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DATA
COMMUNICATIONS
Second Edition
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DATA
COMMUNICATIONS
Second Edition
CHARLES J. SIPPL
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© The Macmillan Press Ltd, 1985
All rights reserved. No reproduction, copy or
transmission of this publication may be made without
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Copyright Licensing Agency, 33-4 Alfred Place, London
WC1E7DP.
Any person who does any unauthorised act in relation to
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and civil claims for damages.
First edition published 1976
Second edition first published 1985 by
THE MACMILLAN PRESS LTD
London and Basingstoke
Associated companies in Auckland, Delhi, Dublin,
Gaborone, Hamburg, Harare, Hong Kong,
Johannesburg, Kuala Lumpur, Lagos, Manzini,
Melbourne, Mexico City, Nairobi, New York, Singapore,
Tokyo.
Paperback reprinted 1991
British Library Cataloguing in Publication Data
Sippi, Charles J.
Dictionary of data communications.
1. Electronic data processing - case studies
I. Title
001.6'03'21 QA76.15
ISBN 978-0-333-37083-4 ISBN 978-1-349-17845-2 (eBook)
DOI 10.1007/978-1-349-17845-2
The paperback edition of this book is sold subject to
the condition that it shall not, by way of trade or
otherwise, be lent, resold, hired out, or otherwise
circulated without the publisher's prior consent in
any form of binding or cover other than that in which
it is published and without a similar condition
including this condition being imposed on the
subsequent purchaser.
A
A AND NOT 8 gate: A binary logic coinci absolute loader: A routine that uses abso
dence (twoinput) circuit used to complete lute coding to load a program into memory
the logic operations of A AND NOT B, i.e., at fixed numerical addresses.
result is true only if statement A is true and
statement B is false. absolute-value device: A transducer that
produces an output signal equal in magni
abend: Contraction for abnormal end. An tude to the input signal but always of one
unexpected halt in a program due to a polarity.
logical error, data that the program cannot
process (such as division by zero, or the absolute-value sign: A sign using the sym
addition of a number and a letter), or other bol as follows @abv indicating that the
similar bugs. Abend, also referred to as absolute value of a number is to be taken,
"bomb," is used as both a noun and a verb. i.e., the value of the number irrespective of
the sign.
abnormal end: See abend.
abstract symbol: 1. (ISO) A symbol
abnormal statement: An element of whose meaning and use have not been
FORTRAN IV which specifies that certain determined by a general agreement but
function subroutines must be called every have to be defined for each application of
time they are referred to. Abnormal declar the symbol. 2. In optical character recogni
ations enable the compiler to optimize the tion, a symbol whose form does not suggest
calling of other (nonabnormal) function its meaning and use. These should be
subroutines. defined for each specific set of applications.
abort: A procedure to terminate execu ac bias (magnetic tape) : The alternating
tion of a program when an irrecoverable current, usually of a frequency several times
error, mistake, or malfunction occurs. higher than the highest signal frequency,
that is fed to a record head in addition to the
absolute alarm: An audio or visual alarm signal current. AC bias serves to linearize
set off by the detection of a variable which the recording process and is used uni
has exceeded high or low limit conditions. versally in analog recording. Generally, a
large ac bias is necessary to achieve max
absolute coding: Coding in the numeric imum long-wavelength output and linear
language form acceptable to the computer ity, but a lower value of bias is required to
arithmetic and control unit. obtain maximum short-wavelength output.
absolute delay: The real-time interval ac communication: Light, radio waves,
from the transmission to reception of a sound, and data-transmission signals in
signal over a circuit. Also called transmis alternating-current (ac) form are all
sion time or circuit delay. described in terms of frequencies. In these
various transmission forms the instant
absolute instruction: A particular com aneous amplitude of the signal at a given
puter instruction which specifies completely point in time varies rapidly, in a manner
a specific computer operation and is capable similar to the displacement of a string on a
of absolute instruction causing the execu musical instrument. The rate of this fluctu
tion of that operation. ation is referred to as the frequency and
1
2 ac coupled flip-flop
is expressed in terms of cycles per second or access scan: A procedure for receiVmg
hertz. The term "hertz" (abbreviated Hz) data from files by searching each data item
has by international agreement replaced the until the desired one is obtained.
earlier term "cycles per second," thus
honoring one of the early pioneers in the access time: 1. The time interval between
field of electrical transmission, Heinrich the instant at which a control unit initiates a
Hertz. call for data and the instant delivery of the
data is completed. Access time equals
ac coupled flip-flop: A flip-flop made up of latency plus transfer time. 2. The time
electronic circuits in which the active interval between the instant at which data
elements, either tubes or transistors, are are requested to be stored and the instant at
coupled with capacitors. which storage is started.
accelerating anode: An electrode given a
accounting checks: Refers to accuracy
high positive potential to speed up the
controls on input data that are based on
moving electrons in the beam of a writing
such accounting principles as control totals,
tube.
cross totals, or hash totals.
acceleration time: The time between the
accounting function: The system of keep
interpretation of instructions to read or
ing track of machine usage and recording it.
write on tape and the transfer of informa
tion to or from the tape into storage, or
accounting machine: 1. A machine that
from storage into tape, as the case may be.
prepares accounting records. 2. A machine
accentuation: A technique for emphasiz that reads data from external storage
ing particular bands in an audio-amplifier. media, such as cards or tapes, and automa
tically produces accounting records or tabu
accept ion: An atom in a doped semicon lations, usually on continuous forms.
ductor crystal which accepts an electron or
gives up a hole. accumulator register: The part of the
arithmetic unit in which the results of an
acceptance cone: The imaginary cone at operation remain, and into which numbers
the end of an optic fibre whose half-angle is are brought to and from storage.
the angle of incidence of the core/cladding
interface. Any beam of light entering the accumulator shift instruction: A com
fibre that is inside this cone (at an angle less ter instruction which causes the contents of
than the half-angle) will reflect and be an accumulator register to shift to the left or
propagated inside the fibre to the other end. right.
accepted signal call: Using data channel
accuracy: 1. (ISO) A qualitative assess
signalling transmission, a signal sent in a
ment of freedom from error, a high assess
backward direction indicating a specific call
ment corresponding to a small error. 3.
can be completed.
(ISO) A quantitative measure of the magni
tude of error, preferably expressed as a
acceptor circuit: Tuned circuit responding
function of the relative error, a high value of
to a signal of one specific frequency.
this measure corresponding to a small error.
access arm: A part of a disc storage unit Contrast with precision.
that is used to hold one or more reading and
writing heads. accuracy control character: A specific
character designed with a function to con
access mode: Used in COBOL program trol a given block of data, to indicate if the
ming, the name of a technique used to dataare in error, to indicate if they are to be
obtain a record from, or to place a recording disregarded or whether they can or cannot
in a file contained in a storage device. be represented on a particular device.
active element 3
ACH: See automated clearinghouse. acoustic coupler: A device which provides
the facility to transmit and receive messages
ACK: See acknowledgment. using the standard telephone handset as the
coupling to the line.
ACK (ARPANET): A short transmission
between interface message processors acoustic delay line: A device used to store
(IMP) to indicate the successful reception digital information cyclically in the form of
of a message segment (referred to as a sound pulses. It consists of (1) a piezoelec
packet). tric transmitter which converts normal
digital information into an acoustic wave,
ACKO, ACKl, Affirmative, Acknowledg (2) the acoustic transmission path, and (3) a
ment: These replies indicate the previous piezoelectric receiving unit which converts
block was accepted without error and the the acoustic data back into its original form.
receiver is ready to accept the next block.
Alternating these replies assists in the acoustic-sonic storage: Sonic delay line
error-recovery procedures ACK1 is the storage types and techniques.
response to the first transmission and suc
cessive odd blocks. ACKO is the response to
acquisition time: The interval time a
the second block and all even-numbered
sample-hold circuit needs to acquire the
blocks, and is the positive response to
input signal to within the stated accuracy. In
selection (multipoint) or line bid (point-to
conservative specifications, it includes the
point) (BSC).
settling time of the output amplifier. In
some cases a signal can be acquired fully
acknowledgment (ACK): In data trans
(and the circuit switched into hold) before
mission, data are usually grouped into
the output has settled. The output of the
fixed-length blocks. After transmitting a
sample-hold is not meaningful until it has
data block, the transmitting terminal sends
settled.
a check character, calculated from the con
tent of the data block. The receiving termi
action line: When a cathode ray storage
nal compares this character with its own
tube is operating in a serial mode, it refers
computation of the check character. If the
to that tine of the raster which is used during
values agree, then no transmission error has
the active period.
occurred and the receiving terminal sends
the control character ACK to the trans
mitter to signify that no error occurred. The action spot: The spot of the raster on the
transmitting terminal then continues trans face of an electrostatic storage tube which
mission of another data block. If the check stores the digits and holds a charge.
characters differ, then an error occurred
and the receiver sends a NAK (negative activate key (button): A primary switch on
acknowledgment) character to indicate an various control panels which when pressed
error to the transmitter. The transmitter or initiated will cause the first part or step of
then repeats transmission of the same data a program cycle or a procedure to begin.
block and the process repeats. Same as Same as start key (button or switch) and
acknowledge character. initiate button.
acknowledgment character (AKC): A active element: 1. An element in use or in
specific character for communications con its excited state, i.e., a tube, transistor or
trol transmitted in an affirmative response device which is on or alive rather than off,
from a message-receiving program. Most dead or in a ground state. 2. A file, record,
often used as an accuracy control character or routine which is being used contacted, or
transmitted after a string of characters has referred to. Computing components are
been received with proper vertical and active when they are directed by the control
longitudinal redundancy check characters. unit.
4 active me
active me: A file which is being used in adaptive tree walk protocol: A limited
which entries or references are made on a contention protocol with stations organized
current basis. in a binary tree.
active intruder: An intruder who can add time (in microseconds): The time
record messages to hear later, send his own required to acquire from memory and exe
messages on the desired communication cute one fixed-point add instruction using
channel, or alter legitimate messages before all features such as overlapped memory
they reach the intended receiver. banks, instruction look-ahead and parallel
execution.
active master file: A specific master file
add-to-storage concept: The process in
that contains items relatively active or
which the sum of two numbers is calculated
frequently used as contrasted to static or
by adding the first number to the second and
reference items.
the results replace the second number (all in
one operation).
active master item: The most active items
on a master file by usage data.
adder-subtracter: (ISO) A device that
acts as an adder or subtracter depending
active network: A electronic network upon the control signal received. The
which contains any sources of power other adder-subtracter may be constructed so as
than signal inputs. to yield the sum and the difference at the
same time.
active state: The state of an interrupt level
that is the result of the central processor addition without carry: A logical opera
starting to process an interrupt condition. tion applied to two operands that produce a
result relying on the bit patterns of the
active transducer: Any transducer in operands and according to rules for each bit
which the applied power controls or modu position.
lates locally supplied power, which
becomes the transmitted signal, as in a additional character: A character which is
modulator, radio transmitter. neither a letter nor a number, but which is
usually a punctuation mark,%,-,#; i.e.,
activity level: The value taken by a struc a member of a specialized alphabet. A
specific meaning is assigned to this charac
tural variable in an intermediate or final
solution to a programming problem. ter to use it to convey special information.
additional label processing: The use of the
actuating signal: A particular input pulse
input/output label system to verify or create
in the control circuitry of computers.
a standard label and then, by user's
routines, verify or insert additional
ADAPSO: An association of U.S. and
information in the optional field of the
Canadian data processing service organ
standard label.
izations.
address: 1. A character or group of
add-on: Hardware attached to a computer characters that identifies a register, a parti
to increase performance or memory. cular part of storage, or some other data
source or destination. 2. To refer to a device
add/subtract time: The time required to or an item of data by its address.
perform an addition or subtraction, exclu
sive of the time required to obtain the address, control data, and cbeeksulll
quantities from storage and put the sum or ftelds: Four kinds of fields in bit oriented
difference back into storage. protocol frames.
AFIPS 5
address comparator: A device used to location where the address of the operand
verify that the correct address is being read. may be found.
The comparison is made between the
address being read and the specified adjacent channel: The channel whose fre
address. quency band is adjacent to that of the
reference channel.
address conversion: The translation of the
adjacent channel interference: The pres
relative or symbolic addresses into absolute
ence of undesirable energy in a channel
addresses by use of a computer, or
caused by one or both sidebands of modu
manually.
lated carrier channels in close frequency
proximity extending from one into another
address field: The portion of an instruc
through electrostatic or electromagnetic
tion word that contains the operand
coupling.
address.
adjoint system: A method of computation
address format: 1. The arrangement of based on the reciprocal relation between a
the address parts of an instruction. The system of ordinary linear differential equa
expression "plus-one" is frequently used to tions and its adjoint.
indicate that one of the addresses specifies
the location of the next instruction to be administrative data processing: An ex
executed. Such as one-plus-one, two-plus pression usually meaning business data pro
one, threeplus-one, four-plus-one. 2. The cessing such as the recording, classifying, or
arrangement of the parts of a single address summarizing of transactions, activities,
such as those required for identifying chan events, etc. Usually of a financial nature, or
nel, module, track, etc. in a disk system. the collection, retrieval, or control of such
items.
address generation: A number or symbol
generated by instructions in a program and admissible mark: Specific rules or con
used as an address part, i.e., a generated ventions determine which marks, symbols,
address. and numerals or characters are permitted in
various areas of computing for all install
address immediate instruction: Specific ations and for various languages.
instructions designed to contain the value of
the operand in its address part rather than advanced data communication control pro
cedure (ADCCP): A version of synchro
the address of the operand. It is used most
often for incrementing a count by a fixed nous data link control (SDLC) modified by
amount or masking a partial-word field of the American National Standards Institute
data, or for testing a special character for (ANSI).
identical characteristics with the immediate
Advanced Research Project Agency Net·
character in the instruction.
work (ARPANET): The long-haul com
munications network maintained by an
address register: A register in a computer
agency (ARPA) of the United States Fed
where an address is stored.
eral Government. ARPANET is one of
America's most important networks
addressing level: A determination of the because it links not only government
number of steps of indirect address which computers, but research computers at
have been applied to a particular program. virtually every major American university
First level is direct addressing, i.e., the as well.
address part of the instruction word has the
address of the operand in storage. In second AFIPS: An organization of computer
level addressing (indirect), the address part related societies. Its members include: The
of the instruction word gives the storage Association for Computer Machinery; The
6 air movement data
Institute of Electrical and Electronic algorithm: A prescribed set of well
Engineers Computer Group; Simulation defined rules or processes for the solution of
Councils, Inc.; American Society for a problem in a finite number of steps, for
Information Science. Its affiliates include: example, a full statement of an arithmetic
American Institute of Certified Public procedure for evaluating sin x to a stated
Accountants; American Statistical Associ precision. Contrast with heuristic.
ation; Association for Computational
Linguistics; Society for Industrial and algorithm translation: A specific, effec
Applied Mathematics; Society for Informa tive, essentially computational method for
tion Display. Headquarters-Montvale, N.J. obtaining a translation from one language
to another.
agenda: The set of control-language
statements used to prescribe a solution path algorithmic language (computer): An
or run procedures; an ordered list of the arithmetic language by which numerical
major operations constituting a procedure procedures may be precisely presented to a
for a solution or computer run. (This usage computer in a standard form. The language
corresponds roughly to the ordinary is intended not only as a means of directly
"agenda" for a meeting.) presenting any numerical procedure to any
suitable computer for which a compiler
agent: A process whose job is to provide a exists, but also as a means of communicat
uniform interface to all hosts in a network ing numerical procedures among individ
operating system. uals. The language itself is the result of
international cooperation to obtain a stan
air movement data: Data presented most dardized algorithmic language. The Inter
often with digital displays relating to flight national Algebraic Language is the forerun
plan information such as present position, ner of ALGOL.
future position, estimated time of arrival,
algorithmic routine: That specific routine
etc.
which directs the computer in a program to
solve a problem in a finite or specified
alertor: A device which consists of a small
number of steps, but not rely on a trial and
box connected to a large floor pad laced
error procedure. The solution and solution
with with wires. It sounds an alarm when
method are exact and must always reach the
the operator has not operated the pad for a
specific answer.
specific period of time.
alias: 1. An alternate label. For example,
algebraic language: An algorithmic lan
a label and one or more aliases may be used
guage many of whose statements are struc
to refer to the same data element or point in
tured to resemble the structure of algebraic
a computer program. 2. An alternate name
expression, e.g., ALGOL, FORTRAN.
for a member of a partitioned data set. 3. In
pulse code modulation telecommunication
ALGOL (ALGOrithmic Language): An
links, a spurious signal resulting from beats
international algebraic procedural language
between the signal frequencies and the
for a computer programming system.
sampling frequency.
ALGOL-Dartmouth: The Dartmouth
alien tones: Frequencies, harmonics and
ALGOL is essentially ALGOL-60 with
other products introduced in sound repro
only a few restrictions and extensions made
duction because of nonlinearity in some
to allow operation within the BASIC
part of the transmission path.
system timesharing framework.
alignment: See boundary alignment.
algoristic: A step-by-step methodology;
an exact answer; a systematic computation allocate storage: To assign storage loca
guaranteeing accurate solution. tions or areas of storage for specific
