Telecoms
Telecommunications glossary
62 terms that come up as soon as fax, lines, numbers or proof 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.
PSTN
The PSTN, or public switched telephone network, sets up a dedicated end-to-end circuit for each call over analogue copper lines.
FTTH fibre
FTTH, or fibre to the home, runs optical fibre all the way into the subscriber's home or premises, replacing the copper pair.
ADSL
ADSL is an internet access technology that carries high-speed data over the telephone copper pair, on frequencies the ear cannot hear.
VDSL
VDSL is the successor to ADSL on the copper pair: it offers much higher speeds, but only on short lines.
Local loop unbundling
Local loop unbundling opens the incumbent's local loop to other operators, who rent the copper line and install their own equipment on it.
ATA adapter
An ATA converts the signal of an analogue phone or fax machine into voice over IP, so it can connect to a packet network.
Modem
A modem, or modulator-demodulator, turns digital data into a signal that can travel over a phone line, then converts it back at the other end.
Codec
A codec is the algorithm that digitises and compresses voice so it can travel over a packet network, then rebuilds it at the other end.
G.711
G.711 is the reference codec of digital telephony: voice is sampled 8,000 times a second at 8 bits, giving 64 kbit/s, with no compression.
Jitter
Jitter is the variation in packet delivery delay on an IP network: two packets sent at a regular interval do not arrive with the same delay.
Packet loss
Packet loss is the share of data packets that never reach their destination, dropped by a congested network or arriving too late to be used.
Echo cancellation
Echo cancellation is the processing that removes from a call the return of the sender's own signal, reflected back by the line or the network.
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.
SIP
SIP is the signalling protocol of voice over IP: it sets up, modifies and ends calls, without carrying the sound itself.
V.34
V.34 is the ITU-T modem standard that reaches 33.6 kbit/s over a phone line, used in fax by so-called Super G3 machines.
V.17
V.17 is the ITU-T modem standard designed for fax, sending the image at up to 14.4 kbit/s, with fallbacks to 12,000, 9,600 and 7,200 bit/s.
Super G3
Super G3 refers to Group 3 fax machines fitted with the V.34 modem, which transmit at up to 33.6 kbit/s instead of the 14.4 kbit/s of classic fax.
TSI
The TSI is the identifier the sending fax machine announces to the recipient during negotiation, normally its fax number, up to twenty characters long.
MH, MR and MMR
MH, MR and MMR are the three standard compression methods for a fax image, from the simplest to the most efficient.
JBIG
JBIG is a lossless compression standard for black-and-white images, more efficient than MMR, which some fax machines use to transmit faster.
Group 4
Group 4 is the class of digital fax machines designed for ISDN, which sent a page in a few seconds at 64 kbit/s, without a modem.
CNG and CED tones
CNG and CED are the tones of a fax call: a 1,100 Hz beep repeated by the calling machine, then a continuous 2,100 Hz tone from the one answering.
The faxed document
Fax header
The fax header is the line printed at the top of every page sent, showing the date, time, sender's identity and page number.
Transmission report
The transmission report is the summary printed after a fax is sent: date, time, number called, recipient's identifier, pages and result.
Email to fax
Email to fax is a service that converts an email and its attachments into a fax, then sends it to the recipient's fax number.
Fax to email
Fax to email is a service that receives the faxes sent to a number and forwards them by email, usually as a PDF attachment.
Numbers and routing
Numbering plan
A numbering plan sets the structure of a country's phone numbers and the use of each range; in France, it is managed by the regulator, Arcep.
Geographic number
A geographic number is a landline number tied to an area of the country; in France, it starts with 01, 02, 03, 04 or 05 depending on the region.
Non-geographic number
A non-geographic number is a landline number tied to no region; in France, it starts with 09 and often comes with a broadband router.
Premium-rate number
A premium-rate number costs more to call than an ordinary call, the extra paying for the service; in France, these numbers start with 081 to 089.
International prefix
The international prefix is the code dialled before a country code to leave the national network: 00 in France and most countries.
Number portability
Number portability lets you keep your phone number when changing operator; in France, the request uses the RIO code, obtained by calling 3179.
Arcep
Arcep is the independent administrative authority that regulates electronic communications, postal services and press distribution in France.
Caller ID spoofing
Caller ID spoofing means displaying a caller number that is not your own, to mislead the recipient about where a call comes from.
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.
Direct inward dialling
Direct inward dialling gives each internal extension of an organisation its own public number, reachable without going through the switchboard.
Fax server
A fax server is software or a device that centralises sending and receiving faxes for an organisation, from users' workstations.
Proof, compliance and data
Evidential value
Evidential value is the weight a document can carry to prove a fact or an act before a court or a public authority.
Reliable copy
Under French law, a reliable copy has the same evidential value as the original; reliability is assessed by the judge, unless a decree presumes it.
Timestamping
Timestamping attaches a certain date and time to a document, attested by a third party, proving that the document existed in that form at that moment.
Electronic signature
An electronic signature links a document to its signatory and guarantees its integrity; a qualified one is equivalent to a handwritten signature.
eIDAS
eIDAS is the European regulation on electronic identification and trust services: electronic signatures, seals, timestamps and registered delivery.
Electronic registered letter
The French electronic registered letter (LRE) is the digital equivalent of registered post, with the same legal effect when it meets the legal requirements.
GDPR
The GDPR is the European regulation on personal data protection, in force since May 2018 for any organisation that processes such data.
HDS
HDS certification, for health data hosting, is mandatory in France for any provider that hosts health data on behalf of others.
TLS encryption
TLS is the protocol that encrypts exchanges between a browser and a website; it is what protects https addresses and the padlock icon.
PDF/A
PDF/A is the standardised version of PDF for long-term archiving: the file contains everything it needs to be displayed identically decades from now.
Evidential archiving
Evidential archiving stores electronic documents so that, years later, you can prove they have not been altered since they were filed.
Digital fingerprint
A digital fingerprint is a short value computed from a file by a hash function, which changes completely if a single byte of the file changes.