Port – a physical interface between a device and a circuit.  The device may be a system (mainframe / PC), a switch (PBX/ exchange) or router, a hub or bridge, a buffer, a printer or other peripheral … or virtually any other device.  The port and circuit connect through a plug and socket arrangement.

Trunk – a communication line between two switching systems, which typically include equipment in a central / public exchange (the telephone company – Telkom) and PBX’s.  A tie-line / trunk connects PBX’s.  Central office trunks (CO lines) connect a PBX to the switching system at the central / public exchange.

Exchange Connection (excon) – A line between the PSTN (Telkom) and a subscriber, with an individual phone number that can be used for incoming and outgoing calls; or a line coming in from the PSTN to the PBX – not linked to a hunting group and often used as a fax, modem, internet or dedicated line at a company.

Junctions – (incoming Service Group / ISG.)  Exchange Lines / auxiliary numbers (more than one) allocated to a company that are set up to hunt from the main number to the next available number in sequence. PBXs are programmed for multiple telephone lines so that when a call comes in it does not encounter ‘busy’ tone, but rolls over to one or more auxiliary lines.  Linked to a hunting facility provided by the PSTN.

Hunting facility – A procedure applied to a group of incoming lines / junctions.  The call will try the first line of the group – main number; if that line is busy, it will try the second line, then the third, etc., until a free line is found.

Mains Fail – The facility whereby in the event of a power / PBX failure, and in the absence of battery backup or UPS on the PBX, calls can still be routed to a pre-programmed analogue extension port / analogue telephone instrument.  Although calls will not ring on the switchboard, callers will still be forwarded to a minimum of two analogue extension phones.

Tie Line trunk – A dedicated circuit linking two PBXs without having to dial the normal telephone number.

Outdoor Extension – Also known as an off-premises extension (OPX).  Using a line circuit out of the PBX, it is an extension or telephone terminating in a location other than the location of the PBX. 

Telephone Jack – A receptacle used in conjunction with a plug to make electrical contact between communication circuits.  Jacks are used to connect lines / telephone instruments to PBXs. (RJ = Registered Jack)

RJ11 – Most common telephone jack in the world.  Six conductor modular jack usually wired for four conductors.  Used for connecting telephone instruments, modems, and fax machines to a female RJ-11 jack on thefloor or in the wall.  That jack in turn is connected to twisted wire coming in from the ‘network’ – a PBX or the PSTN.

RJ45 – 8-PIN connector used for data transmission over standard telephone cable.