Glossary CS601

Broadband : Two definitions exist in normal usage: 1) As data transmission channel which has a bandwidth greater than voice grade (VG) channels of 3000 Hz and potentially capable of much higher rates. Also known as wideband. 2) In local area networks (LAN), whereby broadband facilities can carry many voices or data channels simultaneously and can also be used for high speed digital data communications at speeds of up to 1.544 mbps, usually via coaxial cable using radio-frequency modems.

Broadcast,Terminal Broadcast : Two definitions apply to broadcast: 1) As a terminal transmission of a message intended for all points on a circuit simultaneously, rather than for a specific station. 2) In LAN technology as a transmission procedure used in a bus topology network sending all messages to all stations despite specific terminal addressing.

Buffering : The storing of data in a memory device, allowing the devices to change data rates, perform error checking and error retransmission.

Byte Multiplexer Channel : A mainframe input/output channel that provides multiplexing or interleaving of data in bytes. Contrast with Block Multiplexer channel.

Carrier System : The method of transmitting a number of channels over a single path by modulating each channel on a different carrier frequency at the originating end, then demodulating at the receiving end to return the signals to their original form.

CCITT : The international advisory committee, established under the United Nations that sets international recommendations which oftentimes are accepted as standards. Membership includes PTT 's, scientific and trade associations and private companies. CCITT operates within the International Telecommunications Union (UTI), a United Nations treaty organization in Geneva, to recommend worldwide standards. Note: The CCITT has been known since 1993 as the ITU-T (International Telecommunications Union - Telecommunications Standards Section. Click here to access the ITU web site.

Centralized : Processing with one CPU, which may support remote terminals/job entry stations.

Channel : A method for one way transmission, with several definitions of common usage: 1) In and IBM system, a high speed data link that serves to connect the CPU with its peripheral devices. See Block Multiplexor and Byte Multiplexor channels. 2) In State and Federal tariffs, a path for electrical transmission between two or more points without common carrier provided terminal equipment such as a local connection to DTE . Also called a circuit, path or facility.

Channel, Voice grade : A channel suitable for the transmission of speech, digital or analog data, or facsimile, typically with a frequency range of about 300 to 3300 Hz.

Character Parity : A method of adding an overhead bit to a character code to provide error-checking capability.

Character Set : A code, such as ASCII or EBCDIC used to represent data in a computer system. A collection of characters including special symbols and functions.

Circuit : In data communications, a circuit is a communications path between two points. In electronic design, a circuit is defined as one or more components that act together to perform one or more functions.

Circuit Switching : A method of communications in which physical circuits are transferred or switched to complete connections for exclusive use until the connection is released. Contrast with packet-switched networks.

Clear Channel : Any transmission path where the full bandwidth is available to the user.

Code Level : The number of bits defined in a code set to represent one character.

Collision : Simultaneous use by two stations of a shared transmission medium in a LAN environment. The result of both DTE's attempting to transmit data simultaneously in a half-duplex environment.

Communications Satellite : A microwave repeater, orbiting in a typically geosynchronous orbit, 22,300 miles above the earth, designed to relay signals between communications stations.

Compression : Two forms of compression are typically available: 1) Analog compression, where the bandwidth for analog transmission is reduced. Also known as compaction . 2) Data compression where the number of bits required to transmit data is reduced. This is performed in a variety of ways, often using a unique code to represent groups of repeated bytes or simply using fewer bits to represent the more frequent characters in the data.

Connection : The physical attachment of a path, or the data transmission path itself. Establishing a transmission path.

Connector : An electrical device for making one or more connections such as RJ11C or EIA RS-232 C, typically with male and female components.

Crosstalk : Any undesirable transfer of energy form one circuit, called the disturbing circuit, to another, called the disturbed circuit.

CSMA/CA : A CSMA protocol using a slotted TDM to minimize a collision reoccurrence. For optimum results, CSMA/CA will work best if the time slot is short as compared to the length of the packet.

CSMA/CD : (Carrier Sense Multiple Access with Collision Detection) - A LAN access method where all stations attached to the network listen for transmissions before attempting to transmit. If two or more devices begin transmit ting at the same time, each stops for a random period of time before attempting to re transmit. See also IEEE 802.3 and Ethernet.

CXR Carrier : A data communications signal, similar to CD ( carrier detect) that is used to indicate the intention to transmit data.

Cycle : One iteration or a loop through a set of logical steps

CRC (Cyclic Redundancy Check) : An error checking control method in which the block check character (BCC) is the remainder after dividing all the serialized bits in a transmitted block by a prespecified binary number.

Data : The representation of facts, instructions or concepts in a structured manner suitable for communication

Data Circuit : A telecommunications medium for the transmission of information in analog or digital form.

DCE (Data Communications Equipment) : The device installed on premises to provide the functions needed to establish, maintain and terminate a connection as well as the signal conversion required for communications between the DTE and the telephone line or data circuit . Typically, DCE is a modem.

Decentralized : A processing method where intelligence is located at several remote locations of the same processing system.

Dedicated Line : Any telecommunications line that is reserved for the exclusive use of a customer and is not dialed. A dedicated line may be either point-to-point or multi point. Also known as a leased line or a private line.

Delivery Time : A measurement of time beginning with the start of transmission at the transmit ting terminal to the reception at the receiving terminal.

Demodulator : The internal portion of a modem designed to convert the received analog line signals back to digital form

Destination : A field in a data message that contains the address of the terminal to which a data message is directed.

Dial Line : Also known as dial-up line or dial-in line, any communications line that must be dialed. Contrast with Dedicated line .

Digital Loopback : A diagnostic technique for testing the digital circuitry of a communications device, usually a modem . The loop is formed at the modem 's DTE interface, either initiated locally or remotely via communications circuits.

Distortion : The unwanted changes in signal or signal shape from its true form occurring during transmission between two points, e.g. amplitude distortion, delay distortion.

Distributed Processing : Refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. More often, however, distributed processing refers to local-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them. Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

DLC (Data Link Control) : A telecommunications protocol designed to control, set up, perform error checking and terminate the transfer of information between two stations on a data link . Compare with HDLC and SDLC .

Earth Station : The transmitter and related antenna located on earth for communication with a satellite.

External Modem : A modem designed to be physically located externally from the terminal device instead of internally as in an integrated modem.

Fast Select : A packet-switched transmission method whereby the user is able to transmit small amounts of data (approx. 128 characters) with the call request packet, instead of transmit ting the data information in packets following the call request packet. This method allows a user to have small amounts of information arrive at the destination quickly.

Fiber Loss : The weakening of light signal strength in fiber optic transmission.

Fiber Optics, Fiber Optic Cable : A transmission medium using plastic or glass fibers to carry light rays containing information. See optical fibers.

Filter : The electronic device or devices used to attenuate undesirable signals within frequencies in the transmission circuits and pass through, unchanged, desirable signals within frequencies.

Flow Control :  A method of preventing the loss of data whereby the transfer of messages or characters to a receiving device would be controlled via the use of a control character (s) such as X-ON (transmit on) or X-OFF (transmit off), allowing the receiving devices buffer to drain before accepting more data.

Format : A method for structuring transmitted data whereby the positioning of information and related control data would insure identification at the receiving device.

Frequency : The number of times that a sine wave would repeat, or cycle in one second.

FSK (Frequency Shift Keying) :  A method of frequency modulation (FM) where one frequency would represent a mark (one) and another frequency would represent a space (zero).

gHz (Gigahertz) : A measurement of frequency equal to 10 to 9th power.

Group Addressing : Any address that is shared by two or more devices or stations.

Half-Duplex Transmission (HDX) : The common use definition is a circuit designed for transmission in either direction but not both directions simultaneously. Contrast with FDX, full-duplex transmission.

Hamming Code : A method of forward error correction (FEC) named for its inventor and designed to detect and correct a single bit received in error.

Handshaking, Handshake : Communications line interplay used to establish a data path via the exchange of predetermined signals, usually performed by communications protocol or modems.

Hertz (Hz) : The same as cycles per second, used as a measurement of bandwidth or frequency.

FAX (Facsimile Terminal) : An image transmission system designed to reproduce the communicated image (such as documents or photographs) on a paper forms.

FEC (Forward Error Correction) : The inclusion of additional data contained in a transmit ted block, to be used by the receiver in case of errors.

Peripheral, Peripheral Device : Hardware connected to a computer to function as an input/output device, such as a tape or disk unit, printer, etc.

Phase : The time position of a sine wave, the point at which the cycle advances.

Phase Modulation : One of three basic ways of modifying a sine wave signal to make it transmit information, whereby the phase of the sine wave, or carrier, is modified in accordance with the information to be transmitted.

PSK (Phase Shift Keying) :  A method of performing phase modulation whereby the signaling elements would be represented by phase shifts.

Public : For the customers use; a common carrier provided service.

Pulse Amplitude Modulation (PAM) : A technique of analog transmission that modulates the amplitude of each pulse.