Glossary of Terms

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Term Definition
Public Switched Telephone Network

Public Switched Telephone Network (PSTN) is the standard telephone service provided over basic analogue phone lines.


The public switched telephone network is the name given to the wider telephone network used to make calls locally and globally that is independent from the internet. If you have a home telephone then it is likely that you make and receive calls via the PSTN that your phone connects to via a port in the wall. Some businesses still use old fashioned PSTN lines where each phone has a set phone number and line, though this is considered redundant technology and will be phased out by 2025.

Private Cloud

Private cloud is a term used to describe the common cloud computing model whereby a service provider makes resources like software or data storage available over the Internet.

Point of Presence

A Point of Presence (PoP) is the point at which a telecoms carrier establishes a physical presence in a geographic area, and at which the local exchange carriers (LECs) terminate access services. The PoP can consist of high-speed telecommunications equipment and technologies that enable users to connect to the Internet via their ISP. The PoP can include call aggregators, modem banks, routers, and high-speed Asynchronous Transfer Mode (ATM) switches.


A Private Branch Exchange is a physical device, normally located within the client’s premise. A PBX manages the internal call switching within an office and allows users, whose VOIP phones are connected to it, to share a limited number of public telephone lines.
A PBX is connected internally to the office telephones either directly or via a switch or router and externally to the internet via a dedicated ADSL line or the primary EOF connection. Once connected to the internet SIP trunks enable the PBX to connect to the public telephone network.
For example, a small office with 10 staff all have VOIP desk phones that are connected, using Ethernet cables, to a switch, the switch is then connected to the PBX and is responsible for sending data to and from the PBX to the correct telephone. In this scenario the 10 staff all share 7 external phone lines, meaning that no more than 7 of the team can call an external number at the same time and it’s the PBX’s job to dynamically allocate external phone lines and connect internal calls over the local network.

Packet Switching

A form of data transmission in which data is broken into small packets that are transmitted independently and reassembled at the destination. This is in contrast with circuit-switching, traditionally used for voice telephony, in which the transmission occurs over a dedicated circuit.


PaaS (Platform-as-as-Service) is a category of Cloud Computing services that provides a platform allowing customers to develop, run, and manage applications without the complexity of building and maintaining the infrastructure.