Twisted Pair (TP1)
TP1 was the first introduced KNX communication medium, it literally is a twisted pair of wires, core = 0.8 mm² and 5 twists/m.
The base component for a TP1 segment is a TP1 choke.
By definition, a segment is any equipment being electrically connected together
In order to power up a TP1 segment, its TP1 choke needs to be connected to a PSU (Power Supply Unit).
In KNX the principle of distributed PSU applies, this means that the same PSU can also be used in order to power up other TP1 segments, the most important requirement for a PSU is to make sure that its capacity is not exceeded.
PSU (capacity) variants: 160 mA, 320 mA, 640 mA, 960 mA, 1280 mA
PL was introduced in order to offer a solution for (renovation) projects with the requirement to use the installed mains electricity cabling as network.
PL devices use the conventional power cabling as communication medium.
A PL device can only communicate with another PL device if they belong to the same PL domain. A PL domain is a collection of PL devices with the same PL domain address. The PL domain address is a PL device parameter, which can be set via ETS. A KNX installation can contain several PL domains.
Between a KNX installation containing PL devices and the public grid a band-stop filter shall be installed. The band-stop filter makes sure that PL telegrams will be not be sent from the KNX installation into the public grid and vice versa.
The purpose of KNX IP is to set up a performant backbone between TP1 areas or lines and to provide access to other IP networks. In principle a KNX installation can for 100% exist out of KNX IP devices, but this is not considered useful.
Any IP standardized cable and/or IP standardized equipment can be used for connecting KNX IP devices.
Radio Frequency (RF)
Since there is no wiring involved installing RF devices is obviously quit easy and is therefore, especially for push buttons, considered as a useful extension to TP1. In principle a KNX installation can entirely exist out of RF devices, but this is not considered useful, especially for actuators.
An RF device can only communicate with another RF device if they belong to the same RF domain. An RF domain is a collection of RF devices with the same RF domain address. The RF domain address is an RF device parameter, which can be set via ETS. A KNX installation can contain several RF domains.