Business telecoms glossary
Plain-English definitions of the terms you will meet when buying phones, numbers and connectivity.
A C D E F G H I J L N O P Q R S T V
A
ACD
Automatic call distribution. The part of a phone system that decides which agent receives each queued call, using rules such as longest idle or skills.
Auto attendant
An automated greeting that offers callers menu options. Another name for an IVR menu.
C
Call barge
A supervisor joins a live call so that both parties can hear them.
Call whisper
A short message played to the person answering, before the caller is connected, for example the number dialled. Also a supervisor speaking to an agent without the caller hearing.
CLI
Calling line identification. The number shown to the person you call.
Codec
The method used to compress and decompress voice for transmission, such as G.711, G.722 or Opus.
Contention
How many users share the same bandwidth. Leased lines are uncontended; broadband is contended.
CTPS
Corporate Telephone Preference Service. A register for businesses that do not want unsolicited sales calls.
D
DDI
Direct dial inward. A number that rings a specific person or team directly.
Direct Routing
A way to connect Microsoft Teams to a telecoms provider using session border controllers.
E
eSIM
A digital SIM built into a phone, activated by downloading a profile rather than inserting a card.
F
Failover
Automatically moving calls or data to a backup route when the main one fails.
FTTC
Fibre to the cabinet. Fibre runs to a street cabinet and copper covers the last stretch.
FTTP
Fibre to the premises, or full fibre. Fibre runs all the way into the building.
G
Geographic number
A number starting 01 or 02 that is linked to a UK area code.
H
Hosted PBX
A phone system that runs in a provider's data centre rather than on your premises. Also called a cloud PBX.
Hunt group
A group of phones that ring in a set order until someone answers.
I
ISDN
Integrated Services Digital Network. Legacy digital phone lines (ISDN2, ISDN30) being retired with the PSTN.
IVR
Interactive voice response. A menu that lets callers choose where their call goes.
J
Jitter
Variation in the time voice packets take to arrive. High jitter makes calls choppy.
L
Latency
The delay between speaking and being heard. Under 150 ms one way is good for calls.
Leased line
A dedicated, symmetrical, uncontended data connection with a service level agreement.
LOA
Letter of authority. The signed form that lets a new provider port your numbers.
N
Non-geographic number
A number not tied to an area, such as 0800, 0333 or 0845.
Number porting
Moving a phone number from one provider to another.
O
Operator Connect
A Microsoft-managed way to connect Teams to a chosen telecoms provider.
P
PBX
Private branch exchange. The system that connects internal extensions and external lines.
PSTN
Public Switched Telephone Network. The UK's analogue copper phone network, being retired.
Q
QoS
Quality of service. Router settings that prioritise voice traffic over other data.
R
Ring group
A group of phones that all ring at once.
S
SIP
Session Initiation Protocol. The standard used to set up VoIP calls.
SIP trunk
A virtual phone line that connects a PBX to the phone network over the internet.
SLA
Service level agreement. A contractual promise about availability and fault fix times.
Softphone
An app that turns a computer or mobile into a phone on your business system.
SoGEA
Single Order Generic Ethernet Access. Broadband over copper without a phone line.
T
TPS
Telephone Preference Service. The register people join to opt out of unsolicited sales calls.
V
VoIP
Voice over Internet Protocol. Making phone calls over an internet connection.
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