PSTN - Public Switch Telephone Network
The whole infrastructure of telephone networks services for public communication. PSTN consists of telephone lines, fibre optic cables, microwave transmissions, cellular networks, communications satellites and undersea telephone cables. Back in the early days of the connected phone networks where home phones and public phone boxes were the only means of telecommunications, the main connection points for PSTN were the switchboard centres operated by a person connecting wires between locations. Nowadays, almost everything is entirely digital in the network and includes the connection between mobile devices.
ISDN - Integrated Services for Digital Network
The communication standards for simultaneous digital transmission of voice, video, data and other network services over PSTN. A typical ISDN connection should support a transfer rate of 64kb/s or 128kb/s of data. These speeds are very easy to achieve with a modern DSL connection.
FAX - Facsimile
A FAX is the transmission of scanned material (text and images) over a broadband network. Separate from a regular telephonic transmission, a FAX scans and catalogues the text and images of a physical paper file and converts it to a single fixed image known as a bitmap. The bitmap is then transmitting through a series of audio frequency tones over a telephonic network. When it is received by the FAX machine on the receiving end, the bitmap is then reconstructed and printed as a paper copy.
VoIP - Voice over Internet Protocol
Also known as Voice over IP or pronounced voyp, VoIP is the term used for the transmission of voice of multimedia through a broadband IP. VoIP is the most common form of communications nowadays as almost anyone who has a broadband connection, also has a home phone and vice versa. Any form of telecommunication that is done through a broadband connection is a VoIP call.
SIP - Session Initiation Protocol
The SIP is the protocol for signalling and controlling media communication sessions. In basic terms it is the setup part of a phone call or other form of messaging service. The SIP defines the parameters of a media conversation between two or more parties.