Glossary



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-A-

A & B Signalling
A signalling method used in T1 transmission in which one bit, robbed from each of the 24 sub-channels in every sixth frame, is used for carrying and controlling information. See also Robbed Bit Signalling (RBS).

A, B, C & D Signalling
A signalling method in which the A bit is robbed from the 6th frame, the B bit is robbed from the 12th frame, the C bit is robbed from the 18th frame and the D bit is robbed from the 24th frame. See also ESF, Robbed Bit Signalling.

alternating current (AC)
A current which alternates between negative and positive voltage sources in a cyclic manner. Commonly, the 120 volts of electricity delivered by a power utility company to an outlet.

access charge
The cost assessed to communications customers for accessing the interexchange, intrastate and interstate phone network to originate and receive calls.

AccunetT
A family of digital long-distance transmission services from AT&T Communications including the use of leased and high speed lines, and a packet switching digital network.

Adaptive Differential Pulse Code Modulation (ADPCM)
A voice digitization technique which uses various speeds (e.g. 32 kbps) per voice channel.

adaptive equalization
An equalization that is adjusted during a transmission in order to compensate for variations in line characteristics.

adaptive routing
The routing that automatically adjusts to network changes such as traffic patterns or failures.

address
1. The destination of the data sent through a communications system. Multiple terminals on one communications line must each have a unique address.

2. A group of digits that make up a telephone number. Also known as the called number.

aggregate card
A circuit board that interfaces between data terminal equipment and a T1 link. It provides the allocation of bandwidth over a T1 link.

alarm
A signal generated when an abnormal network condition exists. D/I Mux III multiplexers also indicate alarms due to shelf problems. Four types of alarm conditions are:

• System Node Alarm: Indicates abnormal node conditions.
• Major Alarm: Indicates major abnormal conditions where service is disrupted or out.
• Minor Alarm: Indicates minor abnormal conditions where service is not disrupted.
• Status Alarm: Indicates information messages about the status of an action or event.

All Rate Office Channel Unit Data Port (All Rate OCDUP)
A Coastcom programmable channel card that interfaces data applications onto the T1 transmission line(s). The All Rate OCUDP supports Dataphone Digital Service (DDS) primary data rates, switched 56 kbps, dial-out, and a secondary channel. It may be set at various transmission data rates: 2.4, 4.8, 9.6, 19.2, and 56 kbps with the primary channel. The secondary channel supports 4-wire transmission rates of 3.2, 6.4, 12.8, 25.6 and 72 kbps with 1.2, 2.4, 3.2 and 6.4 kbps secondary channel rates.

alternate route
A secondary or backup communications route used when normal routing is temporarily unavailable.

Alternate Mark Inversion (AMI)
A line code that employs a ternary signal to convey binary digits, in which successive binary ones are represented by signal elements that are normally of alternating, positive and negative polarity but equal in amplitude, and in which binary zeros are represented by signal elements that have zero amplitude. This is the primary mode for T1.

amplitude modulation (AM)
A form of modulation in which the amplitude of the carrier is varied in accordance with the instantaneous value of the modulating signal.

ampere (amps)
A measure of electrical current that is equal to watts divided by volts.

amplitude
The extreme range of a voltage or current.

analog
A signal which may continuously vary voltage and/or current.

analog channel
An analog channel is a transmission channel which is provided on audio pairs or analog transmission systems, and which is voice frequency at both ends.

analog trunk
A circuit that interconnects two analog devices.

American Standard Code for Information Interchange (ASCII)

A standard format for representing characters so that data from one computer or communications device can be recognized and understood by other computers and communications devices.

asynchronous
A method of data transmission that allows characters to be sent at irregular intervals by preceding each character with a start bit and following it with a stop bit. In asynchronous data transmission, bits may not be of uniform duration, causing variable time delays between characters. Asynchronous data transmission is usually used for low-speed devices.

attenuation
A decrease in the magnitude of the current, voltage, or power of a signal.

auto answer
The capability of a terminal, modem, computer or similar device to respond to an incoming call on a dial-up telephone line and to establish a data connection with a remote device without operator intervention.

Auto Dial-Up
A modem with the ability to dial into a telephone network and answer incoming data calls.

Automatic Loop Protection Switching (ALPS)
ALPS is a D/I Mux III multiplexer feature. When the T1 transmission paths in a network of D/I Mux III multiplexers are connected in a ring configuration, the ALPS feature protects against single-point or multi-point failures. Up to a total of 24 DS0 channels can be protected within the ring.

ALPS provides automatic protection from a failed transmission path and complete protection from a single transmission path failure. A failed transmission path is detected whenever there is loss of clock or an alarm indication signal (AIS) unframed "all ones." Protection switching occurs within 500 milliseconds without the need for network management control.

Automatic Ringdown
The ringing that occurs when a phone is picked up, off-hook and rings at the other end. Used in point-to-point configurations.

-B-

bandwidth
The range of frequencies available to transmit signals for a specific media. It is measured in Hertz.

baud rate
A measure of signalling speed in data communications that specifies the number of signal elements that can be transmitted per second.

baseband
A form of modulation in which signals are pulsed directly on the transmission medium without frequency division.

baseband signalling
The transmission of a digital or analog signal at its original frequencies, not changed by modulation.

BER
See Bit Error Ratio.

BERT
See Bit Error Ratio Test.

Bipolar Eight Zero Substitution (B8ZS)
A method of satisfying the ones' density requirements of a digital T1 carrier facility in the public network while allowing 64 kbps of clear channel data. Strings of eight consecutive zeros are replaced by an eight-bit code containing two intentional bipolar violations.

binary
A numbering system that describes values with only two mathematical digits: zero (0) or one (1).

bipolar
A signal which varies positively and negatively around zero.

bipolar return-to-zero (BRZ)
A bipolar signal in which each pulse returns to zero amplitude before its time period ends. This prevents the buildup of a DC current on the signal line.

bipolar violation (BPV)
The occurrence of two successive pulses of the same polarity in an AMI bipolar signal. In T1 it is detected as an error and considered a violation of the Alternate Mark Inversion technique.

bit
A basic unit of data in a binary system. A bit is either a one (1) digit or a zero (0) digit. The word "bit" is a contraction of the words "binary digit". See also mark, one.

Bit Error Rate (BER)
The ratio of bits with errors to the total number of bits detected, usually expressed as a number with an exponent to a power of ten. Used to measure the quality of a signal path.

Bit Error Rate Test (BERT)
A type of digital line test in which a known pattern of bits is transmitted and compared with received bits to determine the Bit Error Rate (BER).

bit rate
The rate of transmission of a data signal, stated as bits-per-second (bps). Higher rates are stated as kilobits-per-second (kbps) and megabits-per-second (Mbps).

bit 7 stuffing
A technique to meet ones density requirements wherein the seventh bit in any 8-bit word containing all zeros is changed to one. Used in T1 lines to prevent loss of synchronization from 15 or more consecutive zero (0) bits. This method can only be used on voice channels.

blocking
1. The inability to interconnect to lines in a network cross-connect or switch

because all possible paths between them are already in use.

2. The intentional prevention of data passing through a system.

bps
Bits-per-second. The measure of speed in serial communications.

BPV
See Bipolar Violation.

broadband
A broadband facility (usually a coaxial cable) that can carry numerous voice, video, and data channels simultaneously, each channel taking up a different frequency on the cable. Broadband cables are typically used for broadcasting multiple channels, while baseband is used more frequently for office LANs.

BRZ
See Bipolar Return-to-Zero.

bus
A transmission path or channel with one or more conductors in which all attached devices receive all transmissions at the same time.

byte
A sequence of eight consecutive bits used as a unit to represent information.

bypass
1. To go around a system or device.

2. Private network operation that can access long distance transmission

facilities without going through the local exchange carrier.

3. The connection between the call origin point and the final destination point.

byte stuffing
Insertion of specific information bytes into a data stream which acts as a control for that stream of data.

B8ZS
See Bipolar Eight Zero Substitution.

-C-

Carrier Failure Alarm (CFA)
An alarm that results from an out-of-frame or loss-of-carrier condition.

carrier frequency
The frequency of the carrier wave that is modulated to transmit signals.

Carrier Group Alarm (CGA)
An alarm indicating that a signal derived from multiplexing a group of channels, typically 24, has failed. In T1, a carrier group alarm indicates the failure of the DS1 signal.

carrier signalling
Any signalling techniques used in multi-channel carrier transmission. The most commonly used techniques are in-band signalling, out-of-band signalling, separate channel signalling and common channel signalling.

carrier system
The means of obtaining a number of channels over a single path by modulating each channel on a different carrier frequency and demodulating at the receiving point to restore the signals to their original form.

CB
See Channel Bank.

CCU
See Common Control Unit.

Cellular One Synchronous Data Channel Unit (CEL 1 SDCU)
The Cellular 1 Synchronous Data Channel Unit is a data interface for Coastcom D/I Mux III multiplexers. The CEL1 SDCU is a channel card designed to be used in cellular telephone networks. It is used in conjunction with 4-Wire E&M channel cards to extend the cellular network capability.

Central Processing Unit (CPU)
The intelligent main processor of a computer or other information handling system which controls, organizes and processes all incoming and outgoing information.

Central Office (CO)
A location where communications common carriers terminate customer lines and where switching equipment is located. The central office is also referred to as the exchange or end office.

CFA
See Carrier Failure Alarm.

CGA
See Carrier Group Alarm.

channel
The part of a transmission bandwidth which carries one circuit's information. In T1, the lowest data rate that can be directly multiplexed onto the T1 line. There are 24 channels in a T1 signal. Typically customer premise equipment signals are converted onto a channel.

Channel Bank (CB)
The telecommunications equipment that converts DS0 circuits into a T1 channel format and translates received channels into circuits.

Channel Service Unit (CSU)
The first device encountered by a T1 line entering a facility. The CSU protects the equipment from damage due to disturbances on the T1 line and regenerates the T1 signal to meet specifications. The CSU also provides a network loop point used to test the integrity of the span. A CSU is required in order to interface the Customer Premise Equipment (CPE) to the Public Switch Network (PSN).

circuit
A communications path between two or more points.

circuit switching
The temporary direct connection of one or more channels between two or more points, which provides the user with the exclusive use of an open channel in order to exchange information. A discrete circuit path is set up between the incoming and outgoing lines, in contrast to message switching and packet switching. Also called line switching.

clear channel
A transmission path where the full 64 kbps bandwidth is available to the customer.

clock
The timing pulses used to synchronize transmissions.

clocking
The defining of a time base in a transmission system in order to control the timing of certain functions such as the duration of signal elements. See also Timing.

cloud
The cloud is described as such because the customer can connect at one point on it and expects the data/voice input to continue to the other side, properly sequenced and formatted at the output. Also called the public network.

CODEC
A Coder/Decoder device that converts analog signals to digital signals for transmission over a digital medium and back again to the original analog form. A CODEC is required at each end of the communications channel. It is sometimes referred to as a "de-converter".

common carrier
A public provider of communications services.

Common Control Unit (CCU)
The Common Control Unit (CCU) acts as the master controller for the

D/I Mux III system. The CCU maintains all shelf configuration information and provides a control interface for the user.

common equipment
In the Coastcom D/I Mux III multiplexer, the common equipment consists of a T1 interface or T1 CSU, two line interface units, a common control unit, a strobe and one or more power supplies. In the D/I Mux III, the common equipment performs the essential multiplexing functions.

In telephone systems, common equipment refers to items that are used by more than one phone for processing calls.

concentrator
A device that connects a number of circuits that are not all used at once to a smaller group of circuits for the purpose of economical transmission.

control byte
In T1, a byte that is reserved to only carry control and monitoring information.

controlled slip
The result of an underflow or overflow of a frame buffer. A frame buffer will slip by repeating or deleting all the data bits in a frame. See also frame slip and uncontrolled slip.

control signals
The signals that pass between one part of a communications system and another to control the system.

CPE
See Customer Premise Equipment.

CPU
See Central Processing Unit.

Cyclic Redundancy Check (CRC)
A method of checking the integrity of received data, in which the check uses a polynomial algorithm based on the content of the data.

cross modulation
The interference caused by the interaction of two or more carriers in a transmission system.

cross talk
A form of background noise that occurs when a signal from one channel causes an unwanted signal in another channel.

cross talk attenuation
The extent to which a communications system resists cross talk.

CSU
See Channel Service Unit.

Customer Premise Equipment (CPE)
Any communications equipment owned by the customer and which is connected to the public telephone network.

cutover
The physical changing of lines from one system to another, usually at the time of a new system installation.

-D-

D1, D2
T1 framing that divides the T1 into 24 channels resulting in equal 64 kbps transmission channels (one DS0). The D1D and D2 specify the numbering sequence of the 24 DS0s in a T1 frame.

D1D Channel Assignments
Channel Time Slot Channel Assignments

1 1

2 13

3 2

4 14

5 3

6 15

7 4

8 16

9 5

10 17

11 6

12 18

13 7

14 19

15 8

16 20

17 9

18 21

19 10

20 22

21 11

22 23

23 12

24 24

D2 Channel Assignments
Channel Time Slot Channel Assignments

1 12

2 13

3 1

4 17

5 5

6 21

7 9

8 15

9 3

10 19

11 7

12 23

13 11

14 14

15 2

16 18

17 6

18 22

19 10

20 16

21 4

22 20

23 8

24 24

D3, D4
T1 framing that divides the T1 into 24 channels resulting in equal 64 kbps transmission channels (one DS0 channel). The D3 and D4 specify the numbering sequence of the 24 DS0s in a T1 frame.

D3/D4 Channel Assignments
Channel Time Slot Channel Assignments

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

10 10

11 11

12 12

13 13

14 14

15 15

16 16

17 17

18 18

19 19

20 20

21 21

22 22

23 23

24 24 data bridge
A device which combines two separate data streams into a single data stream.

data circuit
A communications path between two or more points transporting data.

Data Communications Equipment (DCE)
Any devices used to transport information from Data Terminal Equipment to other Data Terminal Equipment (DTE) or a host computer.

Data Line Interface (DLI)
The point at which a data line is connected to a communications system.

data link
Any serial data communications transmission path, generally between two adjacent nodes or devices, and without any intermediate switching nodes.

Data Terminal Equipment (DTE)
The equipment such as a computer or a printer that originates and terminates data transmission signals. In RS-232C connections, the designation of either DTE or DCE determines the signalling role of the handshaking lines.

Data Service Unit (DSU)
A device used to connect terminal equipment to a digital communications line.

data transmission
The process of transmitting information as digital pulses; the movement of information in coded form as electrical energy.

Dataphone Digital Service (DDS)
Private line digital service, typically with data rates at 2400, 4800, 9600 and 56,000 bits per second. Part of AT&T's Accunet(tm) family of offerings.

dB
Decibel. A unit for measuring relative strength of a signal parameter such as power or voltage. The number of decibels is ten times the logarithm (base 10) of the power of two signals, or the ratio of the power of one signal to a reference level:

dBm
Decibels relative to one milliwatt.

dBr
Relative level in decibels.

DDS
Dataphone Digital Service.

dedicated circuit
A transmission line without any switching functions, used exclusively by one circuit.

default (values)
Hardware or software responses that are preset by the manufacturer and allow the equipment or software to operate without any additional programming being supplied by the user.

delay
In communications, the elapsed time between two events; the beginning moment a signal is sent and the ending moment the same signal is received.

Deluxe 4-Wire E&M Channel Card
The Deluxe 4-Wire E&M channel card operates in the Coastcom D/I Mux III multiplexer. The dual capability provides two 4-wire voice frequency circuits plus signalling. Each circuit occupies one standard DS0 channel.

demarc
The demarcation point between carrier equipment and customer premises equipment (CPE).

demodulation
The process of retrieving data from a modulated carrier wave; the reverse of modulation.

diagnostic programs
Software routines used to check for equipment malfunctions and to pinpoint faulty components.

dial-up
The process, equipment, or facilities involved in establishing a connection through the switched network.

Digital Access Cross-connect System (DCS)
The equipment used to route circuits to a specific location and often used to group voice and data calls together, sending them over one T1 line to another location.

digital
Transmission of signals encoded in binary form.

digital loopback
The diagnostic feature for testing the digital processing circuitry of a communications device. A loopback can be initiated locally or remotely. The device being tested will echo back a receive test message after first decoding and will then re-encode it. The results are then compared with the original message.

digital network
A network incorporating both digital switching and digital transmission.

digital signal (DS)
A discontinuous signal whose state consists of ones (1s) and zeros (0s).

Digital Signal Designation
The categories of the North American Digital Hierarchy that specify the transmission data rate and other technical specifications. They are: DS0, DS1, DS2, DS3, and DS4. The DS stands for digital signal level.

digital switching
The process of establishing and maintaining a connection, under stored-program control, in which binary-encoded information is routed between an input and an output port. This method is more efficient than requiring dedicated circuits for the period of time that connections are set up.

Direct Connect Card (DCC)
Data cards with direct connections to interfaces such as V.35, RS-232C or RS-252.

Direct Inward Dialing (DID)
An option that enables a caller from outside a company to call an internal extension without having to pass through an operator or attendant.

distortion
An unwanted change in a waveform that occurs between points in a transmission system.

distribution frame
A structure for terminating permanent wires of telephone exchanges and private branch exchanges and to facilitate the change of connections between them by means of cross-connecting wires.

DNIS
Dial Number Information Service.

downtime
The total time that a system is out of service due to equipment failure.

DP
1. Dial pulse (signalling).

2. Distribution point.

DPC
Digital Program Channel.

drop
The receive connection made available for a terminal unit on a transmission line.

drop and insert
The ability to demultiplex (or drop) up to 24 channels from a T1 line passing through a node and multiplex (or insert) the same number of channels onto that line toward the next node. The remaining channels on the T1 line pass through the node unaffected.

DS0
A 64 kbps channel. There are 24 DS0 time slots in a T1 line.

DSU
See Data Service Unit.

DTE
See Data Terminal Equipment.

DTMF
See Dual Tone Multifrequency Signalling.

Dual Channel Bank (DCB)
In a Dual Channel Bank operation, a D/I Mux III multiplexer terminiates two T1 transmission lines. The Dual Channel Bank mode allows the system to synchronize with the T1 network (loop timing mode) or supply timing to the T1 network (local timing mode). Dual Channel Bank operation requires Coastcom's Line Interface Units with slip buffers. The slip buffer LIUs align all clocks, bytes, frames and multiframes to one common multiframe.

T1 inputs and outputs are synchronized to the same multiframe signal.

Dual Tone Multifrequency Signalling (DTMF)
A method of signalling in which a matrix combination of two frequencies is used to transmit numerical dialing information.

Dual 2-Wire Foreign Exchange Office Channel Card (FXO)
The Coastcom Dual 2-Wire Foreign Exchange Office channel card

(Dual 2-Wire FXO) plugs into the Coastcom D/I Mux III multiplexer. The FXO channel card is perceived by the switch to be a standard telephone. The switch supplies talk battery, ringing, busy signals and all of the other telephone requirements; the FXO channel card provides on-hook, off-hook and dial pulse or touch-tone number signalling.

Dual 2-Wire Foreign Exchange Subscriber (FXS)
Coastcom's Dual 2-Wire Foreign Exchange Subscriber (Dual 2-Wire FXS) channel card plugs into the D/I Mux III multiplexer shelf. Located at a remote or receiving location(s), the FXS channel card transports received digital signals that imitate the original, central office or user switch locations and communicates the information to a standard telephone.

Dual 4-Wire E&M
Coastcom's Dual 4-Wire channel card operates in the D/I Mux III multiplexer. The E&M channel cards offered by Coastcom can connect a group of PBX's together in a private T1 network. Companies with extensive internal communications between various office locations can benefit by dedicating a T1 network to internal communications.

Dual 4-Wire Transmission Only (TO)
Coastcom's Dual 4-Wire TO channel card provides a toll quality E&M interface between the D/I Mux III common equipment and two 4-wire trunks. The difference between this card and other 4-wire channel cards is that this card is hardwired for voice transmission-only mode.

dumb terminal
A data terminal with no processing or programming capability.

duplex circuit
A circuit used for transmission in both directions at the same time. It can be called "full duplex" to distinguish it from "half duplex."

duplex
A two-way data transmission mode in which transmission can occur in both directions simultaneously.

-E-

Ericsson Digital Channel Unit (EDCU)
A Coastcom digital interface channel card used in conjunction with the

D/I Mux III multiplexer. The Ericsson Digital channel unit is designed to extend cellular phone service to remote locations over the public network telephone company, T1, fiber or microwave media. Used with the

D/I Mux III multiplexer and configured with the appropriate channel cards, the EDCU extends the features and increases the cellular phone coverage area without loss of performance.

E&M
A method of signalling that uses separate paths for voice and signalling.

E&M may refer to ear and mouth or earth and magnet.

electromagnetic interference (EMI)
Radiation leakage outside a transmission medium that results mainly from the use of high-frequency wave energy and signal modulation. EMI can be reduced by appropriate shielding.

end office
A central office to which a telephone subscriber is connected.

EPROM
Erasable Programmable Read-Only Memory.

equalization
The technique of altering the output impedance of a circuit to compensate for losses in amplitude and delay due to the line impedance of the transmission medium.

error rate
The ratio of the number of bits, elements, characters or blocks incorrectly received to the total number of bits, elements, characters, or blocks transmitted.

ESF
See Extended Superframe.

exchange, private branch
A private automatic telephone exchange that provides for the internal switching of calls to and from the public telephone network.

expandor
A transducer that, for a given amplitude range of input voltages, produces a larger range of output voltages. An expandor is used in conjunction with a compression system. The compressor lowers the voltage levels and the expandor recreates the original signal.

Extended Superframe (ESF)
A framing format that extends the D4 framing format from 12 to 24 frames. Overhead bit positions are shared between an Extended Superframe (ESF) alignment signal, a Cyclic Redundancy Check (CRC) and a Facility Data Link (FDL).

external clock
An external clocking source to a D/I Mux III multiplexer. Clock rates can be any accepted channel speed and defined for primary and secondary redundancy sources. An external clock is often the primary timing mechanism in synchronous devices, such as a T1 multiplexer.

-F-

far end
The equipment located at the remote end of a communications system.

FCC
United States Federal Communications Commission.

Facilities Data Link (FDL)
In DS1, a four kbps channel that comprises one half of the framing bits in ESF formatted facilities.

FDM
See Frequency Division Multiplexing.

First In, First Out (FIFO)
A protocol used in computer and telephone networks that services requests on a "first-come-first-served" basis.

firmware
Programs stored in permanent or semi-permanent storage devices such as PROMS or EPROMS. Firmware contains software which is so frequently used by the computer or other equipment that it is imprinted or "burned" onto a chip to permanently retain the information.

FM
See Frequency Modulation.

Foreign Exchange Office (FXO)
An interface at the end of a private line that connects to a switch.

Foreign Exchange Subscriber (FXS)
Local telephone service provided from a central office outside of a subscriber's area.

four-wire circuit
A circuit that uses two pairs of conductors; one pair for transmitting and the other pair for receiving. The result is two-way communication to a handset such as the telephone on a desk.

A 4-wire E&M interface uses two wires for Tx, two wires for Rx, and two wires for signalling.

four-wire repeater
A repeater with two amplifiers, one for amplification of the outgoing signal and the other for amplification of the incoming signal.

fractional T1
A portion of the T1 bandwidth.

frame
The control procedure used with mutliplexed digital channels in which bits are inserted so that the receiver can identify the time slots allocated to each channel. A T1 D4 frame consists of 24, eight-bit DS0s and one framing bit.

frame alignments
The correlation between the significant instants of the timeslots within a signal and their ideal positions in time.

frame buffer
A digital storage device used when transmitting data from one device to another to compensate for a difference in data flow or rates.

frame slip
See controlled slip.

framing error
An error that occurs when a receiver cannot find the frames in a T1 data stream.

frequency
The number of repetitions per unit of time during a complete waveform or cycle. Typically expressed in Hertz (Hz).

Frequency Division Multiplexing (FDM)
A technique in which an available transmission bandwidth of a circuit is divided by frequency into narrower bands, each used for a separate voice or data transmission channel.

FM frequency modulation
A form of modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the carrier frequency by an amount proportional to the instantaneous value of the modulating signal.

full duplex
Communications equipment capable of simultaneously transmitting and receiving.

functional test
A test carried out under normal working conditions to verify that a circuit or a particular part of the equipment functions correctly.

FXO
See Foreign Exchange Office.

FXS
See Foreign Exchange Subscriber.

-G-

gain
An increase in signal power for transmission from one point to another, usually expressed in decibels.

gateway
A protocol converter that restructures packets of information so that they can pass between networks using different standards.

GHz
Gigahertz (1 billion Hertz).

gnd
Ground.

ground circuit
1. A circuit in which energy is carried one way over a metallic path and returned through the earth.

2. One circuit connected to the earth at one or more points.

ground start
A signalling method in which a station detects a grounded circuit at the other end as an off-hook condition.

ground station
The equipment that receives and transmits signals to and from a communications satellite. Also called an earth station.

-H-

half duplex
A communications system or equipment capable of transmitting or receiving, but not simultaneously.

handshaking
The exchange of predetermined signals for control when a connection is established between two modems or other data devices.

harmonic distortion
The presence of unwanted harmonic frequencies in a received signal due to nonlinear characteristics of a transmission line.

Hertz (Hz)
A frequency measurement that indicates the number of cycles which pass a specific point per second. One Hertz equals one cycle per second.

high frequency (HF)
The portion of the electromagnetic spectrum usually used in short-wave radio applications.

hum
The electrical interference picked up from a conventional alternating current power supply.

host CPU
The main computer in a system. The host CPU can be a mainframe computer, microcomputer or mini-computer.

-I-

impedance
The effect of resistance, inductance and capacitance on a transmitted signal and expressed in ohms.

inband
The data timeslots of a DS1 frame (non-overhead bits).

I/O Channel
The input and output channel at an electronic device.

interface
The physical connection between two communications devices, such as an electrical plug and socket connection.

insertion loss
The difference in the amount of power received before and after a device is inserted into a circuit or a call is connected.

intelligent terminal
A CRT terminal that is programmable and can process messages or information. It usually consists of a CRT, a keyboard, a CPU, and local storage.

internal clock
A timing source internal to a digital device.

internal clock source
The internal clock source can be defined as the primary master node reference clock (oscillating source), that provides the timing reference for a transmission link.

Integrated Services Digital Network (ISDN)
A digital network that provides a wide range of voice and non-voice services using a limited number standard interfaces.

interrupt
A mechanism by which elements of a computer system can request service from the central processor.

isochronous
A regularly occurring interval. A signal is isochronous if the time interval separating any two significant instants is theoretically equal to the unit interval or to a multiple of the unit interval.

IXC
Inter-Exchange Carrier. Also abbreviated as IEC.

-J-

jack
1. A device used for terminating the permanent wiring of a circuit. It is

accessed by the insertion of a plug.

2. A device provided by the telephone company at a customer site for

connection to the CSU.

jitter
Jitter is unintentional phase modulation which has both an amplitude and a frequency component. When the changes in frequency are greater than 10 Hz they are called jitter because of the magnitude of the phase deviation and the speed of the frequency. The measurement gauge for the amplitude is called the unit interval, which is the time period that it takes one bit to pass a fixed point at the T1 transmission rate of 1.544 Mbps.

Changes in frequency which happen at less than 10 Hz are considered wander because of the very low frequency and long wavelength. The amplitude and frequency of jitter can be severe enough to disrupt data transmission.

jumper
1. A cable or wire used to connect equipment for testing.

2. A small piece of wire or "plug" used to set options on a linecard or common equipment card.

-K-

kbps
Kilobits per second (kbps). See bit rate.

kHz
Kilohertz (one thousand Hertz)

kW
Kilowatt. A measure of power.

kWh
Kilowatt hour. A measure of energy.

-L-

label
Labels are symbolic names assigned to an instruction or data element located in a firmware or software module for the purpose of defining its address in related program operations.

LAN
See Local Area Network.

LAN bridge
The hardware and software used to connect LANs.

leased line
A telephone line reserved for the exclusive use of a leasing customer. A leased line is a permanent circuit which may be point-to-point or point-to-multipoint.

Light Emitting Diode (LED)
A solid state device that emits light when current is passed through it.

line
A transmission path from a non-switching subscriber terminal to a switching system.

Line Build Out (LBO)
A circuit that is used in a CSU interface to equalize or compensate for fluctuations in the T1 line.

line code
Techniques used to modify a signal or pulse during the transmission for T1. AMI is one type of line encoding, B8ZS is another.

line loopback
A signal path and timing mode in which a signal is retransmitted exactly as it was received by the terminal equipment.

line hit
The electrical interference causing the introduction of undesirable signals on a circuit.

line speed
The maximum data rate that can be reliably transmitted over a line.

link
1. A physical circuit between two points.

2. A conceptual or virtual circuit between two users of a packet switched network that allows them to communicate, even when different physical paths are used.

loading
Adding load coils to a transmission line to minimize amplitude distortion.

Local Area Network (LAN)
The interconnection of digital devices that communicate with each other using the same communications protocol and that are located in the same general area.

Local Exchange Carrier (LEC)
The local telephone company.

local alarm
A locally detected failure which generates a Carrier Failure Alarm (CFA). It may also be called a red alarm.

local loop
The part of a communications circuit between the subscriber's equipment and the equipment in the local exchange.

Long Distance Carrier (LDC)
A common carrier that can transmit long distance calls. Also known as Interchange Carrier.

loop
A local circuit between an exchange and a subscriber telephone station.

loop activate
A code which is sent to a remote piece of equipment, such as a CSU, to cause the equipment to go into a loopback condition.

loop deactivate
A code which is sent to a piece of equipment such as a CSU to cause the equipment to cancel any loopback condition.

loopback
Connection of Tx to Rx at one end of a communications link used to test the performance and quality of a line and/or terminating equipment.

loop timing
A timing mode where the transmit timing is derived from the input signal.

loop start
A common method of signalling an off-hook condition between an analog phone set and a switch.

loopback tests
Any tests in which a test signal is injected at one end of a circuit, looped back at the other end of the circuit and monitored at the originating end of the circuit.

Loss of Carrier (LOC)
An alarm condition that occurs when 32 consecutive zeros are transmitted on a T1 line.

Loss of Frame (LOF)
An extended out-of-frame state.

Loss of Signal (LOS)
A state which occurs when there is no detectable signal that operates within specific set parameters.

-M-

major alarm
An AT&T definition for an alarm indicating service failure.

mark
A non-zero pulse representing a binary one. See bit, one.

master clock
A node containing the master reference clock for a network.

matrix
In switch technology, the portion of the switch architecture where input leads and output leads meet, any pair of which may be connected to establish a through circuit. Also called a switching matrix.

Mbps
A notation for megabits per second; a million bits per second. See Bit Rate.

Megacom Mode
A service of AT&T, either a variation on INWATS or OUTWATS. Both are normal WATS services in all respects except that the local T1 lines are the responsibility of the customer.

Megacom 800
An 800 service for Wide Area Telephone Service (WATS) customers.

message
A sequence of characters used to convey information or data.

message feedback
A method of checking the accuracy of data transmission in which the received data is returned to the sending end for comparison with the original data.

message numbering
The identification of each message within a communications system by the assignment of a sequential number.

message switching
The technique of receiving a message, storing it until the proper outgoing line is available, and then retransmitting it. No direct connections between the incoming and the outgoing lines is set up as in line switching.

MHz
Megahertz. One million Hertz or one million cycles (megacycles) per second.

microprocessor
An electronic circuit that performs arithmetic, logic, and control operations, usually with the assistance of internal memory. Typically, the microprocessor contains Read-Only Memory (ROM), permanently stored instructions; Random Access Memory (RAM), and a control decoder for breaking down the instructions stored in ROM into detailed steps.

minimum ones density
A line code that employs a ternary signal to convey binary digits, in which successive binary ones are represented by signal elements that are normally of alternating, positive and negative polarity but equal in amplitude, and in which binary zeros are represented by signal elements that have zero amplitude. This is the primary mode for T1. Also see Alternate Mark Inversion.

mobile earth station
A satellite communications radio transmitter and or receiver situated on a ship, vehicle, or aircraft.

Mobile Telephone Switching Office (MTSO)
The MTSO controls the switching between the public switched telephone network and the cell sites for all wireline-to-mobile and mobile-to-wireline calls as well as for mobile-to-mobile calls.

modem
Modulator-demodulator. A device that converts digital signals into analog signals and then analog back to digital signals.

modulation
The process of varying some characteristics of the carrier wave in accordance with the instantaneous value or sample of the intelligence to be transmitted.

modulator
A device that converts a signal (voice or other) into a form that can be transmitted.

ms
A notation for millisecond. A millisecond equals one thousandth of a second.

multifrequency signalling
A supervisory signalling scheme used between telephone company offices in which the digits and codes are each comprised of a combination of two tones.

multiplex
To simultaneously transmit two or more messages on a single channel.

multiplexer
Equipment that combines individual signals into a composite signal for more efficient transmission. A T1 multiplexer combines 24 channels of 64 kbps plus a framing bit into a single bitstream of 1.544 Mbps. The term generally refers to a device that performs both multiplexing and demultiplexing.

multipoint
1. A system of wiring so arranged that a circuit, a line or a group of lines is accessible at a number of points.

2. A remote end of a broadcast circuit or polled circuit.

multipoint line
A single communications channel (typically a leased telephone circuit) to which more than one station or logical unit is attached, although only one transmits at a time. Such arrangements usually require a polling mechanism under the control of a master station to ensure that only one device at a time transmits data. Also called a multidrop line.

mux
See multiplexer.

-N-

near end
Equipment located at the user site as opposed to equipment located at a remote location.

network
An interconnecting group of computer systems, terminals or data communications facilities, usually three or more stations. It implies that the lines physically extend from one station to another until all are connected. (As contrasted with point-to-point).

Network Communications Controller (NCC)
Coastcom offers several network management software packages to enhance the control of the D/I Mux III.

The NCC2 is a software package that enables the user to connect and communicate with up to 103 Coastcom devices with a standard personnel computer (PC) and dial-up modems.

The NCC5 is a turnkey system which allows a central network manager to dial-up D/I Mux IIIs and DXC IIs in a network.

NCC6 allows a network manager to communicate with D/I Mux IIIs and DXC IIs through customer provided, out-of-band communications channels, or with an inband control channel using a premium Subrate Data Multiplexer (pSDM) channel card.

network management center
A center used for control of a network that provides traffic analysis, call detail recording, configuration control, fault detection and diagnosis or maintenance.

network redundancy
A communications pathway that has redundant links connecting all nodes in case one link fails.

network typology
The physical and logical relationship description of the nodes in a network.

node
A point of interconnection to a network (general).

A unit that is polled (multipoint).

One of the switches forming the network backbone (Packet Switching).

A unit in a ring or station.

node reference
A clock source within a selected node is the reference for all timing clocks within the node. The reference clock can be derived from the internal clock, recovered T1 link clock, clock supplied by a channel card, or by an external clock source.

noise
Random electrical signals generated by circuit components or by natural disturbances that corrupt the data by introducing errors.

non-blocking
A feature designed into the architecture of a switch so that the original call always reaches an ideal line without encountering a busy condition.

non-return-to-zero (NRZ)
A technique for transmitting digital data in which a positive voltage pulse signifies a binary one (1) and a negative voltage pulse signifies a binary zero (0).

Non-volatile Random Access Memory (NVRAM)
A data storage device that retains its memory contents when power is turned off or is disconnected.

North American Digital Hierarchy
A hierarchy of T1 carrier transmission standards and their corresponding characteristics used in North America and Japan.

ns
A notation for a nanosecond. A nanosecond equals one billionth of a second.

-O-

office channel unit
A device used in the central office to terminate DDS circuits. The office channel unit performs functions similar to the CSU at the customer premise.

Office Channel Unit Data Port (OCUDP)
The Coastcom OCUDP is designed to connect to the public network's data transport service. It supports DDS, switched 56 kbps dial-out capabilities. See also All Rate OCUDP.

off-hook
The telephone receiver has been removed from the cradle.

office repeater
A device at the central office which terminates a T1 line and regenerates the T1 signal for routing and switching at the customer office.

ohms
A measurement of the resistance to the flow of current. One ohm allows one ampere to flow when one volt is applied across the resistance.

on-hook
The telephone receiver is in the cradle.

one
A binary digit represented digitally by a non-zero pulse. See bit.

one-way trunk
A trunk between a switch (PBX) and a central office or offices, where traffic begins from only one end. It can only be used to dial out or to receive in.

out-of-band-signalling
A signal that is separate from the voice channel.

outgoing trunk
A line used to make calls.

out-of-frame
A state when the digital terminal or testset cannot detect a valid frame sequence.

-P-

packet switching
A data communications technique where a message is broken down into fixed-length units (packets) which are then transmitted to their destination by the fastest route. All packets may not travel the same pathway, however, and the receiving station determines when all units are received and in the proper sequence before forwarding the complete message to an addressee.

packet-switching network
A network designed to carry and route data in the form of packets. The packet and its format are internal to that network.

parallel transmission
A technique that sends each bit simultaneously over a separate line. Usually used to send a byte at a time to a high speed printer or other locally attached peripherals.

parity, odd or even
The addition of non-information bits to data to make the number of ones in a grouping of bits either always even or always odd. This procedure allows detection of bit grouping that contain single errors. It can be applied to characters, blocks or any specific bit grouping.

pattern errors
Bit errors that occur in the test pattern on a tested signal.

payload
The voice or data information transmitted on a signal.

phase hit
The occurrence of time interval error reaching or exceeding a pre-specified threshold.

phase jitter
The measurement in degrees-out-of-phase that an analog signal deviates from the referenced phase of the main data-carrying signal. Phase jitter is often caused by alternating current components in a telecommunications networks.

PLAR
Private Line Automatic Ringdown. A transmission mode used with VF circuits.

point-to-point
A circuit that connects two points directly where there are generally no intermediate processing nodes,although there could be switching facilities.

polling
A means of controlling terminals on a multipoint line. The computer functions as the master station and sends a message to each terminal, asking for information to be sent.

port
1. A physical interface between a multiplexer and a synchronous data channel, asynchronous data channel or voice channel.

2. A physical connector that provides an entrance and exit for information flow.

port interface
The equipment that provides a connection and marks a boundary between CPE and the T1 communications systems.

POTS
Plain Old Telephone Service.

Private Branch Exchange (PBX)
A private telephone exchange that provides for the transmission of calls to and from the public network.

premium Sub-Rate Data Multiplexer (pSDM)
The premium Subrate Data Multiplexer channel card (pSDM) is an intelligent programmable channel card that combines up to five low speed synchronous and asynchronous RS-232C data circuits onto one 64 kbps DS0 channel. The pSDM is fully integrated into the D/I Mux III multiplexer and provides the functionality of a separate subrate multiplexer within a single channel card.

private line
The channel and channel equipment furnished to a customer as a unit for exclusive use, generally with no access to the public switched telephone network. Also called a leased line.

Private Line Automatic Ringdown (PLAR)
A transmission mode used with VF circuits.

private network
A network established and operated by a private organization or corporation.

processor
The intelligent central element of a computer or other information handling system.

programmable
In telephone and computer equipment, the ability to change a feature or function without rewiring, typically by issuing instructions through a software command.

protocol
In the telecommunications field, protocol means a formal set of conventions that determine the format and the relative timing of message exchanges between two communications processes.

Public Switched Telephone Network (PSTN)
The complete public telephone system including telephones, local loop, trunk lines, and exchanges.

pulse
A brief change of current or voltage produced in a circuit to operate a switch or relay or which can be detected by a logic circuit.

pulse amplitude modulation (PAM)
See Modulation, pulse amplitude.

pulse code modulation (PCM)
The sampling of an analog signal into a binary code to be digitally transmitted.

pwr
An abbreviation for power.

-Q-

Quad 2-Wire FXS Foreign Exchange Subscriber FXS Channel Unit
The Quad 2-Wire FXS channel card plugs into a D/I Mux III multiplexer shelf and provides access to four 64-kbps PCM channels. The Quad 2-Wire fxs channel card also provides access to a 2-wire battery-operated interface between the D/I Mux III common equipment and a variety of 2-wire trunk or line circuits, in both toll and subscriber applications.

QRSS
Quasi-Random Stress Signal is a stress pattern test which does not violate the one's density requirement and used to validate the integrity of the T1 span.

-R-

rack
A structure on which apparatus is mounted, usually by means of shelves or mounting plates.

random access
Computer memory or storage that has the ability to directly address and access any piece of data in the memory.

Random Access Memory (RAM)
The primary memory in a computer. RAM can be overwritten with new information. All data can be located in RAM in an equal amount of time, thus allowing considerably faster access than data that must be accessed serially. RAM memory is considered "volatile" because when the power is off, the contents of RAM are lost.

Read Only Memory (ROM)
A memory device that is programmed at the factory, and whose contents thereafter cannot be altered. ROM memory is also random access, which is faster than serially accessed devices (e.g., magnetic tape). ROM memory is non-volatile because the contents are not lost when power is removed.

real time
1. Actual time in which a process transpires.

2. An application in which response to input is fast enough to effect

subsequent input, as when conducting the dialog that takes place at a

terminal in interactive systems.

recovery from fallback
When a system has switched to a fallback mode of operation and the cause of the fallback has been removed. This is the process that restores the system to its former condition.

red alarm
A local alarm caused by failure of T1 or the loss of framing on T1.

redundancy
Provision of duplicate, backup equipment to immediately take over the function of equipment that fails.

redundancy check
An automatic or programmed check based on the systematic insertion of components or characters used especially for checking purposes.

redundant bits
Extra bits added to a transmission for the propose of detecting and correcting any errors.

redundant power supply
An extra power supply used as a backup for another power supply.

regenerate
To restore a signal to its original shape.

reinitiation time
The time required for a device or system to restart (usually after a power outage).

relay
An electrically operated device that open or closes an electrical circuit.

repeater
In digital transmission, equipment that receives a pulse train, amplifies it, re-times it, and then reconstructs the signal for retransmission. In fiber optics, a device that decodes a low-power light signal, and converts it to electrical energy, then retransmits it through a LED or laser light source, often including some form of signal amplification.

remote access
To send or receive data to and from a computer terminal connected by a telephone link.

remote alarm
A failure in one direction in the transmit or near-to-far direction. See also yellow alarm.

Radio Frequency (RF)
Signal frequencies that range between 10 kHz to 100,000 MHz.

ring network
A network in which each node is connected to two adjacent nodes to form a continuous ring configuration.

robbed bit signalling (RBS)
In Pulse Code Modulation (PCM) it is a scheme in which the signalling bits for each channel are assigned to bit 8 of frames 6 and 12 in Superframe Format (SF) and in frames 6, 12, 18 and 24 in Extended Superframe Format (ESF).

ROM
See Read Only Memory.

router
A sophisticated, protocol-specific device that examines data and finds the best routing for it between sender and receiver by selecting the cheapest, fastest, or least busy of all available routes.

routing
The assigned communications path by which a message or telephone call will reach its destination.

routing code
Address or group of characters in the heading of a message which defines the final circuit or terminal where the message is to be delivered.

RJ-48
An eight position connector used for T1 communications.

RS-232C
An ANSI/IEEE standard physical interface with associated electrical signalling between data communications equipment (DCE) and data terminal equipment (DTE).

RS-422
An ANSI/IEEE standard serial interface for balanced voltage digital interface circuits.

RS-449
An ANSI/IEEE interface for data terminal equipment (DTE) and data communications equipment (DCE) employing serial binary data interchange.

Rx
An abbreviation for "receive".

-S-

schematic
A diagram that shows the electrical elements and connections of a circuit or a system.

scrambler
A security coding device applied to a digital channel that produces an apparently random bit sequence.

screening, shielding
The prevention of electric, magnetic, or electromagnetic fields from escaping or entering an enclosed area by use of a barrier.

sealing current
A current run on an interface loop is used to improve the quality of the transmission by burning the connectors and sealing the connections.

secondary channel (slave channel)
A channel that does not initiate transmission of data but is polled by a master unit to send information.

serial transmission
A method where the bits of a character are sent sequentially on a single transmission channel.

serial port
An input/output port that handles data one bit at a time.

Severely Errored Seconds (SES)
AT&T Publication 54016 defines a Severely Errored Second as a second with 320 or more Cyclic Redundancy Checks (CRC6's) or one or more Out of Frame (OOF) events.

SF
1. Single frequency: A method of in-band signalling which detects a single
frequency as signalling.

2. Superframe: A T1 frame format that consists of twelve D4 frames.

signal
The aggregate waves propagated along a transmission channel intended to act on a receiving unit.

signalling bits
Robbed bits that carry dialing and control information on signal.

sink
The part of a communications system that receives information.

smart jack
A jack with network loopback capabilities.

Smart Omni-orderwire Station Unit (SO/S)
The Smart Omni-orderwire Station Unit (SO/S) provides the
operator with the ability to access a voice channel for communication
to other stations or multiplexers in the T1 network as well as a standard telephone or butt-set unit. The SO/S channel card also serves as a terminating device in both point-to-point applications and drop-and-insert applications. It simultaneously communicates on the T1-1 (west) and the T1-2 (east) transmission paths.

source
The part of a communications system that transmits information.

Software Defined Network (SDN) or Virtual Private Network
Use of the carrier's public telephony network to provide the network functions of private lines. Customers design, change and manage large national network without investing in capital equipment.

span
A T1 line connected at two points.

stop element
The last bit of a character in asynchronous serial transmission, used to mark the end of the data element. Signalling is used to provide communications between the two ends of a circuit, usually for call set-up and call tear-down.

store and forward
An application in which messages are received at intermediate routing points and stored for later transmission to another routing point or to the final receiving point.

subrate
Subrate data multiplexing. Permits the operation of several low-speed synchronous and asynchronous channels on one DS0. The bit rates are 1.2, 2.4, 4.8, 9.6 and 19.2 kbps.

Subrate Data Multiplexer (SDM)
The Subrate Data Multiplexer (SDM) channel card is an intelligent, programmable card that combines low-speed synchronous/asynchronous data applications onto a standard 64 kbps channel. The SDM provides the function of a separate subrate multiplexer within a single channel card.

superframe (SF)
A T1 frame format that consists of twelve D4 frames.

switch
A device that makes, breaks or changes the connections in an electrical circuit. Switch is often used as a synonym for a central office switch or PBX.

switched service network
A network consisting of terminals, transmission links and at least one exchange in which any user can communicate with others at any time.

switch over
In an equipment failure, a switch occurs to an alternative component.

synchronous
A method of data transmission requiring the transmission of timing pulses to keep the sender and receiver synchronized in their communication  (i.e., sending information blocks). Contrast with asynchronous.

Synchronous Data Channel Unit (SDCU)
Synchronous Data Channel Units (SDCUs) are high speed data channel units that are ideal for computer-to-computer data transfer, distributed CAD/CAM, high-speed facsimile, compressed video for teleconferencing, and other applications that require large amounts of data to be transferred. The SDCU acts as the Data Communications Equipment (DCE).

synchronous network
A network in which all the communication links are synchronized to a common clock.

synchronous transmission
Transmission in which the data characters and bits are transmitted at a fixed rate. The transmitter and the receiver are synchronized together.

-T-

T1
A digital transmission link with a capacity of 1.544 Mbps (1.544 million bits per second). A T1 line can handle 24 channels, each of which is digitized at 64 kbps. T1 is a standard for digital transmission in North America.

T-carrier services
High-speed, digital transmission services that provide large-volume transmission between two stations. T1, the most common T-carrier service, operates at an aggregate data rate of 1.544 Mbps and consists of 24 separate channels.

Tandem T1 Unit (TTU)
The Coastcom Tandem T1 channel card (TTU) supports applications where selected channel information from a T1 line can be switched to one of two T1 spans. It also allows a D/I Mux III with Automatic Loop Protection Switching (ALPS) to interface to a network device such as a Digital Cross-connect system such as Coastcom's DXC II.

tandem switching
The switching of circuits between exchanges only.

tariff
The published cost for a specific communications service, equipment, or facility that constitutes a contract between the user and the communications carrier or supplier.

telco
A term used in communications to refer to the local telephone company.

T-Carrier Designation
The categories of the North American Digital Hierarchy that corresponds to the Digital Signal Designations. They are called T1 Carrier because they are time division multiplexed signals. See also North American Digital Hierarchy.

T Carrier
A digital transmission facility designed to carry speech and other signals in digital form.

time-division multiplexing (TDM)
A method of digital multiplexing where the means of obtaining a number of channels over a single path is accomplished by dividing the path into a number of time slots and assigning each channel its own time slot.

timing
The process of one or more communications devices synchronizing to a stable, fixed reference signal (clock) that enables the accurate transfer of information.

TO
Transmission only.

trunk
A facility between the customer premise and the local exchange carrier customer office.

turnkey system
A complete communications system that includes both hardware and software already assembled and installed by a vendor as a complete package.

twisted pair
Two insulated wires twisted together but not covered with an outer sheath.

-U-

unavailable seconds (UAS)
A group of ten or more continuous severely errored seconds. A signal is considered available again after ten seconds that are not severely errored seconds (SES).

uncontrolled slip
The overflow or underflow of an unframed buffer. An unframed buffer slips by repeating or deleting a portion of a frame. Uncontrolled slips result in framing bit positions shifts known as "change of frame alignment." See also controlled slip.

UVG
Universal Voice Grade. A service offered from and designated by the Regional Bell Operating Companies. UVG services are extensive. Check the Bellcore Publications for further details.

-V-

VA
See volt-ampere.

V AC
Volts, alternating current.

V DC
Volts, direct current.

voice circuit
An analog telephone channel used in homes and offices. Its bandwidth may vary between 300 Hz and 3500 Hz.

voice digitization
The conversion of an analog signal into digital symbols for storage or transmission.

Voice Frequency (VF)
An analog signal with an audio frequency range between 300 to 3500 Hz.

voice grade channel (VG)
Circuit used for speech transmission but also suitable for the transmission of analog data, modem data, or facsimile.

voice grade data (VGD)
Data that can be transmitted without distortion and that has good sound quality.

Virtual Private Network
Use of the carrier's public telephony network to provide the network functions of private lines. Customers may design, change and manage a large national network without investing in capital equipment.

-W-

WAN
Wide Area Network. A service that provides customers the ability to call specific zones for a set regular monthly fee.

WATS
Wide Area Telephone Service. A reduced-cost service provided by a telephone company. Certain telephone call arrangements such as In-WATS or 800-number service (calls placed to a location from anywhere) or Out-WATS (calls placed from a central location) are offered at a special price. Cost is usually based on hourly usage per WATS circuit and on distance-based zones from where the calls originate.

watt(s)
A unit of electrical power.

waveform
The shape of a signal over a specific period of time.

wavelength
The length of a wave measured from any specified point on a wave to the corresponding point on the next wave.

wideband channel
A channel wider in bandwidth than a voice grade channel.

wink
A signal indicating that the distant central office is ready to receive the number dialed.

wire pair
Two separate conductors traveling the same route to service a communications channel.

-Y-

yellow alarm
An alarm condition that occurs on a T1 line that signifying a failure at a remote location that is sometimes called a remote alarm.

-Z-

zero
The binary digit 0 also referred to as a "space".

zero code suppression
The insertion of a "one" bit to prevent the transmission of eight or more consecutive zero bits. Zero code suppression is used mostly with digital T1 and related telephone company facilities, which require a minimum ones density in order to keep the individual sub-channels of a multiplexed, high-speed facility active.