Telecoms
Telecommunications glossary
Fifteen terms that come up as soon as fax, lines or protocols are mentioned. A one-sentence definition, a paragraph of explanation, and the pages where the term plays a part.
Network and infrastructure
Local loop
The local loop links a subscriber to the operator's first equipment: historically a pair of copper wires from the premises to the exchange.
Analogue line
An analogue line carries sound as a continuous electrical signal whose shape directly reproduces that of the sound wave.
ISDN
ISDN is the digital telephone network of the 1980s, carrying digitised voice over the same copper pair as the analogue line.
Voice over IP
Voice over IP splits speech into data packets carried by a computer network, instead of reserving a continuous circuit from end to end.
Protocols and standards
ECM
ECM is the error correction mode of the fax protocol: it splits each page into verified blocks, resent whenever they arrive corrupted.
CSID
The CSID is the identification string a fax machine announces to its counterpart during negotiation, usually its own number.
Group 3
Group 3 is the class of fax machines standardised in 1980, transmitting a page in under a minute over an ordinary telephone line.
E.164
E.164 is the standard defining the international format of telephone numbers: a country code followed by the national number, fifteen digits at most.
DTMF
DTMF is tone dialling: each key emits two simultaneous tones that the network interprets as a digit.
Baud
The baud measures how many signal state changes occur per second on a link — not to be confused with the bit rate, counted in bits per second.
TIFF-F
TIFF-F is the TIFF profile used to store a fax: a bitonal, compressed image, one page per sub-image within a single file.
ITU-T
ITU-T is the telecommunication standardisation sector of the International Telecommunication Union, a specialised agency of the United Nations.
Business telephony
PABX
A PABX is an organisation's private telephone exchange: it routes incoming calls to internal extensions and groups outgoing ones.
IP PBX
An IP PBX is a telephone exchange routing calls as packets over the organisation's computer network, instead of dedicated telephone circuits.
SIP trunk
A SIP trunk is the link connecting an organisation's telephone exchange to its operator over the internet, replacing physical lines.