Understanding the Physical Layer in Networking
Key Features of the Physical Layer
The physical layer is responsible for all physical, electrical, functional, and procedural aspects of each network element. It transforms bit streams (link layer) into signals that can be transported by the physical medium and vice versa. This is necessary for data transmission between two hosts through a physical medium.
This includes cabling, connectors, and cables linking network devices, the devices themselves working at the level of electrical impulses and signals, repeaters, hubs, modems, network interface cards, etc.
It is responsible for coding, signaling (transformation of a bit into a signal), signal type (electrical pulse, light, wave, etc.), pulse duration, modulation if needed, etc.
It defines the media, wiring, and connectors that connect devices with cables, compatibility between different types of existing connectors, and the roles each pin of these connectors will play.
It re-synchronizes and amplifies signals on their journey through the medium to alleviate the effects of attenuation and noise.
Step-by-Step Example
The patterns formed in the link layer are joined one after another in “bit streams,” sequences of zeros and ones that contain all the information necessary for communication between hosts. These bit streams must be converted (encoded) into recognizable patterns by layer 1 devices that can be understood at the destination. Encoding adds control information to the end of each frame of bits (a pattern of zeros and ones) to indicate the beginning and end of them. Once the frames are properly coded, the clean sequence of encoded bits is transformed into signals (in some chips or network memory available for the purpose). This bit-processing signal is known as signaling and determines how to represent the pure bit in the physical environment.
The physical layer places the bits one by one in the medium as a signal that arrives at its destination, and layer 1 devices are responsible for decoding them.
The signals must be routed through the wiring. This requires some elements between the cables and motherboards, network interface cards, or modem devices. The physical layer defines the connector (e.g., RJ-45, RJ-45 Jack, BNC male, BNC female, etc.) and the compatibility between them.
It is possible that the signal will travel down the medium and go through intermediate networks with different physical topologies. To adapt the type of signal from one network to another on its journey, a “transceiver” will be used (e.g., Electric Pulse – Light Pulse – Wave).
The length of the physical environment that signals must travel must be considered. Beyond certain limits, it will be necessary to repeat the amplified signal (Switch, Hubs, assets, etc.) and re-synchronize it to mitigate the effects of attenuation and noise. Otherwise, there would come a time when the signal would be incomprehensible or would not reach the destination.
Once the signals reach the destination host, the encoding process is reversed. The signals received are converted into bit streams, decoded by Layer 1, to make up the protocol stack and recover the original message.