Abbreviations and Acronyms

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a	atto (10-18)
A	amperes (current)
Å	angstrom
AAR	automatic alternate routing
AARTS	automatic audio remote test set
ABR	available bit rate
ABS	alternate billing services
ABSBH	average busy season busy hour
ac	alternating current access information
ACC	automatic callback calling
ACD	automatic call distributor
ac-dc	alternating current - direct current
ACG	automatic call gap
ACH	attempts per circuit hour
ACK	acknowledge character
ACM	address complete message
ACP	action point
ACSB	amplitude companded single-sideband
ACSE	association control service element
ACTEL	access telephone number
ACTL	access customer terminal location
ACTS	Advanced Communications Technology Satellite automated coin toll service
ACU	automatic calling unit
A-D	analog-to-digital
ADC	analog-to-digital converter analog-to-digital conversion
ADCCP	Advanced Data Communication Control Procedures
ADH	automatic data handling
ADMD	administration management domain
ADP	automatic data processing
ADPCM	adaptive differential pulse-code modulation
ADPE	automatic data processing equipment
ADPSSO	automatic data processing system security officer
ADS	auxiliary data system
ADU	automatic dialing unit
ADX	automatic data exchange
AECS	Aeronautical Emergency Communications System [Plan]
AERM	alignment error rate monitor
AES	Advanced Encryption Standard
AF	audio frequency
AFC	area frequency coordinator automatic frequency control
AFNOR	Association Francaise de Normalisation
AFRS	Armed Forces Radio Service
AGC	automatic gain control
AGE	aerospace ground equipment
AI	artificial intelligence action indicator
AIC	Automatic Intercept Center
AIG	address indicator group address indicating group
AIM	amplitude intensity modulation
AIN	advanced intelligent network
AIOD	automatic identified outward dialing
AIS	automated information system alarm indication signal automatic intercept system
AITS	acknowledged information transfer service
ASIC	application-specific integrated circuits
AJ	anti-jamming
AK	data acknowledgement (see also “ACK”)
ALBO	automatic line buildout
ALC	automatic level control automatic load control
ALE	automatic link establishment
ALGOL	Algorithmic Computer Language
ALS	application layer structure
ALU	arithmetic and logic unit
A/m	amperes per meter
AM	amplitude modulation
AMA	automatic message accounting
AMARC	automatic message accounting recording center
AMAT	automatic message accounting transmitter
AMC	administrative management complex
AME	amplitude modulation equivalent automatic message exchange
AMI	alternate mark inversion [signal]
AM/PM/VSB	amplitude modulation/phase modulation/vestigial sideband
AMPS	automatic message processing system advanced mobile phone system
AMPSSO	automated message processing system security officer
AMSC	American Mobile Satellite Corporation
AMTS	automated maritime telecommunications system
ANI	automatic number identification
ANL	automatic noise limiter
ANM	answer message
ANMCC	Alternate National Military Command Center
ANS	American National Standard
ANSI	American National Standards Institute
AP	anomalous propagation application process
APAB	all-primary / all-backup
APC	adaptive predictive coding
APCO	Association of Public Safety Communications Officials
APD, apd, a.p.d.	avalanche photodiode
APDU	application protocol data unit
API	application program interface
APL	average picture level
APND	all-primary / no-backup
APOT	additional point of termination
APK	amplitude phase-shift keying
APS	automatic protection switching
APSB	all-primary / some backup
ARP	address resolution protocol
ARPA	Advanced Research Projects Agency [now DARPA]
ARPANET	Advanced Research Projects Agency Network
ARQ	automatic repeat-request
ARS	automatic route selection
ARSR	air route surveillance radar
ARU	audio response unit
ASC	AUTODIN Switching Center access service company access service coordinator
ASC-EC	access service coordination exchange company
ASCII	American Standard Code for Information Interchange
ASE	application service element
ASG	access service group
ASELP	algebraic sum excited linear prediction
ASIC	application-specific integrated circuits
ASN.1	abstract syntax notation one
ASP	aggregated switch procurement application service part adjunct service point assignment source point
ASR	access service request airport surveillance radar automatic send and receive
ASR NO	access service request number
AT	access tandem
ATACS	Army Tactical Communications System
ATB	all trunks busy
ATCRBS	air traffic control radar beacon system
ATDM	asynchronous time-division multiplexing
ATE	automatic test equipment
ATIS	Alliance for Telecommunications Industry Solutions [formerly ECSA]
ATM	advanced testing method asynchronous transfer mode
ATN	account telephone number
ATRS	automated trouble reporting system
ATV	advanced television
au	astronomical unit access unit
AUI	attachment unit interface
AUTODIN	Automatic Digital Network
AUTOSEVOCOM	Automatic Secure Voice Communications Network
AUTOVON	Automatic Voice Network
AV	audiovisual
AVD	alternate voice/data
AWG	American wire gauge
AWGN	additive white Gaussian noise
AZ	azimuth
b	bit
B	bel byte
BAAD	band advance
balun	balanced to unbalanced
basecom	base communications
BASIC	beginners' all-purpose symbolic instruction code
BCC	block check character blocked calls cleared
BCD	binary-coded decimal binary-coded decimal notation blocked calls delayed
BCI	bit-count integrity
BCST	broadcast
Bd	baud
B8ZS	bipolar with eight-zero substitution
bell	BEL character
BER	bit error ratio
BERT	bit error ratio tester
BETRS	basic exchange telecommunications radio service
BEX	broadband exchange
BHMC	busy hour minutes of capacity
BIB	backward indicator bit
BIBR	backward indicator bit received
BIBT	backward indicator bit to be transmitted
BIBX	backward indicator bit expected
BIC	bearer identification code
BIH	International Time Bureau
BIP	bit interleaved parity
B-ISDN	broadband ISDN
bi-sync	binary synchronous [communication]
bit	binary digit
BIT	built-in test
BITE	built-in test equipment
BIU	bus interface unit
BLA	blocking acknowledgment message
BLER	block error ratio
BLO	blocking message
BLR	blocking/unblocking signal reception
BLS	blocking/unblocking signal sending
BNF	Backus Naur form
BOC	Bell Operating Company
BPSK	binary phase-shift keying
bpi	bits per inch bytes per inch
b/s  (formerly “bpi”)	bits per second
b/in (formerly “bps”)	bits per inch
BPSK	binary phase-shift keying
BPSS	basic packet switched service
BR	bit rate
BRAN	broadband radio access networks
BRI	basic rate interface
BS	base station
BSA	basic serving arrangement
BSBH	busy season busy hour
BSE	basic service element basic serving element
BSI	British Standards Institution
B6ZS	bipolar with six-zero substitution
BSM	backward setup message
BSN	backward sequence number
BSNR	backward sequence number received
BSNT	backward sequence number of next signal unit to be transmitted
BSP	Bell System Practices
BSS	base station system basic service set
B3ZS	bipolar with three-zero substitution
BTN	billed telephone number billing telephone number
BW	bandwidth
c	centi (10-2)
CA	communications assets
CACS	centralized alarm control system
CAD	call denial computer-aided design computer-aided drafting
CAG	combined access group
CAI	common air interface
CAISS	common air interfaces for satellite systems
CAM	computer-aided manufacturing
CAMA	centralized automatic message accounting
CAN	cancel character
CAP	competitive access provider customer administration panel
CARS	cable television relay service [station]
CAS	centralized attendant services call associated signaling
CASE	computer-aided software engineering computer-assisted software engineering
CATLAS	centralized automatic trouble locating and analysis system
CATV	cable TV community antenna television
CB	citizens band
CBA	changeback-acknowledgment signal
CBAN	Centrex billing account number
CBD	changeback-declaration signal
CBMS	computer based messaging system
CBN	common bonding network
CBX	computer branch exchange
CC	connection confirm country code
CCBS	completion of calls to busy subscribers
CCC	clear channel capability
C2	command and control
C3	command, control and communications
C3CM	C3countermeasures
C3I	command, control, communications and intelligence
CCA	carrier-controlled approach
CCD	charge-coupled device
CCH	connections per circuit per hour
CCIF	International Telephone Consultative Committee [a predecessor to the CCITT]
CIP	critical infrastructure protection
CCIR	International Radio Consultative Committee
CCIS	common-channel interoffice signaling
CCIT	International Telegraph Consultative Committee [a predecessor to the CCITT]
CCITT	International Telegraph and Telephone Consultative Committee {now ITU-T}
CCL	continuous communications link
CCMDS	common channel multipoint distribution system
CCO	continuity check outgoing
CC-PIC	customer changeable primary interexchange carrier
CCS	hundred call-seconds common channel signaling
CCSA	common control switching arrangement
CCS7	common channel signaling System #7
CCTV	closed-circuit television
CCW	cable cutoff wavelength
cd	candela
CD	collision detection, compact disk
CDA	call data accumulator
CDF	combined distribution frame cumulative distribution function
CDMA	code-division multiple access
CDO	community dial office
CDPD	cellular digital packet data
CDPSK	coherent differential phase-shift keying
CDR	call detail recording
CD ROM	compact disk read-only memory
CDT	call data transmitter control data terminal
CDU	central display unit
CE	connection endpoint
C-E	communications-electronics
CEF	cable entrance facility
CEI	comparably efficient interconnection connection endpoint identifier
CELP	code-excited linear prediction
CEP	circular error probable
CEPT	Conference Europeennes des Administrations des Postes et des Telecommunications
CESID	caller’s emergency service ID
CFA	carrier facility assignment connecting facility assignment
CFE	contractor-furnished equipment
CFL	call failure
CGAP	call gapping interval
CGB	circuit group blocking acknowledgment message
CGC	congestion control
cgs	centimeter-gram-second
CGH	charging message
CHOK	choke network
ChR	channel reliability
CI	customer installation
CIAS	circuit inventory and analysis system
CIC	carrier identification code circuit identification code content indicator code
CIF	common intermediate format
CIFAX	ciphered facsimile
CIGRR	common interest group on rating and routing
CINC	commander-in-chief
ciphony	ciphered telephony
CiR	circuit reliability
CITEL	Inter-American Telecommunications Commission
CK	check bit
CKLT	circuit link test
C/kT	carrier-to-receiver noise density
CKTACT	circuit activity
CKTID	circuit identification number
CL	connectionless
CLASS	custom local area signaling service
CLC	Carriers Liaison Committee
CLEI	common language equipment identification
CLNS	connectionless network service
CLP	cell loss priority (bit)
cm	centimeter
CMDF	combined main distributing frame combined main distribution frame
CMDS	centralized message data system
CMI	coded mark inversion
CMIP	Common Management Information Protocol
CMIS	common management information service
CMOS	complementary metal oxide substrate
CMR	call modification request message
CMRR	common-mode rejection ratio
CMRS	Commercial Mobile Radio Service
CMS	call management system
CNC	concentrator
CNCC	customer network control center
CNI	calling number identification
CNP	connection-not-possible signal
CNR	carrier-to-noise ratio combat-net radio
CNS	complementary network service connection-not-successful signal
C.O.	central office connection oriented
COAM	customer owned and maintained equipment
coax	coaxial cable
COBOL	common business oriented language
codec	coder-decoder
COG	centralized ordering group
COMINT	communications intelligence
COMJAM	communications jamming
compandor	compressor-expander
COMPUSEC	computer security
COMSAT	Communications Satellite Corporation
COMSEC	communications security
CONEX	connectivity exchange
CONUS	Continental United States
COP	Committee of Principals
COR	Council of Representatives
COT	customer office terminal continuity message
COTS	commercial off-the-shelf
CPAS	cellular priority access services cellular priority access system
CPC	call processing control calling party category circuit provision center
CPE	customer premises equipment
cpi	characters per inch
cpm	counts per minute
CPNI	calling party number identification
cps	characters per second cycles per second [deprecated]
CPU	central processing unit communications processor unit
C/R	command/response field bit
CR	channel reliability circuit reliability connection request
CRC	cyclic redundancy check
CRITICOM	Critical Intelligence Communications
CROM	control read-only memory
CRR	customer requested routing circuit reset reception
CRT	cathode-ray tube
CRTS	cellular radio telecommunications service
c/s	cycles per second [deprecated]
CSA	Canadian Standards Association
CSC	circuit-switching center common signaling channel
CSES	consecutive severely errored seconds
CSMA	carrier sense multiple access
CSMA/CA	carrier sense multiple access with collision avoidance
CSMA/CD	carrier sense multiple access with collision detection
CST	connection setup time
CSU	channel service unit customer service unit
CTIA	Cellular Telecommunications Industry Association
CTN	cut-through operation
CTS	clear to send
CTX	Centrex ® [service] clear to transmit
CUG	closed user group
CVD	chemical vapor deposition
CVSD	continuously variable slope delta [modulation]
cw	carrier wave continuous wave
CX	composite signaling
cxr	carrier
D*	specific detectivity
d	deci (101)
DA	directory directory assistance
D()	dispersion coefficient
da	deka (10)
D-A	digital-to-analog digital-to-analog converter
D/L	downlink
DACS	digital access and cross-connect system
DAI	dial address incoming
DAO	dial address outgoing
DAMA	demand assignment multiple access
D-AMPS	digital advanced mobile phone system
DARPA	Defense Advanced Research Projects Agency [formerly ARPA]
dB	decibel
dBa	decibels adjusted
dBa(F1A)	noise power measured by a set with F1A-line weighting
dBa(HA1)	noise power measured by a set with HA1-receiver weighting
dBa0	noise power measured at zero transmission level point
DBAS	database administration system
dBc	dB relative to carrier power
dBm	dB referred to 1 milliwatt
dBm(psoph)	noise power in dBm measured by a set with psophometric weighting
DBMS	database management system
dBmV	dB referred to 1 millivolt across 75 ohms
dBm0	noise power in dBm referred to or measured at 0TLP
dBm0p	noise power in dBm0 measured by a psophometric or noise measuring set having psophometric weighting
dBr	power difference in dB between any point and a reference point
dBrn	dB above reference noise
dBrnC	noise power in dBrn measured by a set with C-message weighting
dBrnC0	noise power in dBrnC referred to or measured at 0TLP
dBrn(f1-f2)	flat noise power in dBrn
dBrn(144-line)	noise power in dBrn measured by a set with 144-line weighting
DBSN	direct broadcast satellite network
dBv	dB relative to 1 V (volt) peak-to-peak
dBW	dB referred to 1 W (watt)
dBx	dB above reference coupling
dc	direct current
DC	disconnect code
DCA	Defense Communications Agency (now DISA)
DCE	data circuit-terminating equipment digital channel equipment
DCF	data communication function
DCL	direct communications link
DCM	digital carrier module
DCN	data communications network
DCP	data collection processor duplex central processor
DCPSK	differentially coherent phase-shift keying
DCS	Defense Communications System
DCT	digital carrier trunk
DCTN	Defense Commercial Telecommunications Network
DCWV	direct-current working volts
DDD	direct distance dialing
DDN	Defense Data Network
DDS	digital data service digital data system
DEL	delete character
demarc	demarcation point
demux	demultiplex demultiplexing
dequeue	double-ended queue
DES	Data Encryption Standard
detem	detector/emitter
DEW	Distant Early Warning (Line)
DFI	digital facility interface
DFSK	double-frequency shift keying
DIA	Defense Intelligence Agency
DIC	digital interface controller
DID	direct inward dialing
DIF	digital interface frame
DIG	digital integrity group
DIN	Deutsches Institut für Normung
DIP	dual in-line package
DIS	Draft International Standard
DISA	Defense Information Systems Agency {formerly DCA}
DISC	disconnect disconnect command
DISN	Defense Information System Network
DISNET	Defense Integrated Secure Network
DIT	directory information tree
DIU	digital interface unit
DLA	Defense Logistic Agency
DLC	digital loop carrier Data Link control (layer)
DLCI	data link connection identifier
DLY DL	delay dial
DLE	data link escape character
DLP	Data Link protocol
DL TU	digital line / trunk unit
DM	degraded minute delta modulation disconnect(ed) mode
DMA	Defense Mapping Agency direct memory access
DME	distance measuring equipment
DMS	Defense Message System
DNA	Defense Nuclear Agency
DNHR	dynamic nonhierarchical routing
DNI	destination network identification
DNIC	data network identification code
DNPA	data numbering plan area
DNS	Domain Name System
DO	design objective
DoC	Department of Commerce
DOC	dynamic overload control
DOD	Department of Defense direct outward dialing
DODD	Department of Defense Directive
DODISS	Department of Defense Index of Specifications and Standards
DOD-STD	Department of Defense Standard
DOJ	Department of Justice
DOS	Department of State
DOT	Department of Transportation
DOV	data over voice
DP	demarcation point dial pulse
DPCM	differential pulse-code modulation
DPSK	differential phase-shift keying
DQDB	distributed-queue dual-bus [network]
DQPSK	differential quadrature phase-shift keying
DR	data receive
DRAM	dynamic random access memory
DRS	delayed release signal
DRSI	destination station routing indicator
DS	data speed digital signal direct support
DS0	digital signal 0
DS1	digital signal 1
DS1C	digital signal 1C
DS2	digital signal 2
DS3	digital signal 3
DS4	digital signal 4
DSA	dial service assistance
DSAM	double-sided amplitude modulation
DSB	double-sideband [transmission] Defense Science Board
DSB-RC	double-sideband reduced carrier transmission
DSB-SC	double-sideband suppressed-carrier transmission
DSC	digital selective calling
DSCS	Defense Satellite Communications System
DSDC	direct services dialing capability
DSE	data switching exchange
DSI	digital speech interpolation
DSL	digital subscriber line
DSN	Defense Switched Network
DSn	digital signal, level n
DSP	digital signal processing
DSR	data signaling rate
DSS	data station selector direct station selection
DSSCS	Defense Special Service Communications System
DS-SMF	dispersion-shifted single-mode fiber
DSSR	digital short range radio
DSSS	direct sequence spread spectrum
DSTE	data subscriber terminal equipment
DSU	data service unit
DSX-n	digital signal cross connect, level n
DTE	data terminal equipment digital terminating equipment
DTG	date time group
DTMF	dual-tone multifrequency [signaling]
DTN	data transmission network
DTO	dial tone office
DTRS	digital trunked radio system
DTS	Diplomatic Telecommunications Service
DTU	data transfer unit digital transmission unit digroup terminal unit direct to user
DU	data unit
DUP	data user part
DUV	data under voice
DVL	direct voice link
DWDM	dense-wavelength division multiplexing
DXE	[See DCE] data circuit-terminating equipment [See DCE] data circuit terminal equipment
DX signaling	direct current signaling duplex signaling
E	exa (1018)
E911	enhanced 911 (emergency service)
EA	equal access expedited data acknowledgment message extended address field bit
EAS	extended area service
EBCDIC	extended binary coded decimal interchange code
Eb/N0	signal energy per bit per hertz of thermal noise
EBO	embedded base organization
EBS	Emergency Broadcast System
EBX	electronic branch exchange
EC	Earth coverage Earth curvature exchange carrier
ECA	emergency changeover acknowledgement signal
ECC	electronically controlled coupling enhance call completion
ECCKT	exchange company cirtuit ID
ECCM	electronic counter-countermeasures
ECM	electronic countermeasures emergency changeover message
ECO	emergency changeover order signal
ECPT	electronic coin public telephone
ECSA	Exchange Carrier Standards Association [now ATIS]
ECT	exchange carrier tandem
ED	expedited data
EDA	electronic directory assistance
EDC	error detection and correction
EDI	electronic data interchange
EDP	electronic data processing
EDTV	extended-definition television
EE	equipment engineering electrical engineering
EEI	equipment-to-equipment interface
EF	extended frame errored frame
EHF	extremely high frequency
EIA	Electronic Industries Association
eirp	effective isotropically radiated power equivalent isotropically radiated power
800DB	800 Data Base
EIS	Emergency Information System
EIT	encoded information type
el	elevation
ELECTRO-OPTINT	electro-optical intelligence
ELF	extremely low frequency
ELINT	electronics intelligence electromagnetic intelligence
ELSEC	electronics security
ELT	emergency locator transmitter
e-mail, E-mail, email	electronic mail
EMC	electromagnetic compatibility
EMCON	emission control
EMD	equilibrium mode distribution
EME	electromagnetic environment
emf	electromotive force
EMI	electromagnetic interference electromagnetic interference control
EMI/EMC	electromagnetic interference and compatibility
EML	expected measurement loss
EMP	electromagnetic pulse
EMR	electromagnetic radiation
EMR hazards	electromagnetic radiation hazards
e.m.r.p.	effective monopole radiated power equivalent monopole radiated power
EMS	electronic message system
EMSEC	emanations security
emu	electromagnetic unit
EMV	electromagnetic vulnerability
EMW	electromagnetic warfare electromagnetic wave
ENQ	enquiry character
EO	end office
E.O.	Executive Order
EOA&M	engineering, operations, administration, and maintenance
EOC	embedded operations channel
EOD	end of data
EOF	end of file
EOL	end of line
EOM	end of message
EOP	end of program end output
EOS	end-of-selection character
EOT	end-of-transmission character end of tape
EOW	engineering orderwire
EPL	electronic switching system programming language
EPROM	erasable programmable read-only memory
EPSCS	enhanced private switched communications system
ERL	echo return loss
ER link	emergency response link
ERP, e.r.p.	effective radiated power
ERR	protocol data unit error
ES	end system errored second expert system
ESC	escape character enhanced satellite capability
ESF	extended superframe
ESM	electronic warfare support measures
ESMR	enhanced specialized mobile radio
ESP	enhanced service provider
ESS	electronic switching system
ET	exchange termination
ETB	end-of-transmission-block character
ETGC	Exchange Telephone Group Committee
ETS	electronic tandem switching electronic translator system
ETSI	European Telecommunications Standards Institute
ETX	end-of-text character
EU	end user
EW	electronic warfare
EXCSA	Exchange Carriers Standards Association facility accepted message
f	femto (10-15)
f	frequency
F	farads (capacitance)
FAA	Federal Aviation Administration
FACS	facilities assignment and control system
FADU	file access data unit
FAQ file	Frequently Asked Questions file
FAX	facsimile
FC	functional component facility code
FCAP	facility capability facility capacity
FCC	Federal Communications Commission
FCM	flow control message(s)
FCS	frame check sequence
FDDI	fiber distributed data interface
FDDI-2	fiber distributed data interface-2
FDHM	full duration at half maximum
FDM	frequency-division multiplex(ing)
FDMA	frequency-division multiple access
FDT	frame due time
FDX	full duplex
FEBE	far end block error
FEC	forward error correction
FECC	Federal Emergency Communications Coordinators
FED-STD	Federal Standard
FEMA	Federal Emergency Management Agency
FEP	front-end processor
FEPS	facility and equipment planning system
FET	field effect transistor
FERF	far-end receive failure
FIB	forward indicator bit
FIC	facility interface code
FID	field identifier
FIFO	first-in, first-out
FIP	facility interface processor Federal Information Processing
FIPS	Federal Information Processing Standards
FIR	finite impulse response
FIRMR	Federal Information Resources Management Regulations
FISINT	foreign instrumentation signals intelligence
FISU	fill-in signal unit
5ESS	#5 Electronic Switching System
flops	floating-point operations per second style="mso-spacerun: yes">
FLMPTS	Future Public Land Mobile Telecommunication Systems
FLTSATCOM	Fleet Satellite Communications
FM	frequency modulation
FO	fiber optics
FOC	final operational capability full operational capability fiber optics communications
FOCC	Fiber Optics Coordinating Committee
FOT	forward-transfer message frequency of optimum traffic frequency of optimum transmission
FPDU	frame relaying protocol data unit
FPGA	field programmable gate array
FPIS	forward propagation ionospheric scatter
ft/min	feet per minute
fps	foot-pound-second
FPS	frames per second focus projection and scanning
FRJ	facility reject message
FRP	Federal Response Plan
FSDPSK	filtered symmetric differential phase-shift keying
FSDU	frame relaying service data unit
FSK	frequency-shift keying
FSN	forward sequence number
FSNR	forward sequence number received
FSNX	forward sequence number expected
FSS	Fixed Satellite Service fully separate subsidiary
FT	fiber optic T-carrier
FTAM	file transfer, access, and management
FTF	Federal Telecommunications Fund
FTR	Federal Telecommunications Recommendation
ft/s	feet per second
FTS	Federal Telecommunications System Federal Telecommunications Service
FTS2000	Federal Telecommunications System 2000
FTSC	Federal Telecommunications Standards Committee
FTSP	Federal Telecommunication Standards Program
FTP	file transfer protocol
FWHM	full width at half maximum
FX	fixed service foreign exchange foreign exchange service
FX OPER	foreign exchange trunk operation
g	profile parameter
G	giga (109)
GAN	global area network
GAS	special autonomous group
GBH	group busy hour
GCT	Greenwich Civil Time
GDF	group distribution frame
GEO	Geostationary Earth orbit Geosynchronous Earth orbit
GETS	Government Emergency Telecommunications Service
GFE	Government-furnished equipment
GGCL	government-to-government communications link
GHz	gigahertz
GII	Global Information Infrastructure
GMT	Greenwich Mean Time
GND	ground
GOS	grade of service
GOSIP	Government Open Systems Interconnection Profile
GOTS	government (-developed) off-the-shelf
GRP MOD	group modulation
GRS	reset circuit group message
GSA	General Services Administration
GSM	global system for mobile communications
GSTN	general switched telephone network
G/T	antenna gain-to-noise-temperature
GTP	Government Telecommunications Program
GTS	Government Telecommunications System
GUI	graphical user interface
h	hecto (102) Henry (inductance) Planck's constant
HALO	high-altitude, long operation
HAPS	high-altitude platform station
HBA	hardware group blocking acknowledgment signal
HBUR	hardware blocking/unblocking reception
HBUS	hardware blocking/unblocking sending
HCS	hard clad silica [fiber]
HCSDS	high-capacity satellite digital service
HCTDS	high-capacity terrestrial digital service
HDLC	high-level data link control
HDTV	high-definition television
HDX	half-duplex [operation]
HE11mode	the fundamental hybrid mode [of an optical fiber]
HEMP	high-altitude electromagnetic pulse
HEO	highly elliptical Earth orbit
HERF	hazards of electromagnetic radiation to fuel
HERO	hazards of electromagnetic radiation to ordnance
HERP	hazards of electromagnetic radiation to personnel
HF	high frequency human factors
HFDF	high-frequency distribution frame
HGA	hardware carrier group alarm
HGB	hardware group blocking signal
HGU	hardware group unblocking signal
HIPERLAN	high-performance radio local area network
HLL	high-level language
HML	hunting multiline group number
HPC	high probability of completion
HPF	hunting preferential list
HSD	high-speed data
HSSDS	high-speed switched digital service
HU	high usage
HV	high voltage
Hz	hertz
I	current (amperes) information
IA	International Alphabet [CCITT]
IAC	initial alignment control
IAM	initial address message
IAPP	inter-access point protocol
I&C	installation and checkout
IBOC	in band, on-channel
IC	integrated circuit interexchange carrier (also “IXC”)
ICAN	individual circuit analysis
ICC	incoming trunk circuit, Interstate Commerce Commission
ICCF	Industry Carriers Compatibility Forum
ICI	incoming call identification
ICIC	Interexchange Carrier Industry Committee
ICN	international closed user group number
ICNI	integrated communications, navigation, and identification
ICSC	Interexchange Customer Service Center
ICT	interexchange carrier tandem
ICW	interrupted continuous wave
ID	identification identifier identity
IDDD	International Direct Distance Dialing
IDF	intermediate distribution frame intermediate distributing frame
IDL	interface definition language
IDN	integrated digital network
IDTV	improved-definition television
IEC	International Electrotechnical Commission
IEEE	Institute of Electrical and Electronics Engineers
IES	Industry Executive Subcommittee
IF	intermediate frequency
I/F	interface
IF1…IF6	interface 1…interface 6
IFF	identification, friend or foe
IFIP	International Federation for Information Processing
IFRB	International Frequency Registration Board (now Radio Regulations Board )
IFRPS	Intercity Facility Relief Planning System
IFS	ionospheric forward scatter
IFx	interface configuration x
IILC	Information Industry Liaison Committee
IIR	infinite impulse response
IITF	Information Infrastructure Task Force
ILD	injection laser diode
ILS	instrument landing system
IM	intensity modulation intermodulation interface module
IMA	individual mobilization augmentee
I&M	installation and maintenance
IMD	intermodulation distortion
IMP	interface message processor
IN	intelligent network
IN/1, IN/1+, IN/2	intelligent network concepts  [versions 1, 1+, 2]
INC	Industry Numbering Committee international exchange carrier international carrier
INF	information message
INFOSEC	information systems security
INR	information request message
INS	inertial navigation system
INTELSAT	International Telecommunications Satellite Consortium
INWATS	Inward Wide-Area Telephone Service
I/O	input/output [device]
IOC	integrated optical circuit input-output controller
IOP	input/output processor
IP	Internet protocol intelligent peripheral interpersonal
IPA	intermediate power amplifier
IPC	information processing center
IPM	impulses per minute interference prediction model interpersonal message interruptions per minute
IPMS	interpersonal messaging system
IPN	interpersonal notification
IPRC	Intellectual Property Rights Committee
IPTF	Infrastructure Protection Task Force
in/s	inches per second
ips	interruptions per second
IPX	Internet Packet Exchange
IQF	intrinsic quality factor
IR	infrared
IRAC	Interdepartment Radio Advisory Committee
IRC	international record carrier Interagency Radio Committee
IS	international standard interim standard
ISB	independent-sideband [transmission]
ISDN	Integrated Services Digital Network
ISL	intersatellite link
ISM	industrial, scientific, and medical (applications)
ISO	International Organization for Standardization
ISP	Internet service provider
ISSI	inter-RF subsystem interface
ISUP	Integrated Services Digital Network user part integrated services user part
IT	integrated test inactivity test information technology
ITA	International Telegraph Alphabet
ITA-5	International Telegraph Alphabet Number 5
ITC	International Teletraffic Congress independent telephone company
ITM	installation, testing, and maintenance
ITS	intelligent transportation system Institute for Telecommunication Sciences
ITSO	International Telecommunications Satellite Organization
ITU	International Telecommunication Union
I2	Next Generation Internet  (also abbreviated “NGI”)
IVDT	integrated voice data terminal
IXC	interexchange carrier
JANAP	Joint Army-Navy-Air Force Publication(s)
JCS	Joint Chiefs of Staff
JMX	jumbo group multiplex
jpeg	Joint Photographic Experts Group (file format)
JS	jack status
JSC	Joint Steering Committee [now JTSSG] Joint Spectrum Center
JTC	Joint Technical Committee
JTC3A	Joint Tactical Command, Control and Communications Agency
JTIDS	Joint Tactical Information Distribution System
JTRB	Joint Telecommunications Resources Board
JTRS	Joint Tactical Radio System
JTSCC	Joint Telecommunications Standards Coordinating Committee
JTSSG	Joint Telecommunications Standards Steering Group [formerly JSC]
k	kilo (103) Boltzmann's constant
K	coefficient of absorption kelvin
kb (or “Kbit”)	1000 bits (kilobit)
kb/s, or kbps	kilobits per second
KDC	key distribution center
KDR	keyboard data recorder
KDT	keyboard display terminal
kg	kilogram
kg•m•s	kilogram-meter-second
kHz	kilohertz  (1000 Hz)
km	kilometer
k, k	kilohm
KP	keypulse
KSR	keyboard send/receive device
kT	noise power density
KTS	key telephone system
KTU	key telephone unit
	wavelength
CO	cutoff wavelength
L1	level 1, Layer 1 (physical/electrical interface)
L2	level 2, Layer 2 (signaling link functions)
L3	level 3, Layer 3 (signaling network functions)
L4	level 4 (ISDN user part)
LAC	loop assignment center
LADT	local area data transport
LAMA	local automatic message accounting
LAN	local area network
LAP-B	Data Link Layer protocol [CCITT Recommendation X.25 (1989)] local access protocol, balanced
LAP-D	link access procedure D link access protocol – D channel
laser	light amplification by stimulated emission of radiation
LASINT	laser intelligence
LATA	local access and transport area
LBO	line buildout
LBS	load balance system
LC	limited capability
LCD	liquid crystal display
LCIE	lightguide cable interconnection equipment
LCN	local communication network
LD	long distance
LDM	limited distance modem
LEC	local exchange carrier local exchange companies
LED	light-emitting diode
LEGACT	leg activity
LEO	low Earth orbit
LERG	local exchange routing guide
LF	low frequency line finder
LFB	look-ahead-for-busy [information]
LIDB	line information data base
LIFO	last-in, first-out
LLC	logical link control [sublayer]
LLN	line link network
LLSC	link set control
l/m	lines per minute
LMCS	local multipoint communications system
LMDS	local multipoint distribution system
LMF	language media format
LMMS	local message metering system
LMR	land mobile radio
LNA	launch numerical aperture
LOCAP	low capacitance
LOF	lowest operating frequency
loran	long-range aid to navigation system long-range radio aid to navigation system
LOS	line of sight loss of signal
LP	linearly polarized [mode] log-periodic [array]
LPA	linear power amplifier, loop-back acknowledgment message
LPC	linear predictive coding
LPD	low probability of detection
LPI	low probability of interception
lpi	lines per inch
lpm	lines per minute
LP01	the fundamental mode (of an optical fiber)
LQA	link quality analysis
LRAP	long route analysis program
LRC	longitudinal redundancy check
LRS	line repeater station
LS	line side
LSAC	signaling link activity control
LSB	lower sideband, least significant bit
LSC	link state control
LSDA	signaling data link allocation
LSI	large scale integrated [circuit] line status indication
LSLA	signaling link activation
LSLD	signaling link deactivation
LSLR	signaling link restoration
LSO	local serving office
LSS	local switching system
LSSU	link status signal unit
LSTA	signaling terminal allocation
LT	the physical termination of the DSL at the network end
LTC	line traffic coordinator
LTE	line terminating equipment
LTF	lightwave terminating frame
LUA	link uninhibit acknowledgment
LUN	link uninhibit message
LUF	lowest usable high frequency
LULT	line-unit-line termination
LUNT	line-unit-network termination
LV	low voltage
m	meter milli (10-3)
M	mega (106) maintenance modifier function bit
mA	milliampere
MAC	medium access control [sublayer]
MACOM	major command
MAN	metropolitan area network
MAP	manufacturers' automation protocol
MAS	mass announcement system
maser	microwave amplification by the stimulated emission of radiation
M[]	material dispersion coefficient
MAU	medium access unit
MB	message blocking
Mb/s also Mbps	megabits per second
MCC	maintenance control circuit master control center
MCDN	microcellular data network
MCEB	Military Communications-Electronics Board
MCM	multicarrier modulation
MCS	Master Control System
MCW	modulated continuous wave
MCXO	microcomputer compensated crystal oscillator
MD	management domain mediation device
MDF	main distribution frame
MDS	message distribution system, multipoint distribution system
MDT	mean downtime
MECAB	multiple exchange carrier access billing
MEECN	Minimum Essential Emergency Communications Network
MEO	medium Earth orbit
MERCAST	merchant-ship broadcast system
MESSPROC	message processing
MET	multibutton electronic telephone
MF	medium frequency multifrequency [signaling] mediation function
MFD	mode field diameter
MFJ	Modification of Final Judgment
MFSK	multiple frequency-shift keying
MFT	metallic facility terminal
MGB	maintenance group blocking signal
MGT	mastergroup translator
MGU	maintenance group unblocking signal
MHF	medium high frequency
MHS	message handling service message handling system
MHz	megahertz
mi	mile
MI	machine interface
MIC	machine interface code medium interface connector mutual interface chart
MII	mobile information infrastructure
MILNET	military network
MIL-STD	Military Standard
min	minute
MIP	medium interface point
MIPS, mips	million instructions per second
MIS	management information system
MKS	meter-kilogram-second
MLPP	multilevel precedence and preemption
MLH	multiline hunt
MLM	multilongitudinal mode
MLPP	multilevel precedence and preemption
MLT	mechanical loop testing
MMDS	multichannel multipoint distribution system
MMGT	multimastergroup translator
MMITS	modular, multifunctional information transfer system(s) [See SDR Forum]
MMUC	minimum monthly usage charge
MMW	millimeter wave
MMX	mastergroup multiplex
MN	mobile node
modem	modulator-demodulator
modified AMI code	modified alternate mark inversion code
mol	mole
MOTIS	message-oriented text interchange system
MOU	minutes of use
mpeg	Motion Picture Experts Group
MPN	mode-partition noise
ms	millisecond (10-3second) message store
MS	mobile station
MSA	metropolitan statistical area
MSB	most significant bit
MSC	media stimulated calling mobile switching center mobile services switching center
MSK	minimum-shift keying
MSS	Mobile Satellite Service mobile satellite system
MSTM	maximum skew one-tenth maximum
MSU	message signal unit
MTA	message transfer agent
MTBF	mean time between failures
MTBM	mean time between maintenance
MTBO	mean time between outages
MTBPM	mean time between preventive maintenance
MTF	modulation transfer function
MTIE	maximum time interval error
MTP	message transfer part
MTS	message telecommunications service message transfer system
MTSE	message transfer service element
MTSO	mobile telephone switching office mobile telecommunications switching office
MTSR	mean time to service restoral
MTTR	mean time to repair
	micro (10-6)
s	microsecond
MUA	maintenance group unblocking acknowledgment signal
MUF	maximum usable frequency
muldem	multiplexer/demultiplexer
MUX	multiplex multiplexer
MUXing	multiplexing
mv	millivolt
mw	microwave
mW	milliwatt
MWI	message waiting indicator
MWV	maximum working voltage
n	nano (10-9) refractive index
N.	numeric characters, 0-9
N0	sea level refractivity spectral noise density
NA	numerical aperture network aspects
NAC	network administration center
NACSEM	National Communications Security Emanation Memorandum
NACSIM	National Communications Security Information Memorandum
NAK (also “NACK)”	negative-acknowledge character
NANA	North American Numbering Administration
NANP	North American Numbering Plan
NANPA	North American Numbering Plan Administration
NASA	National Aeronautics and Space Administration
NASNA	National Association of State 9-1-1 Administrators
NASP	network application service part
NATA	North American Telecommunications Association
NA-TDMA	North American ― Time Division Multiple Access
NATO	North Atlantic Treaty Organization
NAVSTAR-GPS	Navigational Satellite Timing and Ranging ─ Global Positioning System
NBEC	non-Bell exchange company
NBFM	narrowband frequency modulation
NBH	network busy hour
NBRVF	narrowband radio voice frequency
NBS	National Bureau of Standards [now NIST]
NBSV	narrowband secure voice
NC	network channel network connection no current
NCC	National Coordinating Center for Telecommunications
NCI	network channel interface (code)
NCP	network control point network control processor
NCS	National Communications System net control station
NCSC	National Communications Security Committee
NCTE	network channel terminating equipment
NDCC	network data collection center
NDCS	network data control system
NDER	National Defense Executive Reserve
NDIS	network driver interface specification
NEACP	National Emergency Airborne Command Post
NEC	National Electric Code ®
NECA	National Exchange Carrier Association
NEF	network element function
NEP	noise equivalent power
NES	noise equivalent signal
NETS	Nationwide Emergency Telecommunications Service
NF	noise figure
NFS	Network File System
NGI	Next Generation Internet  [also abbreviated  I2]
NGSO	non-Geostationary orbit
NHN	nonhunting number
NI	network interface number identification
NIC	network interface card
NICS	NATO Integrated Communications System
NID	network interface device network information database
NII	National Information Infrastructure
NIOD	network inward/outward dialing
NIST	National Institute of Standards and Technology [formerly NBS]
NIU	network interface unit
NLP	National Level Program
nm	nanometer
NMC	network management center
nmi	nautical mile
NNI	network node interface
NOC	network operations center
NOCS	network operations center system
NOD	network outward dialing
NOF	Network Operations Forum
NORGEN	network operations report generator
NOTIS	network operations trouble information system
NOW	number of WATS
Np	neper
NP	network pause
NPA	numbering plan area
NPCI	network protocol control information
NPN	network provided number
NPNB	no primary / no backup
NPR	noise power ratio
N(r)	receive sequence number
NRI	net radio interface
NRM	network resource manager
NRRC	Nuclear Risk Reduction Center
NRZ	non-return-to-zero
NRZI	non-return-to-zero inverted
NRZ-M	non-return-to-zero mark
NRZ-S	non-return-to-zero space
NRZ1	non-return-to-zero, change on ones
NRZ-1	non-return-to-zero mark
ns	nanosecond
N(s)	send sequence number
NSA	National Security Agency
NSC	National Security Council network service center
NS/EP telecommunications	National Security / Emergency Preparedness telecommunications
NSP	national signaling point
NSPMP	network switching performance measurement plan
NSTAC	National Security Telecommunications Advisory Committee
NTCN	National Telecommunications Coordinating Network
NTMS	National Telecommunications Management Structure
NT	network termination physical termination of the DSL at the user end
NT1	network termination 1
NT2	network termination 2
NTI	network terminating interface
NTIA	National Telecommunications and Information Administration
NTN	network terminal number
NTSC	National Television Standards Committee National Television Standards Committee [standard]
NUL	null character
NVIS	near-vertical-incidence skywave
NXX	3-digit code identifying a central office exchange
O	operations
	ohm
OAM	operations, administration and maintenance
OAMP	operations, administration, maintenance, and provisioning
O&M	operations and maintenance
OC	operating company operations center optical carrier
OC-1	optical carrier Level 1
OC-N	optical carrier Level N
OCC	other common carrier
OCE	other common carrier channel equipment
OCIS	online customer information system
OCM	office carrier module
OCR	optical character reader optical character recognition
OCS	originating call screening
OCU	office channel unit orderwire control unit
OCVCXO	oven controlled-voltage controlled crystal oscillator
OCXO	oven controlled crystal oscillator
OD	optical density outpulsed digits outside diameter
OEC	other exchange company other exchange coordinator
OFC	optical fiber, conductive
OFCP	optical fiber, conductive, plenum
OFCR	optical fiber, conductive, riser
OFDM	orthogonal frequency division multiplexing
OFN	optical fiber, nonconductive
OFNP	optical fiber, nonconductive, plenum
OFNR	optical fiber, nonconductive, riser
OGC	outgoing trunk circuit
OI	optical interface
OMAP	operations, management, and administration part
OMB	Office of Management and Budget
OMEG	Operations and Maintenance Experts Group
ONA	open network architecture
ONI	operator umber identification
OPC	originating point code
OPDU	operation protocol data unit
opm	operations per minute
OPMODEL	operations model
OPS	off-premises station operator services
OPSEC	operations security
OPX	off-premises extension
O/R	originator/recipient
OR	off-route service off-route aeronautical mobile service
ORL	optical return loss
OS	operations system
OSC	oscillator
OSF	operations system function
OSHA	Occupational Safety and Health Administration
OSI	open switch interval open switching interval Open Systems Interconnection
OSI-RM	Open Systems Interconnection―Reference Model
OSP	operator service provider
OSRI	originating stations routing indicator
OSS	operator service system operations support system
OSSN	originating stations serial number
OTAM	over-the-air management of automated HF network nodes
OTAR	over-the-air rekeying
OTC	operating telephone company
OTDR	optical time domain reflectometer optical time domain reflectometry
OUTWATS	Outward Wide Area Telecommunications Service
OW	orderwire [circuit]
p	pico (10-12)
P	peta (1015) provisioning
PABX	private automatic branch exchange
PACA-E	enhanced priority access and channel assignment
PACS	personal access communications system
PAD	packet assembler/disassembler
PAL	phase alternation by line
PAL-M	phase alternation by line―modified
PAM	pulse-amplitude modulation pass along message
PAMA	pulse-address multiple access
p/a r	peak-to-average ratio
PAR	performance analysis and review
PARAMP	parametric amplifier
par meter	peak-to-average ratio meter
PAX	private automatic exchange
PBER	pseudo-bit-error-ratio
PBX	private branch exchange
PC	carrier power (of a radio transmitter) personal computer point code
PCAC	point code allowed control
PCB	power circuit breaker printed circuit board
PCI	protocol control information personal communications interface
PCM	pulse-code modulation process control module
PCMCIA	Personal Computer Memory Card Industry Association
PCME	packetized  circuit multiplication equipment
PCN	Personal Communications Network
PCO	peg count and overflow
PCPC	point code prohibited control
PCR	preventive cyclic retransmission
PCS	Personal Communications Services plastic-clad silica [fiber]
PCSR	parallel channels signaling rate
PD	photodetector protocol discriminator
PDC	personal digital cellular
PDM	pulse delta modulation pulse-duration modulation
PDN	public data network
PDS	protected distribution system program data source
PDT	programmable data terminal
PDU	protocol data unit
PE	emergency proving period peripheral equipment phase-encoded [recording]
PEP	peak envelope power (of a radio transmitter)
pF	picofarad
PF	power factor
PFM	pulse-frequency modulation
PHS	personal handy phone system
PI	protection interval
PIC	plastic insulated cable presubscribed interexchange carrier
PIN	personal identification number(s)
ping	packet Internet groper
PIV	peak inverse voltage
PLA	programmable logic array
PLL	phase-locked loop
PLN	private line network
PL/I	programming language 1
PLR	pulse link repeater
PLS	physical signaling sublayer
pm	phase modulation
PM	mean power preventive maintenance protocol machine pulse modulation
PMB	pilot-make-busy [circuit]
PMO	program management office
PNNI	private network-to-network interface (signaling)
POC	point of contact processor outage control
POI	point of interface
POP	point of presence
POSIX	Portable Operating System Interface for Computer Environments
POT	point of termination
POTS	plain old telephone service
PP	polarization-preserving [optical fiber]
P-P	peak-to-peak [value]
P/P	point-to-point
PPDU	presentation protocol data unit
PPM	pulse-position modulation
pps	pulses per second
PR	pulse rate
PREMIS	premises information system
PRF	pulse-repetition frequency
PRESUB	presubscription
PRI	primary rate interface
PRILOC	primary location
PRM	pulse-rate modulation
PRMD	private management domain
PROM	programmable read-only memory
PROVINT	provisioning interval
PRR	pulse repetition rate
PRSL	primary area switch locator
PS	permanent signal
PSAP	public service answering point presentation service access point
PSDN	public switched digital network
PSDS	public switch digital services
psi	pounds [force] per square inch
PSK	phase-shift keying
PSN	public switched network
PSPDN	public switched packet data network
p-static	precipitation static
PSTN	public switched telephone network
PSWAC	Public Safety Wireless Advisory Committee
PSWN	public safety wireless network
PTE	path terminating equipment
PTF	patch and test facility
PTM	pulse-time modulation
PTT	postal, telephone, and telegraph push-to-talk [operation]
PTTC	paper tape transmission code
PTTI	precise time and time interval
PU	power unit
PUC	public utility commission public utilities commission
PV	parameter value
PVC	permanent virtual circuit polyvinyl chloride [insulation]
pW	picowatt
PWM	pulse-width modulation [deprecated]
pWp	picowatt, psophometrically weighted
pWp0	picowatts, relative to a 0TLP
PWT	Personal Wireless Telecommunications
pX	peak envelope power (in dB)
PX	peak envelope power peak envelope power (in watts)
pY	mean power [in dB]
PY	mean power [in watts]
pZ	carrier power [in dB]
PZ	carrier power [in watts]
Q	speech-to-speech-correlated-noise ratio
QA	quality assurance
QAM	quadrature amplitude modulation
QC	quality control
QCIF	quarter common intermediate format
QMR	qualitative material requirement
QOS	quality of service
QPSK	quadrature phase-shift keying
QRC	quick reaction capability
QRS	quasi-random signal
QRY	query
QSS	quality surveillance system
QTY	quantity
QSTAG	Quadripartite Standardization Agreement
R	resistance (ohms) ring ring conductor route service
R1	ring ring conductor
racon	radar beacon
rad	radian radiation absorbed dose
radar	radio detection and ranging
RADHAZ	electromagnetic radiation hazards
RADINT	radar intelligence
RAM	random access memory reliability, availability, and maintainability
R&D	research and development
RATT	radio teletypewriter system
RBOC	Regional Bell Operating Company
RbXO	rubidium-crystal oscillator
RC	reception control reflection coefficient resource controller retransmission counter
RCC	radio common carrier
RCM	reject connect modify message remote carrier module
RCVR	receiver
RDES	remote data entry system
RDS	radio digital system
RDT	radio digital terminal
RDF	radio direction-finding
RE	return error remote entry
REA	Rural Electrification Administration
REC	receiver
REJ	reject
REL	release message
REM	remote equipment module
REN	ringer equivalency number
RES	radio equipment and systems resume message
RGB	red-green-blue
rf	radio frequency range finder
RFI	radio frequency interference
RFP	request for proposal
RFQ	request for quotation
RH	relative humidity
RHR	radio horizon range
RI	routing indicator
RID	response ID
RISC	reduced instruction set chip
RJ	registered jack reference number reject
RJE	remote job entry
RL	restoral limit
RLC	release complete message
RLMS	return loss measuring set
RLSD	released message
rms	root-mean-square [deviation]
RNR	receive not ready
RO	read only receive only reorder
ROA	recognized operating agency
ROH	receiver off-hook
ROC	required operational capability
ROM	read-only memory
ROSE	remote operations service element protocol
RP	restoration priority
RPI	radio port intermediary
RPLY	reply
rpm	revolutions per minute
RPM	rate per minute
rps	revolutions per second
RPT	radio personal terminal
RQ	repeat-request
RR	receive ready repetition rate return result
RSA	rural service area
RSC	reset-circuit message
RSCM	reset confirmation message
RSM	remote switching module signaling-route-set-test message
RSL	received signal level
RSRM	reset request message
RSRT	signaling route set test control
RSS	remote switching system
rss	root-sum-square
RST	reset circuit
RT	radio termination
R/T	real time
RTA	remote trunk arrangement
RTA	transfer allowed control
RTB	retransmission buffer
RTC	restart confirmation
RTCC	transfer-controlled control
RTM	remote test module
RTPC	transfer prohibited control
RTR	restart request
RTRC	transfer-restricted control
RTS	request to send
RTTY	radio teletypewriter
RTU	remote terminal unit
RTX	request to transmit
RVA	reactive volt-ampere
RVWG	Reliability and Vulnerability Working Group
RWI	radio and wire integration
RX	receive receiver
RZ	return-to-zero [code]
s	second
S	supervisory function bit
SABME	set asynchronous balanced mode extended
SAC	service access code
SAL	service affecting limit
SAM	subsequent-address message
SAP	service access point
SAPI	service access point identifier
SAR	special access request
SARTS	switched access remote test system
SAS	switched access services
SASE	specific application service elements
SBR	subsystem backup routing
SBRC	subsystem backup routing control
SBUR	software blocking/unblocking reception
SBUS	software blocking/unblocking sending
SC	service code standard coding
SCC	specialized common carrier switched control center
SCCP	signaling connection control part
SCCS	switched control center system
SCE	service creation environment
SCEG	experts group on speech coding
SCF	service control facility
SCP	service control point
SCPC	single channel per carrier
SCR	semiconductor-controlled rectifier silicon-controlled rectifier
SCRT	service class routing
SCSR	single channel signaling rate
SCU	selector control unit
SDL	Specification and Description Language
SDLC	synchronous data link control
SDM	space-division multiplexing [deprecated]
SDN	software-defined network
SDO	standards development organization
SDR	software-defined radio
SDR Forum	Software Defined Radio Forum [formerly MMITS]
SDU	service data unit
SECAM	systeme electronique couleur avec memoire sequential couleur avec memoire
SECDEF	Secretary of Defense
SECLC	secondary location
SECLOC	secondary location
SECORD	secure voice cord board
SECTEL	secure telephone
SECTLV	secondary transmission level point
SEG	experts group on security
SEL	selector
SES	satellite earth station(s) severely errored second(s)
SETAMS	systems engineering, technical assistance, and management services
SEVAS	Secure Voice Access System
S-F	store-and-forward
SF	single-frequency [signaling] status field
SG	study group
SGDF	supergroup distribution frame
S/H	sample and hold
SHA	sidereal hour angle
SHARES	Shared Resources (SHARES) HF Radio Program
SHF	super high frequency
SI	International System of Units service indicator status indicator
SIB	status indication “B” (“busy”)
SID	sudden ionospheric disturbance
SIE	status indication “E” (“Emergency Alignment”)
SIF	signaling information field signal information field
SIGINT	signals intelligence
SIM	subscriber identity module
SINAD	signal-plus-noise-plus-distortion to noise-plus-distortion ratio
SIO	service information octet
SIT	special information tone
S()	chromatic dispersion slope
SLC	signaling link code
SLD	superluminescent diode [see superluminescent LED ]
SLI	service logic interpreter
SLM	signaling link management single longitudinal mode
SLP	service logic program
SLS	signaling link selection code
SLTA	signaling link test message acknowledgment
SLTC	signaling link test control
SLTM	signaling link test message
SMAS	switched maintenance access system
SMDF	subscriber main distribution frame subscriber main distributing frame
SMDR	station message-detail recording
SMF	single-mode fiber
SMH	signaling message handling
SMR	specialized mobile radio
SMS	service management system
SMSA	standard metropolitan statistical area
SMTP	simple mail transport protocol
SNA	shared network arrangement
SNI	signaling network interworking
SNMP	simple network management protocol
SNR	signal-to-noise ratio subsystem-normal-routing (message)
SOH	start-of-heading character
SOM	start of message
sonar	sound navigation and ranging
SONET	synchronous optical network
SOP	standard operating procedure
SOR	start of record subsystem-out-of-service-request message
SOW	statement of work
SP	signal processor signaling point
SPC	stored-program control signaling point code
SPCS	stored-program control system
SPDU	session protocol data unit
SPE	synchronous payload envelope
SPNB	some-primary / no backup
SPOT	secondary location point of termination signaling point of termination
SPRC	signaling process control
SPS	signaling protocol and switching
SPSB	some-primary / some backup
(S+N)/N	signal-plus-noise-to-noise ratio
sr	steradian
SR	service request
S/R	send and receive
SRC	service request confirmation
SRM	signaling route management
SRO	standards related organization
SRT	subsystem routing status test message
SRTC	subsystem-routing status test control
SSB	single-sideband [transmission]
SSBAM	single-sideband amplitude modulation
SSB-SC	single-sideband suppressed carrier [transmission]
SSD	second start dial
SSF	subservice field
SSN	station serial number subsystem number
SSP	service switching point service signaling point signal service point subsystem-prohibited message
SSPC	subsystem-prohibited control
SSR	side-mode suppression ratio
SS7	Signaling System No. 7
SST	subsystem-status-test message service transfer point
SSTC	subsystem status test control
SSUPS	solid-state uninterruptible power system
ST	end-of-pulsing signal start signal
STALO	stabilized local oscillator
STANAG	Standardization Agreement [NATO]
STD	subscriber trunk dialing state transition diagram
STFS	standard time and frequency signal [service] standard time and frequency service
STL	standard telegraph level studio-to-transmitter link
STM	signaling traffic management
STP	standard temperature and pressure signal transfer part signal transfer point
STS	synchronous transport signal
STS-1	synchronous transport signal level 1
STS-n	synchronous transport signal level n
STS POH	synchronous transport signal path overhead
STS PTE	synchronous transport signal path terminating equipment
STU	secure telephone unit
STX	start-of-text character
SU	signaling unit signal unit
SUB	substitute character
SUPERNET	Sjared Im;ocemsed {erspma; Radop Metwprl
SUS	suspend message
SVC	switched virtual circuit
SWR	standing wave ratio
SX	simplex signaling
SXS	step-by-step switching system step-by-step system
SYN	synchronous idle character
SYNTRAN	synchronous transmission
SYSGEN	system generation
T	tera (1012) tip tip conductor
T1	1st ANSI Telecommunications Standards Committee tip tip conductor
T1AG	T1 Advisory Group
T1A1	T1 committee on Performance and Signal Processing
T1E1	T1 committee on Interfaces, Power and Protection for Networks
T1EDH	T1 committee on Electronic Data Handling
T1M1	Internetwork Operations, Administration, Maintenance, and Provisioning (IOAM&P)
T1P1	T1 committee on Wireless/Mobile Services and Systems
T1S1	T1 committee on Services, Architectures, and Signaling
T1X1	T1 committee on Digital Hierarchy and Synchronization
TADIL	tactical data information link
TADIL-A	tactical data information link-A
TADIL-B	tactical data information link-B
TADS	teletypewriter automatic dispatch system
TADSS	Tactical Automatic Digital Switching System
TAI	International Atomic Time
TASC	telecommunications alarm surveillance and control (system)
TASI	time-assignment speech interpolation
TAT	trans-Atlantic telecommunication (cable)
TB	transmission buffer
TC	toll center technical committee transport connection
TCAP	transaction capability control part (of SS7) transaction capabilities application part
TCAS	T-carrier administration system
TCB	trusted computing base
TCBC	changeback control
TCC	telecommunications center
TCCF	Tactical Communications Control Facility
TCF	technical control facility transfer controlled
TCIC	trunk circuit identification code
TCIF	Telecommunication Industry Forum
TCL	terminal coupling loss
TCLw	weighted terminal coupling loss
TCM	time-compression multiplexing
TCOC	changeover control
TCP	transmission control protocol
TCPAP	transaction capabilities control part
TCPIP	Transmission Control Protocol/Internet Protocol
TCRC	controlled rerouting control
TCS	trusted computer system
TCSP	tandem cross section program
TCU	teletypewriter control unit
TCVXO	temperature compensated-voltage controlled crystal oscillator
TCXO	temperature controlled crystal oscillator
TD	time delay transmitter distributor
TDAS	traffic data administration program
TDD	telecommunications device for the deaf time division duplex
TDEA	Triple Data Encryption Algorithm
TDM	time-division multiplexing
TDMA	time-division multiple access time division multiplex
TDR	traffic distribution request
TE	transverse electric [mode] terminal equipment
TED	trunk encryption device
TEI	terminal endpoint identifier
TEK	traffic encryption key
TEM	transverse electric and magnetic [mode]
TEMPEST	compromising emanations
TEMS	telecommunications management system
TERM	terminal
TFA	transfer-allowed signal
TFC	transfer-controlled signal
TFLAP	T-carrier fault-locating applications program
TFMI	traffic mix information
TFP	transfer-prohibited signal
TFPC	Toll Fraud Prevention Committee
TFR	transfer-restricted (signal)
TFRC	forced rerouting control
TFS	trunk forecasting system
TFTS	Terrestrial Flight Telephone System
TGID	trunk group identification
TGM	trunk group multiplexer
TGSN	trunk group serial number
THD	total harmonic distortion
THF	tremendously high frequency
THz	terahertz
TIA	Telecommunications Industry Association
TIE	time interval error
TIFF	tag image file format
TIP	terminal interface processor
TK	response timer
TL	Transport Layer transmission level
TLAC	link availability control
TLN	trunk link network
TLP	transmission level point
TL/PVC	Transport Layer / permanent virtual circuit
TL/SVC	Transport Layer / switched virtual circuit
TLV	transmission level
TM	transverse magnetic [mode] transmission and multiplexing
TMD	trunk main distributing
TMDF	trunk main distributing frame
TMN	telecommunications management network
TMS	time-multiplexed switch
TNDS	total network data system
TNOP	total network operations plan
TP	test pad test pattern toll point
TPDU	transport protocol data unit
TPT	test progress tone
TQ	transmission quality
TQTF	Transmission Quality Task Force
TRA	traffic routing and administration
TRANSEC	transmission security
TRC	transverse redundancy check
TRCC	signaling link congestion control
TRD	timed release disconnect
TRF	tuned radio frequency
TRFTYP	traffic type
TRI	traffic routing information
TRI-TAC	tri-services tactical [equipment]
TRM	termination
TRM TYP	termination type
TRMTR also Xmtr	transmitter
TS	trunk side
TSB	Telecommunication Standardization Bureau
TSC	technical subcommittee
TSFC	signaling traffic flow control
TSI	time-slot interchange
TSK	transmission security key
TSP	Telecommunications Service Priority [system] traffic service position
TSPS	traffic service position system
TSR	telecommunications service request terminate and stay resident trunk service record testing services request
TSRC	signaling routing control
TSS	trunk servicing system
TTC	Telecommunication Technology Committee (Japanese)
TTL	transistor-transistor logic
TTTN	tandem tie trunk network
TTY	teletypewriter
TTY/TDD	telecommunications device for the deaf
TUP	telephone user part
TV	television
TW	traveling wave
TWT	traveling wave tube
TWTA	traveling wave tube amplifier
TWX®	teletypewriter exchange service
TX	transmit transmitter
TXC	transmission control
U	unnumbered
UA	unnumbered acknowledgment user agent
UAV	unmanned air vehible
UBA	unblocking-acknowledgment message
UBL	unblocking message
UCC	universal commercial code
UCD	uniform call distribution
UDP	User Datagram Protocol
UHF	ultra high frequency
UI	unit interval unnumbered information
UIM	user identity module
UIS	user-in-service
UITS	unacknowledged information transfer service
ULF	ultra low frequency
U/L	uplink
UNI	unidirectional user-network interface
UP	user part
UPN	user provided number
UPS	uninterruptible power supply
UPT	Universal Personal Telecommunications [service]
UPTAN	Universal Personal Telecommunications access number
URL	universal routing locator
USB	upper sideband universal serial bus
USBS	user signaling bearer service
USDA	U.S. Department of Agriculture
USFJ	U.S. Forces, Japan
USFK	U.S. Forces, Korea
USNO	U.S. Naval observatory
USOC	universal service order code
USR	user-to-user information message
USTA	U.S. Telephone Association  [formerly USITA]
UT	Universal Time
UTC	Coordinated Universal Time
uv	ultraviolet
UWCC	Universal Wireless Communications Consortium
V	volt normalized frequency
VA	value-added [network service] volt-ampere
Vac	volts, alternating current
VAN	value-added network
VAR	value added reseller
VARISTAR	variable resistor
vars	volt-amperes reactive
VC	vacant code virtual circuit
VCC	virtual channel connection
VCL	virtual channel link
VCO	voltage-controlled oscillator
VCXO	voltage-controlled crystal oscillator
V/D	voice/data
Vdc	volts, direct current
VDCL	virtual data link capability (protocol)
VDU	video display unit visual display unit
VER	version identification version number
VF	voice frequency
VFCT	voice frequency carrier telegraph
VFCTG	voice frequency carrier telegraph
VFDF	voice frequency distribution frame
VFO	variable-frequency oscillator
VFTG	voice-frequency telegraph
VHF	very high frequency
VITS	vertical interval test signal
VIU	voiceband interface unit
VLAN	virtual local area network
VLF	very low frequency
V/m	volts per meter
VNL	via net loss
VNLF	via net loss factor
vocoder	voice-coder
VOD	video on demand voice over data (link)
vodas	voice-operated device anti-sing
vogad	voice-operated gain-adjusting device
VoIP	voice over Internet  [protocol]
volcas	voice-operated loss control and echo/signaling suppression
vox	voice-operated relay circuit voice operated transmit
VRC	vertical redundancy check
VSAT	very small aperture terminal
VSB	vestigial sideband [transmission] vestigial sideband [modulation]
VSELP	vector sum excited linear prediction
VSM	vestigial sideband modulation
VSWR	voltage standing wave ratio
VT	virtual terminal virtual tributary
VTU	video teleconferencing unit
vu	volume unit
W	Watt
WADS	wide area data service
WAIS	Wide Area Information Server
WAN	wide area network
WAND	wireless ATM network demonstrator
WARC	World Administrative Radio Conference
WATM	wireless asynchronous transfer mode
WATS	Wide Area Telecommunications Service Wide Area Telephone Service
WAWS	Washington Area Wideband System
WMCCS	Worldwide Military Command and Control System
WDM	wavelength-division multiplexing
WG	working group
WHSR	White House Situation Room
WI	wink
WIN	wireless information network WWMCCS Intercomputer Network
WITS	Washington Integrated Telecommunications System
WLAN	wireless local area network
WLL	wireless local loop
wmATM	wireless mobile ATM
WORM	write once, read many times
wpm	words per minute
wps	words per second
WPBX	wireless PBX
WPS	Wireless Priority Service (Program)
WRU	who-are-you [character]
WS	workstation
W3C	World Wide Web Consortium
WTN	working telephone number
wv	working voltage
WVDC	working voltage direct current
WWAN	wireless wide area network
WWDSA	worldwide digital system architecture
WWMCCS	Worldwide Military Command and Control System
WWW	World Wide Web
XB	crossbar
XBT	crossbar tandem
XID	exchange identification
XMIT	transmit
XMSN	transmission
XMTD	transmitted
Xmtr  also TRMTR	transmitter
XO	crystal oscillator
XOFF	transmitter off
XON	transmitter on
XT	crosstalk
XTAL	crystal
Z	impedance Zulu time
ZBTSI	zero-byte time slot interchange
ZD	zero defects
Zo	characteristic impedance
0TLP	zero transmission level point