The physical layer takes frames (stream of bits) from the data link layer, converts these bits into electrical/electromagnetic/optical signals through different line coding techniques and then transmits these signals through wired/wireless telecommunication links (cables/antennaes) to the adjacent (next hop) nodes peer physical layer.
The diagram given below lists out the typical components that are part of a physical layer:
Different physical components used at the physical layer
As shown in the diagram, the physical components include:
- Transreceiver PHYs, Modems – that typically convert the digital bits into electromagnetic/optical signals through appropriate line coding techniques. Similarly, at the receiving end, the PHYs and Modems do the reverse operation of line decoding, to convert the signals back into a digital stream of bits.
- Sockets & Connectors – These interface between the NICs and the telecommunication link cables and come with different shapes, sizes and pins. The cables/wires of the telecommunication link are plugged into these sockets. Typical examples are : RJ-45, RJ-11, V.35, HDMI etc.
- Telecommunication links – Consists of different types of wired media cables like copper, coaxial, optical cables and different types of wireless media antennaes like omni-directional, bi-directional antennaes etc. The electromagnetic/optical signals are propogated to the peer physical layer receivers via. these cables/antennaes.
- Intermediate devices – These include devices like hubs, repeaters. These devices are used to basically amplify/regenerate the signals at intermediate points. In cases where the telecommunication link connecting the peer physical layers is lengthy, the signals may attenuate (lose strength) if they are not amplified/regenerated at suitable intermediate points.