplexed frame.
Known as the T stage in a multi-stage switch architecture.
- Transport Layer
Layer 4 of the OSI model. Provides reliable, sequenced transfer of data
- Transmission Control Protocol/Internet Protocol (TCP/IP)
A telephone channel between two central offices or switching devices that is
used in providing a telephone connection between subscribers.
- User-Network Interface (UNI)
The demarcation between the network and the customer premises.
- Virtual Circuit
Transmission path set up, end to end, by connection protocol before
transmission. A packet-switching mechanism in which a logical connection
(virtual circuit) is established between two stations at the start of
transmission. All packets follow the same route, need not carry a complete
address, and arrive in sequence.
- Virtual Circuit Identifier (VCI)
An address associated with a specific VC that is part of the packet header.
- Valued Added Network (VAN)
Typically a packet switched network with the added access to data bases and
- Variable Bit Rate (VBR)
VBR traffic is typically from bursty traffic sources and usually requires
packetized bandwidth an demand for effective transport.
- Voice Grade Channel
A communications channel suitable for the transmission of voice.
- Virtual Terminal
A concept that allows an application program to send or receive data to or
from a generic terminal. Other software transforms the input and output to
correspond to the actual characteristics of the real terminal being used.
- Wavelength Division Multiplexing (WDM)
Two or more optical frequencies(colors) are use on the same fiber.
- Wide Area Network (WAN)
A network that covers a large geographic area, requiring the crossing of
public right-of ways and the use of circuits provided by a common carrier.