16QAM

16 point quadrature amplitude modulation - a modulation scheme with sixteen different potential detectable events, would allow 4 bits/baud or quadbits to be produced or detected per signaling event. In this case the transmission rate in bps would be 4 times the baud rate

BACK TO TOP...

American Standard Code for Information Interchange		See ASCII
amplitude		carrier wave charateristic which is manipulated to represent 1s and 0s (wave height)
amplitude modulation		a modulation scheme in which amplitude is manipulated in order to represent discrete detectable events which are then interpreted into 1s and 0s
analog		transmission method characterized by continuously varying tones within a given bandwidth or range of frequencies
ASCII		standardized method for encoding humanly readable characters. ASCII uses a series of 7 bits to represent 128 (27= 128) different characters
asynchronous transmission		synchronization is re-established with the transmission of each character in asynchronous transmission via the use of start and stop bits

BACK TO TOP...

bandwidth		range of frequencies
baud		timed opportunities to identify ones and zeroes by sampling the carrier wave are known as signaling events. The proper name for one signaling event is a baud
baud rate		the number of baud, or signalling events, per second
bit		a binary digit, a 1 or 0
bps		bits per second
breakout boxes		a device used to monitor and manipulate transmission signals
byte		a collection of 8 bits which represents a character

BACK TO TOP...

carrier wave		a reference wave which is manipulated by modems to represent 1s and 0s
Channel Service Unit/Data Service Unit		See CSU/DSU
character encoding		process required to render humanly readable characters into machine language through representation of characters as a series of 1s and 0s
constellation points		a plotted point on a quadrant which represents a particular phase shift and amplitude of a modulation scheme
CSU/DSU		Channel service unit/data service unit used to interface to carriers' digital transmission services

BACK TO TOP...

data circuit terminating equipment		See DCE
data terminal equipment		See DTE
DB-25		A 25 pin physical connector associated with both serial and parallel transmission protocols
DB-9		A 9 pin physical connector associated with a variety of serial protocols
DCE		Data circuit terminating equipment; a generic designation to indicate directionality in a serial transmission. Modems are DCE
DDS		Digital data service; a digital carrier transmission service offering speeds up to 56Kbps
demodulation		conversion of an analog signal to equivalent digital data
dial-up line		circuit switched connection or local loop used to access PSTN
dibit		two bits
digital		a transmission method characterized by discrete voltage levels used to represent logical 1s and 0s
digital data services		See DDS
digital signal processors		See DSP
DS-0		a 64Kbps digital carrier transmission service
DSP		digital signal processor; specialized computer chip able to process digital signals quickly, used in echo cancellation
DTE		data terminal equipment; a generic designation to indicate directionality in a serial transmission. PCs are DTE in a point to point, PC to modem transmission

BACK TO TOP...

EBCDIC		Extended binary coded decimal interchange code; 8 bit encoding scheme, 256 characters
echo cancellation		sophisticated technique which allows some modems to offer full duplex transmission over two wire circuits
extended binary codeddecimal interchange code		See EBCDIC

BACK TO TOP...

fallback		When an analog circuit, dial-up or leased, degrades or has some kind of transmission impairment, many modems use fallbackfallback or lower speeds automatically and continue with data transmissions.
four-wire circuit		A four-wire circuit is comprised of two wires capable of simultaneously carrying a data signal each with its own dedicated ground wire. Typically, four wire circuits are reserved for leased lines
frequency		a wave characteristic which can be manipulated in order represent 1s and 0s
frequency modulation		process of manipulating carrier wave frequency in order to represent 1s and 0s
frequency shift keying		See FSK
FSK		frequency shift keying; shifting carrier wave frequency on analog circuits in order to represent digital 1s and 0s
full-duplex		simultaneous transmission in both directions on a given circuit

BACK TO TOP...

half-duplex		transmission in both directions, only one direction at a time on a given circuit
handshaking		modem initialization which takes place in order to allow modems to agree on carrier wave frequency, modulation scheme, error correction protocols, etc.

BACK TO TOP...

intersymbol interference		Interference between constellation points in a given modulation scheme which can cause misinterpretation is known as intersymbol interference
ISO 10646		More commonly known as Unicode, this encoding scheme used 16bit characters to represent most known languages and symbols (over 65,000 possible characters)

BACK TO TOP...

leased line

a dedicated phone circuit which bypasses central office switching equipment, no dialtone

BACK TO TOP...

M block connector		physical connector most often associated with V. 35 serial transmission standard
modem		data communications device which modulates/demodulates analog/digital conversion
modem cable		cable which attaches a modem to a PC. Pinned straight through
modulation		process of converting discrete digital signals in continuously varying analog signals

BACK TO TOP...

narrowband digitalservices

digital carrier services offering bandwidth of less than 1.544 Mbps

BACK TO TOP...

parallel transmission		transmission method in which all bits in a given character travel simultaneously through a computer bus or parallel transmission cable
phase		one characteristic, (analogous to the wave's pattern) of a wave which can be manipulated in phase modulation schemes in order to represent logical 1s and 0s.
phase modulation		manipulation of a carrier wave's phase via phase shifting in order to represent logical 1s and 0s on an analog transmission circuit
phase shift keying		See PSK
plain old telephoneservice		See POTS
POTS		Dial-up, circuit-switched, analog phone service
PSK		A type of phase modulation in which different phase shifts represent different combinations of 1s and 0s
PSTN		Dial-up, circuit-switched, analog phone service
public switched telephone network		See PSTN

BACK TO TOP...

QAM		quadrature amplitude modulation; modulation scheme in which both phase and amplitude are manipulated
QPSK		Phase shift modulation with four different phases is more properly referred to as quadrature phase shift keying or QPSK.
quadrature amplitude modulation		See QAM
quadrature phase shift keying		See QPSK

BACK TO TOP...

RS-232-C

An EIA serial transmission standard officially limited to 20Kbps over 50 ft distance

BACK TO TOP...

S/N		signal to noise ratio; expressed in decibels, measures power of data signal as compared to power of circuit interference or noise
serial transmission		transmission method in which all bits of a given character are transmitted in linear fashion, one after the other
signal to noise ratio		See S/N
switched line		as opposed to a leased line, a switched line is connected to a CO switch, provides dial-tone, and reaches different destinations by dialing different phone numbers
synchronous transmission		transmission method in which timing is provided by a clocking signal supplied by either modems or the carrier

BACK TO TOP...

T-1		a leased line digital broadband service of 1.544Mbps
T-3		a leased line digital broadband service of 44.736Mbps
transmission rate		rate of actual bits transmitted end-to-end measured in bps, equal to bits/baud x baud rate
turnaround time		time it takes two half-duplex modems to change from transmit to receive mode by manipulating RTS and CTS signals
two-wire circuits		common local loop circuit in which one of these two wires serves as a ground wire for the circuit, thereby leaving only one wire between the two ends of the circuit for data signaling

BACK TO TOP...

UART		Universal Asynchronous Receiver Transmitter)UART (Universal Asynchronous Receiver Transmitter) acts as the interface between the parallel transmission of the computer bus and the serial transmission of the serial port.
Unicode		16 bit character encoding scheme identical to ISO 10646
universal asynchronous receiver transmitter		See UART

BACK TO TOP...

voice-grade leased line

analog leased line with 3100Hz of bandwidth

BACK TO TOP...

wavelength

The distance between the same spots on two subsequent waves is called the wavelength.wavelength The longer the wavelength, the lower the frequencyfrequency and the shorter the wavelength, the greater the frequency