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Glossary of telephone terminology

AFSK   Audio Frequency Shift Keying
System in which two unrelated audio tones – commonly called mark and space – are used to represent the digital values '0' and '1' in order to send digital data over an analogue medium. AFSK is typically used with MODEMs. In telephony, it was also used for passing signalling data (such as caller ID) over a telephone line.  Wikipedia
BDI   Black Digital Interface
Digital interface at the non-secure side of a crypto telephone.
DTMF   Dual-Tone Multi-Frequency
Telecommunications signalling system, used to pass numbers over analogue telephone lines, using voice-band (dual) tones. In the US also known under the Bell Systems trademark Touch-Tone. In the UK also known as MF4. Typically used in (analogue) push-button dialling telephones.  More  Wikipedia
GSM   Global System for Mobile communication
Initially known as Groupe Spécial Mobile (French). Digital mobile communication standard developed by the European Telecommunications Standards Institue (ETSI), used in the first worldwide digital mobile networks. Also known as 2G (second generation).  More  Wikipedia
IDK   Impuls Druktoets Keuze Pulse
Dutch expression for impulse-based dialling systems.
IP   Internet Protocol
Network layer communications protocol in the Internet protocol suite, for relaying datagrams across network boundaries.  Wikipedia
ISDN   Integrated Services Digital Network
Set of communication standards for simultaneous digital transmission of voice, video, data and other network services over the digitalised circuits of the Public Switched Telephone Network (PSTN). Developed by Bell Labs between 1980 and 1988 with the intention to replace POTS, it was superceeded by faster IP-based standards soon after its introduction.  Wikipedia
Loop disconnect   Pulse dialling

MF4   Multi Frequency 4 DTMF
UK name for Dual-Tone Multi-Frequency signalling (DTMF).
MRCELP   Modified Residual Code Exited Linear Prediction
High-quality low-bitrate speech digitiser, used for encrypted voice connections over regluar analogue lines. Improved variant of MELP and MELPe, that produces better results at 9600 baud.
PABX   Private Automatic Branch Exchange
Automatically switched in-house (on-premises) telephone exchange.
PBX   Private Branch Exchange
In-house (on-premises) telephone exchange.
POTS   Plain Old Telephone System
Old analogue telephone system with copper subscriber lines. Also known as Plain Old Telephone Service.  Wikipedia
PSTN   Public Switched Telephone Network
Generic expression for a network of switched voice-grade communication links. It is often used to identify a Plain Old Telephone System (POTS), but can also be used for ISDN and IP-based networks.  Examples  Wikipedia
Pulse   Pulse dialling
Oldest system for dialling a telephone number over an analogue subscriber line on automatically switched networks. Works by interupting the line current at a rate of 10 pulses per second. Also known as Loop disconnect.  Wikipedia
SCCP   Skinny Call Control Protocol
Developed by Cisco.
SIP   Session Initiation Protocol
Digital signalling protocol for IP-based networks, commonly used with the Voice-over-IP (VoIP) communications standard.  Wikipedia
TDK   Toon Druktoets Keuze
Dutch expression for DTMF-based dialling systems.
Touch Tone   DTMF dialling
Bell Labs/AT&T Trademark for DTMF-based dialling systems (US).
UMTS   Universal Mobile Telecommunications System
Third generation (3G) mobile cellular system for networks based on the GSM standards. Developed and maintained by the 3GPP.  Wikipedia
VoIP   Voice over Internet Protocol
Digital protocol for voice communications over IP-based networks. Most VoIP network use out-of-band signalling by means of the Session Initiation Protocol (SIP).  Wikipedia
Further information
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